HYDRODYNAMIC COEFFICIENTS ESTIMATION OF A PROLATE SPHEROID USING COMBINATION OF HYBRID EXTENDED KALMAN FILTER (HEKF) AND COMPUTATIONAL FLUID DYNAMICS

In the present study, a novel method has been introduced to estimate the hydrodynamic coefficients of an axisymmetric submersible prolate spheroid. In this heuristic procedure which is based on combination of the nonlinear Hybrid Extended Kalman Filter (HEKF) observer and Computational Fluid Dynamics (CFD), all of the hydrodynamic derivatives of a prolate spheroid in horizontal plane are estimated to simulate the Three Degrees of Freedom (3DoF) equations of motion. For this purpose, first, a CFD-based numerical model has been developed for an axisymmetric prolate spheroid by the commercial code ANSYS CFX software using the remeshing algorithm in dynamic mesh method. In this algorithm, the grid around objects deform locally using the Arbitrary Lagrangian-Eulerian (ALE) form of the governing fluid equations. When this deformation reduces the mesh resolution, significantly, the grid is re-meshes and improved. By performing the corresponding calculations along with the simulation, some hydrodynamic derivatives were obtained. Then, utilizing the hybrid kalman filter simulation code based on the parameter identification, other unknown derivatives were estimated in the MATLAB software environment by applying the equations of motion governing an ellipsoidal body shape. It should be noted that, for deriving the remaining hydrodynamic coefficients of the mentioned prolate spheroid using HEKF, positions and velocities of the object in each time step are needed. So, the dynamic motion of the vehicle in the fluid is simulated using the transient tool of the ANSYS CFX software while benefiting from the remeshing algorithm. Furthermore, the hybrid form of the Extended Kalman Filter (EKF) is chosen as the equations governing the 3DoF motion of the ellipsoid is continuous and the measurements are discrete. Results obtained from the proposed method indicate a good agreement for estimated added mass derivatives in comparison with the available analytical ones. The following study is an effort made to introduce an innovative strategy to investigate the hydrodynamic coefficients of submersible platforms like submarines, torpedoes and AUVs.