Nonlinear Dynamics of Vehicle Traction

Summary The purpose of this study is to understand the nonlinear dynamics of longitudinal ground vehicle traction. Specifically, single-wheel models of rubber-tired automobiles under straight-ahead braking and acceleration conditions are investigated in detail. Customarily, the forward vehicle speed and the rotational rate of the tire/wheel are taken as dynamic states. This paper motivates an alternative formulation in which wheel slip, a dimensionless measure of the difference between the vehicle speed and the circumferential speed of the tire relative to the wheel center, replaces the angular velocity of the tire/wheel as a dynamic state. This formulation offers new insight into the dynamic behavior of vehicle traction. The unique features of the modeling approach allow one to capture the full range of dynamic responses of the single-wheel traction models in a relatively simple geometric manner. The models developed here may also be useful for developing and implementing anti-lock brake and traction control control schemes.     

路面强度的非破坏评估

准备充分和及时的养护计划或根据交通量的需求进行公路升级,都需要对现有路面能力及路面可服务性进行评估。使用动态荷载非破坏方法,收集大量的路面结构情况现场信息,方便快捷,能节约成本,数据可信度也很高。     

Hydrography and biogeochemistry of the north western Bay of Bengal and the north eastern Arabian Sea during winter monsoon

The north eastern Arabian Sea and the north western Bay of Bengal within the Indian exclusive economic zone were explored for their environmental characteristics during the winter monsoons of 2000 and 2001 respectively. The two regions were found to respond paradoxically to comparable intensities of the atmospheric forcing. There is an asymmetry in the net heat exchange of these two basins with atmosphere because of the varying thickness of barrier layer. During winter, the convective mixing in the Arabian Sea is driven by net heat loss from the ocean, whereas the Bay of Bengal does not contribute to such large heat loss to the atmosphere. It appears that the subduction of high saline Arabian Sea water mass is the mechanism behind the formation of a barrier layer in the northeast Arabian Sea; whereas that in the Bay of Bengal and the southeast Arabian Sea are already established as due to low saline water mass. The weak barrier layer in the Arabian Sea yields to the predominance of convective mixing to bring in nitrate-rich waters from the deeper layers to the surface, thereby supporting enhanced biological production. On the other hand, the river discharge into the Bay of Bengal during this period results in the formation of a thick and stable barrier layer, which insulates vertical mixing and provide oligotrophic condition in the Bay.     

pH variability and CO2 induced acidification in the North Sea

A coupled carbonate system–marine ecosystem–hydrodynamic model is used to simulate the temporal and spatial variability in pH across the southern North Sea as it relates to the environmental and biological processes affecting CO₂, namely, photosynthesis and respiration, riverine boundary conditions and atmospheric CO₂ concentrations. Annual pH ranges are found to vary from < 0.2 in areas of low biological activity to > 1.0 in areas influenced by riverine signals, consistent with observations and previous studies. It is shown that benthic, as well as pelagic, activity is an important factor in this variability. The acidification of the region due to increased fluxes of atmospheric CO₂ into the marine system is calculated and shown to exceed, on average, 0.1 pH units over the next 50 years and result in a total acidification of 0.5 pH units below pre-industrial levels at atmospheric CO₂ concentrations of 1000 ppm. The potential for measurable changes in biogeochemistry are demonstrated by simulating the observed inhibition of pelagic nitrification with decreasing pH. However, we conclude that there is a lack of knowledge of how acidification might affect the complex interaction of processes that govern marine biogeochemical cycles and a consequent need for further research and observations.     

Data assimilation with the Ensemble Kalman Filter and the SEIK filter applied to a finite element model of the North Atlantic

Currently there are different approaches to filter algorithms based on the Kalman filter. One of the most used filter algorithms is the Ensemble Kalman Filter (EnKF). It uses a Monte Carlo approach to the filtering problem. Another approach is given by the Singular Evolutive Extended Kalman (SEEK) and Singular Evolutive Interpolated Kalman (SEIK) filters. These filters operate explicitly on a low-dimensional error space which is represented by an ensemble of model states. The EnKF and the SEIK filter have been implemented within a parallel data assimilation framework in the Finite Element Ocean Model FEOM. In order to compare the filter performances of the algorithms, several data assimilation experiments are performed. The filter algorithms have been applied with a model configuration of FEOM for the North Atlantic to assimilate the sea surface height in twin experiments. The dependence of the filter estimates on the represented error subspace is discussed. In the experiments the SEIK algorithm provides better estimates than the EnKF. Furthermore, the SEIK filter is much cheaper in terms of computing time.     

Dynamics of suprabenthos-zooplankton communities around the Balearic Islands (western Mediterranean): Influence of environmental variables and effects on the biological cycle of Aristeus antennatus

Dynamics of suprabenthos and zooplankton were analyzed in two areas located in the NW (off Sóller harbour) and S (off Cabrera Archipelago) of Mallorca (Balearic Islands, western Mediterranean) at depths ranging between 135–780 m. Four stations situated respectively at 150 m (shelf-slope break), and at bathyal depths of 350, 650 and 750 m were sampled at bi-monthly intervals during six cruises performed between August 2003 and June 2004. Suprabenthos showed maximum biomass in both areas from late spring to summer (April to August), while minimum biomass was found in autumn (September–November). Though variable, temporal dynamics of zooplankton showed peaks of biomass in late winter and summer (February and June), while minimals occurred in autumn (August–September) and, at bathyal depths, in April. Suprabenthos (abundance; MDS analyses) showed a sample aggregation as a function of depth (3 groups corresponding to the shelf-slope break, upper slope — over 350 m; and the middle, deeper part of the slope — over 650–750 m), without any separation of hauls by season. By contrast, zooplankton samples were separated by season and not by depth. There was evidence of three seasonal groups corresponding to summer (June 2004–August 2003), autumn–winter (September and November 2003, February 2004), and spring (April 2004), being especially well established off Sóller. In general, suprabenthos was significantly correlated with the sediment variables (e.g. total organic matter content (% OM), potential REDOX), whereas zooplankton was almost exclusively dependent on Chl a at the surface, which suggests two different food sources for suprabenthos and zooplankton. The increase of suprabenthos abundance in April–June was paralleled by a sharp increase (ca. 2.8 times) in the %OM on sediment during the same period, coupled ca. 1–2 months of delay with the peak of surface Chl a recorded in February–March (from satellite imagery data). Suprabenthos biomass was also correlated with salinity close to the bottom, suggesting a link between suprabenthos abundance and changes in the oceanographic condition of water masses close to the bottom. It is suggested that a higher suprabenthos biomass recorded off Sóller in comparison to that off Cabrera in June could, in turn, be related to a seasonal inflow of Levantine Intermediate Water (LIW) in April–June in this area at mid bathyal depths (350–650 m). This trend would be based on: 1) it was evident only at mid-slope depths between 350–750 m, coinciding with the LIW distribution, and 2) it was not recorded among zooplankton (collected throughout the water column). The possible effect of the fluctuations of suprabenthos and zooplankton on higher trophic levels has been explored studying the diet and food consumption rates of the red shrimp Aristeus antennatus, as indicator species by its dominance in bathyal communities. A. antennatus increased its food consumption from February to April–June 2004 off Sóller, which in the case of large (CL > 40 mm) specimens was found in both areas. In addition, there was a shift of diet from winter to spring–early summer. In this last period, A. antennatus preyed upon euphausiids and mesopelagic decapods and fish, while benthos (e.g. polychaetes and bivalves) decreased in the diet. This indicates an increase in the food consumption and probably in the caloric content of the diet in pre-spawning females in April–June 2004, which is synchronized with the period when gonad development begins in A. antennatus females (May–June). Anyway, macrozooplankton, and not suprabenthos, is crucial as a high energetic food source in the coupling between food intake and reproduction in the red shrimp.     

Experimental study of the flow characteristics in an automotive HVAC system using a PIV technique

Air flow inside an automotive HVAC module was visualized using a high-resolution PIV technique with varying temperature control modes. The PIV (particle image velocimetry) system used for the experiment consisted of a 2-head Nd:YAG laser (125 mJ), a high-resolution CCD camera (2 K × 2 K), optics and a synchronizer. A real automotive HVAC module was used as a test model, and some of its casing parts were replaced with transparent windows to capture the flow images of the laser-light-sheet illumination. In addition, instant velocity fields were measured for three different temperature control modes by adjusting the temperature baffle. Characteristics of the air flow inside the automotive HVAC were then evaluated based on the time-averaged PIV data. Results from the experiment showed that flow for the warm mode loses more momentum due to its complicated flow path. Thus, the present PIV data can be used to validate numerical prediction and to improve the performance of HVAC modules.     

The viability of pure vegetable oil as an alternative fuel for large ships

Heavy fuels are likely to remain the dominant fuel source for two-stroke, low-speed diesel engines for large ship propulsion for the next decade or more. There is however, potential for increased use of pure vegetable oils (PVO) as an alternative and, by emitting lower levels of several pollutants, this can help the attainment of Annex VI of the MARPOL 73/78 convention aimed at large ships using fuels with less than 4.5% sulphur or 1.5% sulphur in SO_X emission control areas The use of alternative fuels can also influence the attainment of the Kyoto protocol that requires greenhouse gas emissions to be reduced by 5% by 2010 compared to 1990. This paper analyses the physical and chemical properties of various pure vegetable oils as an alternative to heavy fuel oil for large ship propulsion.