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Dynamic Responses of Truss Spar Due to Wave Actions  [cached]
V.J. Kurian,C.Y. Ng,M.S. Liew
Research Journal of Applied Sciences, Engineering and Technology , 2013,
Abstract: Spar platforms have been used for drilling, production and storage of oil and gas in the offshore deepwater region. The structure is installed at the deepwater locations in the sea and is exposed to continuous action of wind, wave, current and other environmental forces. Wave force constitutes about 70% of the total environmental force and could be considered as the most significant force affecting the dynamic responses needed for the design of these structures. In this study, the dynamic responses of the truss spar due to wave actions including the wave force theories and wave propagation directions are investigated. Numerical simulations are developed to investigate the accuracy of the wave force theories i.e., Morison equation and Diffraction theory, for large structure such as truss spar. The investigation is further expanded to study responses of the truss spar due to variations directions of the wave propagated. The truss spar is modelled as a rigid body with three degrees of freedom restrained by mooring lines. In the simulation, the mass, damping and stiffness matrices are evaluated at every time step. The equations of motion are formulated for the platform dynamic equilibrium and solved by using Newmark Beta method. To compute the wave force for truss spar, which is large compared to the wave length, Diffraction theory was found to be more appropriate. The Morison equation was found applicable only at the high frequency range. Short crested waves resulted in smaller responses in all the motions than that for long crested waves. Hence, it would be appropriate to consider the short crested wave statistics for the optimum design.
The Nonlinear Bifurcation and Chaos of Coupled Heave and Pitch Motions of a Truss Spar Platform The Nonlinear Bifurcation and Chaos of Coupled Heave and Pitch Motions of a Truss Spar Platform  [PDF]
HUANG Lei,LIU Liqin,LIU Chunyuan,TANG Yougang
- , 2015,
Abstract: This paper presents the results from a numerical study on the nonlinear dynamic behaviors including bifurcation and chaos of a truss spar platform. In view of the mutual influences between the heave and the pitch modes, the coupled heave and pitch motion equations of the spar platform hull were established in the regular waves. In order to analyze the nonlinear motions of the platform, three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs were constructed, the Poincaré maps and the power spectrums of the platform response were calculated. It was found that the platform motions are sensitive to wave frequency. With changing wave frequency, the platform undergoes complicated nonlinear motions, including 1/2 sub-harmonic motion, quasi-periodic motion and chaotic motion. When the wave frequency approaches the natural frequency of the heave mode of the platform, the platform moves with quasi-periodic motion and chaotic motional ternately. For a certain range of wave frequencies, the platform moves with totally chaotic motion. The range of wave frequencies which leads to chaotic motion of the platform increases with increasing wave height. The three-dimensional maximum Lyapunov exponent graphs and the bifurcation graphs reveal the nonlinear motions of the spar platform under different wave conditions
均匀流中深水系泊Truss Spar平台涡激运动试验研究  [PDF]
海洋工程 , 2011,
Abstract: 在工程中广泛应用的TrussSpar平台自诞生之初就为涡激运动问题所困扰,对其运动特性及抑制方法的机理性研究始终都在进行。采用截断系泊系统水池模型试验对设计中的TrussSpar平台在均匀流中的涡激运动响应进行了研究,分析了有无侧板平台的运动轨迹以及不同速度及流向角来流对平台运动的平衡位置的影响。在影响平台涡激运动特性的重要因素中,选取折合速度及流向角分别加以研究,分析了幅值在锁定区间中的变化规律,验证了减涡侧板对涡激运动良好的抑制作用,并对“热点”问题进行了探讨。为进一步研究Spar平台的涡激运动特性奠定了基础。
Truss Decomposition in Massive Networks  [PDF]
Jia Wang,James Cheng
Computer Science , 2012,
Abstract: The k-truss is a type of cohesive subgraphs proposed recently for the study of networks. While the problem of computing most cohesive subgraphs is NP-hard, there exists a polynomial time algorithm for computing k-truss. Compared with k-core which is also efficient to compute, k-truss represents the "core" of a k-core that keeps the key information of, while filtering out less important information from, the k-core. However, existing algorithms for computing k-truss are inefficient for handling today's massive networks. We first improve the existing in-memory algorithm for computing k-truss in networks of moderate size. Then, we propose two I/O-efficient algorithms to handle massive networks that cannot fit in main memory. Our experiments on real datasets verify the efficiency of our algorithms and the value of k-truss.
Truss Spar平台桁架管节点疲劳分析  [PDF]
海洋工程 , 2007,
Abstract: TrussSpar平台在风、浪、流的作用下,结构受力十分复杂,准确分析其疲劳强度相当困难。通过建立TrussSpar平台三维有限元模型,利用HydroD软件进行载荷预报、波浪搜索,得到产生最大应力幅响应的最不利浪向和相位角。运用Sestra软件进行整体有限元分析,得到的结果作为桁架管节点细化模型的边界条件,再用Nastran软件进行局部分析求得节点的热点应力,修正壁厚影响。最后根据DNV规范的S-N曲线计算了管节点的疲劳寿命。
Truss Spar平台垂荡响应频域分析  [PDF]
海洋工程 , 2009,
Abstract: 利用已有水动力试验和数值模拟结果及Morison方程,简化估计了TrussSpar平台垂荡方向水动力贡献,快速有效地预报了平台极端海况下的垂荡响应。在频域内分别采用数值迭代计算和粘滞阻尼线性化方法得到了平台在不同数量垂荡板配置下的垂荡响应幅值算子。在墨西哥湾、西非和中国南海等3种不同地区极端海况以及墨西哥湾工作状态海况下计算了平台的响应极值,分析发现平台波频垂荡响应对入射波浪周期非常敏感。采用JONSWAP波能谱得到了TrussSpar平台垂荡响应谱。通过比较和参数分析,验证了平台在设计上的合理性与实际海况下良好的垂荡运动性能。
Spar平台湿拖阻力性能研究  [PDF]
海洋工程 , 2012,
Abstract: 海洋平台由拖船拖至工作地点,计算海洋平台的湿拖阻力在实际工程应用中具有重要意。采用实验和数值模拟两种方法进行桁架式Spar平台的湿拖阻力性能研究,并将两种结果进行对比。并分析了桁架式Spar平台的垂荡板间流场的变化规律。研究结果表明,Spar平台的湿拖阻力中,摩擦阻力所占总阻力的比例小于10%;在平台拖曳运动的前几秒中,垂荡板间流体剧烈运动,速度和压力显著变化,随后就运动慢慢变缓;Spar平台在低速拖曳时会产生明显的波浪,尾部有回流。
Efficient Truss Maintenance in Evolving Networks  [PDF]
Rui Zhou,Chengfei Liu,Jeffrey Xu Yu,Weifa Liang,Yanchun Zhang
Computer Science , 2014,
Abstract: Truss was proposed to study social network data represented by graphs. A k-truss of a graph is a cohesive subgraph, in which each edge is contained in at least k-2 triangles within the subgraph. While truss has been demonstrated as superior to model the close relationship in social networks and efficient algorithms for finding trusses have been extensively studied, very little attention has been paid to truss maintenance. However, most social networks are evolving networks. It may be infeasible to recompute trusses from scratch from time to time in order to find the up-to-date $k$-trusses in the evolving networks. In this paper, we discuss how to maintain trusses in a graph with dynamic updates. We first discuss a set of properties on maintaining trusses, then propose algorithms on maintaining trusses on edge deletions and insertions, finally, we discuss truss index maintenance. We test the proposed techniques on real datasets. The experiment results show the promise of our work.
Solid Topology Optimization Using Truss Lattices
Mihai-Victor PRICOP
INCAS Bulletin , 2012, DOI: 10.13111/2066-8201.2012.4.3.4
Abstract: This paper presents the development, results and conclusions obtained with a solid topologyoptimization code, using truss lattices as an alternative to continuum elements. Truss elements areused for the simplicity of the implementation in a new code, in all aspects: boundary conditions,loadings, elemental stiffness matrix. Blocked structures, well posed mechanical equilibrium problemsare assured by a proper truss arrangement, lattice driven, similar to structured or unstructuredmeshing.
Calculated and Measured Strength of a Composite Aircraft Undercarriage Spar  [cached]
Vilém Pompe
Bulletin of Applied Mechanics , 2010,
Abstract: The main aircraft undercarriage spar was designed using various criteria for laminate strength. The calculated stress-strain status was evaluated simultaneously with the use of basic phenomenological and mechanistic criteria for the set operating modes and the requested safety factors. Subsequently, prototypes of the spar were manufactured and subjected to structural tests. The obtained results provide important information concerning the reliability of the employed criteria in terms of prediction of the point of critical damage and the level of the corresponding load when applied on an actual aircraft component featuring a general reinforcement structure.
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