西洋海域流场线遥感提取分析

利用遥感影像与同期大丰港实测潮位数据以及2006年江苏908调查流向实测资料,建立辐射沙脊群海域流场线与流向之间的关系。以西洋海域为例,采用纹理分析和非监督分类相结合的方法,分别提取大潮、小潮、涨潮和落潮成像时刻影像的流场线信息,生成流场线分布图,然后与实测流向进行对比分析。研究表明,提取的流场线分布走向与实测流向趋势一致。

基于曲面的贴附送风模式适用性研究——以最速降线曲面为例

曲面型建筑在我国及世界上源远流长,这些曲面造型融合了建筑师的灵感与其环境、功能、结构等因素.曲面形状以多种形体构成,本文以最速降线曲面为例,探究基于曲面贴附送风模式气流组织形式的适用性.通过CFD数值模拟和理论分析相结合的方式,研究了最速降线曲面贴附送风形式在不同曲率、送风速度和温度下室内的速度场和温度场分布.研究表明,贴附送风可以适用于最速降线曲面,且是一种通风效率较高、工作区人员热舒适性较好的气流组织形式,可以推广到圆形、椭圆形和抛物线形等多种形状.

Three-dimensional Spaces of Quasi-constant Curvature

In this paper some properties of three-dimensional spaces of quasi-constant curvature different from those of cases when dimension n≥4 are proved. In particular, two classes of non-conformally flat solutions of them are constructed. In physics,a three-dimensional space of quasi-constant curvature appears as the space-like hypersurface of the rotation-free cosmological model of type D for the fluids with heat flow in General Relativity.

Optimal Design for Open MRI Superconducting Magnet with Active Shielding

The optimal design method for an open Magnetic Resonance Imaging （MRI） superconducting magnet with an active shielding configuration is proposed. Firstly, three pairs of current rings are employed as seed coils. By optimizing the homogeneity of Diameter Sphere Voltnne （DSV）, the positions and currents of the seed coils will be obtained. Secondly, according to the positions and currents of the seed coils, the current density of superconducting wires is determined, and then the original sections for the coils can be achieved. An optimization for the homogeneity based on the constrained nonlincar optimization method is employed to determine the coils with good homogeneity. Thirdly, the magnetic field generated by previous coils is set as the background field, then add two coils with reverse current, and optimize the stray field line of 5 Gauss in a certain scope. Finally, a further optimization for the homogeneity is used to get Final coils. This method can also be used in the design of other axisynmaetfic superconducting MRI magnets.

Numerical simulation of the pulsing air separation field based on CFD

The flow field of pulsing air separation is normally in an unsteady turbulence state.With the application of the basic principles of multiphase turbulent flows,we established the dynamical computational model,which shows a remarkable variation of the unstable pulsing air flow field.CFD(computational fluid dynamics) was used to conduct the numerical simulation of the actual geometric model of the classifier.The inside velocity of the flowing fields was analyzed later.The simulation results indicate that the designed structure of the active pulsing air classifier provided a favorable environment for the separation of the particles with different physical characters by density.We shot the movement behaviors of the typical tracer grains in the active pulsing flow field using a high speed dynamic camera.The displacement and velocity curves of the particles in the continuous impulse periods were then analyzed.The experimental results indicate that the effective separation by density of the particles with the same settling velocity and different ranges of the density and particle size can be achieved in the active pulsing airflow field.The experimental results provide an agreement with the simulation results.

The study of slip line field and upper bound method based on associated flow and non-associated flow rules

At present, associated flow rule of traditional plastic theory is adopted in the slip line field theory and upper bound method of geotechnical materials. So the stress characteristic line conforms to the velocity line. It is proved that geotechnical materials do not abide by the associated flow rule. It is impossible for the stress characteristic line to conform to the velocity line. Generalized plastic mechanics theoretically proved that plastic potential surface intersects the Mohr-Coulomb yield surface with an angle, so that the velocity line must be studied by non-associated flow rule. According to limit analysis theory, the theory of slip line field is put forward in this paper, and then the ultimate beating capacity of strip footing is obtained based on the associated flow rule and the non-associated flow nile individually. These two results are identical since the ultimate bearing capacity is independent of flow role. On the contrary, the velocity fields of associated and non-associated flow rules are different which shows the velocity field based on the associat- ed flow rule is incorrect.

Characterization and Performance Evaluation of Turbulent Plasma Sheath Channel

Radio waves are highly attenuated and distorted by turbulent plasma sheath around hypersonic vehicles in near space, leading to communication blackout. The purpose of the paper is to investigate the plasma channel characteristics and the communication performances over the channel. We treat the turbulent plasma medium as a fast fading wireless channel. The coherence time and the spectrum spread of the plasma sheath channel are obtained in terms of root-meansquare(RMS). Baseband simulation scheme is proposed based on a stratified model of the plasma flow field. Results indicate that the coherence time is on the order of milliseconds and decreases rapidly with the increasing electron density turbulence. The spectrum spread due to plasma turbulence is also significant. Extensive simulations have been carried out to make communication performance evaluations. Quantitative results show that error floor takes place for PSK and QAM, while FSK with noncoherent detection is a promising method to mitigate the blackout problem.

Active Field Canceling System in Next Generation Nano-Fab

ELF （extremely low frequency） magnetic fields from power-line current influence the yield of CMOS foundry. The poor yield happens because of ELF magnetic fields inducing directly the measurement or process equipment for cutting-edge chips below 28 nm process. The equipments of electron microscopes, including SEM （scanning electron microscope）, TEM （transmission electron microscopy）, STEM （scanning transmission electron microscopy） and EBLS （electron beam lithography system） are very susceptible to ELF magnetic fields emanating from various electrical power sources outside of the building and within next generation CMOS foundry recommends a maximum of 0.3 mG. The active canceling method uses active coils with current sensing field via sensor and inducing man-made electromagnetic field to reduce the stray magnetic field. Unfortunately, the conventional system takes more time to products field because of parasitical capacitance and resistance in long coil. The longer canceling coil the system construct, the more time it takes. Besides, canceling system should spend more time on calibrating non-linear current amplifier through software design. This research designs simpler anti-electro-magnetic system instead of typical frame and develops one turn canceling coil structure to reduce delaying time. Several parallel cells generate field up to 23.81 mG controlled by MPU （micro processor unit）. This system decreases the power-line inducing filed below 0.3 mG.

摆线桨非定常动态失速的三维效应

对摆线桨三维全尺寸模型进行了非定常数值模拟。验证了两种嵌套网格方法的可靠性与适用性,针对二维/三维情况下摆线桨非定常涡流动特性及诱导分离特性开展了数值分析,重点研究了展向气动力随方位角的分布与全局流场的诱导速度分布,并分析了尾迹捕捉精度与涡量耗散特征。结果表明:受摆线桨切向速度、展向诱导速度等三维效应影响,两种计算结果的瞬态气动力极值差值达到44%。三维动态失速涡的产生、脱落与再附明显弱于二维翼型情况,这对于摆线桨非定常气动特性有较大影响。

A rapid approach to convective aeroheating prediction of hypersonic vehicles

A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce time cost,and a combination of the mass flow balance technique and the axisymmetric analog is proposed to account for the entropy swallowing effects.A three-dimensional linear method is derived to fit the vehicle surface flowfields.Then a new axisymmetric analog method based on linear flowfields and linear surface equations is developed,with the complexity and computational cost reduced dramatically.In the stagnation region,an implicit surface fitting is introduced to approximate the primary curvatures and a robust aeroheating prediction method is constructed.The proposed approach is verified on a variety of configurations including spherically blunted cone,double ellipsoid and aerospace vehicle.Numerical results indicate the followings:1)The approach predicts aeroheating in about one second and the results agree well with CFD simulations and wind-tunnel measurements;2)with the help of entropy correction,the precision is further improved in the streamline diverging regions on the vehicle surface,while little improvement is found after entropy correction in the regions where the streamlines do not diverge.

Characteristics analysis and parameters optimization for the grating eddy current displacement sensor

The grating eddy current displacement sensor (GECDS) for distance or position measurement used in watertight electronic calipers was described. The sensor relies on repetitive variation of inductance against displacement caused by the change of coupling areas between moving coils and static reflectors. The investigations focused on setting up and utilizing a computer model of the 3D eddy current fields and geometry to analyze causes of the production of measurement blind areas, and to investigate effects of the sensor parameters, such as axial gap between coils and reflectors, reflector length and reflector width on characteristics of the sensor. Simulation results indicated that the sensor has the smallest nonlinearity error of 0.15%, which agrees well with the experimental results.

Energy Stable Schemes for Cahn-Hilliard Phase-Field Model of Two-Phase Incompressible Flows

Numerical approximations of Cahn-Hilliard phase-field model for the two-phase incompressible flows are considered in this paper.Several efficient and energy stable time discretization schemes for the coupled nonlinear Cahn-Hilliard phase-field system for both the matched density case and the variable density case are constructed,and are shown to satisfy discrete energy laws which are analogous to the continuous energy laws.

Study on S-shaped characteristic of Francis reversible unit by on-site test and CFD simulation

The operation parameters （vibration, shaft displacement and pressure fluctuation） of No. 1 Francis reversible unit of Baoquan pumped-storage power station were measured on site in the no-load mode at net heads of 518.04, 522.01 and 530.38 m, re- spectively. The rotational speed fluctuations in the no-load mode at three net heads were beyond synchronization requirement with obvious S-shaped characteristic, and misaligned guide vanes （MGV） had to be put into use for synchronization. Further analysis demonstrated that the rotating frequency signal was generally dominant in vibration and shaft displacement mixing signal in the no-load mode, while the frequency domain was wide without an obvious main frequency in pressure fluctuation mixing signal. Besides, the SSTκ-ω turbulence model was adopted to simulate the four quadrant characteristic curves of Baoquan model pump-turbine at three gate openings, and the relative error between simulation results and model test data was within ±6%, indicating that the simulation method in this paper is feasible and S-shaped characteristic of the pump-turbine can be simulated with CFD method.

Fluid Resistance Characteristics Research of Nanowire Rotation under a Magnetic Field

In this study, a visualization-based experiment was performed to measure the motion of the nanowire under a magnetic field. A simulation method based on a multiple reference flame model （MRF model） was used to calcu- late fluid torque. Here, it was validated with the experimental data and theoretical results. Fluid torque of steady rotated nanowire was simulated and compared using experiment and theoretical models. The unsteady rotated condition was studied using transient simulation to compare with theory and the results showed that the accelera- tion of nanowire did not affect the flow field, indicating that the theoretical models based on the steady condition were still valid. The influence of solid walls on nanowire rotation was also studied here. The results showed that if the nanowire was placed close to the wall, the viscous force of wall would increase the velocity gradient around the nanowire, causing higher torque predictions. The fluid torque decreased quickly when the vertical distance between nanowire and wall exceeded 5 times the diameter of the wire.

Nuclear current and antimagnetic rotation in ^(105)Cd

The effects of the nuclear current in the antimagnetic rotation band of 105Cd have been investigated in a fully self-consistent and microscopic way by using the tilted axis cranking relativistic mean-field model.It was found that the inclusion of nuclear current leads to a higher angular momentum and thus a larger kinetic moment of inertia at a given rotational frequency.As a consequence,the B(E2) values with current are always smaller than those without current.

Numerical Investigation of Centerline Curvature Effects on a Compact S-shaped Intake

Taking into account stealth, structure and maintenance, ultra-compact S-shaped intake has been widely used in modem vehicles. In this paper a series of steady numerical simulation were carried out to investigate the complex flow mechanism in s-shaped intake, particular attention was given to examining the effect of centerline curvature on the performance and flowfield of an ultra-compact S-shaped intake. In order to validate the multi-block model, the computational results for Royal Aircraft Establishment intake 2129-M2129 which had modest centerline cur- vature distribution were corrected with available experimental test data. The numerical simulation results agreed fairly well with the experimental data, and the computational method was then used to investigate the effects of different centerline curvature distributions on performance and flow field in compact S-shaped intake. Detailed analyses of the flow visualization had exposed the different flow topologies between the cases with different cen- terline curvature. It was found that different centerline curvature distributions changed the initial location and the size of separation bubble, as well as the strength of two counter-rotating vortices at the entrance of engine.

Theoretical study of current-voltage characteristics of carbon nanotube wire functionalized with hydrogen atoms

A functionalized single-walled carbon nanotube (SWCNT) of a finite length with a ring-like hydrogenation around its surface is designed toward fabrication of a molecular field-effect transistor (FET) device. The molecular wire thus designed is equipped with a quantum dot inside, which is confirmed by theoretical analysis for electronic transport. In particular, the current-voltage (I-V) characteristics under influence of the gate voltage are discussed in detail.