Questions tagged [modal-analysis]
The modal-analysis tag has no usage guidance.
20
questions
3
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1answer
46 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
votes
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
votes
3answers
76 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
0answers
14 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
vote
2answers
84 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
vote
1answer
79 views
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
votes
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
votes
1answer
101 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
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 ...
1
vote
0answers
25 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 ...
1
vote
2answers
34 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
158 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
vote
0answers
2k 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
votes
3answers
399 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
votes
1answer
150 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
votes
1answer
143 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
vote
1answer
409 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
votes
1answer
655 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
votes
2answers
242 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
votes
1answer
870 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, ...
