Air Gun Launch Simulation Modeling and Finite Element Model Sensitivity Analysis

Abstract

Abstract : This report presents in two parts analytical simulation results of a test item launched in an air gun test. The first part of the report presents a discrete mass-spring model to predict the transient response of a generic artillery component subjected to launch simulation in an air gun test environment. A 2-degree-of-freedom model is developed to simulate the air gun launch environment in which a test object mounted on a projectile is launched through the air gun and decelerated by a crushing aluminum honeycomb mitigator. The mitigator in turn impacts the momentum exchange mass (MEM) before being stopped at the retrieving end. The present model achieved a good prediction of the period and peak acceleration of the on-board recorder. The sensitivity of finite element (FE) model parameters affecting the dynamics of a test object launched in an air gun test is discussed in the second part of the report. An LS-DYNA FE model previously developed to simulate the impact mitigation environment is used to investigate the sensitivity of FE model parameters. The sensitivity study clearly indicates the necessity of honeycomb numerical characterization under very high impact loading for effective modeling of the strain rate effects. The FE analysis also suggests that intermittent eigenvalue analyses during an impact simulation could be useful in identifying the dominant modes of vibration governing the dynamics of the test items and verifying the predictive capability of the FE model. An efficient procedure using a decoupled model is proposed to simulate the response of a test item launched in an air gun test. In this approach, the contact force generated from the discrete analytical model is applied on a detailed FE mesh of the test item for a given impact velocity. The acceleration data obtained with this procedure compared well with those predicted from the full FE analysis. The simplified model runs in less than 1 minute.