With the unique characteristics,electromagnetic launch technology is applicable to launch shipborne anti-torpedo torpedo(ATT).This paper aims to establish an analytic model to pre-evaluate the capture probability of t...With the unique characteristics,electromagnetic launch technology is applicable to launch shipborne anti-torpedo torpedo(ATT).This paper aims to establish an analytic model to pre-evaluate the capture probability of the electromagnetic launched ATT.The mathematics model of the multi-stage coilgun and the trajectory of the ATT is established for analysis.The influence factors of the capture probability are analyzed respectively,including the entry point dispersion of the ATT and the position dispersion of the incoming torpedo.Adopting the advanced angle interception mode,the ATT search model is obtained according to the positional relationship,and the course error is synthetically calculated according to the differentiation of implicit function.A geometric method to calculate the integral boundaries of the probability density function is proposed,based on the relative motion of the ATT and the incoming target.To verify the proposed integral model,the digital simulation and comparison is conducted.The results reveal that the variation trends and the calculation value of the proposed analytic model are coincident with the statistic results from Monte Carlo method.And implications of the results regarding the analytic model are discussed.展开更多
The construction interfaces of RCCD have a distinct influence on the deformation of dams. The characters and rules on deformation of construction interfaces are studied. The methods simulating the deformation of the i...The construction interfaces of RCCD have a distinct influence on the deformation of dams. The characters and rules on deformation of construction interfaces are studied. The methods simulating the deformation of the interfaces at different stages are proposed. A thickness analytic model and a no-thickness analytic model of construction interfaces are built. These models can reflect the elastic deformation, the attenuation creep deformation, the irreversible creep deformation and the accelerating creep defor- mation of interfaces. The example shows that these proposed models can simulate the deformation of the dam structure objectively. Especially, the results of the thickness analytic model which simulates the gradual changing regularities of interfaces can tally with those of monitoring in situ preferably. The methods proposed and the analytic models can be generalized and applied to general concrete dams, especially to the analysis on deformation rules of fault and interlayer in dam base.展开更多
A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composit...A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composite laminates. The theory is based on unit cell analytic model which can provide the ply composite material properties by only using the constituent fiber and matrix properties and the laminate geometric parameters without knowing any experimental information of the laminates. To show that this method is suitable for predicting the strength of composite laminates, the micromechanics strength theory is ranked by comparing it with all the micro-level and the best two macro-level theories chosen from the World Wide Failure Exercise. The results show that this method can be used for predicting strength of any composite laminates and provide a direct reference for composite optimum design.展开更多
An analytical model of gate-all-around （GAA） silicon nanowire tunneling field effect transistors （NW-TFETs） is developted based on the surface potential solutions in the channel direction and considering the band ...An analytical model of gate-all-around （GAA） silicon nanowire tunneling field effect transistors （NW-TFETs） is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling （BTBT） efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane＇s expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.展开更多
This paper proposes a thermal analytical model of current gain for bipolar junction transistor-bipolar static induction transistor （BJT-BSIT） compound device in the low current operation. It also proposes a best the...This paper proposes a thermal analytical model of current gain for bipolar junction transistor-bipolar static induction transistor （BJT-BSIT） compound device in the low current operation. It also proposes a best thermal compensating factor to the compound device that indicates the relationship between the thermal variation rate of current gain and device structure. This is important for the design of compound device to be optimized. Finally, the analytical model is found to be in good agreement with numerical simulation and experimental results. The test results demonstrate that thermal variation rate of current gain is below 10% in 25 ℃-85 ℃ and 20% in -55 ℃-25 ℃.展开更多
A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this work.The complex deformation characteristics of IF are considered in the modeling process,which ca...A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this work.The complex deformation characteristics of IF are considered in the modeling process,which can accurately describe the strain and stress states in IF.Based on strain analysis,the model can predict the material thickness distribution and neck height after IF.By considering contact area,strain characteristics,material thickness changes,and friction,the model can predict specific moments and corresponding values of maximum axial forming force and maximum horizontal forming force during IF.In addition,an IF experiment involving different tool diameters,flanging diameters,and opening hole diameters is conducted.On the basis of the experimental strain paths,the strain characteristics of different deformation zones are studied,and the stable strain ratio is quantitatively described through two dimensionless parameters:relative tool diameter and relative hole diameter.Then,the changing of material thickness and forming force in IF,and the variation of minimum material thickness,neck height,maximum axial forming force,and maximum horizontal forming force with flanging parameters are studied,and the reliability of the analytical model is verified in this process.Finally,the influence of the horizontal forming force on the tool design and the fluctuation of the forming force are explained.展开更多
Selective laser melting(SLM)plays a critical role in additive manufacturing,particularly in the fabrication of complex high-precision components.This study selects the AlSi10Mg alloy for its extensive use in the aeros...Selective laser melting(SLM)plays a critical role in additive manufacturing,particularly in the fabrication of complex high-precision components.This study selects the AlSi10Mg alloy for its extensive use in the aerospace and automotive industries,which require lightweight structures with superior thermal and mechanical properties.The thermal load induces residual tensile stress,leading to a decline in the geometric accuracy of the workpiece and causing cracks that reduce the fatigue life of the alloy.The rapid movement of the laser heat source during the material formation creates a localized and inhomogeneous temperature field in the powder bed.Significant temperature gradients are generated,resulting in thermal stresses and distortions within the part,affecting the quality of the molding.Therefore,understanding the effects of processing parameters and scanning strategies on the temperature field in SLM is crucial.To address these issues,this study proposes a multiscale method for predicting the complex transient temperature field during the manufacturing process based on the heat-conduction equation.Considering the influence of temperature on the material properties,a temperature-prediction model for discontinuous scanning paths in SLM and a temperature field-calculation model for irregular scanning paths are developed.The models are validated using finite-element results and are in excellent agreement.The analytical model is then used to investigate the effects of the laser power,scanning speed,and scanning spacing on the temperature distribution.The results reveal that the peak temperature decreases exponentially with increasing scanning speed and increases linearly with increasing laser power.In addition,with increasing scanning spacing,the peak temperature of the adjacent tracks near the observation point decreases linearly.These findings are critical for optimizing the SLM-process parameters and improving the material-forming quality.展开更多
Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study establis...Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study established five self-imbibition models with idealized pore structures and conducted a comparative analysis of these models.These models include circular,square,and equilateral triangular capillaries;a triangular star-shaped cross-section formed by three tangent spherical particles;and a traditional porous medium representation method.All these models are derived based on Newton’s second law,where capillary pressure is described by the Young-Laplace equation and viscous resistance is characterized by the Hagen-Poiret equation and Darcy’s law.All derived models predict that the fluid imbibition distance is proportional to the square root of time,in accordance with the classical Lucas-Washburn law.However,different pore structures exhibit significantly different characteristic imbibition rates.Compared to the single pore model,the conventional Darcy’s law-based model for porous media predicts significantly lower imbibition rates,which is consistent with the relatively slower uptake rates in actual shale nanoscale pore networks.These findings emphasize the important role played by pore geometry in fluid imbibition dynamics and further point to the need for optimizing pore structure to extend fluid imbibition duration in shale reservoirs in practical operations.展开更多
This study presents a theoretical analysis of the perforation process of finite-thickness metal plates(with a thickness ratio of T_0/D = 0.6–1.5) under normal impact by spherical-nosed projectiles. The model is valid...This study presents a theoretical analysis of the perforation process of finite-thickness metal plates(with a thickness ratio of T_0/D = 0.6–1.5) under normal impact by spherical-nosed projectiles. The model is validated over an impact velocity range of 180–1247 m/s. The entire penetration process is divided into three stages: the crater formation stage, the steady stage, and the shear stage. A thicknessdependent dynamic cavity expansion resistance model is first introduced to quantitatively describe the axial resistance experienced by the projectile during the tip-entry and steady stages. Subsequently, a thickness-related damage parameter is proposed to refine the resistance expression during the transition from the steady stage to the shear stage, thereby eliminating discontinuities in resistance across stages. When the projectile fully perforates the target, the model predicts a gradual decay of resistance to zero as the residual ligament thickness vanishes, which better reflects the actual physical behavior. The model is validated using four sets of experimental conditions. In addition, to illustrate the model's applicability more intuitively, a numerical simulation case from the literature is reproduced, and the resulting resistance-time curve is compared with the model output. The results demonstrate that the proposed model agrees well with experimental data in terms of residual velocity, ballistic limit, and penetration resistance. Finally, a method for adjusting the threshold parameter within the resistance function is provided, and the influence of this coefficient on the model predictions is discussed.展开更多
Departing from an analytical phase transformation model, a new analytical approach to deduce transformed fraction for non-isothermal phase transformation was developed. In the new approach, the effect of the initial t...Departing from an analytical phase transformation model, a new analytical approach to deduce transformed fraction for non-isothermal phase transformation was developed. In the new approach, the effect of the initial transformation temperature and the accurate ＂temperature integral＂ approximations are incorporated to obtain an extended analytical model. Numerical approach demonstrated that the extended analytical model prediction for transformed fraction and transformation rate is in good agreement with the exact numerical calculation. The new model can describe more precisely the kinetic behavior than the original analytical model, especially for transformation with relatively high initial transformation temperature. The kinetic parameters obtained from the new model are more accurate and reasonable than those from the original analytical model.展开更多
Due to interaction among cells, it is too complex to build an exactanalytical model for the power dissipation within the cell membrane in suspensions exposed toexternal fields. An approximate equivalence method is pro...Due to interaction among cells, it is too complex to build an exactanalytical model for the power dissipation within the cell membrane in suspensions exposed toexternal fields. An approximate equivalence method is proposed to resolve this problem. Based on theeffective medium theory, the transmembrane voltage on cells in suspensions was investigated by theequivalence principle. Then the electric field in the cell membrane was determined. Finally,analytical solutions for the power dissipation within the cell membrane in suspensions exposed toexternal fields were derived according to the Joule principle. The equations show that theconductive power dissipation is predominant within the cell membrane in suspensions exposed todirect current or lower frequencies, and dielectric power dissipation prevails at high frequenciesexceeding the relaxation frequency of the exposed membrane.展开更多
The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam insta- bilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase I[ project of the...The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam insta- bilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase I[ project of the Hefei Light Source （HLS II ）. Meanwhile, instabilities driven by higher-order modes （HOM） may limit the performance of the higher-harmonic cavity. In this paper, the parasitic coupled-bunch instability, which is driven by narrow band parasitic modes, and the microwave instability, which is driven by broadband HOM, are both modeled analytically. The analytic modeling results are in good agreement with those of our previous simulation study and indicate that the passive fourth-harmonic cavity suppresses parasitic coupled-bunch instabilities and microwave instability. The modeling suggests that a fourth-harmonic cavity may be successfully used at the HLS II.展开更多
An analytical model of electron mobility for strained-silicon channel nMOSFETs is proposed in this paper. The model deals directly with the strain tensor,and thus is independent of the manufacturing process. It is sui...An analytical model of electron mobility for strained-silicon channel nMOSFETs is proposed in this paper. The model deals directly with the strain tensor,and thus is independent of the manufacturing process. It is suitable for （100〉/ 〈110） channel nMOSFETs under biaxial or （100〉/〈 110 ） uniaxial stress and can be implemented in conventional device simulation tools .展开更多
Dramatic tool temperature variation in end milling can cause excessive tool wear and shorten its life, especially in machining of difficult-to-machine materials. In this study, a new analytical model-based method for ...Dramatic tool temperature variation in end milling can cause excessive tool wear and shorten its life, especially in machining of difficult-to-machine materials. In this study, a new analytical model-based method for the prediction of cutting tool temperature in end milling is presented.The cutting cycle is divided into temperature increase and decrease phases. For the temperature increase phase, a temperature prediction model considering real friction state between the chip and tool is proposed, and the heat flux and tool-chip contact length are then obtained through finite element simulation. In the temperature decrease phase, a temperature decrease model based on the one-dimension plate heat convection is proposed. A single wire thermocouple is employed to measure the tool temperature in the conducted milling experiments. Both of the theoretical and experimental results are obtained with cutting conditions of the cutting speed ranging from 60 m/min to100 m/min, feed per tooth from 0.12 mm/z to 0.20 mm/z, and the radial and axial depth of cut respectively being 4 mm and 0.5 mm. The comparison results show high agreement between the physical cutting experiments and the proposed cutting tool temperature prediction method.展开更多
The analytical model for springback in arc bending of sheet metal can serve as an excellent design support.The amount of springback is considerably influenced by the geometrical and the material parameters associated ...The analytical model for springback in arc bending of sheet metal can serve as an excellent design support.The amount of springback is considerably influenced by the geometrical and the material parameters associated with the sheet metal.In addition,the applied load during the bending also has a significant influence.Although a number of numerical techniques have been used for this purpose,only few analytical models that can provide insight into the phenomenon are available.A phenomenological model for predicting the springback in arc bending was proposed based on strain as well as deformation energy based approaches.The results of the analytical model were compared with the published experimental as well as FE results of the authors,and the agreement was found to be satisfactory.展开更多
In order to improve rolled strip quality, precise plate shape control theory should be established. Roll flat- tening theory is an important part of the plate shape theory. To improve the accuracy of roll flattening c...In order to improve rolled strip quality, precise plate shape control theory should be established. Roll flat- tening theory is an important part of the plate shape theory. To improve the accuracy of roll flattening calculation based on semi infinite body model, especially near the two roll barrel edges, a new and more accurate roll flattening model is proposed. Based on boundary integral equation method, an analytical model for solving a finite length semi infinite body is established. The lateral surface displacement field of the finite length semi-infinite body is simulated by finite element method （FEM） and lateral surface displacement decay functions are established. Based on the boundary integral equation method, the numerical solution of the finite length semi-infinite body under the distribu ted force is obtained and an accurate roll flattening model is established. Different from the traditional semi-infinite body model, the matrix form of the new roll flattening model is established through the mathematical derivation. The result from the new model is more consistent with that by FEM especially near the edges.展开更多
Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be e...Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be employed for transverse waves. In order to investigate the essential deformation law of leveling for plates with transverse waves, a 2.5-dimensional （2.5- D） analytical approach was proposed. In this model, the plate was transversely divided into some strips with equal width; the strips are considered to be in the state of plane strain and each group of adjacent strips are assumed to be deformation compatible under stress. After calculation, the bending deformation of each strip and the leveling effect of overall plate were obtained by comprehensNe consideration of various strips along with the width. Bending of roller is a main approach to eliminate the transverse waves, which is widely accepted by the industry, but the essential effect of bending of roller on the deformation of plates and the calculation of bending of roller are unknown. According to the 2.5-D analytical model, it can be found that, for plates, it is neutral plane offsetting and middle plane elongation or contraction under inner stress that can effectively improve plate shape. Taking double side waves as an example, the appropriate values of bending of roller were obtained by the 2.5-D analytical model related to different initial unevenness, which was applicable to the current on-line adjusting of bending of roller in rolling industry.展开更多
Based on the nondestructive test data of operating railway tunnels in China, this paper summarizes the basic characteristics of the complex contact behavior between the rock mass and lining structure. The contact mode...Based on the nondestructive test data of operating railway tunnels in China, this paper summarizes the basic characteristics of the complex contact behavior between the rock mass and lining structure. The contact modes are classified into dense contact, local non-contact, and loose contact. Subsequently, the corresponding mechanical model for each contact mode is developed according to its mechanical characteristics using the complex variable method. In the proposed mechanical model, a special algorithm is introduced to detect whether the local non-contact zone is re-contacted. Besides, a novel conformal mapping method is also proposed to accurately calculate the mechanical response of the concrete lining. Finally, the accuracy of the proposed method is verified by comparing it with the finite element method(FEM). Several parameter investigations are conducted to analyze the effects of different contact modes on the rock-lining interaction. The results show that:(i) the height of the local noncontact area does not have a significant effect on the contact stress distribution if no re-contact occurs;(ii) backfill grouting can reduce the local stress concentration caused by poor contact modes;and(iii) reducing the friction coefficient of the interface can lead to a more uniform distribution of internal forces in the concrete lining.展开更多
Based on the fundamental equations of the mechanics of solid continuum,the paper employs an analytical model for determination of elastic thermal stresses in isotropic continuum represented by periodically distributed...Based on the fundamental equations of the mechanics of solid continuum,the paper employs an analytical model for determination of elastic thermal stresses in isotropic continuum represented by periodically distributed spherical particles with different distributions in an infinite matrix,imaginarily divided into identical cells with dimensions equal to inter-particle distances,containing a central spherical particle with or without a spherical envelope on the particle surface.Consequently,the multi-particle-(envelope)-matrix system,as a model system regarding the analytical modelling,is applicable to four types of multi-phase materials.As functions of the particle volume fraction v,the inter-particle distances dl,d2,d3 along three mutually per-pendicular axes,and the particle and envelope radii,R1 and R2,respectively,the thermal stresses within the cell,are originated during a cooling process as a consequence of the difference in thermal expansion coefficients of phases rep-resented by the matrix,envelope and particle.Analytical-(experimental)-computational lifetime prediction methods for multi-phase materials are proposed,which can be used in engineering with appropriate values of parameters of real multi-phase materials.展开更多
A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derive...A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation, and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.展开更多
基金National Natural Science Foundation of China(Grant No.51777212).
文摘With the unique characteristics,electromagnetic launch technology is applicable to launch shipborne anti-torpedo torpedo(ATT).This paper aims to establish an analytic model to pre-evaluate the capture probability of the electromagnetic launched ATT.The mathematics model of the multi-stage coilgun and the trajectory of the ATT is established for analysis.The influence factors of the capture probability are analyzed respectively,including the entry point dispersion of the ATT and the position dispersion of the incoming torpedo.Adopting the advanced angle interception mode,the ATT search model is obtained according to the positional relationship,and the course error is synthetically calculated according to the differentiation of implicit function.A geometric method to calculate the integral boundaries of the probability density function is proposed,based on the relative motion of the ATT and the incoming target.To verify the proposed integral model,the digital simulation and comparison is conducted.The results reveal that the variation trends and the calculation value of the proposed analytic model are coincident with the statistic results from Monte Carlo method.And implications of the results regarding the analytic model are discussed.
基金Project supported by the National Natural Science Foundation of China (Nos.50539010, 50579010)the "948" Project of Ministry of Water Resoures (No.CT200612)the Major State Basic Research Development Program of China (973 Program) (No.2002CB412707)
文摘The construction interfaces of RCCD have a distinct influence on the deformation of dams. The characters and rules on deformation of construction interfaces are studied. The methods simulating the deformation of the interfaces at different stages are proposed. A thickness analytic model and a no-thickness analytic model of construction interfaces are built. These models can reflect the elastic deformation, the attenuation creep deformation, the irreversible creep deformation and the accelerating creep defor- mation of interfaces. The example shows that these proposed models can simulate the deformation of the dam structure objectively. Especially, the results of the thickness analytic model which simulates the gradual changing regularities of interfaces can tally with those of monitoring in situ preferably. The methods proposed and the analytic models can be generalized and applied to general concrete dams, especially to the analysis on deformation rules of fault and interlayer in dam base.
基金Funded in part by China Postdoctoral Science Foundation(No.2013M541574)Hi-tech Research and Development Program of China(No.2012AA040209)
文摘A new method to predict the ultimate strength of fiber reinforced composites under arbitrary load condition is introduced. The micromechanics strength theory is used to perform the final failure prediction of composite laminates. The theory is based on unit cell analytic model which can provide the ply composite material properties by only using the constituent fiber and matrix properties and the laminate geometric parameters without knowing any experimental information of the laminates. To show that this method is suitable for predicting the strength of composite laminates, the micromechanics strength theory is ranked by comparing it with all the micro-level and the best two macro-level theories chosen from the World Wide Failure Exercise. The results show that this method can be used for predicting strength of any composite laminates and provide a direct reference for composite optimum design.
基金supported by the National Natural Science Foundation of China(Grant Nos.61274096,61204043,61306042,61306045,and 61306132)the Guangdong Natural Science Foundation,China(Grant Nos.S2012010010533 and S2013040016878)+2 种基金the Shenzhen Science&Technology Foundation,China(Grant No.ZDSY20120618161735041)the Fundamental Research Project of the Shenzhen Science&Technology Foundation,China(Grant Nos.JCYJ20120618162600041,JCYJ20120618162526384,JCYJ20130402164725025,and JCYJ20120618162946025)the International Collaboration Project of the Shenzhen Science&Technology Foundation,China(Grant Nos.GJHZ20120618162120759,GJHZ20130417170946221,GJHZ20130417170908049,and GJHZ20120615142829482)
文摘An analytical model of gate-all-around （GAA） silicon nanowire tunneling field effect transistors （NW-TFETs） is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling （BTBT） efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane＇s expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.
文摘This paper proposes a thermal analytical model of current gain for bipolar junction transistor-bipolar static induction transistor （BJT-BSIT） compound device in the low current operation. It also proposes a best thermal compensating factor to the compound device that indicates the relationship between the thermal variation rate of current gain and device structure. This is important for the design of compound device to be optimized. Finally, the analytical model is found to be in good agreement with numerical simulation and experimental results. The test results demonstrate that thermal variation rate of current gain is below 10% in 25 ℃-85 ℃ and 20% in -55 ℃-25 ℃.
基金supported in part by financial support from the National Key R&D Program of China(No.2023YFB3407003)the National Natural Science Foundation of China(No.52375378).
文摘A new analytical model for geometric size and forming force prediction in incremental flanging(IF)is presented in this work.The complex deformation characteristics of IF are considered in the modeling process,which can accurately describe the strain and stress states in IF.Based on strain analysis,the model can predict the material thickness distribution and neck height after IF.By considering contact area,strain characteristics,material thickness changes,and friction,the model can predict specific moments and corresponding values of maximum axial forming force and maximum horizontal forming force during IF.In addition,an IF experiment involving different tool diameters,flanging diameters,and opening hole diameters is conducted.On the basis of the experimental strain paths,the strain characteristics of different deformation zones are studied,and the stable strain ratio is quantitatively described through two dimensionless parameters:relative tool diameter and relative hole diameter.Then,the changing of material thickness and forming force in IF,and the variation of minimum material thickness,neck height,maximum axial forming force,and maximum horizontal forming force with flanging parameters are studied,and the reliability of the analytical model is verified in this process.Finally,the influence of the horizontal forming force on the tool design and the fluctuation of the forming force are explained.
基金supported by National Natural Science Foundation of the China Youth Program(Grant No.52205485)Sichuan Youth Fund Program of China(Grant No.2025ZNSFSC1275)the Young Scientific Research Team Cultivation Program of SUES(Grant No.QNTD202112)。
文摘Selective laser melting(SLM)plays a critical role in additive manufacturing,particularly in the fabrication of complex high-precision components.This study selects the AlSi10Mg alloy for its extensive use in the aerospace and automotive industries,which require lightweight structures with superior thermal and mechanical properties.The thermal load induces residual tensile stress,leading to a decline in the geometric accuracy of the workpiece and causing cracks that reduce the fatigue life of the alloy.The rapid movement of the laser heat source during the material formation creates a localized and inhomogeneous temperature field in the powder bed.Significant temperature gradients are generated,resulting in thermal stresses and distortions within the part,affecting the quality of the molding.Therefore,understanding the effects of processing parameters and scanning strategies on the temperature field in SLM is crucial.To address these issues,this study proposes a multiscale method for predicting the complex transient temperature field during the manufacturing process based on the heat-conduction equation.Considering the influence of temperature on the material properties,a temperature-prediction model for discontinuous scanning paths in SLM and a temperature field-calculation model for irregular scanning paths are developed.The models are validated using finite-element results and are in excellent agreement.The analytical model is then used to investigate the effects of the laser power,scanning speed,and scanning spacing on the temperature distribution.The results reveal that the peak temperature decreases exponentially with increasing scanning speed and increases linearly with increasing laser power.In addition,with increasing scanning spacing,the peak temperature of the adjacent tracks near the observation point decreases linearly.These findings are critical for optimizing the SLM-process parameters and improving the material-forming quality.
文摘Fluid imbibition from hydraulic fractures into shale formations is mainly affected by a combination of capillary forces and viscous resistance,both of which are closely related to the pore geometry.This study established five self-imbibition models with idealized pore structures and conducted a comparative analysis of these models.These models include circular,square,and equilateral triangular capillaries;a triangular star-shaped cross-section formed by three tangent spherical particles;and a traditional porous medium representation method.All these models are derived based on Newton’s second law,where capillary pressure is described by the Young-Laplace equation and viscous resistance is characterized by the Hagen-Poiret equation and Darcy’s law.All derived models predict that the fluid imbibition distance is proportional to the square root of time,in accordance with the classical Lucas-Washburn law.However,different pore structures exhibit significantly different characteristic imbibition rates.Compared to the single pore model,the conventional Darcy’s law-based model for porous media predicts significantly lower imbibition rates,which is consistent with the relatively slower uptake rates in actual shale nanoscale pore networks.These findings emphasize the important role played by pore geometry in fluid imbibition dynamics and further point to the need for optimizing pore structure to extend fluid imbibition duration in shale reservoirs in practical operations.
基金supported by the National Natural Science Foundation of China (Grant Nos.U2341244,12172179,11772160)。
文摘This study presents a theoretical analysis of the perforation process of finite-thickness metal plates(with a thickness ratio of T_0/D = 0.6–1.5) under normal impact by spherical-nosed projectiles. The model is validated over an impact velocity range of 180–1247 m/s. The entire penetration process is divided into three stages: the crater formation stage, the steady stage, and the shear stage. A thicknessdependent dynamic cavity expansion resistance model is first introduced to quantitatively describe the axial resistance experienced by the projectile during the tip-entry and steady stages. Subsequently, a thickness-related damage parameter is proposed to refine the resistance expression during the transition from the steady stage to the shear stage, thereby eliminating discontinuities in resistance across stages. When the projectile fully perforates the target, the model predicts a gradual decay of resistance to zero as the residual ligament thickness vanishes, which better reflects the actual physical behavior. The model is validated using four sets of experimental conditions. In addition, to illustrate the model's applicability more intuitively, a numerical simulation case from the literature is reproduced, and the resulting resistance-time curve is compared with the model output. The results demonstrate that the proposed model agrees well with experimental data in terms of residual velocity, ballistic limit, and penetration resistance. Finally, a method for adjusting the threshold parameter within the resistance function is provided, and the influence of this coefficient on the model predictions is discussed.
基金Projects (09-QZ-2008, 24-TZ-2009) supported by the Free Research Fund of State Key Laboratory of Solidification Processing, ChinaProject (B08040) supported by the Program of Introducing Talents of Discipline to Universities, China+3 种基金Projects (51071127, 51134011) supported by the National Natural Science Foundation of ChinaProject (JC200801) supported by the Fundamental Research Fund of Northwestern Polytechnical University, ChinaProject (51125002) supported by the National Science Foundation for Distinguished Young Scholars, ChinaProject (2011CB610403) supported by the National Basic Research Program of China
文摘Departing from an analytical phase transformation model, a new analytical approach to deduce transformed fraction for non-isothermal phase transformation was developed. In the new approach, the effect of the initial transformation temperature and the accurate ＂temperature integral＂ approximations are incorporated to obtain an extended analytical model. Numerical approach demonstrated that the extended analytical model prediction for transformed fraction and transformation rate is in good agreement with the exact numerical calculation. The new model can describe more precisely the kinetic behavior than the original analytical model, especially for transformation with relatively high initial transformation temperature. The kinetic parameters obtained from the new model are more accurate and reasonable than those from the original analytical model.
文摘Due to interaction among cells, it is too complex to build an exactanalytical model for the power dissipation within the cell membrane in suspensions exposed toexternal fields. An approximate equivalence method is proposed to resolve this problem. Based on theeffective medium theory, the transmembrane voltage on cells in suspensions was investigated by theequivalence principle. Then the electric field in the cell membrane was determined. Finally,analytical solutions for the power dissipation within the cell membrane in suspensions exposed toexternal fields were derived according to the Joule principle. The equations show that theconductive power dissipation is predominant within the cell membrane in suspensions exposed todirect current or lower frequencies, and dielectric power dissipation prevails at high frequenciesexceeding the relaxation frequency of the exposed membrane.
基金Supported by National Natural Science Foundation of China (10979045, 11175180, 11175182)
文摘The utility of a passive fourth-harmonic cavity plays a key role in suppressing longitudinal beam insta- bilities in the electron storage ring and lengthens the bunch by a factor of 2.6 for the phase I[ project of the Hefei Light Source （HLS II ）. Meanwhile, instabilities driven by higher-order modes （HOM） may limit the performance of the higher-harmonic cavity. In this paper, the parasitic coupled-bunch instability, which is driven by narrow band parasitic modes, and the microwave instability, which is driven by broadband HOM, are both modeled analytically. The analytic modeling results are in good agreement with those of our previous simulation study and indicate that the passive fourth-harmonic cavity suppresses parasitic coupled-bunch instabilities and microwave instability. The modeling suggests that a fourth-harmonic cavity may be successfully used at the HLS II.
文摘An analytical model of electron mobility for strained-silicon channel nMOSFETs is proposed in this paper. The model deals directly with the strain tensor,and thus is independent of the manufacturing process. It is suitable for （100〉/ 〈110） channel nMOSFETs under biaxial or （100〉/〈 110 ） uniaxial stress and can be implemented in conventional device simulation tools .
基金supported by the National Basic Research Program of China (No. 2013CB035802)National Natural Science Foundation of China (No. 51475382)
文摘Dramatic tool temperature variation in end milling can cause excessive tool wear and shorten its life, especially in machining of difficult-to-machine materials. In this study, a new analytical model-based method for the prediction of cutting tool temperature in end milling is presented.The cutting cycle is divided into temperature increase and decrease phases. For the temperature increase phase, a temperature prediction model considering real friction state between the chip and tool is proposed, and the heat flux and tool-chip contact length are then obtained through finite element simulation. In the temperature decrease phase, a temperature decrease model based on the one-dimension plate heat convection is proposed. A single wire thermocouple is employed to measure the tool temperature in the conducted milling experiments. Both of the theoretical and experimental results are obtained with cutting conditions of the cutting speed ranging from 60 m/min to100 m/min, feed per tooth from 0.12 mm/z to 0.20 mm/z, and the radial and axial depth of cut respectively being 4 mm and 0.5 mm. The comparison results show high agreement between the physical cutting experiments and the proposed cutting tool temperature prediction method.
文摘The analytical model for springback in arc bending of sheet metal can serve as an excellent design support.The amount of springback is considerably influenced by the geometrical and the material parameters associated with the sheet metal.In addition,the applied load during the bending also has a significant influence.Although a number of numerical techniques have been used for this purpose,only few analytical models that can provide insight into the phenomenon are available.A phenomenological model for predicting the springback in arc bending was proposed based on strain as well as deformation energy based approaches.The results of the analytical model were compared with the published experimental as well as FE results of the authors,and the agreement was found to be satisfactory.
基金Item Sponsored by National Natural Science Foundation of China(51075353)
文摘In order to improve rolled strip quality, precise plate shape control theory should be established. Roll flat- tening theory is an important part of the plate shape theory. To improve the accuracy of roll flattening calculation based on semi infinite body model, especially near the two roll barrel edges, a new and more accurate roll flattening model is proposed. Based on boundary integral equation method, an analytical model for solving a finite length semi infinite body is established. The lateral surface displacement field of the finite length semi-infinite body is simulated by finite element method （FEM） and lateral surface displacement decay functions are established. Based on the boundary integral equation method, the numerical solution of the finite length semi-infinite body under the distribu ted force is obtained and an accurate roll flattening model is established. Different from the traditional semi-infinite body model, the matrix form of the new roll flattening model is established through the mathematical derivation. The result from the new model is more consistent with that by FEM especially near the edges.
基金Sponsored by National Science and Technology Major Project of China(2012ZX04012011)National Natural Science Foundation of China(51375306)
文摘Waves occurring in cold-rolled plates or sheets can be divided into longitudinal and transverse waves. Classical leveling theories merely solve the problem of longitudinal waves, while no well accepted method can be employed for transverse waves. In order to investigate the essential deformation law of leveling for plates with transverse waves, a 2.5-dimensional （2.5- D） analytical approach was proposed. In this model, the plate was transversely divided into some strips with equal width; the strips are considered to be in the state of plane strain and each group of adjacent strips are assumed to be deformation compatible under stress. After calculation, the bending deformation of each strip and the leveling effect of overall plate were obtained by comprehensNe consideration of various strips along with the width. Bending of roller is a main approach to eliminate the transverse waves, which is widely accepted by the industry, but the essential effect of bending of roller on the deformation of plates and the calculation of bending of roller are unknown. According to the 2.5-D analytical model, it can be found that, for plates, it is neutral plane offsetting and middle plane elongation or contraction under inner stress that can effectively improve plate shape. Taking double side waves as an example, the appropriate values of bending of roller were obtained by the 2.5-D analytical model related to different initial unevenness, which was applicable to the current on-line adjusting of bending of roller in rolling industry.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51738002 and 52108376)Fundamental Research Funds for the Central Universities (Grant No. 2021CZ111)
文摘Based on the nondestructive test data of operating railway tunnels in China, this paper summarizes the basic characteristics of the complex contact behavior between the rock mass and lining structure. The contact modes are classified into dense contact, local non-contact, and loose contact. Subsequently, the corresponding mechanical model for each contact mode is developed according to its mechanical characteristics using the complex variable method. In the proposed mechanical model, a special algorithm is introduced to detect whether the local non-contact zone is re-contacted. Besides, a novel conformal mapping method is also proposed to accurately calculate the mechanical response of the concrete lining. Finally, the accuracy of the proposed method is verified by comparing it with the finite element method(FEM). Several parameter investigations are conducted to analyze the effects of different contact modes on the rock-lining interaction. The results show that:(i) the height of the local noncontact area does not have a significant effect on the contact stress distribution if no re-contact occurs;(ii) backfill grouting can reduce the local stress concentration caused by poor contact modes;and(iii) reducing the friction coefficient of the interface can lead to a more uniform distribution of internal forces in the concrete lining.
基金the Slovak Research and Development Agency under the contract No.COST-0022-06,APVV-51-061505the 6th FP EU NESPA+5 种基金the Slovak Grant Agency VEGA(2/7197/27,2/7194/27,2/7195/27)NANOSMART,Centre of Excellence(1/1/2007-31/12/2010)Slovak Academy of Sciences,by KMM-NoE 502243-2(10/2004-9/2008)NENAMAT INCO-CT-2003-510363COST Action 536 and COST Action 538János Bolyai Research Grant NSF-MTA-OTKA grant-MTA:96/OTKA:049953,OTKA 63609
文摘Based on the fundamental equations of the mechanics of solid continuum,the paper employs an analytical model for determination of elastic thermal stresses in isotropic continuum represented by periodically distributed spherical particles with different distributions in an infinite matrix,imaginarily divided into identical cells with dimensions equal to inter-particle distances,containing a central spherical particle with or without a spherical envelope on the particle surface.Consequently,the multi-particle-(envelope)-matrix system,as a model system regarding the analytical modelling,is applicable to four types of multi-phase materials.As functions of the particle volume fraction v,the inter-particle distances dl,d2,d3 along three mutually per-pendicular axes,and the particle and envelope radii,R1 and R2,respectively,the thermal stresses within the cell,are originated during a cooling process as a consequence of the difference in thermal expansion coefficients of phases rep-resented by the matrix,envelope and particle.Analytical-(experimental)-computational lifetime prediction methods for multi-phase materials are proposed,which can be used in engineering with appropriate values of parameters of real multi-phase materials.
基金Project supported by the National Natural Science Foundation of China(Nos.11171238,51279117,and 11072161)the Program for New Century Excellent Talents in University of China(No.NCET-13-0393)the National Science and Technology Ministry of China(No.2012BAB05B02)
文摘A simple but applicable analytical model is presented to predict the lat- eral distribution of the depth-averaged velocity in meandering compound channels. The governing equation with curvilinear coordinates is derived from the momentum equation and the flow continuity equation under the condition of quasi-uniform flow. A series of experiments are conducted in a large-scale meandering compound channel. Based on the experimental data, a magnitude analysis is carried out for the governing equation, and two lower-order shear stress terms are ignored. Four groups of experimental data from different sources are used to verify the predictive capability of this model, and good predictions are obtained. Finally, the determination of the velocity parameter and the limitation of this model are discussed.
