The effects of a magnetic dipole on a nonlinear thermally radiative ferromagnetic liquidflowing over a stretched surface in the presence of Brownian motion and thermophoresis are investigated.By means of a similarity t...The effects of a magnetic dipole on a nonlinear thermally radiative ferromagnetic liquidflowing over a stretched surface in the presence of Brownian motion and thermophoresis are investigated.By means of a similarity transformation,ordinary differential equations are derived and solved afterwards using a numerical(the BVP4C)method.The impact of various parameters,namely the velocity,temperature,concentration,is presented graphically.It is shown that the nanoparticles properties,in conjunction with the magnetic dipole effect,can increase the thermal conductivity of the engineered nanofluid and,consequently,the heat transfer.Comparison with earlier studies indicates high accuracy and effectiveness of the numerical approach.An increase in the Brow-nian motion parameter and thermophoresis parameter enhances the concentration and the related boundary layer.The skin-friction rises when the viscosity parameter is increased.A larger value of the ferromagnetic para-meter results in a higher skin-friction and,vice versa,in a smaller Nusselt number.展开更多
An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid...An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted,including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials.The experimental results have revealed that when the gas-liquid flow rate is low,the degree of uneven splitting is high,and“extreme”conditions are attained.When the superficial gas velocity is greater than that established in the extreme case,the direction of the liquid-phase displacement is reversed,while that of the gas remains unchanged.Thus,the degree of gas phase bias tends to be mitigated with an increase in the gas velocity,while the uneven splitting degree of liquid approaches 10%.Finally,varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.展开更多
A dynamic model is presented for a chiller working with a composite adsorbent(silica activated carbon/CaCl2)–water pair in a solar-biomass cooling installation.The main objective is determining a link between two pos...A dynamic model is presented for a chiller working with a composite adsorbent(silica activated carbon/CaCl2)–water pair in a solar-biomass cooling installation.The main objective is determining a link between two possible evaporator configurations and the refrigerator’s performances.The two considered evaporators work at different pressure levels.The related time evolution profiles of temperature,pressure and water content are studied.Moreover,the effects of hot water inlet temperature and cooling water inlet temperature on the specific cooling capacity(SCP)and coefficient of performance(COP)are predicted by means of numerical simulations.The results show that an increase in the temperature of hot water and a decrease in the temperature of the cooling water allow an increase in COP and SCP.In particular,for a hot water inlet temperature of 85°C and a cooling water inlet temperature of 40°C,the COP and Qev are 0.67 and 4.3 kW,respectively.展开更多
The accurate forecast of the photovoltaic generation(PVG)process is essential to develop optimum installation sizing and pragmatic energy planning and management.This paper proposes a PVG forecast model for a PVG/Batt...The accurate forecast of the photovoltaic generation(PVG)process is essential to develop optimum installation sizing and pragmatic energy planning and management.This paper proposes a PVG forecast model for a PVG/Battery installation.The forecasting strategy is built on a Medium-Term Energy Forecasting(MTEF)approach refined dynamically every hour(Dynamic Medium-Term Energy Forecasting(DMTEF))and adjusted by means of a Short-Term Energy Forecasting(STEF)strategy.The MTEF predicts the generated energy for a day ahead based on the PVG of the last 15 days.As for STEF,it is a combination between PVG Short-Term(ST)forecasting and DMTEF methods obtained by selecting the least inaccurate PVG estimation every 15 minutes.The algorithm results are validated by measures taken on a 3 KWp standalone PVG/Battery installation.The proposed approaches have been integrated into a management algorithm in order to make a pragmatic decision to ensure load supply considering relevant constraints and priorities and guarantee the battery safety.Simulation results show that STEF provides accurate results compared to measures in stable and perturbed days.The NMBE(Normalized Mean Bias Error)is equal to-0.58%in stable days and 26.10%in perturbed days.展开更多
In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically....In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.展开更多
In order to investigate the burning characteristics of a 0#diesel and 3#jet fuel,a small-scale experimental bench mainly composed of a cone calorimeter was arranged.The heat release and burning rates were investigated...In order to investigate the burning characteristics of a 0#diesel and 3#jet fuel,a small-scale experimental bench mainly composed of a cone calorimeter was arranged.The heat release and burning rates were investigated changing the external irradiance in order to clarify the triadic relationship among these quantities.The effective heat of combustion of 0#diesel and 3#jet fuel were 38.89 MJ/kg and 43.15 MJ/kg,respectively,with the corresponding combustion efficiencies being 96.78%and 99.60%(the effective peak heat of combustion being 1.665 times the mean value for both types of fuel).According to our experimental results,the heat release rate and burning rate of 0#diesel and 3#jet fuel both grow linearly with an increase in the external irradiance.Moreover,the heat release rate and burning rate of 3#jet fuel are greater than the equivalent values for the 0#diesel.The average smoke production rate of 0#diesel grows with an increase in the external irradiance,while for the 3#jet fuel it remains approximately the same.The specific extinction area of these two kinds of fuel shows a subtle decrease with the increase of external irradiance.The time to ignition of 3#jet fuel is smaller than 0#diesel for all the considered external irradiances,which indicates that 3#jet fuel is easier to ignite than the 0#diesel.展开更多
In order to overcome the deficiencies of current methods for the prediction of the productivity of shale gas hor-izontal wells after fracturing,a new sophisticated approach is proposed in this study.This new model stem...In order to overcome the deficiencies of current methods for the prediction of the productivity of shale gas hor-izontal wells after fracturing,a new sophisticated approach is proposed in this study.This new model stems from the combination several techniques,namely,artificial neural network(ANN),particle swarm optimization(PSO),Imperialist Competitive Algorithms(ICA),and Ant Clony Optimization(ACO).These are properly implemented by using the geological and engineering parameters collected from 317 wells.The results show that the optimum PSO-ANN model has a high accuracy,obtaining a R2 of 0.847 on the testing.The partial dependence plots(PDP)indicate that liquid consumption intensity and the proportion of quartz sand are the two most sensitive factors affecting the model’s performance.展开更多
Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode ...Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode shapes,and structure-borne noise in such systems are investigated in this study.The results demonstrate that the maximum displacement and equivalent stress are located in the part with variable cross-sectional area.The aver-age excitation force on theflow channel wall increases with theflow velocity.The maximum excitation force occurs in the range of 0–20 Hz,and then it decreases gradually in the range of 20–1000 Hz.Additionally,as theflow velocity rises from 1 to 3 m/s,the overall sound pressure level associated with theflow-induced noise grows from 49.37 to 66.37 dB.Similarly,the overall sound pressure level associated with the structure-borne noise rises from 40.27 to 72.20 dB.When theflow velocity is increased,the increment of the structure-borne noise is higher than that of theflow-induced noise.展开更多
Reasonable treatment and utilization of waste residuals discharged during the production of ready-mixed concrete is an important problem in the cement industry.In this study,a composite admixture was prepared by using...Reasonable treatment and utilization of waste residuals discharged during the production of ready-mixed concrete is an important problem in the cement industry.In this study,a composite admixture was prepared by using ready-mixed concrete waste residuals,furnace slag,and water granulated slag.The grinding characteristics of such material were investigated.Moreover,the effect of such admixture on cement hydration and pore structure was analyzed by X-ray diffraction,thermogravimetric-differential scanning calorimetry,scanning electron microcopy and mercury intrusion porosimetry.As shown by the results:The grinding characteristics of the waste residuals can be improved significantly by mixing them with furnace slag and water granulated slag.Furthermore,the composite admixture does not change the composition of hydration products;rather it contributes to refine the pore structure of the matrix,thus improving the mechanical properties of these cement-based materials.展开更多
The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field.Most of the sen...The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field.Most of the sensors used for these measurements need to be checked periodically and re-calibrated accordingly.Another bottleneck relates to the need to procure thermal sources that are able to generate reliable reference heat fluxes in the range between 100 and 1000 kW/m^(2)(as order of magnitude).In the present study,a method is presented by which,starting from a calibration system with a capacity of approximately 500 kW/m^(2) only,heat fluxes in the range of interest for hypersonic applications are generated.The related procedure takes advantage of established standards for the characterization of a radiative heat flux.It also builds on the hybrid radiative-convective nature of typical hypersonic heat fluxes and the yet poorly explored possibility to use convective sources of heat to produce high-intensity fluxes.The reliability of such a strategy has been tested using a high enthalpy supersonic flow facility relying on an electric arc-heater and pure Nitrogen as work gas.Stagnation-point heat fluxes have been successfully measured(with reasonable accuracy)in the range between 600 and 1500 kW/m^(2) for values of the centerline enthalpy spanning the interval from to 6 to 24 MJ/kg.展开更多
The STAR-CCM+software is used to investigate the flow inside a cooling water jacket of an in-line six-cylinder diesel engine.The results show that the average flow velocity of the cooling water inside the jacket is 1....The STAR-CCM+software is used to investigate the flow inside a cooling water jacket of an in-line six-cylinder diesel engine.The results show that the average flow velocity of the cooling water inside the jacket is 1.669 m/s while the flow velocity distribution is not uniform for each cylinder.Moreover,the fluid velocity in proximity to the cylinder head is too low,thereby affecting the cooling performances of the water jacket.Two corresponding structural optimization schemes are proposed to mitigate this issue and the post-optimization performances of the water jacket are discussed in detail.展开更多
Carbonaceous shale is a sedimentary rock containing a large amount of dispersed carbonaceous organic material.It is easy to crack and soften when exposed to water.In the present work,the stability of such a rock and i...Carbonaceous shale is a sedimentary rock containing a large amount of dispersed carbonaceous organic material.It is easy to crack and soften when exposed to water.In the present work,the stability of such a rock and its sensitivity to the formation of infiltrations due to rainfall are analyzed numerically using the GeoStudio software.The slope stability coefficient is calculated and verified using the landslide thrust calculation method.The results show that under the action of heavy rainfall,water infiltrates into the slope layer by layer,and,accordingly,the soil volume water content is different with respect to that typical of a homogeneous soil.It is also shown that,although in an initial stage,rainfall infiltration leads to the decline of the slope stability coefficient,with the progress of rainfall,this coefficient can temporarily increase,that is,these phenomena can display a lag phase.展开更多
This paper reports a laboratory investigation of the fuel injection process in a diesel engine.The atomization process of the considered fuel(a hydrocarbon liquid)and the ensuing mixing with air is studied experimenta...This paper reports a laboratory investigation of the fuel injection process in a diesel engine.The atomization process of the considered fuel(a hydrocarbon liquid)and the ensuing mixing with air is studied experimentally under high-pressure conditions.Different types of injector nozzles are examined,including(two)new configurations,which are compared in terms of performances to a standard injector manufactured by the Bosch company.For the two alternate configurations,the intake edges of one atomizing hole(hole No.1)are located in the sack volume while for the other(hole No.2)they are located on the locking cone of the needle valve.The injection process,the fuel atomization fineness and fuel supply speed characteristics are studied as functions of high-pressure fuel pump camshaft speed and rotation angle.The results obtained show that a decrease in the high-pressure fuel pump camshaft speed can produce fuel redistribution depending on the injector operation.In general,however,the hole No.1 can ensure fuel flow with higher speed with respect to the hole No.2 for all the operation modes of the injector.Based on such an analysis,we conclude that the use of certain injectors can enable a fine tuning of the propagation process of fuel sprays into various areas of the diesel engine combustion chamber.展开更多
The design of hydro-bulge molds,able to provide hollow parts with special-shaped cross-sections,is still a pretty complicated task(especially for what concerns the design of the related hydraulic system and its“synch...The design of hydro-bulge molds,able to provide hollow parts with special-shaped cross-sections,is still a pretty complicated task(especially for what concerns the design of the related hydraulic system and its“synchronization”).In the present work,this task is addressed through the introduction of a new type of overhead cylinder hydraulic synchronization system,able to correct automatically any deviation from the optimal process.Using the AMESim software,the displacement synchronization curve of the piston rods of the two cylinders is obtained and it is verified that the system is able to implement an automatic deviation correction function by adjusting the bidirectional servo valve.A mathematical model for the synchronization system is presented,and the transfer function of the closed-loop control system is determined accordingly.The results show that the system response is generated at about 0.1∼0.2 s with the system reaching an equilibrium state at about 0.2 s.展开更多
This work aims to compute stability derivatives in the Newtonian limit in pitch when the Mach number tends to infinity.In such conditions,these stability derivatives depend on the Ogive’s shape and not the Mach numbe...This work aims to compute stability derivatives in the Newtonian limit in pitch when the Mach number tends to infinity.In such conditions,these stability derivatives depend on the Ogive’s shape and not the Mach number.Generally,the Mach number independence principle becomes effective from M=10 and above.The Ogive nose is obtained through a circular arc on the cone surface.Accordingly,the following arc slopes are consideredλ=5,10,15,−5,−10,and−15.It is found that the stability derivatives decrease due to the growth inλfrom 5 to 15 and vice versa.Forλ=5 and 10,the damping derivative declines with an increase inλfrom 5 to 10.Yet,for the damping derivatives,the minimum location remains at a pivot position,h=0.75 for large values ofλ.Hence,whenλ=−15,the damping derivatives are independent of the cone angles for most pivot positions except in the early twenty percent of the leading edge.展开更多
Heat transfer in an Eyring-Powell fluid that conducts electricity and flows past an exponentially growing sheet is considered.As the sheet is stretched in the x direction,the flow develops in the region with y>0.Th...Heat transfer in an Eyring-Powell fluid that conducts electricity and flows past an exponentially growing sheet is considered.As the sheet is stretched in the x direction,the flow develops in the region with y>0.The problem is tackled through a set of partial differential equations accounting for Magnetohydrodynamics(MHD),radiation and Joule heating effects,which are converted into a set of equivalent ordinary differential equations through a similarity transformation.The converted problem is solved in MATLAB in the framework a fourth order accurate integration scheme.It is found that the thermal relaxation period is inversely proportional to the thickness of the thermal boundary layer,whereas the Eckert-number displays the opposite trend.As this characteristic number grows,the temperature within the channel increases.展开更多
A dedicated heat exchanger model is introduced for the optimization of heavy-duty diesel engines.The model is a prerequisite for the execution of CFD simulations,which are used to improve waste heat recovery in these ...A dedicated heat exchanger model is introduced for the optimization of heavy-duty diesel engines.The model is a prerequisite for the execution of CFD simulations,which are used to improve waste heat recovery in these systems.Several optimization methods coupled with different types of working fluids are compared in terms of exergy efficiency and heat exchanger complicity.The three considered optimization methods all lead to significant improvements in the R245fa and R1233zd systems with a comparatively low evaporation temperature.The optimal R245fa system has the highest efficiency increase(77.49%).The cyclopentane system displays the highest efficiency among the optimized ORC(Organic Rankine Cycle)systems,yet achieved by using a much heavier evaporator HEC(Heat Exchanging Core).In contrast,the 96.84%efficiency increase for the optimized R1233zd is achieved with only 68.96%evaporator weight.展开更多
The unsteady stagnation-point flow of a hybrid nanofluid over a stretching/shrinking sheet embedded in a porous medium with mass transpiration and chemical reactions is considered.The momentum and mass transfer proble...The unsteady stagnation-point flow of a hybrid nanofluid over a stretching/shrinking sheet embedded in a porous medium with mass transpiration and chemical reactions is considered.The momentum and mass transfer problems are combined to form a system of partial differential equations,which is converted into a set of ordinary differential equations via similarity transformation.These ordinary differential equations are solved analytically to obtain the solution for velocity and concentration profiles in exponential and hypergeometric forms,respectively.The concentration profile is obtained for four different cases namely constant wall concentration,uniform mass flux,general power law wall con-centration and general power law mass flux.The effect of different physical parameters such as Darcy number Da^(1-1),mass transpiration parameter V_(C),stretching/shrinking parameter (d),chemical reaction parameter(β)and Schmidt number (Sc)on velocity and concentration profile is examined.Results show that,the axial velocity will decreases as the shrinking sheet parameter increases,regardless of whether the suction or injection case is examined.The concentration decreases with an increase in the shrinking sheet parameter and the chemical reaction rate parameter.展开更多
A foot bracket is a metal panel bracket used to mount and support the footrest in two-wheeler systems.It holds the footrest in place while rigidly supporting it.In working conditions,this element has often been observ...A foot bracket is a metal panel bracket used to mount and support the footrest in two-wheeler systems.It holds the footrest in place while rigidly supporting it.In working conditions,this element has often been observed to fail when specific load-fluctuation conditions are established at its rear end.Appropriate materials therefore need to be identified to overcome such a recurring failure.To address these issues,the present study has been implemented with the specific objective to determine the response of selected Al6061-T6 and Al7075-T6 Hybrid Metal Matrix Composites(HMMC).The results,obtained using the ANSYS Software,show that the selected composites can withstand 636,962 N/m^(2)of maximum stress and 8.88×10^(−6)m of minimum displacement.These results are also compared with relevant mathematical models and it is concluded that the identified material combination provides the required improvement of structural stability that can withstand the load fluctuation on the foot bracket.展开更多
Steady,laminar mixed convection inside a lid-driven square cavity filled with nanofluid is investigated numerically.We consider the case where the right and left walls are moving downwards and upwards respectively an...Steady,laminar mixed convection inside a lid-driven square cavity filled with nanofluid is investigated numerically.We consider the case where the right and left walls are moving downwards and upwards respectively and maintained at different temperatures while the other two horizontal ones are kept adiabatic and impermeable.The set of nonlinear coupled governing mass,momentum,and energy equations are solved using an extensively validated and a highly accurate finite difference method of fourth-order.Comparisons with previously conducted investigations on special configurations are performed and show an excellent agreement.Meanwhile,attention is focused on the heat transfer enhancement when different nano-particles:Cu,Ag,Al2O3,TiO2 and Fe3O4 are incorporated separately in different base fluids such as:Water,Ethylene-glycol,Methanol and Kerosene oil.In this framework,the numerical results related to several mixtures are presented and concern flow pattern and heat transfer curves for various values of Richardson number[Ri=0.1,1 and 10].It turns out that the choice of the efficient binary mixture for an optimal heat transfer depends not only on the thermophysical properties of the nanofluids but also on the range of the Richardson number.Special attention is devoted to shedding light on the effect of the shape of the nanoparticles on the heat transfer in the case of Water-Ag nanofluid.It is concluded that the spherical shape is more suitable for a better heat transfer enhancement in comparison to the cylindrical ones.展开更多
文摘The effects of a magnetic dipole on a nonlinear thermally radiative ferromagnetic liquidflowing over a stretched surface in the presence of Brownian motion and thermophoresis are investigated.By means of a similarity transformation,ordinary differential equations are derived and solved afterwards using a numerical(the BVP4C)method.The impact of various parameters,namely the velocity,temperature,concentration,is presented graphically.It is shown that the nanoparticles properties,in conjunction with the magnetic dipole effect,can increase the thermal conductivity of the engineered nanofluid and,consequently,the heat transfer.Comparison with earlier studies indicates high accuracy and effectiveness of the numerical approach.An increase in the Brow-nian motion parameter and thermophoresis parameter enhances the concentration and the related boundary layer.The skin-friction rises when the viscosity parameter is increased.A larger value of the ferromagnetic para-meter results in a higher skin-friction and,vice versa,in a smaller Nusselt number.
基金supported by the National Science and Technology Major Project of China(No.2016ZX05028-004-003).
文摘An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold.A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted,including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials.The experimental results have revealed that when the gas-liquid flow rate is low,the degree of uneven splitting is high,and“extreme”conditions are attained.When the superficial gas velocity is greater than that established in the extreme case,the direction of the liquid-phase displacement is reversed,while that of the gas remains unchanged.Thus,the degree of gas phase bias tends to be mitigated with an increase in the gas velocity,while the uneven splitting degree of liquid approaches 10%.Finally,varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.
文摘A dynamic model is presented for a chiller working with a composite adsorbent(silica activated carbon/CaCl2)–water pair in a solar-biomass cooling installation.The main objective is determining a link between two possible evaporator configurations and the refrigerator’s performances.The two considered evaporators work at different pressure levels.The related time evolution profiles of temperature,pressure and water content are studied.Moreover,the effects of hot water inlet temperature and cooling water inlet temperature on the specific cooling capacity(SCP)and coefficient of performance(COP)are predicted by means of numerical simulations.The results show that an increase in the temperature of hot water and a decrease in the temperature of the cooling water allow an increase in COP and SCP.In particular,for a hot water inlet temperature of 85°C and a cooling water inlet temperature of 40°C,the COP and Qev are 0.67 and 4.3 kW,respectively.
文摘The accurate forecast of the photovoltaic generation(PVG)process is essential to develop optimum installation sizing and pragmatic energy planning and management.This paper proposes a PVG forecast model for a PVG/Battery installation.The forecasting strategy is built on a Medium-Term Energy Forecasting(MTEF)approach refined dynamically every hour(Dynamic Medium-Term Energy Forecasting(DMTEF))and adjusted by means of a Short-Term Energy Forecasting(STEF)strategy.The MTEF predicts the generated energy for a day ahead based on the PVG of the last 15 days.As for STEF,it is a combination between PVG Short-Term(ST)forecasting and DMTEF methods obtained by selecting the least inaccurate PVG estimation every 15 minutes.The algorithm results are validated by measures taken on a 3 KWp standalone PVG/Battery installation.The proposed approaches have been integrated into a management algorithm in order to make a pragmatic decision to ensure load supply considering relevant constraints and priorities and guarantee the battery safety.Simulation results show that STEF provides accurate results compared to measures in stable and perturbed days.The NMBE(Normalized Mean Bias Error)is equal to-0.58%in stable days and 26.10%in perturbed days.
基金the Natural Science Foundation of Shandong Province[Grant Nos.ZR2015EQ017,ZR2018MEE044]the Key Laboratory Open Project of the Ministry of Education of Beijing University of Technology[Grant No.2020B03].
文摘In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.
基金by the National Natural Science Foundation of China(No.51704301)National Defense Technology Project Foundation(No.3604031)Youth Scientific Research Foundation of LEU(No.YQ16-420802),are gratefully acknowledged.
文摘In order to investigate the burning characteristics of a 0#diesel and 3#jet fuel,a small-scale experimental bench mainly composed of a cone calorimeter was arranged.The heat release and burning rates were investigated changing the external irradiance in order to clarify the triadic relationship among these quantities.The effective heat of combustion of 0#diesel and 3#jet fuel were 38.89 MJ/kg and 43.15 MJ/kg,respectively,with the corresponding combustion efficiencies being 96.78%and 99.60%(the effective peak heat of combustion being 1.665 times the mean value for both types of fuel).According to our experimental results,the heat release rate and burning rate of 0#diesel and 3#jet fuel both grow linearly with an increase in the external irradiance.Moreover,the heat release rate and burning rate of 3#jet fuel are greater than the equivalent values for the 0#diesel.The average smoke production rate of 0#diesel grows with an increase in the external irradiance,while for the 3#jet fuel it remains approximately the same.The specific extinction area of these two kinds of fuel shows a subtle decrease with the increase of external irradiance.The time to ignition of 3#jet fuel is smaller than 0#diesel for all the considered external irradiances,which indicates that 3#jet fuel is easier to ignite than the 0#diesel.
基金This study was financially supported by China United Coalbed Methane Corporation,Ltd.(ZZGSSALFGR2021-581),Bin Li received the grant.
文摘In order to overcome the deficiencies of current methods for the prediction of the productivity of shale gas hor-izontal wells after fracturing,a new sophisticated approach is proposed in this study.This new model stems from the combination several techniques,namely,artificial neural network(ANN),particle swarm optimization(PSO),Imperialist Competitive Algorithms(ICA),and Ant Clony Optimization(ACO).These are properly implemented by using the geological and engineering parameters collected from 317 wells.The results show that the optimum PSO-ANN model has a high accuracy,obtaining a R2 of 0.847 on the testing.The partial dependence plots(PDP)indicate that liquid consumption intensity and the proportion of quartz sand are the two most sensitive factors affecting the model’s performance.
基金supported by the Key Research and Development Project of Shandong Province[2019GSF109084]the National Natural Science Foundation of China[51776111]Young Scholars Program of Shandong University[2018WLJH73].
文摘Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode shapes,and structure-borne noise in such systems are investigated in this study.The results demonstrate that the maximum displacement and equivalent stress are located in the part with variable cross-sectional area.The aver-age excitation force on theflow channel wall increases with theflow velocity.The maximum excitation force occurs in the range of 0–20 Hz,and then it decreases gradually in the range of 20–1000 Hz.Additionally,as theflow velocity rises from 1 to 3 m/s,the overall sound pressure level associated with theflow-induced noise grows from 49.37 to 66.37 dB.Similarly,the overall sound pressure level associated with the structure-borne noise rises from 40.27 to 72.20 dB.When theflow velocity is increased,the increment of the structure-borne noise is higher than that of theflow-induced noise.
基金supported by the project of China State Construction Engineering Corporation(CSCEC-2020-Z-39,Zhao,R.X.,https://www.cscec.com.cn/).
文摘Reasonable treatment and utilization of waste residuals discharged during the production of ready-mixed concrete is an important problem in the cement industry.In this study,a composite admixture was prepared by using ready-mixed concrete waste residuals,furnace slag,and water granulated slag.The grinding characteristics of such material were investigated.Moreover,the effect of such admixture on cement hydration and pore structure was analyzed by X-ray diffraction,thermogravimetric-differential scanning calorimetry,scanning electron microcopy and mercury intrusion porosimetry.As shown by the results:The grinding characteristics of the waste residuals can be improved significantly by mixing them with furnace slag and water granulated slag.Furthermore,the composite admixture does not change the composition of hydration products;rather it contributes to refine the pore structure of the matrix,thus improving the mechanical properties of these cement-based materials.
文摘The ability to measure the very high heat fluxes that typically occur during the hypersonic re-entry phase of space vehicles is generally considered a subject of great importance in the aerospace field.Most of the sensors used for these measurements need to be checked periodically and re-calibrated accordingly.Another bottleneck relates to the need to procure thermal sources that are able to generate reliable reference heat fluxes in the range between 100 and 1000 kW/m^(2)(as order of magnitude).In the present study,a method is presented by which,starting from a calibration system with a capacity of approximately 500 kW/m^(2) only,heat fluxes in the range of interest for hypersonic applications are generated.The related procedure takes advantage of established standards for the characterization of a radiative heat flux.It also builds on the hybrid radiative-convective nature of typical hypersonic heat fluxes and the yet poorly explored possibility to use convective sources of heat to produce high-intensity fluxes.The reliability of such a strategy has been tested using a high enthalpy supersonic flow facility relying on an electric arc-heater and pure Nitrogen as work gas.Stagnation-point heat fluxes have been successfully measured(with reasonable accuracy)in the range between 600 and 1500 kW/m^(2) for values of the centerline enthalpy spanning the interval from to 6 to 24 MJ/kg.
文摘The STAR-CCM+software is used to investigate the flow inside a cooling water jacket of an in-line six-cylinder diesel engine.The results show that the average flow velocity of the cooling water inside the jacket is 1.669 m/s while the flow velocity distribution is not uniform for each cylinder.Moreover,the fluid velocity in proximity to the cylinder head is too low,thereby affecting the cooling performances of the water jacket.Two corresponding structural optimization schemes are proposed to mitigate this issue and the post-optimization performances of the water jacket are discussed in detail.
基金This study was supported by the“Reinforcement Theory and Technology of Multipoint Restraint Anchor Cable and Monitoring Warning for Highway High Slope”(Grant:2020-MS3-082)the“Research and Application of Ecological Slope Protection Technology in Carbonaceous Rock Slopes”(Grant:AD19110124).
文摘Carbonaceous shale is a sedimentary rock containing a large amount of dispersed carbonaceous organic material.It is easy to crack and soften when exposed to water.In the present work,the stability of such a rock and its sensitivity to the formation of infiltrations due to rainfall are analyzed numerically using the GeoStudio software.The slope stability coefficient is calculated and verified using the landslide thrust calculation method.The results show that under the action of heavy rainfall,water infiltrates into the slope layer by layer,and,accordingly,the soil volume water content is different with respect to that typical of a homogeneous soil.It is also shown that,although in an initial stage,rainfall infiltration leads to the decline of the slope stability coefficient,with the progress of rainfall,this coefficient can temporarily increase,that is,these phenomena can display a lag phase.
基金supported by the Russian Science Foundation[grant number 19-19-00598].
文摘This paper reports a laboratory investigation of the fuel injection process in a diesel engine.The atomization process of the considered fuel(a hydrocarbon liquid)and the ensuing mixing with air is studied experimentally under high-pressure conditions.Different types of injector nozzles are examined,including(two)new configurations,which are compared in terms of performances to a standard injector manufactured by the Bosch company.For the two alternate configurations,the intake edges of one atomizing hole(hole No.1)are located in the sack volume while for the other(hole No.2)they are located on the locking cone of the needle valve.The injection process,the fuel atomization fineness and fuel supply speed characteristics are studied as functions of high-pressure fuel pump camshaft speed and rotation angle.The results obtained show that a decrease in the high-pressure fuel pump camshaft speed can produce fuel redistribution depending on the injector operation.In general,however,the hole No.1 can ensure fuel flow with higher speed with respect to the hole No.2 for all the operation modes of the injector.Based on such an analysis,we conclude that the use of certain injectors can enable a fine tuning of the propagation process of fuel sprays into various areas of the diesel engine combustion chamber.
基金projects of“The University Synergy Innovation Program of Anhui Province(GXXT-2019-004)Teaching Research Project of Anhui Education DepartmentScience and Technology Planning Project of Wuhu City(2021YF58).”。
文摘The design of hydro-bulge molds,able to provide hollow parts with special-shaped cross-sections,is still a pretty complicated task(especially for what concerns the design of the related hydraulic system and its“synchronization”).In the present work,this task is addressed through the introduction of a new type of overhead cylinder hydraulic synchronization system,able to correct automatically any deviation from the optimal process.Using the AMESim software,the displacement synchronization curve of the piston rods of the two cylinders is obtained and it is verified that the system is able to implement an automatic deviation correction function by adjusting the bidirectional servo valve.A mathematical model for the synchronization system is presented,and the transfer function of the closed-loop control system is determined accordingly.The results show that the system response is generated at about 0.1∼0.2 s with the system reaching an equilibrium state at about 0.2 s.
文摘This work aims to compute stability derivatives in the Newtonian limit in pitch when the Mach number tends to infinity.In such conditions,these stability derivatives depend on the Ogive’s shape and not the Mach number.Generally,the Mach number independence principle becomes effective from M=10 and above.The Ogive nose is obtained through a circular arc on the cone surface.Accordingly,the following arc slopes are consideredλ=5,10,15,−5,−10,and−15.It is found that the stability derivatives decrease due to the growth inλfrom 5 to 15 and vice versa.Forλ=5 and 10,the damping derivative declines with an increase inλfrom 5 to 10.Yet,for the damping derivatives,the minimum location remains at a pivot position,h=0.75 for large values ofλ.Hence,whenλ=−15,the damping derivatives are independent of the cone angles for most pivot positions except in the early twenty percent of the leading edge.
文摘Heat transfer in an Eyring-Powell fluid that conducts electricity and flows past an exponentially growing sheet is considered.As the sheet is stretched in the x direction,the flow develops in the region with y>0.The problem is tackled through a set of partial differential equations accounting for Magnetohydrodynamics(MHD),radiation and Joule heating effects,which are converted into a set of equivalent ordinary differential equations through a similarity transformation.The converted problem is solved in MATLAB in the framework a fourth order accurate integration scheme.It is found that the thermal relaxation period is inversely proportional to the thickness of the thermal boundary layer,whereas the Eckert-number displays the opposite trend.As this characteristic number grows,the temperature within the channel increases.
基金funded by National Engineering Laboratory for Mobile Source Emission Control Technology of China[Grant No.NELMS2019A01]the Undergraduate School of Shandong University,China[Grant No.2022Y155].
文摘A dedicated heat exchanger model is introduced for the optimization of heavy-duty diesel engines.The model is a prerequisite for the execution of CFD simulations,which are used to improve waste heat recovery in these systems.Several optimization methods coupled with different types of working fluids are compared in terms of exergy efficiency and heat exchanger complicity.The three considered optimization methods all lead to significant improvements in the R245fa and R1233zd systems with a comparatively low evaporation temperature.The optimal R245fa system has the highest efficiency increase(77.49%).The cyclopentane system displays the highest efficiency among the optimized ORC(Organic Rankine Cycle)systems,yet achieved by using a much heavier evaporator HEC(Heat Exchanging Core).In contrast,the 96.84%efficiency increase for the optimized R1233zd is achieved with only 68.96%evaporator weight.
文摘The unsteady stagnation-point flow of a hybrid nanofluid over a stretching/shrinking sheet embedded in a porous medium with mass transpiration and chemical reactions is considered.The momentum and mass transfer problems are combined to form a system of partial differential equations,which is converted into a set of ordinary differential equations via similarity transformation.These ordinary differential equations are solved analytically to obtain the solution for velocity and concentration profiles in exponential and hypergeometric forms,respectively.The concentration profile is obtained for four different cases namely constant wall concentration,uniform mass flux,general power law wall con-centration and general power law mass flux.The effect of different physical parameters such as Darcy number Da^(1-1),mass transpiration parameter V_(C),stretching/shrinking parameter (d),chemical reaction parameter(β)and Schmidt number (Sc)on velocity and concentration profile is examined.Results show that,the axial velocity will decreases as the shrinking sheet parameter increases,regardless of whether the suction or injection case is examined.The concentration decreases with an increase in the shrinking sheet parameter and the chemical reaction rate parameter.
文摘A foot bracket is a metal panel bracket used to mount and support the footrest in two-wheeler systems.It holds the footrest in place while rigidly supporting it.In working conditions,this element has often been observed to fail when specific load-fluctuation conditions are established at its rear end.Appropriate materials therefore need to be identified to overcome such a recurring failure.To address these issues,the present study has been implemented with the specific objective to determine the response of selected Al6061-T6 and Al7075-T6 Hybrid Metal Matrix Composites(HMMC).The results,obtained using the ANSYS Software,show that the selected composites can withstand 636,962 N/m^(2)of maximum stress and 8.88×10^(−6)m of minimum displacement.These results are also compared with relevant mathematical models and it is concluded that the identified material combination provides the required improvement of structural stability that can withstand the load fluctuation on the foot bracket.
文摘Steady,laminar mixed convection inside a lid-driven square cavity filled with nanofluid is investigated numerically.We consider the case where the right and left walls are moving downwards and upwards respectively and maintained at different temperatures while the other two horizontal ones are kept adiabatic and impermeable.The set of nonlinear coupled governing mass,momentum,and energy equations are solved using an extensively validated and a highly accurate finite difference method of fourth-order.Comparisons with previously conducted investigations on special configurations are performed and show an excellent agreement.Meanwhile,attention is focused on the heat transfer enhancement when different nano-particles:Cu,Ag,Al2O3,TiO2 and Fe3O4 are incorporated separately in different base fluids such as:Water,Ethylene-glycol,Methanol and Kerosene oil.In this framework,the numerical results related to several mixtures are presented and concern flow pattern and heat transfer curves for various values of Richardson number[Ri=0.1,1 and 10].It turns out that the choice of the efficient binary mixture for an optimal heat transfer depends not only on the thermophysical properties of the nanofluids but also on the range of the Richardson number.Special attention is devoted to shedding light on the effect of the shape of the nanoparticles on the heat transfer in the case of Water-Ag nanofluid.It is concluded that the spherical shape is more suitable for a better heat transfer enhancement in comparison to the cylindrical ones.
