共查询到19条相似文献,搜索用时 15 毫秒
1.
The response of an offshore wind turbine tower and its monopile foundation has been investigated when exposed to linear and fully nonlinear irregular waves on four different water depths. The investigation focuses on the consequences of including full nonlinearity in the wave kinematics. The linear and nonlinear irregular wave realizations are calculated using the fully nonlinear potential flow wave model OceanWave3D [1]. The linear and nonlinear wave realizations are compared using both a static analysis on a fixed monopile and dynamic calculations with the aeroelastic code Flex5 [2]. The conclusion from this analysis is that linear wave theory is generally sufficient for estimating the fatigue loading, but wave nonlinearity is important in determining the ultimate design loads. 相似文献
2.
Recently, various approaches have been introduced to estimate the response of offshore structures in different sea states by stepwisely intensifying records. In this article, a more practical approach entitled Modified Endurance Wave Analysis (MEWA) considering the random and probabilistic nature of wave loading and utilizing optimal time duration is introduced. Generation procedure of this approach is described based on two practical wave theories: random and constrained new-wave. In addition, assessment of a simplified model representing a typical fixed offshore platform under extreme wave conditions in the Persian Gulf is performed making use of MEWA. A comparative analysis has been also carried out to investigate the accuracy and computational costs of MEWA. The results indicate that MEWA can be a time-saving and also reliable method both in design and assessment of offshore platforms. 相似文献
3.
The concept of a shared mooring system was proposed to reduce mooring and anchoring costs. Shared moorings also add complexity to the floating offshore wind farm system and pose design challenges. To understand the system dynamics, this paper presents a dynamic analysis for a dual-spar floating offshore wind farm with a shared mooring system in extreme environmental conditions. First, a numerical model of the floating offshore wind farm was established in a commercial simulation tool. Then, time-domain simulations were performed for the parked wind farm under extreme wind and wave conditions. A sensitivity study was carried out to investigate the influence of loading directions and shared line mooring properties. To highlight the influence of the shared line, the results were compared to those of a single spar floating wind turbine, and larger platform motions and higher tension loads in single lines are observed for the wind farm with shared moorings. The loading direction affects the platform motions and mooring response of the floating offshore wind farm. Comparing the investigated loading directions to the 0-deg loading direction, the variation of mean mooring tension at the fairlead is up to 84% for single lines and 16% for the shared line. The influence of the shared line properties in the platform motions and the structural responses is limited. These findings improve understanding of the dynamic characteristics of floating offshore wind farms with a shared mooring system. 相似文献
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When a ship with a wide, immersed transom stern runs on a deep draft, forward-oriented wave breaking often occurs just behind
the transom stern. In such conditions, stern waves can be considered to consist of two main components: the forward-oriented
breaking wave and the remaining following waves. In our previous study, which was the first part of the present study, we
developed a method to treat the forward-oriented breaking wave, and have clarified that it has a scale effect and its resistance
coefficient decreases with an increase in the size of the model ship. On the other hand, the study also indicated that the
height of the remaining following waves increases with an increase in the model ship size. The purpose of this paper is a
more complete understanding of the two different component characteristics of the stern waves. We have developed a method
to estimate the resistance due to the remaining following waves. Using this method, we have reached three main conclusions.
The resistance increases considerably if the remaining following waves change to forward-oriented breaking waves. The resistance
coefficient of the remaining following waves increases only slightly with an increase in model ship size. This stern wave
resistance coefficient is strongly affected by the forward-oriented breaking waves, and therefore decreases with an increase
in model ship size.
Received: January 5, 2001 / Accepted: May 28, 2001 相似文献
6.
This paper investigates the length scale of ocean surface breaking waves in the spectral range of intermediate wavelength components a few centimeters to a few meters long. The spectral properties of wave breaking are examined first with the dissipation function of the wave action density conservation equation. The analysis reveals a strong breaking signature in wave components between 0.15 and 1.5 m long in the form of a quasi-singular behavior of the dissipation function using the present formulation of the wind-generation and breaking dissipation functions. Independent studies of more-direct breaking observations of radar tracking of sea spikes in the past have shown close correlation between sea spikes and scatterers traveling at the speed of surface waves a few meters long and much shorter than the dominant wavelength. This feature of sea-spike properties is consistent with the breaking signature of the dissipation function in similar wavelengths. The intermediate-scale waves are the primary contributor of the ocean surface mean-square slope. The close correlation between the gas transfer rate and the mean-square slope has been demonstrated repeatedly. A better understanding of the wave dynamics of intermediate-scale waves is important for clarification of various gas transfer mechanisms. 相似文献
7.
Many significant engineering challenges have emerged as the petroleum industry has moved their field development and production activities into increasingly deeper water depths. The design of deepwater marine risers presents the combined challenges to minimize top tensioning requirements, mitigate any flow-induced vibrations, and if possible to increase the expected fatigue life of these slender structural members. As part of the design process to achieve these goals external buoyancy modules and strakes have been employed. To gain insight into the complex multi-mode response behavior a recent experimental study was performed and the analysis of selected data sets is presented. In the experiments a horizontal cylinder with a length to diameter ratio of 263 was fitted with a variety of strake and buoyancy element configurations. The models were towed at uniform speeds ranging from 0.4 to 2.0 m/s and fiber optic strain gages were used to measure both in-line and cross-flow strain response. The resulting time series information was processed utilizing the method of time domain decomposition formulated for strain data input and the introduction of modal assurance criterion to resolve the modal strain information that included frequency, mode shape, and critical damping ratio information. The pre-tensioned cylinder without appendages was used as a base case and the results were basically consistent with expectations. In the case of 0.8 m/s low-tension test, multiple closely spaced non-overlapping peaks were observed in both in-line and cross-flow directions and were identified as being of the same mode with mode shapes distorted away from purely sinusoidal behavior. The test data for the 100% coverage by helical stakes demonstrated the effectiveness of that suppression device over the range of current velocities investigated. The most interesting case was that of a staggered combination of helical strakes and buoyancy element whose total for each type of coverage was equal. This effective asymmetric VIV suppression approach is presented and discussed in detail. 相似文献
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船舶在波浪中航行,纯稳性丧失、参数激振和横甩是造成船舶倾覆的主要原因。针对波长与船长、波高与波长、波与船的波舷角三者对船舶稳性的影响进行讨论,揭示了船舶在波浪中航行时的稳性变化规律,提出了应合理地选择船舶的航行姿态、谨慎用舵等操船建议,保证船舶的航行安全。 相似文献
10.
近岸波浪变形数值模型的比较研究 总被引:2,自引:1,他引:1
外海深水区的波浪传播到近岸浅水区时,受到岛屿、地形与建筑物等影响,发生折射、绕射、反射和破碎等一系列变形。准确计算近岸与港内波浪分布,成为港口与海岸工程研究的重要课题。文章在总结波浪数值模拟发展现状的基础上,对目前常用的基于椭圆型缓坡方程的CGWAVE模型、基于Boussinesq方程的MIKE21-BW模型和基于动谱平衡方程的SWAN模型进行了比较研究。 相似文献
11.
利用数字图像来测定船模运动参数是一种成本低、精度高的方法。该系统利用数字图像技术实现了船模试验在自然光条件下的实时测量、实时数据处理和自动操纵控制。介绍了一套多CCD摄像机的船模自动测控系统,对电视图像变形修正、船模自动识别与跟踪等关键技术进行了详细的讨论。根据船模试验的特点提出了有别与一般目标识别跟踪的方法。 相似文献
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本文对改进后的Dawson方法作了简单的描述,并且给出了船舶在开阔无限水深的海域、限制航道、凹型海底以及其他水下结构物存在的海域中航行时的计算例子。结果显示了改进后的Dawson方法以及计算程序的有效性,是一种可以用来预报不同工程问题中船舶兴波和船舶水动力的简单而实用的方法。 相似文献
13.
大开口型船舶波浪诱导载荷研究 总被引:4,自引:1,他引:4
通过对某5万t级大开口型船舶的各种波浪诱导载荷长期预报,详细讨论了不同波浪散布图、装载工况、航速、水动力计算理论和短峰波对波浪诱导载荷长期预报极值的影响,指出了一些值得注意的问题,以期对类似船型的液体波浪诱导载荷预报提供有用的参考。 相似文献
14.
筒型基础海洋平台拖航研究-波浪影响分析 总被引:2,自引:0,他引:2
文章以锦州9-3筒型基础系缆平台为对象,在拖航速度、筒位置以及平台吃水深度一定的条件下,通过模型试验测定了平台在不同规则波浪中拖航时的平台运动加速度、筒内气压力、筒底水压力以及拖缆力.并对试验数据进行比较分析,用于研究波浪对筒型基础平台随浪、顶浪拖航时的影响分析.试验结果表明:筒型基础平台可在渤海水域十年一遇有义波高4.5m的巨浪中拖航,在波高2m以下,航速2节以内,随浪拖航与顶浪拖航均有较高的稳性以及耐波性;顶浪拖航平台的垂荡运动要比随浪拖航时剧烈,随浪拖航平台的稳性以及耐波性要优于顶浪拖航;平台在大浪中拖航时,随浪拖航容许航速要高于顶浪拖航容许航速. 相似文献
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通航节制闸运行调度原则与常规的船闸工程和水闸工程明显不同,针对其口门宽度、门槛水深、闸门形式、平面布置等关键技术问题,船闸工程和水闸工程规范尚无具体的要求。以邓楼节制闸重建工程为例,对现有的节制闸运行调度原则进行调整以满足开通闸通航的要求,同时通过实施工程补偿措施以满足原节制闸防洪水倒漾、引水灌溉、保护水质的功能。通过理论计算和对比分析等方法得知建设2孔净宽23 m、门槛水深5. 5 m的通航节制闸能够满足船舶安全通航和航道通过能力的要求,并得出"升卧式平面闸门能够适应长期低水头运行、高通航保证率要求特点"的结论。其确定运行规则、建设规模、闸门形式、布置方案的方法对类似项目的建设及船闸标准规范的完善均有借鉴意义。 相似文献
16.
长江沿线的控制测量是进行流域规划和港口建设的基础性工作.由于涉及长距离测量和跨河测量,测量精度要求高,因此,常规的三角网、三边网工作量难以完成长江干线大规模的测量任务.GPS技术具有精度高、测量速度快、进行跨带测量简单的特点,通过实际测量工作,探索GPS技术在长江干线D级控制网建设中的应用及测量布设方案和数据处理方法.实践表明,测量结果完全达到国家标准. 相似文献
17.
一般边界条件下矩形薄板振动声辐射特性分析 总被引:1,自引:0,他引:1
基于改进傅立叶级数方法,将矩形板振型函数表示为包含正弦三角级数的改进傅立叶级数,从而有效地克服结构在边界处存在的不连续性,建立了一般边界条件下矩形薄板结构振动声辐射的分析方法,并对薄板结构的振动声辐射特性进行了研究。文中还建立了薄板结构的位移容许函数,然后基于最小势能原理求解了系统的Lagrange函数,最后利用Rayleigh-Ritz法对方程求解从而获得薄板自由振动的模态信息;在此基础上,基于Rayleigh积分公式推导出了薄板振动、辐射声压和声功率的表达式,研究了结构特性参数及边界条件对薄板振动声辐射的影响,通过有限元软件和参考文献的比对分析,验证了改进方法的正确性和有效性。 相似文献
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Fatigue crack propagation behavior under superimposed stress histories containing different frequency components with several mean stress conditions was investigated. Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for fatigue crack propagation was improved to extract the effective part from the applied stress history for fatigue crack propagation. The parameter, which is based on the plastic hysteresis energy consumed in the vicinity of a crack tip, was applied and implemented into the numerical simulation code of fatigue crack propagation. Fatigue crack propagation tests under various superimposed stress conditions with several mean stress conditions were performed and compared with the fatigue crack propagation histories obtained from the improved numerical simulations. These comparisons show the validity of the proposed procedure for extracting the effective stress history from the superimposed stress histories with different frequency components and mean stresses. Additionally, practical fatigue strength evaluations based on the linear cumulative fatigue damage parameter were conducted to investigate the tendency of the fatigue damage value under these stress conditions. 相似文献