Questions tagged [modal-analysis]

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1answer
20 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 ...
3
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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 ...
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 ...
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 ...
3
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1answer
33 views

Negative Eigenvalues in Ritz Solution of First-Order Shear Deformation Theory

I am trying to write a MATLAb code for determining the natural frequencies of a first-order shear deformation plate using Ritz method. I am using Legendre polynomials as trial functions in Ritz method,...
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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0answers
17 views

How to run a steady state dynamics, Modal step based optimisation using TOSCA?

What design responses must be given in the TOSCA gui. I chose volume reduction as an objective function with the constraints of displacement. Is this approach correct?
1
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2answers
89 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 ...
1
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1answer
105 views

Modelling acoustic instruments — predicting frequencies, decays, levels, and phases of modes of a circular membrane (drum head)

I have been working on some acoustic synthesis software for modelling several acoustic instruments. I am using the principle of modal synthesis, where every mode of vibration is individually ...
2
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0answers
27 views

Plot zero-pole from frequency response matrix

I've represented with Matlab a system with three degrees of freedom. I'm trying to plot a pole-zero map from my Frequency Response Matrix H(w) in the case of Damped-...
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
45 views

Analytical solution for wall eigenvalue analysis

I have a wall with the bottom end of it fixed to the ground. I want to derive from first principles the frequencies and mode shapes of the structure. I know that I will need to start with the ...
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0answers
26 views

Why does Experimental Modal Analysis need a reference signal?

I need to conduct a vibration experiment with 3 accelerometers for a gear box. I'm reading the theory of mainly how to perform the vibration analysis but I don't understand why EMA needs a reference ...
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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 ...
1
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0answers
3k views

How to get mass normalized mode shapes?

I have an MDOF system with 4 degrees of freedom with forced input at one of the dof (4th dof)(it is a sinusoidal wave with a particular frequency expected to be generated using a shaker); displacement ...
5
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3answers
435 views

How to know which modes are excited by a given input in modal analysis?

Consider a simple structure such as a beam, plate, ... Assume that you know how to determine the different modes of vibration of the structure. You are given an external input, such as a force or ...
4
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1answer
159 views

Which mode does get excited under action of dynamic loading?

I am working on the vibration of the continuous system, I have seen lots of books on vibrations which talks about the natural frequency and mode shapes of the continuous system. I am interested in ...
2
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1answer
160 views

FRF based material constant optimization

I need advice on how to optimize a finite element model of a transversely isotropic material. I have modeled the material with 5 nominal moduli in Abaqus and performed an eigenvalue extraction. ...
1
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1answer
438 views

How to handle modal combination in response spectrum analysis for member forces for member with more than 1 element?

My textbook says for mode combination, the peak value $r$ of each response quantity is determined by combining the peak values $r_n$ of the modal contributions to the same response quantity. From ...
0
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1answer
764 views

The distinction between lateral mass participation and vertical mass participation

Refer to the chapter 14 of the Wilson book "Dynamic Analysis of structures": calculation of stiffness and mass orthogonal vectors. The table 14.6 shows the lateral mass participation and vertical ...
5
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2answers
247 views

How do I conduct an experimental modal analysis with a three-axis accelerometer?

How can I compute the Frequency Response Function (FRF) if I use two three-axis MEMS accelerometer to measure the input excitation and output response? I have read from some books that the FRF can be ...
6
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1answer
908 views

FEM modal analysis computing displacements

I have an FEM model that I am doing a modal analysis of. I wanted to check that how I am computing the physical displacement is the correct way, as I've read a lot of about normalizing modes, ...