EXPERIMENTAL INVESTIGATIONS AND NUMERICAL SIMULATIONS OF REDUCING SECONDARY FLOWS AROUND A SPUR DIKE

1 INTRODUCTION The Yangtze River at the Three Gorges Project (TGP) site meanders with a complex morphology, including ridges like Jiuling Hill that projects into the approach navigation channel (Fig. 1). The approach navigation channel consists of a 530-m…     

刮刀钻头钻进中几个问题的讨论

分析了刮刀钻头钻进时刀刃和钻具的受力情况;讨论了“蹩钻”的原因和控制办法。      

利用微震数据对震源下方构造直接成像

现有的微震记录直接成像方法是将微震记录既当作入射记录,也当作散射记录,从而实现偏移成像.但此方法并不能突出透射波所携带的来自震源下方的深层散射波信息.本文在假设已知微震位置与子波的前提下,提出了对微震下方构造进行逆时偏移的成像方法.该方法类似于常规的逆时偏移,只是震源位置在地下.这使得在成像时,地下更深部的入射波场相比震源在地表时会更为精确,因此能够获得更加准确的成像结果.该方法会给成像结果带来一种尾波高频干扰：地下的震源发出的上行波与上方介质作用后,所产生的多级散射波会干扰反传波场.对此,在成像过程中,对入射场和散射场都进行左右行波分离,以压制该噪声.而在子波信息未知,无法重构入射场时,使用了激发时间成像条件,也能够实现同等效果的偏移成像,且不会出现尾波高频干扰.利用数值实验验证了本文方法的有效性.     

Piecewise uniform potential vorticity pancake shielded vortices

Shielded vortices consist of a core of potential vorticity (PV) of a given sign surrounded (or shielded) by a layer of opposite-signed PV. Such vortices have specific properties and have been the focus of numerous studies, first in two dimensional geometries (where PV is just the vertical component of the vorticity vector) and in geophysical applications (mostly in layered models). The present paper focuses on three-dimensional, spheroidal shielded vortices. In particular, we focus on vortical structures whose overall volume-integrated PV is zero. We restrict attention to vortices of piecewise uniform PV in the present research. We first revisit the problem within the quasi-geostrophic model, then we extend the results to the non-hydrostatic regime. We show that the stability of the structure depends on the ratio of PV between the inner core and the outer shield. In particular it depends on the polarity of the core and of the wavenumber of the azimuthal mode perturbed.     

新型圆筒型FPSO垂荡抑制结构优化设计

针对传统圆筒型FPSO垂荡运动剧烈的特点,提出一种带有垂荡抑制结构的圆筒型FPSO。采用1∶77.8的缩尺比制作模型,进行垂荡纵摇衰减试验,得到带有不同垂荡抑制结构模型的固有周期和无因次阻尼系数,进而选取最优的垂荡抑制结构型式。之后计算并对比传统圆筒型FPSO和新型圆筒型FPSO垂荡纵摇运动的固有周期和幅频响应函数。在此基础上,结合我国南海海洋环境条件,设计新型圆筒型FPSO的系泊系统,计算分析自存工况下的耦合动力响应,并与传统圆筒型FPSO进行对比。结果表明,文中提出的垂荡抑制结构可以有效增大系统垂荡纵摇运动的固有周期,改善运动性能,提高系泊的安全性。     

The effect of shroud on vortex shedding mechanism of cylinder

In the present study, flow characteristics were investigated experimentally using particle image velocimetry technique (PIV) in a gap between a solid cylinder and a shroud to reveal the effect of shroud diameter (D_s) and porosity (β) on the vortex shedding mechanism of the cylinder. Porosity (varied from β = 0.3 to 0.7) and diameter ratio (D/D_s = 0.4, 0.5 and 0.6) were main parameters examined at a Reynolds number of Re = 5000. For the porosity values of β ≤ 0.5, it is observed that vortex formation of the cylinder occurs only in the gap and shroud produces its own wake flow patterns. Penetrating flow through the shroud extends the shear layers on the both sides of the shroud through the downstream direction and prevents the interaction of shear layers in the near wake region. The diameter ratio and the porosity are impactful on the wake flow patterns in outer region of the shroud since they are determinant of the penetrating flow rate. Force measurements were also performed in the air tunnel in order to reveal the effect of shroud on the drag coefficient of cylinder. It is found that the drag coefficient of the cylinders are reduced significantly by shrouds when compared with that obtained from the bare cylinder case. However, the drag coefficient of the cylinder together with the shroud is higher than the bare cylinder for all cases since the shrouds enlarge the area exposed to the flow.     

Impact of the displacement damage in channel and source/drain regions on the DC characteristics degradation in deep-submicron MOSFETs after heavy ion irradiation

This paper mainly reports the permanent impact of displacement damage induced by heavy-ion strikes on the deep-submicron MOSFETs. Upon the heavy ion track through the device, it can lead to displacement damage, including the vacancies and the interstitials. As the featured size of device scales down, the damage can change the dopant distribution in the channel and source/drain regions through the generation of radiation-induced defects and thus have significant impacts on their electrical characteristics. The measured results show that the radiation-induced damage can cause DC characteristics degradations including the threshold voltage, subthreshold swing, saturation drain current, transconductance, etc. The radiation-induced displacement damage may become the dominant issue while it was the secondary concern for the traditional devices after the heavy ion irradiation. The samples are also irradiated by Co-60 gamma ray for comparison with the heavy ion irradiation results. Corresponding explanations and analysis are discussed.     

基于移动设备的地理信息数据传输方法

探讨了基于野外调绘功能手持式移动设备的客户/服务器无线网络模型,通过多线程和Socket技术在不同程序之间进行数据通信的可信性和方法。结合实践论述了其中的关键问题和技术,利用无线互联网实现地理信息数据的传输,并运用多线程和WINSOCK完成应用程序之间的通信任务,分别在客户端和服务器端编程实现。     

菱形开洞软钢阻尼器及其在结构减震中的模拟分析

提出了菱形开洞加劲软钢阻尼器及其在整体结构中的数值模拟方法,并据此对菱形开洞软钢阻尼器的循环加载试验以及安装阻尼器的钢框架结构的震动台试验进行了模拟分析。验证了使用AN-SYS有限元程序进行数值模拟分析的可行性和准确性,同时证明了菱形开洞软钢阻尼器具有良好的滞回性能,在整体结构中能够达到较好的减震效果。