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FAQ 003507 | There are two solving methods for a linear time history analysis available in the RF‑/DYNAM Pro add-on module. What is the difference between them?
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There are two solving methods for a linear time history analysis available in the RF‑/DYNAM Pro add-on module. What is the difference between them?Answer
Both solving methods, the "linear modal analysis" and the "linear implicit Newmark analysis," are available.
Linear Modal Analysis
This solving method uses a decoupled structure that is based on eigenvalues and mode shapes of the structure. It is necessary to assign a defined natural vibration case.
This method should only be used if there is a sufficient number of eigenvalues of the structure calculated in the natural vibration case. This means that you should pay attention to achieve an effective modal mass factor of the total structure of approximately 1 in all governing directions. If this is not possible, this method will lead to inaccurate results.
Linear Implicit Newmark Analysis
This is a direct time step method that does not require a natural vibration case, and requires enough small time steps to achieve the exact results.
This method is recommended for complex structures, which would require a very large number of mode shapes in order to achieve an effective modal mass factor of about 1.
If a sufficient number of eigenvalues can be guaranteed by means of the linear modal analysis, both solving methods lead to approximately same results. For more information about both methods, read the manual of RF‑DYNAM Pro.
Keywords
Dlubal FAQ Solving method Solver Time history Newmark Modal analysis Frequently Asked Question FAQ about Dlubal Question and Answer about Dlubal
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Superpositioning Modal Responses in Response Spectrum Analysis Using Equivalent Linear Combination
The response spectrum analysis is one of the most frequently used design methods in the case of earthquakes. This method has many advantages, the most important one is the simplification.
Considering the Stiffness of Gas Solids in Nonlinear Time History Analysis
The stiffness of gas given by the ideal gas law pV = nRT can be considered in the nonlinear dynamic analysis.
The calculation of gas is available for accelerograms and time diagrams for both the explicit analysis and the nonlinear implicit Newmark analysis. To determine the gas behaviour correctly, at least two FE layers for gas solids should be defined.
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