Questions tagged [frequency-response]

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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 ...
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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 ...
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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 ...
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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 ...
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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?
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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
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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 ...
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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?
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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
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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
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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
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1answer
107 views

Eigenfreuency of beam

How would you calculate the eigenfrequency of such a cantilever?
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
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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, ...
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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
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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 ...
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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
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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 ...
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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
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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
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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
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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
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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
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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 ...