Questions tagged [vibration]
Vibration of mechanical systems is a field studied by mechanical engineers and civil engineers
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questions
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17 views
correcting mode shape for modal damping
I have mode shapes and eigen frequencies from FE simulation. I have modal matrix and eigen frequencies corresponding to each mode. The mode shape is mass normalized. I am required to correct each ...
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9 views
Quantifying the amount of structural/hysteretic vibrational damping that occurs in proportion to deformation? (ie. Based on how “bent” something is?)
Three different conceptual types of vibrational damping forces are described here:
Viscous: $f(t) = -c \cdot v$
Coulomb: $f(t) = -c \cdot \text{sgn}(v)$
Structural: $f(t) = -c \cdot |x| \cdot \text{...
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13 views
Can cross correlation be used to see if filtering of a signal has changed it too much?
I am filtering a signal, and want to check if I am not over filtering it , I wanted to use cross correlation , but I am not sure if it is a good technique. usually I get something like the following ...
2
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1answer
69 views
Non-observable effect of low-pass filter on the Transfer function (of Vibration measured with Laser scanner)
I have to study the effect of low-pass filters (if any) on the outcome of the experiment. And the experiment here is to measure the vibration of a (metal) specimen by hitting the said specimen with ...
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26 views
Vibration measurement of rotating blade
In a vibration measurement of a rotating blade, I have the following information. The vibration signal is measured using an ICP accelerometer which has the following specification
Measurement range: ...
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0answers
24 views
How to take the engineering FFT of Signal in Matlab?
All,
The FFT function in matlab gives a theoretical mathematical FFT of the signal, and is not scaled to units and is real imaginary and not amplitude-frequency
is there an alternative way of FFT to ...
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1answer
40 views
I need a solution to a problem. I could not figure out myself how to do it [closed]
I was trying to solve this problem. But I could not figure out how to do it. Please help or provide a hint how can I solve it?
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44 views
How to find nodes of an undamped free-vibrating 2 DOF pitch and bounce system
I am working on a 2DOF non-forced pitch and bounce model for an engineering project.
I've found the values for my natural frequencies, and the initial conditions which make the system resonate in a ...
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2answers
78 views
Why does the frequency of a bottle filling up changes?
Today as I was filling up a bottle of water, and I could hear the distinctive change in pitch that signals that the bottle is near filling up, I started wondering what equation determines the ...
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0answers
32 views
I don't understand a simulation result of frequency vibration analysis of ultrasonic tranducer
I am building a ultrasonic transducer like this (with double-exponential (75%-25%) match and 2 ring PZT8 50x20x6.5 (for the moment I do not take account of pre-stress on bolt) :
When I simulate the 2 ...
7
votes
3answers
467 views
Can gravity be a driving force for a spring-mass system?
If a spring-mass system is undergoing free vibration (oscillating up and down), then does it imply that there is no gravity?
My tutor always consider gravity when finding the Equation of Motion for ...
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2answers
38 views
Coulomb damping time calculation
I'm designing a movable cover on rails under a spring and with added friction to dampen the movement. The model that describes it's movement the best is Coulomb damping model. The cover is moved from ...
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1answer
26 views
How to interpret the phase plot from an accelerometer on vibrating machinery
Attached is a plot of amplitude vs frequency and on the inset phase vs frequency. I have constructed this phase plot via $\arctan\left(\frac{Im}{Re}\right)$
How can I interpret the phase plot or ...
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1answer
42 views
Can I use loadcell for vibrating force measurement?
Is it possible to use a load cell to measure a force that is vibrating? The idea is to measure that force that is getting into the load cell in a sweep of frequencies and vibration is NOT a noise. ...
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1answer
38 views
Estimation of Beam Displacement from Acceleration
Hi Engineering Exchange,
I have a beam with pinned-pinned boundary conditions (free to rotate but not free to translate). A legacy computer analysis provided me with the maximum mid-span acceleration ...
2
votes
1answer
25 views
Are the modal participation factors bounded for shock response spectrum analysis?
Recently dug myself into the theory of shock response spectrum analysis, but one thing is not clear for me.
The theory says that the peak response of the structure can be calculated as the product of ...
-1
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1answer
44 views
Deriving equation of motion of a 1 degree of freedom system
Before solving this system, note that the rigid bars $\mathrm{\overline{OA}}$ and $\mathrm{\overline{OB}}$ are rotating about point $\mathrm{O}$, not their respective CGs. To account for this two ...
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1answer
47 views
Air - rectangular membrane system vibration and natural frequency
I'm struggling with the following problem:
The boundary conditions are $w(x,y) = 0$ around the edges.
I am supposed to find the natural frequencies of the system as a whole, and find the solution ...
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1answer
31 views
Linear actuator with low vibration and low noise
Which kinds of linear actuators offer the lowest levels of noise and vibration?
I am looking for an actuator with these properties that can push a load vertically on the cm scale. Velocity, accuracy ...
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1answer
23 views
Is shock spectrum always obtained for an undamped single degree of freedom system?
I am reading a textbook on fundamentals of vibrations and it has a very brief introduction to shock spectra. It mentions that
For comparison purposes, it is customary to use the response of an
...
6
votes
3answers
604 views
Three-phase versus single-phase operation of a generator
My generator (a Fermont MEP-803A, 4 cyl diesel, 10kW rated) can run in three distinct modes:
Single-phase 120V, in which one terminal is hot, and another is neutral
Single-phase 120V/240V, in which ...
3
votes
2answers
91 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 ...
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2answers
60 views
How do those “dipole-shaped” weights attached to sections of electrical power lines work?
I see these frequently on tall power lines like the one in the image below, sometimes a single one at each end, sometimes pairs as are shown here. Sometimes on one side of the tower but not the other.
...
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1answer
24 views
Estimating the quality factor (decay properties) of an object's vibrational modes?
I am attempting to model the acoustic behaviors of a circular membrane (drum head). I know that software like ANSYS will give me the modes of vibration pretty easy from a simulation.
But what if I ...
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3answers
78 views
which kind of accelerometer/vibration sensor are suitable for sensing vibration of building floor caused by human foot strike?
I want to count human presence in a room through vibration sensing of concrete floor. For this I want an accelerometer with low frequency detection capability. I have used ADXL-345 which is not much ...
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1answer
52 views
How to compare multiple data acquisition systems?
For an application of displacement measurement under 1 kHz, I have 3 options to choose from. The application is automotive. Unfortunately I don't have deep electronics knowledge and the catalogues ...
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22 views
Translation of vibrational motion in the 15-20 Hz range
Is anyone familiar with how to create a "shaking" fluidized bed. With vibrational amplitude in the 2" range and Hz 15-20?
I'm constructing a vibrational fluidized bed dryer for the purpose of drying ...
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0answers
57 views
How to compare two acceleration sensors side-by-side?
I have a single axis analog capacitive acceleration sensor (from PCB Piezotronics) which is very reliable but expensive. Now I need more axis, unfortunately can not afford buying anymore. So I have ...
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29 views
Formula natural frequency double wall
I started with a book (pdf see here: https://www.pdhonline.com/courses/m104/m104_new.htm)
In this book there is the following formulla found
$$f_0 = 170 / \sqrt{M_1 * t / (1 + M_1 / M_2)}$$.
The ...
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1answer
317 views
Car's shock absorbers' damping ratio
I'm trying to find a suitable shock absorber for a small ATV with a specific value (to be determined later). But everywhere I look, no one seems to be giving the damping ratio of the shock absorbers.
...
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2answers
4k views
What is the difference between washer and O-ring? what is their advantages over the other?
I am designing a hydrophone, from the piezo buzzer. To hold the circular piezo plate, I have designed a mechanical fixture. I need to use washer/o-ring to make it leak-proof. I am confused about which ...
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2answers
41 views
Would a cross correlation between vibrations in the X and Y directions help determine vibrations in the Z direction?
I have a 2D vibration sensor that can only measure in the X and Y directions, and it is mounted on top of a motor that is fixed into place, as shown in a rough sketch below.
Would I be able to work ...
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1answer
59 views
Which kind/model of sensor is appropriate for detecting vibration at one end of 1000 m steel block?
We have to detect vibration/sound produced at rail track for upcoming train at 1000 m distances . So which sensor is appropriate here? thanks.
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3answers
99 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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0answers
50 views
How to state the PSD value (random vibration)
In random vibration analysis, the load is given as a PSD (power spectral density). The values are often $G^2/Hz$, but I have an example where the PSD is a pressure $Pa^2/Hz$. The value is written as $(...
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1answer
37 views
Shock/Isolation mounting under tension
I want to secure a box (roughly 20kg in total) that contains electronic equipment to the underside of a flat steel structure. We can weld onto the underside.
The steel structure has a high chance of ...
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1answer
144 views
Vibrations analysis 7x rpm
im monitoring an overhung pump 19kw . and it shows a high peak at 7x rpm . on Thrust Vertical DE of pump.
what does it mean ?
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2answers
87 views
Need Help to Remove Sway from Steel Post + Glass Panels
I have spanned ~15' with 2x 10mm tempered glass panels. They're connected in the middle with a 1.5" x 1.5" 16-gauge, 316 stainless steel post filled with concrete. This post has a 316 base welded on ...
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2answers
2k views
Stiffness of a cantilever beam
I am working on calculating the stiffness of a cantilever beam by applying a distributed load. I wanted to ask if the distribution of the load on the beam effects its stiffness.
For eg., if I apply a ...
2
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1answer
49 views
How to allow only one mode of resonance in a cantilever beam
So I am designing a MEMS structure consisting of cantilever arrays.
For my problem, I want the cantilevers to vibrate only at their 1st mode of resonance and reject all the other modes of resonance ...
3
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3answers
481 views
Resonance vs flutter
Is there any difference between resonance and flutter. Both of them are related to overlap of external excitation frequency and Natural frequency then increase in amplitude even inifite amplitude ...
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2answers
55 views
Vibration table for tests (7-200Hz) from extruded aluminium profiles bolted together - good idea (?)
I need to design a vibration table (approx. 1000mx1000mm) to test products between 7-200Hz.
I was wondering if it is recommended to make the table structure from standardised, extruded aluminum ...
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3answers
346 views
Mechanical vibration: 2 springs attached horizontally to a wheel at a vertical distance a above the center, find the natural frequency of the system
Context: introductory mechanical vibrations, 300-level engineering. ISBN13: 978-0-13-287169-3
See problem solution below
As seen in the "Potential Energy" section, the author writes that the ...
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26 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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1answer
29 views
time interval selection for RMS of vibration
What is the general practice for selecting time interval for RMS calculation for vibration data (mm/s)
Should it be linked to the the frequency of the motor or the sampling rate?
Thanks!
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1answer
32 views
Amplitude RMS vs Amplitude in understanding vibration
I am reading this paper, which talks about dealing with mechanical noise.
When characterizing their existing noise, it says the following:
The integrated RMS vibrations up to 1 kHz on the mixing ...
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2answers
94 views
Analizing Vibrations Influence on Dynamic Weighing
I have a very sensitive scale used for dynamic weighing (by dynamic I mean that the scale and load cells are actually beneath a belt conveyor that actively weight product when it´s being transported ...
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2answers
390 views
How can I measure the vibrations of a solid object?
I want to measure the vibrations of a solid object (a tuning fork, a bone conducting headphone, the chest during singing) and to isolate them from the vibrations of the air. So I am looking for a ...
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1answer
96 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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2answers
39 views
How to measure number of strokes in a small space
I have read about a device called drumometer, which measures the number of strokes of hitting drum stick.
I think this is almost the same, but instead, I would like to measure the number of strokes/...
