High temperature indentation test to improve constitutive model for welding simulation

The high temperature gradients experienced during fusion welding lead to a local dilatation and metallurgical transformations that generate inhomogeneous plastic deformation, residual stresses and distortions in the welded parts which can affect the service life of the structures. To predict such residual stresses and distortions, finite element analysis is nowadays widely used. This work reports a 3D finite element model for welding simulation. The proposed model is based on semi coupled thermo-mechanical analysis using a double ellipsoidal model of heat source. Firstly, a disk heated in its central zone is investigated. Secondly the validation concerns the simulation of a fully 3D two pass butt weld. The idea in this work concerns the calibration of the heat source parameters with the help of the inverse analysis to improve the heat flow predictions. For the stress analysis, an annealing temperature is introduced to force the material to lose its hardening memory above a given temperature. The predicted residual stresses as well as the predicted distortions are found to be sensitive to the annealing temperature.     

裂点的河流地貌演变效应及铁路选线原则

拟建中巴铁路是我国\"一带一路\"倡议中南下通道的重要组成部分。中巴铁路廊道位于喜马拉雅、喀喇昆仑、兴都库什三大山系的交汇区,裂点分布密集,类型齐全。为了增强对裂点地貌效应的认识并合理利用,以中巴经济走廊红其拉普—塔科特段为研究区,首先基于铁路选线对地貌观测尺度的需求,提出了裂点规模的判据并建立了不同类型裂点的判识方法;然后通过对裂点上下游山地灾害数量的对比,证实了裂点上游河段更稳定的规律;最后基于不同类型裂点河流地貌演变效应的分析,提出构造型裂点上游的河流相基座阶地、滑坡型裂点形成的淤积地貌均为铁路布线的良好地形,对于冰川型裂点形成的开阔地形,须确认属小冰期冰川未到达的区域方可利用。     

Cavitation passive control on immersed bodies

This paper introduces a new idea of controlling cavitation around a hydrofoil through a passive cavitation controller called artificial cavitation bubble generator (ACG). Cyclic processes, namely, growth and implosion of bubbles around an immersed body, are the main reasons for the destruction and erosion of the said body. This paper aims to create a condition in which the cavitation bubbles reach a steady-state situation and prevent the occurrence of the cyclic processes. For this purpose, the ACG is placed on the surface of an immersed body, in particular, the suction surface of a 2D hydrofoil. A simulation was performed with an implicit finite volume scheme based on a SIMPLE algorithm associated with the multiphase and cavitation model. The modified k-ε RNG turbulence model equipped with a modification of the turbulent viscosity was applied to overcome the turbulence closure problem. Numerical simulation of water flow over the hydrofoil equipped with the ACG shows that a low-pressure recirculation area is produced behind the ACG and artificially generates stationary cavitation bubbles. The location, shape, and size of this ACG are the crucial parameters in creating a proper control. Results show that the cavitation bubble is controlled well with a well-designed ACG.     

作用在双圆柱桩上波浪力准确解和有限差分解的比较

The wave force exerted on vertical piles of offshore structures is the main criterion in designing them.In structures with more than one large pile,the influence of piles on each other is one of the most important issues being concerned in past researches.An efficient method for determining the interaction of piles is introduced in present research.First the wave force is calculated by the exact method using the diffraction theory,then in the finite difference numerical method the force is calculated by adding the velocity potentials of each pile and integration of pressure on their surface.The results showed that the ratio of the wave force on each of the double piles to a single pile has a damped oscillation around unity in which the amplitude of oscillation decreases with the increase in the spacing parameter.Also different wave incident directions and diffraction parameters were used and the results showed that the numerical solution has acceptable accuracy when the diffraction parameter is larger than unity.     

基于耐波性试验采用棱镜致动器的新型三自由度并行机构开发的高速船运动模拟器的动力分析（英文）

In this study, we focused on a novel parallel mechanism for utilizing the motion simulator of a high-speed boat(HSB). First, we expressed the real behavior of the HSB based on a seakeeping trial. For this purpose, we recorded the motion parameters of the HSB by gyroscope and accelerometer sensors, while using a special data acquisition technique. Additionally, a Chebychev highpass filter was applied as a noise filter to the accelerometer sensor. Then, a novel 3 degrees of freedom(DoF) parallel mechanism(1T2R) with prismatic actuators is proposed and analyses were performed on its inverse kinematics, velocity, and acceleration.Finally, the inverse dynamic analysis is presented by the principle of virtual work, and the validation of the analytical equations was compared by the ADAMS simulation software package. Additionally, according to the recorded experimental data of the HSB, the feasibility of the proposed novel parallel mechanism motion simulator of the HSB, as well as the necessity of using of the washout filters, was explored.     

A fuzzy AHP decision support system for selecting yard cranes in marine container terminals

One of the most important issues that planners and developers of ports have to address at the planning process of container terminals is how to effectively optimize truck turnaround times. The time that a truck spends at a container terminal for loading and/or unloading of cargo is a real cost scenario which affects not only the smooth operation of ports but also the overall cost of the container trade. The main objective of this article is to provide a decision support tool for selecting the best container yard gantry crane for loading/discharging operation of trucks at the landside of marine container terminals. Achieving this goal, this study aims at introducing and recommending the multiple attribute decision-making and the fuzzy analytical hierarchy process models that have been proven to provide a concrete basis for such a selection decision.     

Dynamic network equilibrium for daily activity-trip chains of heterogeneous travelers: application to large-scale networks

Applications of dynamic network equilibrium models have, mostly, considered the unit of traffic demand either as one-way trip, or as multiple independent trips. However, individuals’ travel patterns typically follow a sequence of trips chained together. In this study we aim at developing a general simulation-based dynamic network equilibrium algorithm for assignment of activity-trip chain demand. The trip chain of each individual trip maker is defined by the departure time at origin, sequence of activity destination locations, including the location of their intermediate destinations and their final destination, and activity duration at each of the intermediate destinations. Spatial and temporal dependency of subsequent trips on each other necessitate time and memory consuming calculations and storage of node-to-node time-dependent least generalized cost path trees, which is not practical for very large metropolitan area networks. We first propose a reformulation of the trip-based demand gap function formulation for the variational inequality formulation of the Bi-criterion Dynamic User Equilibrium (BDUE) problem. Next, we propose a solution algorithm for solving the BDUE problem with daily chain of activity-trips. Implementation of the algorithm for very large networks circumvents the need to store memory-intensive node-to-node time-dependent shortest path trees by implementing a destination-based time-dependent least generalized cost path finding algorithm, while maintaining the spatial and temporal dependency of subsequent trips. Numerical results for a real-world large scale network suggest that recognizing the dependency of multiple trips of a chain, and maintaining the departure time consistency of subsequent trips provide sharper drops in gap values, hence, the convergence could be achieved faster (compared to when trips are considered independent of each other).