共查询到19条相似文献，搜索用时 85 毫秒
1.
重力场计算中,经常需要计算以有限阶球谐级数表示的重力场元。常规计算中除需存储(N 1)^2个系数值外,还需迭代计算出(N 2)(N 1)／2个完全正常化勒让德函数值。Clenshaw求和法不需要计算单个球谐函数值而直接计算级数和,因而计算速度上有所提高。总结了球谐函数的零阶导数级数和,并推导了一阶导数级数和。通过数值试验,对于任意点的重力场元,使用C1enshaw求和法计算零阶导数球谐函数和比常规方法节省一半的时间,一阶导数球谐函数之和的计算速度提高幅度不大,并分析了其中的原因。 相似文献
2.
对基于B样条面元法波浪载荷计算、载荷加载及速度势的二阶偏导数计算中存在若干问题的解决办法进行了探讨.对于加载时压力点的参数值计算,给出一种基于最小二乘法的参数值反算方法;对于二阶偏导数计算,给出一种基于B样条面元法求解速度势二阶导数的隐式方法,并通过对一无限水域中椭球潜体定常速度势二阶导数的计算对该方法进行了验证.此外,对B样条面元法的计算效率进行了讨论,并对对称性在B样条面元法中的应用以及其对计算效率的提高进行了说明.所介绍的方法简单实用,对于发展和推广B样条面元法在波浪载荷计算中的应用具有一定的价值. 相似文献
3.
重力异常垂向一阶导数的一种简便算法 总被引：1，自引：0，他引：1
利用拉格朗日插值导出了重力异常垂向一阶导数的计算公式，给出了地面以及地面之上不同高度的求导系数。该公式可以计算地面上的重力垂向一阶导数，还可以直接计算地面之上任意高度上的垂向一阶导数。鉴于该公式除系数不同外，与上延公式完全相同，因此，程序设计尤为简单。使用本公式对模型数据和实际资料进行了处理，证明了本算法的实用性。 相似文献
4.
在建立局部地区的地球重力场模型中,球冠谐分析是一种有效的方法。在球冠坐标系下建立重力场模型时,仅涉及到重力位的垂向分量,不必进行关于极角的微分运算,所以仅用单个正交基来建模,但若要在球冠坐标系下对重力场作进一步分析,如类似于平面处理的导数运算,来突出地质体的边界,要计算极角的微分,利用单个正交基表示则不易收敛,且误差较大。本文中作者采用两个正交基函数在球冠坐标系下对重力场建模,推导计算了径向导数和曲面导数模,并利用棱柱体正演模型进行检验,结果表明双基函数建模更适合曲面上的位场表示。最后计算了冲绳海槽地区卫星测高重力异常数据的曲面导数,径向导数清晰划分了东海陆架上大构造单元,曲面导数梯度带显示了东海陆架外缘隆起带,也指示了陆架盆地内的一些局部构造。这表明双基函数的球冠谐分析是一种有效的曲面位场建模方法。 相似文献
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基于CFD技术和重叠网格技术完成了黏性流场中KVLCC2船模的操纵性水动力导数的数值计算。为保证计算的精确性,进行了网格的收敛性分析,给出了合适的网格划分方法;通过数值模拟斜航运动、纯横荡运动和纯艏摇运动计算出的水动力与相应条件下的试验值对比,计算结果与试验值吻合良好,计算出的水动力导数准确度较高。基于MMG分离建模方法建立KVLCC2船模的操纵性数学模型,利用龙格-库塔算法求解微分方程组,对船舶操纵运动进行仿真。回转试验和Z形操舵试验的仿真结果与试验结果对比,其回转直径和轨迹都非常吻合,表明采用的船舶操纵性预报是可行的。 相似文献
6.
流速逆变张量隐式求解方法及其在航道港池流场计算中的应用 总被引：6，自引：1，他引：5
运用高分辨率的边界适应网格进行流体动力学数值计算时,如何提高计算稳定性和减少计算量成为数值求解的关键性问题.在非正交的边界适应坐标系中,每个动量方程中同时出现了两个交叉方向的水位偏导数项,给隐式求解带来困难,而显式格式下的时间步长由于受与空间步长有关的Courant-Friedrichs-Lewy条件限制,计算量成倍增加.本文从广义曲线坐标系下浅海动力学方程组出发,导出了流速的逆变张量所满足的动量方程组,使方程中的水位偏导数项变成了沿某一协变基向量方向占优的形式,方便地采用了交替方向隐式差分格式,从而提高了计算稳定性并减小了计算量.本文通过对澳门海域航道和港池中流场的计算,证实了该模式是一种进行高分辩率数值计算的有效方法. 相似文献
7.
基于势流理论和时域高阶边界元方法,建立了三维完全非线性数值波浪水槽模型.利用源造波法产生入射波浪,应用五阶斯托克斯波理论给定波浪速度;采用混合欧拉-拉格朗日方法追踪流体瞬时水面,将二阶泰勒级数展开法应用于更新下一时间步的波面和速度势;通过加速势的方法准确计算自由水面速度的法向导数和物面速度势的时间导数.对完全非线性波浪进行了模拟,得到了稳定的波形.当波浪非线性较小时,与四阶Runge- Kutta法(RK4)计算结果和五阶斯托克斯波理论解均吻合良好;随着波浪非线性的增大,计算结果误差逐渐增大.通过数值试验分析,在满足精度要求的基础上,本方法计算时间略大于四阶Runge- Kutta法的四分之一,大大减少了计算量. 相似文献
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实际工程中存在大量的曲边界,因此在曲边界上的计算准确性可以考察出一个数值模型的实用价值。利用Beji的改进型Boussinesq方程建立了一个有限元方法的数值波浪模型。造波方面采用Fenton提出的非线性规则波浪解;在墙边界处,以求解法线方向和切线方向的速度和导数代替求解x、y方向的速度和导数,从而使边界条件直接适用、严格满足,保证了对曲边界计算的准确性。"重开始广义极小残量法"的使用保证了求解方程组的效率和精度,使造波和边界处理方法的有效性和准确性得到了合理地诠释。通过与试验数据、他人数值结果、解析解的比对,显示出该模型计算稳定、结果准确,真正体现出了有限元方法对曲边界适用的优势。 相似文献
10.
一种新的波浪变形三维数值模式──0-1混合型边界元 总被引：4，自引：0，他引：4
为提高边界元法模拟三维波场波浪变形的数值计算精度,借鉴常数元和线性元剖分方式、波势函数及波势函数法向导数对单元节点设定的各自适应性,提出了一种新的单元剖分模式──0-1混合型边界元,以控制和减缓由于计算误差累计而造成的波浪数值计算上的“横向振动”,借此结合边界元法的分区模式可实现较大范围的波场线性波浪变形计算,并为时域内的波浪非线性变形计算提供时间步长的数值保证. 相似文献
11.
研究复合函数高阶导数的计算机算法.给出了组成高阶导数的各项多项式与整数拆分的关系.通过寻找简便的整数拆分的计算机算法,得到了复合函数高阶导数与整数拆分相关的简便公式及计算机算法. 相似文献
12.
Spatial Heterogeneity in Distributions of Chlorophyll a Derivatives in the Subarctic North Pacific during Summer 总被引：1，自引：1，他引：1
The distribution of chlorophyll a derivatives was examined in samples collected from the subarctic North Pacific during July to September 1997. Pheophorbide a, pheophytin a and pyropheophorbide a as determined by high performance liquid chromatography (HPLC) were the major derivatives recorded. The distribution patterns of chlorophyll a and its derivatives showed a strong vertical and horizontal heterogeneity. Patches with high concentration of derivatives seemed to be associated with high concentration of chlorophyll a. A clear east-west gradient was observed in both chlorophyll a and pheophorbide a integrated from the surface to 100 m depth with significantly higher amounts of both the pigments in the Western Subarctic Gyre and in the Bering Sea than in the Alaskan Gyre. In contrast, no apparent gradient was observed in the integrated pyropheophorbide a and pheophytin a. Grazing experiments conducted with the copepod (Neocalanus cristatus) and salp (Cyclosalpa bakeri) fed on five species of phytoplankton cultures, showed a marked difference in the composition of the derivatives in their fecal pellets. Pyropheophorbide a was dominant in the copepod fecal pellet regardless of the phytoplankton species fed on. In the salp, however, pheophytin a and pheophorbide a were found in the fecal pellets, the relative concentrations varying with the algal food. Spatial heterogeneity in the distribution of the derivatives is considered to reflect local variations in dominant herbivorous processes. 相似文献
13.
Michio Ueno 《Ocean Engineering》2010,37(10):879-890
A submersible surface ship (SSS) is based on a novel concept that the SSS goes on surface like conventional ships in moderate seas but goes underwater in rough seas to the depth sufficient to avoid wave effects. The SSS has a wing system that produces downward lift to go underwater with preserving the residual buoyancy for its safety. The SSS is expected to be able to keep both safety and punctuality even if it encounters unexpected bad weather.The motion of the SSS is studied. The equations of motion are formulated and the procedures for estimating hydrodynamic derivatives are presented. The hydrodynamic derivatives are estimated for a SSS having a configuration, a hull with a pair of main wings and a pair of horizontal tail wings. Using these estimated hydrodynamic derivatives, calculation of the SSS motion is carried out.The calculation results show some specific aspects of the SSS especially for effects of the elevator of main wings and horizontal tail wings, aileron of main wings, rudder and propeller revolution. It is confirmed that the existence of static roll restoring moment and having large hull comparing with wing area play important roles in the motion of the SSS. 相似文献
14.
For the non-negligible roll-coupling effect on ship maneuvering motion, a system-based method is used to investigate 4-DOF ship maneuvering motion in calm water for the ONR tumblehome model. A 4-DOF MMG model is employed to describe ship maneuvering motion including surge, sway, roll, and yaw. Simulations of circular motion test, static drift and heel tests are performed by solving the Reynolds-averaged Navier-Stokes (RANS) equations, after a convergence study quantifying the necessary grid spacing and time step to resolve the flow field adequately. The local flow field is analyzed for the selected cases, and the global hydrodynamic forces acting on the ship model are compared with the available experiment data. Hydrodynamic derivatives relating to sway velocity, yaw rate, and heel angle are computed from the computed force/moment data using least square method, showing good agreement with those obtained from EFD data overall. In order to investigate further the validity of these derivatives, turning circle and zigzag tests are simulated by using the 4-DOF MMG model with these derivatives. The trajectories and the time histories of the kinematic variables show satisfactory agreement with the data of free-running model tests, indicating that the system-based method coupled with CFD simulation has promising capability to predict the 4-DOF ship maneuvering motion for the unconventional vessel. 相似文献
15.
As the maneuverability of a ship navigating close to a bank is influenced by the sidewall, the assessment of ship maneuvering stability is important. The hydrodynamic derivatives measured by the planar motion mechanism (PMM) test provide a way to predict the change of ship maneuverability. This paper presents a numerical simulation of PMM model tests with variant distances to a vertical bank by using unsteady RANS equations. A hybrid dynamic mesh technique is developed to realize the mesh configuration and remeshing of dynamic PMM tests when the ship is close to the bank. The proposed method is validated by comparing numerical results with results of PMM tests in a circulating water channel. The first-order hydrodynamic derivatives of the ship are analyzed from the time history of lateral force and yaw moment according to the multiple-run simulating procedure and the variations of hydrodynamic derivatives with the ship-sidewall distance are given. The straight line stability and directional stability are also discussed and stable or unstable zone of proportional-derivative (PD) controller parameters for directional stability is shown, which can be a reference for course keeping operation when sailing near a bank. 相似文献
16.
The paper addresses the problem of autonomous underwater vehicle (AUV) modelling and parameter estimation as a means to predict the dynamic performance of underwater vehicles and thus provide solid guidelines during their design phase. The use of analytical and semi-empirical (ASE) methods to estimate the hydrodynamic derivatives of a popular class of AUVs is discussed. A comparison is done with the results obtained by using computational fluid dynamics to evaluate the bare hull lift force distribution around a fully submerged body. An application is made to the estimation of the hydrodynamic derivatives of the MAYA AUV, an autonomous underwater vehicle developed under a joint Indian-Portuguese project. The estimates obtained were used to predict the turning diameter of the vehicle during sea trials. 相似文献
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A finite-difference approach is used to develop a time-dependent mild-slope equation incorporating the effects of bottom dissipation and nonlinearity.The Euler predictor-corrector method and the three-point finite-difference method with varying spatial steps are adopted to discretize the time derivatives and the two-dimensional horizontal ones,respectively,thus leading both the time and spatial derivatives to the second-order accuracy.The boundary conditions for the present model are treated on the basis of the general conditions for open and fixed boundaries with an arbitrary reflection coefficient and phase shift.Both the linear and nonlinear versions of the numerical model are applied to the wave propagation and transformation over an elliptic shoal on a sloping beach,respectively,and the linear version is applied to the simulation of wave propagation in a fully open rectangular harbor.From comparison of numerical results with theoretical or experimental ones,it is found that they are in reasonable agreement. 相似文献
18.
制备5种氯霉素糖基化衍生物,并对这些衍生物的抑菌活性和安全性进行初步测试。实验结果表明:1)氯霉素被糖基化后水溶性得到了明显提高;2)氯霉素糖基化衍生物时未产生抗菌活性,但经相关糖苷酶水解后,可重新表现出抗菌活性;3)小鼠急毒试验证明,氯霉素糖基化衍生物的毒副作用与原药相比显著降低。该项研究对于设计和合成类氯霉素前药开辟了新领域。 相似文献
19.
This paper presents a calculation method of derivatives of natural frequencies and mode shapes to parameters affecting vertical hull girder vibration based on design sensitivity analysis. The method premises free vibration analysis of hull girder using the transfer matrix method. Governing sensitivity equation is derived from the direct differentiation of state vector and transfer matrix to design variables. Derivatives of natural frequencies and mode shapes are determined after two trial calculations of the equation. By using the obtained derivatives, the changes of natural frequencies can be rationally and efficiently predicted in case of ship design modification and loading variation. 相似文献