Field survey and analysis of hillslopes on tower karst in Guilin,southern China

Limestone dissolution in tropical and subtropical humid southern China created residual hills with steep slopes, a landform that is referred to as tower karst. Two types of tower karst landform feature, fenglin or peak forest (isolated towers) and fengcong or peak cluster (linked‐base towers), were identified in Guilin. Previous studies proposed two hypotheses regarding their origin and evolution. One is the sequential evolution model from peak cluster to peak forest. The other is a parallel development model, which postulates that both peak cluster and peak forest have developed simultaneously. Through detailed field survey and analysis of slope forms on tower karst in Guilin, it was found that the mean slope angle of the towers is very high (62·4°) and ranges from 60° to 75°. There is no significant difference in mean slope angle and slope angle distribution between towers in the peak cluster basin and peak forest floodplain areas. Mean slope angle increases with intensified fluvial dissection. Three levels of caves in the towers of the peak forest in Guilin were identified in previous research. The isolated towers of the peak forest as well as scattered residuals of peak cluster are generally distributed in the centre of the Guilin syncline. Favourable circumstances of allogenic water concentration indicate that development of the peak forest resulted from the combined effects of subcutaneous and subterranean dissolution as well as subsequent collapse and recession by fluvial erosion after uplifting. By contrast, peak clusters generally occur on the limbs of the syncline or at the periphery of the Guilin basin with relatively higher elevations. The thick vadose zone and predominantly vertical flow suggests that peak clusters are mainly formed by the combination of intensive uplifting and the enhancement of original dolines. The evidence of slope survey and slope analysis suggests that both isolated towers and linked‐base towers developed simultaneously but by different mechanisms of formation and different combinations of development processes. Copyright © 2000 John Wiley & Sons, Ltd.     

独立式塔吊基础抗倾覆稳定分析

近年来,塔吊频繁发生重大工程事故,而现行规范中有关独立式塔吊混凝土基础抗倾覆稳定验算的规定存在不足,使设计的独立式塔吊偏不安全,所以,独立式塔吊基础抗倾覆稳定分析具有工程价值。     

基于深度学习和时空特征融合的海洋渔船密度预测方法

为了从海量渔船轨迹数据中挖掘隐含的信息和知识,进而为渔业行政主管部门的决策提供科学依据,本研究以AIS渔船轨迹数据为研究对象,提出了一种基于深度学习和面向时空特征融合的海洋渔船密度预测方法：首先,利用渔船轨迹数据集对渔船行驶区域进行网格划分;其次,筛选出渔船高密度区域进行研究,避免数据稀疏性问题;再次,根据渔船轨迹数据的时空分析,构建三维时空融合矩阵;最后,通过卷积循环神经网络模型捕获渔船分布的时间和空间特征,并利用卷积神经网络的堆叠加强对空间特征的学习。实验通过东海海域渔船真实轨迹数据进行具体测试,结果表明渔船密度预测值与真实值非常接近,平均绝对误差为4×10-4,模型较好地拟合了渔船密度分布特征,有效地提高了渔船捕捞热点预测的准确性和鲁棒性。     

无背索斜拉桥主塔受力及抗震性能分析

为探讨主塔横梁对无背索斜拉桥结构的静动力特性影响,以某无背索斜拉桥为原型,采用三维静\,动力有限元计算方法,分析了实心横梁、大空心横梁、小空心横梁与无横梁四种主塔横梁方案的静、动力结构特性。静力计算结果表明:在最不利荷载作用下,四种对比方案中,实心横梁的拉索应力接近安全系数临界值;横梁重量越大,主梁挠度及主塔顺桥向变形值越小,且未设置横梁的方案在长期荷载作用下产生主跨侧的收缩徐变变形值。动力计算结果表明:大空心横梁方案结构横桥向刚度最大塔底轴力最大、横桥向弯矩值最大;无横梁时横桥向剪力最大,且无横梁方案使得主塔刚度较小,阵型易出现主塔横向失稳。综合考虑结构静、动力特性与施工便利性和后期维护,建议该结构采用实心主塔横梁。     

Comparison of numerical solution and semi-empirical formulas to predict the effects of important design parameters on porpoising region of a planing vessel

Stability of the marine vessels in different conditions is one of the most important problems in the design of a planing vessel. In this research, the effects of some important design parameters (mass, longitudinal center of mass, deadrise angle, and length) of DTMB 62 model 4667-1 planing hull on the drag and also on the longitudinal dynamic stability (porpoising) are investigated in the velocity range of 2.12–8.486 m/s in calm water. In this paper, both numerical simulation of Reynolds Average Naiver Stokes (RANS) equations and semi-empirical formulas of Savitsky are used to analyze the motion of a 4667 planing vessel in calm water with two degrees of freedom (2DOF). For this purpose a finite volume, ANSYS-FLUENT, code is used to solve the Navier-Stokes equations for the simulation of the flow field around the vessel. In addition, an explicit VOF scheme and SST- Kω model is used with dynamic mesh scheme to capture the interface of a two-phase flow and to model the turbulence respectively, in 2DOF model (heave and pitch). Also, the results of both methods are compared with each other. According to the present results, changing the aspect ratio of the vessel and also the longitudinal center of gravity have the most effect on the porpoising region.     

Prediction of ground motion due to the collapse of a large-scale cooling tower under strong earthquakes

The ground motion owing to the collapse of a large-scale cooling tower under strong earthquakes was appropriately predicted using a comprehensive approach. The predicted results can be used for the safety evaluation of nuclear-related facilities adjacent to the cooling tower as well as in the planning of nuclear power plant construction in China. In this study, a cooling tower–soil model was first developed based on a falling weight–soil model, which the authors verified by falling weight tests. Then the collapse process of a cooling tower was simulated, and the collapse-induced ground vibrations were assessed by using the proposed model. Finally, the ground motion, which was a combination of the earthquake-induced ground motion and the collapse-induced ground vibrations, was estimated based on the superposition principle of waves. It was found that the cooling tower may collapse under strong earthquakes with the peak ground accelerations (PGAs) in the range of 0.35–0.45 g in x (EW) and y (NS) directions, respectively. These PGAs are far beyond the PGA range of major earthquakes in the common seismic design in China. The types of the site geologies of towers can significantly affect the collapse-induced ground vibrations. For a typical hard soil consisting of strongly weathered sandy slate, moderate ground vibrations may occur in the considered region. The collapse-induced PGAs were in the range of 0.017–0.046 g for the observed points at distances of 350 m in radial direction. For a rock-like foundation, the collapse-induced radial PGAs may be as high as 0.08 g at distances of 350 m, indicating that the effect of the collapse-induced ground vibrations on the nuclear-related facilities should be seriously assessed in certain scenarios.     

A primary study of the variations of vertical radiation with the Beijing 325-m Meteorological Tower

The Beijing 325-m Meteorological Tower (325MT) is used to observe the vertical variation of solar radiation. Results of the experiments indicate that the automatic radiation monitoring system, including a sun tracker and data collection system, works well and all the specifications meet WMO observation standards. The measurement data show that there is a significant radiation decrease from 320m to the surface, where the difference is only about 30Wm^-2 on light air-pollution days, while the maximum reaches about 110Wm^-2 when heavy pollution appears near the ground. The global UV radiation decreases on heavy air-pollution days and under poor visibility conditions, and the difference between 300m and 8m is larger than on clear days.     

测量船动态吃水测量方法研究

针对测量船特别是中大型测量船的动态吃水问题,提出了单船和双船载波相位差分GPS测定方法,给出了动态吃水计算公式。根据装备现状,对比分析了三种测量方法的适用范围,例举了典型参数值的动态吃水观测误差,旨在为测量作业人员提供借鉴和参考。     

Axial compressive bearing capacity of piles in ‎oil-contaminated sandy soil using FCV

ABSTRACT

Oil and its derivatives contaminate many soils and not only affect their chemical and biological properties but also their geotechnical properties. As oil contamination may deteriorate the functioning of piles, this paper addresses the effects of oil contamination on soil–pile interactions. Axial compressive bearing capacities of two close-ended, instrumented piles were investigated in different oil-contaminated sand using frustum confining vessel. Three different oils (gasoil, crude oil, and used motor oil) at different contamination levels were considered and using some strain gauges, the toe, shaft, and the net total bearing capacity of piles, as well as load distributions along the pile length, were derived. The results show that the presence of oil between soil particles has considerable adverse effects on bearing capacities of model piles, especially the shaft bearing capacity. The oil viscosity and percentage, as well as the contaminated sand bed thickness around the piles, are the most influential parameters. The higher the oil viscosity and oil content, the lower the values of the piles’ bearing capacities in comparison to the uncontaminated sand. With some modifications on the bearing capacity parameters of CFEM method, a good agreement was observed between measured and calculated bearing capacity values.     

采煤沉陷区输电铁塔复合防护板基础抗变形性能及其板厚取值研究

以某采煤沉陷区内的典型输电铁塔及其复合防护板基础工程为背景,考虑地基-基础-上部铁塔结构的共同作用,对不同板厚复合防护板基础的抗采动变形性能进行了研究,并引入＂保护作用＂的概念,对独立基础和复合防护板基础的抗变形性能进行了分析。研究表明,设置复合防护板后,与独立基础相比,可明显减少铁塔支座的水平位移及上部结构的应力,支座位移与结构应力随着复合大板厚度的增大而减小,其减小的幅度随着板厚的增大而趋缓,当板厚达到一定数值以后几乎不再减小。提出的复合防护板的厚度可取铁塔基础长向根开的1/45～1/35的建议,以供采煤沉陷区内复合防护板基础的设计参考。