Honey, I cooled the cods: Modelling the effect of temperature on the structure of Boreal/Arctic fish ecosystems

Historically colder regions of the North Atlantic had fisheries dominated by only a few fish species; principally cod and capelin. Possible population dynamic mechanisms that lead to such dominance are investigated by considering how a charmingly simple published multispecies model of the North Sea would react if the system operated at a lower temperature. The existing model equations were modified to describe temperature effects on growth, fecundity and recruitment and the model was rerun based on typical temperatures for the North Sea and a colder system. The results suggest that total fish biomass in the colder system increases but the community is more vulnerable to a given rate of fishing mortality. In the colder system, within species density dependence is reduced but relative predation rates are higher. Consequently, intermediate-sized species are vulnerable to relatively high levels of predation throughout their life history and tend to be excluded, leading to a system dominated by small and large species. The model helps to explain how temperature may govern coexistence and competitive exclusion in fish communities and accounts for the observed dominance of small and large species in Boreal/Arctic ecosystems.     

Radar cross section analysis of marine targets using a combining method of physical optics/geometric optics and a Monte-Carlo simulation

In this paper, the radar cross section of flat plates on ocean surfaces is statistically investigated. A combining method of physical optics and geometric optics is applied to establish an effective backscattering analysis procedure. This method is a high-frequency analysis method originally derived from a simplified Stratton-Chu integral equation, assuming that the radar is far away from the target so that Kirchhoff approximation is valid. A Monte-Carlo simulation method is adopted to statistically analyze the effects of undulated ocean surfaces. The ocean surfaces are randomly generated by Pierson-Moskowitz ocean wave spectrum and a directional distribution function. Numerical investigations are carried out for flat plates, with the same height and width but with different inclined angles, on ocean surfaces of various significant wave heights.     

基于X波段雷达的表层流估计算法初步研究

对X渡段雷达记录的连续雷达图像进行分析,能够获取海浪和表层流信息.不存在海洋表层流情况下,雷达图像的谱能量分布在静水频散关系确定的平面上,而雷达相时海浪场的运动(比如表层流)使雷达图像的谱能量分布产生多普勒频移,对此频移进行最小二秉拟合.可以确定表层流的大小和方向.     

换道概率对交通系统动能的影响

基于跟车模型的特点,提出了跟车模型的动能变化公式,利用该公式研究换道概率对各车辆动能的影响.数值实验结果表明,换道概率和相对速度对各车辆动能产生较大影响,但换道概率和相对速度会分别降低其动能变化频率和幅度.此外,系统增加的平均动能会随着系统最大换道概率的增加而降低.     

Return period and risk calculations for ocean wave energy applications

The statistical behavior of wave energy at a site strongly depends on the wave characteristics. Wave energy converters fail to produce energy when there are no sufficiently available wave heights. Hence, evaluation of return periods and risk values of the minimum wave height becomes important for wave energy studies. A time index representing the minimum wave height is proposed here for ocean wave applications. Persistence plays a significant role in the calculation of return period and risk. Although ignoring the serial independence makes calculations easy, it leads to overestimations of the real status. In this paper, return periods and risk values are compared with each other by taking into consideration independent and dependent situations. Application of the study is achieved for the stations located in the Pacific Ocean and Gulf of Mexico.     

Analytical method of radiation by a wave energy device with dual rectangular floating bodies

The system with one floating rectangular body on the free surface and one submerged rectangular body has been applied to a wave energy conversion device in water of finite depth. The radiation problem by this device on a plane incident wave is solved by the use of an eigenfunction expansion method, and a new analytical expression for the radiation velocity potential is obtained. The wave excitation force is calculated via the known incident wave potential and the radiation potential with a theorem of Haskind employed. To verify the correctness of this method, an example is computed respectively through the bound element method and analytical method. Results show that two numerical methods. are in good agreement, which shows that the present method is applicable. In addition, the trends of hydrodynamic coefficients and wave force are analyzed under different conditions by use of the present analytical method.     

温差能驱动的水下滑翔器设计与实验研究

论文设计开发了一种新型的温差能驱动的水下滑翔器,并对它做了水域实验研究。文章讨论了温差能驱动的滑翔器运动机理及其在垂直剖面的运动分析,得到稳态运动的参数解。结合能够把水域温差能转变为机械能的热机设计以及滑翔器的主要机械结构和控制硬件系统设计,完成了滑翔器的初步设计与开发。滑翔器在千岛湖进行了水域实验,实验结果表明,此水下滑翔器完全能够利用温差能实现预定的滑翔运动。     

利用臭氧氧化发光光谱特征检测水质污染

利用不同的污染物质在被臭氧氧化时发光特性不同的原理检测水质污染。检测出来的发光光谱与不同污染源的特征光谱进行对比,辅助发光时序等特征,检测几种污染物的含量和确定污染源。对涉及的有关技术问题进行了探讨。     

基于声学调制解调器的声速剖面遥测技术

声速是海洋声呐测量中最重要的声学参数之一。拖缆式声速剖面仪可提供实时测量功能,但其缆长不能满足深海测量要求;自容式声速剖面仪可满足深海测量要求,但工作效率低。如何提高野外深海声速剖面测量工作效率是深海调查一项非常有意义的工作。文中详细介绍了基于声学调制解调器的声速剖面遥测系统的主要结构和功能,揭示了水声通信技术在深海非铠装缆测量中的应用优势。     

先锋孤立子生成的理论平均波阻(Ⅰ).理论

根据作者导得的AfKdV方程，理论上确定了先锋孤立子生成问题的理论平均波阻，能量劈分及能量劈分比。本文的能量劈分是确定先锋孤立子生成参数的理论基础。同时，本理论确定了现有理论中的自由未知参数问题，从而使先锋孤立子生成参数得到理论预报。