Hi All,
I have build a simple model in Abaqus-Simulia which consists of a steel block mass on top of a compression wave spring, the bottom of the spring has been constraint in translations and rotations (basically the boundary condition, 6-DOF motions are all disabled). However, I want to calculate the natural frequency of the spring-mass model, where the mass is not TIED with the top of the spring, i.e. the spring can only be compressed and can NOT be streched. Does anyone know how I can set the interaction between the mass and spring top?
Thanks very much
Hi
Give pretension for the spring mass system so that the interaction exists between spring- mass system. Use combin 39 spring element for easiness of your task.
A natural frequency analysis is, per definition a geometrically and materially LINEAR perturbation analysis around the undeformed base state or around the current nonlinearly deformed base state with fixed unchangeable boundary conditions. LINEAR means, from the theoretical side, infinitesimally small motions or displacements which represents a very idealized setting. This basic theoretical restriction should always be kept in mind when thinking of a classical natural frequency analysis setting. In your case it seems that you want to calculate the nonlinear vibration phenomenon with the contact condition being explicitly active. In physical terms this means that each periodic vibration cycle essentially consists of two phases, i.e. the (massless ?) spring compression phase and the following free - flying - mass phase, provided the static spring pre - compression force due to gravity is small compared to the inertia - related lift - off force. Representing such spring - compression - only behavior is possible by using a nonlinear spring model with suitable force - displacement relationship being prescribed, in simpel tabular form. Best wishes W.G.
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