2. Quantities considered in vibrations with shocks

The primary quantities considered in shock vibrations are identical whether for experimental measurements or numerical calculation, they concern shock forces and displacements at the level of shock points. However, the experimental results present an additional difficulty of analysis due to the errors or biases introduced by the measurement systems.

We will examine the two quantities mentioned above in succession.

2.1. Shock forces

The first concern concerning structures vibrating with shocks is to better understand the forces received by the structure during impacts on its supports with play or between the structures. These data are calculated in a temporal manner by the DYNA_TRAN_MODAL algorithm, they are then archived with a step defined in this same operator. Since shock data has a very high frequency content, care must be taken to have sufficient archiving (do not exceed PAS_ARCH: 10). These forces expressed in a coordinate system local to the obstacle \((\mathrm{Yloc},\mathrm{Zloc})\) are traditionally decomposed into a part normal to the obstacle (\(\mathrm{Fn}\) in the figure below) and a tangential part (\(\mathrm{Ft}\)) if friction is taken into account between the structures. The shock conditions cause the normal shock force to have a constant sign taken to be conventionally positive in*Code_Aster*.

2.2. Shock trips

The movements of the structure at the level of its supports with play are another important information calculated. However, its analysis poses fewer problems because the spectral content is less rich. In the case of obstacles that are circular or described in a polar manner, a polar description of the movement may be interesting.

2.3. Secondary quantities

2.3.1. Shock time

The contact time between the structure and the game supports is an indirect quantity characteristic of the vibration movement with shock. Positive reaction force can be deduced in various ways, based on a displacement criterion. A concept of global shock time, broken down into elementary shock (or rebound) will be introduced in [§3.4].

2.3.2. Calculated quantities

Other secondary quantities may be important in the analysis of shock conditions, these are the impulse during the impact (integral of the force exchanged), the wear power, the maximum force during an impact,… These quantities are specific to each post-treatment and they will be specified in the following two chapters for the post-processing option “ USURE “ and “ IMPACT “.