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Questions tagged [modal-analysis]

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2answers
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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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1answer
42 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 ...
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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-...
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1answer
62 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 ...
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1answer
41 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
23 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
31 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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1answer
89 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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0answers
1k 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 ...
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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 ...
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1answer
100 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 ...
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1answer
92 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. ...
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1answer
273 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 ...
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411 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 ...
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2answers
210 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 ...
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1answer
689 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, ...