Generation of long waves in a basin by short-term displacements of the lateral boundary

A simplified model of generation of tsunamis by earthquakes occurring on the dry land is proposed. The transfer of horizontal momenta to the liquid medium is realized via the horizontal displacements of the vertical lateral boundary according to a given time law. The problem is solved by the method of finite differences for elastic and inelastic displacements of the lateral boundary of the basin. The efficiency of the process of generation of tsunami-type waves by similar external disturbances is analyzed. It is shown that the efficiency of generation of the surface waves by the elastic displacements of the lateral boundaries of the basin is much higher than that in the case of displacements of the boundary with residual deformations     

Displacements induced by breaking waves on axially loaded cylindrical shells

Forced vibrations of the walls of a vertical cylindrical shell under the impact of a breaking wave are studied theoretically. The wave action is modelled as a pressure distribution which varies in time and space. A linear dynamic analysis of the transient response is carried out by means of the modal superposition technique, in which the static stresses are considered. The results show that in thin shells, the transient displacements could be of the order of the thickness of the shell. It is suggested that these large displacements could play an important role in eroding the buckling capacity of the structural component. The problem of limiting the dynamic displacements is discussed by interaction diagrams for static axial load-dynamic lateral pressure, and by examination of the confluence of shell and wave parameters for which the transient displacements do not exceed a given value.     

Towed array shape estimation using Kalman filters-theoreticalmodels

The dynamical behavior of a thin flexible array towed through the water is described by the Paidoussis equation. By discretizing this equation in space and time a finite-dimensional state-space representation is obtained where the states are the transverse displacements of the array from linearity in either the horizontal or vertical plane. The form of the transition matrix in the state-space representation describes the propagation of transverse displacements down the array. The outputs of depth sensors and compasses located along the array are shown to be related in a simple, linear manner to the states. From this state-space representation a Kalman filter which recursively estimates the transverse displacements and hence the array shape is derived. It is shown how the properties of the Kalman filter reflect the physics of the propagation of motion down the array. Solutions of the Riccati equation are used to predict the mean square error of the Kalman filter estimates of the transverse displacements     

基于拉格朗日方法的南海自动剖面浮标轨迹模拟系统*

南海自动剖面浮标轨迹模拟系统包括高分辨率模式流场、拉格朗日追踪模型和垂向浮标运动参数化方案等三个核心部分。该系统可在南海范围内模拟两类自动剖面浮标: 传统自动剖面浮标(停滞深度为1000m, 最大下潜深度为2000m)和新型深海自动剖面浮标(停滞深度为距海底500m)。通过对南海现有的6个传统浮标的模拟, 该系统可以预测其100d内的漂流轨迹。通过与真实浮标轨迹数据的对比, 验证了该模拟系统的准确性。此外, 根据该系统, 我们初步探讨了深海自动剖面浮标阵列(时空分辨率为2°×2°×30d)在南海内区布放方案的可行性。该模拟系统的建立和完善将有助于对现有传统剖面浮标布放策略进行优化, 并对未来深海剖面浮标在南海的推广应用提供初步的理论依据。     

Marine pipeline dynamic response to waves from directional wave spectra

A methodology has been developed to calculate the dynamic probabilistic movement and resulting stresses for marine pipelines subjected to storm waves. A directional wave spectrum is used with a Fourier series expansion to simulate short-crested waves and calculate their loads on the pipeline. The pipeline displacements resulting from these loads are solutions to the time-dependent beam-column equation which also includes the soil resistance as external loading. The statistics of the displacements for individual waves are combined with the wave statistics for a given period of time, e.g. pipeline lifetime, to generate probabilistic estimates for net pipeline movement. On the basis of displacements for specified probability levels the pipeline configuration is obtained from which pipeline stresses can be estimated using structural considerations, e.g. pipeline stiffness, end restraints, etc.     

Creep behavior of submarine sediments

A series of experiments on drained creep of marine sediment indicates that strength degradation results from the creep process, which implies an associated reduction in slope stability. Furthermore, the highest creep potential of a sediment may be at its preconsolidation stress. Results from the experiments on samples from Georges Bank continental slope were also used in conjunction with a preliminary theoretical model to predict creep displacements. For the case illustrated in this report, steep slopes (>20°) and thick sections (>30 m) give rise to substantial creep and probable creep rupture; as angles or thicknesses decrease, displacements rapidly become negligible.Creep may be a significant geologic process on many marine slopes. Not only can it cause major displacements of surface sediment, but it may also be the precursor to numerous slope failures.     

基于Track分析日本3·11地震对周围IGS站的影响

2011年3月11日日本宫城县(38.322°N,142.369°E)发生Ms9.0级地震,利用日本本岛及周围IGS站的观测数据,采用GPS静态定位、动态差分定位两种方法进行数据处理,计算出了若干站点地震前后的位移量。地壳变形分析结果表明:地震对周围IGS站的位移有不同程度的影响,最大可达到2.46m,所有观测站都向东方向运动,并且计算得出GPS速度场;通过选择较稳定的IGS站作为参考站,计算了2个观测站的动态变形,同时得到了地震波的传播速度。     

Hydroelasticity of a floating plate in multidirectional waves

The membrane forces are included in the hydroelastic analysis of a floating plate undergoing large vertical deflections in regular monochromatic multidirectional waves. The first-order vertical displacements induced by the linear wave exciting forces are calculated by the mode expansion method in the frequency domain. The second-order vertical displacements induced by the membrane forces are calculated by the von Karman plate theory. The results show that the membrane contribution both in terms of the axial stresses and the effect on the bending stresses can be important.     

广西海岛海岸线变迁与动态变化及影响分析

海岛不仅具有很高的资源、生态和经济价值,而且对维护国家海洋权益具有重大意义。近年来,全球气候异常,海平面上升、海水入侵的出现改变了岛陆岸线和岛滩的生态环境,同时也使高程较低的海岛面临存在的威胁。文章通过选取广西省具有代表性的海岛,研究了海岛海岸线的变迁与动态变化的成因,同时,对海岛岸线变迁作出了预测及影响分析。     

Dynamic Load Identification in Time Domain

- In the time domain method the dynamic load is successfully identified when the accelerations, velocities and displacements or velocities and displacements of the structure are known. But in engineering practice or experiments usually only the acceleration response is recorded. In this paper an improved time domain method is proposed for dynamic load identification. In this method by using of Duhamel integral, only the acceleration response is required for load identification. As an application of the present method, the dynamic ice load on a Bohai offshore platform is identified based on some measured acceleration. The identified values of ice load are in good agreement with the measured ones.     

Properties of geogrid-reinforced marine slope due to the groundwater level changes

Evaluation of slope stability, especially in the absence of a proper bed such as marine soils, is one of the most important issues in geotechnical engineering. Using geogrid layers to enhance the strength and stability of embankments is regarded as a commendable stabilization method. On the other hand, groundwater level erratically fluctuates in coastal areas. Therefore, the aim of this research is to study the effects of groundwater level changes on stability of a geogrid-reinforced slope on loose marine soils in Qeshm Island, Iran. At first, geotechnical properties of the site were obtained by comprehensive series of geotechnical laboratory and in situ tests. Then, by simultaneous changes of groundwater level and several parameters such as embankment slope, loading, geogrid length, geogrid number, and tensile strength of geogrid, different characteristics such as embankment safety factor (SF), vertical and horizontal displacements at embankment top and embankment base were studied. It was observed that groundwater level had significant effects on behavior of the embankment. For most of the observations, by decreasing the groundwater level, the displacements decreased and consequently safety factor increased. Increasing the length, number, and tensile strength of geogrid led to the reduction of displacements and an increase in the safety factor.     

Effects of backfill on seismic behavior of rectangular tanks

The reliability and/or stability of the lifeline structures against failure under seismic loads are of critical concern, and must be studied carefully. Therefore, the main objective of this paper is to demonstrate the commonly encountered backfill effects on the dynamic response of rectangular tanks. However, only the exterior wall of the tank which interacts with both the backfill and fluid is tackled, as each part of the structure shows considerable differences in terms of both the load bearing mechanisms and the geometrical and positional differences. Finite element analyses are employed, taking into consideration the fluid-wall-backfill interaction. The analyses are conducted to observe whether or not both backfill and wall behavior can be affected by variation of the internal friction angle. For that purpose, some comparisons are made on vertical displacements of the backfill, roof displacements, stress responses, etc., by means of internal friction angle variations of the backfill from 25° to 40°. Consequently, it is observed that the variations on maximum vertical displacements are affected considerably. In contrast, the maximum stress responses are affected partially. However, the inertial effects of the backfill show that pseudo-static approximations may be insufficient to understand the dynamic behavior of the backfill-wall-fluid system.     

Focused wave evolution using linear and second order wavemaker theory

In this paper, the evolution of focused waves using different paddle displacements (piston type) under laboratory conditions is presented. It is well known that in intermediate water depths, linear paddle displacements will generate spurious, free, sub and super harmonics. Thus, a second order correction to suppress these spurious free sub and super harmonics was used to generate the focused waves. The focused waves were generated in the laboratory using a linear superimposition principle, in which the wave paddle displacement is derived based on the sum of a number of sinusoidal components at discrete frequencies, whose phases are accordingly set to focus at a particular location. For this method of generation, the second order wave maker theory proposed by Schäffer [24] can be easily adopted and was used in the present study. Two different centre frequencies (f_c = 0.68 Hz and 1.08 Hz) with three different bandwidth ratios (Δf/f_c = 0.5, 0.75 and 1.0) were tested in a constant water depth, to consider both narrow and broadband spectra. These test cases correspond to wave focusing packets propagating in intermediate and deep water regions. Further, for each wave packet, two different amplitudes were considered in order to analyze non-breaking and breaking cases. Thus, by systematically generating the wave packets using the linear and second order paddle displacements, the analysis was carried out for the spectral and temporal evolution of selected long waves. The temporal evolution of the selected harmonics was analyzed using the Inverse Fast Fourier Transform (IFFT), to show the propagation of the spurious, free, long waves. Further, the variations in energy for the lower, higher and primary frequency ranges are reported for different wave paddle displacements. The analysis revealed that for the broadband spectrum the differences are more pronounced when using linear paddle displacements. We have also noticed a shift in focusing/breaking location and time (i.e. premature) due to the increase in crest height using linear displacements. The experiment data used in this paper has been provided as a supplementary, which can be used to validate the numerical models.     

Cyclic pullout behavior of helical anchors for offshore floating structures under inclined loading condition

Helical anchors are an effective option to support offshore floating structures with mooring and anchoring systems, where wave and tidal forces are the predominant load components leading to cyclic and inclined loading conditions. In this study, the cyclic and inclined pullout load carrying behavior of helical anchors was investigated. Large-deformation finite element (FE) analysis using the coupled Eulerian–Lagrangian (CEL) method was performed to simulate the cyclic pullout load response of helical anchors. Various configuration conditions of the helical anchor and loading direction, including the number and diameter of helical plate, plate arrangement and load inclination angle (θ), were considered in the analysis. Induced displacements were most significant during the first loading cycle, whereas those for subsequent loading cycles were relatively small. The geometry condition of the helical anchor less affected the pullout load carrying behavior as θ increased. The horizontal displacements (δ_h) were larger than the vertical displacements (δ_v) when θ was larger than 30°. When θ was smaller than 30°, δ_v was more dominant component. It was found that the configuration with top-down increasing diameter was more effective to enhance the pullout load carrying behavior than the conventional bottom-up increasing diameter configuration.     

Dynamic response of a poro-elastic soil to the action of long water waves: Determination of the maximum liquefaction depth as an eigenvalue problem

In this work, a theoretical analysis of the dynamic response of a poro-elastic soil to the action of long water waves is conducted. For some combinations of the physical parameters of the soil and the water waves, the vertical stress tends towards zero at a certain unknown depth in the soil, as measured from the top of that medium. Under this condition, the liquefaction of the soil is imminent, at which time the excess pore pressure is essentially equal to the overburden soil pressure. Physical problems of this type have been widely studied in the specialized literature. However, most major studies have focused on solving the governing equations together with a liquefaction criterion. Here, the maximum momentary liquefaction depth induced by long water waves is considered as part of the problem, which is treated as an eigenvalue problem. To solve this problem, the governing equations are written in dimensionless form. The theoretical results show that for long waves, the horizontal displacements are smaller in magnitude than the vertical displacements, and when the wavelength or wave period increases, the maximum liquefaction also increases. Analytical solutions for the excess pore pressure and the horizontal and vertical displacements are obtained. The analytical results for the pore pressure are found to be very close to the analytical results reported in the specialized literature.     

Calculation of Tidal Displacements and Tilts for a Nonelastic Rotating Earth

Izvestiya, Atmospheric and Oceanic Physics - A technique for calculating tidal displacements and tilts for the Earth both with the ocean and without it is presented in this work. This technique...     

Observed foundation behaviour of concrete gravity platforms installed in the North Sea 1973–1978

Available measurements of foundation behaviour of the 13 concrete gravity platforms installed in the North Sea in the years 1973–1978 are presented. The measurements cover both the installation phase and the early part of the operation period. For the installation phase, measurements of dowel and skirt penetration resistance, base contact stresses, tilt, piping and erosion, are presented. For the operation period, the presentation includes measurements of settlements, pore water pressures, base contact stresses, permanent lateral displacements, cyclic displacements, dynamic behaviour and erosion. The measurements are used to back calculate soil properties and to evaluate the adequacy of the design procedures which have been used. The observations give valuable experience with respect to the foundation performance of offshore gravity platforms.     

Residual hydrodynamic fields after tsunami generation by an earthquake

The linear theory of long waves was applied to study horizontal motions of the water layer in a rotating ocean which appear after tsunami generation by an earthquake. The structures of residual potential and eddy fields are analyzed on the basis of the analytical solution of a model axisymmetric problem for an ocean of constant depth. The estimates of the horizontal displacements of water particles, velocity of the eddy current, and energy of the geostrophic eddy are calculated for typical conditions of the tsunami source. Particular features of the residual fields related to the existence of stable stratification are considered. Static and dynamic numerical models are described that allow us to calculate the residual potential field and its evolution related to the realistic events. The field of residual horizontal displacements of water particles for the catastrophic earthquake near the coasts of Japan on March 11, 2011, is calculated and analyzed.     

Transformation of the ocean level under a moving area of disturbances of atmospheric pressure

Within the framework of the linear model of long waves, we study the transformations of the ocean surface under the conditions of uniform motion of a zone of disturbances of atmospheric pressure. The analysis is based on the evaluation of a two-dimensional integral appearing in the exact expression for the shape of the free surface of the ocean. It is shown that Earth’s rotation, the increase in the horizontal scale of the atmospheric anomaly, and the decrease in the depth of the basin make the displacements of the sea level smaller than those predicted by the law of inverted barometer. The motion of the baric anomalies leads to the opposite effect. In the open ocean, the displacements of its surface under a moving front are more pronounced than in the case of a moving circular anomaly of atmospheric pressure. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 3–14, March–April, 2007.     

Mathematical modeling of spatial vibrations of lengthy hose structures

Spatial vibrations of hose constructions are considered with points of fastening under non-stationary kinematic actions. A model of hard rigid string is accepted as a computational model. The finite-difference method for the solution of equations of motion was used. A computational algorithm and a FORTRAN program were developed. The algorithm takes into account physical, geometrical and exploitative peculiarities of the constructions: bending stiffness, non-uniformity, geometrical non-linearity, conditions of fastening, internal/external hydrodynamics and internal dissipation of energy by friction between construction elements. It does not put any restraints on the initial form of construction, displacements and parameters of actions.As an example of practical application, a dynamics analysis of mooring utility systems under rough seas and wind loads was performed. Transient and steady-state modes of vibration were studied. Extreme generalized tensions and displacements of the construction were obtained as a function of roughness parameters, wind velocity and wind orientation, and geometrical and physical parameters of the construction.