加劲肋对焊缝区域应变模式的影响

通过试验和数值分析对工字形梁和箱形柱焊接连接的性能进行探讨,以获得加劲肋和柱翼缘厚度对连接耗能性能的影响。采用有限元法对试验构件进行了建模和分析,并将结果与全尺试验对比。考虑了各类加劲肋的影响,包括:柱加劲肋、侧向加劲肋、翼缘顶部和底部加劲肋。评测了各种加劲肋在塑性变形控制和连接耗能性能方面的贡献。     

水利服务湖北“两圈一带”战略的思考

"两圈一带"战略是湖北省委、省政府按照科学发展观要求提出并实施的重要战略。水利服务"两圈一带"战略要着力实施水利安全工程、水利生态工程和水利开发工程。要在服务"两圈一带"战略中实现新的跨越,必须夯实服务基础,创新思路,真抓实干。     

A Two-network thermomechanical model of a shape memory polymer

The aim of this work is to demonstrate a Helmholtz potential based approach for the development of the constitutive equations for a shape memory polymer undergoing a thermomechanical cycle. The model is able to simulate the response of the material during heating and cooling cycles and the sensitive dependence of the response on thermal expansion. We notice that the yield-stress of the material controls the gross features of the response of the model, and suggests that the material yields differently depending on not just the current value of the temperature but also on whether the temperature of the material dropped or increased from the previous time-step somewhat similar to the Bauschinger effect in plasticity, except that here the controlling parameter is the rate of temperature change rather than rate of plastic strain. The results of the simulation are in qualitative and quantitative agreement with experiments performed on two different shape memory polymer samples: polyurethane and epoxy resin. We find that modeling the hysteresis of the yield stress of the material during temperature changes is the key to the results.     

Trickle flow hydrodynamic multiplicity: Experimental observations and pore-scale capillary mechanism

Trickle bed reactors are encountered throughout the process industry. Considerable attention has been given to the study of the hydrodynamics of this type reactor. It has been identified that, in the trickle flow regime, the hydrodynamic parameters (e.g. pressure drop and liquid holdup) are not unique functions of the operating and system conditions, but depend on the flow history. This study reviews the experimental trends identified in literature on the basis of a limiting cases framework and then evaluates the three-dimensional pore-scale liquid distribution using computed tomography (CT) data. This leads to the identification of 20 phenomenological trends that characterize hydrodynamic multiplicity, including hydrodynamic flow hysteresis as well as the effects of pre-wetting. The CT study yields additional experimental insight into the role of capillary pressure and ultimately leads to the proposal of a capillary gate mechanism based on contact angle hysteresis as the root cause of multiplicity. The mechanism is incorporated into a simple pore-network model. It is shown that the qualitative performance of the model corresponds closely to the majority of phenomenological trends and is capable of explaining the observed experimental behaviour.     

Permeability of soft porous media under one-dimensional compaction

A novel experimental approach to measure permeability of porous material samples under variable longitudinal compaction has been developed. The material has a non-linear structural behavior and exhibits a small hysteresis during mechanical loading and unloading experiments. The new permeameter includes a piston moving inside a Plexiglas cylinder with controllable speed and a test section where the porous material sample is placed under compaction by two grids with adjustable positions. Time-dependent pressure was recorded at four different locations along the sample together with the velocity of the piston. Experiments with two different sample lengths have been performed at three different Reynolds numbers based on the apparatus diameter. The results show that pressure gradient and permeability data do not depend on initial uncompacted sample length. All experiments included measurements at various compaction ratios of the material followed by measurements during relaxation/expansion of the material. No hysteresis was observed in the pressure gradient and permeability data during compaction and expansion of the material for a wide range of compaction ratio. The effects of small velocity fluctuations due to variable friction of the moving piston with cylinder’s wall were also considered. These velocity fluctuations cause pressure fluctuations within the sample which are high close to the inlet part of the material sample and are reduced almost completely towards its outlet. However these pressure fluctuations when scaled with the corresponding mean pressure retained their time-dependent amplitude and phase unchanged along the material. These relative pressure fluctuations cancelled out the flow velocity fluctuations resulting insignificant fluctuations in permeability. It was found that permeability, which is a material property, is drastically reduced with increased compaction ratio of the material while its solid fraction changes substantially but its porosity remains practically unchanged. A comparison with the Cármán–Kozeny expression for random porous media was also examined. Cármán–Kozeny expression predicts qualitatively the reduction of permeability with compaction. However, the predicted values of permeability are very sensitive to the initial value of porosity.     

Energy Evaluation for Ramberg–Osgood Hysteretic Model

Response of structures to static and dynamic loads may be assessed in terms of energy. The energy evaluation depends on hysteretic models used to describe inelastic behavior of structures and their elements. One of the hysteretic models often employed in structural analysis is the Ramberg–Osgood model. In the paper a physically motivated model, which leads to the Ramberg–Osgood force–displacement relationship under monotonic loading and exhibits Masing type of behavior for unloading/reloading, is described. Based on the model formulas to calculate recoverable elastic strain energy and irrecoverable hysteretic energy for systems/elements under monotonic loading are derived. It is also shown how recoverable elastic strain energy and irrecoverable hysteretic energy can be evaluated at any point of unloading/reloading curves for a system/element of Masing type. The application of the derived formulas is illustrated by evaluating the energy of a single-degree-of-freedom system subjected to impulse and seismic loading.     

PREDICTION OF MINIMUM SPOUTING VELOCITY IN TWO-DIMENSIONAL FLAT BOTTOM SPOUTED BEDS

Spouted beds have been used in industry for operations such as drying, catalytic reactions, and granulation. Conventional cylindrical spouted beds suffer from the disadvantage of scaleup. Two-dimensional beds have been proposed by other authors as a solution for this problem. Minimum spouting velocity has been studied for such two-dimensional beds. A force balance model has been developed to predict the minimum spouting velocity and the maximum pressure drop. Effect of porosity on minimum spouting velocity and maximum pressure drop has been studied using the model. The predictions are in good agreement with the experiments as well as with the experimental results of other investigators.     

滞环电流变换器及其在PFC中的应用

从功率因数校正的功能，讨论了滞环电流变换器（HCC）的工作原理，分析了其稳态运行特性。提出了用于功率因数校正时主要储能元件参数的计算方法。     

In-situ horizontal cyclic loading tests on composite foundation composed of soilbags and piles

The authors have been developing a new composite foundation composed of piles and soilbags. The foundation is characterized by the laying of soilbags between the pile heads and the footing on which a superstructure stands. The expected effect of the foundation is to cut off the fixed connection between the piles and the footing in order to reduce the bending moment of the piles and the response acceleration of the structure. In this study, in-situ horizontal cyclic loading tests were conducted on the proposed composite foundation with two piles to investigate the seismic response characteristics of the foundation at real scale. It was found from the tests that the horizontal force reached its peak due to the uplift of the footing during horizontal loading, and that larger hysteresis damping was obtained than that of spread foundations due to the hysteresis effect in the shear deformation of the soilbags. As for the sectional force of the piles and the vertical stress inside the soilbags, it was found that the axial force and bending moment of the piles concentrated on the pile on the front side in the loading direction, and that the vertical stresses inside the soilbags concentrated just above the pile head on the front side in the loading direction. Although residual horizontal displacement and settlement occurred due to the cyclic load, little damage to the soilbags was observed.     

不同剪切历史和热历史对原油滞回环的影响

胶凝含蜡原油由于其蜡晶的三维网状空间结构,具有复杂的流变性。胶凝原油的流变性质一直是研究的重点和热点。通过实验,研究了在不同剪切历史和热历史作用下胶凝原油滞回环的不同变化规律。实验结果表明,对于不同的降温速率,在同一剪切条件下,当降温速率较低时,其原油屈服应力较大,滞回环曲线凸起较高,但随着剪切速率的增加,其应力逐渐接近,滞回环曲线逐渐接近;对于不同的胶凝温度,在同一剪切条件下,胶凝温度越低的,其屈服应力较大,并且随着剪切速率的增加,应力之间的差别虽变小,但胶凝温度低的比胶凝温度高的大,在滞回环曲线上可以看到低温度的曲线比高温度的曲线所对应的应力大;对于不同的剪切速率,剪切速率变化率大的,其屈服应力大,但随着剪切速率的增大,滞回环曲线相接近,即其应力也逐渐相接近。