Numerical determination of flushing time for stratified water bodies

It is often advantageous to model a semi-enclosed estuarine or coastal embayment (e.g. fish farms or tidal inlets, or typhoon shelters) as a separate system within a larger water body connected to the outer sea. The water quality of the system depends crucially on its flushing time—the average time of a particle in the system. The flushing time is governed by the barotropic and baroclinic tidal exchanges between the system and the outer sea. We describe herein a general method to determine systematically the flushing time of a stratified water body via a numerical tracer experiment. Numerical solution of the 3D flow and mass transport equations for many practical problems show that the tracer mass removal process depends on the physical topography and bathymetry, tidal range and the degree of stratification in the outer sea. Field application suggests that the tracer mass variation can be well approximated by a double-exponential decay curve that can be described by three flushing coefficients. Using a simple analytical two-segment model, the flushing coefficients can be given a clear physical interpretation, and the flushing time can be easily determined in terms of the coefficients. The method is illustrated by application to a number of tidal inlets in Hong Kong, in both the dry and wet season. The connection between the numerically determined flushing time and the traditional bulk flushing time obtained from salt-balance methods is established.     

The UNCTAD and WORKPORT models of port development: evolution or revolution?

Around ten years have elapsed since the UNCTAD model on port development was put forward as an explanation of how ports have adapted to incorporate technological, political and operational changes. The UNCTAD Three Generation Port Model is critically examined in the light of research carried out under the WORKPORT project funded by the European Commission, 1998-1999. Evidence from the WORKPORT study shows that, rather than developing in discrete steps, ports evolve continuously, adapting to new technologies, fresh legislation, revised working practices and other influences on an as-required basis. Further, it is demonstrated that several streams of evolution can be observed simultaneously; the pace of change within each stream can vary substantially. One of the prominent features of ports is that they often have several terminals, some operating along traditional lines while others may be leading edge in terms of technology, working practices or other aspects; all of them may be equally effective. The UNCTAD model, implying ports develop in discrete steps, or generations, is therefore shown to be fundamentally flawed.     

Mariner anticipation and performance

Collisions and groundings continue to take their toll on seafarers and the environment. Much has been said about the associated role of human factors. STCW95 endeavored to create a closer relationship between what is taught and what is needed to handle the demands of the operational environment. Technological developments such as ARPA, and in the future AIS, imply access to more data. With a view to determining how data should be presented and used, this study examines the capabilities of mariners to identify and initiate an appropriate course of action in an encounter where the need for two targets to maneuver to avoid collision with each other changes our own vessel’s passing distance from a safe to an unsafe state. Such a capability can generally add to the probability of a successful encounter through anticipating the resulting conflict with our own vessel and through taking appropriate early action. The outcome of this study, reported in this paper, was that very few senior officers and masters displayed the advanced level of anticipation skills that would provide the situation awareness needed for the encounter presented. Such outcomes may point to the need for inclusion of specific training in anticipation skills within the maritime educational system and/or for the provision of decision support systems which assist the development of situation awareness and identification of an appropriate course of action.     

A Versatile Flat Track Tire Testing Machine

Summary A flat track tire testing machine developed by the IMMa group is described. It permits the simulation and study of the dynamic behavior of a great variety of tires under controllable and repetitive highly dynamic realistic working conditions in the laboratory for a diversity of vehicles, from motorcycles to light trucks. The machine incorporates: - a hydraulically operated tire support and loading system with wide operating ranges; - a computer controlled brake system to simulate braking maneuvers with ABS systems; - a complete sensorial system; - a data acquisition and control system continually monitoring and acting on the experimental variables, i.e., tire and belt speed, longitudinal slip, slip and camber angles, tire pressure, tire normal force, etc. As an application example, results are presented that adjust the parameter of the magic formula for a standard 175/70 R14 passenger vehicle tire. Accurate mathematical tire models are recognized as essential for the prediction of vehicle dynamic performances using simulation tools.     

The PROFILE project: an overview

The EC MAST project PROFILE (Processes in Regions of Freshwater Influence, ROFIs) aims to develop process understanding and tested numerical models for ROFIs. This includes the role of physical processes controlling water-property distributions, suspended sediments controlling the availability of light, nutrients and phytoplankton growth. The project comprises: (1) construction of a 3D nearshore model, with high resolution (1 h and one km approx.) and a framework coupling modules for hydrodynamics (tides, effects of winds and waves, currents, temperature, salinity, turbulence and diffusivity), sediments, plankton, nutrients and oxygen, (2) investigation of methods to include ROFI model detail in coarser shelf-wide models, (3) specific tests of model components against measurements, (4) tests of model calculations against measurements in contrasted ROFIs, (5) systematic observations suitable for these model tests (time-series over a seasonal cycle for dynamics and intermittency, good vertical resolution and spatial surveys) of the contrasted Rhine, Clyde and Thermaikos Bay ROFIs, complementing earlier measurements in the ROFI areas of the Rhine, German Bight and Po, (6) interpretation and comparison of the contrasted ROFIs' behaviour, (7) a defined set of observations, model code and output suitable for subsequent integration and promulgation as test data and a nearshore model for wider use.     

Extended Ground-Hook - New Concept of Semi-Active Control of Truck's Suspension

This paper deals with the novel control concept, so called ground-hook for active and mainly semi-active suspension of vehicles with the ultimate objective to minimize the tyre-road forces and thus the road damage. The basic ground-hook concept is extended to the several variants which enable to decrease criteria of road damage as well as to increase driver's comfort for a broad range of road unevennesses. Parameters of control law are determined by the parameter optimization for generally nonlinear model. The influence and interaction of the damping rate limits and time constants of variable shock absorbers are also taken into account. The influence of implementation of more complicated truck models is also discussed.     

Autonomous Lateral Control of Vehicles in an Automated Highway System

Lateral control of vehicles in IVHS requires the installation of on-board sensors as well as the installation of roadway hardware such as cables, magnets, etc. Existing control approaches in PATH require road curvature and vehicle lateral position (with respect to the center of the lane) information. Hence these approaches rely on roadway sensors to obtain relative lateral position. These methods will necessitate infrastructural changes to the highway.

This paper introduces the concept of autonomous lateral control or auto-tracking. The method allows us to use only line-of-sight sensor information to effect vehicle control. We present a detailed vehicle model. Controllers have been proposed to demonstrate the effectiveness of the proposed auto-tracking scheme. We also examine the possibilities of using this method for lane change purposes in an automated highway system.     

Baroclinic eddy formation in a Rhine plume model

A three-dimensional finite difference tidal model, including advective and diffusive transport of salinity, is used in the two-layer model for simulation of Rhine water outflow. Layer depths are adjusted in a way that no advective transports between upper and lower layer take place in case of sufficiently stable stratification.Model results show frontal eddy development related to (limited) growing internal waves in case of weak northeasterly to southeasterly winds. It is shown that baroclinically unstable conditions occur, related to vertical velocity shear, resulting in frontal meanders with wave lengths between 18 and 30 km. Satellite images of sea surface temperature show a comparable behaviour of the temperature front, which is strongly correlated with the salinity front of the Rhine plume.     

海洋浮体非线性水弹性力学分析--结构非线性的初步考虑

前文^[1-3]分别介绍了二阶非线性水弹性分析中流体非线性的理论与部分典型算例结果。本文则在流体线性假定的前提下，介绍结构非线性的考虑方法。以大变形浮动平板在多向规则波中的运动与变形响应为例，介绍了板垂向位移与流体相互耦合的频域分析方法。讨论了板内薄膜力对结构变形与受力的影响。数值算例表明，薄膜力对变形、弯矩和应力都有一定程度的非线性贡献，在某些情况下是不可忽略的。     

High speed driving stability of passenger car under crosswind effects

The driving stability of a passenger car at high-speed and under crosswind conditions is affected by aerodynamic characteristics as well as their dynamic characteristics, suspension, and weight distribution. In this study, the total measuring system was thought up to understand the transient vehicle dynamics and aerodynamics with driver’s control inputs all together. The test results were taken from a full-scale wind tunnel test, a crosswind generator test and an on-road test. We investigated major aerodynamic parameters that affect the driving stability of passenger cars under crosswind effects such as overtaking, passing each other, natural crosswind, etc. The reaction rate of high-speed stability will be improved when we minimize the total lift, side force and especially the yawing moment.