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1.
It is common practice to compute wave-induced loads on the immersed surface of gravity structures exposed to the wave motion and disregard the pore-water pressure variation on the foundation surface. However, when the soil is porous, wave-induced pressures propagate within the soil under the structure and result in a rather significant contribution to overall loads. This paper describes a practical method for numerical modeling of the pore pressure under a gravity platform foundation for compressible water and a rigid, but porous soil. The porous soil may be bounded by an impermeable horizontal layer at some arbitrary depth.

The paper outlines the basic boundary element procedure for pore pressure analysis and presents numerical results for a typical gravity structure as well as results for comparison with an existing analytical solution for a vertical circular cylinder.  相似文献   


2.
In this paper, the problem of incident waves propagating over a submerged poro-elastic structure is studied theoretically. A linear wave theory is used to describe the wave motion. The submerged poro-elastic structure is modeled based on Biot's theory, in which the fluid motion is described using the potential wave theory of Sollitt and Cross (1972). In the present approach, the problem domain is divided into four subregions. Using general solutions for each region and matching dynamic and kinematic conditions for neighboring regions, analytic solutions are derived for the wave fields and poro-elastic structure. The present analytic solutions compare very well with simplified cases of impermeable, rigid structures, and with those of porous structures. Using the present analytic solution, the effects of a poro-elastic submerged structure on waves are studied. The results show that softer poro-elastic structures can induce higher reflection and lower transmission from incident waves. For low permeability conditions, the elasticity of the structure can induce resonance, while higher permeability can depress the resonant effects.  相似文献   

3.
Abstract

Submarine trenching for pipeline installation in potentially unstable sediments has recently been of increasing concern. Although typical pipeline depths are less than 3 or 4 m, trenching operations generally cause local stress concentrations within the sediments and induce excess pore pressures. The result of these stress concentrations and pore pressure increases may be spreading of submarine slumps that can endanger pipelines or other nearby installations. A simplified analytical approach is described to estimate the extent of slump spreading caused by trenching. It is shown that the spreading potential is affected by many geotechnical characteristics of the sediments in addition to geomorphic processes and the oceanographic regimes governing the area. The primary geotechnical factors that influence spreading include the porepressure parameter Af , the degree of consolidation, the coefficient of earth pressure at rest, and the strength characteristics of the soil. Dimensionless parameters are developed to illustrate graphically the functional relationships among these parameters. A Gulf of Mexico soil profile is used to quantify the spreading phenomenon.  相似文献   

4.
A detailed knowledge of the wave-induced seabed instability is particularly important for engineers involved in the design procedure of many marine structures and offshore installations. In this paper, the basic aspects of such instability will be examined. The current understanding of the mechanism of the wave–seabed interaction phenomenon and available approaches will be reviewed. Based on the framework of simplified analysis, the potential for such instability will be formulated that will help engineers to identify potential unstable sediments in the vicinity of a marine structure.  相似文献   

5.
水位波动对临海重力式挡墙基坑稳定性的影响   总被引：1，自引：0，他引：1  
近年来临海(江)建设的地下工程逐渐增多,与常规静水补给条件下的基坑工程相比,受波浪、潮汐等动水作用影响的基坑可能展现出不同的性状,对该类水力条件下基坑响应问题的研究具有重要的工程意义。依托港珠澳大桥珠海连接线拱北隧道海域段基坑工程,采用PLAXIS软件对波浪、潮汐作用下重力式挡墙两侧的水土压力、基坑的稳定性进行了探讨分析。结果表明,对于均质砂质地基上的重力式挡墙,当基坑距防波堤一定距离时,波浪对其稳定性的影响可以忽略不计;潮汐在海床和基坑中的传播有滞后效应,当潮汐为最高潮位时,基坑并非处于最危险状态;潮汐作用下临海重力式挡墙基坑的稳定性可以通过拟静水位法近似分析。  相似文献   

6.
Simplified analytical solutions are presented to model the interaction of linear waves with absorbing-type caisson breakwaters, which possess one, or two, perforated or slotted front faces which result in one, or two, interior fluid regions (chambers). The perforated/slotted surfaces are idealized as thin porous plates. Energy dissipation in the interior fluid region(s) inside the breakwater is modelled through a damping function. Under the assumption of potential flow and linear wave theory a boundary-value problem may then be formulated to describe wave interaction with the idealized structure. A solution to this simplified problem may be obtained by an eigenfunction expansion technique and an explicit analytical expression may be obtained for the reflected wave height. Using the experimental work of previous authors, damping coefficients are determined for both single and double chamber absorbing-type caisson breakwaters. Based on the damping for a single perforated-wall breakwater, a methodology is proposed to enable the estimation of the damping coefficients for a breakwater with two chambers. The theoretical predictions of the reflection coefficients for the two-chamber structures using the present model are compared with those obtained from laboratory experiments by other authors. It is found that the inclusion of the damping in the interior fluid region gives rise to improved agreement between theory and experiment.  相似文献   

7.
The added mass of hull section shapes must be known, in order to carry out any studies of ship motions, which may be associated with either seakeeping or manoeuvring. Determination of the added mass in deep water can involve conformal mapping or surface singularity distributions. However, in shallow water the problem of determining the added mass is made more difficult by the proximity of the seabed. In this paper, three approaches to the problem of finding the added mass of semi-circular sections are explored. Although there is no known exact solution to this problem, the relationships given by the three methods are compared and the approximate nature of the solutions is examined. The first method is a series solution, which is taken here to include more terms than are normally given in the existing literature. The other two solutions are considered to be new, and so are given in some mathematical detail.  相似文献   

8.
We examine the role of basin-shortening on the development of structural compartments in passive margin basins. A coupled flow-deformation model is used to follow the evolution of an idealized prismatic basin during lateral shortening. This includes the deformation-induced generation (lateral compaction) and dissipation (hydraulic fracturing) of pore fluid pressures and the resulting natural evolution of an underlying décollement and subsidiary fault structures. This model is used to examine the influence of strata stiffnesses, strain softening, permeability-strain dependence, permeability contrast between layers, and deformation rate on the resulting basin structure and to infer fluid charge within these structures. For a geometry with a permeability contrast at the base of the basin a basal décollement forms as the basin initially shortens, excess pore pressures build from the impeded drainage and hydrofracturing releases fluid mass and resets effective stresses. As shortening continues, thrust faults form, nucleating at the décollement. Elevated pore pressures approaching the lithostat are localized at the hanging wall boundary of the faults. Faults extend to bound blocks that are vertically offset to yield graben-like structural highs and lows and evolve with distinctive surface topography and separate pore pressure signatures. Up-thrust blocks have elevated fluid pressures and reduced effective stresses at their core, and down-thrust blocks the converse. The development of increased permeability on localized fault structures is a necessary condition to yield this up-thrust and down-thrust geometry. In the anti-physical case where evolution of permeability with shear strain is artificially suppressed, pervasive shear develops throughout the basin depth as fluid pressures are stabilized everywhere to the lithostat. Correspondingly, permeability evolution with shear is an important, likely crucial, feedback in promoting localization.  相似文献   

9.
Chalk compaction is often assumed to be controlled by a combination of mechanical and effective stress-related chemical processes, the latter commonly referred to as pressure solution. Such effective stress-driven compaction would result in elevated porosities in overpressured chalks compared with otherwise identical, but normally pressured chalks. The high porosities that are frequently observed in overpressured North Sea chalks have previously been reported to reflect such effective stress-dependent compaction.However, several wells with deeply buried chalk sequences also exhibit low porosities at high pore pressures. To investigate the possible origins of these overpressures, basin modeling was performed in a selected well (NOR 1/3-5) offshore Norway. This modeling was based on both effective stress-driven mechanical porosity reduction, which enables modeling of disequilibrium compaction, and on stress-insensitive chemical compaction where the porosity reduction is caused by thermally activated diagenesis.The modeling has demonstrated that the present day porosities and pore pressures of the chalks could be successfully replicated with mechanical porosity loss as the only process leading to chalk porosity reduction. However, the modeled porosity and fluid pressure history of the sediments deviated significantly from the porosity and pore pressure versus depth relationships observed in non-reservoir North Sea chalks today. To the contrary, modeling which was based on thermally activated porosity loss due to diagenesis (as a supplement to mechanical compaction), resulted in modeled chalk histories that are consistent with present day observations.It was therefore inferred that disequilibrium compaction could not account for all of the pore pressure development in overpressured chalks in the study area. The observation that modeling including temperature-controlled diagenetic porosity reduction gave plausible results, suggests that such porosity reduction may in fact be operating in chalks as well as in clastic rocks. If this is correct, then improved methods for pore pressure identification and fluid flow analysis in basins containing chalks should be developed.  相似文献   

10.
One of the important geotechnical considerations for many engineering installations, such as pipelines and anchors, in an oceanic environment involving sand deposits is that of potential ocean floor instability due to the development of high pore pressures caused by the direct action of waves. This article presents a procedure for evaluating the magnitude and distribution of wave‐induced pore pressures in ocean floor deposits. The method takes into account the distribution of wave‐induced pore pressures in ocean floor deposits. The method takes into account the distribution of cyclic shear stresses in the soil profile as well as the important factor of pore‐pressure dissipation. The variation of properties within the soil profile can also be easily incorporated into the analytical procedure. The analysis provides the complete time history of pore‐pressure response and shows clearly that failure to include the pore‐pressure dissipation effects would lead to radically conservative design. The results also provide a basis for designing remedial measures, if required, to avert the development of high pore pressures and their deleterious effects.  相似文献   

11.
An analytical solution for the coupling problem of a two-dimensional tension leg structure interacting with a monochromatic linear wave train in an inviscid and incompressible fluid is presented. The tension legs are considered to be linearly elastic. The flow is further assumed to be irrotational and single-valued velocity potentials can then be defined.The boundary value problem is incorporated into a scattering and a radiation problem. The boundary value problems are then solved separately and combined to resolve all unknowns. The complete solutions of the velocity potentials are represented by the series of eigen-functions, and the surge motion of the structure is described in terms of the incident wave properties.The analytical solution is compared with a computer-coded numerical solution utilizing the boundary element method. The solutions agree very well, and both predict a resonant frequency for a specific structure which is different from the natural frequency of the structure due to the presence of the evanescent waves caused by the structure.  相似文献   

12.
《Coastal Engineering》2001,44(2):153-190
This paper summarizes the results of the European Union Marine Science and Technology (EU MAST) III project “Scour Around Coastal Structures” (SCARCOST). The summary is presented under three headings: (1) Introduction; (2) Flow and scour processes with the subheadings: flow and scour processes around vertical cylinders; flow and scour processes at detached breakwaters; flow and scour processes at submerged breakwaters; and the effect of turbulence on sediment transport; and (3) Sediment behaviour close to the structure with the subheadings: field measurement and analysis of wave-induced pore pressures and effective stresses around a bottom seated cylinder; non-linear soil modelling with respect to wave-induced pore pressures and gradients; wave-induced pressures on the bottom for non-linear coastal waves, including also wave kinematics; development of a numerical model (linear soil modelling) to calculate wave-induced pore pressures—the effect of liquefaction on sediment transport; penetration of blocks in non-consolidated fine soil; and cyclic stiffness of loose sand.The paper also includes a discussion of the role of scale effects in laboratory testing and the applicability of the results obtained in supporting engineering design.  相似文献   

13.
In this paper, a multi-channel structure was developed to attenuate waves with various wave periods. By ignoring energy losses and the factor of channel width, a simple and straightforward method was used to tackle this problem. The theoretical solution showed that a single reflected channel structure could attenuate waves of a certain wave period, while a multi-channel structure could attenuate waves with various wave periods. If an interval of 0.05<relative water depth<0.15 is concerned, a structure consisting of four reflected channels could provide a transmission coefficient of less than 0.2. Experimental tests were conducted to verify the theoretical solutions. Both theoretical solution and experimental data indicated that waves with various wave periods would be effectively attenuated after passing through the multi-channel structure. Although some factors are neglected in treating this problem, the method is applicable. An allowed transmission coefficient can be provided by a multi-channel structure only if the computed peak value is not larger than that value.  相似文献   

14.
A new empirical pore pressure transform has been developed that includes many of the advanced, state-of-the-art concepts that are useful in today’s pore pressure estimation and theory. The rhob-velocity-effective stress (Rho-V-e) method produces a model-driven, stand-alone set of “virtual” rock property relationships, which at intermediate positions are consistent with Bowers method default values for the Gulf of Mexico. The RhoVe method uses a single transform to convert both compressional sonic and bulk density to common estimates of effective stress and pore pressure where convergence of the two transformed properties offers a robust solution.Velocity-density conversion functions are mathematically linked to a continuous series of velocity-depth normal compaction trend functions. The calculations are limited by bounding end-member curves that provide a basis for intermediate (fractional) solutions of velocity-effective stress and density-effective stress relationships that are applied to a well of interest.Paired “virtual” velocity-depth compaction trends were iteratively solved by using published theoretical smectite and illite porosity trends and velocity-depth normal compaction trends. By using the RhoVe-derived velocity-density functions that match the well of interest in cross-plot, normal effective stress for each end-member and intermediate solution can be calculated. Effective stress is calculated by taking the difference between the integrated density-depth virtual overburden profile, converted from velocity-depth, and the inclusion of hydrostatic pressure. The method produces robust solutions as tested on multiple deep water Gulf of Mexico wells, and extends the predictability of high-velocity, low-effective stress rock types such as those found in the Deepwater Gulf of Mexico Wilcox-equivalent Paleogene and older section. The velocity-effective stress trend curves can also improve pore pressure characterization of the overlying overburden section extending to the mud line. Advantages of the RhoVe method are that it can be made interactive and fast, relative to the application of other acoustic transform methods.This paper attempts to build on previous efforts by other workers to include the role of clay type, clay volume and diagenesis on altering velocity-effective stress relationships and presents a technique in which the effects of clay diagenesis and other factors may be captured and utilized empirically for pore pressure analysis and prediction.  相似文献   

15.
Let A,B,C denote three mainland‐stations whose positions are unknown. Let D,E,F denote the positions of a moving ship at three different moments of time. At any of the locations D,E,F, the three azimuths to the target‐stations A,B,C are measured. The problem is to determine from these nine measurements the mutual positions of all stations A,B,C,D,E,F up to a common shift and a change of scale. The problem was formulated by J. H. Lambert in 1765. He also specified a mathematical solution. In this paper so‐called “critical configurations”; are investigated. It is shown that there are nontrivial configurations of the six stations A to F, such that solution of the problem is not unique (critical configuration of the first kind). There is a larger set of configurations, such that the linearized problem admits of an infinity of solutions (critical configurations of the second kind). In the latter case, the original nonlinear problem may be solvable, but the solution is highly unstable with respect to perturbations of the measurements. The main result obtained is as follows. If all stations A to F are located on a second degree curve, i.e., on a conic section, then the configuration is critical, at least of the second kind. The configuration continues to be critical if arbitrarily many observations and target‐points are added which are all situated on the second‐degree curve.  相似文献   

16.
Response of a porous seabed around breakwater heads   总被引：1，自引：0，他引：1  
J. Li  D.-S. Jeng   《Ocean Engineering》2008,35(8-9):864-886
The evaluation of wave-induced pore pressures and effective stresses in a porous seabed near a breakwater head is important for coastal engineers involved in the design of marine structures. Most previous studies have been limited to two-dimensional (2D) or three-dimensional (3D) cases in front of a breakwater. In this study, we focus on the problem near breakwater heads that consists of incident, reflected and diffracted waves. Both wave-induced oscillatory and residual liquefactions will be considered in our new models. The mistake in the previous work [Jeng, D.-S., 1996. Wave-induced liquefaction potential at the tip of a breakwater. Applied Ocean Research 18(5), 229–241] for oscillatory mechanism is corrected, while a new 3D boundary value problem describing residual mechanism is established. A parametric study is conducted to investigate the influences of several wave and soil parameters on wave-induced oscillatory and residual liquefactions around breakwater heads.  相似文献   

17.
To simplify the complicated mathematical process, most previous investigations for the water waves-seabed interaction problem have assumed a porous seabed with isotropic soil behavior, even though strong evidence of anisotropic soil behavior has been reported in soil-mechanics literature. This paper proposes an analytical solution of the short-crested wave-induced soil response in a cross-anisotropic seabed. As shown in the numerical results presented, the wave-induced seabed response, including pore pressure, effective stresses and soil displacements, is affected significantly by the cross-anisotropic elastic constants. A parametric study is performed to clarify the relative differences in pore pressure between isotropic and cross-anisotropic solutions.  相似文献   

18.
ABSTRACT

The elastic mechanical response of porous materials under a heat source has many applications in civil engineering and has received considerable attention in the geotechnical literature. In this paper, a Kelvin viscoelastic model is combined with the thermohydromechanical governing equations for marine clay and solved using a numerical inversion of the inverse Laplace transform in the time domain. After validation against existing analytical solutions, numerical parametric studies are conducted to investigate the influence of viscosity on temperature, excess pore pressure, and displacement. It is shown that viscosity has little influence on temperature, a modest influence on displacements, and a quite significant influence on excess pore pressure.  相似文献   

19.
Design analysis of a truss pontoon semi-submersible concept in deep water   总被引：3，自引：0，他引：3  
Truss pontoon semi-submersible (TPS) is a new offshore structure concept in industry, where a truss spar is used to create the added mass by the heave plates. In the present paper, the effect of the heave plates on the vertical motion of the floating structure is demonstrated. A TPS is analyzed by utilizing the linear diffraction theory as well as the linear part of the Morison equation. The close agreement of the analysis results with the experimental results suggests that the simplified Morison equation can be used for the present analysis without sacrificing the quality of the results. However, good engineering judgment is required for estimating the values of the hydrodynamic coefficients as well as the amount of damping introduced in the structure. It is also found that the heave plates indeed introduce large added mass and considerable damping in the system motion in the vertical direction such that the resonant oscillation becomes less of a problem. This suggests that the TSP concept may have merits as a heave-controlled floating production structure in the deepwater development.  相似文献   

20.
Underwater implosion, the rapid collapse of a structure caused by hydrostatic pressure, is a fully coupled, highly dynamic and nonlinear fluid-structure interaction (FSI) problem. The primary motivation behind studying implosion is the short-duration, high-pressure pulse generated in the surrounding water. This paper presents a simplified analytic method to estimate the energy in the pressure pulse, based on potential flow theory. The method accounts for the varying fluid pressure and accompanying FSI. The focus is on long, thin, unstiffened metallic cylindrical shells that collapse in mode 2. The implosion pulse energy is shown to be equal to the maximum system kinetic energy developed during collapse. The kinetic energy is calculated using an energy balance approach and analytic solutions for plastic energy dissipation and energy required to compress the internal air. The time-varying fluid pressure, and subsequently the work done by the fluid on the cylinder, is found using a novel explicit time-stepping methodology. The result is a pseudo-coupled analytic solution for the fluid pressure time history and implosion pulse energy. Solutions for pulse energy agree with RANS numerical simulations within 5%.  相似文献   

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