# Questions tagged [frequency-response]

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### 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 ...
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### 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 ...
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2k 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 ...
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101 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 ...
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### How to determine the dynamic response of a spring-mass system?

The Problem I have the following system for which I would like to determine its dynamic response, taken from these lecture notes pg.20: where the forcing functions are $u_1 = 1-U(t - t_0)$, $u_2=0$, ...
217 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 $K_m$: ...
• 409
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### 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 ...
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### 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 ...
• 31
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, ...
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4k 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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207 views

### Eigenfreuency of beam

How would you calculate the eigenfrequency of such a cantilever?
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### 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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365 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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406 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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### How do I study the frequency response of a physical system with Arduino?

I am a control engineering student and I am studying the frequency response of a system, so the Laplace domain, the Bode plot, poles, zeros,etc. ... I have clear grasp of their meaning, but if I think ...
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### 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 ...
• 409
316 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 ...
50 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?
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### 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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1 vote
355 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: $$\mathbf{M{\ddot q}+{\Omega_c}G{\dot q}+{Kq}=F(t)}$$...
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1 vote
63 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 ...
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1 vote
70 views

### why Type III systems has at least two gain margins?

I heard the following statement https://engineering.stackexchange.com/a/54322/40848 if we have a type III system, or one that has three or more low-frequency poles that we're closing around, then we ...
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1 vote
1k views

### What is the bandwidth for a 2nd order system?

I know that for a first-order system, the bandwidth can be computed known the time constant, tau, where the bandwidth is equal to 1/τ. Is there an equivalent formulation for a second-order system, ...
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1 vote
723 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
5k 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 ...
1 vote
75 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 ...
1 vote
164 views

### Do sound waves caused by a vibrating machines correlate to the vibration waves of the machine itself?

I'm a computer engineer, so please excuse my lack of mechanical knowledge :). We have a machine that has large electrical motors causing massive amounts of vibrations, the machine also consists of ...
1 vote
65 views

### Area under Frequency response function (amplitude vs frequency)

Recently, I was plotting frequency responses of multi-degree spring-mass systems and I was wondering what does the area under the FRF (amplitude vs frequency) (or in general FFT) mean? Does it have ...
1 vote
503 views

### How to find out the sampling rate of an acceleration sensor?

In the sensor catalogs, I cannot find this field. They only depict the frequency response range. For example, Bently Nevada's sensors. How we can find out their maximum sampling rate?
1 vote
21 views

### Transforming a Wireless Computer Mouse into a Wireless Switch [closed]

With no computer involved whatsoever, I want to be able to read oscillator outputs from my wireless mouse and switch an LED on a left click AND off on a right click. I have taken my mouse apart to try ...
1 vote
32 views

### Finding force distribution using accelerometer data

The team I'm currently working for is trying to compare bushings with different durometer ratings in the front suspension using single axis(z) accelerometer data during curb impacts. The current ...
1 vote
49 views

### Where do I start with learning how to transfer data via RF

So I literally have no idea where to start but I know what I want to make. The goal is to somehow transmit 25mb/s of data across 15km with high penetration. Acceptable for reaching through trees and ...
1 vote
333 views

### Z - transform of white noise

I am taking a graduate course in Digital signal processing with no prior knowledge in DSP. So I am struggling because I don't have the foundational knowledge. Please I need help with the following. ...
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1 vote
32 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 ...
1 vote
38 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 ...
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### How can I find the right resonant frequency of a chassis?

Structures have infinite DOFs, so it possess infinite mode shapes. How can we find the right resonant frequency out of the infinite resonant frequencies so that we can save our structure? For example, ...
83 views

### How simultaneous can we trigger multiple cameras' frame acquisition

Say we have ten cameras surrounding an object. The object changes its color with a certain frequency (or any information other than color, such as a text on it). The point is if all cameras are ...
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5k 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 ...
• 409
60 views

### Changing the relative equilibrium position for a 2-mass spring-mass system

I am trying to solve a double spring-mass system that is positioned vertically (I currently have the pendulum at an angle of 0 in my code below). I derived the system of ODE's required, and I get this ...
96 views

### Why are the phase indicators different between the open loop bode plot and the closed loop bode plot?

I have an open-loop transfer function G num=105*conv([1 1],[1 2 43.25]); den=conv([2 0 0],conv([1 2 82],[1 2 101])); G=tf(num,den); and a closed-loop function of G/(1+G). Here are the open-loop bode ...
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### 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 ...
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### Controls System experiment

We performed an experiment in which we turned a bicycle on its side and placed a piece of green tap on one of the spokes. We spun the wheel and recorded the wheel spinning until it came to a complete ...
2k views

### Deflection Equation of a Stepped Beam

Help out a college student. How do you derive the deflection equation y(x) of the shown stepped cantilever beam in the figure? Each segment has a unique Young's modulus and moment of inertia. The ...
454 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,...
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### 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 ...
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### 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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### 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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### What does the resonance frequency mean in inertia matching

Like Kollmorgen shows in this PDF how you can calculate the resonance frequency of a motor coupled to a load. But with what can I Compare this frequency? It is clear that a higher resonance frequency ...
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### How does frequency-response and lead-lag compensators fit in with PID or State Space control

I am new to control theory, as my background is in statistics. In watching a wonderful set of lectures by John Rossiter, and am feeling pretty comfortable with my understanding of the basic concepts ...
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