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ADAMS : US NAVY The United States Navy is developing tactical systems to neutralize anti-tank and anti-invasion mines placed in the surf zone by enemy forces during amphibious assaults. The purpose of the mine countermeasure systems will be to effectively neutralize the existing mines and allow US Navy personnel and materials to proceed safely from ship to shore. The Naval Surface Warfare Center (Indian Head, MD) is developing several mine countermeasure systems that employ high explosives including both net and line systems. The Distributed Explosive Technology (DET) system is a 180 foot long by 180 foot wide array of explosive detonating cord that is packed into a nine foot by five foot container. The system also contains two rocket motors that propel and spread the explosive array over and onto a minefield. Upon ignition, the rocket motors travel along their launch rails and extract the explosive detonating cord array from the container. Parachutes on the rear of the array assist the spreading of the net. The system addresses mines between the high water mark of the beach and out to a three-foot depth. The Shallow Water Assault Breaching (SABRE) system is a 450-foot long line of discrete underwater explosive charges deployed by a single solid propellant rocket. SABRE is designed to eliminate mines in the surf zone between three and ten feet of water. The Navy's M58 is a 350 foot long system with one-half pound charges discretely distributed along its entire length. It is currently fielded for the clearance of land mines by the United States Marine Corps and Army. Models created using ADAMS virtual prototyping and mechanical simulations software from Mechanical Dynamics, Inc. (Ann Arbor, MI) of DET, SABRE, and M58 have proved to be invaluable tools during the design, development, testing, and improvement of these mine systems. Naval engineers Gary Prybyla and David Tassia performed a full scale test correlation with a very complex model that includes elements such as cross winds and rough sea conditions that would exist in real world operating conditions. According to Prybyla, "We found that our ADAMS model was able to simulate the deployment range of actual DET test firings within approximately five percent. This good agreement was possible because of ADAMS flexibility that allowed us to model the effects of critical environmental factors such as wind, sea state, and temperature. Through the use of ADAMS User Written Subroutines, we were able to create a model with the necessary sensitivity to these environmental inputs." Using ADAMS, Prybyla and Tassia realized the benefits of virtual prototyping and the ability to predict complex behavior and information in the design process versus just being able to verify designs. "With the correlation that I see in this model," notes Prybyla, "and the complex phenomena that is happening in the real world, the ability to predict what will happen with various designs under various conditions can mean a lot of money in development savings." Without using ADAMS to perform virtual modeling of candidate mine countermeasure designs, it would have been necessary to build and flight test numerous prototypes at a cost of approximately $100,000 per test. Prybyla adds, "By using ADAMS during the DET design process, we were able to avoid having to manufacture several prototype systems. Since these systems are relatively large and made from expensive materials such as Kevlar and high-explosive detonating cord, the cost savings were significant. In addition, there were inherent cost savings during flight testing attributable to the robustness of our ADAMS models as well, since we did not have to wait - at considerable expense - for the ideal test conditions on a given test day." Both the DET and SABRE mine clearance systems have been designed to be fired from the deck of the Navy's amphibious vehicle, the Landing Craft Air Cushioned (LCAC) hovercraft. Due to the hazardous nature of the DET system, the relatively tight deckspace of the LCAC, and the conditions under which DET must operate including high winds, high seas, and extreme temperatures, there has been rigorous engineering effort undertaken to ensure the launcher platform is cleared. Therefore, a predictive model of the flight trajectory of the DET system with respect to the LCAC launch platform was needed. An ADAMS model capable of simulating the entire flight dynamics of deploying the DET system was created. The model was successfully used to predict the minimum DET-to-LCAC clearances during deployments under extreme environmental conditions. ADAMS predictions of DET system clearances over critical LCAC structures showed good agreement with test measurements . Efforts are ongoing now to increase the fidelity of these predictions under the full range of motion, and environmental conditions and configuration changes. The SABRE system was modeled using ADAMS rigid body parts for each component including the rocket motor, connector, inert interface unit, 130 live charges, and the fuse. An ADAMS model of the M58 systems was created, similar to the SABRE model. The number of charges in the M58 model was increased to 700 to match the actual number of charges in the system. ADAMS models have been and continue to be instrumental in the development of mine clearance systems. Large, complex models have been created to represent the systems and simulate a variety of conditions of interest. Prybyla adds, "To date, the models have proven versatile for estimating clearance of the DET system over a bow ramp, estimating line loads, determining safety factors for the SABRE and M58 systems, and other issues such as deployment range and coverage area, performance in various sea states, and performance at extreme operating conditions. The models are cost effective since many of these conditions are difficult, it not impossible, to recreate in a test environment. "The US Navy uses ADAMS modeling to address many of its difficult problems in mine countermeasures. Future work will likely include additional tensile tests to better characterize strength members used in mine clearance systems and deployment of new unconventional mine clearance systems." Click here for an image in tif format (891k). Author: Laura Carrabine |