Calculation method of still water shear force and bending moment based on STL model
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摘要: 为了提高船舶强度计算精度, 提出了一种基于STL模型的船舶静水剪力与弯矩计算方法。在计算总纵强度时, 采用常规算法计算船舶浮态初值, 然后采用迭代算法计算船舶吃水、横倾角与吃水差; 按照船舶肋位切割船舶外壳得到每个肋位的横剖面, 采用格林公式计算每个剖面水下部分的面积, 纵向积分得到浮力曲线; 通过对船舶舱室STL模型的切割, 离线建立每个舱室的质量分布表, 用舱室实际质量分布代替梯形分布来计算船舶质量分布曲线; 最后基于散货船“太行128”和“SPRING COSMOS”, 通过浮力与质量分布曲线计算了5种典型载况下的剪力与弯矩。计算结果表明: 计算值与采用软件NAPA的设计值相比, 剪力与弯矩的平均误差约为1%, 最大误差为2.6%, 计算误差较小, 因此, 船舶静水剪力与弯矩计算方法精度较高; 采用浮态迭代算法只需计算出船舶任意浮态下的排水体积与浮心坐标, 程序实现简单、稳定与可靠; 静水剪力与弯矩计算方法适用于船舶任意浮态, 通过直接切割船舶外壳计算船舶浮力曲线, 弥补了常规方法只能计算船舶纵向强度的不足; 通过建立舱室的质量分布表与采用舱室的实际质量分布代替传统的梯形分布, 减少了计算量, 提高了计算精度。Abstract: To improve the calculation accuracy of ship strength, a method based on STL model was proposed to calculate still-water shear force and bending moment of ship.In calculating the total longitudinal strengths, the initial values of ship floating condition were calculated by the conventional method, and then the draught, heeling angle and trim of ship were calculated by the iteration method.The transverse section of each rib was obtained by cutting the hull according to the rib position, the area of underwater part of each section was calculated by using the Green formula, and the buoyancy curve was obtained by the longitudinal integration.The mass distribution table of each cabin was established offline by cutting the STL model of ship cabin, and the actual mass distribution of cabin was used instead of the trapezoid mass distribution to calculate the mass distribution curve.Finally, based on the distribution curves of buoyancy and mass, the bulk carriers "Taihang 128"and "SPRING COSMOS"were taken as examples tocalculate the shear forces and bending moments under 5 typical loading conditions.Calculation result shows that the average relative errors of shear forces and bending moments calculated by the proposed method and the design software NAPA of ship are about 1%, the maximum error is 2.6%, the errors are smaller, so the accuracy of proposed method is higher.The iterative algorithm of ship floating condition only needs to calculate the drainage volume and buoyancy center coordinates of ship in free floating condition, so the program is simple, stable and reliable.The proposed method is applied to any floating condition of ship, the buoyancy distribution curve of ship can be calculated by directly cutting the hull, so the proposed method makes up for the deficiency of the conventional method that can calculate only ship's longitudinal strength.By establishing the mass distribution table of ship cabins and using the actual distribution of mass instead of the traditional trapezoid distribution of mass, the calculation precision of ship strength rises, and the calculated amount reduces.
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Key words:
- ship engineering /
- still-water shear force /
- bending moment /
- STL model /
- free floatation /
- loading computer
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图 14 压载出港剪力与弯矩相对误差
Figure 14. Relative error of shear forces and bending moments under ballasting departure
图 15 满载到港剪力与弯矩相对误差
Figure 15. Relative errors of shear forces and bending moments under fully loaded arrival
图 17 许用剪力与弯矩相对误差
Figure 17. Relative errors of allowable shear forces and bending moments
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