Figure 1: After designing this valve in Solid Edge, Coastal Systems Station engineers captured the exact geometry with ALGOR’s InCADPlus with no file translation, creating a very fine surface mesh on which an accurate finite element analysis could be performed.

Coastal Systems Station, Naval Surface Warfare Systems Center in Panama City, Florida, supports the U.S. Navy in the area of Littoral warfare, which includes mine, amphibious and special warfare, underwater systems and diving and salvage equipment. Recently, engineers at Coastal Systems Station designed a valve body in Solid Edge and then captured the geometry with ALGOR’s InCAD^Plus and performed finite element analysis with ALGOR to ensure that it could withstand high pressures.

The valve is designed to control the flow of gases such as helium, nitrogen and oxygen into the breathing loop of a deep sea diving rig that goes beyond the limit of conventional scuba gear. For diving beyond traditional depths of self-contained underwater breathing apparatus, a mixture of inert gases including helium and oxygen is used to prevent potentially deadly conditions such as oxygen poisoning, high pressure nervous syndrome and nitrogen narcosis. The 7,500-psi valve connects two spherical 5,000-psi Inconel flasks to a manifold that recirculates the gases. These components need to withstand high pressures because the breathing system must contain a large amount of gas in a compact area to provide sufficient life support for the duration required.

K-Monel material was chosen for the valve because it withstands pressure, is self-extinguishing to avoid the possibility of oxygen fires, resists the corrosive effects of seawater, and enables removal of the adjacent bottle without galling the threads.

After removing a threaded area from the model in Solid Edge, Coastal Systems Station engineers captured the geometry of the valve with ALGOR’s InCAD^Plus, creating a very fine surface mesh (Figure 1). The surface mesh was subsequently refined using ALGOR’s Merlin Meshing Technology to reduce the number of elements in non-critical areas. The model was then automatically meshed in ALGOR using the hybrid mesh option that combines bricks on the surface and tetrahedra inside. The result was a model with approximately 40,000 elements, with the majority of the elements on the surface, where accuracy is most critical.

A 7500-psi loading was applied to the inner surfaces and force loadings were applied at each end to simulate the "pull" that adjacent components exert on the valve. The model was restrained on one side at the extension nub where the valve attaches to the high-pressure gas supply cylinder. This linear static stress analysis simulated the basic internal pressure load and end attachment loads (Figure 2). Coastal Systems Station engineers later analyzed the model with additional loads replicating worst case forces that could be induced onto the assembly during usage in order to produce a conservative design.

Figure 2: The ALGOR linear static stress analysis of the valve shown here simulated the basic internal pressure load within the valve and end attachment loads during operation in a deep sea diving rig.

Prototypes of this valve have not only withstood laboratory hydrostatic tests without any evidence of plastic deformation but are currently in use in prototype diving equipment being tested. The computer-aided design and analysis work of Coastal Systems Station engineers ensured that only one set of prototype parts were required prior to manufacturing.