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Background: Although the role of endogenous mechanical stresses in regulating morphogenetic movements and cell differentiation is now well established, many aspects of mechanical stress generation and transmission in developing em...
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Background: Although the role of endogenous mechanical stresses in regulating morphogenetic movements and cell differentiation is now well established, many aspects of mechanical stress generation and transmission in developing embryos remain unclear and require quantitative studies.
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In elasticity theory, harmonic holes are designed to leave the mean stress inside the surrounding material as a constant. In this paper, we present the design of periodic harmonic holes with surface tension in an elastic plane und...
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In elasticity theory, harmonic holes are designed to leave the mean stress inside the surrounding material as a constant. In this paper, we present the design of periodic harmonic holes with surface tension in an elastic plane under a uniform remote loading. We identify the special shapes of such holes by solving a problem of the existence of a holomorphic function defined in a strip with one of the holes and satisfying specific boundary values. Several examples are given to illustrate the size-dependent effects of surface tension on the shapes of periodic harmonic holes.
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The induction period of various proportion of urea-thiourea mixed crystal in water has been measured experimentally by the visual observation method.The induction period,which is inversely proportional to the nucleation rate,has b...
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The induction period of various proportion of urea-thiourea mixed crystal in water has been measured experimentally by the visual observation method.The induction period,which is inversely proportional to the nucleation rate,has been used to estimate the interfacial tension between the urea-thiourea mixed crystal and water,hence the nucleation parameters like critical radius(r*),number of molecules in the radius(r*)and Gibbs free energy change for the formation of a critical nucleus(DLETA G*)have been calculated.
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In offshore engineering long slender risers are simultaneously subjected to both axial and transverse excitations. The axial load is the fluctuating top tension which is induced by the floater's heave motion, while the transverse ...
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In offshore engineering long slender risers are simultaneously subjected to both axial and transverse excitations. The axial load is the fluctuating top tension which is induced by the floater's heave motion, while the transverse excitation comes from environmental loads such as waves. As the time-varying axial load may trigger classical parametric resonance, dynamic analysis of a deepwater riser with combined axial and transverse excitations becomes more complex. In this study, to fully capture the coupling effect between the planar axial and transverse vibrations, the nonlinear coupled equations of a riser's dynamic motion are formulated and then solved by the central difference method in the time domain. For comparison, numerical simulations are carried out for both linear and nonlinear models. The results show that the transverse displacements predicted by both models are similar to each other when only-the-random transverse excitation is applied. However, when the combined axial dynamic tension and transverse wave forces are both considered, the linear model underestimates the response because it ignores the coupling effect. Thus the coupled model is more appropriate for deep water. It is also found that the axial excitation can significantly increase the riser's transverse response and hence the bending stress, especially for cases when the time-varying tension is located at the classical parametric resonance region. Such time-varying effects should be taken into account in fatigue safety assessment. (C) 2017 Elsevier Ltd. All rights reserved.
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We compute time-periodic solutions of a simple model for the vortex sheet with surface tension. The model has the same dispersion relation as the full system of evolution equations, and it also has the same destabilizing nonlinear...
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We compute time-periodic solutions of a simple model for the vortex sheet with surface tension. The model has the same dispersion relation as the full system of evolution equations, and it also has the same destabilizing nonlinearity (if the surface tension parameter were to be set to zero, then this nonlinearity would cause an analogue of the Kelvin-Helmholtz instability). The numerical method uses a gradient descent algorithm to minimize a functional which measures whether a solution of the system is time periodic. We find continua of genuinely time-periodic solutions bifurcating from equilibrium.
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The induction period of various proportion of urea-thiourea zinc chloride crystal in water has been measured experimentally using the visual observation method. The induction period, which is inversely proportional to the nucleati...
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The induction period of various proportion of urea-thiourea zinc chloride crystal in water has been measured experimentally using the visual observation method. The induction period, which is inversely proportional to the nucleation rate, has been used to estimate the interfacial tension between the urea-thiourea zinc chloride and water; hence, the nucleation parameters like critical radius (r*), number of molecules in the radius (r*) and Gibbs free energy change for the formation of a critical nucleus (δG*) have been calculated.
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The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter, and 650 mm i...
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The strain monitoring and stress analysis of a new type of post-prestressed tunnel liner were carried out. The instrumentation block of the tunnel liner, with the dimensions of 12.06 m in length, 6 500 mm in diameter, and 650 mm in thickness, was post-prestressed with the unbonded tendons, each of which consists of 8 pieces of double-looped strands and the axial spacing of the tendons is 500 mm. Concrete strain meters, rebar meters, load cell and zero-stress meters were installed for the strain monitoring. The tensioning loads were applied incrementally in three cycles (50 percent, 77 percent and 100 percent) at the concrete age of 28 d and the tensioning work lasted for 187.1 h. Strain readings were taken before and after each cycle during tensioning period and at the specified time interval after tensioning period. It is found that concrete creep developed over tensioning period is 30 percent of total strain and 41.5 percent of elastic strain respectively. Prestress force in the unbonded tendon and concrete stress in the liner were evaluated according to the observed strain variations. Both of them are time-dependent, and about 5.3 percent, 8. 3 percent and 9.0 percent of the prestress losses are observed at the age of 1 d, 30 d and 60 d respectively after stressing. The distribution of prestress in the liner is relatively uniform and meets the design requirement.
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In this study, through-the-thickness stress field and the maximum stress location of flat plates with periodic blunt notches by using the three-dimensional finite element analysis are investigated. In particular, the effect of var...
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In this study, through-the-thickness stress field and the maximum stress location of flat plates with periodic blunt notches by using the three-dimensional finite element analysis are investigated. In particular, the effect of variation of six geometrical parameters as: the plate thickness, the ratio of notch depth to width of the plate, the pitch of periodic notches, the notch opening angle and the notch tip radius on the through the thickness stress state and location of the maximum stress are studied. More than five hundred three-dimensional geometrical configurations are analyzed. Results of this study show that, for relatively thin plates, the maximum stress of middle notch appears to be at the mid-plane and that confirms the plane stress assumption of two-dimensional finite element models. However, increasing the plate thickness leads to a shift in the location of maximum stress from the mid-plane towards the free surface of the plate. Increasing the number of notches with the purpose of decreasing stress values at the notch tip is possible, just when the pitch of the notches is relatively small. Furthermore, among the mentioned geometrical parameters, pitch variation (in particular for the case of relatively thin plates) has the most important influence on the location of the maximum tensile stress at the middle notch of periodic notched plates.
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In the mechanical analysis of a structure/composite with periodic holes/inhomogeneities based on analytic techniques, the holes/inhomogeneities are usually assumed to be circular. In this paper, we develop an efficient method (bas...
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In the mechanical analysis of a structure/composite with periodic holes/inhomogeneities based on analytic techniques, the holes/inhomogeneities are usually assumed to be circular. In this paper, we develop an efficient method (based on complex variable techniques) to calculate the surface tension-induced stress field in a porous material containing a periodic array of unidirectional holes of arbitrary shape. In this method, we use conformal mapping and Faber series techniques to address a finite representative unit cell (RUC) consisting of a single arbitrarily-shaped hole with a constant surface tension imposed on the hole's boundary and periodic deformations imposed on the edge of the RUC. Several numerical examples are presented to verify the accuracy of our method and to study the influence of the shape and volume fraction of the periodic holes on the stress concentration in the structure. We show that the maximum hoop stress around periodic holes of some shapes (such as triangle, pentagon or hexagon) may appear exactly at the point(s) of maximum curvature when the hole volume fraction exceeds a certain value. Moreover, when the hole volume fraction falls below about 7%, it is found that the surface tension-induced stress concentration around periodic holes can be treated approximately as that around a single hole with the same hole shape and size in an infinite plane.
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In the present study, we have performed molecular dynamics simulations to describe the microscopic behaviors of the anionic, nonionic, zwitterion, and gemini surfactants at oil/water interface. The abilities of reducing the interf...
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In the present study, we have performed molecular dynamics simulations to describe the microscopic behaviors of the anionic, nonionic, zwitterion, and gemini surfactants at oil/water interface. The abilities of reducing the interfacial tension and forming the stable interfacial film of the four surfactants have been investigated through evaluating interfacial thickness, interface formation energy and radial distribution function. The results show that the four kinds of surfactants can form in stable oil/water interface of monolayer, and the gemini surfactant can form the more stable monolayer. The results of the above three parameters demonstrate that the gemini surfactant has the best simulation effect in the four surfactants. From the calculated interfacial tension values, the gemini surfactant possess the more powerful ability of reducing the interfacial tension than others, so it is more suitable to be used as the surfactant for flooding. In addition, the effects of different electric field intensities on surfactants were calculated, through the radial distribution function of the hydrophilic group in the surfactant and the oxygen atom in the water. We have found that the adding of the periodic electric field can significantly affect the diffusion behavior of the molecules, and nonionic surfactant has stronger demulsification capability than others.
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