流场环境对柔性立管湿模态的影响

为了研究静水压力和瞬态流场载荷对三维柔性立管湿模态的影响,本文基于声-固耦合模型对考虑水介质、顶张力情况下的立管进行湿模态计算,并与理论计算结果以及实验数据对比,验证了该模型的准确性;采用不考虑流-固耦合的计算流体力学(computational fluid dynamics,CFD)方法和考虑流固双向耦合的计算流体力学/计算结构力学(computational fluid dynamics/computational structure dynamics,CFD/CSD)方法分别计算了立管的瞬态流场载荷,并与实验数据对比;将水深产生的静水压力和瞬态流场载荷分别加载到三维柔性立管表面进行静力学分析,计算其湿模态。计算结果表明:立管湿模态频率比干模态频率小很多,且随着顶张力增大而增大;静水压力和瞬态流场载荷都使得湿模态频率略微增加;静水压力和瞬态流场载荷对湿模态低阶振型影响较大,对高阶振型几乎没有影响。

基于单向耦合方法的潜射导弹发射动力学研究

分别建立潜射导弹发射流场和发射动力学模型。通过对发射流场模型分析获取导弹所受非定常流场载荷。将流场载荷数据传递至发射动力学模型中作为导弹结构所受外载荷,分析得到导弹的受载与离筒姿态信息。分析结果表明,导弹前端截面与后端截面间所受轴力变化趋势一致,但在幅值上差别较大;弹体所受弯矩载荷随着导弹出筒长度增加而增加并伴有明显偏转;导弹结构设计应以保证横向刚度和强度为主。结论可作为导弹强度设计评估依据。

结构参数对带凸肩风扇静力学特性的影响分析

为研究结构参数变化对叶片稳态流场载荷的影响规律,通过数值求解方法开展不同转-静轴向间距和周向栅距工况下带凸肩风扇叶片的稳态流场计算。利用自行开发的插值程序将稳态载荷施加于叶片,分析叶片受力规律。基于稳态气动载荷和离心载荷,分析各工况下叶片的静力学特征。结果表明:随着上游静子与转子叶片轴向间距的减小,叶片受力和力矩增大。轴向间距减小3mm,周向力和力矩分别增大1.51%和1.48%;随着栅距的减小,叶片受力和力矩减小。转子叶片数增加两片,周向力和力矩分别减小6.26%和6.35%。

Non-Point-Source Nitrogen and Phosphorus Loadings from a Small Watershed in the Three Gorges Reservoir Area

Non-point-source pollution has become a major threat to the water quality of the Three Gorges Reservoir(TGR);however,nutrient loadings from terrestrial sources are unclear due to a lack of in situ monitoring.A representative small watershed in the central part of the TGR area was selected to monitor the loss of nitrogen(N) and phosphorous(P) continuously along with the runoff from 2007 through 2009 to understand the exact sources and loadings.Results show that the non-point-source nitrogen and phosphorus comes mainly from the storm runoff from residential areas,citrus orchards and sloping croplands,which contributes up to 76% of the loadings in this watershed.Thus,a crucial measure for controlling non-point-source pollution is to intercept storm runoff from the three sources.Paddy fields provide a sink for non-point-source N and P by intercepting the runoff and sediment along with their different forms of nitrogen and phosphorus.The N and P removal efficiency by paddy fields from residential areas is within the range of 56% to 98%.Paddy fields are an important land-use option for reducing the non-point-source loading of N and P in the TGR area.

The effects of Haversian fluid pressure and harmonic axial loading on the poroelastic behaviors of a single osteon

In order to well understand the mechanism of the mechanotransduction in bone, we propose a new model of transverse iso- tropic and poroelastic osteon cylinder considering Haversian fluid pressure. The analytical pore pressure and velocity solutions are obtained to examine the fluid transport behavior and pressure distribution in a loaded osteon on two different exterior sur- face cases. Case I is stress free and fully permeable and case I1 is impermeable. The following are the results obtained. （i） The Haversian fluid may not be ignored because it can enlarge the whole osteonal fluid pressure field, and it bears the external loads together with the solid skeleton. （ii） The increase of both axial strain amplitude and frequency can result in the increase of fluid pressure and velocity amplitudes, while in case II, the frequency has little effect on the fluid pressure amplitude. （iii） Under the same loading conditions, the pressure amplitude in case II is larger than that in case I, while the velocity amplitude is smaller than that in case I. This model permits the linking of the external loads to the osteonal fluid pressure and velocity, which may be a stimulus to the mechanotransduction of bone remodeling signals.

Engineering of multiferroic BiFeO grain boundaries with head-to-head polarization configurations

Confined low dimensional charges with high density such as two-dimensional electron gas(2 DEG)at interfaces and charged domain walls in ferroelectrics show great potential to serve as functional elements in future nanoelectronics.However,stabilization and control of low dimensional charges is challenging,as they are usually subject to enormous depolarization fields.Here,we demonstrate a method to fabricate tunable charged interfaces with~77°,86°and 94°head-to-head polarization configurations in multiferroic Bi Fe O_(3) thin films by grain boundary engineering.The adjacent grains are cohesively bonded and the boundary is about 1 nm in width and devoid of any amorphous region.Remarkably,the polarization remains almost unchanged near the grain boundaries,indicating the polarization charges are well compensated,i.e.,there should be two-dimensional charge gas confined at grain boundaries.Adjusting the tilt angle of the grain boundaries enables tuning the angle of polarization configurations from 71°to 109°,which in turn allows the control of charge density at the grain boundaries.This general and feasible method opens new doors for the application of charged interfaces in next generation nanoelectronics.

Characteristics of low altitude ionospheric electric field over Hainan Island,China

A sounding rocket experiment undertaken by the Chinese Meridian Project from a low latitude station on Hainan Island(19.5°N,109.1°E),China,measured the DC electric field during 05:45-05:52 LT on April 5,2013.The data observed using a set of electric field double probes,as part of the rocket's scientific payload,revealed the special profile of how the vectors of the DC electric field vary with altitude between 130 and 190 km.During the experiment,the vertical electric field was downward,and the maximum vertical electric field was nearly 5.1 mV/m near the altitude of 176 km.The zonal electric field was eastward and slightly less than 0.6 mV/m.The plasma drift velocity was estimated from the E×B motion,and the zonal drift velocity was eastward and of the order of 100 m/s.The zonal wind velocity was also estimated using the drift velocity near the maximum density height in the F1-region,and it was found to be nearly 120 m/s.This work constituted the first in situ measurement of the DC electric field conducted within the Fl-region(between 130 and 190 km) in the East Asian Sector.