自升式平台拖航阻力评估

本文选定了自升式平台离岸拖航的环境条件,利用经验公式、CFD软件和数值积分方法,分别计算得到平台在拖航过程中受到风载荷、流载荷和波浪载荷。计算结果表明自升式平台桩腿长度对拖航阻力的影响非常大,流载荷在拖航阻力中所占比例很小,主尺度变化的对拖航阻力的影响主要体现在波浪载荷上。     

Variational principles in water-wave problems (wave radiation conditions and their variational treatment)

To discuss water-wave problems in unlimited waters, it is important to know what type of wave radiation condition should be placed on a virtual surface corresponding to infinity. For this kind of problem, the Sommerfeld radiation condition is well known. In this article, the condition is extended to treat a case with an incident wave. Furthermore, a more general wave radiation condition is introduced from a different point of view. The above-mentioned wave radiation conditions are introduced into the variational principles of the Kelvin, Hellinnger–Reissner, and Dirichlet type. The Dirichlet-type variational principles are then used in numerical calculations for bending waves in a bar, and the effectiveness of the wave radiation conditions and the variational principles is shown. The numerical results for one-dimensional water-wave problems are then given. As expected, the region required for the numerical solution is reduced drastically compared with that required by the Sommerfeld-type formulation. Furthermore, the amplitude of the diverging wave is obtained in the process of reaching the variational solution. Finally, two-dimensional water-wave problems are briefly discussed. Received: August 9, 2001 / Accepted: September 17, 2001     

穿浪双体船兴波阻力研究

对穿浪双体船（WavePiereingCatamaran,简称WPC）兴波阻力理论计算方法进行了研究,在此基础上对一艘穿浪双体船模型的兴波阻力进行了理论计算,并将理论计算结果与模型试验结果、25°系列阻力图谱计算结果进行比较,探讨了片体修长系数、片体间距对WPC兴波阻力影响的规律。     

Three-dimensional equivalent static analysis for design of submerged floating tunnel

Stress evaluation of a submerged floating tunnel (SFT) is an issue important for determining the section dimensions required to resist environmental loads. However, the complex interaction between an SFT and surrounding fluid has confined most research on SFTs to longitudinal global time-history analyses based on Morison's equation [1]. Even though these analyses give sufficient information in the longitudinal direction, too little information about the circumferential direction compels an SFT section to be designed conservatively. This means that SFT design requires additional information on the structural behavior of the tunnel in the circumferential direction for efficient design. Accordingly, a supplementary approach by which to obtain structural responses in the circumferential direction is introduced in this paper. Upon consideration of the static responses equivalent to the dynamic behavior, three-dimensional (3-D) finite-element analyses of an SFT were performed by application of static loads corresponding to dynamic loads equivalent to those of wave, current and earthquake. The validation of each equivalent static load was supported by the results from comparison of the tension forces in mooring lines obtained using OrcaFlex [2] and ABAQUS [3]. These were used mainly for longitudinal dynamic analysis and 3-D stress evaluation, respectively, of an SFT. Based on the stresses obtained in the longitudinal and circumferential directions, the selection of suitable section dimensions for an SFT is considered.     

Semi-submersible wind turbine hull shape design for a favorable system response behavior

Floating offshore wind turbines are a novel technology, which has reached, with the first wind farm in operation, an advanced state of development. The question of how floating wind systems can be optimized to operate smoothly in harsh wind and wave conditions is the subject of the present work. An integrated optimization was conducted, where the hull shape of a semi-submersible, as well as the wind turbine controller were varied with the goal of finding a cost-efficient design, which does not respond to wind and wave excitations, resulting in small structural fatigue and extreme loads.The optimum design was found to have a remarkably low tower-base fatigue load response and small rotor fore-aft amplitudes. Further investigations showed that the reason for the good dynamic behavior is a particularly favorable response to first-order wave loads: The floating wind turbine rotates in pitch-direction about a point close to the rotor hub and the rotor fore-aft motion is almost unaffected by the wave excitation. As a result, the power production and the blade loads are not influenced by the waves. A comparable effect was so far known for Tension Leg Platforms but not for semi-submersible wind turbines. The methodology builds on a low-order simulation model, coupled to a parametric panel code model, a detailed viscous drag model and an individually tuned blade pitch controller. The results are confirmed by the higher-fidelity model FAST. A new indicator to express the optimal behavior through a single design criterion has been developed.     

Wave climate evolution in the Bay of Biscay over two decades

As a background, a review of long term evolution of wave climate in the North Atlantic is discussed. Most studies show that interannual evolutions in wave heights may be related to climatic factors, such as the North Atlantic Oscillation Index for example.Data of a waverider, consisting of a time series of 20 years in the Bay of Biscay (off Biscarosse, France), are analysed. Based on these data obtained from 1980, wave heights tend to decrease over the period. Also, interannual evolutions exist, particularly in the wave period. The fact that the annual wave periods at Biscarosse are found to vary more significantly than the annual wave heights led us to assume that it is an indirect effect of the evolution in the location of generating storms relative to the buoy. The relationships between wave parameters and climatic factors such as the North Atlantic Oscillation Index and the Garonne discharge have been derived: they show that the NAO index is negatively correlated with the river discharge and positively correlated with the wave period. This result is in agreement with the general climate scheme associated with NAO cycle proposed by Kushnir et al. [Kushnir, Y., Cardone, V.J., Cane, M., 1995. Link between Atlantic climate variability of surface wave height and sea level pressure. Proc. Fourth Int. Workshop on Wave Incasting and forecasting, Banff, AB, Canada, 59–64.]: NAO+ shifts storm tracks northward and dry weather are encountered in the southern part of Europe (conversely NAO− brings storm tracks and rainfall closer). Concerning wave heights, the lack of dependence on NAO index may be associated with compensation effects between wind intensity and storm tracks: wave energy is partly dissipated while reaching the Bay of Biscay in case of severe but distant storms (NAO+), which is not the case for storms generated nearer to the buoy and associated with moderate westerly winds (NOA−). However, the reason of the decrease in wave heights is not clear.     

常见机车车轴实物对比试块的新应用

介绍利用目前现有的几种常见机车车轴实物对比试块,校验DF8B(滚抱)和DF7G型内燃机车分体轮、SS6B型电力机车整体轮、8K型机车轮对的车轴齿轮座镶入部横波探伤灵敏度的方法,以实现齿轮座镶入部和内侧卸荷槽的全面扫查。     

海洋平台机座阻尼结合阻振质量减振分析

应用波分析法研究结构声在机座板结构中的传导特性,并对比分析层合阻尼结构的解析解和数值解,验证阻尼建模方法的正确性.依据阻尼材料的工程选用原则对阻尼材料进行选型,并基于有限元法研究阻尼粘贴方式对机座结构的动力学特性影响规律,分析表明多层复合阻尼材料相比于普通阻尼材料具有更好的减振效果.在此基础上研究某平台发电机组机座敷设多层复合阻尼结构对平台舱室振动特性的影响,并分析阻尼层厚度对平台振动特性的影响.研究阻振质量对贴敷多层复合阻尼减振特性的影响,研究表明阻振质量结合阻尼减振可使减振效果相比单独应用阻尼有较大程度提高.     

Assessment of uncertainty in the CFD simulation of the wave-induced loads on a vertical cylinder

The paper addresses different uncertainty analysis methods commonly used for uncertainty quantification in Computational Fluid Dynamics (CFD) studies and compares a constant Courant–Friedrichs–Lewy (CFL) number based approach for uncertainty estimation to the ITTC recommended grid and time-independent procedures. Four different uncertainty estimation procedures are presented and discussed. To compare their performance and better understand CFD related uncertainty quantification in wave load simulations on offshore structures, the methods are applied to a case study of the wave loads on a fixed vertical cylinder. The numerical or CFD wave tank is generated using the open-source CFD toolkit OpenFOAM. Uncertainty is assessed for the case study using four different uncertainty estimation procedures for verification and later, validation is attempted by comparing the CFD results with experiments. The study concludes that a constant CFL number based uncertainty study provides more stable results and is better suited for uncertainty estimation in CFD than the ITTC recommended individual grid and time step uncertainty study.     

Probabilistic analysis of the hull-girder still water loads on a shuttle tanker in full load condition,for parametrically distributed collision damage spaces

Box-shaped damage affected volumes are applied, with parametric variation of their positions and extensions, to an otherwise intact shuttle tanker in full load condition. The vessel's deadweight is numerically calculated and the lightweight is estimated using semi-empirical formulations to a great extent. For each damage configuration, the final position attained by the ship is investigated and the corresponding global loads are assessed, in terms of still water vertical bending moment and shear force. The ship is considered to be floating in the absence of waves and a quasi-static version of a generalized adaptive mesh pressure integration technique code, for progressive flooding of floating objects, is used to model the progression of the floodwater and the vessel's attitude. The probabilistic model suggested by the Marine Environment Protection Committee of the International Maritime Organization (MEPC-IMO) is considered for the collision induced probabilistic distribution of the damage boxes. A total of 90 damage cases are considered and comparisons of the maximum loads and the location where these take place is carried out relative to the intact case. The minimum design values for still water bending moment and shear force, included in the Common Structural Rules for Bulk Carriers and Tankers of the International Association of Classification Societies (IACS), are introduced in the analysis and their envelopes are compared with the numerically obtained values in light of a probabilistic assessment. Several conclusions are taken regarding the effects of the damage parameters variation, and important findings are presented specifically when accounting for the MEPC-IMO probabilistic distribution, in opposition to a uniform distribution of the damage cases.