大尺度结构物的二阶波浪荷载

本文提出了一个在有限水深条件下大尺度物体上二阶波浪荷载的数值计算方法。用表面布源法求二阶散射势的特解,提出了有限水深满足非齐次表面边界条件的格林函数,给出了格林函数的积分和级数形式,研究了表面布源范围对解的影响。

层化海洋中的二阶波散射作用问题

引入Stokes有限振幅水波的多色波作用机制 ,采用二层层化海洋模型 ,分析了层化海洋中非线性波对结构的散射作用问题。提出了二层海洋中二阶水波散射条件的数学表达式 ,进而推导了二层海洋中二阶波对一般型圆柱散射作用的格林积分解式 ,并给出了对解式中自由面及分层界面无限积分的递推算式。

圆柱结构的二阶波浪渗流压力解的探讨

在波浪渗流力问题的研究中,首次引入了S tokes有限振幅波的波浪模型.通过推广应用特征函数展开法和表面布源法,分析了作用在可渗弹性海床上固立圆柱结构底面由二阶绕射波浪所致渗流压力的问题.对波浪场和渗流场分别采用分区法与迭加法,并引入一个B esse l级数展开的数学解;给出了S tokes二阶波关于两种垂直型圆柱结构绕射波浪场波势及压力分布解,进而将表面布源法推广应用于对圆柱底面下海床内的二阶波渗流压力场的解析求解,取得了相应的积分解式和对应的格林函数.

基于二阶规则波模拟的数值波浪水槽优化

基于CFD开源软件包OpenFOAM,建立了基于Navier-Stokes方程的二维数值波浪水槽模型。模型采用体积函数(VOF)法捕捉自由水面,采用k-ω SST紊流模型封闭控制方程。针对不同波陡(i=0.01~0.06)的Stokes二阶波,分别采用速度边界法或推板造波法进行造波,采用阻尼消波法、辐射边界法或松弛区域法进行消波;通过对不同造波和消波方法组合方式计算结果的比较,分析了数值波浪水槽在不同波陡工况下的消波效果和造波效果。模拟结果表明:对于小波陡(i=0.01~0.03)工况,采用速度边界造波和松弛区域法消波的组合方式具有较高的模拟精度;对于大波陡(i=0.04~0.06)工况,采用推板造波法造波和基于平方形式阻尼函数的阻尼消波法消波的组合方式具有较高的模拟精度。

层化海洋中二阶多色波对可渗透结构的绕射问题

可渗透结构具有使波浪作用减弱的效应,而海水的层化及水波的非线性使结构的波绕射产生多层复杂机制。将可渗透结构应用于复杂海况条件中,海水的层化性、波浪的非线性及结构的透空性构成了波绕射的一个十分复杂的数学问题。该问题存在理论研究的必要性,而文章则着重探讨其数学分析的可能性。通过引入二层海的层化海模式及Stokes二阶波的非线性波模式,给出了二阶多色波对透空结构的波绕射的定解问题提法,提出了复合形式的二阶多色波辐射条件式及可渗透结构的二阶物面条件式,应用特征函数解法与积分法推导了多色波对结构绕射的一阶势解与二阶作用的耦合积分解式,并讨论了解式所涉及无穷积分的算法。

二阶多色波对结构的绕射问题

引入二层海的层化海模型及二阶水波的多色波作用机制，对层化海条件下的二阶多色波的绕射作用问题进行了分析．推导了二层海二阶绕射波的远场解式．指出了二层海条件下二阶绕射波作用积分解建立的数学过程。

海上风电场工程海流设计流剖面计算模型研究

为满足海上风电场工程设计与建设需要,研究合理可靠且简单易行的海流设计流剖面计算方法十分必要。基于海流成因及组成项分析,本文提出采用潮流、风海流与设计波生流的矢量求和,并考虑综合安全系数的海流设计流剖面计算模型。风海流由季节性的盛行风持续吹拂海面形成,波生流则由大风引发大浪生成。波生流分层流速计算采用基于Stokes二阶波的非周期性项Russel-Osorio修正式,适用于海上风电场所在的深水区及绝大部分过渡区,由其参与组成的海流不会对波流共同作用下的波浪荷载重复计量。根据工程海域水文气象条件经分层计算组成设计流剖面,可避免简单流剖面模型的经验性与任意性。研究结果有利于合理确定海上风电场及类似工程的海流载荷与基础冲刷的水动力条件。

波浪作用下海底隧道氯离子侵蚀劣化时变分析

浅水区海底隧道处于复杂波动水力环境中,既有理论研究一般只在静水环境中计入氯离子自由扩散对隧道衬砌的侵蚀作用,而较少考虑海洋波浪力对衬砌结构腐蚀的促进作用。首先采用适用于浅水区的Stokes二阶波浪理论确定了海床表面的波浪压力,基于Biot固结理论获得了隧道衬砌周围的水压响应;接着利用改进的Fick第二定律同时考虑水压和浓度梯度驱动下的氯离子扩散,并采用指数型强度劣化模型描述服役时间内衬砌混凝土的劣化效应;最后结合波浪作用下衬砌氯离子侵蚀效应进行了海底隧道衬砌承载力计算,并将理论解析解与数值模型和既有的试验结果进行了对比,获得了较好的一致性。结果表明,忽略动态波浪压力对衬砌混凝土中氯离子渗流的促进作用,将低估衬砌混凝土内部的氯离子扩散速度,随着波浪周期增加,衬砌内部氯离子侵蚀入渗的最大深度明显增大;而不考虑衬砌强度劣化效应会明显高估隧道结构的服役寿命,不利于海底隧道服役期间的安全储备。

应用两种不同的波浪理论计算方形网箱水平波浪力

运用莫里森(Morison)和库兹涅佐夫(Kuznetsov)的计算方法对方形网箱及其构件受到的水平波浪力特性进行分析,分别依据正弦波和司托克斯二阶波理论,导出相应水平波浪力的迭加计算公式,并把计算结果与两种尺寸的网箱水槽试验进行对比验证。结果显示,正弦波理论计算值与试验值平均误差分别为11 19%和13 67%,二阶波计算平均误差分别为11 03%和13 87%,表明两者计算结论的差异性和计算方法的可行性。在波长、周期、波高和水深分别为150m、10 2s、10m、40m情况下模拟计算实物网箱水平波浪力,其二阶波受力峰值范围比正弦波的要窄、波谷值曲线要平坦,两者波浪力计算相差达8 70%,并且相差率与波高、波长成正比例关系,与水深成反比例关系,从而说明不同的波浪水域环境下应用不同波浪理论计算具有重要意义。

可渗透型结构的非线性水波绕射作用问题

含孔型结构的可渗透性具有对波浪的减弱效应,研究非线性波对该类结构的绕射作用机制有重要意义。分析了椭圆余弦波、孤立波以及STOKES二阶波对可渗透圆柱群结构的波绕射问题,给出了各类波对结构的绕射势解及STOKES二阶波对结构绕射作用的积分解式。

基于OLC拐点的车体结构较优设计

基于OLC理论,研究了正面碰撞中车体结构设计与乘员损伤的关联性。基于56 km/h正面刚性壁障(Frontal Rigid Barrier,FRB)碰撞工况,通过二阶波简化得到一阶加速度a_1、二阶加速度a2、动态位移D三个车体结构设计指标。分析了不同车体结构设计指标与OLC的关系,发现在D不变的情况下,当a_1≤215.82 m/s^(2)时,随着a_1的增加,OLC呈现降低的趋势;当a_1> 215.82 m/s^(2)时,OLC呈现增加的趋势,OLC存在明显"拐点";a_1不变的情况下,OLC随着D的降低呈现降低趋势。基于对标模型分析了不同车体结构设计指标下的乘员损伤,发现乘员损伤与OLC的变化趋势保持一致,同样存在"拐点现象"。采用线性拟合,乘员损伤与OLC的决定系数R~2为0.95。为验证"拐点现象"的普适性,继续研究了50 km/h FRB碰撞工况下的现象,得到同样结论。研究结果指导了某款车型的车体结构设计。

Identification algorithm for a kind of fractional order system

The state-space representation of linear time-invariant (LTI) fractional order systems is introduced, and a proof of their stability theory is also given. Then an efficient identification algorithm is proposed for those fractional order systems. The basic idea of the algorithm is to compute fractional derivatives and the filter simultaneously, i.e., the filtered fractional derivatives can be obtained by computing them in one step, and then system identification can be fulfilled by the least square method. The instrumental variable method is also used in the identification of fractional order systems. In this way, even if there is colored noise in the systems, the unbiased estimation of the parameters can still be obtained. Finally an example of identifying a viscoelastic system is given to show the effectiveness of the aforementioned method.

Anti-interference beam pattern design based on second-order cone programming optimization

When signal-to-interference ratio is low, the energy of strong interference leaked from the side lobe of beam pattern will infect the detection of weak target. Therefore, the beam pattern needs to be optimized. The existing Dolph-Chebyshev weighting method can get the lowest side lobe level under given main lobe width, but for the other non-uniform circular array and nonlinear array, the low side lobe pattern needs to be designed specially. The second order cone programming optimization （SOCP） algorithm proposed in the paper transforms the optimization of the beam pattern into a standard convex optimization problem. Thus there is a paradigm to follow for any array formation, which not only achieves the purpose of Dolph-Chebyshev weighting, but also solves the problem of the increased side lobe when the signal is at end fire direction The simulation proves that the SOCP algorithm can detect the weak target better than the conventional beam forming.

Simultaneous determination of trace Cu^(2+), Cd^(2+), Ni^(2+) and Co^(2+) in zinc electrolytes by oscillopolarographic second derivative waves

Simultaneous determination of impurity metal ions in high concentration zinc solution is very important for zinc hydrometallurgy,and the purpose is to establish a method for determining the trace Cu^2+,Cd^2+,Ni^2+and Co^2+in zinc electrolytes at the same time using the second derivative waves of single sweep oscillopolarography.Factors affecting the derivative waves of the ions were researched in a medium of dimethylglyoxime(DMG)-sodium citrate-sodium tetraborate.The results indicated that the interferences of a high concentration of Zn^2+and most other coexisting ions on the determination can be eliminated;when the Cu^2+,Cd^2+,Ni^2+and Co^2+are in the ranges of1×10^-7-3×10^-4,6×10^-7-2×10^-4,2×10^-8-1×10^-5and1×10^-8-3×10^-5mol/L,respectively,the relationships between the peak currents of the second derivative waves and the concentrations are linear;the detection limits to determine the Cu^2+,Cd^2+,Ni^2+and Co^2+are8×10^-8,2×10^-7,6×10^-9and4×10^-9mol/L,respectively.Without any sample pretreatment,the method was used to directly determine the trace Cu^2+,Cd^2+,Ni^2+and Co^2+in actual zinc electrolytes with satisfactory results.The method is simple,sensitive and rapid.

A second order volume of fluid (VOF) scheme for numerical simulation of 2-D breaking waves

Among all environmental forces acting on ocean structures and marine vessels, those resulting from wave impacts are likely to yield the highest loads. Being highly nonlinear, transient and complex, a theoretical analysis of their impact would be impossible without numerical simulations. In this paper, a pressure-split two-stage numerical algorithm is proposed based on Volume Of Fluid （VOF） methodology. The algorithm is characterized by introduction of two pressures at each half and full cycle time step, and thus it is a second-order accurate algorithm in time. A simplified second-order Godunov-type solver is used for the continuity equations. The method is applied to simulation of breaking waves in a 2-D water tank, and a qualitative comparison with experimental photo observations is made. Quite consistent results are observed between simulations and experiments. Commercially available software and Boundary Integral Method （BIM） have also been used to simulate the same problem. The results from present code and BIM are in good agreement with respect to breaking location and timing, while the results obtained from the comrnercial software which is only first-order accurate in time has clearly showed a temporal and spatial lag, verifying the need to use a higher order numerical scheme.

Nonlinear Random Motion Analysis of Coupled Heave-Pitch Motions of a Spar Platform Considering lst-Order and 2nd-Order Wave Loads

In this study, the coupled heave-pitch motion equations of a spar platform were established by considering lst-order and 2nd-order random wave loads and the effects of time-varying displacement volume and transient wave elevation. We generated random wave loads based on frequency-domain wave load transfer functions and the Joint North Sea Wave Project （JONSWAP） wave spectrum, designed program codes to solve the motion equations, and then simulated the coupled heave-pitch motion responses of the platform in the time domain. We then calculated and compared the motion responses in different sea conditions and separately investigated the effects of 2nd-order random wave loads and transient wave elevation. The results show that the coupled heave-pitch motion responses of the platform are primarily dominated by wave height and the characteristic wave period, the latter of which has a greater impact. 2nd-order mean wave loads mainly affect the average heave value. The platform＇s pitch increases after the 2nd-order low frequency wave loads are taken into account. The platform＇s heave is underestimated if the transient wave elevation term in the motion equations is neglected.

Optimization of Routing Considering Uncertainties

A route optimization methodology in the frame of an onboard decision support/guidance system for the ship＇s master has been developed and is presented in this paper. The method aims at the minimization of the fuel voyage cost and the risks related to the ship＇s seakeeping performance expected to be within acceptable limits of voyage duration. Parts of this methodology were implemented by interfacing alternative probability assessment methods, such as Monte Carlo, first order reliability method （FORM） and second order reliability method （SORM）, and a 3-D seakeeping code, including a software tool for the calculation of the added resistance in waves of NTUA-SDL. The entire system was integrated within the probabilistic analysis software PROBAN. Two of the main modules for the calculation of added resistance and the probabilistic assessment for the considered seakeeping hazards with respect to exceedance levels of predefined threshold values are herein elaborated and validation studies proved their efficiency in view of their implementation into an on-board optimization system.

Side-chain maleimide based electro-optic polymer for second-order nonlinear optics

The electro-optic properties of a poled second-order nonlinear optical maleimide polymer system were reported.This polymer was synthesized by doping disperse red 1 moieties into the maleimide system as the side chains.Its glass transition temperature was measured to be 202 ℃ by Differential Scanning Calorimetry (DSC) technology.After being poled,the measured electro-optic coefficient of PHSD at the wavelength of 1 550 nm is as large as 3.03 pm/v.Except for an initial decay after being poled,PHSD exhibits little electro-optic relaxation in a long term and its electro-optic coefficient remains about 2.46 pm/v after 15 days.

Calculating Binding Energy for Odd Isotopes of Beryllium （7 ≤ A ≤ 13）

In this article, we present exact solution of the Schr6dinger equation （for an N-identical body-force） for odd-A isotopes of Beryllium in the presence of Yukawa potential by Nikiforov-Uvarov （NU） method. The NU method can be used to solve second order differential equation. By this method, we find the wave equation and binding energy. Numerical results of binding energy are presented and show that these results are in good agreement with experimental values.

Wave Functions for Time-Dependent Morse Potentials

The one dimensional Schrodinger equation associated with a time-dependent Morse potentials is studied. We use the invariant operator method （Lewis and Riesenfeld） to obtain approximate solution of the Schrodinger equation in terms of solution of second order ordinary differential equation describes the amplitude of the Morse potentials.