Advection schemes for shelf sea models

Numerical models of shelf seas must handle sharp gradients in thermoclines and fronts, and at the edges of patches of passive tracer, often in the presence of strong tidal currents, without introducing excessive numerical diffusion or spurious oscillations. In a sigma coordinate model there is an additional problem, since then purely horizontal motion over a sloping sea bed may introduce strong numerical diffusion in the vertical, which can artificially erode thermoclines.In this paper, two advection schemes applicable to shelf sea models are examined. They are based on TVD (Total Variation Diminishing) and PPM (Piecewise Parabolic Method) techniques. They are demonstrated to give satisfactory performance for tracer advection in one, two and three dimensions. They are both monotonic, and the PPM scheme has particularly low numerical diffusion. In two and three dimensions directional splitting is used, which is handled by following advection with each horizontal velocity component by adjustment of the sigma levels in each water column using the same advection scheme. The artificial vertical diffusion is then small, particularly with PPM.The two schemes are also compared in a three-dimensional model of a cylindrical eddy of relatively fresh water, released from rest in an open sea region. Here, both salinity and momentum are advected. Laboratory experiments show that after an initial period of adjustment the eddy should become unstable, with a growth of cyclonic-anticyclonic eddy pairs. This is reproduced in the model, with the PPM scheme again producing sharper results than the TVD scheme.Integrated second moment calculations are used to compare the schemes. These demonstrate the lower numerical diffusion of the PPM scheme. This advantage is achieved at the cost of greater computing time.     

The market for ship demolition

Little has been written about the ship demolition market, an essential element in the supply/demand balance for shipping. Either technical or economic obsolescence may be the cause for scrapping a ship, where the latter is strongly influenced not only by anticipated freight market levels, but the rate at which more efficient ships are being introduced. The scrap value of a ship is a function both of the realizable value of the materials within the ship and cost of demolition. Both are strongly influenced by the cost structures prevailing in the likely country of demolition. The paper explores not only the fundamentals of the ship demolition market, but the trends from the 1960s to the present. The shipbreaking market has moved in that time from being West European-centred to Asian-centred, concentrating for some years in Taiwan, but now shifting to the Indian subcontinent.     

Book Review

Vehicle Replacement — A Management Guide. By John E. Sussams. (Gower, 1983.) [Pp. 102.] £19.50.     

Adaptability and vulnerability of zooplankton species in the adjacent regions of the Black and Marmara Seas

During 2005–2008 species composition, abundance patterns, natural mortality rates and salinity effects on zooplankton were studied in the Bosphorus regions of the Black and Marmara Seas. The tendencies to diminish for abundance and biomass of the Black Sea originated zooplankton species and to increase for the proportion of their carcasses in the direction from the Black Sea toward the Marmara Sea were found. The mortality in the Black Sea species increased with depth in the Marmara Sea. The contribution of organic matter of carcasses of the Black Sea originated organisms to bacterial processes in the deep strata of the Marmara Sea was estimated. Different salinity and temperature regimes restrict mutual penetration of the species in these seas.     

Examining Local Coastal Zone Management Capacity in U.S. Pacific Coastal Counties

The coastal zone has critical natural, commercial, recreational, ecological, industrial, and esthetic values for current and future generations. Thus, there are increasing pressures from population growth and coastal land development. Local coastal land use planning plays an important role in implementing the U.S. Coastal Zone Management Act (CZMA) by establishing goals and performance policies for addressing critical coastal issues. This study extends the CZMA Performance Measurement System from the national level to the local land use level by measuring coastal zone land use plan quality and political context in fifty-three Pacific coastal counties. Plan quality is measured using an evaluation protocol defined by five components and sixty-eight indicators. The results indicate a reasonable correspondence between national goals and local coastal zone land use planning goals, but a slight gap might exist between the national/state versus local levels in the overall effectiveness of coastal zone management (CZM) efforts. The results show many U.S. Pacific coastal counties lack strong coastal zone land use plans because the average plan quality score was only 22.7 out of 50 points. Although these plans set relatively clear goals and objectives, they are somewhat weaker in their factual basis, identify a limited range of the available planning tools and techniques, and establish few coordination and implementation mechanisms. The regression analysis results indicate that CZM plan quality was not significantly related to any of the jurisdictional characteristics.     

Optimal fuel-cut driving method for better fuel economy

Eco-drive methods are being applied in modern passenger cars in the form of LCD displays showing real-time fuel consumption rates. The eco-drive is one of the most promising methods to enhance the fuel economy of vehicles. The ecodrive method can be made more effective by using the fuel-cut function. The fuel is not injected when the driver does not depress the gas pedal of a vehicle with engine speeds higher than approximately 1,500 rpm above the mid-vehicle speed range. This function is known as the fuel-cut function, and almost every modern vehicle is equipped with this function. The fuel-cut is most frequently activated on downhill sections of highway. Therefore, the CO₂ exhausted from the vehicle can be zero in this downhill section. In this study, the fuel-cut function is simulated with CRUISE of AVL to find the most effective driving pattern in downhill sections. Simulations with the CRUISE software showed that the lower limit of the vehicle speed for fuelcut should be raised to improve fuel economy on steeper downhill sections. The fuel economy can be optimized when the fuelcut coasting and reacceleration is completed in the downhill part of the road. The simulation result was also compared to previous test results. Fuel consumption was reduced by approximately 4% in both the experimental and simulated results for the West Coast Highway in South Korea.     

Yaw rate and side-slip control considering vehicle longitudinal dynamics

Most conventional vehicle stability controllers operate on the basis of many simplifying assumptions, such as a small steering wheel angle, constant longitudinal velocity and a small side-slip angle. This paper presents a new approach for controlling the yaw rate and side-slip of a vehicle without neglecting its longitudinal dynamics and without making simplifying assumptions about its motion. A sliding-mode controller is used to develop a differential braking controller for tracking a desired vehicle yaw rate for a given steering wheel angle, while keeping the vehicle’s side-slip angle as small as possible. The trade-off that exists between yaw rate and side-slip control is described. Conventional and proposed algorithms are presented, and the effectiveness of the proposed controller is investigated using a seven-degree-of-freedom vehicle dynamics model. The simulation results demonstrate that the proposed controller is more effective than the conventional one.     

Enhanced selective forwarding scheme for alert message propagation in vehicular <Emphasis Type="Italic">ad hoc</Emphasis> networks

Vehicle-based applications were recently introduced to improve traffic safety and efficiency. These applications are classified into either safety-oriented or non-safety-oriented applications. Safety-oriented applications are typically provided by means of vehicle-to-vehicle (V2V) communications to support reliable and fast alert message propagation to all surrounding vehicles when an emergency occurs on the road. In vehicular ad-hoc network (VANET) broadcast-based packet forwarding is typically preferred for the propagation of urgent traffic-related information to all reachable nodes within a specified dangerous region. However, this approach may cause broadcast storm problems, which can lead to serious contention between transmissions from adjacent nodes. In this paper, we propose an alert message propagation scheme that is based on selective forwarding and aims to i) minimize the number of rebroadcasting nodes and ii) guarantee reliable and fast alert message delivery to all reachable nodes. Our scheme was evaluated using two different highway scenarios. The simulation results demonstrated that the performance of the proposed scheme was better than that of existing broadcast schemes in terms of the message delivery latency, the message delivery ratio, and the message rebroadcasting ratio.