Interagency Collaboration for Integrated Coastal Zone Management: A Bangladesh Case Study

Protection, conservation, and development of coastal resources of Bangladesh are being pursued by a number of agencies on narrowly defined subject-matter specialization like agriculture and fisheries. Coastal resources, however, have competitive uses and need to be approached holistically. A Program Development Office set up to start the preparatory work for an ICZM program commissioned an institutional review of 15 agencies most intimately connected with activities in the coastal area to assess their institutional capacity to take part in an ICZM program. The actual performance of one of the top-ranked organizations under review was further evaluated by drawing upon case materials from five completed multisector projects in which it was the lead agency. The case study revealed that institutional capacity was a necessary but not a sufficient condition for successful joint execution of multisector programs. Organizations tend to cooperate in a multisector program only when they are given full control over the management of their own components. Any arrangements short of that will not yield the desired result. An integrated approach needs to be formalized in a manner that allows each agency to maintain its independent status while at the same time allowing it to carry out its activities within a commonly agreed framework. This model contains the elements of an institutional design for carrying out an integrated coastal zone management program in Bangladesh.     

钢-混凝土组合连续弯箱梁抗火性能与设计方法

为研究提高钢-混凝土组合连续弯箱梁抗火性能的策略,选取某三跨钢-混凝土组合连续弯箱梁为研究对象,利用通用有限元软件ANSYS建立了其在火灾下的三维非线性两阶段分析模型;基于已有热-结构耦合分析方法,模型考虑了钢箱梁内空腔辐射传热过程和其上翼缘与混凝土板的接触边界条件;将模型得到的预测结果与试验数据进行了比较,验证了模型的可靠性;采用建立的模型在不同纵向受火位置、火灾强度和荷载水平作用下对钢-混凝土组合连续弯箱梁跨中挠度进行了参数敏感性分析,研究了其极限承载能力和刚度衰变规律;以火灾下跨中挠度为评估指标,提出了针对钢-混凝土组合连续弯箱梁的抗火设计方法。研究结果表明：在对称火和结构荷载作用下,钢-混凝土组合连续弯箱梁外边缘挠度大于内边缘挠度,且荷载越大,火灾越严重,这一效应越显著;在油罐车等过火面积较大的火灾作用下,刚度较极限承载能力衰退更快,与常温下的钢-混凝土组合连续弯箱梁极限承载能力和刚度相比,边跨受火16 min时极限承载能力和刚度分别降低至29%和14%,中跨受火28 min时极限承载能力和刚度分别降低至31%和22%;在钢-混凝土组合连续弯箱梁抗火设计中,应首先提高外侧钢箱梁在火灾下的刚度,增多和加宽外侧钢箱梁底板纵向加劲肋可使边跨受火20 min后内外侧钢箱梁跨中挠度差分别减小23%和30%,中跨受火32 min后内外侧钢箱梁跨中挠度差分别减小22%和27%。     

Theoretical studies of active power/angle sub-matrix in power flow Jacobian for power system analysis

Properties of the active power/angle sub-matrix in the power flow Jacobian for power system analysis are studied. The sub-matrix is a dominant and irreducible matrix under very general conditions of power systems, so that it is invertible. Also the necessary conditions for its singularity are given. These theoretical results can be used to clarify the ambiguous understanding of the sub-matrix in current literature, and also provide the theoretical foundations for the applications based on reduced power flow Jacobian. Numerical simulation on the IEEE 118-bus power system is used to illustrate our results.     

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行程时间的不确定性是影响货运车队路径选择的一个重要因素，特别是对于要求货物准时送达的配送任务（例如商品混凝土的配送），提出了在车辆调度中考虑由拥挤路段交通流量波动引起的行程时间不确定性的方法，建立了考虑行程时间可靠性要求的车辆优化调度数学模型，给出了相应的启发式算法，通过算例介绍了该模型和算法的应用。结果表明配送总成本随行程时间可靠性要求的提高而增加。     

Analysis of a Passive Sequential Hydraulic Damper for Vehicle Suspension

Vibration isolation characteristics of a sequential hydraulic damper, employing external pressure relief valves, are investigated via analytical means. The sequential hydraulic damper is modelled as a nonlinear dynamical system incorporating nonlinearities due to orifice flows, gas spring and pressure relief mechanisms. The damping characteristics of the sequential hydraulic damper, are compared to those of a constant orifice and a semi-active sequential damper, and discussed in view of their vibration isolation performance. It is established that the performance characteristics of the sequential hydraulic damper are similar to that of a semi-active sequential damper. A tuning methodology to achieve appropriate control of the resonant peak and effective vibration isolation is proposed. The shock and vibration isolation performance of the vehicle model employing a sequential damper are evaluated and compared to those of the vehicle model employing a constant orifice hydraulic damper. It is concluded that the vehicle ride performance can be improved considerably using an adequately tuned sequential damper.     

A Nonlinear Analysis of the Generic Types of Loss of Stability of the Steady State Motion of a Tractor-Semitrailer*

All different types of loss of stability which occur generically for a tractor semitrailer vehicle are studied when varying two parameters namely the speed V of the vehicle and the position d of the center of mass of the trailer. For a fixed value of d and varying V it turns out that only two cases either a divergence or a Hopf bifurcation can occur typically. By means of a nonlinear analysis the post-bifurcation behavior for both cases is treated showing that it is critical in both cases. This latter result means that the system is an imperfection sensitive one for which the calculation only of the linear stability limit, does not have very much practical meaning, because small perturbations of the system (changes of parameters) can lead to a drastic reduction of the critical speed. Our paper furthermore indicates how a nonlinear investigation of stability problems in vehicle dynamics with no restriction to the number of degrees of freedom of the system can be done in a straight forward manner.     

Comparison of results of two models of transportation demand in Hong Kong: CDAM and a version of microTRIPS

CDAM is a new computer program for solving the combined trip distribution and assignment model for multiple user classes, which enables transport planners to estimate consistent Origin-Destination (O-D) matrices and equilibrium traffic flows simultaneously if the trip production and attraction of each user class at zone centroids are available. This paper reports an application of CDAM to the central Kowloon study area in Hong Kong. The coefficients of the model related to the components of generalized costs are calibrated on 1986 travel data. A comparison of results of CDAM and a version of MicroTRIPS models of transportation demand in Hong Kong are presented. Finally, some conclusions are drawn and the advantage of the CDAM are discussed.     

Dynamic Performance of a Bulkhead Flat Car

The dynamic performance of a flat car is studied herein. The performance indices include roll angles, lateral accelerations, center plate loads, side bearing loads, wheel loads and spring deflections. These variables are maximum when the car is running at its critical speed, corresponding to either the rock and roll, or the bounce mode. The Association of American Railroads' (AAR) Flexible Carbody Model was used. The input for vertical track irregularities used in the simulation was generated from published spectra for U.S. Federal Railroad Administration (FRA) Class 4 track. After studying the car's performance with various column loads and spring suspensions, it was found that the most commonly used column load of 4,000 lbs. (17.8 kN) should be used. The spring suspension used in the original car design should also be adopted, in order to avoid spring. bottoming.     

Container terminal productivity: a perspective

The increasing competitiveness of the marine transportation industry has brought about demands that container terminal productivity be improved. MARAD, in cooperation with the National Research Council, has responded by developing a number of quantitative measurements for container terminal productivity. In this paper we discuss the problems and prospects of using such measurements to estimate or compare the productivity of terminals or ports. Because physical or institutional factors, or a combination of the two, act to limit the productivity of every container terminal, quantitative productivity comparisons among terminals or ports may lead to misplaced efforts to improve the productivity of particular operational elements in piecemeal fashion. By contrast, a sensible strategy for managing productivity would involve the linking of productivity and cost data, so that existing productivity constraints can be intelligently shifted from one area of operations to another.