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Several popular frequency-based fatigue damage models (Wirsching and Light, Ortiz and Chen, Larsen and Lutes, Benascuitti and Tovo, Benascuitti and Tovo with α.75, Dirlik, Zhao and Baker, and Lalanne) are reviewed and assessed. Seventy power spectrum densities with varied amplitude, shape, and irregularity factors from Dirlik’s dissertation are used to study the accuracies of these methods. Recommendations on how to set up the inverse fast Fourier transform to synthesize load data and obtain accurate rainflow cycle counts are given. Since Dirlik’s method is the most commonly used one in industry, a comprehensive investigation of parameter setups for Dirlik’s method is presented. The mean error and standard deviation of the error between the frequency-based model and the rainflow cycle counting method was computed for fatigue slope exponent m ranging from 3 to 12.

Fatigue analysis in the time domain using the rainflow cycle counting algorithm is considered the most accurate method for estimating damage. Dirlik's method has been found to be very accurate for damage estimation in the frequency domain. Previous studies have demonstrated the usefulness of Dirlik's method for ocean engineering and wind turbines but few have shown how well Dirlik performs in automotive applications. This study compares Dirlik's method with the rainflow cycle counting and with other frequency domain methods. The study analyzes measured data for an automotive component subjected to five test track load conditions. In addition, fourteen of Dirlik's original spectra and seven additional spectra which combine sine and random spectra are studied. It was found that Dirlik's method predicts more damage than the rainflow cycle counting method when applied to the original data used in creating the method.

This paper addresses the use of virtual environments and associated visualization methods in the design of military ground vehicles. The focus is increased accuracy and correlation to the physical environment in a virtual environment. The motivation is to enable position-based design studies in a virtual environment as a substitute for a physical buck. Techniques for the use of visualization for large assembly flythrough are well-known [ 1 ]. Many virtual environment software products are available and CAD data access is streamlined. Virtual environment technology is often used in aerospace, architecture, automotive and armored ground combat vehicle design. However, in order to conduct a study representative of the intended design, the virtual environment system must be calibrated and accurate. This is particularly important in reach and vision studies for human interface design including the placement of the controls and displays.

To stay competitive, new products require faster development time at low cost and good quality. Defense as well as commercial industries are forced to use analytical tools to stay competitive in a tough market. The use of simulation tools and approximation techniques in evaluating product performance during the early stages of the product development has a major impart on the product development efficiency, effectiveness, and lead time. Building physical prototypes of complex systems is expensive and it is difficult and time consuming to develop them. It is extremely beneficial to know as much as possible about the product performance and to optimize its dynamic characteristics before the first physical prototype is built.

The National Automotive Center (NAC), part of the U.S. Army's Tank-automotive and Armaments Command (TACOM) and General Dynamics Land Systems have designed, fabricated and will demonstrate a series hybrid electric propulsion system integrated into a 20-ton Gross Vehicle Weight (GVW) 8×8 ground vehicle. The technologies of this vehicle, namely the Advanced Hybrid Electric Drive (AHED) Technology Demonstrator, may be candidates for inclusion into the automotive platform of the Future Combat Systems (FCS) ground vehicles. This paper discusses the logistical advantages of hybrid electric propulsion systems. It addresses fuel economy, technology maturity, platform commonality, and automotive performance as it relates to fighting, maintaining and supporting the FCS ground force.

The performance of ground vehicles of all types is influenced by the cooling and ventilation of the engine compartment. An increased heat load into the engine compartment occurs after engine shut down. Heat is transferred from the hot components within the engine compartment by natural convection to the surrounding air and by radiation to the adjacent surfaces. The heat is then dissipated to the ambient mostly by convection from the exterior surfaces. The objective of this study is to develop a Computational Fluid Dynamics (CFD) simulation methodology to predict the airflow velocity and temperature distributions within the engine compartment, as well as the surface temperature of critical engine components during the after-boil condition. This study was conducted using a full-scale, simplified engine compartment of an armored combat vehicle. Steady-state simulation was performed first to predict the condition prior to engine shut down.

The subject of this paper is centered on presenting a top-level design for an advanced automotive drive-by-wire architecture for a Military Ground-based Vehicle System. A redundant, reconfigurable, inherently safe drive-by-wire design was developed for a 21st Century Self-Propelled Howitzer and Resupply Vehicle for the Crusader Program. The technology selected is composed of reusable hardware and software modules to facilitate technology transition/transformation to Future Combat Systems variants and other non-military vehicles. This drive-by-wire design provides a complete digital data-bus with analog wired back-up solution for vehicle drivability control (throttle/braking/steering).

Model-based simulation and analysis tools have been used in the design of both commercial and military hybrid ground vehicles. The goal of the US Army's Future Combat Systems (FCS) is to develop a number of vehicles, called variants, fulfilling different missions on the battlefield. Design goals include reduced weight for air transport and increased agility, while maintaining a common chassis, power generator and energy storage system. In this paper we describe a unique tool that facilitates the development of such a series of vehicles. The modeling and analysis environment is flexible, modular and reconfigurable. It has been developed on commercially available MathWorks tool suite consisting of MATLAB®1, Simulink® and Stateflow®. A library of loads representing different energy usage events is first created. With the common generator and energy storage system, a different variant model is easily generated by selecting the appropriate mission loads.