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Hi,
I am working on numerical simulation of ultrasonic wave propagation through an elastic medium without any defect. I calculated the velocity of wave by using time and distance relationship. But when i used model with void or crack, i got less time to detect the first wave, while it should be longer as there is hole in model and wave propagation through it should be more. Can anyone help me out this problem i.e. how wave velocity is calculated in the model with defect.
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I am trying to slove the standard rayleigh lamb frequency equation in isotropic plate using the newton Rapson method ( FORTRAN code ) but I am not able to capture all the root of the equation and modes, even not getting how to generate the data for plotting the dispersion curves... Kindly , please help.
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Hello to all
Two questions
1. Does the use of metals with high magnetic permeability, such as iron alloy in the waveguide, cause insertion losses?
2- What about chrome or copper plating?
If you know the article in this field, please introduce it. Thank you
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Please find the attached files.
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I want complete information about calibration methods of Network Analyzer. I want step-by-step calibration steps.
Is it better to measure waveguide components SOLT or TRL ??
What is the difference between SOLT and TRL?
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Dear all,
I want to apply the "periodic" boundary condition to the existing boundaries along wave propagation direction in a curved cell unit (attached image); However, this boundary condition does not appear to be applicable to curved surfaces, and some changes to the coordinate system used are required.
Unfortunately, I do not know what coordinate system to use and how to use it in "orientation of source".
I would be grateful if someone would help me.
Any help would be extremely appreciated.
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Mehran Ebrahimi, I think you should add a new coordinate system, cylindrical one. In Definitions - Coordinate systems - Cykindrical system
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When we need to conduct a FE simulation of guided wave propagation, small element size and time step must be used to capture the waves, especially for high-frequency cases. Millions of elements would be normal for a model with a small size, say a plate with a dimension of 200mm*200mm*1mm. Is there any shortcut to avoid this type of difficulty or software that is more suitable for this work than ABAQUS or ANSYS, .etc?
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Hi Han Lu
Whether/how much you can simplify this problem depends on many different factors. You may consider the following aspects:
- Is a two-dimensional model sufficient? -> Employ plane strain assumption.
- If not, can it be treated as axisymmetric? -> Exploit rotational symmetry in FEM or even solve (semi-)analytically
- Is the frequency very low? -> Use plate elements to avoid discretizing the thickness
- Is the frequency high? -> High-oder elements can be worthwhile, together with explicit solvers (if not frequency domain)
- Is the material linear? -> Solving in the frequency domain may be more effective.
- Is the structure of (piece-wise) constant cross-section? Semi-analytical approaches (SBFEM, TLM, SAFE) can be extremely efficient.
- Can the dimensions of the model be reduced by applying absorbing boundary conditions? -> Use SBFEM, PML, absorbing regions....
I hope this gives you some ideas to start. Feel free to ask about details of any of the approaches.
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Modeling multi-phase flow propagation using Ansys Fluent, OpenFOAM, Flow-3D, etc., how the force, such as Drag force and Surface Tension, apply to each of the phases?
What about other forces? Do the forces such as, Added Mass, and Basset Force apply in the all phases? How?
Is there any concise reference or instruction for the modeling of multicomponent fluids?
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Some math about your questions and useful references.
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Hello .
I want to design and build a waveguide load in X Band.
1- How to design that the VSWR is maximum 1.1? (What should I use inside the waveguide, what material? With what dimensions?)
2-How to test it with Network Analyzer after making it?
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Buy a sheet of microwave absorber, cut a long triangle with a sharp point and glue it to one large wall of the waveguide with the point pointing towards where the power comes from, or glue two to both large walls. The longer the triangle and the sharper the point the better the match, generally. You can do it with stepped absorbers, or a pyramidal absorber too. It is hard to design to a vswr of 1.1 unless you design a stepped absorber and are very sure of its complex dielectric and magnetic constants, but making a taper longer will usually improve the vswr. The sharpness of the point is important. If it needs to cope with high power the sharpness of the point can be a problem because it may melt if the absorber has high absorption.
You could glue it to the side walls but it may need to be longer, depending whether the loss is magnetic or resistive.
You can also use a vane of nichrome on kapton film between slits on the centre-lines of the wide faces of the waveguide. If you do this you can adjust the way it tapers in while looking at the S11. https://www.dupont.com/products/kapton-rs.html might also be suitable.
You can test it on a Vector Network Analyser (VNA) with a good coax to waveguide adaptor. 1.1 vswr is about -26 dB so if you want to be reasonably accurate the adaptor needs to have S11 less than -40, unless you can calibrate on the waveguide side, using waveguide open short and load, for instance.
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I was wondering if surface electromagnetic waves can propagate at interface between two dielectrics, both isotropic and homogeneous, but having different relative permittivities.
The literature shows that their characteristics must be different.
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Yes., there will be propagation of surface waves at the interface between the two dielectrics of the same properties. It is because they will have a different set of characteristics, which arise due to the difference in disturbance of equilibrium of positive and negative charges (Polarization). These displaced charges create an electric field of varying magnitude. It is different from the field produced by the surface wave.
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In an absorbing medium, the reflective index becomes a complex number: 𝑛̃ = 𝑛 ′ + 𝑖𝑛 ′′. Assume that a plane wave 𝐸⃗ (𝑥,𝑡) = 𝐸⃗ 0𝑒 −𝑖(𝜔𝑡−𝑘𝑥) is incident on this medium. (a) Starting from the plane wave dispersion in a medium (ω = 𝑐 𝑛 𝑘), show that the field intensity (|𝐸| 2 ) decreases exponentially over distance (i.e. |𝐸| 2 ∝ e −𝛼𝑥). (b) Express the absorption coefficient α in terms of other parameters.
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Looks like you are trying to get someone to do your homework for you.
Use (n'+in")k instead of k
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Hi
I wanna solve partial differential equation in terms of x and t (spatial and time), As I know one of the most useful way for solving pde is variable separation. well explained examples about mentioned way are wave equation, heat equation, diffusion....
wave equation is Utt=C^2 .Uxx
in other word; derivatives of displacement to time, equals to derivatives of displacement to spatial multiplied by constant or vice versa.
however my equation is not like that and derivatives are multiplied to each other.for example : Uxx=(1+Ux)*Utt
Im wondering how to solve this equation.
I will be thankful to hear any idea.
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Partial differential equations can be solved with Mathematica. They have a free version online.
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I have heard that SWAN software is free software. But I am unclear whether SWAN software independtly exists or is it used in conjunction with Delft3d software.
Also, if there are any other software, please suggest.
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That is a good question. I want to follow this.
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I want to apply a pulse-echo methodology (by using one single transducer as both transmitter and receiver). Do you know how to connect the transducer to the wave generator and oscilloscope to detect both transmitted pulse and echoes?
I have been trying to use the burst feature in manual mode by pressing the trigger button in the wave generator. However, when I do that, the oscilloscope is only capable of reading the wave generated instead of receiving as well the back-wall echo.
I am also using these types of transducers from Stemininc: Piezo Ceramic Plate 20x15x2.1mm 1 MHz, Piezo Ceramic Plate 7x7x0.2mm 250 KHz, and Piezo Ceramic Plate 20x15x3mm 710 KHz. Thus, I'm not sure if they are indicated to use this pulse-echo methodology.
I have two alligator cables connected to the oscillator and to the transducer: 1 to work as the transmitter and one to work as the receiver; and they are both connected in the same wires of the transducer. However, so far, it seems that these alligator cables connected to the same transducer are giving me the same wave. 
Do you know if this equipment as it is is capable of doing these readings:
  • reading of the transmitted and received waves (of amplitude vs. time), separately, by using this setup as is (when using two different cables), or
  • reading of the transmitted and received waves combined in the same curve: maximum peak sent and resultant received echoes (back-end wall or cracks, for example)?
I am using a manually triggered pulse sine wave of amplitudes of either 10Vpp or 24Vpp, but the outcome is always identical. Should I be using a higher amplitude to make sure I receive the echoes?
Any help would be much appreciated.
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You basically need a T/R (Transmit/Receive) switch between your signal generator and your transducer, and your oscilloscope and your transducer. When your signal generator is producing the outgoing periodic pulses used to drive your transducer, the T/R switch disconnects the oscilloscope from the transducer. While your transducer is receiving the reflected signal between the periodically generated pulses from the signal generator, the T/R switch connects the oscilloscope to the transducer, but disconnects the signal generator from the transducer. Note, be aware of the concept of range ambiguity, i.e., if the reflecting surface is further away than the round trip time between two of the signal generator's pulses, then the incoming reflected signal may fall between the next two pulses of the signal generator making the reflecting surface's distance appear shorter than it actually is.
How you actually realize your T/R switch will depend on your drive signal amplitude, and the input impedance of your oscilloscope.
Regards,
Tom Cuff
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Recently, I got a revision on one of my papers in which the reflection and transmission phenomenon of waves has been studied in a piezoelectric medium with the consideration of a flexoelectric effect.
In the said article I used the classical method for finding the amplitude ratios of the waves.
However, the reviewer suggests that
" It would have been better if the solution methodology was based on Lame displacement potentials where the dilatational and the distortional character of the waves are more easily distinguished."
But as far I know this methodology, the Lame potentials are best suited for the isotropic media.
So,
Is the Lame displacement potential method can be used for transversally isotropic media?
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Dear Sonal
If the problem of electroactive, plane deformation in a piezoelectric is formulated in the isotropy plane of a piezoelectric, then the method of introducing potentials is possible.
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I want to establish the influence of prestress on the propagation characteristics of guided waves, and analyze which guided waves in which modes or frequencies are most sensitive to stress changes
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Dear Li Jiaxin,
A good discussion of the foundations of initial stresses effect on guided waves can be found the literature, among them those published by Otmani et al.: https://doi.org/10.1016/j.compstruct.2020.112085
Generally, The fundamental guided modes can achieve superior of sensitivity to disturbances due to acoustoelastic effect, that could be considered for characterize the performance of the selected composite and structure.
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While going through different Rayleigh wave propagation papers. I have seen sometimes author is using Helmotz decomposition and sometimes not. What is rule? When should we use it? Any suggestions will be helpful.
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Dear Dinesh, using HD reduces the model to simple system so that you would get the frequency equation. If would not use HD, you might be in trouble sometimes to get the frequency equation and related parameters of interest. If your model is simple one (for isotropic), then you can go in anyway. Hope you understand.
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Hello everyone,
I'm trying to implement a material with non-diagonal conductivity in my FDTD code. By the way, I'm using Dr. Elsherbeni's code for my purpose. Although I managed to implement diagonal anisotropy in my code, my code seems to be unstable for non-diagonal matrices. Through research, I've found out that my updating equations are not correct. Since it is necessary to interpolate the fields in irrelevant positions, it seems the updating equations also have to be organized differently than the isotropic case.
I attach the equations in a PDF below. the first equation on every page represents the equations in half-steps and the second one represents the updating equations implemented in the code.
Any help or hint would be appreciated.
I also have to point out that the source for the equations is the paper in the link below:
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Actually the implementation is not that difficult - if you like you can check my lecture notes, pp. 202-203:
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We are currently investigating the shock response of materials using molecular dynamics (MD). This project showed us that the preparation of properly equilibrated MD models can be very challenging even for someone with a strong background in molecular modeling. Therefore, we thought of sharing some of our recent MD models with the research community. We would like to share the LAMMPS input and data files required to run MD simulations of shock wave propagation and ballistic impacts. I have provided ~3-minute video overview of the files here: https://youtu.be/hgZXvUdr-Qo
You can download the shock model from here: https://github.com/nuwan-d/MD_model_JAM-21-1174, and the impact model from here: https://github.com/nuwan-d/md_impact_tests
(Added on 2022/01/14): We recently published two more articles, and our MD (LAMMPS) and DFT (VASP) models are freely available.
The first is “Quantum and classical molecular dynamics simulations of shocked polyurea and polyurethane” (https://doi.org/10.1016/j.commatsci.2021.111166). The models are available here: https://github.com/nuwan-d/quantum_md_of_shocked_polymers
The second paper is “Molecular dynamics study on the shock induced spallation of polyethylene”( https://doi.org/10.1063/5.0072249). The models are available here: https://github.com/nuwan-d/shock_response_pe
(Added on 2022/06/08): Our latest MD (LAMMPS) and DFT (VASP) models of phase-separated polyurea are available here: https://github.com/nuwan-d/shock_response_of_polyurea
Good luck with your MD simulations.
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Thank you Vadym Slyusar.
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I am doing simulation in Abaqus. My topic is damage detection by using lamb wave propagation.
I am giving input data as sine sweep(48 sec). For that what is the time step and how much increment should use to get the output result and what is the approximate mesh size should be used. And what are the inputs we have to include in f-output and history output.
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Feel free to get in touch with me for more explanation.
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I am currently modelling an acoustic planar wave, generated by a speaker, travelling through an expanding cross sectional area duct/horn system. When plotting a graph of transmission coefficient against frequency, the model suggests the transmission coefficient is between 0.5 and 1 for all frequencies. Should transmission coefficient, defined as the ratio of output to input amplitude, have a transmission coefficient above one, or do my results seem feasible?
Note, the medium through which the wave propagates is constant (air).
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Sound is not water progressing in a pipe... You have to bring into your picture the notion of impedance matching between your sound source (the speaker membrane moved by a linear electromagnetic driver) and the medium (air in open field). The horn contributes to reduce the impedance gap hence increases the radiation effectiveness of the speaker - this is true only in a limited frequency band where the extent of the membrane is a fraction of the acoustic wavelength (every one knows you need bigger loudspeakers for lower frequencies). With a poor impedance matching only a mere fraction of the mechanical power will turn into acoustic power. This means that, for the same electro-mechanical driving force (or membrane velocity), you will increase the SPL in the open space by inserting your horn thanks to the better impedance matching, without contradicting the principle of energy conservation. This is what you have seen maybe - depending of the choice of "input" defining your global "transmission coefficient". As rightly commented by Anders, the impedance mismatch at any step of an "acoustic path" acts as a partial reflector: when the impedance matching is poor, the electromagnetic driver of the loudspeaker is unable to deliver "active power" in the open field. You can separate active and reactive power indirectly by measuring the out-phasing between tension and current in the coil (but you have to factor the Joule effect), or directly by measuring the sound intensity (e.g. from the pressure gradient https://en.wikipedia.org/wiki/Sound_intensity) anywhere along the acoustic path...
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Talking to Dr. Jörn Schliewe inspired me to raise this illustrated question and how you may call these barriers in the experiment of diffraction? Would you call it n-slits or n-obstacles?
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Well, first, it’s N+1 obstacles or if you don’t want to count the long walls at either end for some reason, N-1obstacles, but certainly not N obstacles.
It certainly doesn’t matter what you call it. In your picture the two terms are both correct, and not mutually exclusive. It is in, in fact, N+1 obstacles forming N slits.
I don’t think anyone misunderstands that slits are formed by barriers, and if you talk about N slits everyone will instantly picture a barrier with slits in it. However, on a practical note, at optical wavelengths it generally isn’t possible to have free standing barriers like this. Instead the solid wall continues above and below. Generally a transmissive grating looks like a solid barrier with ”slits” cut into it. So the ”slits” term is constructivist. It is indicative of how the structure is created. You cut slits into a foil or similar. That is the dictionary definition of slit: a narrow cut. That is also how this became the standard terminology in optics because in the early experiments that is literally how gratings were made. We’ve greatly improved our “knife”, but fundamentally that is still how subtractive transmission gratings are still made today.
Terminology is for understanding, and often it uses similarity for recognition. No one thinks the arrow slits in a castle wall were literally made by cutting, but they look like cuts. If you call them slits everyone understands what you are talking about. That is the only important cr for terminology.
In optics we always talk about the slits. This is probably because we are focused on the light. Each slit is treated as a source, we propagate on using Huygen’s principle, etc. It doesn’t really matter what the barriers are so long as they exist. However, we have to talk about slit width and slit spacing, so in what an artist might call “negative space” we are inevitably also describing the barrier. Everyone gets that. I don’t think I’ll switch to explicitly talking about the barriers any time soon
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Staggered grid finite-difference (FD) methods are widely used for elastic wave equation modelling because of their high computational efficiency, smaller memory requirement and easy implementation. I am looking for the mathematical foundation for higher order (8th) of finite difference staggered-grid method on 2D P-SV elastic wave propagation.
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Dear Dr.
Ijaz Durrani
,
Thank you for suggesting me this article to me. I will read it.
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If water waves are disturbance of the water medium , the light is electromagnetic waves, and the gravity is space-time waves, then what is the medium in which the quantum waves propagate?
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I agree that electromagnetic waves do not need a medium to propagate; however to propagate they do need a (spacetime) metric. I think that the same would be true of quantum waves.
Thus they do not need a medium to propagate in, but nevertheless need a metric to propagate "on".
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I am using transient solution type in HFSSv15, and two same UWB Antennas are in far field of each other. One antenna is transmitting and other antenna is receiving antenna.
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I don't think so , you have to use a Matlab script to calculate it
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I have read numerous research papers on various mechanisms of excitation of surface plasma wave. But why do we need to excite a wave? Is it necessary? Can't the wave propagate without being excited?
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The excitation of surface plasma waves (SPW) by an intense short laser pulse is a useful tool to enhance the laser absorption and the electron heating in the target. In this work, the influence of the transverse laser profile and the pulse duration used to excited SPW is investigated from Fluid and 2D Particle-in-Cell simulations. We show the existence of a lobe of surface plasma wave modes. Our results highlight surface plasma waves excitation mechanism and define the laser parameters to optimise the SPW excitation and the kinetic energy of the associated electron trapped in the wave. It opens the door to monitor the spectral mode distribution and temporal shape of the excited surface waves in the high relativistic regime. The most important result of the study is that—at least in 2D—the charge and the energy of the electron bunches depend essentially on the laser energy rather than on temporal or spatial shape of the laser pulse.@
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I need information concerning the penetration and reflection capacity of ultraviolet and infrared radiation wavelengths on different most common materials.
Edit.
Can somebody recommend a book to learn about? I'm especially interested in spectrogroscopy with a city environment materials and albedo.
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First of all it depends to the material studied, and for me i guess that IR is more better then UV cause its wavelength is bigger than UV.
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Dear everyone,
I performed some experiements with a FMCW Radar Instrument emitting waves of 3.8mm. I can see some "movements" when I am looking on the relative displacements (+/- 0.15mm) over multiple stable points (corner reflectors). I assume part of this "displacements" is caused by temperature, humidity and pressure variation over the time of measurement (outdoor experiment). However, when applying Rüeger (2002, Refractive Index Formulae for Radio Waves) formula then the values are about a factor of 10x too small. There does not seem to be an error of units. The paper mentions resonance lines at about 67GHz and I am wondering if this could have an influence on the measurements with 79.5GHz and is there a publication specifically for the frequencies around 80 GHz?
Would anyone have a suggestion what else could cause this "movements". The radar and the targets are mounted on a concrete pillar and I assume that there is no relative displacements due to the similar setup.
Thank you very much and best regards,
Andreas
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Very interesting question
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Can someone provide the wave propagation assumption that applies to the transfer function-based square impedance tube method. How it differs from a cylindrical impedance tube?
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Ijaz Durrani
Thanks Sir
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If we consider a marine communication scenario, what are the factors affecting the propagation of radio waves other than reflection, refraction, diffraction, scattering, and antenna height?
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absorption
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As part of my research, I need to couple a loaded, custom-sized, rectangular, waveguide (in which a hybrid mode propagates at 8.5GHz) to either a) a coaxial transmission line or b) to a standard X-band waveguide.
I need to understand the design and optimization processes for both including impedance matching and/or mode conversion as required.
What is the best, most efficient way of approaching such a task?
Any useful resources on the topic would also be very much appreciated.
Kind Regards
Simon
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ok I see ..some metamaterial..which definition for the "wave impedance" are you using.?.500 Ohm appears rather high to me and depends on the type of mode.For more detail you can consult the books by Pozar on microwave engineering
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Hi,
I am looking for a good summary of advances done in the field of multiscale modeling. Would appreciate it if people working in this domain could link me to relevant publications/ articles.
Thanks,
Pranoy Nair
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I recommend the follow reviews on computational approaches of metal-organic-framework by Professor Coudert's group:
Fraux, G.; Chibani, S.; Coudert, F.-X., Modelling of framework materials at multiple scales: current practices and open questions. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 2019, 377 (2149), 20180220.
Evans, J. D.; Fraux, G.; Gaillac, R.; Kohen, D.; Trousselet, F.; Vanson, J.-M., et al., Computational Chemistry Methods for Nanoporous Materials. Chemistry of Materials 2016, 29 (1), 199-212.
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I wish to apply Floquet boundary condition at left-right ends and up-down ends, and the wish to find out the dispersion relation for the unit cell.
But I fail to find any option of Periodic condition in the list. If I make this an area-type geometry or a volume-type geometry, I can find the option, but not for the geometry provided (see attached image).
Please help me on how to do it. Thanks in advance.
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Floquet-Bloch periodic BC in COMSOL is applied on surfaces in 3D or edges/lines in 2D. This is because the source point is computed using a rotation of the position relative to the destination, i.e. rotation matrix R is computed. This is usually evaluated from the cross product of the source and destination boundary normal directions. Since normal directions are not defined for a point (which is exactly what you intend to select in your particular FE setup), the software does not provide that option.
The "Spadoni et al., Wave Motion, 40(7) (2009)" paper uses the discretized FE model approach by treating the rigidly connected lattice links as Timoshenko beams. In fact, the best way would be to model the 2D/3D geometry of the unit cells without making an assumption of rigid connectors/beam theories.
Check below the two papers that model periodic BCs of the auxetic unit cells, one uses the beam model approach while the other uses full geometry:
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To draw fragility surface based on the peak ground acceleration (PGA) and wave propagation velocity (PV), it is necessary to make accelerogram with different values ​​of the PGA and PV.
Is it possible to change the wave propagation velocity in earthquake accelerogram? Or can I produce accelerograms with different wave propagation velocity?
Thank's
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Kutubuddin Ansari Thanks for your answer.
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Hi, I am trying to create a computation model of acoustic plane wave propagation through multiple layers of fluid. What should be the appropriate boundary conditions in my fluid-fluid interface? Thank you.
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The pressure and the normal components of the velocity have to be continuous across the boundaries. See for example in Fundamentals of Acoustics by Kinsler, Frey, Coppens, and Sanders Chapter 6.
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I have the following scenario.
In a marine environment, an object X moves below the surface of water from point A to point B. As it moves it displaces water around it which creates ripples (or increases detectable pressure levels) in the surroundings. We have sensors Si installed underwater at distance di with known geographic positions. I want to know the following.
1. How do we measure the intensity I of the ripples (generated by the object) at any sensor Si located di meters away from the object?
2. How do we measure the time required for the propagation of the ripple from its origin to sensor Si such that sensor Si can detect intensity I.
Thanks
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Hi Tariq. It was a suggestion i have given. Hope it works.
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I am in a urgent need for material explaining the basics of wave propagation in soils. I came across lot of advanced material, which deals with specific conditions. Kindly suggest a good book or article about this.
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Dear;
Kindly check:
Ground penetrating radar 2004 2 ed
Regards
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I am conducting a project where underground blasting effects are analysed on soil and structures above the soil. I've currently only have a very basic Abaqus model of a soil block with an implicit dynamic step. A time history amplitude was induced on this basic block model of soil. It shows the stress wave propagations. It has parameters for the Mohr-Coloumb plasticity. I am looking for books or any literature to further understand how the vibration of the blast will effect the soil layer, and possibly different layers of soil (rocks, clay, silty, soil etc). Any help or advice is appreciated!
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ERT
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I did an experiment on a glass composite thin plate and generated Lamb wave. I increased the stiffness of the plate by forming a sandwich structure. I could find Ao mode with very attenuated amplitude but So is very diminishing. Confused, as per my understanding, I should get both modes frequencies even if the amplitude is small. But only Ao I could obtain its frequency but So not.
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The dimensions of the thin plate, the configuration of shaker or input device, support and/or constraint of the specimen during testing, the location or distribution of area being measured for signal to test for Ao & So, as well as what transducer(s) or optical technique(s) is/are being used for those measurements, and what circuits and software are being used to condition and process the signal after acquisition.
The are many reasons that may be causing attenuation or lack of effective detection or isolation of the desired or expected signals, including that they actually may not be there at sufficient energy level for effective detection. Are you sure your estimated values for So of the increased-thickness sandwich plate are reasonable and don't actually predict the lower So values? Are you measuring 'lamb' waves on one skin of the sandwich only or of the entire plate (i.e. do you have transducers on both surfaces of the plate with careful and accurate reproduction of phase in both cases, and relative to one and other? Do you isolate or effectively filter frequency or wavelength anywhere in the process of your data collection, conditioning and/or post-acquisition processing? Are the 'lamb' waves on the skin or in the overall plate, what is the ratio of characteristic wavelength to plate thickness and how did this change by your structural alteration?).
Without knowing more of your setup, you experiment and your instrumentation, it is difficult or impossible to offer meaningful guidance.
In terms of a general vibration measurement problem, what signal are you expecting and why? Does the measured value represent something that seems impossible or not, it the result within or nearly within the expected range, and if not, is there something in the method or instrumentation or conditioning/processing that might explain any observed discrepancy? Hope this helps.... -TH
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As we know,the pulse propagates in wave form and the velocity of wave propagation depends on the propagation medium features. So,Is it possible to use the measurment of velocity of pulse propagation in the body to diagnose cardiovascular problems such as hypertension and hypotension?
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I used the waveguide port to excite the momopole antenna and get appropriate results and now i want to alter the type of port to discrete port but I got different results with discrete the port.
Any one have experienc to help?
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I am not familiar with CST, I work in HFSS. In HFSS if the port is inside radiation box instead of waveport, a lumped port I used
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Hello i attached system of wave equation which is solved by using FDM. But i could not run this in matlab program as like wave propagation.
So i need your help can any one help me to write a code of that Scheme which i attached.
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What part of it troubles you? It is a simple system of PDEs with an explicit scheme to solve. You can introduce a 2D square grid of points, introduce the initial condition on the grid points, and write a for loop for the last two equations. Then save the results of each step for all points and then you will get your space-time solution.
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Hello,
I am working on the finite element modeling of the ultrasound wave propagation. I want to check the wave transmission from water (impedance 1.5 *10^6 kg/(m^2.s)) to two different materials:
#1: Density=1050 kg/m^3 wave speed=2297.2 m/s acoustic impedance=2.41 (*10^6 kg/(m^2.s))
#2: Density=2000 kg/m^3 wave speed=1664.5 m/s acoustic impedance=3.33 (*10^6 kg/(m^2.s))
Based on my model, the reflection from water to material 1 is higher than 2. What is the reason for it? Material 2 has higher impedance, therefore should lead to higher reflection!
The wave speed in material 2 is really close to the wave speed in the water (1500 m/s). Does this cause less reflection at the boundary?
Thanks,
Hamed
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Hi Abdolrasol,
What about the transmission amplitude, for the two cases?
How did you connect the Solid boundary to the water boundary?
At the boundary, if you have an option to choose the slave/master material, do not give water as the master material.
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Hello,
I am working on the lamb waves based on the semi-analytical finite element method (SAFEM) in the laminate structures.
When drawing dispersion curves, a number of additional curves are created in the system. I wanted to know what caused these curves to form and how can I eliminate them.
You can see the diagram in the attached files.
Thanks a lot for comments and answers
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Hi,
I resolved similar issue by using Tangent delta (Tan D) parameter .
To calculate and plot the dispersion curves , the wave-number from SAFE need to thresholded by choosing the appropriate value of Tan D value.
Hope this helps!!
Regards,
Dileep
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I have submitted a paper in a journal where a primary radiator is surrounded by 36 periodic symmetrical structures similar to what is shown in the attached picture.
I have named it a metsurface patch antenna. The reviewer thinks it is it is a "CP patch antenna coupled with parasitic elements" NOT a metsurface patch antenna.
I want to know how we can differentiate between parasitic elements and metsurface?
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It's about propagation: desired effects, versus undesired effects.
Do you agree?
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I am simulating wave propagation in a plate. In that process, I need to apply nodal displacement in the radial direction at the actuator position. I entered the wave excitation signal in the amplitude module. But when I am trying to select the displacement direction, I am not finding any option to apply radial displacement. I have attached the image of what I want to achieve. If anyone can help me out, I will be grateful.
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You are welcome. Good Luck.
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I am trying to run a coupled model (HD and SW MIKE 21), for a one year period (8760 time steps; 3600 time step interval). However, after approx 200 time steps there is an Abnormal Run error, 'Blow-Up wave height too large'. What are some reasons that would cause this, and some solutions?
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Ariel Mohan Aesthetics in cities are not merely a matter of taste, but something that is linked to culture and what is most noble in a community. It reflects a world of meaning about that space and the people who occupy it, in addition to maintaining order and a sense of transcendence. Urban aesthetics is a way to exalt this world of meaning and express the ideals and values of a people. It is not a question of preserving the traditional because it is old, but of preserving the past due to its importance and beauty. Beauty is a spiritual good and, as a spiritual good, it is part of who we are. I recommend reading the attached text.
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Hello! I apologize for the long question, but I’m a bit lost so I’ll try to be as precise as I can.
I am trying to implement a time-domain PML formulation for wave propagation, which can be found in this work
Here, the author has developed a set of equations to deal with the wave propagation in fluid and solid medium (please refer to eq. 5.9 of the work as I can't copy-paste them here). They are valid throughout the whole domain (PML and the physical domain), and within the physical domain the equations simplify to the general wave equation.
I'm using FEniCS as the Finite Element solver, and I need to provide the weak form of the PDE I'm willing to solve. Fortunately the weak form is in the work too (please see eqs. 5.10a-d).
I'm concerned only with the wave propagation in the fluid region, so I consider only eqs. 5.10a and 5.10c. Moreover, in eq. 5.10a, I believe the term with the integral over gamma vanishes as there is no fluid-solid interface.
The problem is I need to provide the Weak Form in only one equation. I'm confused with the term d phi/dxj and I'm not sure how to rewrite eqs. 5.10a and 5.10c in the form a=L.
Can someone help me with this?
Many thanks!
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Well, I have some experience with FEniCS. I think my question could be summarized into "how to write a linear system AX = b or a variational form a==L or F==0 out of this system of two equations?"
I think it is possible to rewrite the equations in a coordinate free form, this can help. But still, as far as I know, I have to put them all together to solve this using FEniCS.
Is it possible?
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I established a simple model in ABAQUS to simulate the stress wave propagating in a plane.
I set up the Infinite element CINPE4 on the border of the plane in .inp file. it more or less had some effects, but the boundary reflected wave can not be completely absorbed on the boundary.
Does anyone have the similar problem? How to deal with it? Thank you!
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dear Dr. wang, did resolved your problem ? Which infinite or semi-infinite elements did you choose?
follow
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Hello everyone!
I wonder way EM wave propagates in vacuum space unlike sound waves. As we know EM waves are generated by charges in motion. Similar question for Light propagation from the distant stars to earth. Is there any alternative physical interpretation of propagation phenomena ?
The propagation velocity of EM waves depends on quality of wave guide and thier physical properties (for example, it depends on the permeability and permitivity of medium, etc.) and less than light C velocity. This may be mean that EM magnetic propagation need to "medium" to propagate" with physical properties. In the other hand, some cosmic particles have speed more than light speed.
Thank you for your comments!
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Dear Ait,
The electromagnetic waves propagate in the space by transferring its energy from the magnetic field to the electric field and then transferring its energy from the electric field to magnetic field and this cycle repeats it self in space requiring a distance of one wavelength. It is an electromagnetic pendulum in space. The detailed mechanism of propagation is explained in the elementary books of the electromagnetic fields and waves.
The acoustic waves are pressure waves established in materials.
Best wishes
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Dear all. Sensors are often used to detect specific physical phenomena (displacement, magnetic fields, temperature, etc.). The acquired signal is generally in the form current, voltage, etc. The signal waveform reflects the physical behavior of the phenomena to be inspected, but in no case the physical phenomena. Does the particle wave duality represent two ways of observing particle behavior ? Thank you for your comments.
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We know light as a wave but when it interacts with matter, it exhibits particle properties (Photoelectric effect and Compton scattering) and we know electrons as particles but they exhibit the wave properties of interference and diffraction. They are carriers of momentum and energy and have both particle and wave characteristics!
You must know that, macroscopic objects such as electrons, display wave behavior but the corresponding wavelengths are too small to detect. At the microscopic level, the waves associated with material particles are of the same size or exceed the size of the system, so, microscopic particles exhibit clearly discernible wave-like aspects. The general rule is: whenever the de Broglie wavelength of an object is in the range of or exceeds its size, the wave nature of the object is detectable but if its de Broglie wavelength is much too small compared to its size, the wave behavior of this object is undetectable.
In classical physics, particles and waves are mutually exclusive and they exhibit different behaviors but Photons, electrons, and any other microscopic particles behave unlike classical particles and unlike classical waves. The theory of quantum mechanics can simultaneously make statements about the particle behavior and the wave behavior of microscopic systems. The true reality of a quantum system is that it is neither a pure particle nor a pure wave. Depending on the type of equipment used to detect, particles have the capacity to display either “particle” or "wave" features. For example, based on the double-slit experiment (that's amazing and you must read more about it), if we wanted to look at the particle aspect of the electron, we would need only to block one slit or leave both slits open but used an observational tool, but if we were interested only in its wave features, we would have to leave both slits open and don't used observational tools. This means that both the “particle” and “wave” features are embedded into the electron (all of the materials), and by modifying the detect tools, we can suppress one aspect of the electron (As a fundamental particle of the whole universe) and keep the other. When we subject an electron to Compton scattering, we observe only its particle aspects, but when we involve it in a diffraction experiment (double-slit experiment), we observe its wave behavior only. So if we measure the particle properties of a quantum system, this will destroy its wave properties and vice versa. Any measurement gives either one property or the other, but never both at once. We can get either the wave property or the particle but not both of them together!!!!
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We are all familiar with the presentation of the light-ray as a sequence of photons/energy-packets just like the figure shown.
What is the relation among "wave-length λ", the length between the black lines (name?), and the length between the red lines (name?) in the figure shown?
Does the overall amplitude (of black modes or red modes) have any relation to the amplitude of the sinoid-wave of monochromatic light?
4/5/2020
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You wrote: " In vacuum, a monochromatic electromagnetic wave moves from a source to a receiver as a pure transverse EM wave, along the Poynting vector direction. Therefore, we agree that kind of signal is transmitted via a non-packeted wave ... At the same time, the same signal can be considered as a flux of monochromatic photons, which are "particles" in a quantum approach.
I agree.
Actually, a monochromatic electromagnetic "wave" in the classical sense involves the existence of some underlying medium if it can succed in propagating. The same for the traditional view of longitudinally propagating monochromatic photons.
Louis de Broglie however, proposed in the 1930's a solution for particle style monochromatic photons that could be self propelling from part of its energy while the other part is carried forward while in standing transverse electromagnetic oscillation that requires no underlying medium.
Although the traditional wave treatement is perfectly adequate from our macroscoscopic perspective, sort of treating energy as a flux of countless localized photons, the de Broglie quantized approach seems much more interesting at the subatomic level. Just like we treat water as a fluid without internal structure at our macro level, while knowing perfectly well that at the submicroscopic level, it is made of clearly identifiable separate molecules.
If interested in seeing what this de Broglie solution proposes, it is described here:
Michaud A (2016) On De Broglie’s Double-particle Photon Hypothesis. J Phys Math 7: 153. doi: 10.4172/2090-0902.1000153
Best Regards, André
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Tools in Matlab for modelling ultrasonic wave propagation in composite material
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Dear Elango,
Hope you are well!
One important point is to consider is the acoustical properties of the material, they must be known. After that you can use acoustic wave equations to describe the sound propagation in a material. The material parameters are> The material density roh and the modulus of bulk elasticity for gas mediums C.
Then the speed of the acoustic wave propagation c = sqr C/roh.
Best wishes
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In a structural dynamic wave propagation problem, is the displacement at a point a continuous function of time or is it a continuous function of time only after the wave reaches the point?
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Hi Mir Aamir Abbas
I believe that it depends a bit.
For unbounded systems, there would not be much of a response before the wave reaches the receiver position. More on this below.
For bounded systems, one must cater for rigid body modes. These have infinite (or a very high) wave speed.
This may at first sound strange, but once we think about it a little, it becomes obvious (or there could simply not be any wave propagation on planet earth which has a high velocity indeed when viewed from the galaxy centrum).
To exemplify, in the case or airbag firing inside cars, there is a pressure increase at the driver's ear before the acoustic wave reaches it. This took the industry about 20 years to figure out and it can be correctly detected when using both pressure transducers and microphones. The former tracks Line Pressure and Sound, while the microphone only tracks sound.
So, for an unbounded system, the 'rigid body' response would still be there, but it would very low and thus something that can be ignored.
Now, let us complicate matters a bit. There is an amplitude dependent portion in wave propagation that causes the wave front to distort - it is referred to as steepening. Simply put, waves with a high amplitude travel faster than the linear free wave speed. After a distance, the peak catches up with the trough and the wave collapses and the process starts anew.
So, when %LP = 100*Pulsation/LinePressure = 100*Sound/Ambient is high, things may happen faster than we would otherwise expect. This is generally the case whenever LP is low, e.g. in vacuum systems, on the suction side of machines and so on.
More on the differences of pressure and steepening is found here. https://qringtech.com/2010/09/15/wave-steepening-increase-peak-pressure-piping-pumps/
I am sure one can compound the issue further if one would want to do so.
Just my 2 cents
Claes
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Hi guys,
I hope you are in the best of your health.
I am working on Lamb wave propagation in anisotropic composite laminates. I want to apply the non-reflection boundary conditions in the simulation model. I am expecting to avoid the reflections from the plate edge by using non-reflection edges. Any idea how it can be done in ABAQUS? Or any other way to avoid these unwanted reflections?
Thank you!
Saqib
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Hi Saqib Hameed,
to remove reflections in transient simulations of Lamb waves, you can use an area with exponentially increasing damping. I modified the approach from Liu and Jerry
and used it successfully with CFRP structures. Unfortunately, my results are only published in German, but you can find equations, parameters and figures in section 4.2.5 of my thesis:
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I know that for isotropic materials, a rule for the maximum element size L_max is:
L_max < lambda_min / 10
where lambda_min is the min. wavelength, defined as:
lambda_min = c_T / f
where f is the excitation frequency and c_T the transverse wave speed:
c_T = sqrt(G/rho)
Now I wonder:
- Can I take the same approach for an orthotropic material?
- If so, how can I calculate or obtain the transverse wave speed?
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In general it is possible to formulate the Christoffel equation for any given elasticity tensor assuming plane wave motion. This allows you to assemble the Christoffel matrix Gamma with
Gammaij = rho * Cijkl * dk * dl
for a particular (unit) direction vector d = {d1 d2 d3} (in which the assumed plane wave is moving) and with elasticity tensor C.
This in turn allows you to compute the quasi long wave speed and quasi shear wave speeds in any given direction as the eigenvalues of Gamma.
Consequently, you can find the minimum wave speed in all directions, which, in theory, should be allowed to be plucked in as a "substitute" to cT.
Indeed, the minimum wave speed for an isotropic elasticity tensor converges exactly to sqrt(G/rho). In case of weak transverse isotropy, it converges to sqrt(Gmin/rho). I have observed relevant effects on the minimum wave speed especially in cases of strong orthotropy or anisotropy.
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Hi,
I want to find an analytical model for the wave propagation of acoustic sound from a vibrating area (for example circular piston) without any baffle around it. I read many acoustic reference books, but i'm confused about this problem. The analytical models don't match with the F.E.A results!!
I'm appreciate if any body can guide me about this problem?
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Thank you Mr. Durrani for your helpful attention
The articles you mentioned are about Acoustic Emission (It's generally stated as acoustic emission in solids).
But my problem concentrated on sound propagated from vibrating subject in air. I studied important books about acoustic and there are tow approaches in solving acoustic wave propagation: 1- by using Rayleigh integral form and 2- by using dipole sound source model. I think the Dipole model is better. The results i achieved, have the same forms but the numerical values are not similar at all. I want to know what model i must use and how? and is there an integral form for this problem is useful?
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The diffraction of light has been referred to as its wave quality since it seemed there was no other solution to describe that phenomenon as its particle quality and subsequently, it exhibited wave-particle duality.
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Berndt Barkholz Similarly, I would say electrons cannot be particles too, because they behave like photons in many experiments, such as double slit experiment.
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Hello,
In Balanis pp.67. he refers to fact that we should modify CP phase difference in the wave propagates in +Z direction. it not clear for me how to modifying these two relations.
can any one help with this ?
thank you
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Malcolm White thank you .
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We want to establish a metamaterial laboratory at mechanical faculty. What equipments do we need to have? our focus will be on vibration and wave propagation.
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Dear Resarcher,
To conduct experiments with emphasis on wave propagation(in meta-material) in open area test site (OATS) it is interesting to have a vector network analyzer (perform S12 measurements), Antennas and a spectrum analyzer.
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It is said that light passing through a single slit forms a diffraction pattern. However, I couldn't find any research to say whether where this phenomenon starts? Before? Inside? Or after the single slit? At the inlet edges? Or at the outlet edges?
Please let me know if there is any reference for it.
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Finally, I finished making a device to check out where the diffraction starts. Here is a photo and I will explain the details.
Let's see how it is going on.
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After getting the view of guided waves propagating in Honeycomb sandwich structure, I am unable to view the Deformed Shape of the simulation results in ABAQUS....Any ideas would be appreciated gratefully.
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How to distinguish between travelling wave solutions and solitary wave solutions of nonlinear dispersive equation like KdV-Burgers' equation? While analysing the wave propagation of solution figue, how actually one identifies it as soliton?
Thanks in advance
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Dear Amitha,
Travelling waves arise naturally in many physically systems, usually described by partial differential equations. Solitary waves, also known as 'solitons', are are a particular class of travelling waves that have special properties.
Solitons can usually propagate over large distances without dissipation due to certain nonlinear effects cancelling out dispersive effects. They also have the additional property that they can interact with other solitons such that they emerge following a collision without changing shape, apart for a small phase change.
John Scott-Russel was the first person to report, in 1844, the sight of a solitary wave on the Edinburgh-Glasgow canal. It travelled approximately 2 miles at around 9 miles/hour.
There is a very comprehensive literature on the subject, and a famous equation that sustains solitons is the Korteweg-deVries equation - see Wikipedia entry. Many additional resources will be found on the Internet.
I hope this helps a little.
Kind regards,
Graham W Griffiths
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Can you give me an idea regarding THz wave propagation in human body, any model or any experimental measurements to get some sort of ideas.
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The absorption of the water molecules to the electromagnetic waves is due to the polarization mechanism where there is orientation polarization at relatively low frequencies after which comes the absorption due to ionic polarization at the long infrared and after that comes the electronic polarization at extremely high frequency. There is also the attenuation due to the conductivity of the water because of the salt contained in it. May be the salty water is very similar in response to the human body.
Best wishes
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Recently, I have got familiar with metamaterials which exhibit no wave propagation in some frequency intervals. The unit cell contains 2D sketch that form a lattice structure with periodic boundary condition. Secondarily, I need to know how to define parameters such as basis vectors, wave vectors (k), and etc to have a completely user-defined evaluation of my unit cell. I would appreciate if anyone could help me.
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Thank you for your kindly attention and help Dr. Ahmed Mohamed.
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I am interestet in simulating the distribution of energy from sea waves onto a shore line.
Ex. Helmholz would do the job I think as we can approximate sea waves with ordinary wave equation for shallow water, but this is to slow for the purpose.
Thank you.
Ivar Bratberg
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Hi Mashia
thank you very much for the link.
Ivar
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Im working on wave propagation
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Dear Majid,
writing your own code for mesh generation is not something I would recommend. it is very complex and will be much less general than existing (commercial) mesh generators such as those from Abaqus, Ansys, Hyper Mesh, etc. Alternatively you could also try to employ Gmsh, Tetgen, Netgen which are free alternatives. This you could then couple with a spectral element solver you could program in MATLAB. Considering the spectral element method I would recommend two books which are very helpful
Pozrikidis, C.: Introduction to Finite and Spectral Element Methods using MATLAB, Chapman and Hall/CRC, 2014 , 830
Karniadakis, G. E. & Sherwin, S. J.: Spectral/ hp Element Methods for Computational Fluid Dynamics, Oxford Science Publications, 2005
These monographs contain all details regarding SEM.
For general comments about programming FEM in MATLAB have a look at
Ferreira, A. J. M., Gladwell, G. M. L. (Ed.) : MATLAB Codes for Finite Element Analysis, Springer Verlag, 2009
Hope this helps.
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I want to model 2D wave propagation in a different medium and its reflex from the boundary with different shapes like rectangular or circle. Is any software or Matlab script that can do this?
thanks a lot for your helping
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It highly depends if you have continuum or discrete system. If you have linear or nonlinear interactions, or convex nonconvex material model. A little bit more info regarding your research, would help to find the best tool.
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Hi everyone.
I have built three 2D plane strain model in Abaqus, each model was applied dynamic concentrated forces (1 MHz, last 10 microsecond), which are equivalent, at point A as shown in the figure named 'resultant decomposed force', and the results were the displacement of Rayleigh wave in the far field (at point B) on the free surface.
Except for the forces are different, everything else for the three models are the same, the results should be the same since the forces are equivalent. However, the results are not the same, results of force 2 and 3 are the same, results of force 1 is different.
The results for force 1, 2, 3 can be found in the attached pictures. I have no idea why the results are not the same. Does the synthesis and decomposition of forces not apply to dynamics?
Would you please help me, thank you a lot.
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You are most welcome Wang Chuangyong . I hope it helps. Have a very nice day.
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I am working on lamb waves propagation in isotropic and in anisotropic plates.
I am interested in plotting dispersion curves based on SAFE method. I have tried to program the SAFE method in Matlab, but I did not get the right dispersion curves for 2D Aluminium plate. You find in the attached files my program. So I would like to ask you if it is possible to guide me more to get the right curves.
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Thanks Hauke Gravenkamp for your reply. I will take your remarks into consideration, i will send you the modified version :)
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Which module can I use to simulate nonlinear acoustic wave propagation in micro damaged materials?
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Dear Nesrin,
This problem can be solved using the numerical method previously used in CAE IMPULSE:
This approach has good stability and very low computational costs (time and memory).
The simulation time on standard desktop computers is about 1-10 minutes (depending on the specific task).
Regards
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Hi, I built a 2D plain strain model, put a concentrated time-harmonic force below the free surface, and detected Rayleigh wave on the free surface, I found that the amplitude of Rayleigh wave decay with the distances increasing. The material is aluminum, I just set density, Young modulus, no damping. I have no idea why the amplitude of Rayleigh wave would decay with distance.
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