基于MFAPC的动力换挡变速箱湿式离合器压力控制方法

针对大功率拖拉机动力换挡过程中湿式离合器充油压力实际值与理想值之间存在偏差的问题,提出了基于紧格式动态线性化的离合器压力无模型自适应预测控制（Model free adaptive predictive control,MFAPC）算法,以实现离合器油缸压力的跟随控制。考虑到外界干扰和离合器液压控制系统参数的不确定性,构建湿式离合器驱动执行机构的完整非线性动力学模型和AMESim仿真模型,以离合器油缸压力为控制目标,采用紧格式动态线性化方法将非线性离合器液压执行机构数学模型等价转换为动态线性化数据模型,并设计了基于MFAPC的湿式离合器压力控制器,经Matlab/Simulink仿真试验验证了动态线性化模型的正确性及控制算法的可靠性。结果表明,与PID、MFAC等算法相比,本文算法控制跟踪效果更优,且具有较好的鲁棒性;MFAPC能够快速调整控制参数,响应期望压力变化;在方波信号激励下的响应时间仅为0.119s,在正弦信号激励下的稳态误差仅为±0.0281MPa,比传统PID算法降低了48.91%。此外,MFAPC的抗干扰能力优于其他算法,在接合过程中,湿式离合器最大冲击度仅为16.57m/s3,证明该算法具有较好的动态性能,有利于提高动力换挡的换挡品质,保证大功率拖拉机工作过程中的动力性。     

Developing a new tool based on a quantile regression mixed‐TGC model for optimizing gilthead sea bream (Sparus aurata L) farm management

In this work, a seasonal quantile regression growth model for the gilthead sea bream (Sparus aurata L) based on an aggregation of the quantile TGC models with exponent 1/3 and 2/3, named the “Quantile TGC‐Mixed Model”, is presented. This model generalizes the proposal of Mayer, Estruch and Jover (Aquaculture, 358‐359, 2012, 6) in the sense that the new model is able to describe the evolution of weight distribution throughout an entire production cycle, which could be a powerful tool for fish farm management. The information provided by the model simulations enables us to estimate total fish production and final fish size distribution and helps to design and simulate production and sales plan strategies considering the market price of different fish sizes, in order to increase economic profits. The most interesting alternative in the studied case results in sending all production when 0.25 quantile fish reach 600 g, although on each fish farm it would be necessary to evaluate optimum strategy depending on its own quantile regression model, the production cost and the market price.     

Qualitative modelling and indicators of exploited ecosystems

Implementing ecosystem-based fisheries management requires indicators and models that address the impacts of fishing across entire ecological communities. However, the complexity of many ecosystems presents a challenge to analysis, especially if reliant on quantification because of the onerous task of precisely measuring or estimating numerous parameters. We present qualitative modelling as a complementary approach to quantitative methods. Qualitative modelling clarifies how community structure alone affects dynamics, here of exploited populations. We build an array of models that describe different ecosystems with different harvesting practices, and analyse them to predict responses to various perturbations. This approach demonstrates the utility of qualitative modelling as a means to identify and interpret community-level indicators for systems that are at or near equilibrium, and for those that are frequently perturbed away from equilibrium. Examining the interaction of ecological and socio-economic variables associated with commercial fisheries provides an understanding of the main feedbacks that drive and regulate exploited ecosystems. The method is particularly useful for systems where the basic relationships between variables are understood but where precise or detailed data are lacking.     

Otter occupancy in the Cape Peninsula: Estimating the probability of river habitat use by Cape clawless otters,Aonyx capensis,across a gradient of human influence

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Forgotten fishes: What is the future for small threatened freshwater fish? Population risk assessment for southern pygmy perch,Nannoperca australis

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Habitat suitability modelling for sardine juveniles (Sardina pilchardus) in the Mediterranean Sea

Identification of potential juvenile grounds of short‐lived species such as European sardine (Sardina pilchardus) in relation to the environment is a crucial issue for effective management. In the current work, habitat suitability modelling was applied to acoustic data derived from both the western and eastern part of the Mediterranean Sea. Early summer acoustic data of sardine juveniles were modelled using generalized additive models along with satellite environmental and bathymetry data. Selected models were used to construct maps that exhibit the probability of presence in the study areas, as well as throughout the entire Mediterranean basin, as a measure of habitat adequacy. Areas with high probability of supporting sardine juvenile presence persistently within the study period were identified throughout the Mediterranean Sea. Furthermore, within the study period, a positive relationship was found between suitable habitat extent and the changes in abundance of sardine juveniles in each study area.     

Modelling sea lice dispersion under varying environmental forcing in a Scottish sea loch

The spread of infectious larval sea lice, Lepeophtheirus salmonis (Krøyer, 1838), between wild salmonids and farmed Atlantic salmon, Salmo salar , remains a contentious area of uncertainty. However, as laboratory and field experiments increase our knowledge of sea lice behaviour under environmental forcing, numerical modelling tools can be used to predict the spread of infectious sea louse larvae from a point source. A three-dimensional numerical model has been developed and recently validated within Loch Torridon, a fjordic sea loch on the west coast of Scotland. Output from the numerical model is used to drive a particle tracking model which follows statistical representations of sea lice through the planktonic stages of a louse life cycle. By including maturation and mortality, the models can be used to predict the dispersion and transport of infectious sea lice from a point source and can be used to produce maps of infectivity under varying environmental conditions. Results highlight the importance of the wind-driven circulation for larval lice transport and suggest that local environmental conditions have considerable impact on the probability of sea lice infection spreading between wild and farmed fish populations.     

Prey abundance, channel structure and the allometry of growth rate potential for juvenile trout

Abstract  The application of a drift-foraging bioenergetic model to evaluate the relative influence of prey abundance (invertebrate drift) and habitat (e.g. pool frequency) on habitat quality for young-of-the-year (YOY) and yearling juvenile cutthroat trout, Oncorhynchus clarki (Richardson) is described. Experiments and modelling indicated simultaneous limitation of fish growth by prey abundance and habitat, where depth and current velocity limit the volume of water and prey flowing through a fish's reactive field as well as swimming costs and prey capture success. Predicted energy intake and growth increase along a depth gradient, with slower deeper pool habitat generating higher predicted growth for both YOY and yearling trout. Bioenergetic modelling indicated that fish are constrained to use progressively deeper habitats to meet increasing energy requirements as they grow. Sensitivity of growth to prey abundance identified the need to better understand how variation in invertebrate drift and terrestrial drop affects habitat quality and capacity for drift-feeding fishes.     

Quantifying allowable harm in species at risk: application to the Laurentian black redhorse (Moxostoma duquesnei)

• 1. When a species is identified for conservation, often the only way to effect recovery is to reduce the harm imposed by stressors threatening the survival of the species. Ideally all threats would be removed; however, this is often not feasible or practical. Within this context, a demographic approach is presented to assess how much human‐induced harm could be allowed without impairing the persistence of the species. Harm is defined as a negative perturbation that can target one or more vital rates and life stages simultaneously.
• 2. Allowable harm, defined as a level of harm that will not jeopardize survival or recovery, will be a function of the vital rates affected by human actions, the sensitivity of population growth to changes in these vital rates (their elasticities), the population growth rate prevailing before harm occurs, and the set of demographic parameters considered safe for long‐term persistence. This life‐history based approach requires minimal data, can link demography with habitat‐explicit information, is flexible enough to encompass complex life histories, and follows a precautionary approach.
• 3. Quantification of allowable harm could be applied to any species at risk. This approach is introduced by applying it to a Canadian population of a freshwater fish, the black redhorse (Moxostoma duquesnei), demonstrating that in the absence of habitat constraints population dynamics of this species are most sensitive to the survival of young adults, but population fitness is particularly sensitive to the loss of habitat used by young‐of‐the‐year fish under current levels of habitat supply.

Copyright © 2009 John Wiley & Sons, Ltd.