Design Development of a Hydrostat : Construction of a hydrostat used in an underwater SAI-unit

Sammanfattning: Working with and providing different military and industrial solutions, SBD’s (Saab Dynamic) work also involve underwater equipment and underwater weapon (UW) systems. Nowadays, there are a number of standards that should be followed to make weapon systems safe to use, transport and handle. SAI-units (Safety, Arming, and Ignition) are components with capacity to handle weapon systems such as UWs in a safe manner. An underwater SAI-unit contains a mechanical sensor part, called hydrostat, which acts as a pressure transmitter to initiate the function in the system. This component senses the hydrostatic pressure of water depending on the depth and transmits the data into other subsystems in the SAI-unit.The hydrostat used in a specific SAI-system has previously been utilizing conventional techniques in its construction, including a spring and a piston which acts in response to water pressure. SBD wanted to develop the hydrostat further to increase its performance and adaptability to today’s technology. Toachieve this, the systematic method of product development and safety requirements were considered. Because SBD’s work in this field involved military solutions, some values and data included in this report were obtained by arbitrary assumptions. The company would like the design solution for the current hydrostat to be minimized in cost, minimized in shape factor, but at the same time fulfill requirements regarding operating environment such as temperature and loading. A design solution was introduced, which was illustrated by a 3D-model in details. Strength analysis was done through the Computer Aided Engineering (CAE) software Abaqus. Underwater loading case was analyzed using the FEM, named UNDEX (Underwater Explosion).It was concluded that the temperature, load, and safety requirements were achieved. However, regarding the cost and the relative shape factor, the goals were not achieved when comparing the result data. The cost showed to be dependent mostly on material type, manufacturing method and number of pieces to be produced.