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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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Bu-Geun Paik Jin Kim Young-Ha Park Ki-Sup Kim 《Journal of Marine Science and Technology》2007,12(2):72-82
The vortex structure of the wake behind a marine propeller was investigated in terms of loading variation by using particle
image velocimetry. One hundred and fifty instantaneous velocity fields were ensemble averaged to study the spatial evolution
of the wake and the behavior of the tip vortices in the region ranging from the trailing edge to one propeller diameter downstream.
The trailing vorticity was found to be related to the radial velocity jump, and the viscous wake was affected by the boundary
layers developed on the blade surfaces. A vortex identification method using the swirling strength was employed to extract
the location of the tip vortex. The loading on the blade made a clear difference to the contraction angles. Slipstream contraction
occurred in the very near wake region, and unstable oscillation occurred because of reduced interaction between the tip vortex
and the wake sheet behind the maximum contraction point for each loading condition. The maximum tangential velocity around
the tip vortex center revealed the average radius of its core, which was used for calculating the vortex strength. Additionally,
variation of the average radius of tip vortices with the change of blade loading was related to vortex tube stretching in
the wake region. The nearly constant vortex strength continued up to one diameter downstream for light loading and design
loading conditions. 相似文献
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The computational fluid dynamics(CFD) method is used to numerically simulate a propeller wake flow field in open water.A sub-domain hybrid mesh method was adopted in this paper.The computation domain was separated into two sub-domains,in which tetrahedral elements were used in the inner domain to match the complicated geometry of the propeller,while hexahedral elements were used in the outer domain.The mesh was locally refined on the propeller surface and near the wake flow field,and a size function was used to control the growth rate of the grid.Sections at different axial location were used to study the spatial evolution of the propeller wake in the region ranging from the disc to one propeller diameter(D) downstream.The numerical results show that the axial velocity fluctuates along the wake flow;radial velocity,which is closely related to vortices,attenuates strongly.The trailing vortices interact with the tip vortex at the blades’ trailing edge and then separate.The strength of the vortex shrinks rapidly,and the radius decreases 20% at one diameter downstream. 相似文献
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Bu Geun Paik Choung Mook Lee Sang Joon Lee 《Journal of Marine Science and Technology》2005,10(3):123-130
In order to investigate the effects of a free surface on the wake behind a rotating propeller, experiments were carried out in a circulating water channel for two cases: one with an open free surface and one with a closed free surface covered by a rigid plate. Four hundred instantaneous velocity fields were measured using a two-frame particle image velocimetry (PIV) technique at four different blade phases. These were ensemble-averaged to investigate the time-averaged flow structure in the near-wake region. For a surface ship, the flow behind the propeller is influenced by the hull wake and the free surface. The phase-averaged mean velocity fields show the potential wake and the viscous wake formed by the boundary layers developed on the blade surfaces. The interaction between the bilge vortices and the incoming flow along the ship’s hull deforms the wake structure. Tip vortices are generated periodically, and the slipstream contraction occurs in the near-wake region. The free surface was found to affect the axial velocity component and vortex structure behind the propeller. As the flow goes downstream, the tip and trailing vortices dissipate due to turbulent diffusion and active mixing with adjacent vortices. 相似文献
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A flow field around a streamlined body at an intermediate angle of incidence is dominated by cross-flow separation and vortical flow fields. The separated flow leads to a pair of vortices on the leeside of the body; therefore, it is essential to accurately determine this pair and estimate its size and location. This study utilizes the element-based finite volume method based on RANS equations to compute a 3D axisymmetric flow around a SUBOFF bare submarined hull. Cross-flow vortex structures are then numerically simulated and compared for a submarine with SUBOFF and DRDC STR bows. Computed results of pressure and shear stress distribution on the hull surface and the strength and locations of the vortex structures are presented at an intermediate incidence angle of 20°. A wind tunnel experiment is also conducted to experimentally visualize the vortex structures and measure their core locations. These experimental results are compared with the numerical data, and a good agreement is found. 相似文献
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风力转子推进装置节能环保,降低推力成本,有利于船舶行业的绿色发展。基于多松弛格子Boltzmann方法,对并列风力助推转子绕流进行数值模拟。首先模拟单圆柱绕流的流动特性,以验证程序的可靠性,重点探究双圆柱的间距比和转速比对圆柱绕流特性的影响。获取圆柱的升阻力系数以及尾流流型,验证临界转速比的存在。结果显示:旋转可以有效地抑制涡的生成和脱落,当转速比达到临界转速比时,漩涡彻底消失,流场变得稳定;时均升力系数的绝对值和时均阻力系数随转速比的增大分别增大和减小。 相似文献
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旋转圆柱绕流的流场特性 总被引:1,自引:0,他引:1
在亚临界区Re=1.4×105条件下,基于大涡模拟(LES)方法对均匀来流作用下的旋转圆柱绕流进行了数值模拟。通过与非旋转时的实验和计算结果比较,验证了文中计算的准确性。在此基础上,对不同转速条件下(0≤α≤2,α为圆周线速度与自由来流速度的比值)的圆柱绕流进行了数值研究。结果表明,圆柱旋转可以有效地抑制其旋涡脱落,随着转速的增加,可大幅提高其升阻比,主要表现为阻力系数减小而升力系数线性增大。当α=2时,阻力系数和升力系数在经过短暂过渡期后达到稳定。 相似文献
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We studied the effects of the surface roughness and initial gap on the responses of vortex-induced vibration (VIV) of a circular cylinder near a stationary plane wall, employing numerical methods. The VIV response amplitudes, lock-in regions, hydrodynamic forces, VIV trajectories and flow fields for three different surface roughnesses and two different initial gaps were systematically compared. The results reveal that the reduced velocity range can be divided into three regions based on the VIV amplitude as pre-lock-in, lock-in, and post-lock-in regions. The width of the lock-in region is not sensitive to the variation of the roughness. The mean drag coefficient has a decreasing tendency with the increased roughness. For a small initial gap, the clockwise wall boundary layer vortices has coalesced with the clockwise vortices shed from the upper side of the cylinder, which further suppresses the shedding of the counter-clock wise vortices from the lower side of the cylinder. The vortex shedding flow pattern displays a weak 2S mode. However, for a large initial gap, there is no coalescing action operating in the wake region and hence most of the vortex shedding flow patterns show an asymmetric 2S mode. 相似文献
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通过分离涡模拟法(detached eddy simulation,DES)对半潜式钻井服务支持平台拖航阻力进行了研究,重点对平台拖航阻力、阻力系数和平台表面附近流场分布等特性进行了研究。研究表明:流方向下平台各结构所受阻力各不相同,下浮体占据总阻力比最大(尤其是90°来流方向下)。阻力系数及升力系数时历曲线变化具有“脉动性”。通过平台表面附近流场分布可以分析涡形成及受力原因,逆方向流及涡之间相互作用使得阻力有所减小。 相似文献
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[目的]旨在研究跨域无人平台从水面垂直起飞过程中平台的运动及动力学特性.[方法]采用黏流CFD方法结合重叠网格技术和多自由度DFBI(dynamic fluid body interaction)运动模型,针对跨域无人平台在水面垂直起飞至空中的跨域过程的动态特性,开展数值模拟研究.[结果]模拟结果显示:在垂直起飞过程中... 相似文献
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The seasonal variation of the surface circulation in the Japan/East Sea (JES) and the Tsushima/Korea Straits (TKS) is reviewed and discussed, focusing on mesoscale and submesoscale variabilities.The monsoon modified by coastal geographical features near Vladivostok generates a dipole of vortex off Vladivostok which induces dramatic changes in the surface circulation in the northwest JES, splitting the Subpolar Gyre into two smaller gyres by generating the Vladivostok Dome. Between these two smaller gyres, the Northwest Thermal Front is formed and current reversal is induced along the North Korean coast. The winter monsoon also induces a current reversal along the Sakhalin coast. The volume transport of the surface Subpolar Gyre has two maxima in January and August. The maximum in August is induced by the summer intensification of the Liman-North Korean Cold Current and the shallow and narrow surface coastal jet generated by the sea ice and snow melting. The maximum in January is induced by the northwest monsoon and associated cooling.Salient features in the TKS are the submesoscale variabilities. In the western channel, submesoscale eddies with length scale of about 80 km and time scale of 5–6 days develop in the cold period. On the lee side of the Tsushima Islands, Karman-like vortex pairs are generated in the warm period. Anticyclonic vortices generated at the northern tip of the Tsushima Islands have a time scale of 5 to 8 days, length scale of 35 to 60 km, and propagate toward the JES with a phase speed of 8 cm/s. Cyclonic vortices south of the anticyclonic counter part of the vortex pairs are rather stationary with intermittent occasional propagation toward the east. The development of stratification seems to be necessary for the development of Karman-like vortex pairs.Summarizing the results above, a schematic surface circulation with seasonal change is proposed. 相似文献
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针对一种具有半潜-水面航态变换功能的新型潜伏式高速船型,基于非稳态RANS方程组与VOF模型求解粘性流场,结合动态流域边界与滑移网格技术,对目标船在垂直面内三自由度运动及其喷水推进器叶轮随船定轴高速旋转的耦合运动进行数值模拟。结果表明:在相同主机平均转速条件下,所预报自航点体积傅氏数与自航模型试验结果的相对误差在7%以内;从半潜到水面的航态变换过程中,船体有显著的纵倾与升沉,船体主要克服压差阻力,船体兴波由相互叠加的首波、肩波、尾波逐渐发展为首尾分明的两个波系,在喷水推进器射流区内捕捉到生成和发展的高强度涡系。 相似文献
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本文基于计算流体力学(CFD)方法,对多重参考系模型(MRF)及滑移网格模型(SM)在计算螺旋桨水动力性能时的差异进行了探讨。将以上两种模型应用到4381螺旋桨的水动力性能计算中,首先将计算得到的推力系数及转矩系数与试验数据进行了对比,考察了两种计算模型对螺旋桨的敞水性能的预测情况,并进一步对两种模型计算得到的螺旋桨盘面的速度场、桨叶的压力分布、桨后涡量云图等进行了对比分析。计算结果表明,滑移网格模型相较于多重参考系模型,对螺旋桨的推力系数的模拟结果误差更小,扭矩系数方面,两种模型的模拟结果相差不大;对于进速系数较大时,两种模型模拟得到的压力分布及速度分布较为相似,但对于高负荷情况,滑移网格模型可以更好地捕捉桨叶的压力分布及桨盘面处的速度分布情况;进速系数较小时,多重参考系模型可以模拟出涡结构的发散现象,而滑移网格模型可以更好的在高进速系数情况下捕捉到梢涡结构。 相似文献
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Numerical simulations of wind turbine blade-tower interaction by using the open source OpenFOAM tools coupled with arbitrary mesh interface(AMI) method were presented.The governing equations were the unsteady Reynolds-averaged Navier-Stokes(RANS) which were solved by the pimpleDyMFoam solver,and the AMI method was employed to handle mesh movements.The National Renewable Energy Laboratory(NREL) phase VI wind turbine in upwind configuration was selected for numerical tests with different incoming wind speeds(5,10,15,and 25 m/s) at a fixed blade pitch and constant rotational speed.Detailed numerical results of vortex structure,time histories of thrust,and pressure distribution on the blade and tower were presented.The findings show that the wind turbine tower has little effect on the whole aerodynamic performance of an upwind wind turbine,while the rotating rotor will induce an obvious cyclic drop in the front pressure of the tower.Also,strong interaction of blade tip vortices with separation from the tower was observed. 相似文献
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水下拖曳体的艉部线型是决定其水动力性能的重要特征之一,良好的艉部线型对减小拖曳体的形状阻力系数,提高拖曳航速,减小拖缆的张力等都有积极意义。选用带十字尾翼的水下拖曳体作为研究对象,应用k-ε模型对其艉部流场特性进行精细分析,分析静压力系数Cp沿拖曳体长度方向的分布,并对水下拖曳体与尾翼交接部上游马蹄涡流动的产生及发展过程进行计算,得出拐角区的流线及流场。计算和实验结果表明,所采用的计算模型和方法合理,可在此基础上应用到其他水下拖曳体的外形优化设计中。 相似文献
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