numerical simulation

摘要： Municipal sludge is a sedimentation waste produced during the wastewater process in sewage treatment plants.Among recent studies,pilot and field tests showed that chemical conditioning combined with vacuum preloading can effectively treat municipal sludge.To further understand the drainage and consolidation characteristics of the conditioning sludge during vacuum preloading,a large deformation nonlinear numerical simulation model based on the equal strain condition was developed to simulate and analyze the pilot and field tests,whereas the simulation results were not satisfactory.The results of the numerical analysis of the pilot test showed that the predicted consolidation degree was greater than that measured by the field tests,which is attributed to the relatively low permeability layer formed during the preloading process of the prefabricated vertical drain.To better reflect the consolidation process of the conditioned sludge,a simplified analysis method considering the low permeability layer around the prefabricated vertical drain was proposed.The initial permeability coefficient of the low permeability layer is determined via numerical simulations using finite difference method.The predicted settlement curve was in good agreement with the measured results,which indicated that the numerical simulation based on the equal strain condition considering the relatively low permeability layer can better analyze the consolidation process of ferric chloride-conditioning sludge with vacuum preloading.

摘要： Drying crack is a common phenomenon occurring during moisture discharge from wood,reducing efficient wood utilization.Drying crack is primarily caused by drying stress,and the reasonable methods for determining drying stress are sparse.In this study,the initiation and propagation of cracks during wood discs drying were simulated using the extended finite element method(XFEM).The distribution of drying stress and displacement was analyzed at different crack conditions based on the simulation results.This study aimed to solve the problem of the limitation of drying stress testing methods and provide a new idea for the study of wood drying stress.The numerical simulation results are found in good agreement with the experimental results,thus corroborating the feasibility of XFEM in modeling drying crack of wood discs.The stress concentration was observed at the crack tip region,while a minor stress was presented in the region of crack passing through,indicating that the crack formation process was also a process of releasing drying stress.Further,more energy was required to form double cracks in comparison with the single crack mode.

摘要： Environmental contamination has been caused by petroleum-based polymeric materials in the melt deposition process.Nowadays biodegradable materials have been widely used in the fused deposition modeling(FDM)industry,such as polylactic acid(PLA).However,internal complex thermal stress and deformations in part caused by an uneven distribution of PLA filament deposition temperatures during FDM,which will seriously affect the geometric accuracy of the printed part.In order to reduce material waste and environmental pollution during the printing process,the accuracy of PLA part can be improved.Herein,numerical simulation was carried out to investigate the temperature field and stress field during the building and cooling process of cuboid specimens.The effects of printing path on the thermal stress and temperature field during the building process were mainly studied.The results show that the printing path has a significant effect on the stress distribution.The most uni-form stress distribution and the smallest deformation were obtained using the Zig Zag printing path.Finally,the residual stress during the cooling process was collected using strain gauges embedded at the mid-plane of the FDM built cuboid specimens.The simulation results are consistent with the experimental results.

摘要： Leakage occurring in the tube sockets of the main steam thermometers can seriously threaten the safe operation of coal-fired power plants.Here,assuming a 300 MW unit as a relevant testbed,this problem is investigated numerically through solution of the equations of fluid-dynamics in synergy with the mathematical treatment of relevant statistics.The results indicate that the steam can form a large-scale spiral flow inside the tube socket and continuously scour the inner wall.In the model with the protective casing setting angle of 60°,the average tangential fluid velocity can reach up to 4.8 m/s,which is about twice higher than that in the model with the protective casing setting angle of 0°.The wake disturbance generated by the flow around the thermo-sensitive body leads to differences in the fluid motion inside the tube sockets between the upstream and downstream thermometers.These differences are affected by the distance between the thermometers,the setting angle of protective casing,and other factors.The pressure of the main steam inside the tube socket for a R3 thermometer,located outside the curved pipeline,is about 1756 Pa higher than that of the L3 thermometer located outside the straight pipeline,indicating that the secondary flow generated in the curved pipeline is able to provide stronger energy for the large-scale spiral flow inside the tube socket.On the basis of these findings,an improvement scheme for the installation of long-itudinal ribs in the tube sockets is proposed.The simulation results show that the average tangential velocity of the fluid within the near-wall area of tube sockets decreases by more than 90%,which should be enough to effectively alleviate the damage to the inner wall caused by high-pressure fluid or particles.

摘要： After steam discharge in heavy oil reservoirs,the distribution of temperature,pressure,and permeability in different wells becomes irregular.Flow channels can easily be produced,which affect the sweep efficiency of the oil displacement.Previous studies have shown that the salting-out plugging method can effectively block these channels in high-temperature reservoirs,improve the suction profile,and increase oil production.In the present study,the optimal dosage of the plugging agent is determined taking into account connection transmissibility and inter-well volumes.Together with the connectivity model,a water flooding simulation model is introduced.Moreover,a non-gradient stochastic disturbance algorithm is used to obtain the optimal plugging agent dosage,which provides the basis for the high-temperature salting-out plugging agent adjustment in the field.

摘要： We propose new hybrid Lagrange neural networks called LaNets to predict the numerical solutions of partial differential equations.That is,we embed Lagrange interpolation and small sample learning into deep neural network frameworks.Concretely,we first perform Lagrange interpolation in front of the deep feedforward neural network.The Lagrange basis function has a neat structure and a strong expression ability,which is suitable to be a preprocessing tool for pre-fitting and feature extraction.Second,we introduce small sample learning into training,which is beneficial to guide themodel to be corrected quickly.Taking advantages of the theoretical support of traditional numerical method and the efficient allocation of modern machine learning,LaNets achieve higher predictive accuracy compared to the state-of-the-artwork.The stability and accuracy of the proposed algorithmare demonstrated through a series of classical numerical examples,including one-dimensional Burgers equation,onedimensional carburizing diffusion equations,two-dimensional Helmholtz equation and two-dimensional Burgers equation.Experimental results validate the robustness,effectiveness and flexibility of the proposed algorithm.

摘要： Computational fluid dynamics(CFD)and the finite element method(FEM)are used to investigate the wind-driven dynamic response of cantilever traffic signal support structures as a whole.By building a finite element model with the same scale as the actual structure and performing modal analysis,a preliminary understanding of the dynamic properties of the structure is obtained.Based on the two-way fluid-structure coupling calculation method,the wind vibration response of the structure under different incoming flow conditions is calculated,and the vibration characteristics of the structure are analyzed through the displacement time course data of the structure in the crosswind direction and along-wind direction.The results show that the maximum response of the structure increases gradually with the increase of wind speed under 90°wind direction angle,showing a vibration dispersion state,and the vibration response characteristics are following the vibration phenomenon of galloping;under 270°wind direction angle,the maximum displacement response of the structure occurs at the lower wind speed of 5 and 6m/s,and the vibration generated by the structure is vortex vibration at this time;the displacement response of the structure in along-wind direction increaseswith the increase of wind speed.The along-wind displacement response of the structure will increase with increasing wind speed,and the effective wind area and shape characteristics of the structurewill also affect the vibration response of the structure.

摘要： To study the dynamic mechanical properties of tuff under different environmental conditions,the tuff from an ancient quarry in Shepan Island was prepared.The impact damage to the rock was tested using a triaxial dynamic impact mechanical testing system(TDIMTS)with different ground stresses,temperatures,and groundwater pressures.The time-strain relationship,dynamic stress-strain relationship,energy dissipation law,energy-peak strain relationship,and the impact damage pattern of the tuff specimens under impact air pressures were investigated.The TDIMTS experiment on ancient underground rock mass under impact loading was also simulated using the finite element analysis software LS-DYNA based on the Holmquist-Johnson-Cook(HJC)material model.The dynamic failure process,failure pattern and peak stress of tuff specimen were calculated.The simulation results obtained using the above methods were in good agreement with the experimental results.The results of the dynamic experiment show that with the same local stress,groundwater pressure,and temperature,the damage to the tuff specimens caused by blasting and quarrying disturbances gradually increases as the impact pressure increases.Under the same local stress,groundwater pressure,and temperature,the energy required to rupture the tuffs in ancient underground caverns is relatively small if the impact pressure is low accordingly,but as the impact pressure increases,the damage to the tuff caused by quarrying disturbance gradually increases.The damage gradually increases and the degree of damage to the tuff and the strain energy exhibit asymptotic growth when the tuff specimens are subjected to the greater strain energy,increasing the degree of rupturing of the tuff.In addition,the average crushing size decreases with increasing strain energy.By comparing the simulation results with the experimental results,it was found that the HJC model reflected the dynamic impact performance of tuff specimen,and the simulation results showed an evident strain rate effect.These results of this study can offer some guidance and theoretical support for the stability evaluation,protection,and safe operation of the ancient underground caverns in future.

摘要： During subway operation,various factors will cause long-term land subsidence,such as the vibration subsidence of foundation soil caused by train vibration load,incomplete consolidation deformation of foundation soil during tunnel construction,dense buildings and structures in the vicinity of the tunnel,and changes in water level in the stratum where the tunnel is located.The monitoring of long-term land subsidence during subway operation in high-density urban areas differs from that in low-density urban construction areas.The former is the gathering point of the entire urban population.There are many complex buildings around the project,busy road traffic,high pedestrian flow,and less vegetation cover.Several existing items requiremonitoring.However,monitoring distance is long,and providing early warning is difficult.This study uses the 2.8 km operation line between Wulin Square station and Ding’an Road station of Hangzhou Subway Line 1 as an example to propose the integrated method of DInSAR-GPS-GIS technology and the key algorithm for long-term land subsidence deformation.Then,it selects multiscene image data to analyze long-termland subsidence of high-density urban areas during subway operation.Results show that long-term land subsidence caused by the operation of Wulin Square station to Ding’an Road station of Hangzhou Subway Line 1 is small,with maximumsubsidence of 30.64 mm,and minimumsubsidence of 11.45 mm,and average subsidence ranging from 19.27 to 21.33 mm.And FLAC3D software was used to verify the monitoring situation,using the geological conditions of the soil in the study area and the tunnel profile to simulate the settlement under vehicle load,and the simulation results tended to be consistent with the monitoring situation.

摘要： In this paper,some typical methods to promote mixing in supersonic combustion are reviewed,and the fluid-dynamic mechanism underpinning the development of the supersonic shear layer in the presence of a streamwise vortex is analyzed through computational fluid dynamics.It is proven that the streamwise vortex-couple method is an excellent approach to enhance mixing.A specific combustor design is proposed accordingly.

摘要： Forced convective condensation in circular cylindrical channels is investigated numerically．The condensation boundary layers that occur due to temperature difference between the wall and saturation temperature of steam is simulated by the volume of fluid (VOF)method．The effect of variation in the hydraulic diameter and variation in the velocity，Reynolds number and temperature difference between the wall and saturation temperature of inlet steam on heat transfer coefficient are investigated as parametric study in this Paper．Results showed that the condensation length and heat transfer coefficient increase by the increase in the amount of inlet velocity and Reynolds number of inlet steam and the decrease in the temperature difference between the wall and saturated steam．By means of the calculated heat transfer coefficient．the parametric study will help designers to achieve the best configuration for heat exchangers in multiple effect desalination systems．

摘要： Forced convective condensation in circular cylindrical channels is investigated numerically．The condensation boundary layers that occur due to temperature difference between the wall and saturation temperature of steam is simulated by the volume of fluid (VOF)method．The effect of variation in the hydraulic diameter and variation in the velocity，Reynolds number and temperature difference between the wall and saturation temperature of inlet steam on heat transfer coefficient are investigated as parametric study in this Paper．Results showed that the condensation length and heat transfer coefficient increase by the increase in the amount of inlet velocity and Reynolds number of inlet steam and the decrease in the temperature difference between the wall and saturated steam．By means of the calculated heat transfer coefficient．the parametric study will help designers to achieve the best configuration for heat exchangers in multiple effect desalination systems．

摘要： Forced convective condensation in circular cylindrical channels is investigated numerically．The condensation boundary layers that occur due to temperature difference between the wall and saturation temperature of steam is simulated by the volume of fluid (VOF)method．The effect of variation in the hydraulic diameter and variation in the velocity，Reynolds number and temperature difference between the wall and saturation temperature of inlet steam on heat transfer coefficient are investigated as parametric study in this Paper．Results showed that the condensation length and heat transfer coefficient increase by the increase in the amount of inlet velocity and Reynolds number of inlet steam and the decrease in the temperature difference between the wall and saturated steam．By means of the calculated heat transfer coefficient．the parametric study will help designers to achieve the best configuration for heat exchangers in multiple effect desalination systems．

摘要： Forced convective condensation in circular cylindrical channels is investigated numerically．The condensation boundary layers that occur due to temperature difference between the wall and saturation temperature of steam is simulated by the volume of fluid (VOF)method．The effect of variation in the hydraulic diameter and variation in the velocity，Reynolds number and temperature difference between the wall and saturation temperature of inlet steam on heat transfer coefficient are investigated as parametric study in this Paper．Results showed that the condensation length and heat transfer coefficient increase by the increase in the amount of inlet velocity and Reynolds number of inlet steam and the decrease in the temperature difference between the wall and saturated steam．By means of the calculated heat transfer coefficient．the parametric study will help designers to achieve the best configuration for heat exchangers in multiple effect desalination systems．

摘要： In the manufacturing of long hollow plastic parts with closed ends,like test tubes,unevenly advancing melt front around the cores results in core deflection,which becomes a pervasive problem especially when the parts are thin-walled.Therefore.injection molding thin-wailed parts with such cores is challenging since this deflection not only causes uneven wall thickness.but also itself accelerates melt flow behind the deflection.In this study,an effective 3D numerical approach is developed to provide a convenient tool for practitioners to predict core deflection,and a single dimensionless group called core deflectability is introduced in the following discussion.To validate our simulation,we compare our core deflection predictions with a recent analytical solution(Giaeomin and Hade,2005).

摘要： In the manufacturing of long hollow plastic parts with closed ends,like test tubes,unevenly advancing melt front around the cores results in core deflection,which becomes a pervasive problem especially when the parts are thin-walled.Therefore.injection molding thin-wailed parts with such cores is challenging since this deflection not only causes uneven wall thickness.but also itself accelerates melt flow behind the deflection.In this study,an effective 3D numerical approach is developed to provide a convenient tool for practitioners to predict core deflection,and a single dimensionless group called core deflectability is introduced in the following discussion.To validate our simulation,we compare our core deflection predictions with a recent analytical solution(Giaeomin and Hade,2005).

摘要： In the manufacturing of long hollow plastic parts with closed ends,like test tubes,unevenly advancing melt front around the cores results in core deflection,which becomes a pervasive problem especially when the parts are thin-walled.Therefore.injection molding thin-wailed parts with such cores is challenging since this deflection not only causes uneven wall thickness.but also itself accelerates melt flow behind the deflection.In this study,an effective 3D numerical approach is developed to provide a convenient tool for practitioners to predict core deflection,and a single dimensionless group called core deflectability is introduced in the following discussion.To validate our simulation,we compare our core deflection predictions with a recent analytical solution(Giaeomin and Hade,2005).

摘要： In the manufacturing of long hollow plastic parts with closed ends,like test tubes,unevenly advancing melt front around the cores results in core deflection,which becomes a pervasive problem especially when the parts are thin-walled.Therefore.injection molding thin-wailed parts with such cores is challenging since this deflection not only causes uneven wall thickness.but also itself accelerates melt flow behind the deflection.In this study,an effective 3D numerical approach is developed to provide a convenient tool for practitioners to predict core deflection,and a single dimensionless group called core deflectability is introduced in the following discussion.To validate our simulation,we compare our core deflection predictions with a recent analytical solution(Giaeomin and Hade,2005).