Exciting forces for a wave energy device consisting of a pair of coaxial cylinders in water of finite depth

Two coaxial vertical cylinders-one is a riding hollow cylinder and the other a solid cylinder of greater radius at some distance above an impermeable horizontal bottom,were considered.This problem of diffraction by these two cylinders,which were considered as idealization of a buoy and a circular plate,can be considered as a wave energy device.The wave energy that is created and transferred by this device can be appropriately used in many applications in lieu of conventional energy.Method of separation of variables was used to obtain the analytical expressions for the diffracted potentials in four clearly identified regions.By applying the appropriate matching conditions along the three virtual boundaries between the regions,a system of linear equations was obtained,which was solved for the unknown coefficients.The potentials allowed us to obtain the exciting forces acting on both cylinders.Sets of exciting forces were obtained for different radii of the cylinders and for different gaps between the cylinders.It was observed that changes in radius and the gap had significant effect on the forces.It was found that mostly the exciting forces were significant only at lower frequencies.The exciting forces almost vanished at higher frequencies.The problem was also investigated for the base case of no plate arrangement,i.e.,the case having only the floating cylinder tethered to the sea-bed.Comparison of forces for both arrangements was carried out.In order to take care of the radiation of the cylinders due to surge motion,the corresponding added mass and the damping coefficients for both cylinders were also computed.All the results were depicted graphically and compared with available results.     

Comfort and Safety as Perceived by Wheelchair-Seated Bus Passengers

Abstract

Wheelchair-seated passengers on European and Swedish urban transit buses can travel rearwards, resting against a bulkhead, without the use of tie-down equipment. However, users sometimes disapprove of being the only passengers who have to travel rearwards, and also unrestrained. In order to investigate comfort and safety as perceived by wheelchair-seated bus passengers riding either forwards or rearwards, an experimental field study was carried out. Participating subjects were 31 wheelchair users and a group of 44 ambulant passengers. Each subject made two consecutive, identical 15-minute trips, randomly beginning either forwards or backwards, and interviews were conducted after each trip. During the trips, three-axis bus motion was recorded. The concept of categorization was used as a theoretical background and basis for discussion of the comfort and safety constructs. The results indicated that while the majority preferred the forward-facing position regarding comfort issues, a minority felt that the level of perceived safety was better. Wheelchair-seated passengers were more positive towards the rearward position than the ambulant group.     

钢桁连续刚构桥模型简化方案

特大桥梁模型试验规模较大,制作、测试均较复杂,因此,需要在尽可能反映实桥真实应力的情况下简化试验模型。通过不同模型方案计算分析后得知,在一定的边界条件下,钢桁连续刚构桥全桥一半模型完全能够真实地反映实桥受力状态。这样就能将模型所需的资源减小一半,而且可以在有限的试验室空间内将模型尺寸相对做大。     

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本文基于快速路交通流分布参数系统模型,利用快速路交通流系统具有重复运行的显著特点,设计一种新的入口匝道分布参数迭代学习边界控制方案.所提出的方法采用带有反馈的PD-型控制律,不仅可以从以前重复过程中学习有用的知识,提高系统的控制精度;还可以有效的抑制当前运行过程中系统的量测噪声和扰动等不确定影响因素.该方法的另一个显著特点在于充分利用了快速路交通系统的分布参数模型描述,更全面地利用了系统的时空控制信息,从而提高了整个路段的控制性能.本文基于Matlab仿真进一步说明所提出方法的有效性和适用性.     

基于电子助力器的冗余防抱死制动算法研究

自主研发一种带踏板推杆的半解耦电子助力器(eBooster),基于变增益PID控制算法,对eBooster液压力进行精准控制;当车辆ABS系统失效时,通过对车辆各状态变量的估算和监测,基于eBooster对制动主缸液压力的主动调整;以冗余制动防抱死(ABS)功能实现为要求、制动强度和舒适性提升为目标,提出一种基于滑模控...     

Integrating visual management into the coastal zone planning process: The Massachusetts experience

Abstract

This paper concerns the limitations on integrating visual management into the coastal zone planning process as exemplified by the Commonwealth of Massachusetts, a state with a strong tradition of “home rule”; and a CZM implementation program based on a “networking”; of existing state authorities. The implications of the Massachusetts experience are that: (a) management of esthetic resources at the state level continues to be much less of a priority than management of ecological resources such as wetlands or floodplains; (b) visual management has yet to engender a strongly supportive constituency beyond that concerned with historic preservation; (c) project review focusing on visual impacts may be a more appropriate activity for local rather than state government; and (d) the technical aspects of visual management or impact assessment are far more advanced than their political acceptability. Political realities, together with the decision that implementation of the program should be based on a networking of existing authorities, thus determined the degree to which visual management could be incorporated into the state's program. As a result, the program's principal instruments of visual management became a strengthening of existing programs such as Wild and Scenic Rivers, reliance on wetland protection statutes to indirectly protect natural scenic values, and the use of the federal consistency provisions of the Coastal Zone Management Act to foster focused growth patterns through provision of publicly funded infrastructures. Esthetically oriented project review, with the exception of potential impacts on historic sites, was left to the discretion of local government, and a technical assistance program was created to provide funding or professional skills to communities interested in developing their own esthetic controls or design review processes. Maine, Rhode Island, and other New England states have followed a similar course.     

基于人-车-路耦合振动系统的儿童乘坐舒适性

根据拉格朗日原理,建立了基于人-车-路耦合振动的12自由度动力学数学模型;借助MATLAB/Simulink平台,分析车速、路面不平度、汽车前后轮迟滞性及左右轮相干性的特点;构建了随机路面激励时域模型;采用时域和频域分析了在不同路面及不同车速下汽车对儿童头部、臀部振动影响。研究表明:通过提高路面等级及车速可以提高儿童的乘坐舒适性;儿童对5～10 Hz的低频及15,23 Hz的中频振动最为敏感;适当地降低座椅刚度、提高阻尼及合理地布置座椅位置可以提高儿童的乘坐舒适性。     

惯性释放法在大型复杂结构焊接变形预测中的应用

在进行大型结构焊接变形有限元分析时,为了固定整体结构刚体位移必须施加不少于6个自由度的约束,但对于自由状态下的结构而言,如何施加这6个最少约束是非常的困难,长期以来是困扰研究人员的难题,也是焊接结构有限元分析在工业现场应用的一个瓶颈。所谓惯性释放法就是可以在不加约束的情况下模拟自由结构的变形。该文将在航海航空领域得到广泛应用的惯性释放法引入大型焊接结构变形分析,解决了自由状态下结构必须施加约束的问题。首先以典型的对接接头为例,比较了两种不同的约束方法之间的差别。然后通过一个典型的船体焊接变形预测的实例,验证了惯性释放法在大型结构中应用的可行性,为焊接结构变形分析在工业生产中广泛应用提供了一个有效的方法。     

粘结橡胶环的载荷-压缩关系

粘结橡胶环在很多工程领域被广泛应用于缓冲冲击。这些应用一般都要求掌握橡胶垫准确的载荷压缩关系。但以往的研究仅讨论了橡胶柱体而忽略了橡胶环,而且仅少数研究是基于连续介质力学理论的。文章推导了刚性板间不可压缩橡胶环在三种边界条件下的载荷—压缩关系,考虑了Mooney-Rivlin材料,并基于连续介质力学理论进行了推导。文中将推导公式的计算结果与有限元计算结果进行了比较,证明了这些公式有足够的精度,适用于各种形状系数和材料参数,在有限应变下仍然适用。最后,文中还给出了典型橡胶环的载荷—压缩曲线,并对不同边界条件下的压缩刚度特性进行了讨论。     

Optimisation of active suspension control inputs for improved vehicle ride performance

A collocation-type control variable optimisation method is used in the paper to analyse to which extent the fully active suspension (FAS) can improve the vehicle ride comfort while preserving the wheel holding ability. The method is first applied for a cosine-shaped bump road disturbance of different heights, and for both quarter-car and full 10 degree-of-freedom vehicle models. A nonlinear anti-wheel hop constraint is considered, and the influence of bump preview time period is analysed. The analysis is then extended to the case of square- or cosine-shaped pothole with different lengths, and the quarter-car model. In this case, the cost function is extended with FAS energy consumption and wheel damage resilience costs. The FAS action is found to be such to provide a wheel hop over the pothole, in order to avoid or minimise the damage at the pothole trailing edge. In the case of long pothole, when the FAS cannot provide the wheel hop, the wheel is travelling over the pothole bottom and then hops over the pothole trailing edge. The numerical optimisation results are accompanied by a simplified algebraic analysis.