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排序方式: 共有743条查询结果,搜索用时 15 毫秒
671.
The nonlinear aeroelastic response of a two-degree-of-freedom airfoil with freeplay and cubic nonlinearities in supersonic flows is investigated. The second-order piston theory is used to analyze a double-wedge airfoil. Then, the fold bifurcation and the amplitude jump phenomenon are detected by the averaging method and the multi-variable Floquet theory. The analytical results are further verified by numerical simulations. Finally, the influence of the freeplay parameters on the aeroelastic response is analyzed in detail. 相似文献
672.
基于连续时间随机行走(CTRW)理论,实现反常扩散条件下对跳跃步长和等待时间分布函数的抽样,改进Metropolis抽样判定方法以适用于存在非线性势的情况.数值研究布朗粒子在亚稳势下的逃逸速率.结果显示,稳定逃逸速率γst随反常指数α非单调变化,在超扩散条件下存在极大值和位垒相消现象. 相似文献
673.
青藏高原冻土工程地质特性与选线原则探讨 总被引:1,自引:0,他引:1
青藏±500kV直流联网工程穿越青藏高原多年冻土区,冻土特有的工程问题将对工程设计、施工和安全运营产生重要影响。由于输电线路属于点线结构的工程特点,即塔基的稳定性关系到整条线路的稳定性,而塔基点位又具有一定的可调性,因此,多年冻土及厚层地下冰的分布特征对于输电线路的选线、选位较其他线性工程更具重要意义。本文主要在输电线路沿线冻土分布的基础上,重点对微地貌条件下冻土和厚层地下冰的分布发育规律进行了分析和研究。并在此基础上,结合输电线路工程特点,就线路的选线选位的原则进行了分析和确定。 相似文献
674.
This paper investigates the absorptive spectral lines of four-level
atomic system driven by a coupling, probe and microwave fields. Due
to the perturbation of the microwave field, the original
electromagnetically induced transparency is changed to
electromagnetically induced absorption and the absorptive spectral
line can be very narrow. This ultranarrow spectral line has
potential applications to the microwave atomic frequency standard and
the measurement of very weak magnetic field. 相似文献
675.
An Algebraic Multigrid Method for Nearly Incompressible Elasticity Problems in Two-Dimensions 下载免费PDF全文
Yingxiong Xiao Shi Shu Hongmei Zhang & Yuan Ouyang 《advances in applied mathematics and mechanics.》2009,1(1):69-88
In this paper, we discuss an algebraic multigrid (AMG) method for
nearly incompressible elasticity problems in two-dimensions. First,
a two-level method is proposed by analyzing the relationship between
the linear finite element space and the quartic finite element
space. By choosing different smoothers, we obtain two types of
two-level methods, namely TL-GS and TL-BGS. The theoretical analysis
and numerical results show that the convergence rates of TL-GS and
TL-BGS are independent of the mesh size and the Young's modulus, and
the convergence of the latter is greatly improved on the order $p$.
However, the convergence of both methods still depends on the
Poisson's ratio. To fix this, we obtain a coarse level matrix with
less rigidity based on selective reduced integration (SRI) method
and get some types of two-level methods by combining different
smoothers. With the existing AMG method used as a solver on the
first coarse level, an AMG method can be finally obtained. Numerical
results show that the resulting AMG method has better efficiency for
nearly incompressible elasticity problems. 相似文献
676.
Carmichael DW Hamandi K Laufs H Duncan JS Thomas DL Lemieux L 《Magnetic resonance imaging》2008,26(7):870-873
In pathological conditions interpretation of functional magnetic resonance imaging (fMRI) results can be difficult. This is due to a reliance on the assumed coupling between neuronal activity and changes in cerebral blood flow (CBF) and oxygenation. We wanted to investigate the coupling between blood oxygen level dependant contrast (BOLD) and CBF time courses in epilepsy patients with generalised spike wave activity (GSW) to better understand the underlying mechanisms behind the EEG-fMRI signal changes observed, especially in regions of negative BOLD response (NBR). Four patients with frequent GSW were scanned with simultaneous electroencephalographic (EEG)-fMRI with BOLD and arterial spin labeling (ASL) sequences. We examined the relationship between simultaneous CBF and BOLD measurements by looking at the correlation of the two signals in terms of percentage signal change on a voxel-by-voxel basis. This method is not reliant on coincident activation. BOLD and CBF were positively correlated in patients with epilepsy during background EEG activity and GSW. The subject average value of the Delta CBF/Delta BOLD slope lay between +19 and +36 and also showed spatial variation which could indicate areas with altered vascular response. There was not a significant difference between Delta CBF/Delta BOLD during GSW, suggesting that neurovascular coupling to BOLD signal is generally maintained between states and, in particular, within areas of NBR. 相似文献
677.
传统Spar平台垂荡主共振时非线性耦合响应的研究 总被引:1,自引:0,他引:1
考虑瞬时波面影响,建立了Spar平台垂荡-纵摇运动的参数激励耦合运动方程,应用多尺度法导出了波浪频率接近垂荡固有频率时响应方程的一阶摄动解并做数值验证。计算结果显示:当波浪高度达到一定值时,纵摇运动中出现大量的亚谐频率成分;随着波浪高度进一步增大,纵摇运动将出现明显的幅值跳跃现象。研究结果表明,能量渗透现象是纵摇运动失稳的主要原因,波浪激励力矩对于纵摇本身的贡献很小。由于垂荡模态存在能量饱和现象,多余的垂荡能量将会向纵摇模态转移,导致出现大幅值的纵摇运动。 相似文献
678.
679.
Xiufeng Yang Manjil Ray Song-Charng Kong Chol-Bum M. Kweon 《Proceedings of the Combustion Institute》2019,37(3):3279-3286
The interaction of liquid drops and heated surfaces is of great importance in many applications. This paper describes a numerical method, based on smoothed particle hydrodynamics (SPH), for simulating n-heptane drop impact on a heated surface. The SPH method uses numerical Lagrangian particles, which obey the laws of fluid dynamics, to describe the fluid flows. By incorporating the Peng–Robinson equation of state, the present SPH method can directly simulate both the liquid and vapor phases and the phase change process between them. The numerical method was validated by two experiments on drop impact on heated surfaces at low impact velocities. The numerical method was then used to predict drop-wall interactions at various temperatures and velocities. The model was able to predict the different outcomes, such as rebound, spread, splash, breakup, and the Leidenfrost phenomenon, consistent with the physical understanding. 相似文献
680.
Time-resolved imaging of mode-conversion process of terahertz transients in subwavelength waveguides
Yao Lu Qiang Wu Qi Zhang Ri-De Wang Bin Zhang Wen-Juan Zhao Deng Zhang Hao Xiong Cheng-Liang Yang Ji-Wei Qi Chong-Pei Pan Jing-Jun Xu 《Frontiers of Physics》2019,14(4):42502
We studied the mode-conversion process of terahertz pulses from a planar subwavelength waveguide to a tilted rectangular subwavelength waveguide. An unusual wavefront rotation, which led to an extra conversion time, was observed using a time-resolved imaging technique. We simulated the mode conversion process by a finite-difference time-domain method, and the results agreed well with the experiments. According to the simulations, the conversion time was demonstrated to become longer as the tilt angle or width of the rectangular waveguide increased. This work provides the possibility to optimize the future high-speed communications and terahertz integrated platforms. 相似文献