VIBROACOUSTIC ANALYSIS WITH DETERMINISTIC APPROACH (FEM AND IGA) UNDER STRONG FLUID-STRUCTURE COUPLING

THIS PHD THESIS PROPOSES A UNIFIED METHODOLOGY FOR VIBROACOUSTIC ANALYSIS BASED ON ISOGEOMETRIC ANALYSIS (IGA), WITH THE AIM OF DIRECTLY INTEGRATING THE GEOMETRIC DESIGN AND NUMERICAL SIMULATION STAGES. THE SCIENTIFIC AND INDUSTRIAL RELEVANCE OF THIS APPROACH LIES IN ITS ABILITY TO OVERCOME THE INTRINSIC LIMITATIONS OF TRADITIONAL METHODS SUCH AS THE FINITE ELEMENT METHOD (FEM) AND THE BOUNDARY ELEMENT METHOD (BEM), WHICH OFTEN SUFFER FROM GEOMETRIC INACCURACIES, FIELD DISCONTINUITIES, AND HIGH COMPUTATIONAL COSTS.

THIS PHD THESIS PROPOSES A UNIFIED METHODOLOGY FOR VIBROACOUSTIC ANALYSIS BASED ON ISOGEOMETRIC ANALYSIS (IGA), WITH THE AIM OF DIRECTLY INTEGRATING THE GEOMETRIC DESIGN AND NUMERICAL SIMULATION STAGES. THE SCIENTIFIC AND INDUSTRIAL RELEVANCE OF THIS APPROACH LIES IN ITS ABILITY TO OVERCOME THE INTRINSIC LIMITATIONS OF TRADITIONAL METHODS SUCH AS THE FINITE ELEMENT METHOD (FEM) AND THE BOUNDARY ELEMENT METHOD (BEM), WHICH OFTEN SUFFER FROM GEOMETRIC INACCURACIES, FIELD DISCONTINUITIES, AND HIGH COMPUTATIONAL COSTS. THE THESIS DEVELOPS A COMPREHENSIVE THEORETICAL AND COMPUTATIONAL FRAMEWORK THAT COMBINES GEOMETRIC FIDELITY, NUMERICAL EFFICIENCY, AND CAD INTEGRATION, OUTLINING A RESEARCH PATH THAT EXTENDS FROM THE PHYSICAL–MATHEMATICAL FOUNDATIONS TO INDUSTRIAL APPLICATIONS. AFTER DEFINING THE GOVERNING EQUATIONS OF VIBROACOUSTIC PHENOMENA AND THEIR VARIATIONAL FORMULATION, THE WORK INTRODUCES A RIGOROUS ISOGEOMETRIC REPRESENTATION OF STRUCTURAL AND ACOUSTIC FIELDS, HIGHLIGHTING HOW THE HIGH CONTINUITY OF NURBS FUNCTIONS ENABLES SMOOTHER AND MORE ACCURATE SOLUTIONS COMPARED TO EQUIVALENT FEM MODELS. ONE OF THE MAIN CONTRIBUTIONS LIES IN THE APPLICATION OF A REDUCED-ORDER MODAL APPROACH, ALLOWING THE COUPLED VIBROACOUSTIC BEHAVIOR TO BE DESCRIBED THROUGH A LIMITED NUMBER OF MODAL SHAPES. THIS TECHNIQUE ACHIEVES A DRASTIC REDUCTION IN COMPUTATIONAL COST WHILE MAINTAINING HIGH MODEL FIDELITY WITH RESPECT TO THE FULL-ORDER SOLUTION (FOM), AS DEMONSTRATED BY SYSTEMATIC NUMERICAL COMPARISONS WITH BOTH IGA AND FEM. A SECOND INNOVATIVE AXIS CONCERNS THE DIRECT INTEGRATION BETWEEN CAD AND IGA, PURSUED THROUGH AN IMMERSED ADAPTIVE REFINEMENT APPROACH BASED ON HIERARCHICAL B-SPLINES (HB-SPLINES). IN PARTICULAR, A METHODOLOGY IS PROPOSED FOR THE VOLUMETRIC RECONSTRUCTION OF THE FLUID DOMAIN STARTING FROM CAD BOUNDARY REPRESENTATIONS (B-REP), ENABLING THE EXTENSION OF A TWO-DIMENSIONAL GEOMETRIC DESCRIPTION INTO A VOLUMETRIC MODEL COMPATIBLE WITH ISOGEOMETRIC ANALYSIS. THE RECONSTRUCTED DOMAIN IS THEN COUPLED WITH A KIRCHHOFF–LOVE STRUCTURAL MODEL, ACHIEVING A FULLY AUTOMATED CAD-TO-IGA WORKFLOW. THE FINAL PART OF THE THESIS DEMONSTRATES THE VALIDITY AND VERSATILITY OF THE METHOD THROUGH APPLICATIONS TO COMPLEX INDUSTRIAL SCENARIOS, IN WHICH IMMERSED IGA IS DIRECTLY APPLIED TO REAL CAD MODELS. THE RESULTS CONFIRM NOT ONLY THE SUPERIOR ACCURACY AND SMOOTHNESS OF IGA BUT ALSO THE FEASIBILITY OF AN EFFECTIVE INTEGRATION BETWEEN DESIGN AND ANALYSIS, REDUCING MODELING TIME AND ENHANCING THE ROBUSTNESS OF THE SIMULATION PROCESS. OVERALL, THE THESIS REPRESENTS AN ORIGINAL METHODOLOGICAL AND APPLICATIVE CONTRIBUTION TO THE FIELD OF COMPUTATIONAL VIBROACOUSTICS, SHOWING HOW ISOGEOMETRIC ANALYSIS CAN SERVE AS AN EFFECTIVE BRIDGE BETWEEN CAD AND NUMERICAL SIMULATION. THIS RESEARCH PAVES THE WAY FOR A NEW GENERATION OF VIBROACOUSTIC ENGINEERING TOOLS CAPABLE OF COMBINING GEOMETRIC PRECISION, NUMERICAL EFFICIENCY, AND DIRECT INTEGRATION WITHIN THE INDUSTRIAL DESIGN ENVIRONMENT.