Ship Hull And Compartment Surface Modeling And Its Application To The Damaged Stability

With the development of critical technologies for ensuring ship navigation safety,real-time and accurate damaged stability calculation is one of the critical technologies affecting ship safety navigation and life-saving decisions.Damaged stability refers to the remaining stability of a damaged ship.Quickly determining the damaged stability of an accident ship can shorten decision-making time,such as life-saving,and avoid personnel and property losses caused by ship capsizing.The thesis takes " Ship Hull and Compartment Surface Modeling and its Application to the Damaged Stability " as the topic.It uses chemical ship as an example to systematically study and propose algorithm models related to the entire curve and surface modeling process.It is applied to damage stability calculation,and some critical problems are solved by further proposing algorithms.The main works are as follows.(1)The problem of fast inversion of NURBS curve points was investigated systematically under conventional and high-precision conditions.A Bisection Feedback Search(BFS)algorithm with feedback search mode is proposed to solve the problem of slow inversion seeking speed and easy falling into local optima under conventional accuracy.This algorithm can solve the problem of easily falling into local optima with stable calculation results and high accuracy,but the solving speed needs to be faster.Furthermore,considering the lack of guidance in the search process of the BFS algorithm,an interval refinement(IR)method considering the convex hull of NURBS curves was designed to provide the optimal search interval for the BFS algorithm,collectively known as the IR-BFS algorithm.This algorithm has a global search capability,which can significantly reduce computational time while ensuring solution accuracy and stability.In response to the problem of insufficient convergence in inversion of the IR-BFS algorithm under high-precision conditions,the relationship between the number of iterations and the convergence threshold was analyzed.A high-precision Fast High Precision Bisection Feedback Search(FHP-BFS)algorithm combining the IR-BFS algorithm and Newton Raphson(NR)method was proposed,and the optimal threshold of the algorithm was determined through extensive experiments.Comparative experiments have shown that the FHP-BFS algorithm performs best regarding computational efficiency and stability and can significantly improve the solving speed.(2)The continuity and efficiency issues of generating hull compartment curves and surfaces were investigated systematically.A NURBS Curve Generation with Uniform Continuity(NCG)algorithm is proposed to address the issue of non-uniform continuity at the junction of NURBS composite curves,which combines curve deformation and global fitting.In response to the problem of low efficiency in inversion seeking boundary points in surface deformation,the smoothing algorithm for curve deformation was improved based on the IR-BFS and FHP-BFS algorithms.A strategy of gradually refining nodes was designed to reduce the complexity of the smoothing curve,and the optimal parameter range in the strategy was determined through experiments.Comparative experiments have shown that the NCG algorithm generates stable NURBS curves with uniform continuity and good curve smoothness.In response to the problem of low efficiency in generating NURBS surfaces,a NURBS Surface Hybrid Generation(NSG)algorithm was designed based on the NCG algorithm to generate cross-sectional curves,taking into account the relationship between the number of control points and the expression details of hull cross-sectional curve features.A Fast NURBS Surface Generation with Uniform Continuity(FNSG)model with unified continuity was proposed.Comparative experiments have shown that the NURBS surfaces generated by the FNSG model have good smoothness and continuity,significantly improving the efficiency of surface generation.(3)The problem of accurately and adaptively expressing ship hull surfaces using surface patches was investigated.Firstly,the problem is transformed into a problem of adaptive distribution of boundary profiles along the longitudinal direction of the hull surface,and a similarity measure based on the Section Longitudinal Adaptive Distribution(SLAD)model is proposed.In response to the problem of low efficiency in generating profiles by intersecting NURBS surfaces in the model,the relationship between surface parameters and 3D spatial profile coordinates was analyzed.A fast profile generation method based on the FNSG model was proposed,greatly improving the efficiency of profile generation.To address the issue of measuring profile similarity in the model,the Multi-Line Position Distance(LIP)is introduced to measure profile similarity using three-dimensional spatial positions and shape features.A site adaptive allocation strategy was designed to address the issue of site adaptive distribution in the model,taking into account the extremum of profile similarity,rate of change,and cumulative amount,ensuring the uniformity of site distribution in different parts of the ship’s hull.In response to the problem of low efficiency in reverse engineering of surface points in the model,the distribution characteristics of profile sites in surface parameter space were analyzed.The reverse engineering of 3D surface points was transformed into a 2D curve point reverse engineering problem.A fast reverse engineering algorithm for profile sites based on FHP-BFS was proposed,which ensured the accuracy of reverse engineering parameters and improved calculation speed.The experiments on ship hull expression and static hydraulic element calculation show that the SLAD model adaptively generates profiles that significantly improve the accuracy of static hydraulic element calculation,achieving the effect of expressing ship hull features with fewer profiles.(4)Some critical technical issues in the calculation process of ship damaged stability were studied.In response to the issue of the inability to accurately calculate the performance elements of the ship’s hull under free-floating conditions using the Bonjon curve and type value table,a NURBS surface of the ship’s cabin based on the FNSG model was established.The longitudinal distribution profile was adaptively generated based on the SLAD model,and the profile feature points were extracted based on the Douglas Puker(DP)algorithm.A fast intersection method between the profile and the waterline surface was introduced to construct an ordered closed point column between the longitudinal adaptive distribution profile and the waterline surface;a quasi-Bonjon curve method for calculating the performance elements of ship compartments has been proposed,which achieves accurate calculation of the performance elements of ship compartments under any draft,heel angle,and longitudinal angle.A multi-objective optimization model for the free-floating state of damaged ships was established to address the complex calculation and multiple parameters involved.A model-constrained optimization method based on a prior restoration arm was proposed,and the model was solved using the Non dominated Sorting Genetic Algorithms II(NSGA-II).The actual ship calculation has verified that the hull performance elements and stability parameters calculated based on the quasi-Bonjon curve method have high accuracy,and the floating parameters calculated by the free-floating multi-objective optimization model have high accuracy.The model constraint optimization method based on a prior restoration arm enables the NSGA-II algorithm to converge quickly.