Computational Strategies to Minimize Transient Response During Time-Domain Analysis of Structures Under Vibratory Loading

Time-domain dynamic analysis of vibratory systems becomes useful in finite element analysis (FEA) when the structure’s response can no longer be assumed linear, as frequency-domain (spectral superposition) methods require. Time-domain analysis also permits the use of cycle-counting methods when assessing the vibration durability of electronic assemblies. The analyst is often limited to simulating only the first few cycles of the vibration response in very complex models, to minimize the computational burden. However, the accuracy of time domain analysis can be questionable during these first few cycles, due to unwanted transients, unless the initial conditions are properly modeled to correctly produce the steady state response. This paper explores this sensitivity to initial conditions for undamped and damped structures. Strategies for calculating and implementing proper initial conditions within FEA are discussed. Two illustrative examples are presented for simplicity. The first consists of a simple cantilever beam so that the numerical results can be compared to known analytic solutions and the basic theory can be demonstrated. The second example is a 2D representation of a circuit card assembly containing multiple leadless chip resistor components, so that implementation details can be demonstrated for more complex structures. This paper is intended to have tutorial value to FEA users who have to conduct time-domain dynamic analysis.