用极大似然法研究部分熔透十字接头疲劳性能

利用极大似然法测试疲劳寿命曲线,研究未熔透尺寸对十字接头疲劳强度的影响。应用有限元方法,可确定疲劳裂纹的开裂位置(焊根或焊趾)。经疲劳试验表明,极大似然法实用性及曲线拟合合理性较好,而且十字焊接接头存在一个临界未熔透尺寸,低于临界值,承受轴向载荷作用的焊接接头疲劳强度不会受到影响。

“然”的用法知多少

古汉语中,“然”用作动词,作“燃烧”解,许慎的《说文解字》:“然,烧也。从火(目犬)声……如延切。”这个意义后来通作“燃”。如: ①若火之始然。(《孟子·公孙丑上》) ——象火开始燃烧。 “然”用作指示代词,作“这样”、“那样”、“如此”解。如: ②子无然。(《左传·襄公二十三年》) ——您不要这样。

先秦汉语代词“然”和连词“然”及其关系研究

殷商甲骨文时期没有"然"字出现。西周金文时期,"然"的本义为"燃烧",后来通过假借和虚化的方法新增了代词和连词的用法。这两种用法在春秋战国时期不断完善和结合,并且在合用代词"然"的情况中,经过语言的演变,"然"的实词义逐渐消退、虚化,让原本独立的两个词凝固成了一个单一的词汇。

Crack detection using a frequency response function in offshore platforms

Structural cracks can change the frequency response function (FRF) of an offshore platform. Thus, FRF shifts can be used to detect cracks. When a crack at a specific location and magnitude occurs in an offshore structure, changes in the FRF can be measured. In this way, shifts in FRF can be used to detect cracks. An experimental model was constructed to verify the FRF method. The relationship between FRF and cracks was found to be non-linear. The effect of multiple cracks on FRF was analyzed, and the shift due to multiple cracks was found to be much more than the summation of FRF shifts due to each of the cracks. Then the effects of noise and changes in the mass of the jacket on FRF were evaluated. The results show that significant damage to a beam can be detected by dramatic changes in the FRF, even when 10% random noise exists. FRF can also be used to approximately locate the breakage, but it can neither be efficiently used to predict the location of breakage nor the existence of small hairline cracks. The FRF shift caused by a 7% mass change is much less than the FRF shift caused by the breakage of any beam, but is larger than that caused by any early cracks.

Analysis of geophone properties effects for land seismic data

The properties of the seismic geophones are important factors for high-resolution seismic exploration and have a great influence on data quality. For this reason, we have tested three kinds of geophones currently used in several regions with different geological features： desert, saline-alkali farmland, and carbonate areas in mountainous regions in order to test their property indexes. Based on the geophone vibration equation and from the property index effects ofgeophone and the connection of the geophones on seismic data, we analyzed seismic data quality acquired inthe tested regions and suggest that suitable geophone property indexes, reasonable choice of geophone types, and the suitable geophone connection can enhance the signal/noise ratio of seismic data.

Theory on Chinese Character Derivation

Character derivation means that if a graph represents several meanings, a new graph based on the original one will be created to bear one or two of the meanings, which is a natural law in Chinese writing system. The old graph is called original character, and the new generated one is called derived character. Two kinds of phenomena-derivation of cognate words （同詞孳乳） and differentiation of unidentical words （異詞別異）-promote the derivation of Chinese characters. In return, derived characters not only bear meaning of the original one, but also serve as a symbol of an independent word and consolidate the graph-meaning relationship. It deserves much attention to the law of the process of character derivation.

Study of coal and gas outbursts by numerical modeling approach

Abstract During mining or road-way development, the distribution of stress and coal pore pressure in the coal face and rib around the new opening will change, under certain conditions, dynamic failure of coal in the form of an outburst can occur. In the modeling studies presented in this paper, an outburst was considered to consist of three distinct stages： preinitiation, initiation and post-initiation, which takes into account the major processes and mechanisms that can influence both outburst-proneness and post-initiation outburst behavior. The model has been applied to simulate the effects of mechanisms in the coal matrix, coal strength, coal damage, geological structures on outbursts. The model constructed using the FLAC software, which were undertaken to research the effects on outbursts of coal strength pressure gradient, and other factors.

IDENTIFICATION OF INPAINTED IMAGES AND NATURAL IMAGES FOR DIGITAL FORENSICS

Image forensics is a form of image analysis for finding out the condition of an image in the complete absence of any digital watermark or signature.It can be used to authenticate digital images and identify their sources.While the technology of exemplar-based inpainting provides an approach to remove objects from an image and play visual tricks.In this paper, as a first attempt, a method based on zero-connectivity feature and fuzzy membership is proposed to discriminate natural images from inpainted images.Firstly, zero-connectivity labeling is applied on block pairs to yield matching degree feature of all blocks in the region of suspicious, then the fuzzy memberships are computed and the tampered regions are identified by a cut set.Experimental results demonstrate the effectiveness of our method in detecting inpainted images.

Application of deviation rate in oil and gas reservoir exploration

Three dimensional geophysical models were abstracted and established according to characteristics of oil and gas reservoir.Then direct current fields for different models were simulated with finite element software(finite element program generator) by hole-to-surface resistivity method.Numerical solution was compared with analytical one for the homogeneity earth model.And a new parameter of deviation rate was proposed by analyzing different plot curves.The results show that the relative error of solution for homogeneity earth model may attain to 0.043%.And deviation rate decreases from 18% to 1% and its anomaly range becomes wide gradually when the depth of oil and gas reservoir increases from 200 to 1 500 m.If resistivity ratio of oil and gas reservoir to sur-rounding rock decreases from 100 to 10 for the resistive oil and gas reservoir,the amplitude attenuation of deviation rate nearly reaches 8%.When there exists stratum above oil and gas reservoir,and influence of resistive stratum may be eliminated or weakened and anomaly of oil and gas reservoir can be strengthened.

Two Dimensional Numerical Simulation of Transient Natural Convection in Freezer

A two dimensional model of the transient natural convection in a freezer is studied numerically by finite volume approach.The temperatures of the freezer outside surfaces and the evaporator vary in specified manners,which were taken from an experimental work.The fluid in the freezer is of the Bousinnesq type and the flow is assumed laminar,The transient heat conduction in the insulating layers and the temperature and velocity fields of the fluid are solved conjugately.The radiation heat transfer between the freezer inner surfaces is taken into account by using the additional source term method.The distributions of the local Nusselt number along the upper and lower surfaces of the evaporator and their average values in the period of periodically unsteady operation are calculated.Comparisons are made between the results with and without consideration of inner surface radiative heat transfer.It is found that the radiative heat transfer between the inner surfaces has a profound effect on the evaporator heat transfer characteristics.

Numerical Simulation of Natural Convection in Circular Enclosures with Inner Polygonal Cylinders,with Confirmation by Experimental Results

Numerical computations are performed for the natural convection in circular enclosures with inner polygonal cylinders.The polygon surface and the outer envelope are at constant but different temperatures,A body-fitted coordinate system is used,The coordinate system is generated via simple algebraic equations.The transformed governing equations are discretized on a control volume basis with power-law finite difference scheme.The SIMPLE-like algorithm is used to deal with the linkage between pressure and velocities.The numerical results are compared with the experimental data available in the literature,and the agreement between the numerical and experimental results are very good.