半椭圆型防波堤水动力特性的数值模拟

该文提出了一种新型防波堤结构：半椭圆型防波堤。采用FLOW 3D建立数值波浪水槽，模拟了波浪与半椭圆型防波堤的相互作用，并通过物理模型试验验证了数值模型的合理性。结合数值模拟结果分析了波浪参数变化对半椭圆型防波堤水动力特性的影响，结果表明：反射系数随着堤顶高程和水位之差h_s与设计波高H的比值h_s/H增大而增大，透射系数随h_s/H增大而减小；在本研究波浪周期范围内，水深D不变时，半椭圆型防波堤对周期T较大的波浪的挡浪效果优于周期较小的工况。随着D与半椭圆型防波堤立轴b的比值D/b的增大，挡浪效果变差。波浪力随着h_s/H的减小而增大，随H与波长L的比值H/L的增大而减小。相同工况下，随着半椭圆型防波堤卧轴a与立轴b的比值增大，结构所受水平波浪力减小，竖直波浪力增大，防波堤自重增大，防波堤稳定性增强。半椭圆型防波堤的优势在于，其卧轴和立轴的大小关系可以根据不同的工程条件自行设计，若以椭圆长轴卧放，则比防范相同水深的半圆型防波堤更适用于软弱基床，从而更加安全可靠；若以短半轴立放，则在防范相同水深的前提下，比...     

新型半潜式浮式风机动力特性试验研究

以新型半潜式浮式风机系统为研究对象,建立全耦合物理水池试验模型。通过系列水池模型试验,对浮式风机的固有特征和多物理场全耦合作用下系统总体响应进行试验研究。研究结果表明,系统六自由度固有周期均远离实际海上波浪频率范围,作业环境3.92 m有义波高和极端环境9.5 m有义波高下纵/横摇运动最大值显著小于设计要求最大值约50%和10%,这表明新型浮式平台具有优良的运动稳性。试验中还发现,作业过程中塔筒顶部载荷存在叶片3P振动与塔筒一阶固有频率多模态叠加谐振现象,应当在结构优化中给予关注。     

基于标准化水平残余位移的沉入式钢圆筒防波堤抗震性能研究

根据国际航运协会《港口结构抗震设计指南》、日本港口结构震害调查结果和钢圆筒结构特点,将标准化水平残余位移作为沉入式钢圆筒防波堤的抗震性能指标,同时运用振动台试验和数值模拟研究了回填砂地基防波堤的动力特性,并评估了防波堤的抗震性能。结果表明,当设计地震动为1.7 m/s2时回填砂地基防波堤处于可服役状态,设计地震动为3.2 m/s2时防波堤处于可修复状态,不满足防波堤性能等级为S的要求,建议在设计中考虑远场地震和近场地震对防波堤抗震性能的影响。振动台试验研究发现当地震波加速度峰值为3.2 m/s2时筒外回填砂由于液化导致其对防波堤的侧向力改变,防波堤试验模型发生明显的倾斜现象,建议在地基加固设计过程中重点考虑筒外回填砂。当地震波加速度峰值为1.7 m/s2和3.2 m/s2时,钢圆筒筒壁应力最大值随高度的增加均呈现减小的趋势,同时钢圆筒防波堤存在两处薄弱环节,分别位于筒底及泥面处,因此结构设计时应优先考虑。     

基于EEMD-HHT的近岸冲流带波浪非线性波动特征分析

冲流带复杂水流运动特性是研究近岸带物质输运的关键,其中波要素的历时变化具有非平稳性、非对称性和多尺度变化等复杂非线性波动特性,分析其作用周期及趋势规律,对认识冲流带的复杂水沙动力过程至关重要。基于溃坝原理产生涌波,采用水槽试验对涌波作用下不同坡度下冲流带波浪非线性波动特征开展研究。结合EEMD和HHT方法对试验波要素数据进行统计分析,得出波浪归一化能量谱、边际谱和边际能量谱,并结合功率谱密度分析水体波动对岸滩作用的影响。结果表明,冲流带的波浪波能主要集中在低频处,约低于1 Hz。在该研究的3种试验工况下,沿着岸滩向岸方向冲流带断面最大瞬时能量会逐渐衰减,当水流分别作用2～3 s,3～5 s和3～6 s时接近波浪最大瞬时能量,对岸滩作用达到最大;岸滩坡度越陡,最大瞬时能量值出现的时间越早,对床面的作用越大。     

独柱墩-自浮式防船撞装置波浪荷载研究

针对独柱墩-自浮式防船撞装置耦合体系,开展室内波浪力试验并总结相关规律,利用试验结果验证校准AQWA数值模型。根据结构所受波浪压强的分布情况,利用Morison公式提取相应的荷载并得到结构水动力系数。考虑波浪高度、波浪周期、防撞装置断面形式和大小、防撞装置自浮比等影响因素,计算结构惯性力系数和接触力系数与相关因素的定量关系。研究表明：自浮式防撞装置起伏运动产生辐射波浪,使墩柱波压强数值偏大但不改变总体分布趋势。结构间接触力随机变化,可把结构接触力与墩柱波浪力之间的比值定义为接触力系数。计算得耦合体系中墩柱的惯性力系数达到2.175左右,防撞装置的惯性力系数达到2.125左右,接触力系数达到1.340左右。     

漂浮式潮流能发电装置振动与波浪响应试验研究

为了研究基于竖轴水轮机的漂浮式潮流能发电装置的振动与波浪响应,设计试验模型和装置,进行水轮机转与不转的静水拖航试验和波浪试验,测量系泊链拉力和模型的纵摇响应。试验发现,系泊系统具有高频振动现象,V等于0.7m/s、0.9m/s,水轮机不转时,以及V等于0.9m/s,水轮机转动时,系泊系统具有明显的慢摇现象,水轮机转动还带来了系泊链的低频拉力响应。水轮机转动使系泊系统的纵摇周期增大,载体模型的共振波长增加。与水轮机不转时相比,水轮机转动使低波长-载体模型长度比下模型的纵摇运动响应减小,对高波长-载体模型长度比下模型的纵摇运动影响较小。试验研究可为基于竖轴水轮机的漂浮式潮流能发电装置的理论研究与工程应用提供参考和借鉴。     

卷破波冲击新型桩板桥梁结构水动力特性试验研究

依托福建省滨海国道涉海浅滩段新型桩板桥梁结构工程,通过波浪水槽开展卷破波冲击桩板桥梁结构水动力特性试验,研究了三个阶段卷破波冲击作用下波浪爬高和桩板桥梁结构所受波浪力水动力特征,并与规则波冲击作用试验结果进行对比,分析了入射波高、波浪周期、水深对波浪爬高和波浪力的影响规律。结果表明：三个阶段卷破波冲击新型桩板桥梁结构的水动力特性显著不同,破碎前阶段和破碎中阶段卷破波会出现明显的波浪爬高现象,破碎前阶段卷破波爬高后的波面高程可达规则波的1.99倍;破碎前阶段的水平波浪力最强,是同阶段竖向波浪力幅值的4.48倍,可达规则波水平波浪力的3.08倍。波浪特征参数和水深对三个阶段卷破波冲击水动力特性影响显著,入射波高和水深的增加会使破碎中阶段卷破波的波面高程和竖向波浪力超过其他阶段;波浪周期的增加会使破碎后阶段卷破波冲击前波面高程和破碎前阶段的竖向波浪力超过破碎中阶段卷破波。     

浮式鲆鲽类网箱在波流场中动态响应的数值模拟

根据浮式鲆鲽类养殖网箱的结构特点,基于有限元方法对波流共同作用下网箱的运动受力进行数值模拟,并将数值模拟结果与水槽模型实验结果进行比较分析。结果显示:在3种工况条件下,计算机模拟值与实验值吻合较好,验证了程序及数学模型的可靠性。借助于计算机3D可视化技术,可对波流场中网箱结构的运动过程进行虚拟呈现。其中,当流速为26cm/s时,网箱底框架最大倾角可达9°;波浪作用下底框架最大倾角为12°。当波流联合作用时,底框架最大倾角与最大锚绳受力值均高于波浪或水流单独作用时。当水流入射方向与波浪成角度时,底框架最大倾角与锚绳受力随着夹角的增加而减小。今后将通过海上实测进一步对模拟结果进行验证,使数值模拟能够更加精确。     

复式防波堤断面尺度对波浪爬高的影响研究

数值模拟是求解防波堤爬高问题的重要方法。以Navier-Stokes方程为控制方程,该文建立了基于紧致插值曲线法(CIP法)的二维不可压缩流体的有限差分数值模型。通过分步算法对时间积分求解控制域,采用双曲正切函数自由面捕捉法(THINC法)对自由液面进行捕捉,采用浸入边界法IBM对固体边界进行处理,将波浪爬高问题视为固-液-气多相流问题。通过建立二维数值水槽,对波浪爬高越浪问题进行数值验证;进而在相同波浪条件下,对不同断面尺寸的复式防波堤进行波浪爬高的数值模拟。结果表明:该模型可以较好地模拟波浪过程中的变形、翻卷、破碎等强非线性现象,得出最大爬高与复式防波堤尺寸之间的关系,从而给出了最小爬高时对应的防波堤断面尺度。     

防波堤帷幕尺度对波浪力和消浪性能的影响研究

帷幕式防波堤下部透水,利于港内外的海水交换,防止水质恶化,维持原始水域生态平衡,因此模拟波浪与防波堤的相互作用具有重要的现实意义。该文基于高阶紧致插值CIP(Constrained Interpolation Profile)方法的二维波浪数值模型水槽,通过与文献结果进行比较,结果表明：该文数值模型能够有效地模拟孤立波在冲击帷幕式防波堤过程中的波浪破碎等强非线性现象。通过数值模拟,描述了帷幕式防波堤在不同的宽度和浸没深度情况下与孤立波之间的相互作用中流速和涡度的演变过程,并讨论了孤立波波高和帷幕式防波堤结构尺寸对反射、透射、耗散系数以及在帷幕式防波堤上冲击力的影响。研究表明：帷幕式防波堤的相对浸没深度越大时,消浪效果良好,同时帷幕式防波堤的相对宽度对消浪效果的影响较大。     

Irregular wave transmission over a submerged breakwater

Irregular wave tests were conducted in a laboratory flume with an ‘Odessa-type’ bevelled-block submerged breakwater on a sloping bottom. The incident and transmitted waves were subjected to probabilistic and spectral analysis. Although the incident wave heights and periods are described respectively by the Gluhovski and the Rayleigh distributions, for the square of the wave periods, the transmitted heights and periods conform to the Rayleigh distribution irrespective of the depth of submergence of the breakwater. The significant wave heights (H _s) give transmission coefficients comparable to the corresponding monochromatic waves, but theH _max and give 50% higher and upto 28% lower values respectively, the difference increasing with the depth of submergence of the breakwater. The peak frequency of the spectrum does not vary on transmission. Resonant frequencies, where the wave energy is transmitted almost completely, are observed in the process. The resonance occurs at frequencies 1·4, 3·8, 5·6 and 7·0 rad/s, and they remain constant for different submergences of the breakwater. The presence of similar frequencies is also found in the case of monochromatic waves, although the tests are limited. Application of irregular wave tests is recommended in the design of submerged breakwaters. The laboratory studies were conducted under the guidance of Prof A V Mihailov and Dr I S Halfin of the Moscow Civil Engineering Institute,ussr, as a part of the author’s Ph. D. dissertation.     

Effect of current on spectrum of breaking waves in water of finite depth

This paper presents an approximate method to compute the mean value, the mean square value and the spectrum of waves in water of finite depth taking into account the effect of wave breaking with or without the presence of current. It is assumed that there exists a linear and Gaussian ideal wave train whose spectrum is first obtained using the wave energy flux balance equation without considering wave breaking. The Miche wave breaking criterion for waves in finite water depth is used to limit the wave elevation and establish an expression for the breaking wave elevation in terms of the elevation and its second time derivative of the ideal waves. Simple expressions for the mean value, the mean square value and the spectrum are obtained. These results are applied to the case in which a deep water unidirectional wave train, propagating normally towards a straight shoreline over gently varying sea bottom of parallel and straight contours, encounters an adverse steady current whose velocity is assumed to be uniformly distributed with depth. Numerical results are obtained and presented in graphical form.     

An integral equation method for the diffraction of oblique waves by an infinite cylinder

A hybrid integral equation method is formulated to study the diffraction of oblique waves by an infinite cylinder. The water depth and the geometry of the floating cylinder are assumed to be uniform in the y-direction (one of the horizontal axes). Numerical discretization and integrations are performed in the vertical plane. Analytical solutions are used in far fields such that radiation boundary conditions are satisfied. Numerical results are obtained for the case of wave scattering by a floating rectangular cylinder in a constant water depth. The accuracy and efficiency of present method are compared with those obtained by other numerical techniques.     

Wave propagation passing over a submerged porous breakwater

A linear model of waves propagating over a submerged porous breakwater is derived from two coupled boundary-value problems, each of which represents the governing equation in a different medium. The model is similar to the shallow-water equations (SWE), with a damping term proportional to the character of the porous breakwater. Therefore, waves traveling above the breakwater will be absorbed, and the amplitude decreases. The wave propagation passing over the submerged breakwater for monochromatic and solitary waves is analyzed. For monochromatic waves, the numerical solution agrees with the analytical. The amplitude decreases exponentially with respect to the space variable in the region above the breakwater. The reflected wave is also analyzed when the model is combined with a model using the shallow-water equations.     

Hydroelastic Behavior of a Floating Ring-Shaped Plate

The interaction between incident surface water waves and floating elastic plate is studied. This paper considers the diffraction of plane incident waves on a floating flexible ring-shaped plate and its response to the incident waves. An analytic and numerical study of the hydroelastic behavior of the plate is presented. An integro-differential equation is derived for the problem and an algorithm of its numerical solution is proposed. The representation of the solution as a series of Hankel functions is the key ingredient of the approach. The problem is first formulated. The main integro-differential equation is derived on the basis of the Laplace equation and thin-plate theory. The free-surface elevation, plate deflection and Green’s function are expressed in polar coordinates as superpositions of Hankel and Bessel functions, respectively. These expressions are used in a further analysis of the integro-differential equation. The problem is solved for two cases of water depth infinite and finite. For the coefficients in the case of infinite depth a set of algebraic equations is obtained, yielding an approximate solution. Then a solution is obtained for the general and most interesting case of finite water depth analogously in the seventh section. The exact solution might be approximated by taking into account a finite number of the roots of the plate dispersion relation. Also, the influence of the plate’s motion on wave propagation in the open water field and within the gap of the ring is studied. Numerical results are presented for illustrative purposes.     

Deflection of a floating sea ice sheet induced by a moving load

A large number of time-deflection curves was obtained from a field experiment carried out on the sea ice sheet at Lake Saroma, Hokkaido, Japan, using a Skidoo snowmobile as a moving load with the test speed changed from 0 to 14.2 m/s. The thickness of the ice sheet was 0.17–0.18 m, the ice temperature was ?2.5 to ?4°C at the surface, and the water depth was 6.8 m beneath the ice sheet. The experimental results indicated the existence of a critical speed u_c and its value was estimated to be 5.8 m/s. At speed above it two ice waves were generated, one ahead of and the other behind the vehicle. A variation of wavelength with vehicle speed was expressed by a modified dispersion relation for the flexural ice wave in a floating ice sheet. The ice deflection pattern was classified into five stages. At u_c the depression around the vehicle was maximal in depth and minimal in width. The center of the depression began to lag behind the vehicle even at fairly low speeds below u_c.     

Short term motion analysis of icebergs in linear waves

The need for the analysis of the motion of icebergs in waves is presented and the possible interaction effects between the iceberg and waves as well as its interaction with offshore structures is briefly discussed along with the hydrodynamic aspects involved in the analysis of wave induced motions of icebergs. A combined theoretical and experimental study for the estimation of the first order wave induced motions in surge and heave of a free floating iceberg in a regular wave field is presented. The theoretical model is based on the mathematical formulations of Garrison (1979) and Standing (1979) which employ a three dimensional source distribution technique. The computed model results have been compared with the previous analytical model and good agreement has been found. The computed results are then compared with the measured heave and surge motions of the model icebergs which agree quite well, within the limits of experimental error. The computational and experimental models are not meant to address in detail all the hydrodynamic aspects of wave interaction with a free floating iceberg. Only the oscillatory motions of icebergs have been computed and measured. The results indicate that the surge and heave velocity of model icebergs, with a draft to water depth ratio of less than 0.1 can be greater than 0.8 times the water particle velocity when the iceberg horizontal dimension is less than 0.3 times the wavelength. Additional computational and experimental model studies showed that the surge motion is reduced to less than 0.1 times the particle velocity when the draft to depth ratio is about 0.9 and the horizontal dimensions of the iceberg are increased to 0.5 times the wavelength. The heave motion for the same situation is reduced to about 0.5 times the particle velocity.     

Scattering of oblique water waves by two thin unequal barriers with non-uniform permeability

The scattering of obliquely incident water waves by two unequal permeable barriers with variable permeability is investigated for two types of barriers, namely partially immersed barriers and bottom-standing barriers, under the consideration of the theory of linear water waves. The barriers are present in water of uniform finite depth. The velocity potential is expanded by using Havelock’s expansion of water wave potential and employing Havelock’s inversion formula together with the conditions on the permeable barriers; the boundary value problem is reduced to a coupled Fredholm-type vector integral equations. The integral equations are solved using the multi-term Galerkin approximation where the unknown functions are approximated in terms of Chebyshev polynomials. The numerical results for the reflection coefficient, the transmission coefficient and the energy dissipation are depicted graphically. Known results for two identical as well as two non-identical impermeable barriers and for a single and twin permeable barriers are recovered in the limiting cases.     

Numerical modelling of wave-induced currents in a breakwater situation

A numerical model system is developed to describe waves and wave-induced currents in a breakwater situation, where refraction, diffraction, reflection and wave–current interaction may all play important roles in the transformation of waves. A turbulence transport model is employed to estimate the eddy viscosity, and the friction factors associated with the major variables are clearly defined using a high level closure of combined flow bed friction. The model system is tested against a laboratory situation, and the effects of reflection are demonstrated on the wave-induced currents as well as on the wave distribution.