垂直轴流体动能转换装置设计

"垂直轴流体动能转换装置"是一种叶片和回转轴都垂直设置的流体动能转换装置。它可以是风力机,也可以是水轮机。它的特征是能实现目前国内外所有同类装置中最高的转换效率。本文简单介绍了"水平轴螺旋桨式风力机"存在的一些缺陷,以及"垂直轴流体动能转换装置"可以获取很高风能利用率的原因。

复杂地形强降雪过程中垂直运动诊断分析

利用WRF模式对2018年11月30日伊犁河谷和天山北坡强降雪过程进行数值模拟,并分析复杂地形强降雪过程垂直速度和垂直动能变化机制。研究表明,冷锋过境造成地表气压升高,干空气气柱质量增大,从而导致垂直气压梯度力和干空气气柱浮力发生变化,进而引起垂直运动发生发展。垂直速度局地时间变化主要取决于扰动垂直气压梯度力、水物质拖曳力和扰动干空气浮力。在天山北坡,气流过山时,迎风坡的扰动垂直气压梯度力较大,扰动干空气浮力较小,二者合力促进上升运动;在背风坡,扰动垂直气压梯度力和扰动空气浮力形成向下的合力,产生下沉加速度,导致背风坡下沉大风。扰动垂直气压梯度力做功和扰动干空气浮力做功情况基本相反,背风坡扰动垂直气压梯度力和综合强迫做功项抑制垂直动能,扰动干空气浮力和水物质拖曳力做功项增强垂直动能。此外,扰动垂直气压梯度力和扰动干空气浮力做功项主要出现在中低层,水物质拖曳力做功项主要位于低层,平缓地形处的综合强迫做功明显小于地形复杂处。

HL-2A装置同心圆线圈测量逆磁效应

介绍了HL-2A装置上同心圆逆磁测量的原理以及同心圆系统的设计,包括线圈面积差的确定和积分电路的设计。对实验数据的分析表明,通过对杂散场的有效补偿,同心圆逆磁测量系统可获得较高的信噪比,能够在一些较复杂的放电条件下可靠地获取等离子体逆磁信号。

Sport specificity background affects the principal component structure of vertical squat jump performance of young adult female athletes

Purpose： Long-term training specificity is thought to alter performance in tests evaluating strength and power production capability. The aim of the present study was to provide additional information to the limited existing knowledge concerning the possible differences of the force/time profile of squat jumping among different groups of young female athletes. Methods： One hundred and seventy-three adult women （20.1 ± 2.8 years, 1.71 ± 0.09 m, 65.6 ± 10.3 kg, mean± SD for age, height, and mass, respectively） engaged in track and field （TF）, volleyball （VO）, handball （HA）, basketball （BA）, and physical education students （PE） executed maximal squat jumps （SQJ） on a force plate. Pearson＇s correlation was used to identify the relationship between SQJ performance, the anthropometric characteristics and the biomechanical parameters. Differences concerning the biomechanical parameters among groups were investigated with analysis of variance, while the force- （FPD） or time- （TPD） dependency of SQJ execution was examined using principal components analysis （PCA）. Results： SQJ was unrelated to body height but significantly correlated with body mass （r = -0.26, p = 0.001）. TF jumped higher and produced larger peak body power output compared to all the other groups （p 〈 0.05）. All athletes were superior to PE since they performed the SQJ with a longer （p 〈 0.05） vertical body center of mass trajectory during the propulsion phase. PCA results revealed that TF significantly differentiated than the other groups by relying on FPD. Conclusion： Various different profiles of FPD and TPD were detected due to different sporting background in young female athletes. Since TF superiority in SQJ was relied on the larger power production and a greater FPD, female indoor team sport athletes are suggested to execute jumping exercises adopting the jumping strategies utilized by TE

On the physical significance and use of a set of horizontal and vertical helicity budget equations

For better understanding the variation of helicity and its governing mechanisms,based on the primary momentum equation under the local Cartesian coordinate,a set of horizontal and vertical helicity equations are derived in this study.On this basis,a storm-relative helicity budget equation is derived,the main factors that govern the variation of helicity are discussed,and the key mechanisms underlying the helicity variation are illustrated by using schematic images.Both scale analysis and real case diagnosis are used to compare the relative importance of di erent factors on the variation of helicity.For a meso-α system,it is found that:(i)horizontal helicity is much larger than vertical helicity,and they show signi cantly di erent variation mechanisms;(ii)for the vertical helicity,the vertical perturbation pressure gradient force,buoyancy,the diver-gence-related e ect,and the conversion between vertical and horizontal helicity govern its variation(whereas,the conversion is negligible for the evolution of horizontal helicity);and(iii)baroclinity is crucial for the variation of horizontal helicity,but it is only of secondary importance for the vertical helicity variation.

Oblique Wave Motion over Multiple Submerged Porous Bars near a Vertical Wall

This study examines oblique wave motion over multiple submerged porous bars in front of a vertical wall. Based on linear potential theory, an analytical solution for the present problem is developed using matched eigenfunction expansions. A complex dispersion relation is adopted to describe the wave elevation and energy dissipation over submerged porous bars. In the analytical solution, no limitations on the bar number, bar size, and spacing between adjacent bars are set. The convergence of the analytical solution is satisfactory, and the correctness of the analytical solution is confirmed by an independently developed multi-domain BEM （boundary element method） solution. Numerical examples are presented to examine the reflection and transmission coefficients of porous bars, CR and Cv, respectively, for engineering applications. The calculation results show that when the sum of widths for all the porous bars is fixed, increasing the bar number can significantly improve the sheltering function of the bars. Increasing the bar height can cause more wave energy dissipation and lower CR and Cr. The spacing between adjacent bars and the spacing between the last bar and the vertical wall are the key parameters affecting CR and Ct. The proposed analytical method may be used to analyze the hydrodynamic performance of submerged porous bars in preliminary engineering designs.

Budget analysis of mesoscale available potential energy in a heavy rainfall event over the eastern Tibetan Plateau

Using model simulated data,the distribution characteristics,genesis,and impacts on precipitation of available potential energy(APE)are analyzed for a heavy rainfall event that took place over the eastern Tibetan Plateau during 10–11 July 2018.Results show that APE was mainly distributed below 4 km and within 8–14 km.The APE distribution in the upper level had a better correspondence with precipitation.Northwestern cold advection and evaporation of falling raindrops were primary factors leading to positive anomalies of APE in the lower level,while positive anomalies of APE in the upper level were caused by a combination of thermal disturbances driven by latent heat and potential temperature perturbations resulting from the orography of the Tibetan Plateau.Budget analysis of APE indicated that APE fluxes and conversion between APE and kinetic energy(KE)were the main source and sink terms.Meridional fluxes of APE and conversion of KE to APE fed the dissipation of APE in the lower level.Vertical motion enhanced by conversion of APE to KE in the upper level was the major factor that promoted precipitation evolution.A positive feedback between APE and vertical motion in the upper level generated a powerful correlation between them.Conversion of KE to APE lasted longer in the lower level,which weakened vertical motion;whereas,northwestern cold advection brought an enhanced trend to the APE,resulting in a weak correlation between APE and vertical motion.

Turbulent dissipation and mixing in Prydz Bay

In this paper, we present measurements of velocity, temperature, salinity, and turbulence collected in Prydz Bay, Antarctica, during February, 2005. The dissipation rates of turbulent kinetic energy （e） and diapycnal diffusivities （Ks） were estimated along a section in front of the Amery Ice Shelf. The dissipation rates and diapycnal diffusivities were spatially non-uniform, with higher values found in the western half of the section where E reached 10.7 W/kg and Kz reached 10.2 mVs, about two and three orders of magnitude higher than those in the open ocean, respectively. In the western half of the section both the dissipation rates and diffusivities showed a high-low-high vertical structure. This vertical structure may have been determined by internal waves in the upper layer, where the ice shelf draft acts as a possible energy source, and by bottom-generated internal waves in the lower layer, where both tides and geostrophic currents are possible energy sources. The intense diapycnal mixing revealed in our observations could contribute to the production of Antarctic Bottom Water in Prydz Bay.

Effect of wind-current interaction on ocean response during Typhoon KAEMI(2006)

The Weather Research and Forecasting （WRF） model, the Princeton Ocean Model （POM）, and the wave model （WAVEWATCH III） are used to develop a coupled atmosphere-wave-ocean model, which involves different physical pro- cesses including air-forcing, ocean feedback, wave-induced mixing and wave-current interaction. In this paper, typhoon KAEMI （2006） has been examined to investigate the effect of wind-current interaction on ocean response based on the coupled atmosphere-ocean-wave model, i.e., considering the sea surface currents in the calculation of wind stress. The results show that the wind-current interaction has a noticeable impact on the simulation of 10 m-winds. The model involving the effect of the wind-current interaction can dramatically improve the typhoon prediction. The wind-current interaction prevents excessive momentum fluxes from being transferred into the upper ocean, which contributes to a much smaller turbulence kinetic energy （TKE）, vertical diffusivity, and horizontal advection and diffusion. The Sea Surface Temperature （SST） cooling induced by the wind-current interaction during the initial stage of typhoon development is so minor that the typhoon intensity is not very sen- sitive to it. When the typhoon reaches its peak, its winds can disturb thermocline, and the cold water under the thermocline is pumped up. However, this cooling process is weakened by the wind-current interaction, as ocean feedback delays the decay of the typhoon. Meanwhile, the temperature below the depth of 30 m shows an inertial oscillation with a period about 40 hours （-17°N） when sudden strong winds beat on the ocean. Due to faster currents, the significant wave height decreases as ignoring the wind-current interaction, while this process has a very small effect on the dominant wave length.