发动机结构噪声的计算机仿真分析

以一台四缸发动机为例,应用计算机仿真技术分析了发动机的结构振动噪声。首先建立发动机总成有限元模型,通过模态分析,为发动机的结构修改提供依据。根据车用发动机的实际使用工况,在不同转速及爆发压力下对其进行动力学计算,得到发动机的表面振动速度级。通过改进发动机结构,使发动机的表面振动速度级降低了5.6dB(A)。     

无人潜器光学引导回收技术的仿真研究

该文介绍了无人潜器UUV(UnmannedUnderwaterVehicle)光学引导回收技术方面最新的研究结果 ,提出了回收过程的光学引导系统的模型 ,给出了不同光源配置条件下的光学引导系统仿真结果及其精确性和可靠性。这些仿真结果也可以帮助建立一个光学引导和控制模式。     

A microscopic simulation model for merging control on a dedicated-lane automated highway system

The automated highway systems (AHS) are not designed as stand-alone transportation facilities. Drivers will by necessity drive from their origins to the AHS entrance, and from the AHS exit to their final destinations. Therefore, the AHS will affect other transportation facilities, and should be integrated with all other facilities in the transportation system. Interfaces create much of the congestion for today’s transportation systems. Likewise, AHS interfaces may cause a similar problem, due to either AHS interactions with conventional systems or internal limitations from AHS merging capabilities. If these problems exist, either the AHS or the conventional road network cannot function properly. Consequently, the system as a whole may break down and the AHS could potentially become a detriment to the overall transportation system.Clearly, not enough is known about the automated merging process to determine what conditions would lead to congestion at interface points. The current macroscopic analysis techniques assume parameters that are not applicable to an AHS, and no detailed AHS merging models have been developed and validated. This paper addresses the interface problem between an AHS, and conventional roadway. Specifically, it presents a microscopic simulation model for one scenario of the automated merging maneuver. The results of the model show that for low flows and conventional highway speeds, an one-lane AHS merging section with a dedicated automated entrance ramp has many similar characteristics as a two-lane conventional freeway with or without fixed-time ramp metering. However, when the conventional freeway starts to “break down” near its capacity, the AHS continues to perform with little delay. The model also validates that the minimum ramp length requirements are a function of the merging vehicle’s speed, the mainline vehicles’ speed, and the acceleration and deceleration rates of the merging vehicle.     

Closing the loop in real-time railway control: Framework design and impacts on operations

Railway traffic is heavily affected by disturbances and/or disruptions, which are often cause of delays and low performance of train services. The impact and the propagation of such delays can be mitigated by relying on automatic tools for rescheduling traffic in real-time. These tools predict future track conflict based on current train information and provide suitable control measures (e.g. reordering, retiming and/or rerouting) by using advanced mathematical models. A growing literature is available on these tools, but their effects on real operations are blurry and not yet well known, due to the very scarce implementation of such systems in practice.In this paper we widen the knowledge on how automatic real-time rescheduling tools can influence train performance when interfaced with railway operations. To this purpose we build up a novel traffic control framework that couples the state-of-the art automatic rescheduling tool ROMA, with the realistic railway traffic simulation environment EGTRAIN, used as a surrogate of the real field. At regular times ROMA is fed with current traffic information measured from the field (i.e. EGTRAIN) in order to predict possible conflicts and compute (sub) optimal control measures that minimize the max consecutive delay on the network. We test the impact of the traffic control framework based on different types of interaction (i.e. open loop, multiple open loop, closed loop) between the rescheduling tool and the simulation environment as well as different combinations of parameter values (such as the rescheduling interval and prediction horizon). The influence of different traffic prediction models (assuming e.g. aggressive versus conservative driving behaviour) is also investigated together with the effects on traffic due to control delays of the dispatcher in implementing the control measures computed by the rescheduling tool.Results obtained for the Dutch railway corridor Utrecht–Den Bosch show that a closed loop interaction outperforms both the multiple open loop and the open loop approaches, especially with large control delays and limited information on train entrance delays and dwell times. A slow rescheduling frequency and a large prediction horizon improve the quality of the control measure. A limited control delay and a conservative prediction of train speed help filtering out uncertain traffic dynamics thereby increasing the effectiveness of the implemented measures.     

汽车变速器装配线可视化装配工艺仿真技术的研究与应用

以某汽车变速器装配线为对象,利用三维数字化工厂仿真软件DELMIA/QUEST,对变速器虚拟装配线的对象建模方法、装配工艺仿真环境的规划和搭建进行了研究。分析了装配线中存在的瓶颈、不平衡、物流运送不顺畅等问题,并结合实际仿真数据对装配线的规划进行了优化和调整,得到了较理想的装配线优化方案。     

考虑土体渗透性径向变化的砂井地基数值模拟分析

土体渗透性是影响砂井地基固结的重要因素。为研究复杂条件下砂井地基的固结性状,通过编制用户子程序在ABAQUS中建立了渗透系数沿径向变化的砂井地基固结计算数值模型,对固结过程中的孔压分布及固结性状进行了研究。结果表明:渗透系数在径向上的变化情况会对砂井固结性状产生很大的影响。假定涂抹区渗透系数为常数时固结速率最慢;假定涂抹区渗透系数呈抛物线变化时固结速率最快;而假定涂抹区渗透系数呈线性变化时固结速率介于以上两种情况之间。此外,砂井地基的固结性状还受排水条件和土层特性等因素的影响。     

Uncertainty in traffic forecasts: literature review and new results for The Netherlands

This paper provides a review of transport model applications that not only provide a central traffic forecast (or forecasts for a few scenarios), but also quantify the uncertainty in the traffic forecasts in the form of a confidence interval or related measures. Both uncertainty that results from using uncertain inputs (e.g. on income) and uncertainty in the model itself are treated. The paper goes on to describe the methods used and the results obtained for a case study in quantifying uncertainty in traffic forecasts in The Netherlands.

Electric vehicles in car sharing networks – Challenges and simulation model analysis

In this paper, we examine the operation of electric vehicles in urban car sharing networks. After surveying strategic and operational differences and comparing them to gasoline-fueled cars, a simulation study was carried out. The proposed discrete event simulation tool covered important operational characteristics of electric vehicles, including realistic charging routines. Different vehicle types were compared under various conditions and on multiple markets to determine their performance. The data obtained indicated the competitiveness of electric vehicles in car sharing networks. Key success factors included advantageous relations between the market environment (e.g. electricity and fuel prices) and important characteristics of electric cars (e.g. price and range).     

An investment appraisal method to compare LNG-fueled and conventional vessels

Ever stricter emission regulations stimulate vessel owners to consider the adoption of alternative marine fuels, such as Liquefied Natural Gas (LNG). In deciding whether to invest in LNG-fueled vessels, initial investment and operating costs are decisive factors that have not yet been fully studied in the literature. In this paper, we present a new investment appraisal method to compare the costs of LNG-fueled vessels with conventional vessels. We analyze the fuel costs and overall exploitation costs by simulating bunker planning decisions under stochastic fuel prices, presence in emission controlled areas, and route lengths. Our analyses reveal that the fuel costs of LNG-fueled vessels are often lower than those of conventional vessels, even under unfavorable LNG prices. Due to the higher initial investment costs in LNG-fueled vessels, these fuel cost reductions do not always translate into lower overall exploitation costs. By conducting numerical experiments, we identified conditions under which the exploitation costs of LNG-fueled vessels are lower than conventional vessels.     

Vehicle detection grammars with partial occlusion handling for traffic surveillance

Traffic surveillance is an important topic in intelligent transportation systems (ITS). Robust vehicle detection is one challenging problem for complex traffic surveillance. In this paper, we propose an efficient vehicle detection method by designing vehicle detection grammars and handling partial occlusion. The grammar model is implemented by novel detection grammars, including structure, deformation and pairwise SVM grammars. First, the vehicle is divided into its constitute parts, called semantic parts, which can represent the vehicle effectively. To increase the robustness of part detection, the semantic parts are represented by their detection score maps. The semantic parts are further divided into sub-parts automatically. The two-layer division of the vehicle is modeled into a grammar model. Then, the grammar model is trained by a designed training procedure to get ideal grammar parameters, including appearance models and grammar productions. After that, vehicle detection is executed by a designed detection procedure with respect to the grammar model. Finally, the issue of vehicle occlusion is handled by designing and training specific grammars. The strategy adopted by our method is first to divide the vehicle into the semantic parts and sub-parts, then to train the grammar productions for semantic parts and sub-parts by introducing novel pairwise SVM grammars and finally to detect the vehicle by applying the trained grammars. Experiments in practical urban scenarios are carried out for complex traffic surveillance. It can be shown that our method adapts to partial occlusion and various challenging cases.