This approach allows the separation of their damping and stiffness matrices into symmetric and asymmetric portions, which consist. Modal frequency response analysis is widely used in structural dynamic analysis because of its computational saving over direct frequency response analysis. Now most people are amazed at how the structure has these natural characteristics. Using the modal method, determine the frequency response of the. Graphical display of a frequency response function. In this case a simple model of a cantilever plate under a singlepoint cyclic load is used. Modal frequency response analysis of a flat plate video interactive tutorial demonstrating how to import an existing fe model, apply boundary conditions, and perform a modal frequency response analysis on a flat plate. Pdf direct and modal frequency response analysis of sound fields. The frequency response function frf measurement removes the force spectrum from the data and describes the inher ent structural response between the. Structural testing part 2, modal analysis and simulation br0507. Accurate determination of the frequency response function. In proceedings of the 3rd international electronic.
It isnt related to a loading at this stage, only to the geometry. Responses such as displacement, stress and force can be calculated inexpensively for a large number of loading frequencies after obtaining. Clearly the frequency response function is easier to evaluate. Pdf direct and modal frequency response analysis of. For lightly damped structures, high resolution analysis is required to measure. Make sure units are consistent and density is defined. Modal is the simplest analysis and the only thing it does is telling you what are the resonance frequencies of your geometry. Theoretical background for calculations in nastran. Calculations of frequency response functionsfrf using. Direct and modal frequency response analysis of sound fields in small rooms by finite element method article pdf available in the journal of the acoustical society of america 1235. Now experimental modal analysis a simple nonmathematical presentation. Pdf modal frequency response optimization in optistruct. The step by step process can be found at the following link.
The new method is based on the modelling of rotating machines as structural assemblies of rotating and nonrotating components. Resonance frequencies change due to the shape of your model and the way it is constrained only. On the use of pztpatches as exciters in modal analysis. Modal analysis is the process of characterizing the dynamic response of a system in terms of its modes of vibration. The frequency response function is very simply the ratio of the output response of a structure due to an applied force. The response can be measured as displacement, velocity or acceleration. Modal analysis with altair optistruct hypermesh some hints all components in the model must have material and properties assigneddefined. We measure both the applied force and the response of the structure due to the applied force simultaneously. Frequency response functions because it is a complex quantity, the frequency response function cannot be fully displayed on a single twodimensional plot.
Then, as in the modal analysis, two methods are employed. Workshop 6 modal frequency response analysis mscnastran102 exercise workbook 63 model description. Structural testing part 2, modal analysis and simulation. If the input to an lti system is a sinusoid, the steadystate output is a sinusoid of the same frequencybut.
In frequency analysis, a complex signal is resolved into a set of simple sine waves with individual frequency and amplitude parameters. Although the response variable for the previous discussion was displacement, it could also be velocity or acceleration. Analytical modal analysis depends on the generation of the equations of motion of a system through a finite element model. In this section, a very brief description is given. In modal analysis a complex deflection pattern of a vibrating structure is resolved into a set of simple mode shapes with individual frequency and damping parameters. Modal frequency response analysis of a flat plate video. It can, however, be presented in several formats, each of which has its own uses.
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