Reduced Order Modeling for Rapid Simulation of Blast Events of a Military Ground Vehicle and its Occupants

Army TARDEC, Warren, Michigan

Improvised Explosive Devices (IEDs) pose a significant threat to military ground vehicles and soldiers in the field. Full-system end-to-end models, as well as Reduced Order Modeling and Simulation (M&S) methodologies, are extensively used for the development of blast-worthy ground vehicles.

Due to the severity of forces exerted by a blast, ground vehicles may undergo multiple sub-events subsequent to IED explosion, including local structural deformation of the floor, blast-off, free flight, and slam-down. Depending on the location of the IED under the vehicle, the vehicle may also be subjected to rollover. To understand injuries sustained by soldiers under all of the various loading conditions, it is imperative to analyze the impact of each sub-event on soldier injuries. Using traditional finite element analysis techniques to evaluate an entire event is inefficient, as calculation times may exceed several days for one simulation of up to 300 milliseconds. Therefore, there is a need for a computationally efficient tool or methodology to simulate the entire blast event in faster turnaround simulation time.

The main objective of this project was to develop a computationally efficient reduced order simulation model capable of analyzing end-to-end performance of military ground vehicles subjected to blast loading. This model will be used to determine the effects of blast loading on soldier injuries, including during the blast-off, potential rollover, and slamdown phases. MADYMO is a leading design and analysis software for occupant safety systems in the safety/crashworthiness industry, and is known for fast and accurate calculation of injury risks and safety system performance, and for its accurate library of crash dummy and human body computer models.

Execution of the project was divided into four major tasks: development of the vehicle model, integration of occupant and restraint systems, implementation of several blast loading methods, and analysis of vehicle and occupant results and comparison of models.

For development of the vehicle model, a simplified generic ground vehicle model was integrated in MADYMO using a combination of rigid body and finite element techniques equivalent to the LSDyna full finite element ground vehicle model. The integration consisted of required geometric details of each component and sub-assembly of the vehicle, material properties of the structure and seats, and energy absorption characteristics of the seats. Typical suspension and seat models were integrated into the MADYMO ground vehicle model.

A commercial 50th Percentile Hybrid III occupant model was integrated into the MADYMO ground vehicle model, and a standard seatbelt was routed around the occupant model and connected to the vehicle anchor locations.

Different loading methods in MADYMO were developed and implemented to apply representative blast loading to the underbody of ground vehicle model. Loading methods identified were impulse-based vertical loading into the vehicle, prescribed accelerative vertical motion, and prescribed effective blast pressure map to the vehicle structure. The modified ground vehicle model was integrated with the loading method to develop a reduced order blast simulation model.

An analysis captured sub-events of floor deformation, vehicle rigid body response, and occupant response during the blast-off phase, and vehicle/occupant response consisting of potential rollover during the slam-down phase.

Several different methods were attempted to model the blast loading on the vehicle and the occupant in MADYMO. A vertical acceleration pulse was applied to the vehicle rigid body. The sample pulse has a maximum acceleration of about 180 g’s. When the model ran with this acceleration, the motion of the vehicle was not changed when the mass of the vehicle changed. Due to the limitation of the acceleration pulse-based loading method, a force (or impulse)-based loading method was developed. In this method, instead of prescribing the vehicle motion through acceleration pulse, a force profile (time-history) would be applied to the vehicle.

In the first case, loading was applied to the center of gravity of the vehicle, causing blast-off and slam-down. Next, a load was applied to the center of the hull side edge, causing blast-off, partial rollover, and slam-down. Finally, a load was applied to the lower front corner of the vehicle, which also caused lift-off, partial rollover, and slam-down. These load application points are shown in the figure.

Three different vehicle model types were developed and integrated with three different loading methods for reduced order simulation of full blast events. Occupant responses were based on generic seat properties and assumed dummy position, which can be modified for different vehicle configurations. For blast pressure models, the head, chest, and pelvis accelerations are relatively low. However, the tibia forces are high due to the deformation of the floor, which contacts the feet, applying force. For a jump and roll model – which simulates blast-off, partial rollover, and slam-down – the head, chest, and pelvis accelerations are high due to the acceleration of the vehicle.

This work was done by Jaisankar Ramalingam and Ravi Thyagarajan of the Army TARDEC, and Sherri Chandra of TASS International. ARL-0171