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To optimize offshore wind turbine (OWT) design, an engineering tool has been developed allowing for a detailed investigation of the effects of nonlinear soil stiffness and damping on foundation dynamics. We have studied the response of a vertically oscillating offshore wind monopile foundation in a realistic soil profile subjected to loads between 1 and 200 MN in the frequency range 0–10 Hz with pseudo-static and equivalent linear dynamic model. The non-linear soil behaviour is modelled with an equivalent linear method with shear modulus reduction and damping curves as input. The tool is verified and validated by comparison with elasto-dynamic model and experiments. With increasing load amplitudes foundation stiffness increases and damping decreases. For large load amplitudes the lower part of the pile foundation contributes more to foundation damping. The results indicate the nonlinear foundation stiffness and damping can be modelled rationally by combining stiffness and hysteretic damping from nonlinear static tools with apparent mass and radiation damping from elasto-dynamic analysis. The tool can be used to compute soil springs and dampers based on laboratory-based soil stiffness and damping. 相似文献
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Estimation of natural frequencies and damping using dynamic field data from an offshore wind turbine
The dynamic characteristics of offshore wind turbines are heavily affected by environmental loads from wave and wind action and nonlinear soil behaviour. In the design of the monopile structures, the fatigue load due to wind and wave loading is one of the most important problems to consider. Since the fatigue damage is sensitive to the foundation stiffness and damping, increasing the accuracy of analysis tools used in the design and optimization process can improve the reliability of the structure and reduce conservatism, thereby leading to a more cost-efficient design. In this context, analysis of field data is important for calibrating and verifying purposes. This paper presents analysis of measured accelerations and strains from a wind farm in the North Sea with monopile foundations. Field data during idling conditions, collected over long periods of operation, are analysed and the natural frequencies are determined, and damping is estimated. The measured natural frequencies are compared to calculated values using an aero-servo-hydro-elastic code, showing a good agreement in the frequency range below 2 Hz. Variation of the natural frequencies with intensity of loading may indicate effect of soil nonlinearity on the overall OWT response. Since the first natural bending modes have the largest potential to mobilize soil reactions, they are of primary interest in this context. The effect of load (wave, wind and dynamic bending moment) on the first natural frequency is investigated using different analysis techniques in the frequency domain and time domain. A clear correlation between load level and first natural frequency is demonstrated. A simple nonlinear SSI model of the tower/soil system is employed to numerically investigate the observed changes in the measured first natural frequency with the level of loading and increased overall damping. The simulated results reproduce the general trends in the observed reduction in the first natural frequency and increased damping ratio with the load level. However, the effect of the load level is less than that observed in the measurements, indicating contribution also from other factors than soil nonlinearity. 相似文献
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提出大直径灌注长桩工作性状并同时考虑负摩阻力的桩侧荷载传递模型,桩端采用双曲线荷载传递模型模拟土的非线性变形特性,并引入混凝土的Rusch模型来考虑高荷载水平作用下桩身混凝土的弹塑性性状,采用Mindlin解答以考虑桩侧摩阻力在桩端处产生的桩端位移,从而建立了层状地基中大直径负摩擦灌注长桩的荷载传递分析理论。根据该理论计算得到的荷载一沉降曲线与实测的曲线较为吻合,可作为确定大直径灌注长桩承载力的依据,经过对工程实例的计算与实测对比分析,证明该理论可靠、方法简单,且具有较好的适用性。 相似文献
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A systematic study was performed in laboratory model tests to assess the response of cement-improved reinforced monopiles to lateral monotonic and cyclic loading in clay. The overall load‒deflection behavior and profile of the bending moment was fully studied in monotonic tests, in addition to the p-y curves of the reinforced and unreinforced piles. Cyclic loading tests were carried out at different cyclic magnitude values and load ratios, and the cement-improved soil reinforcement range was also varied. This study provides several insights into the ongoing development of the deflection, unloading stiffness and bending moment of cement-improved soil reinforced piles as cycling progresses, which can provide empirical design recommendations for cement-improved soil reinforced monopiles subjected to lateral cyclic loading. Based on the typical p-y curve models of pile in soft clay and stiff clay, by considering the proportion of soil resistance shared by cement-improved soil and soft clay around a pile under lateral load, the modification factors of two parameters pu and y50 are derived, and then a modified p-y curve model of cement-improved soil reinforced piles in soft clay is established. 相似文献
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Marine engineering structures may be subjected to various levels of vessel collisions, causing different degrees of damage to the RC piles. However, the influence of different combinations of impact mass and velocity under the same initial kinetic energy or momentum on the impact behavior of RC piles has not been explored. A numerical investigation of the impact responses of RC pile structures (including plumb piles and inclined pile groups) considering the material strain rate effect is carried out using the software ABAQUS/Explicit in this paper. Parametric studies are conducted based on the validated finite element models of RC piles subjected to horizontal impact. The internal force distributions, as well as the effect of the impact kinetic energy and the momentum (including different combinations of impact mass and initial velocity) on the impact response of RC piles, are discussed. The results indicate that the development path of the bending moment‒overall structural displacement curves in the plastic hinge regions of RC piles are almost identical under both impact and static loading conditions. Compared to momentum, the impact response of RC piles is insensitive to the variation of impact kinetic energy with different combinations of impact mass and velocity. Therefore, the impact kinetic energy is more suitable for evaluating the structural deformation of RC piles after impact. Finally, a performance-based impact-resistance design framework for RC piles is proposed. 相似文献
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劲芯搅拌桩的试验研究 总被引:5,自引:0,他引:5
劲芯搅拌桩是由搅拌桩和钢筋混凝土芯桩组合而成的新型桩,具有高承载力、低造价、施工便捷等优点,为掌握其荷载传递机理和承载力影响因素,进行了19根桩的荷载试验,包括11根劲芯水泥搅拌桩、4根钻孔灌注桩及4根水泥搅拌桩;并对劲芯搅拌桩进行了有限元分析。研究表明:芯桩对劲芯搅拌桩的荷载传递起关键作用,提高了劲芯搅拌桩的承载力;劲芯搅拌桩的承载力高于水泥搅拌桩和钻孔灌注桩;芯桩的长度、体积含芯率、面积含芯率存在一个最优值;水泥土的固化效应、芯桩的挤土效应和芯桩的荷载传递是劲芯搅拌桩高承载力的主要来源。 相似文献
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为深化针对复合地基计算理论和设计方法的研究,通过建立带垫层桩体复合地基弹塑性有限元数值模型,采用基于Mohr—Coulomb破坏准则的理想弹塑性本构模型描述地基土的弹塑性本构关系,采用接触对算法描述桩-土界面非连续接触特性,采用无限单元边界模拟半空间地基特征,通过改变垫层刚度、筏板厚度和桩基刚度进行变参数化分析,探讨了复合地基体系中垫层、筏板及桩基三部分对整体受力变形特性的影响,从而更全面和深入地揭示了复合地基体系的工作性能和承载机制,更好地为工程设计与实践提供现实指导与参考。 相似文献
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Subsea pipelines buried in the seabed may undergo large lateral displacement under environmental, operational, and accidental loads at different interaction rates and hence different drainage conditions. The undrained shear strength is commonly used in practice to assess the pipe-soil interaction assuming a sufficiently high displacement rate. This approach neglects consolidation effects and the rate-dependent response of the soil and may significantly underestimates the lateral resistance for a pipeline moving slowly relative to the ground. In this study, a coupled large deformation finite element (LDFE) framework is developed via a remeshing and interpolation technique with small strain (RITSS). A Modified Cam-Clay (MCC) model with efficient numerical integration is used. The proposed coupled LDFE framework is verified against selected physical model tests. Effects of the interaction rate and hence drainage condition on the p-y curve, excess pore pressure generation and dissipation, and failure mechanisms are discussed. An empirical relationship between the ultimate resistance and the normalized velocity of the pipe (denoting the drainage condition) is proposed, which may be applied for the integrity and safety analysis of buried pipes in landslide or fault-crossing regions. 相似文献
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Today, an important challenge for offshore wind energy is to design efficient and reliable offshore wind turbines (OWTs). The overall damping of OWTs plays an important role in the design process as it limits the amplitude of the OWT dynamic response at frequencies near resonance. Therefore, an accurate estimation of OWTs damping is necessary for the efficient design of these systems. The foundation damping is one of the main sources overall turbine damping and is the least well understood. This paper presents a critical review of recently published studies on foundation damping for OWTs on monopiles and explains how soil damping contributes to the total damping of OWTs. It also reviews the main methods that have been used for the estimation of foundation damping in numerical and experimental studies. In addition, the importance of damping to the OWTs fatigue life is discussed. Finally, a discussion is provided on the challenges to be overcome and recommendations for the accurate estimation of foundation damping. 相似文献
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针对海上风电整机结构其低阶固有频率的控制问题,基于有限元分析技术开展小直径桩土相互作用的数值模拟分析,与试验结果、API规范计算结果进行对比,验证了数值模型的适用性,分析大直径单桩结构桩内土芯、冲刷深度、表层土置换措施对整机固有频率的影响,结果表明,基于有限元实体单元计算所得一、二阶整机固有频率要明显大于传统p-y方法计算结果;桩内土芯对一、二阶整机固有频率影响很小;在一定范围内,随着泥面冲刷深度的增加,一、二阶固有频率降低不明显,认为传统p-y方法对于大直径单桩的适用性有待研究;在实际工程设计中,桩内土芯的影响可忽略;对于大直径单桩,在一定范围内可以忽略冲刷的影响。 相似文献
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临水船闸基坑由于需要提供坑内较大作业空间而较多地采用重力式水泥土搅拌桩作为支护结构,基坑外侧常采用钢板桩作为临时的挡水围堰。针对水泥土搅拌桩施工过程对钢板桩围堰产生位移过大的问题,以某船闸基坑为例,采用数值模拟与现场监测数据相结合的方法研究搅拌桩施工过程中对于钢板桩临时围堰的影响,分析钢板桩围堰变形过大的原因。通过现场孔隙水压力试验得出搅拌桩施工过程中土体孔压在深度和宽度上的变化规律和水泥土搅拌桩施工对周围土体的影响范围,并提出一种钢板桩围堰变形过大的解决方案。本研究可为类似基坑的设计和施工提供借鉴。 相似文献
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Seabed in regions, such as the Gulf of Guinea and North West Shelf of Australia, may exhibit a crust layer where the undrained shear strength can be an order of magnitude higher than that of the immediately underlying sediment. This can complicate design of steel catenary risers, where fatigue depends on the cyclic vertical stiffness of the pipe-soil interaction. Potential punch-through of the riser into the underlying soft soil may invalidate design assumptions based on the pipe-soil stiffness within the crust layer. The long-term evolution of pipe-soil stiffness within the crust layer, which exhibits similar properties to an over-consolidated soil, is also poorly understood. This paper describes centrifuge model tests undertaken in a clay sample with a crust layer, simulating the punch-through process of a pipe under load control and investigating the pipe-soil stiffness during long-term cyclic loading tests under displacement control. Results confirm that the potential for punching-through the crust layer depends strongly on the relative ratio of pipe diameter to crust layer thickness. The long-term evolution of pipe-soil stiffness showed a steady increase after an initial remoulding stage in contractile soils (normally consolidated and lightly over-consolidated), but a steady reduction in the heavily over-consolidated, more dilatant, crust. The magnitude of pipe-soil stiffness changes (during both remoulding and reconsolidation) is governed by the over-consolidation ratio of the soil and the amplitude of the cyclic displacements. This study provides insights on the relevant cyclic stiffness to consider when assessing SCR fatigue life in over-consolidated soils and soils exhibiting a superficial crust layer. 相似文献
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高桩码头构件众多,不同位置、程度、数量的构件损伤会对码头动力特性造成不同的影响。采用概率灵敏度分析方法,研究混凝土基桩损伤、上部结构损伤等情况下码头动力特性的变化。通过建立高桩码头有限元模型,分析不同参数对码头整体动力特性的影响,发现码头结构动力特性对土体参数、桩有效截面面积以及部分桩的弹性模量较为敏感;对横梁和纵梁的损伤并不敏感;码头前三阶自振频率的变化可以作为反映整体损伤的指标,四阶以上频率因其振型为桩自身的局部振型,其频率值仅对部分单桩损伤敏感,而对其他桩的损伤不敏感;码头前三阶频率间相关性强,三阶以上频率与前三阶频率中等强度相关。 相似文献