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根据冲量相似的要求进行船舶在冲击作用下的模型试验，并将模型试验结果与理论计算及实际试验进行了对比和分析。 相似文献
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评估结构耐撞性能最可靠的方法是实尺度碰撞试验,然而对于大尺度结构物的碰撞试验,因其耗资巨大而不易开展,适当开展比例模型试验可以为简化解析算法及数值仿真计算提供验证依据,也可在一定程度上评估结构的耐撞性能。但是在进行碰撞模型试验时,材料应变率的敏感性会使得缩尺模型的动态响应与实尺度结构结果出现偏差,模型试验得到的数据与实际结构的动响应不完全遵循相似关系,这就限制了相似理论在大型结构物冲击问题上的应用。本文给出了一种通过改变冲击质量来修正应变率效应的方法,不同于传统量纲分析法中选取时间、质量和长度为基本量纲,而是以冲击质量、初始冲击速度和动态应力代替,得到计及应变率效应的质量相似关系。以此为基础,将该修正方法应用于船舶-自升式海洋平台的碰撞分析中。研究结果表明,该修正方法可以有效降低由于应变率效应而造成的缩尺误差,修正后的缩尺模型在碰撞冲击载荷下的位移、碰撞力和撞击时间等动态响应参数与实尺度模型结果的一致性更好。本文研究成果可以为大型结构物冲击模型试验设计提供技术支撑。 相似文献
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板翼动力锚是依靠自重完成安装并靠自重和海床土的抗力来锚固的新型动力锚。板翼动力锚高速(15~25 m/s)贯入地基过程中涉及到高应变率、流固耦合、土体软化和大变形等难题,模型试验可避免上述计算困难,能直接得出不同的贯入速度所对应的沉贯深度。本文首先推导了模型相似关系,然后在常规重力条件下,进行了两组26个工况的板翼动力锚在均质黏土中动力安装过程的模型试验,根据试验结果确定了率效应参数的取值范围,并研究了每一项受力对沉贯深度的影响。最后提出了在均质黏土中预测板翼动力锚沉贯深度的经验公式。 相似文献
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为揭示张力腿平台涡激运动响应规律,采用数值模拟与模型试验相结合的方法研究了全水深系泊张力腿平台涡激运动响应。根据张力腿平台主尺度参数,按照几何相似制作了水池试验模型,在满足运动相似和动力相似的条件下开展了均匀流、剖面流模型试验,并将模型试验结果与数值模拟结果进行了对比,验证了数值模拟与模型试验结果的一致性。分析结果表明在均匀流作用下张力腿平台涡激运动的锁定区间在5.5<Ur<8.5,来流角对涡激运动影响较大。剖面流作用下平台涡激运动规律与均匀流作用基本一致,但剖面流造流引起的能量分散,使平台在XY平面的运动轨迹变得不规律,系泊系统提供的回复力对涡激运动幅值有抑制作用,来流角和流速对张力腿或立管模态影响明显。论文得到结论对于张力腿平台的工程设计有一定借鉴意义。 相似文献
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模型沙干重度在动床模型试验中是影响起动流速比尺和冲淤时间比尺的重要参数，其随淤积历时、粒径变化、埋置深浅和加工方法的不同有着不同的变化规律。通过试验，结合已有的成果，对模型沙干重度受以上几种因素的影响进行了研究，并进一步分析了其变化规律在动床模型试验中的作用。 相似文献
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等向压缩线不唯一及V-lgp空间内非线性变化是砂土压缩模型构建过程中存在的两大问题。通过分析砂土的等向压缩曲线变化特征,结合其力学特性提出了与临界状态线在0点相交并与其它等向压缩线在高压下相互汇聚的等向压缩线作为参考压缩线。采用ln(V-Vmin)-(p/pa)ξ空间内线性函数来描述参考压缩线与临界状态线。利用当前体积到参考压缩线的距离构建状态参量并建立修正函数以获取其它体积下的压缩曲线斜率。参考压缩线及弹性变形规律。基于参考压缩线建立的砂土压缩模型不仅表现出砂土在低应力段的小变形特征及高压下的近似线性关系,而且能够描述极限体积附近的低压缩性特征。模型预测与Toyoura砂等向压缩试验及循环压缩试验、弯曲元试验及共振柱试验对比结果表明,提出的砂土压缩模型不仅能够很好地描述Toyoura砂的压缩特性,而且能够较为可靠地预测砂土弹性变形趋势。 相似文献
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Robert J. Hallermeier 《Coastal Engineering》1985,9(1):37-70
Review of four available proposals for designing coastal movable-bed models demonstrates that each suggested model-scaling law contradicts all the others. Accurate laboratory models providing the separate empirical bases, however, all appear fairly consistent with the new design guidance developed here. This formal development considers sediment excursions under wave action by means of a parameter including bed slope and the threshold of sediment movement. The consequent relationship for sedimentation similitude between model and prototype indicates that appropriate model sediment and horizontal scale depend on the selected vertical scale along with wave period and prototype sand characteristics. Explicit forms derived from the general design guidance recover two expressions resembling those previously reported by E.K. Noda (1972) and by P. Vellinga (1982); the route towards Noda's result indicates that guidance is not appropriate for small models of large situations, but the present development yields an independent basis and a needed refinement for Vellinga's empirical results. Considerations of sedimentation similitude are also shown to be supported by successful new laboratory models using sand profiles developed in a large wave tank as prototypes. Spatial distortion seems to be the advisable strategy for small models but proper distortion is rather modest with prototype materials, according to present results. 相似文献
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Vertical uplift static loading tests of single model pile were conducted in the in-lab calcareous sand and quartz sand by emulating practical condition of full-size piles in site. The settlement, lateral deflection, axial force, and friction distribution of the pile are analyzed for each physical test. The pile behaviors in calcareous sand and quartz sand are compared. From the test results, it can be found that the pile top displacement of uplift pile in calcareous sand can be divided into two stages: the pile–sand synchronous stage and pile–sand asynchronous (relative displacement) stage. Data from uplift tests show that the heave of calcareous sand around pile top is very small, which is resulted from the mutually restraint of surface particle. The mutual restriction of surface particle leads to “bottleneck effect” and strengthens ultimate side friction of upper pile segment. In addition, the shear dilatancy and particle breakage of calcareous sand lead to the upper harden and the lower soften of side friction, respectively. Cases of calcareous sand and quartz sand show different responses to pile forming methods, which due to the sands’ different characteristics of particle breakage when compressed as well as plastic deformation under loading–unloading conditions. 相似文献
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为了研究蓬莱西庄海岸侵蚀原因、揭示泥沙运移规律，利用萤光示踪砂和染色砾石进行侵蚀岸段的泥沙示踪研究．其主要结果如下：１．海滩泥沙运动完全由波浪控制，泥沙运移的速度和方向取决于破波的大小和方向．２．海滩泥沙以群体形式沿岸输移．３．在平直海岸上，泥沙可超越粘土质海蚀平台进入另一砂质海滩。 相似文献
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沙脊沙波泥沙数学模型的研究 总被引：1，自引：0，他引：1
在剪切水流条件下,基于水沙两相流动量方程,推导出描述海底沙脊沙波内在演变规律的基本方程。将此方程与二维浅水环流方程、波浪折射-绕射方程进行耦合,建立大范围海区平面二维波、流、泥沙数学模型,并结合海区实际观测水文地质、潮汐、波浪、泥沙资料进行模型验证。通过对比分析发现,数值模拟值与实测站位观测值二者吻合较好,表明了模型的可靠性。应用此模型对东方1-1气田穿越的大范围海底沙脊沙波在相应海动力条件下的移动规律及演变趋势进行定量预测,结果显示,随着时间的推移,沙脊沙波移动距离逐年递增,但发展变化趋势基本稳定。 相似文献
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利用水饱和法制备含天然气水合物试样,进行等向压缩试验和不排水三轴试验.采用天然气水合物临界状态(M HCS)模型同时预测排水条件和不排水条件下的三轴试验,并进行变动参数分析.不排水条件下,密实纯砂发生应变硬化,而相近密实度的含水合物试样出现应变软化,峰值偏应力随水合物饱和度和围压增大.通过与排水和不排水三轴试验结果的对... 相似文献
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Jebbe J. van der Werf Jolanthe J.L.M. Schretlen Jan S. Ribberink Tom O'Donoghue 《Coastal Engineering》2009
A new database of laboratory experiments involving sand transport processes over horizontal, mobile sand beds under full-scale non-breaking wave and non-breaking wave-plus-current conditions is described. The database contains details of the flow and bed conditions, information on which quantities were measured and the value of the measured net sand transport rate for 298 experiments conducted in 7 large-scale laboratory facilities. Analysis of the coverage of the experiments and the measured net sand transport rates identified the following gaps in the range of test conditions and/or the type of measurements: (i) graded sand experiments, (ii) wave-plus-current experiments and (iii) intra-wave velocity and concentration measurements in the ripple regime. Furthermore, it highlights two areas requiring further research: (i) the differences in sand transport processes and sand transport rates between real waves and tunnel flows with nominally similar near-bed oscillatory flow conditions and (ii) the effects of acceleration skewness on transport rates. The database is a useful resource for the development and validation of sand transport models for coastal applications. 相似文献
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For a concave-up power Bruun beach profile, the following two energetics-based sediment transport models are developed: (1) a Bagnold-type model and (2) a combined wave-current stress model. The stress model is calibrated with the Bagnold model using observed transport rates on planar beaches. The sediment transport profiles for the two models are in agreement within the surf zone for the planar beach case; but the stress model is also applied seaward of the breaker line where the Bagnold model is not. A mean swash transport of sand is predicted by the Bagnold model for a power least-squares approximation to total depth including setup/setdown on a Bruun beach profile. The total longshore transport of sand is determined for each transport model as a function of the turbulent lateral mixing strength. The total sand transport is found to be less on a concave-up beach profile than for the corresponding planar beach case. 相似文献
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This paper presents a finite element approach to calculate the full resistance profile of a spudcan deeply penetrating in dense sand overlying clay, in which a potential for an installing spudcan to experience a sudden uncontrolled punch-through failure exists. A modified Mohr-Coulomb model characterized by incorporating a four-phase variation of the mobilized strength and dilation parameters with an equivalent accumulated plastic strain is developed and tested for the overlying dense silica sand. An extended Tresca model is used for the strain softening of the underlying clay. A series of large deformation finite-element (LDFE) analyses are carried out, varying the strength and dilation parameters as well as the spudcan geometries. A fairly good performance of the present approach is verified by validating against groups of centrifuge tests data, allowing the numerical study to be extended parametrically. The four-phase variation of the mobilized strength and dilation parameters involved in the progressive failure of the upper dense sand is parametrically studied and extended to cover the range of sand relative densities that are of practical interest. Additionally, comparisons with the typical existing LDFE analyses using both simple and sophisticated constitutive models are carried out. It shows that the present approach performs fairly well to calculate the full resistance profile of a spudcan deeply penetration in both thin and thick dense sand overlying clay, especially the peak and post-peak resistance, within around 5% of the corresponding centrifuge tests results. 相似文献
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《Coastal Engineering》2006,53(10):825-843
A newly developed two-phase flow model was applied to simulate the sediment movement under 2nd-order Stokes wave sheetflow conditions with different sediment sizes and wave periods. As for the distribution of eddy viscosity and sediment diffusion coefficient, the difference between onshore and offshore phases was considered by using an equivalent sinusoidal velocity amplitude for the asymmetric velocity profile. Sophisticated comparisons between laboratory measurements [O'Donoghue, T., Wright, S., 2004b. Flow tunnel measurements of velocities and sand flux in oscillatory sheetflow for well-sorted and graded sands. Coast. Eng., 51 (11–12), 1163–1184.] and the present numerical simulation were performed for sediment concentration, sediment velocity, sand flux and net transport rate. Four existing engineering models, together with the present two-phase flow model, were introduced for net transport rate prediction. Taking both the net sand transport rate magnitude and direction into account, the present process-based two-phase flow model provided the best estimations, which can simulate both the onshore net transport for medium/coarse sand cases and offshore net transport for fine sand cases with the agreement by a factor of 2 for almost all the considered cases. 相似文献