DDAM (Dynamic Design Analysis Method) is a U.S. Navy-developed analytical procedure for shock design. It helps validate the design of onboard equipment and structures subject to dynamic loading caused by underwater explosions (UNDEX). It is a widely accepted procedure for safety evaluation for civil and military ship building. The keyword for response spectrum analysis (*FREQUENCY_DOMAIN_RESPONSE_SPECTRUM) in LS-DYNA has been extended to run DDAM analysis for shipboard components, with the option _DDAM. This paper first gives a brief review of the theory for DDAM analysis. Then, with several examples, this paper shows how to run DDAM analysis with LS-DYNA and how to perform post-processing of the results. For purpose of cross-validation, the results of DDAM analysis with LS-DYNA in the first example are compared with that given by other commercial code.
Eddy current problems are typically modelled by a combination of Ampère’s law, Ohm’s law, the non-existence of magnetic monopoles and Faraday’s law of induction. Using a magnetic vector potential A, such that the magnetic flux intensity is given by B = curl A, we end up with the equation σ ∂ t A + curl ν(A) curl A = Js [1]. Here, Js are applied source currents, ν(A) the magnetic reluctivity whose dependence on A implies the possible non-linearity of the material behaviour, and σ is the electrical conductivity. In most applications, the domain of interest consists of conducting (e.g. metal parts) and non-conducting regions (e.g. air). In the non-conducting regions, the part σ ∂ tA is dropped from the equation and the model is that of magnetostatics.
A series of frequency domain analysis and fatigue analysis features have been implemented to LS-DYNA, since version 971 R6 [1]. The frequency domain features include FRF (Frequency Response Function), SSD (Steady State Dynamics), random vibration, response spectrum analysis, and acoustic analysis based on BEM (Boundary Element Method) and FEM (Finite Element Method). The fatigue analysis features include fatigue damage solvers in both time domain and frequency domain (based on random vibration and steady state vibration). The main applications of these features are in NVH and durability analysis of structures and components [2]. A bunch of new options were implemented to the frequency domain analysis and fatigue analysis features since the last European LS-DYNA Conference in Salzburg, Germany, 2017.
Only time and resource constraints limit the size and complexity of the implicit analyses that LS-DYNA users would like to perform. Rolls-Royce is an example thereof, challenging its suppliers of computers and mechanical computer aided engineering (MCAE) software to run ever larger models, with more physics, in shorter periods of time. This will allow CAE to have a greater impact on the design cycle for new engines, and is a step towards the long-term vision of digital twins. Towards this end, Rolls-Royce created a family of representative engine models, with as many as 66 million finite elements. Figure 1 depicts a cross-section of the representative engine model.
DDAM Analysis with LS-DYNA