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21.
厚壁管道在特种承压设备领域中广泛使用,常规无损检测技术难以实现其快速有效地检测。本文采用数值模拟与实验相结合来研究周向导波快速检测厚壁管道的方法。首先,利用有限差分软件研究了不同角度激励下外径269mm、壁厚32mm的厚壁管道中周向导波的传播特性,优化了探头激励角度范围;然后分别制作了55°和45°的斜楔,并搭建了实验系统,研究了周向导波与厚壁管道壁厚方向不同位置缺陷的相互作用规律。研究结果表明,周向导波适用于厚壁管道快速检测。检测时需选择角度适中的探头。激发角度过小时,厚壁管中形成的周向导波模式较多,使得波包宽度较大,影响检测分辨率;而角度过大时,会使得盲区增大,导致靠近内壁区域缺陷漏检。本文的研究结论为厚壁管道缺陷周向导波的实际检测应用提供了指导。 相似文献
22.
The problem on large deformations of round cylinders made of homogeneous and fiber-reinforced elastomeric materials under
the action of inertia forces caused by rotatory motion is solved. The solution is given in a plane axisymmetric statement,
where the deformation parameters of the cylinders depend only on the radial coordinate. Based on the mathematical model presented,
the deformation of revolving cylinders made of homogeneous elastomeric materials and reinforced with fibers in the axial,
circumferential, and radial directions is investigated. The ultimate rotational speeds for cylinders with different reinforcement
schemes and tight and loose fits are found at which their limiting configurations are reached.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 45, No. 3, pp. 347-366, May-June, 2009. 相似文献
23.
Summary If water molecules are strongly bound at a protein-ligand interface, they are unlikely to be displaced during ligand binding. Such water molecules can change the shape of the ligand binding site and thus affect strategies for drug design. To understand the nature of water binding, and factors influencing it, water molecules at the ligand binding sites of 26 high-resolution protein-ligand complexes have been examined here. Water molecules bound in deep grooves and cavities between the protein and the ligand are located in the indentations on the protein-site surface, but not in the indentations on the ligand surface. The majority of the water molecules bound in deep indentations on the protein-site surface make multiple polar contacts with the protein surface. This may indicate a strong binding of water molecules in deep indentations on protein-site surfaces. The local shape of the site surface may influence the binding of water molecules that mediate protein-ligand interactions. 相似文献
24.
25.
W.W. Mullins 《Interface Science》2001,9(1-2):9-20
Surface energetics is reviewed including expressions for the chemical potential of a curved surface element and the Legendre transform relation between the projected surface free energy as a function of orientation and the Wulff equilibrium shape. A well known equation is derived describing surface evolution by surface diffusion, assuming local equilibrium. Solutions are reviewed including a decaying sinusoid and a developing thermal groove. Breakdown of local equilibrium is considered. The structure, energetics and dynamics of steps on a vicinal surface are discussed. Facet sizes on the Wulff shape and the surface profile at the edge of a facet are related to the step self and interaction free energies respectively. Fourier analysis of step fluctuations is described, revealing the underlying transport processes. Analysis of the decay of a sinusoidal profile on a vicinal surface in terms of step behavior is given. Finally, examples are reviewed of surface evolution below the roughening temperature T
R in which case facets move by the lateral spreading of steps. Results differ greatly from those of the continuum theory applicable above T
R. 相似文献
26.
Martin E. Glicksman 《哲学杂志》2020,100(14):1789-1817
ABSTRACT Grain boundary grooves (GBGs) are local features that develop along polycrystalline solid–liquid interfaces. Interest in GBGs lies in their ability to form interface defects during crystallization that promote, in fact, dominate, morphological instability and affect microstructure formation in cast alloys. Recently, we reported on unobserved subtle aspects of the thermodynamic behaviour of GBG microstructures by combining sharp-interface field theory with diffuse-interface phase-field simulations. A surprising feature revealed about steady-state GBGs is that despite their stationarity they nonetheless support persistent capillary-mediated energy fluxes with divergences that continuously cool their interfaces and increase local curvatures. We now analyse the energetic behaviour of GBGs as ‘open’ thermodynamic systems, and report further details of their formation free energy that show how geometric constraints and capillary-mediated thermodynamic fields self-interact and influence the steady-state shapes of GBGs. 相似文献
27.
This paper presents a method to measure the in-plane displacement fields of curved surface by moire interferometry of partial
coherent light. The method has the following advantages: simple optical system, no requirement on vibration isolation, high
sensitivity, large measuring range, high contrast of interference fringes and availability to in situ structural testing.
the present paper also gives theoretical analysis of the method and the formulas of light intensity and displacement field,
and introduces a replication technique to form a high frequency reflectance grating on the curved surface. The expriments
achieved the measurement of the surface displacement field of a cylindrical shell— the simultaneous circumferential, axial
and 45° displacement fields. The torsional test data for surface displacement of a circular bar agree well with the theoretical
result.
The project supported by National Natural Science Foundation of China. 相似文献
28.
29.
针对现有单光束激光同步扫描周视探测对脉冲重复频率要求较高,难以实际应用的问题,提出单光束扩束扫描激光周视探测方法.基于单光束扩束扫描激光周视探测工作原理,推导了最低扫描频率和脉冲频率解析式;分析了圆柱目标回波特性及关键参数截面衰减系数,建立了脉冲扩束激光圆柱目标回波功率数学模型,讨论了系统参数对截面衰减系数的影响,得到最大相邻脉冲光束夹角表达式;重点分析了脉冲频率、光束角和光束入射角对不同直径目标的探测能力的影响;得到了探测系统对典型条件下最大光束角、最低脉冲频率的计算方法.结果表明,对扫描光束稍加扩束可有效降低脉冲重复频率要求.研究结果可为单光束脉冲激光周视探测系统设计、优化提供理论依据. 相似文献
30.
Periodic wall oscillations in the spanwise or circumferential direction can greatly reduce the friction drag in turbulent channel and pipe flows. In a concentric annulus, the constant rotation of the inner cylinder can intensify turbulence fluctuations and enhance skin friction due to centrifugal instabilities. In the present study, the effects of the periodic oscillation of the inner wall on turbulent flows through concentric annulus are investigated by the direct numerical simulation (DNS). The radius ratio of the inner to the outer cylinders is 0.1, and the Reynolds number is 2 225 based on the bulk mean velocity Um and the half annulus gap H. The influence of oscillation period is considered. It is found that for short-period oscillations, the Stokes layer formed by the circumferential wall movement can effectively inhibit the near-wall coherent motions and lead to skin friction reduction, while for long-period oscillations, the centrifugal instability has enough time to develop and generate new vortices, resulting in the enhancement of turbulence intensity and skin friction. 相似文献