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.     

Simplified analysis for estimation of the behavior of a submerged floating tunnel in waves and experimental verification

To achieve rational design in waves for a submerged floating tunnel which has emerged as a new offshore transportation infrastructure, it's necessary to understand its hydrodynamic behavior. For simple but accurate estimation of hydrodynamic forces, a theoretical method is proposed and the tests with physical models in a wave flume were carried out for verification. Morison's equation was used to estimate wave loads composed of inertia force and drag force. Forces calculated by applying the linear wave theory to Morison's equation coincided well with those measured by the tests. The test results showed that mooring systems played a significant role in the movement of the submerged floating tunnel in waves. A pendulum model could be used to describe the motion of the submerged floating tunnel with a single vertical mooring. Based on the verified relations, a simple slack condition which causes the submerged floating tunnel to be unstable was also proposed. The simplified approach proposed by this study proved to be useful in designing the submerged floating tunnel in the initial stage.     

节能车发动机活塞改进设计

为提高发动机效率,节省燃油,文章根据发动机的功率压缩比特性,结合节能车发动机的实际情况,制作出相应形状的压缩比块以使其满足一定压缩比的要求来达到节油的目的。利用pro／e软件建模,用wave软件进行功率曲线模拟。根据仿真结果初步估计压缩比,并结合进排气门大小及发动机燃烧室形状的限制制作让坑,得出在发动机现有情况下最佳压缩比块的形状。,大量试验证实：加入压缩比块,适当提高压缩比可以较好地改善发动机的燃油经济性。     

浅谈近岸、浅海海域波浪对船舶的危害——A轮沉没引发的思考

近岸，浅海海域的波浪与深海海域的波浪性质相异，航海驾驶人员必须特别重视，以防其造成船舶的浪损或更严重的海事发生。     

超大跨度悬索桥的动力特性及地震反应分析

以构想中的1座主跨跨度达3000m的悬索桥为研究对象,建立了空间有限元模型,推导了基于大质量法的多支承激励运动方程,在此基础上研究了该桥的动力特性和非线性多支承激励地震响应,探讨了桩-土-结构相互作用、行波效应对超大跨度悬索桥地震反应的影响,综合评价了该桥的抗震性能。