Uncoupled analysis of stabilizing piles in weathered slopes

This paper describes a simplified numerical approach for analyzing the slope/pile system subjected to lateral soil movements. The lateral one-row pile response above and below the critical surface is computed by using load transfer approach. The response of groups was analyzed by developing interaction factors obtained from a three-dimensional nonlinear finite element study. An uncoupled analysis was performed for stabilizing piles in slope in which the pile response and slope stability are considered separately. The non-linear characteristics of the soil–pile interaction in the stabilizing piles are modeled by hyperbolic load transfer curves. The Bishop's simplified method of slope stability analysis is extended to incorporate the soil-pile interaction and evaluate the safety factor of the reinforced slope. Numerical study is performed to illustrate the major influencing parameters on the pile-slope stability problem. Through comparative studies, it has been found that the factor of safety in slope is much more conservative for an uncoupled analysis than for a coupled analysis based on three-dimensional finite element analysis.     

A spatial dynamic model of population changes in a vulnerable coastal environment

This study developed a spatial dynamic model to examine the coupled natural–human responses in the form of changes in population and associated developed land area in the Lower Mississippi River Basin region. The goal was to identify key socioeconomic factors (utility) and environmental factors (hazard damages, elevation, and subsidence rate) that affected population changes, as well as to examine how population changes affected the local utility and the local environment reciprocally. We first applied areal interpolation techniques with the volume-preserving property to transform all the data at Year 2000 into a unified 3 km by 3 km cellular space. We then built an Elastic Net model to extract 12 variables from a set of 33 for the spatial dynamic model. Afterward, we calibrated the neighborhood effects with a genetic algorithm and use the spatial dynamic model to simulate population and developed land area in 2010. Furthermore, we took a Monte Carlo approach for analyzing the uncertainty of the model outcome. Our accuracy assessment shows that the model on average slightly overpredicts the number of population and the developed land percentage at 2010, as indicated by the low values of mean absolute deviation (MAD) due to quantity. On the other hand, the MADs due to allocation are larger than the MADs due to quantity, with most outliers found in the New Orleans region where population and urban development declined significantly during 2000–2010 after Hurricane Katrina. The proposed model sheds light on the complex relationships between coastal hazards and human responses and provides useful insights to strategic development for coastal sustainability.     

Urbanization on the Mongolian Plateau after economic reform: Changes and causes

In response to changes in human and natural environments over the past three decades, transitional countries have experienced dramatic urbanization. In the context of socioeconomic and biophysical changes, our knowledge on these urbanization processes remains limited. Here, we used the Mongolian Plateau (i.e., Inner Mongolia (IM) and Mongolia (MG)) as a testbed and applied the coupled natural and human (CNH) concept to understand the processes and causes of urbanization. We selected six cities on the Mongolian Plateau, classified their urban built-up areas using Geographic Object-Based Image Analysis (GEOBIA) from 1990 through 2015, and examined the driving forces of urbanization (i.e., economy, social goods, and environmental variables) through Partial Least Squares Structural Equation Modeling (PLS-SEM). We found that the spatial characteristics of urbanization in IM and MG have both similarities and differences. The cities in IM and MG have experienced rapid urban expansion, with urban areas increasing by 4.36 times and 3.12 times, respectively, since 1990. Cities in IM, however, were less dense and more sprawling whereas cities in MG were linearly aggregated. We also found through PLS-SEM that multiple driving forces affected urbanization in IM and MG during the transitional period. Results (path coef.) demonstrated that economic development (0.559) is a major driver for urbanization in IM, whereas social goods (0.646) and economic development (0.433) strongly influence urbanization in MG. These differences are likely due to the divergent governmental roles in urban development and in infrastructure/social support, as well as the differing economic structures in IM and MG.     

腾格里沙漠包气带水,汽,热运动的耦合模型及水热状况模拟

采用中子水分仪、负压计和电子测温器同步测定腾格里沙漠邓马营湖包气带０～４２５ｃｍ范围内不同深度含水量、基质势和温度,确立有关的水热特征参数。基于Ｐｈｉｌｉｐ、ＤｅＶｒｉｅｓ提出的土壤内水热运动理论,建立并解算了该包气带水、汽、热运动的耦合模型,并对不同气象条件下沙漠包气带水热状况进行数值模拟和预报,其结果反映了沙漠包气带含水量变化及温度分布特征。     

Sensitivity of the modelled thermohaline circulation to the parameterisation of mixing across the Greenland–Scotland ridge

The Hadley Centre climate model HadCM3 simulates a stable thermohaline circulation driven by deep water formation in the Norwegian and Labrador Seas without the need for flux adjustments. It has however been suggested that this result is the fortuitous consequence of the local use of the Roussenov convection scheme in this region, and that the model simulation may depend sensitively on this parameterisation. Here we investigate the sensitivity of the thermohaline circulation (THC) to the model’s treatment of the overflows from the Nordic Seas for both pre-industrial and increasing greenhouse gas forcings. We find that although the density structure in the Labrador Sea does depend upon the specifics of how the overflows are modelled, the global thermohaline circulation and climate responses are not sensitive to these details. This result gives credibility to previously published modelling studies on the response of the thermohaline circulation to anthropogenic greenhouse gas forcing, and implies that research may profitably be focussed on the large scale transports, where models are known to disagree.     

Application of a coupled discontinuous–continuous Galerkin finite element shallow water model to coastal ocean dynamics

A coupled discontinuous–continuous Galerkin (DG–CG) shallow water model is compared to a continuous Galerkin generalized wave-continuity equation (GWCE) based model for the coastal ocean, whereby local mass imbalance typical of GWCE-based solutions is eliminated using the coupled DG–CG approach. Two mass imbalance indicators for the GWCE-based model are presented and analyzed. The indicators motivate discussion on the suitability of using a GWCE-based model versus the locally conservative coupled DG–CG model. Both realistic and idealized test problems for tide, wind, and wave-driven circulation form the basis of the study. For the problems studied, coupled DG–CG solutions retain the robustness of well-documented solutions from GWCE-based models and also capture the dynamics driven by small-scale, highly advective processes which are problematic for GWCE-based models. Issues associated with the coupled DG–CG model are explored, including increased cost due to increased degrees of freedom, the necessary application of slope limiters, as well as the actual coupling process.     

Coupled dynamic analysis of a mini TLP: Comparison with measurements

The dynamically coupled interaction between the hull of a floating platform and its risers and tendons plays an important role in the global motions of the platform and the tension loads in the tendons and risers. This is an especially critical design issue in the frequency ranges outside the wave frequencies of significant energy content. This study examines the importance of this coupled dynamic interaction and the effectiveness of different approaches for their prediction. A numerical code, named COUPLE, has been developed for computing the motions and tensions pertaining to a moored floating structure positioned and restrained by its mooring/tendon and riser systems. In this study the experimentally measured motions of a mini-TLP are compared with those computed using COUPLE and alternative predictions based upon quasi-static analysis. The comparisons confirm that COUPLE is able to predict the dynamic interaction between the hull and its tendon and riser systems while the related quasi-static analysis fails. The comparisons also show that wave loads on the mini-TLP can be accurately predicted using the Morison equation provided that the wavelength of incident waves is much longer than the diameters of the columns and pontoons and that the wave kinematics used are sufficiently accurate. Although these findings are based upon the case of a mini-TLP, they are expected to be relevant to a wide range of floating or compliant deepwater structures.     

Study on coupling effects of ship motion and sloshing

This study considers the coupling effects of ship motion and sloshing. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite-difference method. The IRF method requires the frequency-domain solution prior to conversion to time domain, but the computational effort is much less than that of direct time-domain approaches. The developed scheme is verified by comparing the motion RAOs between the frequency-domain solution and the solution obtained by the IRF method. Furthermore, a soft-spring concept and linear roll damping are implemented to predict more realistic motions of surge, sway, yaw, and roll. For the simulation of sloshing flow in liquid tanks, a physics-based numerical approach adopted by Kim [2001. Numerical simulation of sloshing flows with impact load. Applied Ocean Research 23, 53–62] and Kim et al. [2004. Numerical study on slosh-induced impact pressures on three-dimensional prismatic tanks. Applied Ocean Research 26, 213–226] is applied. In particular, the present method focuses on the simulation of the global motion of sloshing flow, ignoring some local phenomena. The sloshing-induced forces and moments are added to wave-excitation forces and moments, and then the corresponding body motion is obtained. The developed schemes are applied for two problems: the sway motion of a box-type barge with rectangular tanks and the roll motion of a modified S175 hull with rectangular anti-rolling tank. Motion RAOs are compared with existing results, showing fair agreement. It is found that the nonlinearity of sloshing flow is very important in coupling analysis. Due to the nonlinearity of sloshing flow, ship motion shows a strong sensitivity to wave slope.     

Deep convection seesaw controlled by freshwater transport through the Denmark Strait

Observations of deep ocean temperature and salinity in the Labrador and Greenland Seas indicate that there is negative correlation between the activities of deep convection in these two sites. A previous study suggests that this negative correlation is controlled by the North Atlantic Oscillation (NAO). In this study, we discuss this deep convection seesaw by using a coupled atmosphere and ocean general circulation model. In this simulation, the deep convection is realistically simulated in both the Labrador and Greenland Seas and their negative correlation is also recognized. Regression of sea level pressure to wintertime mixed layer depth in the Labrador Sea reveals strong correlation between the convection and the NAO as previous studies suggest, but a significant portion of their variability is not correlated. On the other hand, the convection in the Greenland Sea is not directly related to the NAO, and its variability is in phase with changes in the freshwater budget in the GIN Seas. The deep convection seesaw found in the model is controlled by freshwater transport through the Denmark Strait. When this transport is larger, more freshwater flows to the Labrador Sea and less to the Greenland Sea. This leads to lower upper-ocean surface salinity in the Labrador Sea and higher salinity in the Greenland Sea, which produces negative correlation between these two deep convective activities. The deep convection seesaw observed in the recent decades could be interpreted as induced by the changes in the freshwater transport through the Denmark Strait, whose role has not been discussed so far.     

Numerical simulation of mitigation for liquefaction-induced soil deformations in a sandy ground improved by cement grouting

This paper presents a numerical study of mitigation for liquefaction during earthquake loading. Analyses are carried out using an effective stress based, fully coupled, hybrid, finite element-finite differences approach. The sandy soil behavior is described by means of a cyclic elastoplastic constitutive model, which was developed within the framework of a nonlinear kinematic hardening rule. In theory, the philosophies of mitigation for liquefaction can be summarized as two main concepts, i.e. prevention of excess pore water pressure generation and reduction of liquefaction-induced deformations. This paper is primarily concerned with the latter approach to liquefaction mitigation. Firstly, the numerical method and the analytical procedure are briefly outlined. Subsequently, a case-history study, which includes a liquefaction mitigation technique of cement grouting for ground improvement of a sluice gate, is conducted to illustrate the effectiveness of liquefaction countermeasures. Special emphasis is given to the computed results of excess pore water pressures, displacements, and accelerations during the seismic excitation. Generally, the distinctive patterns of seismic response are accurately reproduced by the numerical simulation. The proposed numerical method is thus considered to capture the fundamental aspects of the problems investigated, and yields results for design purposes. From the results in the case, excess pore water pressures eventually reach fully liquefied state under the input earthquake loading and this cannot be prevented. However, liquefaction-induced lateral spreading of the foundation soils can be effectively reduced by the liquefaction mitigation techniques. An erratum to this article can be found at