Advanced Finite Element Solutions for Simulating Dynamic Response and Structural Modifications
FEMtools Dynamics contains tools for:
Frequency Response Functions (FRF)
To obtain FRFs, the response function is divided by the excitation force. Because these functions do not contain force information, they only depend on mass, stiffness and damping properties of the structure, just like the modal properties. Therefore they are also suitable as responses for correlation analysis, sensitivity analysis and model updating.
Harmonic Response Analysis
Harmonic response analysis studies the response of a structure under harmonic loading all of the applied forces are known at each forcing frequency. Depending on the formulation, operational displacement, velocities or accelerations are obtained. In general, the results are referred to as Operational Shapes or Operational Displacement Shapes (ODS). ODS can be used in correlation analysis to compare experimental ODS with analytical predictions.
Residual Vectors (RESVEC) are used to extend the modal base that is used for modal superposition methods. They can compensate the effects of modal truncation and often improve the dynamic response without the need to increase the number of mode shapes or use a direct method. FEMtools supports methods to compute residual vectors that are based on inertia relief, viscous damping and applied loads.
Dividing assembled structures into sub-structures is an efficient approach to solve dynamic problems. When applied to large numerical models, substructuring techniques allow creating superelements and reducing the complexity of each component so that the assembled problem is manageable yet accurate. The Craig-Bampton method is a well-known tool for such procedures, but other response-based or modal-based approaches are available too. Substructuring also allows combining models obtained from measured components so that, through an hybrid assembly process, a representation of the full structure can be constructed and used in further engineering and design tasks.
Substructuring methods are enabling efficient re-analysis for applications like model updating and optimization, but also to vary joint properties for nonlinear analysis and probabilistic analysis.
A superelement is defined by grouping a number of elements
and solve for this substructure separately. Superelements offer
great time-savings in application that require significant re-analysis
like time-domain and frequency domain responses analysis, design
Modal-Based Assembly (MBA)
Modal-Based Assembly (MBA) is a modal domain substructuring method to rapidly assess the influence of structural changes on the modal parameters and derived results like FRFs or operational shapes. The main advantage of the MBA approach is its high computational efficiency. This technique can be used to investigate the effect of different modeling assumptions on the level of correlation with test data. Other applications are in vibration troubleshooting or are design-oriented, for example to find the most efficient structural modification that will shift resonant frequencies away from excitation frequencies.
MBA is an extension of Structural Dynamics Modification (SDM) that
supports FEA data, test data or a combination of FEA and test data (hybrid
supports FEA data, test data or a combination of FEA and test data (hybrid modeling).
FRF-Based Assembly (FBA)
FRF-based Assembly (FBA) is a frequency domain substructuring method to combine multiple sub-components and predict the response of the assembly from the FRFs computed or measured on each component. In case of FBA the dynamic properties of the subcomponents, as well as the computed behavior of the assembled structure are described with frequency response functions (FRFs). FBA is an alternative to Superelements (using system matrices) and modal-based assembly (using mode shapes only). FBA is a computationally efficient method that focuses on the coupling between components and is therefore suitable for larger assemblies with many components and for studying the transmission of forces by the connections.
Time Domain Simulation
Time Domain Simulation (TDS) provides a set of tools to compute the transient response of structures in a computational efficient way. The FEMtools TDS solver first derives a state-space model from the normal modes of the structure and then uses this model to compute the time series of the responses. In combination with the modal parameter extractor, TDS can be used in a pretest analysis phase to simulate a vibration test.
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