To enhance seamless source mobility support in the mobile NDN(Named Data Networking) environment,we propose a novel Locator Based Mobility support Approach,dubbed LBMA.In this approach,we assign a unique topologically...To enhance seamless source mobility support in the mobile NDN(Named Data Networking) environment,we propose a novel Locator Based Mobility support Approach,dubbed LBMA.In this approach,we assign a unique topologically layered locator to each AR(Access Route)in NDN network,and extend the AR with additional functionalities,such as caching and forwarding Interest packets on behalf of the source.Meanwhile,we add an optional field to the original NDN packet,and modify the Outgoing Interface(s) field in the AR's original FIB(Forwarding Information Base)entries,to record the mobility status and the current locator of the source.Specifically,the consumer in LBMA can continue the interrupted communication,without delivering Interest packets towards the old location of the source,nor waiting for all relevant devices completing the FIB entries updating.The performance analysis result indicates that LBMA has lower handoff cost and shorter handoff latency,compared with other existing source mobility support approaches.展开更多
The flow behavior in porous media with threshold pressure gradient(TPG) is more complex than Darcy flow and the equations of motion, and outer boundary and inner boundary with TPG are also different from Darcy flow fo...The flow behavior in porous media with threshold pressure gradient(TPG) is more complex than Darcy flow and the equations of motion, and outer boundary and inner boundary with TPG are also different from Darcy flow for unsteady flow of a producing well in a reservoir. An analytic method to solve this kind of problem is in a need of reestablishment. The classical method of Green's function and Newman product principle in a new way are used to solve the unsteady state flow problems of various shapes of well and reservoir while considering the TPG. Four Green's functions of point, line, band and circle while considering the TPG are achieved. Then, two well models of vertical well and horizontal well are built and simultaneously the function to calculate the moving boundary of each well model is provided. The results show that when considering TPG the pressure field is much different, which has a sudden pressure change, with a moving boundary in it. And the moving boundary of each well model increases with time but slows down rapidly, especially when the TGP is large.展开更多
In this paper, a model is proposed for the prediction of the width of arching in hoppers resulted from sudden changes in solid feed rates. Such changes in solid feed rate usually come from the collision on the surface...In this paper, a model is proposed for the prediction of the width of arching in hoppers resulted from sudden changes in solid feed rates. Such changes in solid feed rate usually come from the collision on the surface of the moving-bed in the standpipe. The model also takes into account the effect of the powder height in the standpipe of the hopper. The model proves to be adaptable for predicting operational conditions to avoid arching by keeping constant powder height in the main standpipe with interstitial gas flow.展开更多
Cellular networks are overloaded due to the mobile traffic surge,and mobile social networks(MSNets) can be leveraged for traffic offloading.In this paper,we study the issue of choosing seed users for maximizing the mo...Cellular networks are overloaded due to the mobile traffic surge,and mobile social networks(MSNets) can be leveraged for traffic offloading.In this paper,we study the issue of choosing seed users for maximizing the mobile traffic offloaded from cellular networks.We introduce a gossip-style social cascade(GSC) model to model the epidemic-like information diffusion process in MSNets.For static-case and mobile-case networks,we establish an equivalent view and a temporal mapping of the information diffusion process,respectively.We further prove the submodularity in the information diffusion and propose a greedy algorithm to choose the seed users for traffic offloading,yielding a sub-optimal solution to the NP-hard traffic offloading maximization(TOM) problem.Experiments are carried out to study the offloading performance,illustrating that the greedy algorithm significantly outperforms the heuristic and random algorithms,and user mobility can help further reduce cellular load.展开更多
A 2D vertical (2DV) numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynol...A 2D vertical (2DV) numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.展开更多
Many specified business needs in enterprise context cannot be effectively satisfied using current business process technology.This phenomenon is called the "long tail" of business processes.In addition,more ...Many specified business needs in enterprise context cannot be effectively satisfied using current business process technology.This phenomenon is called the "long tail" of business processes.In addition,more and more business applications need to be accessed from mobile devices such as smartphones by enterprise end users.This paper attempts to solve both two challenges above.A lightweight event-driven process model is proposed aiming at satisfying the spontaneous business needs in enterprise.And we design an innovative wizard,which works like a tutorial,guiding end users in creating this lightweight process model.Moreover,end users are allowed to interact with the process created by themselves on smartphones.Finally,the usability of our approach was evaluated on a small set of users in a real business scenario.The results show that end users can effectively build their personalized business processes using our approach and interact with them in mobile environment.展开更多
In order to determine the combined effects of migration and gene flow on evolution of insecticide resistance in the mosquito Culex pipiens, four samples were collected in China, among which two were collected along th...In order to determine the combined effects of migration and gene flow on evolution of insecticide resistance in the mosquito Culex pipiens, four samples were collected in China, among which two were collected along the railway from Beijing to Guangzhou. Bioassay data showed that the resistance levels of the four populations to dichlorvos were high and to parathion moderate as compared with the susceptible strain and there was no significant difference among the four populations to the same organophosphate (OP) insecticide. Starch electrophoresis was done to identify the frequency of known overproduced esterases and to analyze genetic diversity among various populations by electrophoretic polymorphism of five presumably neutral loci. The results indicated that the gene flow between populations existed and the number of effective migrants (Nm) was related to collection geography (Nm from 1.67 to 40.07). In contrast with lower genetic differentiation between two nearby populations (between GZ and ZS, ZZ and SQ) and higher genetic differentiation between two distant populations (between GZ and ZZ), there was a significant and inconsistent difference in the distribution of resistance alleles, A2-B2 when explained only with active migration. This divergent situation could be straightened out when considering passive migration (such as railway transport) which increased the spread of A2-B2 along the railway, i.e., in GZ and ZZ. The resistance alleles, A2-B2, dispersing to around areas by active migration suffered from the limitation of gene flow and the speed of invasion.展开更多
Basing on a prototype of DCA airfoil and axial displacement overlap of 10% chord,seven kinds of tangential displacements are taken to simulate the flow conditions in tandem cascade with numerical methods to select a b...Basing on a prototype of DCA airfoil and axial displacement overlap of 10% chord,seven kinds of tangential displacements are taken to simulate the flow conditions in tandem cascade with numerical methods to select a better geometry with higher performance.The configuration with tangential displacement b/t=0.83 would gain better flow performance than the others.On this basis,two configurations with tangential displacement b/t=0.67 and 0.83 among several configurations are chosen to take into experimental investigations by using TR-PIV system to capture the flow velocity instantaneously.The configuration with b/t=0.83 is observed a better flow field performance than b/t=0.67.Its injection flow in the gap zone is much stronger,wake zone area of the front and rear blade is smaller and the stream flow is more improved.It shows that the flow performance in experimental investigation is quite in the same trend as the numerical results predict.展开更多
A comparative experimental study of heat transfer characteristics of steam and air flow in rectangular channels roughened with parallel ribs was conducted by using an infrared camera. Effects of Reynolds numbers and r...A comparative experimental study of heat transfer characteristics of steam and air flow in rectangular channels roughened with parallel ribs was conducted by using an infrared camera. Effects of Reynolds numbers and rib angles on the steam and air convective heat transfer have been obtained and compared with each other for the Reynolds number from about 4,000 to 15,000. For all the ribbed channels the rib pitch to height ratio(p/e) is 10, and the rib height to the channel hydraulic diameter ratio is 0.078, while the rib angles are varied from 90° to 45°.Based on experimental results, it can be found that, even though the heat transfer distributions of steam and air flow in the ribbed channels are similar to each other, the steam flow can obtain higher convective heat transfer enhancement capability, and the heat transfer enhancement of both the steam and air becomes greater with the rib angle deceasing from 90° to 45°. At Reynolds number of about 12,000, the area-averaged Nusselt numbers of the steam flow is about 13.9%, 14.2%, 19.9% and 23.9% higher than those of the air flow for the rib angles of 90°,75°, 60° and 45° respectively. With the experimental results the correlations for Nusselt number in terms of Reynolds number and rib angle for the steam and air flow in the ribbed channels were developed respectively.展开更多
The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety.In the paper,the viscous flow field around a KVLCC2 model moving obliquely in shallow water...The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety.In the paper,the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag,lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics(CFD) package FLUENT with shear-stress transport(SST) k—ωturbulence model.The numerical computation is performed at different drift angels and water depths.The numerical results are compared with experimental results,and a good agreement is demonstrated.展开更多
Two-flux method can be used, as a simplification for the radiative heat transfer, to predict heat flux in a slab consisting of gas and particles. In the original two-flux method (Schuster, 1905 and Schwarzschild, 1906...Two-flux method can be used, as a simplification for the radiative heat transfer, to predict heat flux in a slab consisting of gas and particles. In the original two-flux method (Schuster, 1905 and Schwarzschild, 1906), the radiation field was assumed to be isotropic. But for gas-particles mixture in combustion environments, the scatterings of particles are usually anisotropic, and the original two-flux method gives critical errors when ignoring this anisotropy. In the present paper, a multilayer four-flux model developed by Rozé et al. (2001) is extended to calculate the radiation heat flux in a slab containing participating particles and gas mixture. The analytic resolution of the radiative transfer equation in the framework of a two-flux approach is presented. The average crossing parameter ε and the forward scattering ratio ζ are defined to describe the anisotropy of the radiative field. To validate the model, the radiation transfer in a slab has been computed. Comparisons with the exact analytical result of Modest (1993) and the original two-flux model show the exactness and the improvement. The emissivity of a slab containing flyash/CO2/H2O mixture is obtained using the new model. The result is identical with that of Goodwin (1989).展开更多
The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxe...The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design.展开更多
Effects of wall properties and slip condition on the peristaltic flow of an incompressible pseudoplastic fluid in a curved channel are studied. Series solution of the governing problem is obtained after applying long ...Effects of wall properties and slip condition on the peristaltic flow of an incompressible pseudoplastic fluid in a curved channel are studied. Series solution of the governing problem is obtained after applying long wavelength and low Reynolds number approximations. The results are validated with the numerical solutions through the built-in routine for solving nonlinear boundary value problems via software Mathematica. The variations of different parameters on axial velocity are carefully analyzed. Behaviors of embedding parameters on the dimensionless stream function are also discussed. It is noted that the axial velocity and size of trapped bolus increases with an increase in slip parameter. It is also observed that the profiles of axial velocity are not symmetric about the central line of the curved channel which is different from the case of planar channel.展开更多
Many marine plankton species are motile and perform daily vertical migrations,traveling across water columns over distances of tens of meters.It is intriguing that these tiny and slow swimmers can travel in a certain ...Many marine plankton species are motile and perform daily vertical migrations,traveling across water columns over distances of tens of meters.It is intriguing that these tiny and slow swimmers can travel in a certain direction within a turbulent environment.One way to do that is by exploiting gravitaxis,which is a form of taxis characterised by the directional movement of an organism in response to gravity.Many plankton species are able to generate a gravitational torque(e.g.,due to a nonuniform mass distribution)that reorients them upwards.However,the swimming direction is disturbed by the shearing motions and the velocity fluctuations that characterise oceanic turbulence:these can generate a viscous torque that may destabilize the swimmer.The directed locomotion resulting from the combination of gravitational and viscous torques in a flow is termed gyrotaxis,which is known to lead to a non-uniform spatial accumulation of swimmers in patches or layers.These phenomena depend strongly on the non-linear dynamics that originate from the fluid motions,and the study of gyrotactic swimmers in complex flows is attracting growing attention.Numerical simulations of the Navier-Stokes equations coupled with suitable models of gyrotactic swimmers have proven their capability to provide valuable insight into the dynamical and statistical properties of self-propelled organisms.In this paper,we review recent studies and key findings on gyrotactic swimmers in turbulent flows.First,we introduce the most recent results concerning the orientation and vertical migration of gyrotactic swimmers in isotropic turbulence.Second,we discuss the findings on the accumulation of the swimmers.Last,we review recent progresses concerning the behaviour of gyrotactic swimmers in free-surface turbulence.展开更多
In this paper, steady incompressible micropolar fluid flow through a non-uniform channel with multiple stenoses is considered. Assuming the stenoses to be mild and using the slip boundary condition, the equations gove...In this paper, steady incompressible micropolar fluid flow through a non-uniform channel with multiple stenoses is considered. Assuming the stenoses to be mild and using the slip boundary condition, the equations governing the flow of the proposed model are solved, and closed-form expressions for the flow characteristics (resistance to flow and wall shear stress) are derived. The effects of different parameters on these flow characteristics are analyzed. It is observed that both the resistance to the flow and the wall shear stress increase with the heights of the stenoses and the slip parameter; but decrease with the Darcy number, b^rthermore, the effects of the wall exponent parameter, the cross-viscosity coefficient and the micropolar parameter on the flow characteristics are discussed.展开更多
基金ACKNOWLEDGEMENT This work was partially supported by the National Basic Research Program of China (973 program) under Grant No. 2013CB329100 National Natural Science Foundation of China under Grants No. 61271200, No. 61232017, No. 61271202+1 种基金 National S&T Major Program under Grant No. 2012ZX03005003 the Doctoral Fund of Ministry of Education of China under Grant No. 20130009110014, and the Program for New Century Excellent Talents in University (NCET) under Grant No. NCET-12-0767.
文摘To enhance seamless source mobility support in the mobile NDN(Named Data Networking) environment,we propose a novel Locator Based Mobility support Approach,dubbed LBMA.In this approach,we assign a unique topologically layered locator to each AR(Access Route)in NDN network,and extend the AR with additional functionalities,such as caching and forwarding Interest packets on behalf of the source.Meanwhile,we add an optional field to the original NDN packet,and modify the Outgoing Interface(s) field in the AR's original FIB(Forwarding Information Base)entries,to record the mobility status and the current locator of the source.Specifically,the consumer in LBMA can continue the interrupted communication,without delivering Interest packets towards the old location of the source,nor waiting for all relevant devices completing the FIB entries updating.The performance analysis result indicates that LBMA has lower handoff cost and shorter handoff latency,compared with other existing source mobility support approaches.
基金Project(51304220) supported by the National Natural Science Foundation of ChinaProject(3144033) supported by the Beijing Natural Science Foundation,ChinaProject(20130007120014) supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘The flow behavior in porous media with threshold pressure gradient(TPG) is more complex than Darcy flow and the equations of motion, and outer boundary and inner boundary with TPG are also different from Darcy flow for unsteady flow of a producing well in a reservoir. An analytic method to solve this kind of problem is in a need of reestablishment. The classical method of Green's function and Newman product principle in a new way are used to solve the unsteady state flow problems of various shapes of well and reservoir while considering the TPG. Four Green's functions of point, line, band and circle while considering the TPG are achieved. Then, two well models of vertical well and horizontal well are built and simultaneously the function to calculate the moving boundary of each well model is provided. The results show that when considering TPG the pressure field is much different, which has a sudden pressure change, with a moving boundary in it. And the moving boundary of each well model increases with time but slows down rapidly, especially when the TGP is large.
基金Supported by the China Petrochemical Corporation.
文摘In this paper, a model is proposed for the prediction of the width of arching in hoppers resulted from sudden changes in solid feed rates. Such changes in solid feed rate usually come from the collision on the surface of the moving-bed in the standpipe. The model also takes into account the effect of the powder height in the standpipe of the hopper. The model proves to be adaptable for predicting operational conditions to avoid arching by keeping constant powder height in the main standpipe with interstitial gas flow.
基金supported by the National Basic Research Program of China(973 Program) through grant 2012CB316004the Doctoral Program of Higher Education(SRFDP)+1 种基金Research Grants Council Earmarked Research Grants(RGC ERG) Joint Research Scheme through Specialized Research Fund 20133402140001National Natural Science Foundation of China through grant 61379003
文摘Cellular networks are overloaded due to the mobile traffic surge,and mobile social networks(MSNets) can be leveraged for traffic offloading.In this paper,we study the issue of choosing seed users for maximizing the mobile traffic offloaded from cellular networks.We introduce a gossip-style social cascade(GSC) model to model the epidemic-like information diffusion process in MSNets.For static-case and mobile-case networks,we establish an equivalent view and a temporal mapping of the information diffusion process,respectively.We further prove the submodularity in the information diffusion and propose a greedy algorithm to choose the seed users for traffic offloading,yielding a sub-optimal solution to the NP-hard traffic offloading maximization(TOM) problem.Experiments are carried out to study the offloading performance,illustrating that the greedy algorithm significantly outperforms the heuristic and random algorithms,and user mobility can help further reduce cellular load.
基金Supported by the National Natural Science Foundation of China(Nos.51579036,51579030)the Fundamental Research Funds for the Central Universities of China(No.DUT14YQ108)
文摘A 2D vertical (2DV) numerical model, without o-coordinate transformation in the vertical direction, is developed for the simulation of flow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-e nonlinear turbulence model. The modified Youngs- VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-e model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verification of the model using laboratory data shows that the model is able to adequately simulate flow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear flow scenarios.
基金supported by the National 973 Programs(Grant No.2013CB329102)the National Natural Science Foundation of China (Grant No.61003067)Key Project of National Natural Science Foundation of China (Grant No.61132001)
文摘Many specified business needs in enterprise context cannot be effectively satisfied using current business process technology.This phenomenon is called the "long tail" of business processes.In addition,more and more business applications need to be accessed from mobile devices such as smartphones by enterprise end users.This paper attempts to solve both two challenges above.A lightweight event-driven process model is proposed aiming at satisfying the spontaneous business needs in enterprise.And we design an innovative wizard,which works like a tutorial,guiding end users in creating this lightweight process model.Moreover,end users are allowed to interact with the process created by themselves on smartphones.Finally,the usability of our approach was evaluated on a small set of users in a real business scenario.The results show that end users can effectively build their personalized business processes using our approach and interact with them in mobile environment.
文摘In order to determine the combined effects of migration and gene flow on evolution of insecticide resistance in the mosquito Culex pipiens, four samples were collected in China, among which two were collected along the railway from Beijing to Guangzhou. Bioassay data showed that the resistance levels of the four populations to dichlorvos were high and to parathion moderate as compared with the susceptible strain and there was no significant difference among the four populations to the same organophosphate (OP) insecticide. Starch electrophoresis was done to identify the frequency of known overproduced esterases and to analyze genetic diversity among various populations by electrophoretic polymorphism of five presumably neutral loci. The results indicated that the gene flow between populations existed and the number of effective migrants (Nm) was related to collection geography (Nm from 1.67 to 40.07). In contrast with lower genetic differentiation between two nearby populations (between GZ and ZS, ZZ and SQ) and higher genetic differentiation between two distant populations (between GZ and ZZ), there was a significant and inconsistent difference in the distribution of resistance alleles, A2-B2 when explained only with active migration. This divergent situation could be straightened out when considering passive migration (such as railway transport) which increased the spread of A2-B2 along the railway, i.e., in GZ and ZZ. The resistance alleles, A2-B2, dispersing to around areas by active migration suffered from the limitation of gene flow and the speed of invasion.
文摘Basing on a prototype of DCA airfoil and axial displacement overlap of 10% chord,seven kinds of tangential displacements are taken to simulate the flow conditions in tandem cascade with numerical methods to select a better geometry with higher performance.The configuration with tangential displacement b/t=0.83 would gain better flow performance than the others.On this basis,two configurations with tangential displacement b/t=0.67 and 0.83 among several configurations are chosen to take into experimental investigations by using TR-PIV system to capture the flow velocity instantaneously.The configuration with b/t=0.83 is observed a better flow field performance than b/t=0.67.Its injection flow in the gap zone is much stronger,wake zone area of the front and rear blade is smaller and the stream flow is more improved.It shows that the flow performance in experimental investigation is quite in the same trend as the numerical results predict.
基金funded by the National Natural Science Foundation of China(Funding No.51206109)
文摘A comparative experimental study of heat transfer characteristics of steam and air flow in rectangular channels roughened with parallel ribs was conducted by using an infrared camera. Effects of Reynolds numbers and rib angles on the steam and air convective heat transfer have been obtained and compared with each other for the Reynolds number from about 4,000 to 15,000. For all the ribbed channels the rib pitch to height ratio(p/e) is 10, and the rib height to the channel hydraulic diameter ratio is 0.078, while the rib angles are varied from 90° to 45°.Based on experimental results, it can be found that, even though the heat transfer distributions of steam and air flow in the ribbed channels are similar to each other, the steam flow can obtain higher convective heat transfer enhancement capability, and the heat transfer enhancement of both the steam and air becomes greater with the rib angle deceasing from 90° to 45°. At Reynolds number of about 12,000, the area-averaged Nusselt numbers of the steam flow is about 13.9%, 14.2%, 19.9% and 23.9% higher than those of the air flow for the rib angles of 90°,75°, 60° and 45° respectively. With the experimental results the correlations for Nusselt number in terms of Reynolds number and rib angle for the steam and air flow in the ribbed channels were developed respectively.
基金the National Natural Science Foundationof China(No.10572094)the Natural Science Foundation of Shanghai(No.06ZR14050)
文摘The viscous hydrodynamic force and moment on ships moving obliquely in shallow water are important for ship navigation safety.In the paper,the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag,lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics(CFD) package FLUENT with shear-stress transport(SST) k—ωturbulence model.The numerical computation is performed at different drift angels and water depths.The numerical results are compared with experimental results,and a good agreement is demonstrated.
基金the sponsorship by le Ministère de la Recherche de France the Programme Sino-Francais de Recherches Avancées (PRA E01-06: Combustion propre : aspects numériques et expérimentaux) the National Natural Science Foundation of China (Grant No.N50106015).
文摘Two-flux method can be used, as a simplification for the radiative heat transfer, to predict heat flux in a slab consisting of gas and particles. In the original two-flux method (Schuster, 1905 and Schwarzschild, 1906), the radiation field was assumed to be isotropic. But for gas-particles mixture in combustion environments, the scatterings of particles are usually anisotropic, and the original two-flux method gives critical errors when ignoring this anisotropy. In the present paper, a multilayer four-flux model developed by Rozé et al. (2001) is extended to calculate the radiation heat flux in a slab containing participating particles and gas mixture. The analytic resolution of the radiative transfer equation in the framework of a two-flux approach is presented. The average crossing parameter ε and the forward scattering ratio ζ are defined to describe the anisotropy of the radiative field. To validate the model, the radiation transfer in a slab has been computed. Comparisons with the exact analytical result of Modest (1993) and the original two-flux model show the exactness and the improvement. The emissivity of a slab containing flyash/CO2/H2O mixture is obtained using the new model. The result is identical with that of Goodwin (1989).
基金financially supported by the National Natural Science Foundation of China(Grant No.51778511)the Hubei Provincial Natural Science Foundation of China(Grant No.2018CFA029)the Key Project of ESI Discipline Development of Wuhan University of Technology(WUT Grant No.2017001)
文摘The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design.
文摘Effects of wall properties and slip condition on the peristaltic flow of an incompressible pseudoplastic fluid in a curved channel are studied. Series solution of the governing problem is obtained after applying long wavelength and low Reynolds number approximations. The results are validated with the numerical solutions through the built-in routine for solving nonlinear boundary value problems via software Mathematica. The variations of different parameters on axial velocity are carefully analyzed. Behaviors of embedding parameters on the dimensionless stream function are also discussed. It is noted that the axial velocity and size of trapped bolus increases with an increase in slip parameter. It is also observed that the profiles of axial velocity are not symmetric about the central line of the curved channel which is different from the case of planar channel.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11911530141 and 91752205).
文摘Many marine plankton species are motile and perform daily vertical migrations,traveling across water columns over distances of tens of meters.It is intriguing that these tiny and slow swimmers can travel in a certain direction within a turbulent environment.One way to do that is by exploiting gravitaxis,which is a form of taxis characterised by the directional movement of an organism in response to gravity.Many plankton species are able to generate a gravitational torque(e.g.,due to a nonuniform mass distribution)that reorients them upwards.However,the swimming direction is disturbed by the shearing motions and the velocity fluctuations that characterise oceanic turbulence:these can generate a viscous torque that may destabilize the swimmer.The directed locomotion resulting from the combination of gravitational and viscous torques in a flow is termed gyrotaxis,which is known to lead to a non-uniform spatial accumulation of swimmers in patches or layers.These phenomena depend strongly on the non-linear dynamics that originate from the fluid motions,and the study of gyrotactic swimmers in complex flows is attracting growing attention.Numerical simulations of the Navier-Stokes equations coupled with suitable models of gyrotactic swimmers have proven their capability to provide valuable insight into the dynamical and statistical properties of self-propelled organisms.In this paper,we review recent studies and key findings on gyrotactic swimmers in turbulent flows.First,we introduce the most recent results concerning the orientation and vertical migration of gyrotactic swimmers in isotropic turbulence.Second,we discuss the findings on the accumulation of the swimmers.Last,we review recent progresses concerning the behaviour of gyrotactic swimmers in free-surface turbulence.
文摘In this paper, steady incompressible micropolar fluid flow through a non-uniform channel with multiple stenoses is considered. Assuming the stenoses to be mild and using the slip boundary condition, the equations governing the flow of the proposed model are solved, and closed-form expressions for the flow characteristics (resistance to flow and wall shear stress) are derived. The effects of different parameters on these flow characteristics are analyzed. It is observed that both the resistance to the flow and the wall shear stress increase with the heights of the stenoses and the slip parameter; but decrease with the Darcy number, b^rthermore, the effects of the wall exponent parameter, the cross-viscosity coefficient and the micropolar parameter on the flow characteristics are discussed.