Vibration - Science topic

Vibrational modes involve all of the atoms in a molecule, not just a selected few bonds, and while C=O stretching modes tend to be relatively localized, C=C stretching modes tend to be less localized, often involve C-H motion, and will at a minimum involve multiple C=C bonds in the phenol molecule. Perhaps it would help to define more precisely what you mean by "the angle between the vibrating modes" and perhaps what question you are trying to answer with that information?

Dear Thaker, to allow making a reasonable answer, you must describe far more precisely the vibration problem you want to solve! (graphics, sketches of the affected plant, on-site pictures, vibration records...) Thanks!

Your information contains too little information.

As a general comment - industry tends to build systems assuming component property specifications suffice. Often, they do not. One has to take into account that components interact.

Very simply stated - if it was super easy to slap components together and get a well functioning system, then there would not exist a difference between, say, a Rolls Royce and a low cost entry level car. Both will take you from A to B, albeit differently when comfort is evaluated.

That said - aeroacoustics is a rather complicated field. Here is an introduction to the very basics

https://qringtech.com/2014/04/04/flow-induced-noise-explained/

Dear Umer Hameed Shah,

I suggest you look at the following relevant links:

(If you have further questions please contact me at any time)

Dear Pablo Ortega Álvarez,

Your separated reactants have 3 translational (they can move in the x, y and z directions), and 3 rotational (they can rotate around the x, y and z axes) degrees of freedom each (thus, 6 DoF each). This amounts to 12 DoF. When they associate (as the VdW complex, or as the TS), the complex moves and rotates as a whole, so only 6 DoF now. Six DoF were lost during association, which has an entropy cost. The same applies when you calculate your reactants in the same run, separated by an arbitrary distance. This is why your VdW complex will frequently have a positive DG of formation with respect to the free reactants.

Regarding the specific energy values you got, it is really method-dependent. Which protocol did you use with Gaussian? If your method is not dispersion-corrected, very high barriers are commonplace. M06-2X accounts for dispersion, but I am not sure if previous studies with this functional have shown how well it performs with this specific class of reactions.

Now, if you used the exact same protocol with both Gaussian and Orca, there is definitely something suspicious going on. I can gladly give a look at your outputs if there seems to be some unidentified problem.

Finally, some unrequested advice. The cc-pVTZ basis set (and its family) was optimized for correlated wavefunction methods, and using it with DFT, although not wrong at all, tends to be unnecessarily expensive. I would recommend the Ahrlichs basis def2TZVP instead. Or, if you are in the exploratory phase, I would optimize and calculate frequencies with the def2svp basis set, and then a single point on top with the def2tzvp basis set. This can be a huge time-saver that you can easily benchmark against a set of reactions you already calculated with a larger basis.

Good luck!

Mauricio

To expand on the answer provided by Vyacheslav Ryaboy, when performing the increasing-frequency sine sweep test, you would pass through the first resonance frequency of the cantilever beam. This is what is referred to as "hitting" the first resonance frequency. If you continue to increase the frequency, you will eventually reach and pass through the second resonance frequency. If you continue to increase the frequency further, you will eventually reach and pass through the third resonance frequency.

Depending on the equipment at your disposal, you may wish to use an impact hammer to simultaneously excite a number of modes of vibration. The measurement system would likely have the ability to compute the transfer function between the response and the excitation force. The frequency response curve would generally show the first few natural frequencies of vibration of the cantilever beam, dependent somewhat on the bandwidth of the force impulse and also the point of application of the transient excitation force.

The links provided by Om Prakash Chhangani and Mohamed-Mourad Lafifi give the formulas for the first three natural frequencies of a cantilever beam, as well as a graphical representation of the associated mode shapes. There are some suggestions for how to go about experimental testing there too.

What test equipment do you have available to conduct the experiments with?

Dear Til, I am afraid there is no answer to your question... For sure the scale will be shorter than the audio one, as our ear+brain system is extremely powerful and well trained compared to touching. You might get better results with a log scale of vibration thresholds as human perception is not linear, but the key issue will be training: untrained people might only detect few thresholds while training could result maybe into a ten level scale - just try! And you don't explain why you choose 205Hz, which is clearly a very high frequency for the muscle-skeleton system (the sensitivity might be elevated if the frequency activates a resonance of the hand/finger structure, which is in the tens of Hertz, not hundreds)

We are probably more sensitive to pressure: would you solve your actuation challenge by a sequence of pressure pulses at few Hz exerted by an inflatable glove cell driven by a servo-valve? You can play both with pressure and pulse length/ rate to build a collection of signals conveying the information to the holder...

Good luck, my only advice is to multiply trials as you try to address an uncharted domain of biodynamics...

240 Hz is in the audible range. Do you hear any sound while your spindel is rotating? Perharps, it is friction-induced sound, because, for example, spindel is not well oiled.

We have developed this software for OMA https://github.com/dagghe/PyOMA

It also has a GUI!

To cite this tool:

Pasca, D. P., Aloisio, A., Rosso, M. M., & Sotiropoulos, S. (2022). PyOMA and PyOMA_GUI: A Python module and software for Operational Modal Analysis. Software X, In press

Dag Pasquale Pasca Marco Martino Rosso Stefanos Sotiropoulos

Hai

sir, as of my knowledge you can choose the Mechanical submodule of the interaction property module , it contains the damage criteria option in the submodule

Thank you so much for your reply, and have a nice day. Best regard.

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...).

I tried EMD and its modifications. Also Hilbert transform and Teager kaiser Energy operator for the estimation of parameters. If you find any difficulties in these methods, please let me know, I can help.

Nowadays several quantum chemical program packages contain not only geometry optimization but also force field calculation. I have personal experience with ChemBio3DUltra 13.0. The reliability of the result depends on the level of approximation (from semiempirical to ab initio), an can be used for medium sized molecules. I remember when I was young and wrote my PhD you needed a considerable size computer to perform such calculations. Nowadays such programs run on PCs. It does not replace careful interpretation of experiments, but it can be helpful, especially in comparative studies.

Dear Zhang Shuai

Kindly for datasets check these resources:

Kaggle

Google Dataset Search

The cycle load module can completely solve this problem

as i had not found any paper in which ansys simulation is done for the underwater pipe if you find can you please refer me

as i had to submit my project@claudio Pedrazzi

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/ ;

I wish you all the best I apologize that this is not my specialty

Hi Thomas,

You might need to read Dr. Bredge McCarren and the research that is published by this group. You will find answers in these publications.

Group has shown that the expiratory flow rate produced by vibration is approximately equal to the sum of the flow rates due to recoil of the lung and due to the compression and oscillation components of vibration https://pubmed.ncbi.nlm.nih.gov/16515421/ PMID: 16515421

In terms of an intrapleural pressure (IPP), what is proposed is that vibrational forces applied to the chest wall are transmitted to the lungs and airways. Also, that high frequency oscillation component of vibration influences IPP and expiration. An application of vibration during the expiratory phase increases expiratory flow rates PMID: 17132121

These forces increase IPP, which in turn increases expiratory flow rate hence helping to mechanically unload secretions (if you are interested in this).

I am interested how these forces influence hemodynamics. It looks like, they decrease an afterload, if applied during expiration.

Good luck with your studies, hope this helps.

Filip

You can also connect with the group on RG

Hi,

Here is the update to this question, please take a look at links on the topic.

Best regards

adenine, guanine, cytosine, thymine

the rate at which the amplitude of a free damped vibration decreases

Hi Murana Awad

Is it possible for you to share your data with me? I have some idea to solve your problem but I need your data.

I'm in touch by : ahmadi.v.1380@gmail.com

Hi Masoud,

I'd propose you try the following two solutions:

1. Try to measure the resonance frequency of your cantilever using a laser interferometer without actuation. At 7.7 MHz, I'd expect there to be very little ambient noise and also that your cantilever has a pretty high Q-factor. This means that the cantilever will self-resonate at its resonance frequency, acting as a signal filter, which you will be able to observe.

2. As Vinod suggested, use a piezo element, firmly connected to the base of the cantilever chip. Connect the piezo element to a signal generator that will sweep the frequency in the range of interest.

Good luck with your experiment!

Raman and FTIR spectroscopy differ in some key fundamental ways. Raman spectroscopy depends on a change in polarizability of a molecule, whereas IR spectroscopy depends on a change in the dipole moment. Raman spectroscopy measures relative frequencies at which a sample scatters radiation, unlike IR spectroscopy which measures absolute frequencies at which a sample absorbs radiation. FTIR spectroscopy is sensitive to hetero-nuclear functional group vibrations and polar bonds, especially OH stretching in water. Raman on the other hand is sensitive to homo-nuclear molecular bonds. For example, it can distinguish between C-C, C=C and C≡C bonds.

Thank you for your suggestion and your kind reply Dayong Zheng .

Certainly, electric signals to detect mechanical malfunction on the transmission contain weaker information. However, I was thinking, as a target of Condition Monitoring, on robotics systems (e.g. robotic arms). In such systems, is not so easy to add extra sensors, like accelerometers, while the current measurements are already available from the controller. Moreover, these systems use a relatively short drive train (each joint has its motor and a speed reducer). Thus, maybe, could be possible to detect mechanical and electrical malfunctions using only electric measurements.

I will continue studying and investigating in this direction.

Thank you also Bhupendra Desai for your information, I will have a look at your work.

Dear Masoud Jedari Ghourichaei

The MEMs are actuated either electrically by means of electrostatic charge or it can be actuated magnetically if it is made of magnetic material or it can be actuated mechanically by subjecting it to a mechanical knock or subjecting it to a mechanical vibration from a piezo transducer.

Best wishes

Dear Mehran Shahpari

First you should find the mass matrix and the stiffness matrix. Afterwards, you should solve the eigenvalue problem associated with the problem at hand and these specific matrices. The structural damping coefficient is equivalent to the fraction of Im(lambda) over Real(lambda), where lambda is the complex eigenvalue and Im and real, respectively denote imaginary part and real part of the eigenvalue. I have attached a triple of screenshots to my comment for your perusal.

For forced vibration (for example in presence of air dynamic pressure), the solution of the eigenvalue problem is a bit harder than to find a solution to an ordinary eigenvalue problem. For concreteness, in this regard, I have attached a PDF of my own original idea to this comment. The PDF is also available in my ResearchGate project:

Linear Aeroelastic Analysis of Laminated Composite Plates with Fully Elastic Boundaries

Under the title:

Eigenvalue problem for aeroelastic vibrations: The solution

Usually, when the restriction orifice plates (ROs), installed in the pipes, vibrate by the pass of flow through them, is because they have cavitation if the fluid is liquid or they have an excessive pressure drop if the fluid is gas or steam.

Another reason, in the case of liquids, could be that the flow is pulsating.

If the cause is the cavitation, change the 1 hole orifice plate by a multi-hole orifice plate.

In the other cases, increase the thickness of the plate, taking into account that values of t/d (t = plate thickness and d = hole diameter) equal or greater than 1, change the RO thin plate to a RO thick plate that have different hydraulic coefficients.

See the book Vibration Problems in Engineering of S. Timoshenko that in the Chapter VI analyzes the vibration of circular plates.

Kindly visit..

Very interested in the topic

If ai understood good, for vibration suppression, you can use a dynamical absorber (flow divider), if the space allows this.

René Christensen

Prescribed displacement is not a excitation. If you apply prescribed displacement of 1m in z direction. then the boundary will be displaced by 1m only. it does not depend on frequency.

Hi Akash,

Sample preparation for Raman is very simple. Disperse a small amount of sample in a solvent in which the sample is soluble, and place the solution in a sample holder. Ideally, do different tests at various proportions and contrast the result with that of the solvent alone. There are times when the signal is not very strong and you have to increase your concentration a bit.

Not clear what you mean

Dear Dr Hoffmann,

Thank you for sharing this interesting topic and I would be happy to participate in the future step of this project. the below paper might be interesting to read,

I agree with Nitesh Anerao.

Please read carefully the discussion https://www.researchgate.net/post/What_is_the_relationship_between_the_acoustic_pressure_and_the_amplitude_of_ultrasound as your question on the loss of cleaning efficiency when you exceed some intensity levels is largely similar...

At high level, the ultrasonic generator becomes largely non-linear meaning widening the frequency spectrum, including low frequency components able to induce unstable horn vibration, but also large fluctuations of pressure in the fluid and unstable cavitation bubbles size.

The only way to remain under control is to stay in the quasi-linear electric power/piezo-electric conversion/fluid coupling domain...

Dear

Thank you very much for sharing, it is really helpful to me!

Regards,

Zhenyu

Dear Adib Amini

Have a look: https://www.cfd-online.com/Forums/fluent-udf/168994-can-i-change-flow-direction-using-udf.html

Kind Regards

Reduce the printing speed; examine the Z-axis level; the machine may need a complete calibration; and inspect the mechanical components that hold the extruder.

Dear Sourabh Lahiri , yes, it is indeed possible to couple a phonon mode with an electromagnetic wave, to create a sort of hybrid quasiparticle called polariton.

Rigorously speaking a polariton is a quantum superposition state between a photon and a matter excitation. The matter excitation can be a collective mode (a phonon) in solids or an electron in atoms or molecules.

A good description of different polaritons can be found in the following article and review, please have a look to them:

Polaritons are also fairly well described on the book by Le Ru and Etchegoin:

Hope this helps. Good luck with your research work and my best wishes.

Dear Felix Schmid

Thank you for your answer!

Regards,

Zhenyu

Hi Raymond,

400m is challenging but should work.

a pressure level sensor should work, if they are able to manufacture a 400m gauge wire.

I’ve worked a lot with these devices and they are quite durable. You can set up them for automatic monitoring. If you need a high failure safety, you can setup them in a array of 2 or 3.

if you are looking for manual monitoring devices, a contact gauge is a easy to use tool.

There are some other methods, like pneumatic level monitoring but I have no practical experience in terms of durability.

the diameter of the borehole should be at least 100mm with smooth edges.

Nitish Kumar Guru I have added the example to the PERMAS4EDU project. See the project log at https://www.researchgate.net/project/PERMAS4EDU

Yes the NIST data is often a bit confusing.

You are correct there are 9 NORMAL modes of methane there's a nice animation here:

You could predict the number and degeneracy (and the atom movements) using group theory (Td point group).

Problem is when you come to experimentally measure the spectrum:

1. Many of the modes "couple"

2. Many are only Raman active. Raman and IR often show at (slightly) different frequencies.

3. Gas phase and liquid phase will have different frequencies

4. There will also be rotational excitation.

So it is often difficult to find two frequency tabulations that agree (exactly).

Don't quite understand the problem. Am I correct in assuming that the electric motor is connected to the gearbox using the sprocket and chain? If this is not the case, then how are they connected?

Hi, J. Rafiee

thanks for your reply. I'm not trying to generate coloured noise but denoise.

Erfan Shamsolketabi if you are trying to simulate this problem in the Laminar flow regime you have to know in laminar flow, wall roughness is neglected and we use this boundary condition just in the turbulent flow.

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.

It is possible to greatly reduce the noise level using moving averages within the equipment you use for measurements.

Ahmed Youssef Dear Sir,

Thank you for suggesting me this article to me. But this article is on the free vibration of nanobeams based on various nonlocal theories with an application of DQM.

On the other hand, I'd want to address the problem of nonlinear free vibration of the beam. So, for this, I'm searching for literature that will provide me with a clear grasp of how to deal with the nonlinear components that arise in the equation of motion, as well as the solution technique.

How they are activated Open your phone's Settings. Next, look for the Notifications section and access it. Access the Advanced Settings. The name may vary in some manufacturers, such as Advanced Settings. Once there, look for the Wireless Emergency Alerts tab.

I agree with Ashten Stambersky

Hi Mohammed,

thank you for your quick answer. Generally, vibrometer measurements on rotating objects are more difficult compared to stationary vibrating objects. The major drawback is the increased noise level, caused by speckle effects due to the object rotation in combination with the surface roughness. "Speckle noise" is increasing with rpm rate and concentrates in "speckle peaks" at multiples of the rpm rate, leading to a typical comb-sprectrum. The amplitudes of the speckle peaks are nearly constant over the measurement band width. So it is much harder to detect a vibration , especially when it is correlated with the rpm rate, which is mostly the case. In that case the vibration signal is on top of a speckle peak. If the vibration amplitude is big enough (say 3 xor 5 x of the speckle peak height), then its easy to detect. But when the vibration amplitude is in the same range as the height of the speckle peak, it is nearly impossible to detect. Furthermore, an investigation of the vibration signal in time domain is virtually impossible- independant if you look at velocity or displacement data, because of the high noise level. Especially the displacement signal will additionally increase or decrease continuously, because the vibrometer will acquire the part of the circumferential veloctiy, which is projected on to the laser beam.

Mohammed, this is a how-long-is-a-piece-of-string question. It is very difficult to give a useful answer without knowing more details, such as:

1. What is the scale of machinery you are studying? Power stations and mega-ships, micromotors or something in between? If you are studying non-portable systems, you will need a portable lab. If you are studying large systems, the rpms will be lower, which affects your choice of suitable accelerometers and signal analysers. If you are studying tiny systems where the vibrations are small, you may need vibration isolation platforms to get usable measurements.

2. How many people does the lab need to accommodate and how many experiments do you plan to run at once? Is the lab for research only or will it also be used for teaching?

3. Do you want to study the effects of loading? If so, you will need to consider braking devices, dynamometers or other forms of loading systems.

4. Laboratories usually provide calibration services, at the very least for the lab users, but often for outside clients as well. What level of calibration do you intend to provide? Do you just want secondary calibration to verify that your equipment is operating correctly or do you want primary calibration to check the secondary calibrators? Calibration and traceability are important in any research work, but they are particularly important in any forensic or expert witness work.

5. Do you need ventilation and/or cooling systems for combustion engines?

6. Do you need soundproofing for noisy equipment or vibration isolation for shaky equipment to avoid disturbance to other building occupants?

7. Do you plan any destructive testing? If so, you may need safety enclosures and other safety equipment.

8. What is your budget? How much floor area do you have? Are you adapting an existing lab space or creating a new one from scratch?

9. Do you plan to make acoustic measurements as well as vibration measurements?

10. Vibration studies may need to measure the modes of vibration as well as the amplitudes. High-speed video and/or strobes may be needed for this. Laser interferometry may also be needed. Appropriate lighting will be needed for video work.

Hi, you can also check our dataset from the Hardager Bridge.

Dear Indra Agustian

This paper may help you

There are two ways-

1. Spectral simulation method- Find output spectral density (So) using harmonic transfer function and input (force) spectral density (Sf). Then calculate the required mean square response (MS) from the area under Sf curve over required frequency band using the numerical integration of Sf function.

2. Time domain method- First you are required to generate the time-domain force f(t) signal using ‘wgn’ function in the MATLAB and save it as data file. Then solve the equations of single DOF system in by using f(t) as input with MATLAB solvers such as ode45.

The white-noise produced by the ‘wgn’ is essentially the band-limited and max frequency is equal to half of the sampling frequency. The ideal white-noise has infinite variance but ‘wgn’ requires to specify it as follows.

Var of wgn = Spectral Ht of white noise required (N^2/rad/s)* sampling frequency(rad/s)/2

In your case choose the sampling time (dt) such that, dt<=1/(2*10*fn), this ensures that the generated white-noise contains the highest harmonic of frequency 10*fn. Where fn=sqrt(k/m)/(2*pi). The factor more than 10 can be used but it is sufficient for lightly damped single dof system.

Then Sampling freq (Hz) = 1/dt.

3. SIMULINK is convenient for this use and it is not required to save the signal f(t). The blocks ‘Band Limited White Noise’ and ‘WGN’ can be used.

Hope this will help.

Note that. the suggestion presented by Chandrashekhar Dharankar.

If you're already observing the vibration with an oscilloscope (and I'm assuming a transducer or accelerometer?) then why not just take an FFT of that signal if all you need is the resonant frequency? Don't trust the built in FFT function on a scope, those typically don't use enough points to be useful. Transfer the data to a computer and do it there. If you need the complex impedance then use a NA measuring a sweep of the reflection.

What machine fault was introduced?

Some machine faults could behave like that it is not allowing the shaft to move and could reduce max amplitude of the vibrations.

What are the values of the RMS of velocity for this measurements?

Have you got answer about it?

Dear Merwan Behar

I recommend the Spectral Finite Element Method.

I am not sure what you mean by "oscillation".

The core mechanism of UV-Vis absorbance is the induction of electric dipole transitions between the electronic states of an atom/molecule/solid by photons of appropriate energy/frequency.

The core mechanism of Raman is inelastic scattering of photons by coupling to vibrations of bonds in a molecule/solid, or also rotations in the case of a molecule (although less commonly studied).

You can use a simple DC motor which rotates a half disk (you can buy both of them as a vibration motor) and a variable DC power supply( or dimmer ) to change RPM of motor. If you want to make linear vibration, you can use a simple speaker and a pulse generator program (PC or mobile app) to generate a sine wave with arbitrary frequency.

Interested!

Hi 姚冬霜 冬霜 Yao

There are two options:

1. (Easier) Measure the voltage of a resistor placed into the piezoelectric eletrical terminals. Then, you have the value of the resistor and the measured voltage. Thus, it is possible to calculate the current by I=V/R.

2. (Harder but more comprehensive) Connect a frequency analyzer equipment into the terminals of the piezoelectric device. Then, it is possible to extract the frequency response (gain as function of frequency). Usually, frequency analyzers can provide voltage gain as function of frequency. You can also use a resistor as load in this case.

I hope this helps