Interceptor design for optimum trim control and minimum resistance of planing boats

Interceptors are vertical blades installed symmetrically aft of the craft. This article aims to investigate the main geometrical (height and span length) parameters in interceptors. Different Models with and without interceptors at different heights and spans have been analyzed based on the finite volume method and SIMPLE algorithm using dynamic mesh. In order to validate CFD results, the grid convergence index (GCI method) has been used to estimate the uncertainties caused by grid-spacing and time-step. Although it has been proved that the interceptors are very useful in trim control and resistance reduction, choosing wrong size interceptors could not only destroy their effectiveness, but also endanger the planing boat due to the creation of a strong moment leading to negative trim. The results of this study show that among all effective variables, the boundary layer thickness (h) at the stern (where the interceptor is installed), is far more important than, some other particular parameter, on interceptor performance and should be taken into account in estimating the interceptor height (d) and span (s). Generally, the interceptor height should not be higher than 60 percent of boundary layer thickness at transom. For optimum efficiency, when the interceptor height equals 60 percent of the boundary layer, the interceptor span length should be seven times as much as the interceptor height. At the end, based on Reynolds number the paper presents three figures, setting the basis for optimal interceptor sizes for its use in planing boats.     

System-based investigation on 4-DOF ship maneuvering with hydrodynamic derivatives determined by RANS simulation of captive model tests

For the non-negligible roll-coupling effect on ship maneuvering motion, a system-based method is used to investigate 4-DOF ship maneuvering motion in calm water for the ONR tumblehome model. A 4-DOF MMG model is employed to describe ship maneuvering motion including surge, sway, roll, and yaw. Simulations of circular motion test, static drift and heel tests are performed by solving the Reynolds-averaged Navier-Stokes (RANS) equations, after a convergence study quantifying the necessary grid spacing and time step to resolve the flow field adequately. The local flow field is analyzed for the selected cases, and the global hydrodynamic forces acting on the ship model are compared with the available experiment data. Hydrodynamic derivatives relating to sway velocity, yaw rate, and heel angle are computed from the computed force/moment data using least square method, showing good agreement with those obtained from EFD data overall. In order to investigate further the validity of these derivatives, turning circle and zigzag tests are simulated by using the 4-DOF MMG model with these derivatives. The trajectories and the time histories of the kinematic variables show satisfactory agreement with the data of free-running model tests, indicating that the system-based method coupled with CFD simulation has promising capability to predict the 4-DOF ship maneuvering motion for the unconventional vessel.     

Numerical Study on Air Turbines with Enhanced Techniques for OWC Wave Energy Conversion

In recent years, the oscillating water column (OWC) wave energy converter, which can capture wave energy from the ocean, has been widely applied all over the world. As the essential part of the OWC system, the impulse and Wells turbines are capable of converting the low pressure pneumatic energy into the mechanical shaft power. As an enhanced technique, the design of endplate or ring attached to the blade tip is investigated numerically in this paper. 3D numerical models based on a CFD-software FLUENT 12.0 are established and validated by the corresponding experimental results from the reports of Setoguchi et al. (2004) and Takao et al. (2001). Then the flow fields and non-dimensional evaluating coefficients are calculated and analyzed under steady conditions. Results show that the efficiency of impulse turbine with ring can reach up to 0.49 when φ=1, which is 4% higher than that in the cases for the endplate-type and the original one. And the ring-type Wells turbine with fixed guide vanes shows the best performance with the maximal efficiency of 0.55, which is 22% higher than that of the original one. In addition, the quasi-steady analysis is used to calculate the mean efficiency and output-work of a wave cycle under sinusoidal flow condition. Taking all together, this study provides support for structural optimization of impulse turbine and Wells turbine in the future.     

Smith＇s rent gap theory and evolution of gentrification

从居民效用与开发商收益视角下,以Smith租差理论为基础,构建多智能体模型,并结合纳什均衡解决居民修缮决策博弈,模拟中产阶层化进程。研究表明：在效用最大时,增加居民收入将降低中产阶层化发生频率。而在利润最大时,开发商资本的投入与中产阶层化发生频率正相关。资本投入越大,中产阶层化发生频率越高。但资本并非万能,当它的投入超出限值时,中产阶层化进程渐趋稳定。提高开发商投资门槛,将强化房地产业的垄断,开发商为获取巨额垄断利润,一方面,他们可能故意提高局部地区的资本化地租,这导致了中产阶层化更快、更多地发生;另一方面,他们在任意区位开发都能获取高额利润,这间接造成中产阶层化程度下降。     

Smith租差理论与中产阶层化动态演绎

从居民效用与开发商收益视角下,以Smith租差理论为基础,构建多智能体模型,并结合纳什均衡解决居民修缮决策博弈,模拟中产阶层化进程。研究表明:在效用最大时,增加居民收入将降低中产阶层化发生频率。而在利润最大时,开发商资本的投入与中产阶层化发生频率正相关。资本投入越大,中产阶层化发生频率越高。但资本并非万能,当它的投入超出限值时,中产阶层化进程渐趋稳定。提高开发商投资门槛,将强化房地产业的垄断,开发商为获取巨额垄断利润,一方面,他们可能故意提高局部地区的资本化地租,这导致了中产阶层化更快、更多地发生;另一方面,他们在任意区位开发都能获取高额利润,这间接造成中产阶层化程度下降。     

基于CFD的高能射流式液动冲击器活塞与缸体密封特性研究

通过计算流体动力学分析与实验室测试,对SC-86H型高能射流式液动冲击器活塞与缸体密封特性进行研究,分析了活塞密封段长度、环状间隙尺寸、活塞往复运动速度、角速度以及活塞外表面螺旋槽螺距与半径等参数对射流式冲击器前后腔之间泄漏量的影响。结果表明:活塞密封段长度、环状间隙尺寸、角速度以及活塞表面螺旋槽螺距均对射流式液动冲击器性能影响较小;活塞运动速度与泄漏量近似成正比例关系;随着活塞螺旋槽半径的增大,泄漏量会明显增大。活塞回程与冲程初期阶段,活塞运动速度较小,活塞处瞬时泄漏量占进入缸体前后腔流体流量的比例较大,使活塞无法快速加速运动,尤其是当活塞杆直径较大时,回程阶段泄漏量对活塞运动的影响更显著,导致冲击器工作性能大幅下降,甚至无法工作。     

Scientific role of ACA for low-mass star-formation study

We discuss the scientific role of the Atacama Compact Array (ACA), the Japanese contribution to the ALMA project, for low-mass star-formation study. Our recent observations of several low-mass protostellar envelopes in the submillimeter CS (J=7–6) and HCN (J=4–3) lines with the SMA and ASTE have revealed that these submillimeter emissions are more extended than ∼2000 AU and show different velocity structures from those traced by millimeter lines. These results suggest the importance of taking short-spacing informations the ACA can offer. Our comprehensive imaging simulations of these protostellar envelopes, as well as prestellar cores and debris disks, unprecedentedly demonstrate the scientific importance of ACA.     

海气耦合对MJO数值模拟的影响

采用一种基于降水异常追踪MJO（Madden–Julian Oscillation）东传的MJO识别方法（MJO Tracking）评估了参与MJOTF/GASS（MJO Task Force/Global Energy and Water Cycle Experiment Atmospheric System Study）全球模式比较计划的全海气耦合模式（CNRM-CM）、半海气耦合模式（CNRM-ACM）和大气模式（CNRM-AM）1991～2010年模拟MJO的能力,探究了海气耦合过程对模式模拟MJO能力的影响机理。CNRM-CM模式模拟的MJO结构更加接近观测,该模式不仅具有最高的MJO生成频率,也能够模拟较强的MJO强度以及较远的传播距离。海气耦合过程会造成CNRM-CM和CNRM-ACM模式中印度洋—太平洋暖池区域海温气候态的冷偏差。但是这种海温气候态的偏差基本没有改变模式模拟MJO的能力。CNRM-CM中MJO对流中心东（西）侧存在较强的季节内尺度海温暖（冷）异常,纬向梯度明显,而CNRM-ACM和CNRM-AM中不存在这样的海温东西不对称结构。结果表明在CNRM模式中海气耦合过程调控模式海温季节内尺度变率对模式MJO模拟能力的影响比调控模式海温气候态更加重要。