Effect of rotation speed on temperature field and axial shortening of inertia friction welded GH4169 joints by numerical simulation

A 2D finite element model was established for inertia friction welding of GH4169 nickel-base superalloy based on the ABAQUS environment. The remeshing and map solution techniques were adopted to solve the problem of element distortion. The effect of rotation speed on the temperature field and axial shortening of joints was investigated. The results show that the interface temperature increases rapidly to higher than 900°C within 1 s. And then, it increases slowly to a quasi-stable value. The axial shortening begins to augment quickly when a uniform interface temperature field has formed and the plasticized material is extruded from the interface to form an obvious flash. The rotation speed of the flywheel controls the welding process and has a significant influence on the temperature evolution and axial shortening of joints.     

Investigation of improved approaches to bayes risk decoding

Bayes risk (BR) decoding methods have been widely investigated in the speech recognition area due to its flexibility and complexity compared with the maximum a posteriori (MAP) method regarding to minimum word error (MWE) optimization. This paper investigates two improved approaches to the BR decoding, aiming at minimizing word error. The novelty of the proposed methods is shown in the explicit optimization of the objective function, the value of which is calculated by an improved forward algorithm on the lattice. However, the result of the first method is obtained by an expectation maximization (EM) like iteration, while the result of the second one is achieved by traversing the confusion network (CN), both of which lead to an optimized objective function value with distinct approaches. Experimental results indicate that the proposed methods result in an error reduction for lattice rescoring, compared with the traditional CN method for lattice rescoring.     

Wrinkle analysis of the space inflatable paraboloid antenna

The presence of wrinkles in the membrane is the main factor to induce the reflector surface inaccuracy of the space inflatable antenna. Based on the commercial finite element package ABAQUS, a numerical procedure for membrane wrinkle analysis was set up and used to analyze a space inflatable antenna which was under inner pressure to evaluate its wrinkle characteristics. First, the inner pressure effect on the reflector’s wrinkle pattern was studied thoroughly. As inner pressure increases, both the number and the amplitude of the wrinkles decrease, but the total deformation of the whole reflector surface increases much. Second, the influence of the interactions between antenna’s parts was investigated comprehensively. Any kind of unwanted interaction deteriorates reflector’s wrinkle characteristics. The works are valuable to the development and research of the space inflatable antenna.     

Risk factors and theory building: a study to improve passenger vessel safety

Given the inherent complexity of the maritime transportation system, developing effective policy can be challenging. Using risk factors identified by an elicitation and aggregation of expert judgment, a relative-risk rating scheme was developed in the theory-building tradition of the social sciences. The model was empirically evaluated using 18 months of data from the US small passenger vessel sector. The model identified that the top 10% of relatively highest risk vessels accounted for 50% of all marine casualties during the period of examination. A policy for deploying the model nationally is proposed.     

Design of the lines of underwater vehicles based on collaborative optimization

A generalized collaborative optimization (CO) framework is proposed to the optimization design of the lines of an underwater vehicle. The resistance and maneuvering performances are concerned about and taken as the optimization objectives in the optimization framework. The resistance, lateral force and yaw moment are calculated by RANS method. To improve the optimization efficiency, an automatic integration optimization platform is constructed in which a surrogate model is adopted. A SUBOFF model is taken as the verification model. The optimal results demonstrate the validity of the optimization strategy proposed.     

Shift of reference point and implications on behavioral reaction to gains and losses

It is widely recognized that individual decision-making is subject to the evaluation of gains and losses around a reference point. The estimation of discrete choice models increasingly use data from stated choice experiments which are pivoted around a reference alternative. However, to date, the specification of a reference alternative in transport studies has been fixed, whereas it is common to observe individuals adjusting their preferences according to a change in their reference point. This paper focuses on individual reactions, in a freight choice context, to a negative change in the reference alternative values, identifying the behavioural implications in terms of loss aversion and diminishing sensitivity. The results show a significant adjustment in the valuation of gains and losses around a shifted reference alternative. In particular, we find an average increase in loss aversion for cost and time attributes, and a substantial decrease for punctuality. These findings are translated to significant differences in the willingness to pay and willingness to accept measures, providing supporting evidence of respondents’ behavioural reaction.     

A GIS‐based traffic analysis zone design: technique

The main purpose of this paper is to develop an efficient method to design traffic analysis zones (TAZs), which is necessary for implementing a planning process with Geographic Information System (GIS) for Transportation (GIS‐T), using statistical spatial data analyses and GIS technology. The major roles of GIS in this method are: (1) to produce basic spatial units (BSUs) with topological data structure; (2) to integrate various procedures during the TAZ generation including computer program routines; and (3) to visualize the output of each TAZ generation. One of the most significant reasons for obtaining well‐defined TAZs is the fact that they are defined at the outset of transportation demand modeling, used from trip generation to trip assignment, and will ultimately affect transportation policy decisions.

Toward obtaining well‐defined TAZs, this paper concentrates on two important constraints: homogeneity and contiguity. Iterative partitioning technique is adopted to promote the optimum homogeneity of generated TAZs, while a contiguity checking algorithm is developed to ensure contiguous TAZs are generated by the iterative partitioning technique.     

Experimental study and 3D CFD analysis on the optimization of throttle angle for a convergent vortex tube

Seven adjustments of convergent-type Vortex Tube (VT) with different throttle angles were applied. The adjustments were made to analyze the influences of such angles on cold and hot temperature drops as well as flow structures inside the VTs. An experimental setup was designed, and tests were performed on different convergent VT configurations at injection pressures ranging from 0.45 to 0.65 MPa. The angles of the throttle valve were arranged between 30° to 90°, and the numbers of injection nozzles ranged between 2 and 6. Laboratory results indicated that the maximum hot and cold temperature drops ranged from 23.24 to 35 K and from 22.87 to 32.88 K, respectively, at four injection nozzles. Results also showed that temperature drop is a function of hot throttle valve angle with the maximum hot and cold temperature drops depending on the angle applied. We used graphs to demonstrate the changes in the cold and hot temperature drops with respect to hot throttle angle values. These values were interpreted and evaluated to determine the optimum angle, which was 60°. The CFD outputs agreed very well with the laboratory results. The proposed CFD results can help future researchers gain good insights into the complicated separation process taking place inside the VTs.     

Imprecise reliability assessment for heavy numerical control machine tools against small sample size problem

Small sample size problem is one of the main problems that heavy numerical control (NC) machine tools encounter in their reliability assessment. In order to deal with the small sample size problem, many indirect reliability data such as reliability data of similar products, expert opinion, and engineers’ experience are used in reliability assessment. However, the existing mathematical theories cannot simultaneously process the above reliability data of multiple types, and thus imprecise probability theory is introduced. Imprecise probability theory can simultaneously process multiple reliability data by quantifying multiple uncertainties (stochastic uncertainty, fuzzy uncertainty, epistemic uncertainty, etc.) together. Although imprecise probability theory has so many advantages, the existing natural extension models are complex and the computation result is imprecise. Therefore, they need some improvement for the better application of reliability engineering. This paper proposes an improved imprecise reliability assessment method by introducing empirical probability distributions to natural extension model, and the improved natural extension model is applied to the reliability assessment of heavy NC machine tool spindle to illustrate its effectiveness.     

基于CPS的超大城市地铁机电设备智能运维体系设计

以北京、上海、广州为代表的超大城市地铁网络呈现出"规模体量大、线路分布广、枢纽数量多、运营负荷强度大"的特点,这对地铁机电设备运维管理提出了更高要求。传统运维主要以"人工经验型"维修为主,辅助一定的自动化检测装置,存在检测手段不足、数据传输实时性差等问题,难以实现对全网机电设备运行状况的实时跟踪和分析。针对上述问题,文章通过建立具有 CPS 技术特征的超大城市地铁机电设备智能运维体系,实现设备的运行状态在线检测、故障诊断、库存物料动态调整等功能,助力超大城市地铁安全、可靠地运营。