Efficiency of reduced-order, time-dependent adjoint data assimilation approaches     

Ibrahim Hoteit  Armin Köhl 《Journal of Oceanography》2006,62(4):539-550

Applications of adjoint data assimilation, which is designed to bring an ocean circulation model into consistency with ocean observations, are computationally demanding. To improve the convergence rate of an optimization, reduced-order optimization methods that reduce the size of the control vector by projecting it onto a limited number of basis functions were suggested. In this paper, we show that such order reduction can indeed speed up the initial convergence rate of an assimilation effort in the eastern subtropical North Atlantic using in situ and satellite data as constraints. However, an improved performance of the optimization was only obtained with a hybrid approach where the optimization is started in a reduced subspace but is continued subsequently using the full control space. In such an experiment about 50% of the computational cost can be saved as compared to the optimization in the full control space. Although several order-reduction approaches seem feasible, the best result was obtained by projecting the control vector onto Empirical Orthogonal Functions (EOFs) computed from a set of adjusted control vectors estimated previously from an optimization using the same model configuration.  相似文献   

二阶亚线性中立型微分方程解的振动性     

姜福德 《中国海洋大学学报(自然科学版)》1995,(3)

本文在证明了二阶亚线性中立型微分方程的非振动解满足的基础上，给出了所有解振动的某些充分条件。  相似文献   

On the Spectral Moments of Wind Waves   总被引：2，自引：0，他引：2  

LI  Luping 《中国海洋工程》2002,16(1):135-140

In order to obtain high order spectral moments, the residual moment , as proposed by De-nis, is presented for approximate estimation of spectral moment Glazman's partial averaging idea isdiscussed. It is pointed out that Glazman's method and definition of non-dimensional spectral moment can not be used to es-timate spectral moments for engineering purposes and that method is not supported by theory and computation. The non-dimensional spectral moment of PM spectrum, which should be expressed as is related to wind speed. The0 - 8th moments of PM spectrum are estimated for wind speeds of 10, 20 and 30 m/s and some discussions are given.  相似文献   

High-Order Models of Nonlinear and Dispersive Wave in Water of Varying Depth with Arbitrary Sloping Bottom   总被引：4，自引：0，他引：4  

Hong Guangwen Professor  Coastal  Ocean Engineering Research Institute  Hohai University  Nanjing  P. R. China. 《中国海洋工程》1997,(3)

High-order models with a dissipative term for nonlinear and dispersive wave in water of va-rying depth with an arbitrary sloping bottom are presented in this article.First,the formal derivations toany high order of μ(=h/λ,depth to deep-water wave length ratio)and ε(=α/h,wave amplitude todepth ratio)for velocity potential,particle velocity vector,pressure and the Boussinesq-type equations forsurface elevation η and horizontal velocity vector U at any given level in water are given.Then,the exactexplicit expressions to the fourth order of μ are derived.Finally,the linear solutions of η,U,C(phase ce-lerity)and C_g(group velocity)for a constant water depth are obtained.Compared with the Airy theory,excellent results can be found even for a water depth as large as the wave legnth.The present high-ordermodels are applicable to nonlinear regular and irregular waves in water of any varying depth(from shal-low to deep)and bottom slope(from mild to steep).  相似文献   

浅水浮式生产储油系统(FPSO)二阶定常力数值仿真研究     

王磊  李欣  杨建民 《海洋工程》2006,24(1):9-13

应用三维线性势流理论和Ir J A Pinkster的近场分析方法,对超大型浮式生产储油系统(32万吨FPSO)的二阶波浪定常力进行了数值仿真分析,研究浅水情况下,不同水深对FPSO受到二阶波浪定常力的影响,对浅水油田中FPSO的设计应用有一定的实用意义。  相似文献   

Asymptotic Calculation of the Wave Trough Exceedance Probabilities in A Nonlinear Sea   总被引：1，自引：0，他引：1  

WANG Ying-guang 《海洋工程》2018,32(2):189-195

This paper concerns the calculation of the wave trough exceedance probabilities in a nonlinear sea. The calculations have been carried out by incorporating a second order nonlinear wave model into an asymptotic method. This is a new approach for the calculation of the wave trough exceedance probabilities, and, as all of the calculations are performed in the probability domain, avoids the need for long time-domain simulations. The proposed asymptotic method has been applied to calculate the wave trough depth exceedance probabilities of a sea state with the surface elevation data measured at the coast of Yura in the Japan Sea. It is demonstrated that the proposed new method can offer better predictions than the theoretical Rayleigh wave trough depth distribution model. The calculated results by using the proposed new method have been further compared with those obtained by using the Arhan and Plaisted nonlinear distribution model and the Toffoli et al.’s wave trough depth distribution model, and its accuracy has been once again substantiated. The research findings obtained from this study demonstrate that the proposed asymptotic method can be readily utilized in the process of designing various kinds of ocean engineering structures.  相似文献   

Second‐order work analysis for granular materials using a multiscale approach     

François Nicot  Nejib Hadda  Félix Darve 《国际地质力学数值与分析法杂志》2013,37(17):2987-3007

It has been established that the second‐order work criterion is a general necessary condition for all instabilities by divergence in rate‐independent granular materials. The relation between the values of discrete second‐order work at the intergranular contact point level and its global macroscopic value is recalled at the beginning of this paper. Then, the basic purpose of the paper is tackled by an analysis of the main features of second‐order work criterion in relation with the granular microstructure. For that, it is considered a novel micromechanical model (the so‐called ‘H‐microdirectional model’), which has the property to involve three scales: grain scale, mesoscale with a specific granular configuration and continuum mechanics macroscale. Eventually, these exhibited features (a bifurcation stress domain and some instability cones) are qualitatively compared with the ones provided by direct numerical simulations issued from a discrete element model. The ultimate goal is to analyse what happens at the granular scale, when the macrosecond‐order work is vanishing at the macrolevel. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Fractional order constitutive model of geomaterials under the condition of triaxial test     

Deshun Yin  Hao Wu  Chen Cheng  YangQuan Chen 《国际地质力学数值与分析法杂志》2013,37(8):961-972

Fractional calculus has been successfully applied to characterize the rheological property of viscoelastic materials; however, geomaterials were seldom involved in fractional order constitutive models (FOCM), and the topic of first loading and then unloading is rarely discussed through fractional calculus. In this paper, mechanical properties are considered as a ‘spectrum’, both ends of which are elasticity and viscosity, and the fractional order can be utilized to describe such properties quantitatively. In addition to conditions such as creep, stress‐relaxation, and constant‐strain‐rate loading, stress‐strain relationship under the condition of first loading and then unloading was also derived using FOCM. FOCM is then adopted to simulate triaxial tests of geomaterials under corresponding conditions. A comparison of test and numerical results demonstrates that FOCM can reasonably describe the mechanical characteristics of geomaterials.Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

适用于堆石料的分数阶下加载面模型     

李海潮  马博  张升 《岩土力学》2021,(1):68-76

堆石料的应力-应变曲线具有应变硬化和软化的特性,并且体积变形会伴随着剪缩和剪胀现象的发生;此外,应力水平、应力路径和密度等因素均会对堆石料的力学特性产生显著的影响。基于临界状态土力学的理论框架,建立了适用于堆石料的分数阶下加载面模型,该模型为典型的双屈服模型。在平均主应力p-剪应力q平面,剪切过程中堆石料当前应力状态点和参考应力点分别位于下加载面和参考屈服面上,两者之间的相对位置与孔隙比之差ρ相关。相比于状态参量Ψ,ρ能够额外考虑应力路径对堆石料剪胀特性的影响。新模型的另一个显著特点在于能够考虑堆石料塑性流动方向与加载方向之间的差异性。在不引入塑性势函数的情况下,新模型对屈服函数进行Caputo微分并得到分数阶塑性流动法则,进而统一描述相关联和非相关联的塑性流动法则。新模型具有形式简单且参数较少等优点,所包含的7个材料参数均具有明确的物理意义,并且可以采用常规的室内试验结果进行标定。通过将模型计算结果与Tacheng堆石料在不同初始孔隙比和围压条件下的三轴压缩排水试验结果进行对比分析,结果表明新模型能够准确地描述堆石料的应力-应变曲线和体积变形特点;同时,新模型也能够合理地描述初始孔隙比对堆石料在e-lnp平面(e为孔隙比)临界状态线的影响。  相似文献   

Second-order Taylor expansion boundary element method for the second-order wave radiation problem     

《Applied Ocean Research》2015

A novel Boundary Element Method (BEM) named the second-order Taylor Expansion Boundary Element Method (the 2nd order TEBEM) is developed for the solution of the second-order wave radiation velocity potential and sum-frequency wave loads for floating bodies. The radiation condition is enforced by a hybrid method of the multi-transmitting formula and damping zone. For the interior domain problem of a cube and a sphere, numerical results demonstrate that the 2nd order TEBEM can accurately solve the first and second-order gradients of velocity potential on the no-smoothed and smoothed boundary compared to the low-order BEM. The double frequency forces acting on the truncated cylinder are calculated under finite water depth. The agreement between the 2nd order TEBEM and others' numerical results is good. Moreover, all of the singular integrals in the 2nd order TEBEM can be solved analytically, so its implementation is much easier compared to the high-order BEM.  相似文献