An effcient shape parametrisation by free-form deformation enhanced by active subspace for hull hydrodynamic ship design problems in open source environment

摘要

In this contribution, we present the results of the application of a parameterspace reduction methodology based on active subspaces property tothe hull hydrodynamic design problem. In the framework of such typicalnaval architecture problem, several parametric deformations of aninitial hull shape are considered to assess the influence of the shape parametersconsidered on the hull total drag. The hull resistance, which isthe performance parameter associated with each parametric hull, is typicallycomputed by means of numerical simulations of the hydrodynamicflow past the ship. Such problem is extremely relevant at the preliminarystages of the ship design, when several flow simulations are typicallycarried out by the engineers to establish a certain sensibility onthe total drag dependence on the hull geometrical parameters consideredand on other physical parameters. Given the high number of geometricand physical parameters involved which might result in a high numberof time consuming hydrodynamic simulations assessing whether the parametersspace can be reduced would lead to considerable computationalcost reduction at the design stage. Thus, the main idea of this work isto employ the active subspaces to identify possible lower dimensionalstructures in the parameter space, or to verify the parameter distributionin the position of the control points. To this end, a fully automated procedurehas been implemented to produce several small shape perturbationsof an original hull CAD geometry which are then used to carry out highfidelityflow simulations in dierent cruise conditions and collect datafor the active subspaces analysis. To achieve full automation of the opensource pipeline described, both the free form deformation methodologyemployed for the hull perturbations and the high fidelity solver based onunsteady potential flow theory, with fully nonlinear free surface treatment,are directly interfaced with CAD data structures and operate usingIGES vendor-neutral file formats as input files. The computational costof the fluid dynamic simulations is further reduced through the applicationof dynamic mode decomposition to reconstruct the final, steady statetotal drag value given only few initial snapshots of the simulation. Theactive subspaces analysis is here applied to the geometry of the DTMB-5415 naval combatant hull, which is a common benchmark in ship hydrodynamicssimulations, within the SISSA mathLab applied mathematicslab. The contribution will discuss several details of the implementationof the tools developed, as well as the results of their application to thetarget engineering problem.