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Harmonics - Science topic

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Dear Researchers,
I am looking for methods to mesh a twisted blade in order to get more structure mesh.
I tried several mesh size yet the quality metric are a bit bad.
I am analyzing regarding the skewness and the orthogonal quality.
My objective will be performing modal and harmonic in order to determine the stress distribution adequate to the natural frequencies.
Thanks in advance for your advise.
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Mohammed Lamine Mekhalfia I didn't receive an email.
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Dear all,
I am trying to perform harmonic analysis with the forcing term which is not harmonic but periodic. I converted the forcing term to harmonic series of sine and cosine. Now the problem arises when I have to incorporate this force in ANSYS analysis.
Is there any way to input non harmonic forcing term, or the another way to input series of sine and cosine term ??
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I agree with Hiba Kaoaz . Harmonic response analysis simulates how a structure will respond to sinusoidally repeating dynamic loading. You can define load as a specific sin and cos function with domain and frequency to your model and harmonic analysis, but you should be done with modal analysis before that. Still, if you have a specific function for your forcing vibration, you can use it in the APDL program of your model.
regards;
Ehtisham
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I am currently working on my project of crack detection in cantilever beams using an Ansys, and I did modal analysis and harmonic response to find the natural frequencies and frequency response of the deformation.
I have found the maximum amplitude of all 6 modes and how does it really work in crack detection?
amplitude gets lower when frequencies get higher.?
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Nazanin Fallahi
Hi,
Thank you so much for your response and its so helpful.
I need to know about how it works with cracks detection?
absolutely the natural frequencies of the healthy and unhealthy varies.
also amplitude of the healthy and unhealthy varies as well. I need a clear idea about detection working?
it would be helpful if someone could clarifying this..
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I am trying to solve an isolator suspension problem in which a mass is suspended using 4 Nos of 3D springs(Isolators). I want to carryout response studies to find harmonic and random response on mass.
I tried using bushing element in ANSYS mechanical. Here in connections I have provided relevant stiffness and damping in matrix form for bushing elements.
Also overall damping ratio of 0.02 % is given as input under harmonic analysis tab.
Analysis shows that response is function only of harmonic damping ratio not one given in bushing element . Can anyone pls comment on this?
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Claudio Pedrazzi
How did you connect (RBE2 or RBE3) the bushing with the rectangular block? I guess that all DOFs of Node 4198 are suppressed. Am I right?
Where did you apply the harmonic load?
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hello everyone
i'm asking about any mathmatical methode that can calculate the(total harmonic distortion) for ramp function ?
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42.11
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In the VIV process of a cylinder or a bridge, we can always find harmonic frequencies in the flow field. How does the harmonic frequency come into being and what does it mean? What does the harmonic frequencies represent and what effects can it bring?
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Generation of harmonics in fundamentals are depending on many factors and are frequency depending too. In radio and audiowave(se/my)the electromagnetic disturbance could produce harmonics disturbances. For law power frequency, vibration frequency, the stress strain frequency etc when the fundamental wave go out of linear variations the harmonics distortEd wave would produce, (the B-H curve of core material of transformers generate third harmonics in secondary side if magnetizing current peak touch saturation) ….
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Using Quantum espresso I was able to converge through SCF calculation for my structure. I have also optimized the geometry by vc-relax. Now I want to fit forcefield parameters for bond, angle, torsion, improper, non bonded Buckingham/coul potentials. How can I do so?
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The answer depends significantly upon which force field you intend to use. There is no unique definition of parameters like partial charges on atom types. Each force field's developers have adopted a strategy to provide consistent definitions within their own parameterization. Thus, one cannot copy a set of Amber parameters that you found somewhere and plug them into a Charmm calculation.
Generally, creating force field parameters is a lengthy, tedious process. Developers have also documented their processes. There are, alternatively, some more user-friendly, parameter-generating codes out there but I cannot speak to their veracity or accuracy. I always used the painful, tedious approach.
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Hello World,
I am trying to perform the modal analysis and harmonic response analysis for forced vibration in rotating cantilever beam through ANSYS. Is there any way to incorporate the rotational velocity and add Coriolis and centrifugal effect for the analysis?
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Hello Amrit Tiwari ,
You have not the possibility to insert a rotational velocity in the Harmonic Response, because this kind of analysis uses mode superposition in RESPONSE to a load. The rotational velocity has its effect on the modes of the structure, then the loads from Harmonic Response are "projected" onto the structures modes and the response is than rebuilt up form each mode response.
In the Harmonic response only periodic loads are accepted (a constant acceleration is considered a periodic load with 0 frequency, therefore it is acceptable).
I suggest to perform a static structural analysis and use the pre-stressed state as input to the modal analysis (see project schematic in the annexed archive .wbpz).
Warning: the prestressed structure must have results different from zero everywhere, otherwise, there will be no difference with respect to fixed beam.
See the different response with and without rotational velocity when the prestressed state is different from zero.
Last remark: when I toggle "Coriolis effect" to on, the prestressed solution is zero everywhere, therfore the rotational velocity is completely ineffective. I don't know why, this is unexpected.
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Hi there, I am running a targeted molecular dynamics job on NAMD and an error occurs, FATAL ERROR: Number of atoms in constraint constant PDB doesn't match coordinate PDB ,
in the procedure of minimization that I can't fix. it doesn't progress any further than making the "harmonic restraint" pdb. so, has any one ever encountered this error ?
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Dear Aria,
In addition to what Rezvan Marjani mentioned, You should check your equilibration.tcl script or if you're using simulation.tcl if it's not already messed up.
Alternatively, you should try and follow this tutorial. It will help you a lot.
Best regards
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I am trying to simulate harmonic dynamic loading applied on square machine foundation using ABAQUS. While doing experiment, I have used rotating mass type mechanical oscillator. The loading intensity of the same is dependent on the angular frequency(w), [F(t) = F_0.Sinwt = m_e.w^2.Sinwt]. In the numerical modeling, to apply the load on the footing I need to convert the load in terms of real and imaginary components. I am quite confused, how to do that. Can anyone explain, how to calculate the real and imaginary components of the dynamic load. I have mentioned the variation of force amplitude with the rotating frequency of the mechanical oscillator.
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Thank you Hassan Nasser for your answer.
I have earlier gone through the link that you have suggested. The page shows the procedures for the direct solution of steady state dynamics analysis. However, my concern is how to divide the force magnitude (amplitude vector) in terms of real and imaginary part. I am confused, how much load I should assign for the real part and how much for the imaginary part. Please see the image given. I have given the values in "CF3" since the dynamic load is acting Z direction.
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Hello all,
I want some recommendations for spectrometers of UV to near IR (230 nm to 900 nm), with High resolution, have a good price, can distinguish between second and third harmonic, and are easy to use.
Thank you.
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Avantes spectrometer is highly recomnded in terms of product price and benfits
you can perform easily spectral scanning.
If you are interested in photon counting and high resolution Andor is one posibility, but you should know your need for that.
Good luck,
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SNS is a feeding tube device provides babies supplemental feeding , it helps in inducing and maintaining lactation by triggering harmonal release. Any practical experience about the nursing system?
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There are photos of homemade supplementers in the WHO courses on breastfeeding.
If you are writing a paper or doing research take care with the term that you use, Supplementary nursing system (SNS) is a trademarked term for the Medela product. It is not a generic term.
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I have been trying to get a sub synchronous resonance scenario in the "Wind Farm - Detailed DFIG Model (available on mathworks website)" in Simulink as a part of my project. For that I have to identify the possible frequencies where the harmonics can occur. To identify these, an impedance scan/frequency sweep of the wind farm is required to understand. I have been trying to get give input perturbations to source voltage, measuring the ouput changes at windfarm terminals and then using script to calculate the Fourier Transform. But the results are not ok as my impedance scan actually shows lower impedance at higher frequencies.
Is there any other way to get an impedance scan for the wind farm in Simulink?
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I don't know now if there's any other way to get a wind farm impedance scan in Simulink, but I recommend a few measurement systems located at different key points (inverter outputs) for monitoring (U, I, P, Q, S, Lambda , THD-I, THD-U etc.) and then try to analyze them according to the wind direction, temperature and humidity in that area in a certain range ...
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I was looking into audio classification using handcrafted features fed into an artificial neural network.
Here is a list of features that I could collect so far
Time-domain features: 
Zero-crossing rate
energy
energy entropy
RMS value
Frequency domain features: 
spectral centroid
spectral entropy
spectral flux
spectral roll-off
Mel frequency cepstral coefficients (MFCC), 
harmonic ratio
Fundamental frequency
Chroma vector 
Are there more features available? I would also like to know if there is a single tool to extract them all
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Here is our work: a deep neural network architecture designed for audio classification. There are also a list of features that can be extracted (which we used for comparison purposes) for the so called "shallow learning".
Code provided. Do not forget to cite our work
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I understand there will be exact multiple of fundamental frequency based bearing rotation with respect to fundamental, based on gear rotation with respect to fundamental. But what exactly means for multiples of bearing rotations, multiples of blade passes like 1x, 2x, 3x etc.,
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Honestly, it depends...
It depends on the specific machinery and source mechanism.
It can be nonlinearities in the system (e.g., nonlinearities in linear drives like speakers), it can be (periodic) elements in the system (e.g. number of teeth in gears), it can be wear in components (which needs to be periodic on rotating parts, e.g. higher harmonics on railcar wheels - polygonalization), it can be impulsive behaviour triggered periodically by a rotating part (e.g. combustion impulses in internal combustion engines), it can be linearly moving parts that are not rotating (e.g. pistons), it can be some additional higher order torque components from inbalances, ...
The key point is that for all of these processes (except of some non-linearities that might generate subharmonics), you can only get integer multiples of the base period.
Nevertheless, it is important to mind the base period. For a 4-stroke engine, for example, this is 2 rotations, which is why you might also find "half orders" at internal combustion engines (and only full and half orders, no third or something...).
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Greetings,
I have modeled a faulty system (Bowed rotor) in MATLAB. By increasing the sampling frequency, a frequency component appeared in the FFT graph (after the 1X), but the location (frequency in which the component appeared) is constant, i.e., by changing the system's angular velocity, the coordinate of the X-axis (frequency) is constant and does not show a harmonic component (such as 2X or 3X) while the fault has been modeled as a harmonic force. On the other hand, by increasing defect severity the amplitude of this harmonic component has been raised. Now, does anybody know and could explain it physically, please.
Yours sincere,
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Hi dear Nima Rezazadeh ,
Perhaps the constant frequency component belongs to the fault harmonic force.
Best regards
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In the context of designig a VAR compensation system with switched capcitors and a TCR, due to the switching of these two components there will be harmonics introduced to the network, the in order to supress those harmonics one must use harmonic filters, but, ¿is it necessary to take in count the power consumption of those filters in order to calculate the size in VAr of the capacitor bank and reactor ?
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You can add traps filters to suppress the harmonics as a series resonance circuit.
This circuit must be act as a short circuit at the intended harmonic frequency. It is also called a notch filter. Which means it must have resonance at the intended harmonic frequency. At the fundamental frequency the filter will act as an effective capacitance. So, it can be share in improving the power factor of the grid in case of inductive loads or lag phase. Otherwise it will affect the reactive power by the energy stored in this equivalent capacitance. But its value is relatively small as it is combined with an inductor to resonate at the intended harmonic frequency.
Best wishes
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Hello everyone, I am analyzing the harmonic response of a beam in ANSYS workbench and I need to assign the loss factor (hysterisis or structural damping) to the beam I am studying . My question is is it possible, in my case, to add the following APDL command (MP,DMPS,MATID,0.01) below the object in the geometry branch?
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The command MP, defines a linear material property as a constant or a function of temperature. So I suppose you can use MP, DMPR to define constant material damping.
Also the discussion in the following link provides some useful information on this subject:
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Can anyone help me to write review article on harmonization topic ..special reference to India.....means giving outline ..which topic should be covered under this head..please help me..i think this topic should be address.
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@, samar..thank alot..i will try to use your given outline in preparation of my manuscript.
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Hello everybody
Is there any software other than Matlab to produce data for sinusoidal excitation with gradually increasing amplitude like attached plots?
Thanks
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You can do this with any programming software. for example LabVIEW, Python and ... .
You just have to multiply the sine function with the desired frequency by a function with gradually increasing amplitude.
Best regards
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The stress strain curve of rubber is not linear and follows a curved line both as the strain increases and as it decreases again. Does this hysteresis lead to formation of harmonics or other non lienar phenomena in eg a vibration insulated system?
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My experience with elastomeric vibration isolators is limited by vibration control of precision instruments, that is, small vibrations (micron and sub-micron range). Hysteresis leads to dissipation of mechanical energy (damping) that can be described in terms of complex stiffness incorporating a (rather large) loss factor. In frame of this model, the dynamic reaction includes a phase shift but stays linear, described by complex transfer functions. See more in Vibration Control for Optomechanical Systems, by V.M. Ryaboy, World Scientific, 2021, ISBN 9789811237331, pages 132-137. https://www.amazon.com/Vibration-Control-Optomechanical-Systems-Vyacheslav/dp/9811237336/ ;
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What are the challenges and update s regarding harmonization among food safety rules in india and worldwide.
Kindly suggest articles and reviews.
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Hello everyone, I am analyzing the harmonic response of a beam in a frequency range [0-50 Hz] but I noticed that the results for the 0 Hz frequency are not provided by ANSYS workbench. would like to know is there a possibility to have the amplitude of the displacement of the beam for the frequency 0Hz?
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That's the least I could do.
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Hello all, i'm trying to analyse the vertical deflection of a beam traversed by a point load as shown in the figure. The load has the following format: F=Pcos( ωt+ϕ) where P is the load amplitude (N), ω is the radial frequency of the applied load (rad/sec), V is the speed of the moving load (m/s) and t is the time (s). ϕ is an initial phase applied to the load to ensure that for every frequency, it will arrive at the mid-span with maximum amplitude. Please guide me, how would I define that in Ansys workbench?
Thank you.
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Hi @Hajar Rhylane.
I would like to add a method to do this without programming using Ansys Workbench.
You may resort to solid modeling of the beam and create a body that has contact with the solid beam. The contact between the body and the solid beam should be only at one location along length at any point of time. The contact surface should be the solid beam surface and the target should be the edge of the body in contact with the solid beam. The acceleration can be applied on the body and should be adjusted to match the required contact force that has to be applied to the solid beam by contact. Hence the acceleration can be defined by a function something like a.cos(wt+phi). The type of contact can be defined as no separation contact. The linear velocity v cab be applied to the body directly.
However it has to be noted that the linear velocity v and the angular velocity w are not independent and cannot be defined arbitrarily because of the requirement that it has to arrive at the centre with the maximum amplitude. The relation between v and w can be determined by solving the two equations 1) wt1+phi = n.pi and 2) vt1= L/2. Where t1 is the time at which the body reaches the mid length of the beam. The parameter t1 can be eliminated to get the relation between w and v. The parameter n can take any whole number value.
And please remember to switch on finite sliding in the contact settings. Hope this helps.
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I am doing vibrational analysis of mono-acetic acid after wavefunction and geometry optimisation. In the output file of vibrational analysis the following lines were present containing harmonic frequencies of mono-acetic acid.
****************************************************************
HARMONIC FREQUENCIES [cm**-1]:
-93.9446 -56.8345 -14.9036 79.1124
83.2432 123.7967 180.8622 415.9833
465.7580 564.8411 581.9038 795.9969
942.4123 1030.7040 1139.4888 1218.9753
1356.8784 1433.9457 1447.8727 1776.4078
2976.9823 3023.5483 3084.8354 3634.5117
PURIFICATION OF DYNAMICAL MATRIX
****************************************************************
HARMONIC FREQUENCIES [cm**-1]:
-55.0883 -0.0000 0.0000 0.0000
80.2766 101.0671 159.3476 415.9277
465.5977 564.8100 581.8316 795.9872
942.4062 1030.6968 1139.4801 1218.9731
1356.8769 1433.9456 1447.8725 1776.4022
2976.9823 3023.5483 3084.8354 3634.5117
ChkSum(FREQ) = 0.26286465E+05
Can some one help me understand what is meant by "Purification OF DYNAMICAL MATRIX" and interpret the above results CH3COOH should have 18 modes of vibrations (3N-6). but I am getting 20 modes of vibrations? Furthermore is -55.0883 cm-1 a false flag or is it because of incorrect optimisation of structure?
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Getting all zeros for the first 6 modes enforces the requirement of invariance of the PES with respect to translation/rotation. Harmonic frequencies obtained by finite differences may often lead, for lack of numerical precision, to non-zero values in these modes. The "purification" should consist (at least if it is the same as in GAMESS) in a procedure of transforming back and forth the matrix between cartesian and internal coordinates, which effectively helps zeroing the freqs and IR absorptions of the translational and rotational modes.
The fact that you still get those -55. and +88. cm-1 is a possible sign of your structure not being close enough to a true minimum, but I can't be sure on this. In some cases, a solution is met by simply repeating the optimisation with increased numerical precision in the DFT integration scheme and/or SCF convergence.
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Application of these 3 Means (AM, GM and HM) individuality? where can we use this? welcome with research papers?
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Arithmetic mean is calculated by adding all the sample values followed by dividing it by the number of samples taken... Geometric mean is the square root of the product of the values of each sample and harmonic mean is the reciprocal of the arithmetic mean of the reciprocal of the values of the sample... example calculation of AM, GM and HM of the values A, B and C will be
AM= (A+B+C)/3
GM= √A×B×C
HM= 3/ {(1/A)+(1/B)+(1/C)}
Arithmetic mean is used for calculation of average of anything because it consider all the observations like plant height, average speed when time is fixed, calculation of so many yield attributes. It is frequently used in agriculture and will be most authentic average... Geometric mean is used to calculate bacterial growth, cell division etc...if one value is zero, then whole GM value will be zero, because product of the value is used here..In case of harmonic mean, average of small value can be used like Average of rate or ratio because we have take reciprocal values of each samples whereby taking reciprocal of very small values obtained value is comparatively larger..
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its like,why does the power system network still affected by effects of harmonics yet mitigation measure in place.
thanks
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There are so many moving parts in the power system that have a lot to do with the mechanics of the system. Mitigations are there but most of them are physics related like the resistivity which is affected by the length of the wire and area then we can also look at overheating and this is because there is work done and magnetic fields hence we can control or reduce them but we can't get rid of them completely.
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Does anyone have access to any of these articles? I have already tried to contact some of the authors, but without success. I don´t speak Mandarin so is very difficult with CNKI where they are available through payment. I can not understand even the payment method or if I would have access from Brazil. Thanks in advance for any help.
P.S. Even with google translator it was impossible understand the database.
1. DC Bias and Saturation Protection of Converter Transformer
WEN Ji-feng,ZHANG Xiao-yu,CHENG Xiao,XIONG Hui,LI Hai-ying,CHEN Song-lin(Nanjing NARI-relays Electric Co.Ltd.,Nanjing 211102,China)
This paper analyzes main causes of DC bias of converter transformer,and summarizes electrical characteristics of exciting current during DC bias of converter transformer and the mechanism of DC bias leading to damage of converter transformer.In addition,the principle of saturation protection of converter transformer and the implement method of the protection are introduced.Finally,points for attention in the engineering application of overexcitation protection of converter transformer are discussed.
2. Analysis on maintenance and operation of earth electrode shared by some HVDC systems
Lei X.,China Electric Power Research Institute | Li X.,China Electric Power Research Institute | Lin S.,China Electric Power Research Institute | Sun X.,China Electric Power Research Institute | And 4 more authors.
Dianwang Jishu/Power System Technology | Year: 2015
There are many inconveniences of maintenance and operation for HVDC systems with sharing earth electrode. When earth electrode line maintenance is implementing, personal security may be at risk because of DC current flowing through earth electrode line. As an example of sharing earth electrode of two HVDC systems, DC current distributions of earth electrode line and effect factors were analyzed according theoretical analysis and the actual project parameters. And operation suggestions of HVDC systems were proposed during earth electrode line maintenance. The results show that DC current distributions of earth electrode line are mainly affected by earth electrode resistance, earth electrode line resistance, maintenance grounding location and soil conditions. Besides, DC bias of converter transformers may be affected by DC current from earth electrode line, in serious condition, HVDC systems are blocked because of saturation protection action of converter transformer. © 2015, Power System Technology Press. All right reserved.
3. Analysis on the Transformer Saturation Protection in Fengxian Converter Station
LI Yueting,HAO Yuedong,LI Tengliang(Shanghai Management Office,Grid Operation Branch of State Grid Corporation of China,Shanghai 201413,China)
Fengxian Station is the receiving end of ± 800 kV Xiangjiaba–Shanghai UHVDC transmission project,and the transformer DC saturation protection(TSP) in the station has alarmed and even triped under the unbalanced operation mode while the transformer was charged.This paper introduces the operation principle of TSP,and analyzes its action logic and the rationality of its settings,and then discusses the cause of leading to TSP maloperation and related solution for the manufacturer.
4. The Influence of DC Bias and Harmonic on Sympathetic Inrush of Converter Transformer
Lingfeng Xia;Xiangfei Sun;Junwei He;Jianping Zhou;Kunming University of Science and Technology;
Compared with common transformer, converter transformer shows some differences from the perspectives of DC bias and harmonic and so on, which has significant influences on sympathetic inrush. There are few researches about that. Therefore, taking the characteristics of converter transformer as the starting point, this thesis analyzes the influence of DC bias and harmonic on sympathetic inrush of converter transformer. Emulation proof is processed with utilization of PSCAD/EMTDC and MATLAB. It's found by study that the influences of DC bias on sympathetic inrush mainly depend on its relationship with the direction of the magnetic linkage of transformer. Content of characteristic harmonic in sympathetic inrush is relatively high and the content of each subharmonic has linear correlation with the intensity of DC bias.
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Hello,
I am working on project that consists of analyzing power quality. The grid is connected to a nonlinear load which will evidently causes appearance of harmonics and potential swell and sag on the wave form of load current.
Basically, the measured voltage and current will be processed to determine and detect any possible disturbances, for instance swell and sag .
I am asking for an algorithm to do so(especially for sag/swell).
Thank you.
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@abbas jamshidi Gahrouei, thanks for your response.
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Hi
Sir how is useful in power electronic system for measure harmonic is MATLAB or PLECS
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If you build your power electronic model in Matlab/Simulink then you can calculate your current and voltage waveforms. One you get these waveforms use the tool box of the fast Fourier transform to resolve the waveform into its fundamental and harmonics sinusoids provided that you have to sample the waveform with a sampling frequency greater than 2 times the highest possible harmonic frequency.
You can also measure the waveform of any experimental circuit and acquire it by using data acquisition cards then store the waveforms and analyze them using the FFT tool box.
Best wishes
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i used CHARMM-GUI membrane builder module to prepare the necessary files for simulating a membrane using NAMD and while inspecting the configuration input files, i noticed that it uses collective variables (ColVar) to apply a harmonic potential on some atoms of the head groups of the lipids during equilibration only. why would i need to apply these potentials? and why selecting the centers values to be of these specific values (ex: 18 for the cholesterol lipid)?
these are the first and last colvar lines included in the first equilibration step:
###Lipid Head###
Colvarstrajfrequency 100
Colvarsrestartfrequency 100
colvar {
name chl1_head_upper
distanceZ {
ref {
dummyAtom ( 0.000, 0.000, 0.000 )
}
main {
atomsFile restraints/chl1_head_upper.ref
atomsCol B
atomsColValue 1.0
}
}
}
harmonic {
colvars chl1_head_upper
centers 18
forceConstant 5
}
....
....
....
colvar {
name psm_head_lower
distanceZ {
ref {
dummyAtom ( 0.000, 0.000, 0.000 )
}
main {
atomsFile restraints/psm_head_lower.ref
atomsCol B
atomsColValue 1.0
}
}
}
harmonic {
colvars psm_head_lower
centers -21
forceConstant 5
}
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I think it is important to make some restraints on the membrane to not lose the bilayer configuration when preparing the system for the simulation.
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Please suggest any algorithm diagram for understanding the concept of an active power filter for removing harmonics.
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For harmonic elimination only, the concept is that your reference current is described as the difference between the measured distorted load current minus the fundamental component of the measured distorted load current.
Assuming fixed dc bus voltage this reference can be used in a conventional inverter pwm scheme with feedback to apply the necessary correction.
In this idealized case the source current should be sinusoidal.
There are several techniques in the literature to achieve this, describe above is only the concept.
See: TC Green, JH Marks great review titled Control techniques for active power filters
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Hello,
I have a circular loop absorber with two dielectric substrates. I want to reduce the reflection at 3GHz. When i set the circumference to half of the effective wavelength, I got this simulation result.
My equation is why the second resonance is obtained at 12 GHz instead of the 2nd harmonic (6GHz)? And why is the reflection coefficient at 12 GHz smaller than at 3 GHz?!
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I think you will need to provide a better description of your ring absorber, the direction it is illuminated from, and the polarization you used, if you want an explanation.
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In the attached file, the harmonic-like sequence is defined. Is this kind of a sequence known in the literature? Do you know any source with the properties of such numbers?
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Thanks for the answer.
I don't need to do anything special, I just want to know if there are any properties of it.
The question comes from obtaining the formula from the attached file (omega function stands for prime omega function in number theory).
I don't get your observation about the derivative though (why did you change notation?). It doesn't really use any property of the sequence h_m^(r). Unless they do, but your anwser wasn't clear enough for me.
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Dear Lammps users, a vaste literature is available on the matter of molecular mechanics simulations of layers, “slabs”so to say, of different materials floating on each other. Typical examples are layers or bilayers of lipids on water.
In the final simulation, more often than not we may find a central water slab with two molecular layers symmetrically disposed adjacent to the opposite surfaces of the water slab, so, for example, the disposition in, let’s say the z direction, is “molecular layer A” – “water slab” – “molecular layer A”
Additionally, two empty spaces are added on top (and below) the molecular layers to avoid mutual interactions between the molecules of the layers. I forgot to clarify that the system is periodic in all 3 directions.
Layers are usually “built” alone and equilibrated (with either fix NVT or NPT) and subsequently combined to give rise to the above described system, which is then submitted to the desired simulation.
I tried several times to follow this procedure and the major issue was to avoid to have images conflict which immediately stops the simulation rising an error.
I found a trick which consists of preparing the water and organic molecules slabs separately by using fix addforce to constrain the molecules (water and organic) of each box inside a relatively narrow layer. This system is somehow equilibrated with fix NVT.
In a second step, with a specific program I wrote, the complete system A-water-A is submitted to simulation.
Actually, the simulation finally runs, even if I am getting an “inconsistent image flags warning” .
Honestly, I feel uneasy with my “trick”. It seems to me unphysical and I doubt that the authors in literature made use of such a cumbersome procedure.
I hope to find some “ultra-patient” and competent gentleman willing to comment on this.
My field of research is the regular synthesis of 2-dimensional polymers at the liquid-air interface.
MD simulations are an essential tool in my research.
Thanks a lot for your attention
Paolo Botto
p.s. herebelow please find the Lammps input script of a “toy” system of 16 molecules:
# LAMMPS INPUT SCRIPT M44 16 filename: in-M44-16-00
units real
boundary p p p
atom_style full
pair_style lj/cut/coul/cut 10 12
bond_style harmonic
angle_style harmonic
dihedral_style opls
improper_style cvff
atom_modify map array
pair_modify table 0
read_data lamdata-M44-16-00
velocity all create 300 887723
fix mynve all nve
fix mylange all langevin 300 300 100 314159
group mygroup type 2 4 # force acts on Oxygen and Nitrogen only
region myregion1 block 1.0 10.0 -42.0 42.0 -42.0 42.0
fix myforce 1 mygroup addforce -1.0 0.0 0.0 region myregion1
region myregion2 block -10.0 -1.0 -42.0 42.0 -42.0 42.0
fix myforce2 mygroup addforce 1.0 0.0 0.0 region myregion2
neighbor 2 bin
neigh_modify delay 0 every 1 check yes page 100000 one 10000
thermo 1000 thermo_style custom cpu step etotal temp press density dump mydump all custom 1000 dump-M44-16-00 id type mol xs ys zs
restart 1000 rest1 rest2 run 500000
write_data dat-M44-16-00 write_restart restart-M44-16-00
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Dear Sun, it is exactly as you say.
The way I build the system might affect results of later simulations.
Any recommendation?
Thanks
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I have completed the simulation of grid tied inverter and got voltage, current, harmonics distortion at PCC but i don't know how to extract features and process the simulation outputs for SVM training and classification in MATLAB
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Also you may take a look at this article:
"A novel Multi-LSTM based deep learning method for islanding detection in the microgrid".
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Is there a definitive way to determine the delay between the fundamental (800 nm) and it's second harmonic (400 nm) generated by a type 1 BBO?
Our Ti-Sapphire laser generates 800 nm pulses at 30 fs, a Mach–Zehnder interferometer is constructed. One arm is made to pass through a type 1 beta-BBO of 100 microns, while the other is not disturbed. The delay between 800 and 800 nm was determined quite easily before the type-1 BBO was placed, but a delay is introduced between the 800 and 400 nm pulses in one arm due to the type-1 BBO. Is there any way to determine the delay between them?
PS: The THG generation method was not advisable since control of individual intensities was not guaranteed in the said method.
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I do not quite understand your conclusion that type-I phase matching will give rise to a delay between fundamental and SHG as both pulses travel at identical phase velocities in the crystal. Of course, this does not mean that group velocities are identical, too, but as the SHG becomes most intense during the final stretch of the propagation I would not expect much of a measurable delay from that effect.
You can theoretically investigate this by setting up the coupled propagation equations for fundamental and SHG, including a group velocity mismatch. If you want to measure this then you can certainly try to set up an auto/cross correlator with a broadband nonlinearity, e.g., tightly focusing on a quartz substrate using surface SHG/SFG. However, you would unavoidably see dispersive effects due to beam splitters, lenses and air paths rather than the delay incurred during the original SHG process. There are ways around this, but this would be a rather challenging experiment for an effect that probably does not even exist.
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Greetings all. I am writing an input file for my simulation but I get error on the improper_style. I used opls force field so I used 'harmonic' style for it. But, it gives out error like so:
ERROR: Incorrect args for improper coefficients (src/MOLECULE/improper_harmonic.cpp:219)
Does anyone know where it went wrong or how to fix this?
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Israel Zadok thank you so much sir. Much appreciated.
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the @GLEONetwork #Zooplankton as Indicators Group #ZIG needs your help! We will harmonize zoop #data from #lakes globally & we still have a lot of white space! If you think your data can help, here’s our big project & DM if you have questions!
We’re so excited to have the support of 73 (!) #ZIG members already, but the more, the #data merrier! If you know of any #notwitter #zooplankton people who may be interested in joining the project, feel free to reach out and send information along! #PlanktonAreAwesome
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I investigated the Calanoid Copepod Centropagidae fauna of some 650 Tasmanian (Australian) subalpine lake and wetland systems and found that there were 3 distinct geographical provinces base on distribution of species. IS this of any use to you ?
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Goldbach and Euler’s proof is a typical example of what some historians consider a misuse of divergent series  , for it starts by assigning a “value” to the harmonic series ∑1/n and proceeds by manipulating it by substraction and replacement of other series until the desired result is reached.
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Incidentally, it is "normal" for pure mathematicians to bury proofs under mountains of guesswork and ambiguous expressions.
------------------------
I agree with Gioacchino de Candia.
And the most striking example of such behavior is the so-called "Great" Fermat's theorem, FLT. Almost 400 years of fun or tragic searches. Searches for "nothing".
But, in fact, this is nothing more than a lemma under the really Great Pythagorean Theorem, PT. This lemma can be easily proved using no more than a couple of lines on a sheet of standard paper.
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Let me consider harmonic oscillations x'' + x = f_t(t), where f_t(t) describes thermal stochastic force <f_t(t) f_t(t')> \sim \delta(t - t'). I have already understood, that I can switch from such differential equation to the integral equations, where the integrals can be performed in Ito or Stratanovich sense. Which one relates to the real situation?
Another case: escape probability. If I want to numerically extract mean lifetime of a classical particle in a potential well due to thermal fluctuations, what kind of stochastic modeling should I use?
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All this and more is described in van Kampen’s book ``Stochastic processes in physics and chemistry".
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Eigen energies of Hydrogen atom, treated as a central force problem, can be derived with Bohr model. Given the basic nature of the harmonic oscillator problem, it is a bit surprising why its solution may not exist in old quantum theory.
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The can be found exactly if you modify the Bohr-Sommerfeld quantization conditions slightly i.e. assume Closed_Integral p dx = 2 Pi hbar (n +1/2) but not
2 Pi hbar n . For the harmonic oscillator the integral p dx over one harmonic oscillator period between the turning points V(x_i) = E (back and forth from the one turning point) can be readily calculated as simply the area integral under the semicircle of the radius proportional to the square of the energy E i.e.proportional to Pi E /2 or 2 Integ_x1^x2 p dx =
2 Integ_x1^x2 Sqrt(2 m (E_n - V(x))) dx
2 Pi hbar (n+1/2) where V(x) = m omega^2/2 from what E_n = (n + 1/2) hbar omega can be obtained.
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I am trying to expand an explicit piecewise equation as a Fourier series formulation using Wolfram Mathematica software.
An example of these expansions is depicted in this paper ( ).
The two piecewise multi-parameter equations (eq. 12 & 13) are transformed into two Fourier series equations (eq. 14 & 15).
What is the best way to go about performing this expansion and how?
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You would perform an FFT on the time series and the value for the Fourier coefficients would be produced. You'll get a quite a few, so, truncating the coefficient series will be in order. From the truncated set of coefficients, you could could then build an analytic model.
If you want analytic expansions, you would need to produce the model first, then expand or fit that model to the time series, whether it were in time or frequency, regardless.
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I am trying to reproduce a paper which has followed a simulated annealing procedure with a simultaneous decrease in harmonic force constant.
a) Starts at 60 K, force constant = 5.0 x 104 kJ/(mol nm2)
b) After 20 ps, temp = 120 K, force constant = 2.5 x 104 kJ/(mol nm2)
c) After 40 ps, temp = 180 K, force constant = 1.25 x 104 kJ/(mol nm2)
d) After 60 ps, temp = 240 K, force constant = 0.6 x 104 kJ/(mol nm2)
e) After 80 ps, temp = 300 K, force constant = 0.3 x 104 kJ/(mol nm2)
d) After 100 ps, NPT step with 1 bar pressure, followed by production run.
Is there a way to automate this in a single mdp file? I understand how to perform simulated annealing using the nvt.mdp file, but how can I use a different posre.itp file (with the appropriate force constant) for each step of the annealing? Any suggestions would be really helpful.
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I don't think you can use only one .mdp file.
One choice is having multiple .itp files with the different values of force constants as Rezvan Marjani suggested. In that case you will have to include all the #ifdef statements in your topology file, and use the define keyword in the .mdp file. If you have (taking from the comment above)
#ifdef STRONG_POSRES
#include "posre_25kcal.itp"
#endif
#ifdef WEAK_POSRES
#include "posre_5kcal.itp"
#endif
in your topology, then the .mdp file for the run with 25k constant will contain the line
define = -DSTRONG_POSRES
while the .mdp file for the run with 5k constant will contain the line
define = -DWEAK_POSRES
Although the two .mdp files may be identical in the other parameters, you still have to modify the define keyword.
A similar approach which doesn't require many .itp files and gives more freedom is to generate a .itp restraint file with a variable, something like
[ position_restraints ]
1 1 X_VALUE Y_VALUE Z_VALUE
2 1 X_VALUE Y_VALUE Z_VALUE
3 1 X_VALUE Y_VALUE Z_VALUE
4 1 X_VALUE Y_VALUE Z_VALUE
...
Then, you include this file (let's call it restraints_file.it) in the topology with the keyword to define it, e.g.
...
...
#include "topology_of_the_thing_you_want_to_restrain.itp"
#ifdef POSRES
#include "restraints_file.itp"
#endif
...
...
In this case, in your .mdp file you define the keyword to 'activate' the restraints and also define the values of the restraints, something like
define = -DPOSRES -DX_VALUE=alpha -DY_VALUE=beta -DZ_value=gamma
where here alpha, beta and gamma are the values for the force constants you want to use. In this case you are saying to gromacs that you want to use the restraints (with -DPOSRES as you defined it in the topology) and then define the values to be used (note the -D in front of the variable names).
In this way you need just one .itp file with the restraints defined and play with their values from the .mdp file. Again, each simulation will require a different .mdp file, that is an .mdp file where you modified the alpha/beta/gamma values to match the values you need.
If your question was related to achieve something like the annealing, that is, run a single equilibrium run while modifying during the run the value k of the restraints (if T = a, then k = A, if T = b, then k = B etc, so that during the anneal the values change alone) then I don't think it can be possible with GROMACS, but maybe I'm mistaken.
Hope this helps,
Nicola
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Hello dear
There is a significant variation between official statistics of FAO, NRCS, and HWSD about the amount of global SOC over 0-100 cm depth of soils around the world. all of them have studied same areas of lands with almost same methods and even more, they shared database with each other. For example, one of the main resources of HWSD to calculate global SOC comes from FAO. However, there is a considerable difference between them:
total global SOC over 0-100 cm depth:
HWSD: 2469 Pg
NRCS: 1399 Pg
FAO: 1459 Pg
references:
1- Hiederer, R. and M. Köchy1 (2011) Global Soil Organic Carbon Estimates and the Harmonized World Soil Database. EUR 25225 EN. Publications Office of the European Union.79pp
2- Hiederer, R. Kochy, M. 2012. Global Soil Organic Carbon Estimates and the Harmonized World Soil Database. EUR Scientific and Technical Research series †“ISSN 1831-9424 (online), ISSN 1018-5593 (print), ISBN 978-92-79-23108-7, doi:10.2788/1326.
3- 1. Köchy, M. Hiederer, R. Freibauer, A. 2015. Global distribution of soil organic carbon – Part 1: Masses and frequency distributions of SOC stocks for the tropics, permafrost regions, wetlands, and the world. SOIL, 1: 351–365. http://www.soil-journal.net/1/351/2015/
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Dear Bajgai
Thanks. Over the past three weeks, more than 500 researchers and experts have read this key question, but apparently, there is not a clear answer for this tremendous gap between global-official statistics. Needless to say, such global-official statistics have been considered as the cornerstone of global environmental agreements, such as the Paris Climate Change Agreement. I want you to share this question with all of your followers to see can we found a possible answer or we have to wait for more.
Sincerely
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I'd like to discuss the question of the Role of Digital Shadows and Digital Triggers in the Digital Twin Concept. I think both terms play an important rule but they are not exactly defined til now.
You can see my point of view about in an attached poster for an order-oriented Digital Control Twin.
The Digital Shadow (DS) is only a Snapshot of a real object at a certain time, a certain location and for a certain 'cutout' that represents the actual state but not the entire object itself. To interpretate the DS it is very important therefor to define the exact time, location and cutout of the DS. and to store this data.
The Digital Trigger (DT) is only an impuls of the virtual twin at a certain time, location etc., to 'influence' the real twin but it is not the entire virtual twin itself.
The virtual and real twin are connected by a certain kind of regulator to detect and evaluate deviations of DS and DT and to harmonize them. The kind of regulation can be very different and depends on the object itself, the environment and the purpose.
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Hi Wilmjakob, I think your interpretation has the right to life – in the end, any digital control can be represented as a trigger. To be precise, I have not met the term “digital trigger” in this context before – it seems this is your term.
If I understand correctly, your goal is to give a general cybernetic scheme of DT in a broad sense (Concept of DT). I agree that the regulator (as in any cybernetic scheme) is determined by the features of the control task. But in the classical control theory, a model (in our case, DT in a narrow sense) is a part of the controller (“a model in the control loop”). The model (namely its structure, detail, accuracy) is also determined by the characteristics of the control task (that is, it is not a comprehensive model of the "whole" original, which is both difficult and unnecessary to build). At the same time in your scheme, DT exists independently, and a regulator is located between it and the original.
I understand and welcome the desire to separate DT. Psychologically, it seems that DT is more than just a model: it is a model that is permanently synchronized with the original, often (although not necessarily) in the form of a machine learning model (which was not previously in classical control schemes); DT may differ from the original (it is also an extension of the classical understanding).
In a word, your attempt (and the whole discussion) it seems to me very timely and productive, but it requires further research.
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  • Hello everyone, I have trouble getting a graph like this in ansys? The horizontal axis represents the x- coordinate and the vertical axis shows x axis displacement. Can anybody help? I can’t found this function in harmonic response.Thanks a lot.
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%Here is a simple code:
%=======================
clc;
clear;
c=0;
t=0;
for c=1:1000
t=t+0.0001;
w=2*pi*50;
wt=w*t;
x(c)=c;
a=exp(10*t);
y(c)=abs(a*sin(wt));
end
plot(x,y)
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I have a nonlinear ODE (second order) and exponential force in right side of equation ( q(t)=p0(1-t/t0)EXP[(-r*t)/t0] ) . p0, t0 and r are constant. I see in Nayfeh and Mook book only harmonic force. but i have a exponential force. How I can use from the Method of multiple scale to solve this problem?
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thank you Mr Anders Buen for your response.
yes, this is a sudden pressure wave that changes exponentially.
if I want to explain completely, I have 3 PDE-coupled equations for a plate. at the first, by use of some method, I changed 3 equations to 1, and then, by use of Galerkin method, I have 1 ODE equation that is a function of T. after use of the Galerkin method, the equation is in the frequency domain, But I do not know how to solve it when I have an exponential force.
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The Van der Pol oscillator can be give in state model form as follows:
dx/dt = y
dy/dt = mu (1 - x^2) y - x,
where mu is a scalar parameter.
When mu = 0, the Van der Pol oscillator has simple harmonic motion. Its behavior is well-known.
When mu > 0, the Van der Pol oscillator has a stable limit cycle (with Hopf bifurcation).
While we can show the existence of a stable limit cycle with a MATLAB / SCILAB plot with some initial conditions and some positive value for mu like mu = 0.1 or 0.5 (for simulation), I like to know if there is a smart analytical proof (without any simulation) showing the existence of a limit cycle.
Specifically I like to know - is there any energy function V having time-derivative equal to zero along the trajectories of Van der Pol oscillator? Is there some smart calculation showing the existence of a stable limit cycle..
I am interested in knowing this - your help on my query is most welcome. Thanks!
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The following steps are helpful for finding the dynamics of the system:
1. Check the stability of equilibrium by the Jacobian method.
2. Find the parametric conditions of stability/unstability.
3. Check what type of Hopf bifurcation (subcritical/supercritical) is there.
4. If the Hopf bifurcation is supercritical, then there is a stable limit cycle.
5. You can also solve the system numerically in Matlab/Mathematica and plot the limit cycle.
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Hello,
I have a question regarding the zero-sequence voltage injection in three-phase SSTs with bypassed modules in a failure case. I investigated some literature and it is clear that only the fundamental harmonic can shift power between the 3 arms (for power balance).
A 3rd harmonic is often used to reduce the peak arm voltages (-13.4%). However, I investigated asymmetrical fault cases and a 5th and 7th harmonic can help tofurther reduce the arm voltage by a small percentage like 5% (so less redundant modules are needed):
My question is: Do you know other methods to handle asymmetrical fault conditions in cascaded H-bridges or SSTs? Can I handle grid-imbalances like module faults, since the modules in the phase with an over-voltage have to transmit more power (if no zero-voltage injection takes place)?
I thank you for your suggestions and ideas.
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Or do you have experience in three-phase systems with a floating star point?
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Hi all,
Are there any standard benchmark power systems for harmonic power flow studies approved by organizations such as IEEE, IEC, etc or widely used by researchers to compare their methods?
Many thanks in advance for any hints or answers.
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The most widely used standard for power quality and harmonics is IEEE 519 standard 2014. The pdf is attached. Hope it helps.
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No matter what laser we use, or what sample we use (even if we use no sample) we are getting a peak at 804 nm, which is 12,437 cm-1 and a Raman shift of 6359 cm-1, if using the 532 laser. We are not sure if it's a harmonic, because its not an integer multiple. It is around 1.5 times of the second harmonic of 532, and about 75% of 1064, the overtone from the laser. It has shown up with no sample, and different samples in glass and plastic and quartz cuvettes, so we think it might have something to do with the laser. Does anyone have an explanation for this?
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Before starting of measurement first calibrate Raman Spectrometer using standard sample like silica substrate.It may be due to the detector (quality may be not good) used in Raman spectrometer. However, you may overcome this draw back by increasing the intensity of your laser, on increasing the intensity false signal will suppress (If you have power dependent laser source).
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I am trying to model the combined effect of a static and dynamic load on a cantilever beam. I have calculated the dynamic response as follows
1) Natural frequency and mode shape extraction (modes 1-5), see image
2) Steady-state modal analysis gives the steady-state response across a range of frequencies. I am looking for deflection with direct model damping of 2%. If I am not mistaken, this form of analysis require a load independent of time and essential applies harmonic loading to each of the natural frequencies and calculates the response at each frequency.
I am unable to apply a static load at this stage (steady-state modal dynamics) to observe the combined effect. See image for the deflection as a function of frequency. This is precisely the plot I want if I was just considering dynamic response. But surely, this would change significantly with a static load.
I tried setting up a static load in a step prior to the frequency and steady-state modal dynamics step but that was of no use.
Any tips on how to do this.
FYI, I am actually trying to model a chassis experiencing cyclic and static loading from an engine and am using this to fully understand the problem.
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Gabriel Zenkner, I had the same issue and I think I have found the solution. Create 2 steps, the static and the dynamic, and submit the analysis. Then, once you have the solutions to both problems, go to Visualization Module -> Tools -> Create Field Output from Fields. There, you can select Fields from each Step and Frame Increment. Once you pick one, it automatically adds the Field Variable to the big white upper box where you can write whatever expression you want. Also, to the right, you have a list of available operators. In the following example, I wanted to obtain the combined stress state due to static and harmonic loads, therefore: s3f1_S + complexReal(s2f2_S) (stress tensor due to static loads on frame 1 + real part of stress tensor due to harmonic loads on frame 2). The complexReal() operator is necessary since it appears that the harmonic stress tensor in stored in complex form.
Even though I selected to compute the real response only in the steady-state dynamic step, some errors show up when I tried to do the sum without the complexReal() operator.
Hope you find it helpfull.
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I´ve read about a platform that is starting, which is called RONDA, and I would like to know if anyone has some experience with it: https://rondadna.wixsite.com/ronda/research
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Hi Leandro
in the full variety of databases, you should have a look in OMIM (https://www.omim.org) and get some interests in UCSC (https://genome.ucsc.edu) where you'll get access in lot of data such as OMIM in a browser way.
fred
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What are the power quality problems produced through a solar inverter other than harmonics, overvoltage, overcurrent, overfrequency, undervoltage, undercurrent, underfrequency and surge?
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Dear Rounak Mohanty,
The main problem of energy quality in a solar power plant is the lack of stability of energy supplies due to changes in the weather and the cyclical nature of the power source, i.e. solar energy in the range of the day (day - night) and changes of seasons in the temperate climate zone. It is therefore necessary to improve the technology of energy storage. In addition, when developing energy storage technology, battery technology should be improved in order to create more environmentally friendly solutions when used batteries are recycled.
Have a nice day, Best wishes,
Dariusz Prokopowicz
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Hello
Anyone who has experience with operating a bidirectional DC-power supply as a load. I have an "ITECH6006C-500-40" and plan to operate a set-up with two motors as described in the simple sketch attached. I was primarily wondering if can directly just connect the 3-phase rectifier bridge (https://no.rs-online.com/web/p/bridge-rectifiers/0462130/) between the generator and the DC-supply(sink)? Are there any need to reduce the ripple output of the rectifier? I tried to simulate a simplified model in Simulink where I had the load represented by a resistor or a current source. See attached figure. The input current is alternating, though it does have harmonics.
best regard
Sveinung Attestog
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The nominal speed of my 4-pole motors are 3000 rpm. So the output voltage wil have a frequency of 100 Hz and after passing through the rectifier the ripple will have a fundamental frequency of 600 Hz. This exceeds the maximum frequecy of 200 Hz the DC-supply/sink can handle, which the maufacture ITECH recently informed me. So the filter is needed to recude the voltage ripple. But when I set a capacitor across the rectifer DC output terminals, the input current gets amplitude peaks that is 2 to 3 times larger than the average value of the output current. I also obsered this with experiment.
Is there a filter which is less harsh on the input? Smaller pk-pk amplitude and less smaller harmonics magnitudes relative to the fundamental component.
The attaced figure show the input (yellow) and output (blue) of voltage (top) and current (bottom). The output/load current is set by a current source.
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Is it possible in practice to choose 10% (5th and 7th) harmonics injected to the grid for harmonic mitigation of grid current for a grid-tied PV system?
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Have a look, this article might be helpful:
Kind Regards
Qamar Ul Islam
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I generated files for minimization in Gromacs through Charmm-gui. But, when I was searching the bonds between Mg and amino acid in the section [bond], there were not. On the other hand, I could find possible interactions in the section [pairtype].
I would like to know if I could change the function from 1 to 6 in the section [pairtype] for harmonic restraints, because this change would not be possible according to the manual.
I attached my topology file
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So amezing
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Hello,
I'm looking for examples in the human body which show periodicity, more precisely, I'm looking for examples of oscillating reactions that occur in the human body which can be modelled using the Hamiltonian of the harmonic oscillator such as described here:
for example, as mentioned in the comments, the circadian rhythm is controlled by the oscillation of protein concentration.
I want to read more about it, and I will be grateful to hear more examples so I can look for information about it online or if anyone could refer me to some reading material regarding this subject.
Thank you very much for your time and attention.
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The edocannabinoid system (ES) of the body, a regulator of cell signaling came to mind. I am learning a bit about it myself.
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Relation between electrostatic based problem and time harmonic electrodynamics problem.
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Dear Thomas Cuff, my doubt is for the analysis of the time-harmonic electromagnetic field, how can we take electrostatic behavior like inductance and capacitance into account. As the field behavior is completely different and wavelength is comparable with the physical dimension of the device, is it sufficient by considering capacitance per unit length or inductance per unit length? Whether we can calculate the field correctly by this approach.
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What is the reason of higher order harmonics in grid-connected converters and How these harmonics are eliminated?
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Harmonics
With modern switching converters distinction between low- and high-frequency harmonics is not so evident any longer. "Old" rectifiers and square-wave inverters caused clear harmonics such as 5th, 6th, 7th. PWM inverters have harmonic groups at the switching frequency, often in the order of 39th and higher (let's say up to about 200th). Then, only for inverters, think of Neutral Point Clamped and other solutions that allow an overall faster formation of thee waveforms, resulting in a higher equivalent switching frequency.
If then we move the attention to DC/DC converters (for connection to a DC grid), the switching frequency may be quite high.
One note: high-order harmonics can hit against network resonances, more easily than low-order ones.
Elimination
First of all, the architecture allows interleaving suppressing the lower order harmonics, moving the distortion to higher orders. There is a significat effort to do this, that implies that high-order harmonics are preferable. Why?
Although heating inside cables and transformers is larger (more skin effect, more iron losses), they can be filtered more easily, and they propagate to shorter distances inside the network.
So, filtering. There is a wide range of filters, usually built around LC elements (correction to Elyazid Amirouche 's typo, not a passive "RL"). The reason: L does not dissipate as R (some winding resistance, yes, remains) and reactance increases with frequency.
Which filter architectures?
1) for inverter output it is traditionally a LC gamma filter (series L, shunt C), where the C are joint in the neutral point, either fictitious or real.
2) what about network resonances and how to interface with variable network impedance?
> "modern" filters for e.g. PV inverters and in general used in microgrids are LCL (L series, C shunt) for a exigency of decoupling from the network. Think in fact that all LC gamma filters look into the network with their shunt C: you increase the chance of resonances and the flow of current between the filters -> put an additional series L for decoupling from network.
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One of the first things we learned about PDEs, is how the cylindrical harmonics (e.g. the Bessel functions J, I, K, and Y ) can be used to solve cylindrical boundary conditions. However I have never seen a paper discussing elliptical boundary conditions.
1) Is there another function that can be used for elliptical boundary conditions (NOT an ellipsoid but a prism with an elliptical cross-section) ?
2) What is the relation of these elliptical harmonics to the cylindrical harmonics?
3) If the answer to the above is yes, how might I compute these efficiently in MATLAB?
4) Is there a corresponding analog to Graf's addition theorem within the open literature?
Best Regards and Thanks!
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see
Elliptic PDE formulation and boundary conditions of the spherical harmonics method of arbitrary order for general three-dimensional geometries
Michael F. Modest, Jun Yang
Journal:
Journal of Quantitative Spectroscopy and Radiative Transfer
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my project is power quality and harmonic analysis ubder balancee load conditions under 0-2 Khz.
i was asked to measure each harmonic up to 2 kHz at different power levels and THD. i made a multidrive system upto 20 drives using Dipde rectifier and nonlinear loads
Change the grid impedance (1%, 5% and 15% base impedance) and see the differences.
so what frequency should i take my source and grid impedance values?
What does upto 2khz mean??
Do i keep my source at 2 khz ?
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I concur with Abdallah Adawy
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I read a review paper on СOVID. See the file. There is nothing about the
role of water in the process of infection and treatment from СOVID. How does a virus receive information from a cell that it can be attacked? How orders are transmitted in a cell about the beginning and end of complex processes of synthesis of biological molecules. Meanwhile, the role of water as a matrix of these processes is very great. Using the simplest models of the hydrophobic process, we have shown that in the water of the body, which is responsible for the hydrophobic interaction, there should be a large contribution of the water zero point energy (ZPE). A simple ZPE model is a harmonic oscillator whose energy is quantized. ZPE is a quantum phenomenon. The presence of ZPE in the body can be easily checked by the isotope effect. If there is a ZPE contribution in the cell water, then there must be an isotope effect.
To do this, you need to do the following experiment. To a certain concentration, humans and mice tolerate D2O well. It is necessary to select this concentration and compare the infection with COVID without the addition of D2O and with H2O.
I have not found any such research. If someone has such opportunities, I will consult in detail.
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I am not sure what you mean by water. Do you mean the composition on the cytosol? (Around 7).
About the virus, the virus seeks the molecular recognition to take place. However, thismight be the mechanism sensed by the innate inmune response, or why the eyes and brain are "difficult" almost hermetic to open (like a lock). The inmune system recognises the proper molecules otherwise we have autoinmune diseases. Allergies are mistakes, but the minor allergies can be corrected with the help of a doctor.
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Hi Everyone,
Could anyone please help me find a good reference book in which I can find detailed information (including the basic formulas) about working of 3-phase inverters, harmonics, as well as their control techniques SPWM and SVM.
Thankyou in advance.
Kind regards,
Silpa
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I recommend the following list:
1-voltage source converter: modulation, control and applications in power systems by Grain Adam
2- Voltage-Sourced Converters in Power Systems : Modeling, Control, and Applications by Yazdani
3-T thesis Cooperative power sharing control in multi-terminal VSC-HVDC Authors Hasan Alsiraji
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The OTA (Single Ended) is an amplifier consisting of a current mirror, controlled sources and a differential pair. It is advised to study / implement the different structures separately before making the complete design of the OTA. Explain the type of structure you choose for your design (topology)
This OTA must have:
to. Gain in tension> 70 dB
b. Gain band width> 100 dBMHz
c. CMRR> 110 dB
Emphasize in the specifications:
- Slew Rate
- Gain
- Power dissipation
- Common Mode rejection rate (CMRR)
- Power Supply Rejection ratio (PSRR)
- Band pass
- Total harmonic distortion
- Distortion of the 3rd harmonic
- The transconductance
- The power of supply
- Polarization current
- Offset
Thanks a lot
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The first step for OTA design is by using the power constraint to find the tail current. After that, using the bandwidth criteria you can calculate gm of the first stage. Then simulate the design to check the gain. in case you need to increase gain, you can enlarge the length of the output devices and run again until you achieve the gain. Be careful about the phase margin which can always cause fluctuations. You can always increase the phase margin by compensation. In fact, Slew rate and power have strict trade off, therefore, satisfying both may be impossible which may force you to change the topology.