【作者】 唐颖；

【导师】 任慧龙；

【作者基本信息】 哈尔滨工程大学 ， 船舶与海洋结构物设计制造， 2023， 博士

【摘要】 大型船舶艏部常具有大外飘结构,在高航速或高海况下极易发生砰击现象,引起船体产生高频颤振,使其载荷呈现强非线性特征,对船舶的航行安全造成威胁。国际船级社协会、美国船级社、中国船级社相继发布了考虑砰击颤振的设计载荷及强度评估指南文件,但指南只给出了评估流程和方法,并未提供有效的计算工具。因此,急需一款能够真实反映船体水动力特征及振动特性的数值软件,研究计及砰击颤振的强非线性载荷响应,为大型船舶在恶劣海洋环境下的航行提供技术支撑及安全保障。基于上述原因,本文开发了可以考虑艏艉出入水的大型船舶全非线性时域数值计算方法,并结合水弹性理论建立了计及颤振响应的全非线性水弹性时域数值方法,开展了极端海况下的分段水弹性模型试验研究,通过数值与试验手段的综合分析确定了大型船舶的设计载荷,并探究了高频响应对疲劳与极限强度设计载荷的影响。主要研究工作如下:(1)建立了有航速船舶在波浪中航行的三维全非线性时域数值模型,对于高航速及高海况下船体的运动及载荷预报具有较高精度。该方法采用全非线性自由面边界条件,瞬态更新船体湿表面及自由液面,能够模拟船体在波浪中的出入水过程,提供船体砰击压力的时空分布。通过21000TEU集装箱船验证了本文全非线性数值方法的正确性与准确性。开展了 S175、13500TEU等典型集装箱船波浪载荷的特征分析,发现了临界航速与大幅波浪下船体的特殊水动力现象。由于该数值方法可以展示自由面波面升高及湿表面压力分布的时历过程,在分析船舶水动力响应方面具有独到优势。(2)开展了极端工况下的分段水弹性模型试验研究,探究了大型船舶的强非线性载荷及砰击颤振响应的耦合机理。在拖曳水池及综合试验水池中开展了船模的迎浪规则波、迎浪不规则波及斜浪规则波试验,对运动及垂向弯矩随波高、航速、浪向等变化规律开展了特性分析。对船体弯矩中拱、中垂的非对称性及波形非线性等原因进行了探究,通过傅里叶变换分析了高频响应的影响,探究了非线性倍频响应与颤振响应的耦合关系。对不规则波下的船体载荷结果进行了统计,比较分析了不同方法的统计值水平差异。(3)开发了考虑颤振响应的全非线性水弹性数值方法,强调了大型船舶高频水动力载荷的特征。将船体看作是两端自由的铁木辛柯梁,建立了梁与三维水动力模型之间的耦合关系。考虑弹性变形的影响,推导了适用于弹性体船的辅助函数方法解耦运动、变形及水动力。基于响应幅值、时历结果及傅里叶变化得到的频谱分布,本文开展了相近尺度的船舶、S175集装箱船、ULCS-1等船舶的数值验证研究工作,验证了数值方法的准确性。并通过S175集装箱船及ULCS-1的数值结果分析,讨论了不同尺度船舶的载荷特征差异,强调了大型船舶高阶倍频及颤振载荷的影响。(4)对大型集装箱船,提出基于服务工况及极限工况开展非线性设计波下的设计载荷预报,并探究了高频响应对于大型船舶设计载荷的影响。采用全非线性水弹性时域数值方法,预报非线性设计波下的载荷水平,与船级社规范及分段模型试验结果进行综合对比分析,确定了船体的设计载荷。利用数值及试验方法开展典型短期海况下的载荷预报,统计不同航速及海况下颤振等高频响应对疲劳损伤的影响,研究了高频响应对疲劳强度及极限强度设计载荷的影响,该研究工作可为船级社规范的完善提供参考。更多还原

【Abstract】 Slamming events may easily occur at high speeds or high sea conditions for large ships,especially when there is a large bow flare.Then the high-frequency whipping happens,and loads exhibit strong nonlinear characteristics,which may threaten the safety of hull structure.The International Association of Classification Societies(IACS),American Bureau of Shipping(ABS),and China Classification Society(CCS)have successively issued guidance documents on whipping responses.However,there still lacks effective numerical tools to predict the nonlinear loads and assess the effects of whipping on strength analysis.Thus,a numerical software is urgently needed to provide technical support and safety assurance for large ships in rough waves.Therefore,the paper develops a fully nonlinear time-domain numerical method for large ships,by which the water entry and exit of bow are simulated.Then a fully nonlinear hydro-elastic numerical method is established to analyze the whipping responses.Segmented model tests are conducted under extreme sea conditions,and the design loads of large ships can be determined through comprehensive analysis of numerical and experimental results.The influence of high-frequency responses on the designed loads of fatigue and ultimate strength is explored.The main research work has been listed as follows:(1)A three-dimensional fully nonlinear time-domain numerical model of ships navigating in waves with forward speed is established,which can predict the motion and loads in large-amplitude waves accurately.The fully nonlinear free surface boundary conditions are applied and the wetted body surface and free surface are updated transiently,thus water entrt and exit can be simulated.Based on the analysis of numerical results of 21000TEU container ship,the correctness and accuracy of the present fully nonlinear numerical method are verified.The hydrodynamic performance of S175 container ship under critical speed and 13500TEU container ship under large-amplitude waves are investigated.The numerical method has unique advantages in hydrodynamic analysis under high advancing speeds and high sea conditions,due to its ability of simulating transient wave elevation of free surface and pressure distributions around wetted body surface.(2)The segmented model tests of an ultra large container ship in extreme waves are carried out to investigate the nonlinear loads and whipping responses.The model tests are conducted in head regular waves and irregular waves in the towing tank,and oblique waves in the integrated test tank.The characteristics of motion and vertical bending moment with wave height,speed,and wave headings are analyzed.The reasons for the asymmetry of the hogging and sagging peaks as well as the nonlinear waveform of vertical bending moments are investigated.The influence of high-frequency response is analyzed through Fourier transform,and the mechanism of the high-frequency harmonics and whipping response under largeamplitude wave condition is explored.Statistical analysis is conducted on the results of wave loads under irregular waves,and the differences in statistical values by different methods are compared and analyzed.(3)A fully nonlinear hydro-elastic numerical method is developed,in which the whipping loads are included and the hydrodynamic performances of large ships are addressed.The modes of the ship are analyzed using Timoshenko beam theory.The coupling relationship between the beam and the three-dimensional hydrodynamic model is established.An auxiliary function method for elastic ships is deduced to decouple the motion,elastic deformation and nonlinear hydrodynamic forces.Through the amplitudes,time records and the amplitude spectra of vertical bending moment,the present method is applied to predict the results of ships of similar scales,S175 container ship and ULCS-1.The comparative analysis verifies the accuracy of the present numerical method.The high-frequency loads of ships with different scales are investigated,effects of high-order harmonics and whipping loads of large ships are emphasized.(4)The effects of high-frequency responses on the design loads of large ships are analyzed.The fully nonlinear hydro-elastic numerical method is adopted to calculate the vertical bending moment under nonlinear design waves.The numerical results are compared with results of classification society rules and segmental model tests.The load prediction of typical short-term sea conditions is carried out using present hydro-elastic numerical method and experimental results.The contribution of high-frequency responses to the fatigue damage is counted.The coefficients of high-frequency responses on the design loads of fatigue strength and ultimate strength are studied.The research work could provide a reference for the improvement of current rules.更多还原