Questions tagged [frequency-response]
The frequency-response tag has no usage guidance.
34
questions
-1
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1answer
19 views
Phase shift of transfer function using MATLAB
I'm trying to compute the phase shift of a transfer function (accelerance) in MATLAB, but I'm having issues.
The transfer function was computed by dividing the magnitude of the system output by the ...
3
votes
0answers
29 views
Getting the damping ratio from a frequency response function v.s. transfer function
I'm trying to find the damping values of a specimen, based on sweeping the forcing frequency from 0-10 kHz. As shown in the diagram, I measure the input force from the shaker, and the subsequent ...
0
votes
1answer
68 views
Could Tesla have REALLY shaken a building with a little oscillator?
I came across this story while reading about Nikola Tesla ground-power scheme. Supposedly, he created a little oscillator that could be plugged into the ground, tuned to the right (resonant) frequency,...
2
votes
1answer
55 views
What is the frequncy range of seismic vibrations?
I'm working on a structure which needs to sustain common seismic vibrations due to earthquakes. So I want to do some modal analysis to find natural frequencies of the structure and make sure they are ...
0
votes
1answer
69 views
Physical interpretation of a Bode plot
I have a few questions regarding the physical interpretation of the information presented on a Bode plot. I believe it is one of those cases where I "don't know what I don't know", so please bear with ...
1
vote
1answer
56 views
Why phase margin and gain margin should be positive?
In many textbooks it's given that gain margin (in db) and phase margin of the system needs to be positive for the system to be stable. I could not find the reason behind this. Could someone explain ...
3
votes
2answers
77 views
Relation between natural frequency and the thickness
If I have a solid material, let's say two bricks, one of which is thicker and I do modal/vibration testing. What would be the relation between thickness and natural frequency of any of them, is there ...
-1
votes
1answer
14 views
Construct “Modal Coordinates Time History” from transfer function and test accel-time data
I have a query regarding the calculation of the so called “Modal Participation Factor time signal” from a combination of
a) transfer functions (amplitude and phase for each eigenmode) obtained from "...
2
votes
0answers
29 views
Mobile Frequency and Carrier Frequency not Matching
I am using a Google Nexus 6 Mobile in India with Airtel as Network Provider. Recently Airtel has upgraded their Network to 2300 Mhz 4G. Whereas Google Nexus 6 Operates on Band 3 (1800Mhz) LTE.
When ...
0
votes
1answer
33 views
How do I verify the reaction forces of an FE model due to a response spectrum
In the case of a static calculation of a structural model, one can verify the model by checking the applied and reacting forces to be equal zero.
I would like to adapt the same principle for a ...
0
votes
1answer
84 views
Nastran / Frequency Response / Free-Free
There are examples of using SOL 108 and SOL 111 to create a frequency response. In Siemens Simcenter (NX Nastran), the examples focus on a tower with a seismic mass. The model drives the mass with ...
2
votes
3answers
86 views
Do internal / external stresses affect modal frequency?
Imagine a cantilevered beam, fixed on one end and with a tension line connecting the other end to ground (e.g. perpendicular to the length of the beam).
If I increase the tension, does the modal ...
1
vote
5answers
287 views
What can be the reason of the constant 50 Hz sound in my home?
I am suffering from a strange hum in my home. I have just bought my home and living in 3 months. A month ago I've started to hear a humming noise. Then, I recorded the sound and looked at its ...
0
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0answers
25 views
Frequency domain analysis of steering system of a car
Can anyone share the equations involved, or some relevant theory material for frquency domain analysis of steering rack and pinion using bode plot?
1
vote
0answers
34 views
What's the best way to get an ultrasonic sensor that can vary its operating frequency
Long story short I'm looking to build an ultrasonic sensor that can also be used to communicate with a seperate sensor. (So it must be able to send out a pitch around ~42kHz, but also alter the pitch ...
0
votes
1answer
89 views
Base Driven Tuning Fork Mechanical Response Spectrum
I am new to vibration analysis/simulation etc. so I may be missing something very basic here so please forgive me if I'm explaining things poorly or not making sense.
To familiarize myself with ...
0
votes
1answer
39 views
Fourier series with frequency response
I have seen many times that people gets the frequency response function using DTFT. Can I use the Fourier series, and when I do that?
1
vote
1answer
48 views
MIMO control: static inverse plant decoupling
I am using techniques explained in the book of Skogestag, Multivariable feedback control, for feedback control of a MIMO plant. In this book they explain the phenomena of static inverse plant ...
6
votes
1answer
141 views
Elastic (Young's) Modulus relation to the Eigenfrequency
I would like to compare the shape of the frequency spectrum of a plastic and aluminium component. Now if we assume that the plastic and aluminium component only differ in the material, while the mass ...
2
votes
2answers
206 views
How the amount of bolt's preload in a single lap joint can change the natural frequencies?
Few days ago someone told me that the amount of bolt's preload in a single lap joint can influence the natural frequency of the beam. So to test that out I modeled a 3D single lap joint in ABAQUS and ...
3
votes
1answer
107 views
2
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1answer
108 views
Modal Testing and Frequency Response Interpretation
I'm studying vibrations in a gearhead, for which I have a general dynamic model of 12 degrees of freedom (only translational coordinates) and I have calculated its natural frequencies.
Now I want to ...
0
votes
1answer
186 views
Undamped forced vibration for a multi dof system
I'm trying to determine the amplitude vs the excitation frequency of a multi dof dynamic system. I'm very confused from reading different methods, although I understand there's a very general one, ...
1
vote
3answers
130 views
What's the difference of using different state-space forms for solving eigenvalue problem?
I have a set of equations of motion describing a planetary gear train of 18 DoF (sun, 3 planets, carrier and ring), they have the general form of:
$$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{Kq}=F(t)}$$...
2
votes
1answer
47 views
Are there any variable frequency drives that work digitally?
By this I mean can any DC to AC variable frequency drives invert digitally (no moving parts) and if so how do these work? Is this possible for both sine and square wave inverters?
2
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0answers
97 views
What is the maximum frequency of an AC current?
I saw that the rpm of a synchronous motor is proportional to the frequency of current alteration and I was wondering if there is a theoretical maximum frequency (regardless of magnet strength)? Also ...
1
vote
2answers
35 views
What is Experimental and Operational MODAL ANAYLIS?
EMA and OMA are two methods used for determining the mode shapes of the natural frequencies of mechanical systems. I understand it until that point. I know that for EMA we need an artificial ...
2
votes
1answer
177 views
What does multiplicity of a multiple natural frequency mean?
I'm doing some vibration tests on planetary gear sets and a lot of the information I´ve read mentions a lot about mode shapes and multiplicities of the natural frequencies. I understand how one can ...
0
votes
2answers
3k views
How to get natural frequencies from accelerometer measurements?
I will be performing some tests and measuring the vibrations of a planetary gearbox. The accelerometer I will be using stays attached to the gearbox and saves the data into a log, which is available ...
3
votes
1answer
147 views
How to simulate the Natural Frequencies of a Planetary Gearbox?
I have a dynamical model of a planetary gearbox of the form:
$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{[K_b+K_m-\Omega_c^2K_\Omega]q}=T(t)+F(t)} $
$K_b$: bearing stiffness symmetrical matrix
$K_m$: ...
6
votes
1answer
819 views
Is a 3 Hz beat frequency from my neighbor's HVAC a sign of a malfunction?
I'm being annoyed by a pulsating hum which comes from my neighbor's HVAC system. I read up a little on the design of HVAC systems and I came to a tentative conclusion that what I'm hearing is a ...
2
votes
1answer
2k views
Definition of stiffness for structural dynamics: How would you find the stiffness of an unusual beam directly?
I have a structure which is essentially a curved beam (not an arch or anything simple) which I have modeled in microstran/spacegass. It looks something like this:
Or for something more simple, ...
4
votes
2answers
908 views
Generating a Blank Seismic Tripartite Graph
I am performing a calculation in which I need to plot a generated response spectrum to a seismic tripartite graph. However, I am having a heck of a time finding a blank tripartite graph online. A ...
3
votes
2answers
567 views
What type of test signal is appropriate for frequency response analysis of string instruments?
I want to test the frequency response of stringed musical instruments . My test set-up includes a piezo film transducer which is just taped onto the instrument and fed a signal which then vibrates the ...
