Stable and fully developed gas flow field is crucial for realizing accurate measurement of gas ultrasonicflow meter. To reduce the flow field distortion, a flow conditioner is usually used. However, the traditionalmon...Stable and fully developed gas flow field is crucial for realizing accurate measurement of gas ultrasonicflow meter. To reduce the flow field distortion, a flow conditioner is usually used. However, the traditionalmonotype flow conditioner can only improve the flow field distribution partly. The measurement accuracy of thetransit time ultrasonic flow meter is still affected because of its serious flow field distortion in the complex pipelineconditions. In this paper, to further improve the flow field distribution, a combined conditioner is investigated.The combined flow conditioner is composed of fan-shaped section, turbulent mixing cavity, and honeycomb-shapedsection. The effects of fan blade angle and cavity length on the flow field of the DN50 flow meter are studied usingcomputational fluid dynamics (CFD) simulation. Simulation results indicate that compared with the monotypeconditioner, the combined conditioner has better performance on effectively reducing the swirl and turbulence andproviding more stable and repetitive velocity profiles. Experiments also validate the effectiveness of the combinedconditioner. The flow meter with the combined conditioner has better repeatability of less than 0.2%, which isbetter than those of the monotype conditioners under the same conditions. This work is very useful for accuratemeasurement of gas ultrasonic flow meter, especially for the complex pipeline conditions.展开更多
The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce th...The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce the risk of anastomotic thrombosis due to the size mismatch。展开更多
Hydroabrasion in particulate flows plays an important role in various industrial and natural processes. To predict the effects of particulate flow and the resulting phenomena such as erosion/abrasion in a pipeline, ch...Hydroabrasion in particulate flows plays an important role in various industrial and natural processes. To predict the effects of particulate flow and the resulting phenomena such as erosion/abrasion in a pipeline, channel or a fitting, it is essential to characterize the effects in a simple standardized geometry. For this purpose, it is vital to initially understand the particulate flow behavior and motion in such geometries. In the present work, two series of experimental works by application of the LDA measurement technique were successfully conducted. First, the particulate flow behavior at downstream of a flow conditioner inside a channel with square cross-section was investigated. Shorter lengths for fully development of velocity profile by using the self-constructed flow conditioner were observed. Moreover, the flow at downstream of the conditioner was modeled with the CFD tool (ANSYS-CFX V. 14.57) and the simulation results were compared and validated by the LDA experimental data. Better agreement between the simulation results and experimental data was observed in the fully developed region. However, there are some deviations due to the actual pressure loss through the experimental loop and the calculated pressure loss value, which includes some assumptions for the loss coefficients. Furthermore, the particulate flow behavior and vortex generation inside the deformed locations of a channel surface were studied in detail. With the help of the Matlab program, it was possible to calculate and visualize the velocity vectors for each measured point inside the channel accurately.展开更多
Mini centrifugal pumps having a diameter smaller than lOOmm are employed in many fields. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized...Mini centrifugal pumps having a diameter smaller than lOOmm are employed in many fields. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, mini cen- trifugal pumps with simple structure were investigated by this research. Splitter blades were adopted in this re- search to improve the performance and the internal flow condition of mini centrifugal pump which had large blade outlet angle. The original impeller without the splitter blades and the impeller with the splitter blades were prepared for experiment. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on performance and internal flow condition of mini centrifugal pump. On the other hand, a three dimensional unsteady numerical flow analysis was conducted to investigate the change of the internal flow according to the rotor rotation. It is clarified from the experimental results that the performance of the mini cen- trifugal pump is improved by the splitter blades. The blade-to-blade low velocity region was suppressed in the case with the splitter blades. In addition to that, the unsteady flows near the volute casing tongue were suppressed due to the splitter blades. In the present paper, the performance of the mini centrifugal pump is shown and the un- steady flow condition is clarified with the results of the numerical flow analysis. Furthermore, the effects of the splitter blades on the performance and the unsteady internal flow condition are investigated.展开更多
Apart from the direct threat to human lives, the flood waves as a result of the rapid catchment response to intense rainfall, breaches of flood defences, tsunamis or storm surges may induce huge impact forces on struc...Apart from the direct threat to human lives, the flood waves as a result of the rapid catchment response to intense rainfall, breaches of flood defences, tsunamis or storm surges may induce huge impact forces on structures, causing structural damage or even failures. Most existing design codes do not properly account for these impact forces due to the limited understanding of the underlying physical processes and the lack of reliable empirical formulae or numerical approaches to quantifying them. This paper presents laboratory experiments to better understand the interaction between the extreme flow hydrodynamics and the hydraulic structures and uses the measured data to validate a numerical model. The model solves the two-dimensional shallow water equations using a finite volume Godunov-type scheme for the reliable simulation of complex flow hydrodynamics. New model components are developed for estimating the hydrostatic and hydrodynamic pressure to quantify the flow impact on structures. The model is applied to reproduce two selected experiment tests with different settings and satisfactory numerical results are obtained, which confirms its predictive capability. The model will therefore provide a potential tool for wider and more flexible field-scale applications.展开更多
Small-sized axial fans are used as air cooler for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotation...Small-sized axial fans are used as air cooler for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotational speed design is conducted,although,it causes the deterioration of efficiency and the increase of noise.Then,the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance.In the case of contra-rotating rotors,it is necessary to design the rotor considering the unsteady flow condition of each front and rear rotor.In the present paper,the fan performance of the contra-rotating small-sized axial fan with 100mm diameter at a designed and a partial flow rates is shown,and the unsteady flow conditions at the inlet and the outlet of each front and rear rotor are clarified with unsteady numerical results.Furthermore,the relation between the performance and the unsteady flow condition of the contra-rotating small-sized axial fan is discussed and the methods to improve the performance are considered.展开更多
Nitrogen （N） and phosphorus （P） released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red so...Nitrogen （N） and phosphorus （P） released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil （RS） was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N （TN）, ammonium （NH4＋-N）, total P （TP） and soluble reactive P （SRP） of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.展开更多
The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply ...The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply cooling water to the condenser. The circulating pump, which operates without a motor drive under natural flow conditions, is a large resistance component in the cooling system. However, it is also the primary noise source, significantly impacting the vessel’s safe operation and acoustic stealth performance. This study investigates the induced noise characteristics of a multi-stage pump under natural flow conditions by experiment, computational fluid dynamics (CFD), and acoustic finite element method. The analysis encompasses the distribution of the flow field, variations in acoustic power, spectral features of flow-induced noise, and directivity of external field radiation noise under different natural flow conditions. The results show that the acoustic power distribution is correlated with the flow field. When the impeller is stuck, the noise sources primarily concentrate in the flow separation area at the blade’s leading edge, the interface area between the impeller and the guide vane, and the flow shock area inside the guide vane. Conversely, when the impeller rotates passively, the blade wake area has a higher acoustic power. The flow noise spectrum under natural flow conditions mainly exhibits broadband and discrete characteristics. Additionally, the pump structure influences the external field radiation noise, and its directivity varies with different flow rates and characteristic frequencies. This study provides valuable insights into optimal design to reduce the noise of the circulating pump in the vessel’s natural flow cooling system. It is essential for ensuring the safe operation and acoustic stealth performance of high-speed vessels and nuclear-powered submarines.展开更多
Navigable flow condition simulations can provide detailed information on water depth and velocity distribution, simulation speed is one of the key factors which influence real-time navigation. In this paper, a navigab...Navigable flow condition simulations can provide detailed information on water depth and velocity distribution, simulation speed is one of the key factors which influence real-time navigation. In this paper, a navigable flow condition simulation system is developed to provide useful information for waterway management and shipping safety. To improve the simulation speed of 2-D hydrodynamic model, an explicit finite volume method and Open MP are used to realize parallel computing. Two mesh schemes and two computing platforms are adopted to study the parallel model＇s performance in the Yangtze River, China. The results show that the parallel model achieves dramatic acceleration, with a maximum speedup ratio of 34.94？. The parallel model can determine the flow state of the navigable channel in about 4 min, efficiency is further improved by a flow simulation scheme database. The developed system can provide early warning information for shipping safety, allowing ships to choose better routes and navigation areas according to real-time navigable flow conditions.展开更多
The peristaltic transport of viscous fluid in an asymmetric channel is concentrated. The channel walls exhibit convective boundary conditions. Both cases of hydrodynamic and magnetohydrodynamic(MHD) fluids are conside...The peristaltic transport of viscous fluid in an asymmetric channel is concentrated. The channel walls exhibit convective boundary conditions. Both cases of hydrodynamic and magnetohydrodynamic(MHD) fluids are considered. Mathematical analysis has been presented in a wave frame of reference. The resulting problems are non-dimensionalized. Long wavelength and low Reynolds number approximations are employed. Joule heating effect on the thermal equation is retained. Analytic solutions for stream function and temperature are constructed. Numerical integration is carried out for pressure rise per wavelength. Effects of influential flow parameters have been pointed out through graphs.展开更多
This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous-heterogeneous reactions.Three kinds of ferroparticles,namely,magne...This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous-heterogeneous reactions.Three kinds of ferroparticles,namely,magnetite(Fe_3O_4),cobalt ferrite(CoFe_2O_4) and manganese zinc ferrite(Mn-ZnFe_2O_4) are taken into account with water and kerosene as conventional base fluids.The developed model of homogeneous-heterogeneous reactions in boundary layer flow with equal and unequal diffusivities for reactant and autocatalysis is considered.The governing partial differential equations are converted into system of non-linear ordinary differential equations by mean of similarity transformations.These ordinary differential equations are integrated numerically using shooting method.The effects of pertinent parameters on velocity and concentration profiles are presented graphically and discussed.We found that in the presence of Fe_3O_4-kerosene and CoFe_2O_4-kerosene,velocity profiles increase for large values of α and β whereas there is a decrement in concentration profiles with increasing values of if and K_s.Furthermore,the comparison between non-magnetic(A1_2O_3) and magnetic Fe_3O_4 nanoparticles is given in tabular form.展开更多
Debris flow simulations are useful for predicting the sediment supplied to watersheds from upstream areas. However, the topographic conditions upstream are more complicated than those downstream and the relationship b...Debris flow simulations are useful for predicting the sediment supplied to watersheds from upstream areas. However, the topographic conditions upstream are more complicated than those downstream and the relationship between the topographic conditions and debris flow initiation is not well understood. This study compared the use of several entrainment rate equations in numerical simulations of debris flows to examine the effect of topographic conditions on the flow. One-dimensional numerical simulations were performed based on the shallow water equations and three entrainment rate equations were tested. These entrainment rate equations were based on the same idea that erosion and the deposition of debris flows occur via the difference between the equilibrium and current conditions of debris flows, while they differed in the expression of the concentration, channel angle, and sediment amount. The comparison was performed using a straight channel with various channel angles and a channel with a periodically undulating surface. The three entrainment rate equations gave different amounts of channel bed degradation and hydrographs for a straight channel with a channel angle greater than 21° when water was supplied from upstream at a steady rate. The difference was caused by the expression of the entrainment rate equations. For channels with little undulation, the numerical simulations gave results almost identical to those for straight channels with the same channel angle. However, for channels with large undulations, the hydrographs differed from those for straight channels with the same channel angle when the channel angle was less than 21°. Rapid erosion occurred and the hydrograph showed a significant peak, especially in cases using the entrainment equation expressed by channel angle. This was caused by the effects of the steep undulating sections, since the effect increased with the magnitude of the undulation, suggesting that a debris flow in an upstream area develops differently according to the topographic conditions. These results also inferred that numerical simulations of debris flow can differ depending on the spatial resolution of the simulation domain, as the resolution determines the reproducibility of the undulations.展开更多
The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the sys...The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the system. There is an obligation, like UN Kyoto Protocol, EU MAC Directive and Japan METI Directive to find an alternative low-GWP refrigerant with excellent thermophysical properties. In this paper, the global warming effect of an air-conditioning system is analyzed theoretically using few low-GWP refrigerant mixtures. New refrigerant mixtures are formed based on low GWP, high volumetric capacity, and refrigerating effect. After analyzing, refrigerant blends of R1234yf/R32 (40/60, 50/50, and 60/40 by wt%) and R1234ze/R32 (40/60, 50/50, and 60/40 by wt%) are found promising to replace the widely used R410A. The best performance of the refrigerant blend is found for R1234yf/R32 (40/60). These analyses are crucial for selecting suitable refrigerants for domestic air conditioning systems.展开更多
Natural water bodies often contain a significant amount of suspended colloidal particles,which not only reduce water transparency but also have a high adsorption capacity for soluble pollutants.These composite polluta...Natural water bodies often contain a significant amount of suspended colloidal particles,which not only reduce water transparency but also have a high adsorption capacity for soluble pollutants.These composite pollutants can migrate rapidly with water flow,which are usually difficult to degrade and remove by traditional methods.Aiming at suspended contaminated waterbodies,this study introduced a multilevel loading method to prepare carbon nanotube/sulfur doped carbon nitride(CNT/SCN)composite photocatalytic purification beads.The surface of the obtained core-shell structured purification beads is loaded with CNT/SCN photocatalysts which exhibit three-dimensional conductive and porous characteristics.TC–HCl was introduced as the target pollutant,and the removal efficiency of the composite purification beads under different water turbidity and hydrodynamic conditions were investigated.The results showed that during 15 h of degradation process,at the depth of 20 cm,with the flow rate of 0.015 m^(3)/h and water turbidity of 10.3 NTU,the purification beads achieved a removal efficiency of 54.9%for tetracycline hydrochloride(TC–HCl),which was 2.03 times higher than that of SCN purification beads.The three-dimensional porous structure of the surface exhibited excellent adsorption and trapping capabilities for suspended colloidal particles.The introduction of carbon nanotubes enhanced charge transfer ability of the surface layer and reduces the local charge accumulation effect caused by surface adsorption,which effectively enhances the adsorption of suspended colloid,and also significantly improved the degradation efficiency of TC–HCl.This study provides a valuable insight for the engineering application of photocatalytic technology.展开更多
文摘Stable and fully developed gas flow field is crucial for realizing accurate measurement of gas ultrasonicflow meter. To reduce the flow field distortion, a flow conditioner is usually used. However, the traditionalmonotype flow conditioner can only improve the flow field distribution partly. The measurement accuracy of thetransit time ultrasonic flow meter is still affected because of its serious flow field distortion in the complex pipelineconditions. In this paper, to further improve the flow field distribution, a combined conditioner is investigated.The combined flow conditioner is composed of fan-shaped section, turbulent mixing cavity, and honeycomb-shapedsection. The effects of fan blade angle and cavity length on the flow field of the DN50 flow meter are studied usingcomputational fluid dynamics (CFD) simulation. Simulation results indicate that compared with the monotypeconditioner, the combined conditioner has better performance on effectively reducing the swirl and turbulence andproviding more stable and repetitive velocity profiles. Experiments also validate the effectiveness of the combinedconditioner. The flow meter with the combined conditioner has better repeatability of less than 0.2%, which isbetter than those of the monotype conditioners under the same conditions. This work is very useful for accuratemeasurement of gas ultrasonic flow meter, especially for the complex pipeline conditions.
基金supported by Grants-in-Aid from the National Natural Science Foundation of China No.10632010,30670517
文摘The size mismatch in an end-to-end vascular anastomosis between the host vessel and the graft may cause flow disturbance and predispose to thrombosis [1].Although a number of techniques have been employed to reduce the risk of anastomotic thrombosis due to the size mismatch。
文摘Hydroabrasion in particulate flows plays an important role in various industrial and natural processes. To predict the effects of particulate flow and the resulting phenomena such as erosion/abrasion in a pipeline, channel or a fitting, it is essential to characterize the effects in a simple standardized geometry. For this purpose, it is vital to initially understand the particulate flow behavior and motion in such geometries. In the present work, two series of experimental works by application of the LDA measurement technique were successfully conducted. First, the particulate flow behavior at downstream of a flow conditioner inside a channel with square cross-section was investigated. Shorter lengths for fully development of velocity profile by using the self-constructed flow conditioner were observed. Moreover, the flow at downstream of the conditioner was modeled with the CFD tool (ANSYS-CFX V. 14.57) and the simulation results were compared and validated by the LDA experimental data. Better agreement between the simulation results and experimental data was observed in the fully developed region. However, there are some deviations due to the actual pressure loss through the experimental loop and the calculated pressure loss value, which includes some assumptions for the loss coefficients. Furthermore, the particulate flow behavior and vortex generation inside the deformed locations of a channel surface were studied in detail. With the help of the Matlab program, it was possible to calculate and visualize the velocity vectors for each measured point inside the channel accurately.
文摘Mini centrifugal pumps having a diameter smaller than lOOmm are employed in many fields. But the design method for the mini centrifugal pump is not established because the internal flow condition for these small-sized fluid machines is not clarified and conventional theory is not suitable for small-sized pumps. Therefore, mini cen- trifugal pumps with simple structure were investigated by this research. Splitter blades were adopted in this re- search to improve the performance and the internal flow condition of mini centrifugal pump which had large blade outlet angle. The original impeller without the splitter blades and the impeller with the splitter blades were prepared for experiment. The performance tests are conducted with these rotors in order to investigate the effect of the splitter blades on performance and internal flow condition of mini centrifugal pump. On the other hand, a three dimensional unsteady numerical flow analysis was conducted to investigate the change of the internal flow according to the rotor rotation. It is clarified from the experimental results that the performance of the mini cen- trifugal pump is improved by the splitter blades. The blade-to-blade low velocity region was suppressed in the case with the splitter blades. In addition to that, the unsteady flows near the volute casing tongue were suppressed due to the splitter blades. In the present paper, the performance of the mini centrifugal pump is shown and the un- steady flow condition is clarified with the results of the numerical flow analysis. Furthermore, the effects of the splitter blades on the performance and the unsteady internal flow condition are investigated.
基金supported by the National Natural Science Foundation of China(Grant Nos.51379074,51411130125)the Chinese Government "Recruitment Program of Global Experts"
文摘Apart from the direct threat to human lives, the flood waves as a result of the rapid catchment response to intense rainfall, breaches of flood defences, tsunamis or storm surges may induce huge impact forces on structures, causing structural damage or even failures. Most existing design codes do not properly account for these impact forces due to the limited understanding of the underlying physical processes and the lack of reliable empirical formulae or numerical approaches to quantifying them. This paper presents laboratory experiments to better understand the interaction between the extreme flow hydrodynamics and the hydraulic structures and uses the measured data to validate a numerical model. The model solves the two-dimensional shallow water equations using a finite volume Godunov-type scheme for the reliable simulation of complex flow hydrodynamics. New model components are developed for estimating the hydrostatic and hydrodynamic pressure to quantify the flow impact on structures. The model is applied to reproduce two selected experiment tests with different settings and satisfactory numerical results are obtained, which confirms its predictive capability. The model will therefore provide a potential tool for wider and more flexible field-scale applications.
基金supported by Japan Science and Technology Agency and University of Tokushima and Komiya research aid
文摘Small-sized axial fans are used as air cooler for electric equipments.But there is a strong demand for higher power of fans according to the increase of quantity of heat from electric devices.Therefore,higher rotational speed design is conducted,although,it causes the deterioration of efficiency and the increase of noise.Then,the adoption of contra-rotating rotors for the small-sized axial fan is proposed for the improvement of performance.In the case of contra-rotating rotors,it is necessary to design the rotor considering the unsteady flow condition of each front and rear rotor.In the present paper,the fan performance of the contra-rotating small-sized axial fan with 100mm diameter at a designed and a partial flow rates is shown,and the unsteady flow conditions at the inlet and the outlet of each front and rear rotor are clarified with unsteady numerical results.Furthermore,the relation between the performance and the unsteady flow condition of the contra-rotating small-sized axial fan is discussed and the methods to improve the performance are considered.
文摘Nitrogen （N） and phosphorus （P） released from the sediment to the surface water is a major source of water quality impairment. Therefore, inhibiting sediment nutrient release seems necessary. In this study, red soil （RS） was employed to control the nutrients released from a black-odorous river sediment under flow conditions. The N and P that were released were effectively controlled by RS capping. Continuous-flow incubations showed that the reduction efficiencies of total N （TN）, ammonium （NH4＋-N）, total P （TP） and soluble reactive P （SRP） of the overlying water by RS capping were 77%, 63%, 77% and 92%, respectively, and nitrification and denitrification occurred concurrently in the RS system. An increase in the water velocity coincided with a decrease in the nutrient release rate as a result of intensive water aeration.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52279087,51879122).
文摘The natural flow cooling strategy is commonly employed in modern high-speed vessels and nuclear-powered submarines. These vessels rely on the energy generated by their own speed to drive the cooling system and supply cooling water to the condenser. The circulating pump, which operates without a motor drive under natural flow conditions, is a large resistance component in the cooling system. However, it is also the primary noise source, significantly impacting the vessel’s safe operation and acoustic stealth performance. This study investigates the induced noise characteristics of a multi-stage pump under natural flow conditions by experiment, computational fluid dynamics (CFD), and acoustic finite element method. The analysis encompasses the distribution of the flow field, variations in acoustic power, spectral features of flow-induced noise, and directivity of external field radiation noise under different natural flow conditions. The results show that the acoustic power distribution is correlated with the flow field. When the impeller is stuck, the noise sources primarily concentrate in the flow separation area at the blade’s leading edge, the interface area between the impeller and the guide vane, and the flow shock area inside the guide vane. Conversely, when the impeller rotates passively, the blade wake area has a higher acoustic power. The flow noise spectrum under natural flow conditions mainly exhibits broadband and discrete characteristics. Additionally, the pump structure influences the external field radiation noise, and its directivity varies with different flow rates and characteristic frequencies. This study provides valuable insights into optimal design to reduce the noise of the circulating pump in the vessel’s natural flow cooling system. It is essential for ensuring the safe operation and acoustic stealth performance of high-speed vessels and nuclear-powered submarines.
基金Project supported by the 13th Five-Year National Key Research and Development Program of China(Grant No.2016YFC0401407)the 12th Five-Year National Key Tech-nology R&D Program(Grant No.2012BAB05B05)the National Natural Science Foundation of China(Grant No.51722901)
文摘Navigable flow condition simulations can provide detailed information on water depth and velocity distribution, simulation speed is one of the key factors which influence real-time navigation. In this paper, a navigable flow condition simulation system is developed to provide useful information for waterway management and shipping safety. To improve the simulation speed of 2-D hydrodynamic model, an explicit finite volume method and Open MP are used to realize parallel computing. Two mesh schemes and two computing platforms are adopted to study the parallel model＇s performance in the Yangtze River, China. The results show that the parallel model achieves dramatic acceleration, with a maximum speedup ratio of 34.94？. The parallel model can determine the flow state of the navigable channel in about 4 min, efficiency is further improved by a flow simulation scheme database. The developed system can provide early warning information for shipping safety, allowing ships to choose better routes and navigation areas according to real-time navigable flow conditions.
基金support from Higher Education Commission (HEC) of Pakistan through Ph.D Indigeous Scheme.
文摘The peristaltic transport of viscous fluid in an asymmetric channel is concentrated. The channel walls exhibit convective boundary conditions. Both cases of hydrodynamic and magnetohydrodynamic(MHD) fluids are considered. Mathematical analysis has been presented in a wave frame of reference. The resulting problems are non-dimensionalized. Long wavelength and low Reynolds number approximations are employed. Joule heating effect on the thermal equation is retained. Analytic solutions for stream function and temperature are constructed. Numerical integration is carried out for pressure rise per wavelength. Effects of influential flow parameters have been pointed out through graphs.
文摘This study deals with the stagnation point flow of ferrofluid over a flat plate with non-linear slip boundary condition in the presence of homogeneous-heterogeneous reactions.Three kinds of ferroparticles,namely,magnetite(Fe_3O_4),cobalt ferrite(CoFe_2O_4) and manganese zinc ferrite(Mn-ZnFe_2O_4) are taken into account with water and kerosene as conventional base fluids.The developed model of homogeneous-heterogeneous reactions in boundary layer flow with equal and unequal diffusivities for reactant and autocatalysis is considered.The governing partial differential equations are converted into system of non-linear ordinary differential equations by mean of similarity transformations.These ordinary differential equations are integrated numerically using shooting method.The effects of pertinent parameters on velocity and concentration profiles are presented graphically and discussed.We found that in the presence of Fe_3O_4-kerosene and CoFe_2O_4-kerosene,velocity profiles increase for large values of α and β whereas there is a decrement in concentration profiles with increasing values of if and K_s.Furthermore,the comparison between non-magnetic(A1_2O_3) and magnetic Fe_3O_4 nanoparticles is given in tabular form.
基金partially supported by Grant-in-Aid for Scientific Research 26292077, 2014, from the Ministry of Education, Science, Sports, and Culture of Japanby the River Fund in charge of the River Foundation, Japan
文摘Debris flow simulations are useful for predicting the sediment supplied to watersheds from upstream areas. However, the topographic conditions upstream are more complicated than those downstream and the relationship between the topographic conditions and debris flow initiation is not well understood. This study compared the use of several entrainment rate equations in numerical simulations of debris flows to examine the effect of topographic conditions on the flow. One-dimensional numerical simulations were performed based on the shallow water equations and three entrainment rate equations were tested. These entrainment rate equations were based on the same idea that erosion and the deposition of debris flows occur via the difference between the equilibrium and current conditions of debris flows, while they differed in the expression of the concentration, channel angle, and sediment amount. The comparison was performed using a straight channel with various channel angles and a channel with a periodically undulating surface. The three entrainment rate equations gave different amounts of channel bed degradation and hydrographs for a straight channel with a channel angle greater than 21° when water was supplied from upstream at a steady rate. The difference was caused by the expression of the entrainment rate equations. For channels with little undulation, the numerical simulations gave results almost identical to those for straight channels with the same channel angle. However, for channels with large undulations, the hydrographs differed from those for straight channels with the same channel angle when the channel angle was less than 21°. Rapid erosion occurred and the hydrograph showed a significant peak, especially in cases using the entrainment equation expressed by channel angle. This was caused by the effects of the steep undulating sections, since the effect increased with the magnitude of the undulation, suggesting that a debris flow in an upstream area develops differently according to the topographic conditions. These results also inferred that numerical simulations of debris flow can differ depending on the spatial resolution of the simulation domain, as the resolution determines the reproducibility of the undulations.
文摘The use of air conditioning and refrigeration systems improved the standard of living. However, the system contributes to global warming by releasing potential global warming refrigerants directly and powering the system. There is an obligation, like UN Kyoto Protocol, EU MAC Directive and Japan METI Directive to find an alternative low-GWP refrigerant with excellent thermophysical properties. In this paper, the global warming effect of an air-conditioning system is analyzed theoretically using few low-GWP refrigerant mixtures. New refrigerant mixtures are formed based on low GWP, high volumetric capacity, and refrigerating effect. After analyzing, refrigerant blends of R1234yf/R32 (40/60, 50/50, and 60/40 by wt%) and R1234ze/R32 (40/60, 50/50, and 60/40 by wt%) are found promising to replace the widely used R410A. The best performance of the refrigerant blend is found for R1234yf/R32 (40/60). These analyses are crucial for selecting suitable refrigerants for domestic air conditioning systems.
基金supported by the Key Programof National Nat-ural Science Foundation of China(No.92047201)the National Natural Science Foundation of China(No.92047303)the Na-tional Science Funds for Creative Research Groups of China(No.51421006).
文摘Natural water bodies often contain a significant amount of suspended colloidal particles,which not only reduce water transparency but also have a high adsorption capacity for soluble pollutants.These composite pollutants can migrate rapidly with water flow,which are usually difficult to degrade and remove by traditional methods.Aiming at suspended contaminated waterbodies,this study introduced a multilevel loading method to prepare carbon nanotube/sulfur doped carbon nitride(CNT/SCN)composite photocatalytic purification beads.The surface of the obtained core-shell structured purification beads is loaded with CNT/SCN photocatalysts which exhibit three-dimensional conductive and porous characteristics.TC–HCl was introduced as the target pollutant,and the removal efficiency of the composite purification beads under different water turbidity and hydrodynamic conditions were investigated.The results showed that during 15 h of degradation process,at the depth of 20 cm,with the flow rate of 0.015 m^(3)/h and water turbidity of 10.3 NTU,the purification beads achieved a removal efficiency of 54.9%for tetracycline hydrochloride(TC–HCl),which was 2.03 times higher than that of SCN purification beads.The three-dimensional porous structure of the surface exhibited excellent adsorption and trapping capabilities for suspended colloidal particles.The introduction of carbon nanotubes enhanced charge transfer ability of the surface layer and reduces the local charge accumulation effect caused by surface adsorption,which effectively enhances the adsorption of suspended colloid,and also significantly improved the degradation efficiency of TC–HCl.This study provides a valuable insight for the engineering application of photocatalytic technology.
