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Zhou X.,Huazhong University of Science and Technology | Zhou X.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment | Bernardes M.A.D.S.,CRP Henri Tudor | Ochieng R.M.,Maseno University
Energy | Year: 2012

A model of correlating atmospheric cross flow and the fluid flow inside a solar updraft tower (SUT) was presented by assuming SUT inflow as a compressible flow. The influence of atmospheric cross flow on SUT inflow was studied using the model. Results showed that atmospheric cross flow had a large influence on SUT inflow, and the SUT inlet air velocity approximately equaled to 26% of cross flow velocity for collector air temperature rise Δ T= 0 °C. With an increase in atmospheric cross flow velocity, the fluid flow velocity inside SUT was found to increase. The enlargement effect of pressure potential and SUT inlet air velocity induced by atmospheric cross flow increased with higher SUT height, but decreased with higher temperature rise, which is proportional to collector area. The percentage enlargement for cross flow to the pressure potential was between 67% and 102% and that to the SUT inlet air velocity was between 33% and 48%, for H varying from 100 m to 3000 m and Δ T= 20 °C. The enlargement drastically decreased for Δ T varying from 0 °C to 80 °C for H= 900 m. The work would lay a good foundation for accurate predication of potential power production from SUT power plants by considering the effect of atmospheric cross flow. © 2012 Elsevier Ltd.


Wang L.,Huazhong University of Science and Technology | Wang L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2011

In this paper, a new, modified nonlocal beam model is developed for analyzing the vibration and stability of nanotubes conveying fluid, in which one single nonlocal nanoscale parameter is included. Using Hamilton's principle, a new higher-order differential equation of motion and the corresponding higher-order, non-classical boundary conditions are obtained for nanotubes conveying fluid. Based on this modified nonlocal model, effect of nonlocal nanoscale parameter on natural frequencies and critical flow velocities is presented and discussed through numerical calculations. It is found that this factor has great influence on the vibration and stability of nanotubes conveying fluid. In particular, the nonlocal effect tends to induce higher natural frequencies and higher critical flow velocities as compared to the results obtained from the classical and partial nonlocal beam models. © 2011 Elsevier B.V. All rights reserved.


Wang L.,Huazhong University of Science and Technology | Wang L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Acta Mechanica Solida Sinica | Year: 2012

In the past decades, it has been reported that divergence is the expected form of instability for fluid-conveying pipes with both ends supported. In this paper, the form of instability of supported pipes conveying fluid subjected to distributed follower forces is investigated. Based on the Pflüger column model, the equation of motion for supported pipes subjected concurrently to internal fluid flow and distributed follower forces is established. The analytical model, after Galerkin discretization to two degrees of freedom, is evaluated by analyzing the corresponding eigenvalue problem. The complex frequencies versus fluid velocity are obtained for various system parameters. The results show that either buckling or flutter instabilities could occur in supported fluid-conveying pipes under the action of distributed follower forces, depending on the parameter values of distributed follower forces. © 2012 The Chinese Society of Theoretical and Applied Mechanics.


Wang L.,Huazhong University of Science and Technology | Dai H.L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Archive of Applied Mechanics | Year: 2012

In this paper, the vibration and stability properties of fluid-conveying pipes with two symmetric elbows fitted at downstream end are investigated. The fluid, after entering from the upstream end, is pushed downwards and eventually exits from the downstream end fitted with two symmetric elbows. The equation of motion is solved by means of Galerkin's method with a four-mode approximation. Calculations are conducted for cantilevered and also for pinned-pinned slender pipes. It is found that the stability of the pipe system can be greatly enhanced with such downstream elbows. The vibration frequency of the fluid-conveying pipes can be comfortably controlled due to the downstream elbows with a selection of angle of inclination. The proposed geometry configuration of fluid-conveying pipes may be useful for the design and improvement of engineering pipeline systems and fluidic devices. © 2011 Springer-Verlag.


Zhou X.,Huazhong University of Science and Technology | Zhou X.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Acta Mechanica Solida Sinica | Year: 2012

Based on the Flügge shell theory, equations of motion of ring-stiffened thin-walled cylindrical shells conveying fluid are developed with the aid of the Hamilton's principle. Analysis is carried out on the vibration and stability of the ring-stiffened shells conveying fluid, and the effects of fluid velocity, the Young modulus, the size, and the number of the ring stiffeners on the natural frequency and the instability characteristics are examined. It is found that stiffeners can reduce the number of circumferential waves for the fundamental mode, and increase the shell's natural frequency, and thus the critical fluid velocity. For the number of longitudinal half waves being equal to one, the natural frequency and the corresponding critical fluid velocity are the largest for the internal-ring stiffened shell and are the smallest for the symmetrical-ring stiffened shell. The natural frequencies and the corresponding critical fluid velocity predicted by the established model increase with the increase in the Young modulus, the size, or the number of the stiffeners. © 2012 The Chinese Society of Theoretical and Applied Mechanics.


Huang M.,Huazhong University of Science and Technology | Huang M.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment | Li Z.,Huazhong University of Science and Technology | Li Z.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment | Tong J.,University of Portsmouth
International Journal of Plasticity | Year: 2014

The mechanical behavior of a polycrystalline aluminum in tension was modeled using a climb-assisted discrete dislocation dynamics (DDD) technique. Special focus was on how dislocation climb influences the flow stress of the polycrystalline aluminum with regard to selected grain sizes at elevated temperature. A periodical representative cell (PRC) consisting of given number of grains was used in the simulations. Results showed that, at the high temperature considered, dislocation climb plays an important role in defining the mechanical behavior of the polycrystalline crystal. Specifically, dislocation climb decreases significantly the flow stress and hardening rate while increases the dislocation density by relieving the dislocation pile-ups against the grain boundaries (GBs). In addition, the grain size effect on the yield stress of polycrystalline aluminum is significantly weakened by dislocation climb, especially when the grain size falls in the range of submicron. Another interesting result is that, at high temperature, when both dislocation climb and glide are considered, the grain size effect seems to be insignificant with regard to the applied strain rate, although the strength of material increases with enhanced loading rate. © 2014 Elsevier Ltd. All rights reserved.


Wang L.,Huazhong University of Science and Technology | Wang L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Computational Materials Science | Year: 2010

This paper initiates a theoretical analysis of wave propagation of fluid-conveying single-walled carbon nanotubes based on strain gradient elasticity theory with consideration of both inertia and strain gradients, in which two small-scale parameters are accounted for. For comparison purpose, the stress gradient theory for fluid-conveying carbon nanotubes is also discussed. Both theories are formulated using either the Euler-Bernoulli or the Timoshenko beam assumptions. It is found that the results predicted by these beam models are quite different. From a continuum-based point-of-view, the combined strain/inertia gradient Timoshenko beam model and its conclusion regarding wave propagation may be more reliable. Results show that the effect of internal fluid flow on the phase velocity of upstream-travelling wave is significant when the wave number is relatively low. However, this effect may be ignored when the wave number is sufficiently high. Moreover, the two small-scale parameters related to the inertia and strain gradients are shown to significantly affect the phase velocity at higher wave numbers. The present theoretical study highlights the significance of the effects of fluid flow and small scale related to inertia gradients on wave propagation in carbon nanotubes conveying fluid. © 2010 Elsevier B.V. All rights reserved.


Wang L.,Huazhong University of Science and Technology | Wang L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

An analytical model for predicting surface effects on the free vibration of fluid-conveying nanotubes is developed based on the non-local elasticity theory. In the new model, the effects of both inner and outer surface layers on the nanotubes are taken into consideration. The results show that the surface effects with positive elastic constant or positive residual surface tension tend to increase the natural frequency and critical flow velocity. For small tube thickness or large aspect ratio, the stability of the nanotubes will be greatly enhanced due to the surface effect. This study may be useful to accurately measure the vibration characteristics of fluid-conveying nanotubes and to design nanofluidic devices. © 2010 Elsevier B.V.


Wang L.,Huazhong University of Science and Technology | Wang L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
JVC/Journal of Vibration and Control | Year: 2012

In this paper two theoretical beam models are proposed for the vibration analysis of fluid-conveying nanotubes using the theory of strain gradient elasticity combined with inertia gradients. For comparison purposes, two stress gradient elasticity beam models were also discussed. Both theories were formulated using either the Euler-Bernoulli or the Timoshenko assumptions. Unlike the stress gradient beam models, in which only one material length scale parameter is introduced, the combined strain/inertia gradient beam models include two material length scale parameters related to the inertia and strain gradients, which enable us to investigate the size effect on the dynamical behavior of nanotubes conveying fluid. Results show that the size effect predicted by stress gradient beam models is not pronounced. However, for combined strain/inertia gradient beam models, the natural frequencies obtained display size-dependent properties. For small aspect ratios, the natural frequencies predicted by the combined strain/inertia gradient beam models are much smaller than the stress gradient results. Moreover, the critical flow velocities predicted by the combined strain/inertia gradient beam models are slightly higher than those predicted by the stress gradient beam models, showing that the stability of nanotubes is enhanced due to the consideration of inertia gradients. © 2011 The Author(s).


Wang L.,Huazhong University of Science and Technology | Wang L.,Hubei Key Laboratory for Engineering Structural Analysis and Safety Assessment
Journal of Fluids and Structures | Year: 2010

In this paper, a new theoretical model is developed, based on the modified couple stress theory, for the vibration analysis of fluid-conveying microtubes by introducing one internal material length scale parameter. Using Hamilton's principle, the equations of motion of fluid-conveying microtubes are derived. After discretization via the Differential Quadrature Method (DQM), the analytical model exhibits some essential vibration characteristics. For a microtube in which both ends are supported, it is found that the natural frequencies decrease with increasing internal flow velocities. It is also shown that the microtube will become unstable by divergence at a critical flow velocity. More significantly, when the outside diameter of the microtube is comparable to the material length scale parameter, the natural frequencies obtained using the modified couple stress theory are much larger than those obtained using the classical beam theory. It is not surprising, therefore, that the critical flow velocities predicted by the modified couple stress theory are generally higher than those predicted by the classical beam theory. © 2010 Elsevier Ltd.

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