On Impact mechanics in ship collisions

The purpose of this paper is to present analytical, closed-form expressions for the energy released for crushing and the impact impulse during ship collisions. Ship–ship collisions, ship collisions with rigid walls and ship collisions with flexible offshore structures are considered. The derived mathematical models include friction at the contact point so that situation where the collision results in a sliding motion is included. Results obtained by application of the present procedure are compared with results obtained by time simulations and good agreement has been achieved. In addition, a number of illustrative examples are presented. The procedure presented in the paper is well suited for inclusion in a probabilistic calculation model for damage of ship structures due to collisions.     

Influence of train length on in-train longitudinal forces during brake application

It needs some seconds for a signal, which is created from brake application, to travel from the first part of the train system (locomotive) to the end part of it (last wagon). Delay in time of all parts of the system (train) brake is seen which might deteriorate the longitudinal dynamic interaction of the long trains. For instance, this results in running of the rear cars to the front ones and hence producing large in-train forces at the buffers and couplers. Major parts of the rolling stock in railway system repair are known for relative compression and tension forces, which are applied to the whole train system and cause huge expenses for the industry. For trains with long lengths, operating in safe area is another important relation with train forces along the system. By using MATLAB simulation in this study, we investigated the length's effect on train dynamic along the system mainly for freight trains. We did our research on the trains which are currently used in Railways of Islamic Republic of Iran, RIRI. Four diverse cases were under our simulation, in each of which, trains consist of 52, 32, 20 and 12 cars, respectively. Two different forces (tension and compression) are displayed here as of the outcome of the research. Simulations show different forms of interplays in dynamics along the system. Then we compared the graphs to each other to find out detailed influences of length of the whole system (train including different number of wagons and locomotive) on dynamics of system along it while braking is applied.     

舵机电液伺服系统零偏、零漂分析

电液伺服阀是电液控制系统的关键部件.通过对某舵机电液伺服系统零偏、零漂分析,给出了影响电液伺服系统零偏、零漂的主要因素.     

货车旁承间隙对车辆动力学性能的影响

对货车车体相对于摇枕的侧滚运动进行几何简化,导出上旁承下端面位于心盘旋转点之上、之下和上旁承下端面与心盘旋转点位于相同垂向位置时,旁承的垂向位移与车体重心相对于摇枕横向位移的几何关系。在车辆动力学模型中引入侧滚回复力矩和等效摩擦半径,并对心盘进行力学简化。运用多体系统分析方法对货车动力学性能进行仿真。结果表明:侧滚回复力矩可以有效抑制车体由于轨道激励而产生的相对摇枕的侧滚运动;过小或过大的旁承间隙会使车辆的动力学性能恶化。当车体重心横向偏移量小于心盘半径时,车体重力将产生阻止车体侧滚的回复力矩;反之,车体重力产生的力矩将加速车体的侧滚。过小的旁承间隙会使车体上旁承和摇枕下旁承频繁接触,对车体产生较大的冲击;而过大的旁承间隙又使旁承在侧滚回复力矩不足时不能有效抑制车体的侧滚。     

基于系统动力学的港口与区域经济和谐发展的机理研究——以福建省为案例

以系统动力学(SD)模型为主体,结合投入产出表与计量经济学方法,建立港口与区域经济系统互动模型,应用此模型对港口与区域经济和谐发展的机理进行分析,最终找到港口与区域经济动态和谐发展的平衡点,并且对港口自身的发展运行状态作出评价。然后以福建省为案例对系统动力学模型进行仿真和验证。     

Investigation on dynamical interaction between a heavy vehicle and road pavement

This paper presents a model for three-dimensional, heavy vehicle-pavement-foundation coupled system, which is modelled as a seven-DOF vehicle moving along a simply supported double-layer rectangular thin plate on a linear viscoelastic foundation. The vertical tyre force is described by a single point-contact model, while the pavement-foundation is modelled as a double-layer plate on a linear viscoelastic foundation. Using the Galerkin method and quick direct integral method, the dynamical behaviour of the vehicle-pavement-foundation coupled system is investigated numerically and compared with that of traditional vehicle system and pavement system. The effects of coupling action on vehicle body vertical acceleration, suspension deformations, tyre forces and pavement displacements are also obtained. The investigation shows that the coupling action could not be neglected even on a smooth road surface, such as highway. Thus, it is necessary to investigate the dynamics of vehicle and pavement simultaneously based on the vehicle-pavement-foundation coupled system.     

Multiphysic modelling of railway vehicles equipped with pneumatic suspensions

This article presents a multidisciplinary approach of railway pneumatic suspension modelling: both multibody and pneumatic aspects are taken into account. The work aims at obtaining a realistic model of the secondary suspension and coupling it with a multibody model of a train. Various components of the pneumatic circuit such as bellows, tanks, pipes and valves are taken into account. The article focuses on the bellow–pipe–tank subsystem for which several modelling approaches are presented and compared. Differences between differential and algebraic models are highlighted, and an application-dependent choice between them is suggested. A complete model of the pneumatic circuit is then obtained and coupled with a multibody model of the train. As a result, the behaviour of a suburban train equipped with a pneumatic secondary suspension is analysed, in particular undesired oscillating motions which affect the comfort. Topological modifications and improvements of the suspension are also investigated and discussed.     

Large motion mountain biking dynamics

A bond graph model of a mountain bike and rider is created to develop baseline predictions for the performance of mountain bikes during large excursion maneuvers such as drops, jumps, crashes and rough terrain riding. The model assumes planar dynamics, a hard-tail (front suspension only) bicycle and a rider fixed to the bicycle. An algorithm is developed to allow tracking of a virtual tire-ground contact point for events that separate the wheels from the ground. This model would be most applicable to novice mountain bikers who maintain a nearly rigid relationship between their body and the bicycle as opposed to experienced riders who are versed in controlling the bicycle independent of the body. Simulations of a steep drop are performed for various initial conditions to qualitatively validate the predictions of the model. Results from this model are to be compared to experimental data and more complex models in later research, particularly models including a separate rider. The overarching goals of the research are to examine and understand the dynamics and control of interactions between a cyclist and mountain bike. Specific goals are to understand the improvement in performance afforded by an experienced rider, to hypothesize human control algorithms that allow riders to perform manoeuvres well and safely, to predict structural bike and body forces from these maneuvers and to quantify performance differences between hard-tail and full suspension bicycles.     

Three-dimensional analysis of transient slosh within a partly-filled tank equipped with baffles

The directional dynamic analyses of partly-filled tank vehicles have been limited to quasi-static fluid motion due to computational complexities associated with dynamic fluid slosh analyses. The dynamic fluid slosh causes significantly higher magnitudes of slosh forces and moments in the transient state that cannot be characterized through quasi-static approach, which provides reasonably good estimates of the mean responses. In this study, a three-dimensional nonlinear model of a partly-filled cylindrical tank with and without baffles is developed to investigate the significance of resulting destabilizing forces and moments caused by the transient fluid slosh, and the effects of baffles. The baffles and the end caps are modeled with curved shapes. The analyses are performed under varying magnitudes of steady lateral, longitudinal and combinations of lateral and longitudinal accelerations of the tank, and two different fill volumes using the FLUENT software. The results of the study are presented in terms of mean and peak slosh forces and moments, and variations in the mass moments of inertia of the fluid cargo within a clean bore and a baffled tank, for two different fill volumes and different magnitudes of acceleration excitations. The ratios of transient responses to the mean responses, termed as amplification factors, are further described to emphasize the significance of dynamic fluid slosh on the forces and moments induced on the vehicle. The results in general suggest that the mean responses attained from dynamic fluid slosh analyses correlate well with those attained from the quasi-static analyses for a clean bore tank. The amplification ratios of the resulting forces and moments could approach as high as 2. The results clearly show that the presence of baffles helps to suppress the peak as well as mean slosh forces and moments significantly.