Prediction of Height and Period Joint Distributions for Stochastic Ocean Waves     

WANG Ying-guang 《海洋工程》2017,31(3):291-298

This article proposes a new methodology to predict the wave height and period joint distributions by utilizing a transformed linear simulation method. The proposed transformed linear simulation method is based on a Hermite transformation model where the transformation is chosen to be a monotonic cubic polynomial, calibrated such that the first four moments of the transformed model match the moments of the true process. The proposed new approach is applied for calculating the wave height and period joint distributions of a sea state with the surface elevation data measured at an offshore site, and its accuracy and efficiency are favorably validated by using comparisons with the results from an empirical joint distribution model, from a linear simulation model and from a second-order nonlinear simulation model.  相似文献   

Floc size variability under strong turbulence: Observations and artificial neural network modeling     

《Applied Ocean Research》2017

The flocculation of cohesive sediment in the presence of waves is investigated using high-resolution field observations and a newly-developed flocculation model based on artificial neural networks. Vertical profiles of suspended sediment concentration and turbulent intensity are estimated using measurements of current profile and acoustic backscatter. The vertical distribution of floc size is estimated using an artificial neural network (ANN) that is trained and validated using floc size measurements at one vertical level. Data analysis suggests a linear correlation between suspended sediment concentration and turbulence intensity. Observations and numerical simulations show that floc size is inversely related to sediment concentration, turbulence intensity and water temperature. The numerical results indicate that floc growth is supported by low concentration and low turbulence. In the vertical direction, mean size of flocs decreases toward the bottom, suggesting floc breakage due to increasing turbulence intensity toward the bed. A significant decrease in turbulent shear could occur within the bottom few-cm, related to increased damping of turbulence by sediment induced density stratification. The results of the numerical simulations presented here are consistent with the concept of a cohesive sediment particle undergoing aggregation-fragmentation processes, and suggest that the ANN can be a precise tool to study flocculation processes.  相似文献   

J-lay铺管作业力学分析          下载免费PDF全文

刘大辉  阮伟东  白勇 《海洋工程》2017,35(1):51-59

目前J-lay铺管法作为深水和超深水铺管的最适用方法广泛应用于深海油气开发。考虑J-lay铺管时管道几何非线性特征以及触地区边界效应,将J-lay铺管模型划分三构件进行力学分析:悬浮段、边界层段以及触地段。建立Orca Flex模型和引入Wang改进二构件模型,通过对比上述三种方法计算J-lay相应构型、轴力、弯矩和剪力分布,验证该三构件模型的可行性和考虑边界效应的必要性。基于Lamé公式计算管道横截面处轴向、径向以及环向应力,对比分析J-lay铺设管道应力分布特征。结果表明:该改进三构件模型能真实有效地模拟J-lay铺管过程中管道受力情况,特别是触地点附近弯矩和剪力变化情况,能为管道疲劳损伤分析提供理论基础。  相似文献   

液化场地桥梁群桩-土耦合体系强震反应分析          下载免费PDF全文

唐浩  石秀峰  唐亮  蔡德钩  凌贤长  王东洋 《地震工程学报》2016,38(6):869-876

针对振动台试验,采用u-p形式控制方程表述饱和砂土的动力属性,选用土的多屈服面塑性本构模型刻画饱和砂土和黏土的力学特性,引入非线性梁-柱单元模拟桩,建立试验受控条件下液化场地群桩-土强震相互作用分析的三维有限元模型,并通过试验结果验证数值建模途径与模拟方法的正确性。以实际工程中常用的2×2群桩为例,建立桩-土-桥梁结构强震反应分析三维有限元模型。基于此,针对不同群桩基础配置对液化场地群桩-土强震相互作用影响展开具体分析。对比发现,桩的数量相同时,桩排列方向与地震波输入方向平行时比垂直时桩基受力减小5%~10%,而对场地液化情况无明显影响;相同排列形式下,三桩模型中土体出现液化的时间约比双桩模型延缓5s,桩上弯矩和剪力减小33%~38%。由此可见,桩基数量增加,桩-土体系整体刚度更大,场地抗液化性能显著,桩基对上部桥梁结构的承载性能明显增强,其安全性与可靠性更高。这对实际桥梁工程抗震设计具有一定的借鉴意义。  相似文献   

Bistable plant–soil dynamics and biogenic controls on the soil production function          下载免费PDF全文

Norman F. Pelak  Anthony J. Parolari  Amilcare Porporato 《地球表面变化过程与地形》2016,41(8):1011-1017

Soil formation results from opposite processes of bedrock weathering and erosion, whose balance may be altered by natural events and human activities, resulting in reduced soil depth and function. The impacts of vegetation on soil production and erosion and the feedbacks between soil formation and vegetation growth are only beginning to be explored quantitatively. Since plants require suitable soil environments, disturbed soil states may support less vegetation, leading to a downward spiral of increased erosion and decline in ecosystem function. We explore these feedbacks with a minimal model of the soil–plant system described by two coupled nonlinear differential equations, which include key feedbacks, such as plant‐driven soil production and erosion inhibition. We show that sufficiently strong positive plant–soil feedback can lead to a ‘humped’ soil production function, a necessary condition for soil depth bistability when erosion is assumed to vary monotonically with vegetation biomass. In bistable plant–soil systems, the sustainable soil condition engineered by plants is only accessible above a threshold vegetation biomass and occurs in environments where the high potential rate of erosion exerts a strong control on soil production and erosion. Vegetation removal for agriculture reduces the stabilizing effect of vegetation and lowers the system resilience, thereby increasing the likelihood of transition to a degraded soil state. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Transient analysis of concrete gravity dam-reservoir systems by Wavenumber-TD approach     

《Soil Dynamics and Earthquake Engineering》2016

The Wavenumber approach was initially introduced as an ideal substitute for the rigorous type of analysis which had been the basis of extensive studies in seismic analysis of concrete gravity dams. The former technique is formulated in the context of pure finite element programming, while the latter relies heavily on a two-dimensional semi-infinite fluid element (i.e., hyper-element). Recently, a variation of Wavenumber method was proposed which was referred to as Wavenumber-TD approach. The approximation to the original technique improves its realm of application and allows it to be carried out in time domain as well as frequency domain. In that study, the formulation was examined for harmonic type of excitation which proved to be promising. Herein, this will be evaluated for its real intended application, which is transient analysis of dam-reservoir systems. For this aim, the prepared special purpose finite element program is modified and the analysis of Pine Flat dam is considered as a typical example. Several models are considered with different values of normalized reservoir length. In each case, the reservoir truncation surface is treated by Wavenumber-TD and the extensively utilized Sommerfeld conditions. The dynamic loading considered is the S69E component of Taft earthquake record. Furthermore, two types of reservoir bottom condition of full reflective as well as absorptive, are adopted. Overall, this will allow for a thorough examination and evaluation of Wavenumber-TD approach in regard to its effectiveness.  相似文献   

湖南保靖X区页岩气储层“甜点”区地震资料非线性反演预测方法          下载免费PDF全文

梁国华  黄捍东  刘福义  符超  林中月  王向浩  杨亚迪  苗雨新  沈金松  张晓晨 《CT理论与应用研究》2016,25(3):299-310

针对湖南保靖地区地表覆盖层复杂、地下高陡构造多变、地震勘探资料信噪比低,以及页岩气储层与周围泥岩层波阻抗对比度小等特点,研究敏感测井曲线重构与优化处理、地震资料相控非线性反演和叠后地震属性流体检测的综合储层评价方法。通过对多条测线的地震资料反演和流体检测并与实钻井结果对比,获得了良好的地质效果,初步验证了所研究方法的有效性和实用性。   相似文献   

Seismic analysis of diagrid structural frames with shear-link fuse devices     

Nasim S. Moghaddasi B.  Yunfeng Zhang 《地震工程与工程振动(英文版)》2013,12(3):463-472

This paper presents a new concept for enhancing the seismic ductility and damping capacity of diagrid structural frames by using shear-link fuse devices and its seismic performance is assessed through nonlinear static and dynamic analysis.The architectural elegancy of the diagrid structure attributed to its triangular leaning member configuration and high structural redundancy make this system a desirable choice for tall building design.However,forming a stable energy dissipation mechanism in diagrid framing remains to be investigated to expand its use in regions with high seismicity.To address this issue,a diagrid framing design is proposed here which provides a competitive design option in highly seismic regions through its increased ductility and improved energy dissipation capacity provided by replaceable shear links interconnecting the diagonal members at their ends.The structural characteristics and seismic behavior(capacity,stiffness,energy dissipation,ductility) of the diagrid structural frame are demonstrated with a 21-story building diagrid frame subjected to nonlinear static and dynamic analysis.The findings from the nonlinear time history analysis verify that satisfactory seismic performance can be achieved by the proposed diagrid frame subjected to design basis earthquakes in California.In particular,one appealing feature of the proposed diagrid building is its reduced residual displacement after strong earthquakes.  相似文献   

Dynamic interaction numerical models in the time domain based on the high performance scaled boundary finite element method     

Jianbo Li  Jun Liu  Gao Lin 《地震工程与工程振动(英文版)》2013,12(4):541-546

Consideration of structure-foundation-soil dynamic interaction is a basic requirement in the evaluation of the seismic safety of nuclear power facilities. An efficient and accurate dynamic interaction numerical model in the time domain has become an important topic of current research. In this study, the scaled boundary finite element method （SBFEM） is improved for use as an effective numerical approach with good application prospects. This method has several advantages, including dimensionality reduction, accuracy of the radial analytical solution, and unlike other boundary element methods, it does not require a fundamental solution. This study focuses on establishing a high performance scaled boundary finite element interaction analysis model in the time domain based on the acceleration unit-impulse response matrix, in which several new solution techniques, such as a dimensionless method to solve the interaction force, are applied to improve the numerical stability of the actual soil parameters and reduce the amount of calculation. Finally, the feasibility of the time domain methods are illustrated by the response of the nuclear power structure and the accuracy of the algorithms are dynamically verified by comparison with the refinement of a large-scale viscoelastic soil model.  相似文献   

Condensed hyperelements method of non-vertical consistent boundaries for wave propagation analysis in irregular media     

S. Dorafshan  F. Behnamfar  A. Khamesipour  M. Motosaka 《地震工程与工程振动(英文版)》2013,12(4):547-559

The study of wave propagation in finite/infinite media has many applications in geotechnical and structural earthquake engineering and has been a focus of research for the past few decades. This paper presents an analysis of 2D anti- plane problems （Love waves） and 2D in-plane problems （Rayleigh waves） in the frequency domain in media consisting of a near-field irregular and a far-field regular part. The near field part may contain structures and its boundaries with the far-field can be of any shape. In this study, the irregular boundaries of the near-field are treated as consistent boundaries, extending the concept of Lysmer＇s vertical consistent boundaries. The presented technique is called the Condensed Hyperelements Method （CHM）. In this method, the irregular boundary is limited to a vertical boundary at each end that is a consistent boundary at the far-field side. Between the two ends, the medium is discretized with hyperelements. Using static condensation, the stiffness matrix of the far-field is derived for the nodes on the irregular boundary. Examples of the application of the CHM illustrate its excellent accuracy and efficiency.  相似文献