2016 Vol. 37, No. 5

Display Method:
Mechanical Responses of Crosslinked Biopolymer Networks
CHENG Chuan-liang, GONG Bo, QIAN Jin
2016, 37(5): 441-458. doi: 10.3879/j.issn.1000-0887.2016.05.001
Abstract(1161) PDF(1213)
Crosslinked biopolymer networks are composed of filaments randomly distributed and crosslinked by specific binders, and are widespread in cytoskeletons of cells, biological gels and other natural materials. The binding energy of typical crosslinks in such biopolymer networks is relatively low and close to thermal energy, so that the binding status of the interaction is strongly influenced by the deformation of networks and thermal excitations from the environment. Experiments on different types of crosslinked biopolymer networks have demonstrated that these networks exhibit a linear response with low modulus in small deformation, and can be stiffened by more than two orders of magnitude in large strain. However, the network stiffness decreases dramatically when the applied strain exceeds a threshold value. This phenomenon is known as the transition from strain hardening to softening, and draws great attention from many researchers. Theoretical and numerical studies have indicated that such strain hardening is mainly caused by a transition from bending-dominated filament deformation in small strain to stretching-dominated response in large strain, and the strain softening is due to the microscopic unbinding of crosslinks, leading to weakened networks. This paper overviews the key components and representative architectures of crosslinked biopolymer networks, stretching behaviors of biopolymers, types and properties of crosslinks, and experimental methods used to measure the mechanical responses of network structures, with an emphasis on the theoretical, finite element and molecular dynamics models that pave the way to the understanding of the structure-function relations in crosslinked biopolymer networks.
Advances in Research on Bragg Resonance of Ocean Surface Waves by Sandbars and Artificial Sandbars
LIU Huan-wen
2016, 37(5): 459-471. doi: 10.3879/j.issn.1000-0887.2016.05.002
Abstract(849) PDF(622)
On natural beaches nearly periodic shore-parallel sand ripples and sandbars can be often found in bays or on open coasts. When surface waves coming from the ocean propagate over patches of sand ripples and sandbars, once the Bragg condition is met, that is, the wavelength of surface waves is twice of the sandbar spacings, the Bragg resonant reflection may occur to cause a large portion of the incident wave energy to be reflected back to the ocean. Inspired by the Bragg resonant reflection phenomenon of natural sand ripples and sandbars, some pioneering scientists proposed the so-called Bragg submerged breakwater consisting of a series of small-size, low-height, shore-parallel artificial bars placed just outside the surf zone to shelter the coast and near-shore facilities from the attack of storm waves. A brief summary of the advances in research on Bragg resonance between ocean surface waves and natural sandbars as well as Bragg submerged breakwaters since 1980s was presented.
A 5th-Order Theory for Bichromatic and Bidirectional Ocean Surface Waves
HUANG Hu, LIU Guo-liang
2016, 37(5): 472-482. doi: 10.3879/j.issn.1000-0887.2016.05.003
Abstract(721) PDF(770)
The classical Stokes wave theory of pure wave motion for the 3rd-order monochromatic and monodirectional waves was expanded to a 5th-order theory for bichromatic and bidirectional ocean surface waves under the ambient uniform current effect in water of finite depth, which, based on the 3rd-order theory for bichromatic and bidirectional waves, comprised the 4th- and the 5th-order explicit expressions for the free surface elevations, the velocity potential and the nonlinear amplitude dispersion relation. The 5th-order nonlinear amplitude dispersion relation playing a key role in the bichromatic and bidirectional wave theory was generalized to one relation of 2 arbitrary interacting waves with different frequencies and ampitudes in pairs out of infinite waves. The typical characteristics of bichromatic and bidirectional short-crested waves were illustrated in detail with diagrams.
Displacement Responses of Submerged Floating Tunnels Under Impact Loads
ZHANG Yuan, DONG Man-sheng, TANG Fei
2016, 37(5): 483-491. doi: 10.3879/j.issn.1000-0887.2016.05.004
Abstract(700) PDF(664)
The submerged floating tunnel (SFT) was simplified as an elastically supported beam with uniform supporting spacings. The dynamics model was established to solve the vibration problem of the SFT under impact loads. With the Galerkin method, the timedisplacement responses at the central cross section of the SFT was numerically simulated. The influences of the anchor stiffness, the impact mass and the impact velocity on the SFT’s central displacement were analyzed. The present results indicate that the anchor stiffness has significant but bounded negative influence on the SFT’s central displacement. Moreover, the impact mass and the impact velocity have obvious positive effects on the SFT’s central displacement. The work provides a theoretical reference for further study and construction of the SFT.
Analysis on Aerodynamic Characteristics of the UAV Horizontal Tail Under Propeller Slipstream
ZENG Zhuo-xiong, WU Qing
2016, 37(5): 492-500. doi: 10.3879/j.issn.1000-0887.2016.05.005
Abstract(763) PDF(563)
In order to analyze the change law of the aerodynamic characteristics of the unmanned aerial vehicle (UAV) horizontal tail under the effects of the propeller slipstream, the numerical results were compared between cases with and without propeller drive. It is found that, under the propeller slipstream, the flow around the wing is reinforced and a stronger downwash appears. The induced flow changes the local incidence of the horizontal tail and speeds up the flow velocity on the tail surface. So, the lift coefficient of the horizontal tail decreases, the drag coefficient increases a little, and the noseup pitching moment rises. The drag force on the wing under the propeller slipstream changes relatively obviously with the rise of the attack angle.
2-Phase Hemodynamic Analysis Under Bidirectional Fluid-Structure Interaction in the Left Coronary Artery With Stenosis
LIU Ying, ZHANG Wei-zhong, YIN Yan-fei, ZHANG Zhi-liang, ZHANG De-fa
2016, 37(5): 501-509. doi: 10.3879/j.issn.1000-0887.2016.05.006
Abstract(873) PDF(589)
Treated as a 2-phase flow, the blood flow in the left coronary artery with stenosis was transiently simulated with the method of computational fluid mechanics, under the bidirectional fluid-structure interaction between the blood flow and the vascular wall. The blood flow distribution characteristics in the left coronary artery was analyzed at typical moments within a cardiac cycle, and the effects of the 2-phase blood model plus the fluid-structure interaction on the hemodynamics were studied in comparison with those of the Newtonian blood model and the 2-phase blood model. The results show that, in the proximal outside of the obtuse marginal and the distal part of the left circumflex branch there appear low-speed eddy zones where both the wall shear stress and the red blood cells’ volume fraction are relatively small, resulting in a suitable physical environment for the formation and development of atherosclerosis. The wall displacement at the left coronary artery bifurcation is rather large, making a possible cause for the disfunctions of the vascular wall intima, which also prompts the formation of the atherosclerotic plaques. The comparison between different blood models shows, the flow characteristics of red blood cells have considerable influences on the hemodynamics of blood flow velocity and wall shear stress, and the bidirectional fluid-structure interaction model is more consistent with the true situation of the blood flow.
Numerical Simulation of Qingshi Landslide Beside Shennü Stream in the Three Gorges With the Discrete Element Method Under Different Water Levels
TANG Hong-mei, YAN Zhao-qi, CHEN Hong-kai
2016, 37(5): 510-521. doi: 10.3879/j.issn.1000-0887.2016.05.007
Abstract(864) PDF(534)
To study the deformation and failure process of Qingshi landslide located in the Three Gorges reservoir area, a discrete element model was established to simulate this landslide with the PFC2D software under different water levels. The simulation results show that the middle part of the landslide has the largest vertical displacements and velocities at the same time under the water level of 165 m. Besides, the horizontal stresses and strain rates of the landslide toe reach the maximum values firstly in the late period under the water level of 165 m. Qingshi landslide has little deformation under the water level of 145 m. The failure modes are the same under the water levels of 155 m, 165 m and 175 m, and a typical failure process can be divided into 4 periods: weakening and creeping of the slip mass, deformation of the front part, instability and sliding of the middle part, and stabilization of the landslide. In the sliding process, the rock and soil mass near the sliding zone will weaken in strengths to some extent. The simulated steady state of Qingshi landslide is consistent with the measured results in situ under different water levels, i.e. the cracks’appearance and development under the 175 m water level are close to the real situations, with only allowable deviations. It is proved that the deformation and failure process of Qingshi landslide can be simulated satisfactorily with the discrete element method.
3D Scattering and Dynamic Stress Concentration of SH Waves in Spherical Shells With Spherical Inclusions
QIAO Song, SHANG Xin-chun
2016, 37(5): 522-533. doi: 10.3879/j.issn.1000-0887.2016.05.008
Abstract(720) PDF(452)
Spherical shells are widely applied in many engineering fields, and dynamic stress concentration generated by the inclusions (including cavities) will affect the bearing strengths and service lives of the structures directly. The 3D scattering and dynamic stress concentration of SH waves around spherical inclusions in thick spherical shells were investigated theoretically and numerically. 2 spherical coordinate systems, located at the spherical shell center and the inclusion center, were established to express the incidence and scattered waves in the expansion form of spherical wave functions. The addition formulas were employed to perform the coordinate transformation and the analytical solutions of the displacements and stresses were derived. Finally, computation and comparison of wave scattering and dynamic stress concentration by the inclusions of different materials and a cavity were conducted, and the results revealed the influences of the incidence frequency and the inclusion center position on the distributions of the dynamic stress concentration factors. This research provides a theoretical support for the dynamic analysis and nondestructive examination of spherical shells.
A Stress Calculation Method for Guide Thimbles in Fuel Assemblies Under Accident Conditions
QI Huan-huan, SHEN Ping-chuan, WU Wan-jun, JIANG Nai-bin, HUANG Xuan
2016, 37(5): 534-541. doi: 10.3879/j.issn.1000-0887.2016.05.009
Abstract(676) PDF(694)
Through the dynamic analysis of reactor systems, the displacementtime histories of upper/lower core plates and core barrels were obtained. The time history was then treated as the input for seismic and LOCA analysis of the fuel assembly. Then the horizontal row model of the fuel assembly was built for the dynamic analysis under accident conditions. From this analysis, the displacements of the fuel assembly was got as the input for the guide thimble stress calculation. According to the simplified method for the horizontal row model and the guide thimble distribution in the fuel assembly, the calculation method for the membrane stress and bending stress was deduced. The issues in the use of this method were described. The process of stress analysis and evaluation for the guide thimbles was schemed and realized through programming. With the presented method, stress analysis and evaluation of the guide thimbles in one power plant were effectively carried out as an example.
Discussion on ‘Reconstructed Formulas Calculating Bursting Pressures of the Special Spherical Pressure Vessels Based on Experimental Data’
LIU Xiao-ning, LIU Cen, ZHANG Hong-wei, LIU Bing, YUAN Xiao-hui, YANG Fan
2016, 37(5): 542-550. doi: 10.3879/j.issn.1000-0887.2016.05.010
Abstract(578) PDF(712)
In order to provide a basis for the comparison, selection and determination of the appropriate burst pressure calculation formulas for steel spherical vessels, the indexes of accuracy and concentration for the precision evaluation of the calculation formulas were established. By means of 59 groups of measured data, the precisions of 4 different burst pressure calculation formulas were analyzed. The discussion gives conclusions as follow: the formula’s average accuracy ratio (the ratio of the calculated burst pressure value to the measured value) and the coefficient of variation can be reasonably treated as the indexes of accuracy and concentration for the formula’s precision evaluation, respectively; for multi-layer spherical vessels, the average accuracy ratio of the mid-diameter formula is 0.977 0 and the coefficient of variation is 0.035 4, with the yield ratios of the vessel wall materials ranging from 0.720 9 to 0.847 5 and the diameter ratios ranging from 1.053 to 1.107; for single-layer spherical vessels, the average accuracy ratio of the mid-diameter formula is 1.169 1 and the coefficient of variation is 0.108 3, with the yield ratios of the vessel wall materials ranging from 0.336 2 to 0.618 9 and the diameter ratios ranging from 1.109 to 1.257; compared with the results out of the other 3 formulas, the burst pressures calculated with the mid-diameter formula for steel thin-walled multi-layer spherical vessels are more precise, the burst pressures calculated with the mid-diameter formula for steel thin-walled single-layer spherical vessels are more concentrated.