墨吉对虾体长与体重关系的计算及其在生产中的应用

本文研究墨吉对虾(Penaeus merguiensis)体长(L)与体重(W)的关系,经回归分析得其关系式。根据此关系式计算得体长和体重换算表,对指导生产具有现实意义。     

First‐order exchange coefficient coupling for simulating surface water–groundwater interactions: parameter sensitivity and consistency with a physics‐based approach

Distributed hydrologic models capable of simulating fully‐coupled surface water and groundwater flow are increasingly used to examine problems in the hydrologic sciences. Several techniques are currently available to couple the surface and subsurface; the two most frequently employed approaches are first‐order exchange coefficients (a.k.a., the surface conductance method) and enforced continuity of pressure and flux at the surface‐subsurface boundary condition. The effort reported here examines the parameter sensitivity of simulated hydrologic response for the first‐order exchange coefficients at a well‐characterized field site using the fully coupled Integrated Hydrology Model (InHM). This investigation demonstrates that the first‐order exchange coefficients can be selected such that the simulated hydrologic response is insensitive to the parameter choice, while simulation time is considerably reduced. Alternatively, the ability to choose a first‐order exchange coefficient that intentionally decouples the surface and subsurface facilitates concept‐development simulations to examine real‐world situations where the surface‐subsurface exchange is impaired. While the parameters comprising the first‐order exchange coefficient cannot be directly estimated or measured, the insensitivity of the simulated flow system to these parameters (when chosen appropriately) combined with the ability to mimic actual physical processes suggests that the first‐order exchange coefficient approach can be consistent with a physics‐based framework. Copyright © 2009 John Wiley & Sons, Ltd.     

One-Equation Turbulence Modelling for Atmospheric and Engineering Applications

A new algebraic turbulent length scale model is developed, based on previous one-equation turbulence modelling experience in atmospheric flow and dispersion calculations. The model is applied to the neutral Ekman layer, as well as to fully-developed pipe and channel flows. For the pipe and channel flows examined the present model results can be considered as nearly equivalent to the results obtained using the standard k– model. For the neutral Ekman layer, the model predicts satisfactorily the near-neutral Cabauw friction velocities and a dependence of the drag coefficient versus Rossby number very close to that derived from published (G. N. Coleman) direct numerical simulations. The model underestimates the Cabauw cross-isobaric angles, but to a less degree than the cross-isobar angle versus Rossby dependence derived from the Coleman simulation. Finally, for the Cabauw data, with a geostrophic wind magnitude of 10 ms^–1, the model predicts an eddy diffusivity distribution in good agreement with semi-empirical distributions used in current operational practice.     

格网DEM上径流长度计算误差的定量分析

基于格网DEM的径流长度的计算误差主要来源于DEM数据和流径提取算法。通过数据独立的误差分析方法,定量分析流径提取算法模型产生的误差。首先选取5种数学曲面作为模拟DEM数据源,计算出径流长度,以由曲面公式推导的径流长度公式计算的径流长度作为理论真值,通过两者的对比,分析误差及其空间分布。结果表明,汇水区的径流长度计算精度明显高于分水区;分水区的径流长度含有一定的系统误差。     

粗糙元几何参数的交互作用对床面空气动力学粗糙度的影响

 为了全面地揭示粗糙元的所有几何参数的交互作用对空气动力学粗糙度的影响,利用风洞实验研究了粗糙元高度、密度、高度与间距比、孔隙度和方向比率等几何参数交互作用对空气动力学粗糙度的影响。结果表明,密实和孔隙粗糙元的无量纲空气动力学粗糙度（空气动力学粗糙度度/粗糙元高度）均可表示为粗糙元密度/等效密度的正比例函数,而比例系数反映了粗糙元几何参数交互作用。据此,该研究发展了一个全面反映粗糙元高度h、密度/等效密度λ、高度与行间距比Sp和方向比率AR等几何参数交互作用的空气动力学粗糙度模式:Z0h=-0.0028+0.5403S0.32p·AR-0.07·λ。该模式改进了模拟的精度,扩大了适用范围。     

The Effect of Stratification on the Aerodynamic Roughness Length and Displacement Height

The roughness length, z _0u , and displacement height, d _0u , characterise the resistance exerted by the roughness elements on turbulent flows and provide a conventional boundary condition for a wide range of turbulent-flow problems. Classical laboratory experiments and theories treat z _0u and d _0u as geometric parameters independent of the characteristics of the flow. In this paper, we demonstrate essential stability dependences—stronger for the roughness length (especially in stable stratification) and weaker but still pronounced for the displacement height. We develop a scaling-analysis model for these dependences and verify it against experimental data.     

Temporal and Spatial Variations of the Aerodynamic Roughness Length in the Ablation Zone of the Greenland Ice Sheet

To understand the response of the Greenland ice sheet to climate change the so-called ablation zone is of particular importance, since it accommodates the yearly net surface ice loss. In numerical models and for data analysis, the bulk aerodynamic method is often used to calculate the turbulent surface fluxes, for which the aerodynamic roughness length (z ₀) is a key parameter. We present, for the first time, spatial and temporal variations of z ₀ in the ablation area of the Greenland ice sheet using year-round data from three automatic weather stations and one eddy-correlation mast. The temporal variation of z ₀ is found to be very high in the lower ablation area (factor 500) with, at the end of the summer melt, a maximum in spatial variation for the whole ablation area of a factor 1000. The variation in time matches the onset of the accumulation and ablation season as recovered by sonic height rangers. During winter, snow accumulation and redistribution by snow drift lead to a uniform value of z ₀≈ 10⁻⁴ m throughout the ablation area. At the beginning of summer, snow melt uncovers ice hummocks and z ₀ quickly increases well above 10⁻² m in the lower ablation area. At the end of summer melt, hummocky ice dominates the surface with z ₀ > 5  ×  10⁻³ m up to 60 km from the ice edge. At the same time, the area close to the equilibrium line (about 90 km from the ice edge) remains very smooth with z ₀ = 10⁻⁵ m. At the beginning of winter, we observed that single snow events have the potential to lower z ₀ for a very rough ice surface by a factor of 20 to 50. The total surface drag of the abundant small-scale ice hummocks apparently dominates over the less frequent large domes and deep gullies. The latter results are verified by studying the individual drag contributions of hummocks and domes with a drag partition model.     

The Parameterisation of Scalar Transfer over Rough Ice

We test a surface renewal model that is widely used over snow and ice surfaces to calculate the scalar roughness length (z _s ), one of the key parameters in the bulk aerodynamic method. For the first time, the model is tested against observations that cover a wide range of aerodynamic roughness lengths (z ₀). During the experiments, performed in the ablation areas of the Greenland ice sheet and the Vatnajökull ice cap in Iceland, the surface varied from smooth snow to very rough hummocky ice. Over relatively smooth snow and ice with z ₀ below a threshold value of approximately 10^?3 m, the model performs well and in accord with earlier studies. However, with growing hummock size, z ₀ increases well above the threshold and the bulk aerodynamic flux becomes significantly smaller than the eddy-correlation flux (e.g. for z ₀ = 0.01 m, the bulk aerodynamic flux is about 50% smaller). Apparently, the model severely underpredicts z _s over hummocky ice. We argue that the surface renewal model does not account for the deep inhomogeneous roughness sublayer (RSL) that is generated by the hummocks. As a consequence, the homogeneous substrate ice grain cover becomes more efficiently ‘ventilated’. Calculations with an alternative model that includes the RSL and was adapted for use over hummocky ice, qualitatively confirms our observations. We suggest that, whenever exceedance of the threshold occurs (z ₀  >  10^?3 m, i.e., an ice surface covered with at least 0.3-m high hummocks), the following relation should be used to calculate scalar roughness lengths, ln (z _s /z ₀)  =  1.5  ? 0.2 ln (Re _*)  ? 0.11(ln (Re _*))².     

A straightforward approach for using single time domain simulations to assess characteristic extreme responses

Short-term wave design approach of marine structures, using nonlinear time domain simulations, is a design procedure that is recognized by various modern standard codes. One of the most challenging points of this approach is the evaluation of the characteristic extreme values for response parameters used in the design check equations. The most straightforward and recommended way to evaluate a response characteristic value is by fitting an extreme value probability distribution to the N-sample of extreme values extracted from N independent time domain simulations with duration equal to the short-term period indicated by the code, which is usually taken as 3 h. However, this procedure would not be practical for some types of marine structures, such as risers and mooring lines, under numerous design load cases and demanding huge finite element models. A more feasible approach would be to assess the response extreme value distribution using only a single short-term time domain simulation with duration shorter than 3 h. But reduced time simulations always introduce some additional statistical uncertainty into the extreme values estimates. This paper discusses a workable way of properly taking into account the statistical uncertainty associated with the simulation length in the assessment of a characteristic short-term extreme response value based on a single time series.