Structural Optimization Design Of The Pressure Hull Based On Nonuniform Ring-Frames Theory

Ring-stiffened cylindrical shells which are propitious to general arrangement arecommon forms for submersible. For most pressure hulls of submersible，it is easy to satisfythe strength，however， thicker shell plates are still necessary to meet the need of generalstability. Thicker shell plates will result in higher cost. So there is contradiction between thecost and the stability of the pressure shells. It is necessary to raise the general stability ofpressure shells through optimizing the structure instead simply increase the thickness of theshell plates. So far， almost all the pressurized cylindrical shells are designed with the equalstiffness ring-frames isometrically distributed. Taking the general stability of the pressurehull into consideration，this kind of structure is not that reasonable. Because when buckling，the pressure hull presents a semi-sine wave lengthways and the largest radial displacement isin the midsection of the shell. In considering this thought， we assume that rib positionswhich have larger radial displacements should be stiffened more in this paper. The stiffness(inertia moment of cross section) of each ring-frame is determined according to the radialdisplacement of its position. So the pressure hulls reinforced with non-uniform ring-framesare put forward. With energy methods，the formula of general buckling pressure is deducted.Unrevised critical pressure is adopted to weigh the general stability. Several examples ofuniform stiffening pressure hulls are redesigned in this paper. Theoretical calculation andfinite element analysis based on ANSYS are used to compare the change in stability andweight. The conclusion that the stability of the pressure shells reinforced with nonuniformcircular frames are better than the uniform ones. With the secondary development toolsAPDL， a frame tripping check system has been developed based on ANSYS.Basing on this theory and relative research， this paper designs a battery capsule of asubmersible with nonuniform ring-frames reinforcing method. Firstly， make a initial planaccording the volume of the battery. On the basis of this initial plan， a design ofexperiment (DOE) is carried out to choose the design variables in the optimization design.Then aiming at minimizing the total weight the capsule is optimized. Both the DOE and theoptimization process are implemented by ANSYS integrated in iSIGHT. Redesign thering-frames of the optimization plan according the radical displacements and a new planwith higher critical pressure is obtained. Taking the economy into consideration， this paper decreases the thickness of the shell by1mm. The strength and the stability can still satisfythe requirement and the final plan of the battery capsule is fixed.