The identification of the traction acting on a portion of the surface of an anisotropic solid is very important in structural health monitoring and optimal design of structures. The traction can be determined using in...The identification of the traction acting on a portion of the surface of an anisotropic solid is very important in structural health monitoring and optimal design of structures. The traction can be determined using inverse methods in which displacement or strain measurements are taken at several points on the body. This paper presents an inverse method based on the method of fundamental solutions for the traction identification problem in two-dimensional anisotropic elasticity. The method of fundamental solutions is an efficient boundary-type meshless method widely used for analyzing various problems. Since the problem is linear, the sensitivity analysis is simply performed by solving the corresponding direct problem several times with different loads. The effects of important parameters such as the number of measurement data, the position of the measurement points, the amount of measurement error, and the type of measurement, i.e., displacement or strain, on the results are also investigated. The results obtained show that the presented inverse method is suitable for the problem of traction identification. It can be concluded from the results that the use of strain measurements in the inverse analysis leads to more accurate results than the use of displacement measurements. It is also found that measurement points closer to the boundary with unknown traction provide more reliable solutions. Additionally, it is found that increasing the number of measurement points increases the accuracy of the inverse solution. However, in cases with a large number of measurement points, further increasing the number of measurement data has little effect on the results.展开更多
Endoscopic submucosal dissection(ESD)has been developed as a treatment for superficial gastrointestinal neoplasms,which can achieve en bloc resection regardless of the lesion size.However,ESD is technically difficult ...Endoscopic submucosal dissection(ESD)has been developed as a treatment for superficial gastrointestinal neoplasms,which can achieve en bloc resection regardless of the lesion size.However,ESD is technically difficult because endoscopists cannot bring their hand into the gastrointestinal tract,unlike surgeons in regular surgery.It is difficult to obtain sufficient tension in the dissection plane and a good field of vision.Therefore,ESD is associated with a long procedure time and a high risk of adverse events in comparison with endoscopic mucosal resection.Traction methods have been developed to provide sufficient tension for the dissection plane and a good field of vision during the ESD procedure.However,traction direction is limited in most traction methods,resulting in insufficient effect in some cases.Although traction direction is considered important,there have been few investigations of its effect.In the first half of this review,important traction methods are discussed,including traction direction.In second half,appropriate traction methods for each organ are considered.Other important considerations for traction method,such as ability to adjust traction strength,interference between traction device and endoscope,and the need for specialized devices are also discussed.展开更多
To solve the problem of temperature rise caused by the high power density of high-speed permanent magnet synchronous traction motors,the temperature rise of various components in the motor is analyzed by coupling the ...To solve the problem of temperature rise caused by the high power density of high-speed permanent magnet synchronous traction motors,the temperature rise of various components in the motor is analyzed by coupling the equivalent thermal circuit method and computational fluid dynamics.Also,a cooling strategy is proposed to solve the problem of temperature rise,which is expected to prolong the service life of these devices.First,the theoretical bases of the approaches used to study heat transfer and fluid mechanics are discussed,then the fluid flow for the considered motor is analyzed,and the equivalent thermal circuit method is introduced for the calculation of the temperature rise.Finally,the stator,rotor loss,motor temperature rise,and the proposed cooling method are also explored through experiments.According to the results,the stator temperature at 50,000 r/min and 60,000 r/min at no-load operation is 68℃ and 76℃,respectively.By monitoring the temperature of the air outlets inside and outside the motor at different speeds,it is also found that the motor reaches a stable temperature rise after 65 min of operation.Coupling of the thermal circuit method and computational fluid dynamics is a strategy that can provide the average temperature rise of each component and can also comprehensively calculate the temperature of each local point.We conclude that a hybrid cooling strategy based on axial air cooling of the inner air duct of the motor and water cooling of the stator can meet the design requirements for the ventilation and cooling of this type of motors.展开更多
This paper presents a direct traction boundary integral equation method(DTBIEM)for two-dimensional crack problems of materials.The traction boundary integral equation was collocated on both the external boundary and e...This paper presents a direct traction boundary integral equation method(DTBIEM)for two-dimensional crack problems of materials.The traction boundary integral equation was collocated on both the external boundary and either side of the crack surfaces.The displacements and tractions were used as unknowns on the external boundary,while the relative crack opening displacement(RCOD)was chosen as unknowns on either side of crack surfaces to keep the single-domain merit.Only one side of the crack surfaces was concerned and needed to be discretized,thus the proposed method resulted in a smaller system of algebraic equations compared with the dual boundary element method(DBEM).A new set of crack-tip shape functions was constructed to represent the strain field singularity exactly,and the SIFs were evaluated by the extrapolation of the RCOD.Numerical examples for both straight and curved cracks are given to validate the accuracy and efficiency of the presented method.展开更多
Background Animal models of myocardial infarction （MI） have been widely used to study the pathologi- cal and physiological changes that occur in MI, and to objectively evaluate the efficacy of new treatments. They a...Background Animal models of myocardial infarction （MI） have been widely used to study the pathologi- cal and physiological changes that occur in MI, and to objectively evaluate the efficacy of new treatments. They are an important tool in this procedure. However, the mortality rate of MI animal models has so far been higher than in real-life situations. The aim of this study was to explore the use of a modified retrograde traction tracheal intubation （MRTI） method for increasing the success rate of MI models in rats. Methods Sixty male Sprague-Dawley rats were used in the experiment. Using the MRTI method of artificial airway generation, we established the MI model by ligation of the left anterior descending branch of the coronary artery. We analyzed the effects of MRTI, the use of lidocaine, operative details, nursing considerations during the operation, and post-operative factors on the success rate of the MI model in rats. Results The success rate of generating an MI model in rats can be significantly increased using the following methods： 1） Setting up the artificial airway through the use of MRTI by using a single-lumen central venous catheter; 2） Selecting a ligation site 2 mm be- low the midpoint of the connection between the left atrial appendage and the pulmonary cone; 3） Adding a drop of lidocaine to the surface of the heart to slow down the heart rate, make the operation easier to perform, and prevent arrhythmias postoperatively; 4） Clearing up airway secretions timely both intra and postoperative- ly; 5） Making sure that rats are in a warm state both intra and postoperatively; 6） Preventing wound infection. Conclusions Use of the MRTI method can quickly establish an artificial airway in rats. Intraoperative use of lidocaine, selecting a precise vascular ligation site, and appropriate care both intra and postoperatively can in- crease the success rate of MI model generation.展开更多
The mill roller bearing is made up of an internal ring, middlerolls and an external ring, the analysis of which is a multi-bodiescontact problem. In this paper, based on the three-dimensionalelastic contact BEM withou...The mill roller bearing is made up of an internal ring, middlerolls and an external ring, the analysis of which is a multi-bodiescontact problem. In this paper, based on the three-dimensionalelastic contact BEM without friction, and using the structuralcharacteristics of roller bearings, middle rolls are de- scribed byelastic plate units of different shapes, which is placed on theinternal ring.展开更多
The stress intensity factors （SIF） considering arbitrarily distributed surface tractions are evaluated based on the sealed boundary finite element method （SBFEM）. The semi-analytical solving process for the stress...The stress intensity factors （SIF） considering arbitrarily distributed surface tractions are evaluated based on the sealed boundary finite element method （SBFEM）. The semi-analytical solving process for the stress intensity factors including the effects of surface tractions is presented. Provided are the numerical examples for the evaluation of mode I and Ⅱ stress intensity factors with linear and non-linear distributing forces loaded on the crack surfaces. The crack problems of anisotropy and bimaterial interface are also studied and the stress intensity factors of single-edge-cracked orthotropic material and bi-material interface problems with surface tractions are calculated. Comparisons with the analytical solutions show that the proposed approach is effective and possesses high accuracy.展开更多
This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accuratel...This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.展开更多
Repeated Unit Cell（RUC）is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element（DFE）method,and merely applying Periodic Displacement Boundary Conditions（PDBCs）to RUC is ...Repeated Unit Cell（RUC）is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element（DFE）method,and merely applying Periodic Displacement Boundary Conditions（PDBCs）to RUC is almost a standard practice to conduct such analysis.Two basic questions arising from this practice are whether Periodic Traction Boundary Conditions（PTBCs,also known as traction continuity conditions）are guaranteed and whether the solution is independent of selection of RUCs.This paper presents the theoretical aspects to tackle these questions,which unify the strong form,weak form and DFE method of the micromechanical problem together.Specifically,the solution’s independence of selection of RUCs is dealt with on the strong form side,PTBCs are derived from the weak form as natural boundary conditions,and the validity of merely applying PDBCs in micromechanical Finite Element（FE）analysis is proved by referring to its intrinsic connection to the strong form and weak form.Key points in the theoretical aspects are demonstrated by illustrative examples,and the merits of setting micromechanical FE analysis under the background of a clear theoretical framework are highlighted in the efficient selection of RUCs for Uni Directional（UD）fiber-reinforced composites.展开更多
By using multi-grid method, the simultaneous Reynolds, elasticily, film-thickness,rheology, energy and thermal interface temperature equations are solved, and the numerical solution of line-ontact thermal EHL is succe...By using multi-grid method, the simultaneous Reynolds, elasticily, film-thickness,rheology, energy and thermal interface temperature equations are solved, and the numerical solution of line-ontact thermal EHL is successfully obtained and presented in this paper.In addition, the influence of sliding/rolling ratio on the distribution of temperature within the film and on the solid surface. minimum film thickness and traction coefficient are also studied. The results show that the influence of temperature on film thickness is significant and unnegligible, All mentioned above may provide a basis for further investigation of thermal EHL of helical gears.展开更多
Although boundary displacement and traction are independent field variables in boundary conditions of an elasticity problem at a non-singular boundary point, there exist definite relations of singularity intensities b...Although boundary displacement and traction are independent field variables in boundary conditions of an elasticity problem at a non-singular boundary point, there exist definite relations of singularity intensities between boundary displacement derivatives and tractions at a singular boundary point. The analytical forms of the relations at a singular smooth point for 2D isotropic elastic problems have been established in this work. By using the relations, positions of the singular boundary points and the corresponding singularity intensities of the unknown boundary field variables can be determined a priori. Therefore, more appropriate shape functions of the unknown boundary field variables in singular elements can be constructed. A numerical example shows that the accuracy of the BEM analysis using the developed theory is greatly increased.展开更多
基金funded by Vice Chancellor of Research at Shiraz University(grant 3GFU2M1820).
文摘The identification of the traction acting on a portion of the surface of an anisotropic solid is very important in structural health monitoring and optimal design of structures. The traction can be determined using inverse methods in which displacement or strain measurements are taken at several points on the body. This paper presents an inverse method based on the method of fundamental solutions for the traction identification problem in two-dimensional anisotropic elasticity. The method of fundamental solutions is an efficient boundary-type meshless method widely used for analyzing various problems. Since the problem is linear, the sensitivity analysis is simply performed by solving the corresponding direct problem several times with different loads. The effects of important parameters such as the number of measurement data, the position of the measurement points, the amount of measurement error, and the type of measurement, i.e., displacement or strain, on the results are also investigated. The results obtained show that the presented inverse method is suitable for the problem of traction identification. It can be concluded from the results that the use of strain measurements in the inverse analysis leads to more accurate results than the use of displacement measurements. It is also found that measurement points closer to the boundary with unknown traction provide more reliable solutions. Additionally, it is found that increasing the number of measurement points increases the accuracy of the inverse solution. However, in cases with a large number of measurement points, further increasing the number of measurement data has little effect on the results.
文摘Endoscopic submucosal dissection(ESD)has been developed as a treatment for superficial gastrointestinal neoplasms,which can achieve en bloc resection regardless of the lesion size.However,ESD is technically difficult because endoscopists cannot bring their hand into the gastrointestinal tract,unlike surgeons in regular surgery.It is difficult to obtain sufficient tension in the dissection plane and a good field of vision.Therefore,ESD is associated with a long procedure time and a high risk of adverse events in comparison with endoscopic mucosal resection.Traction methods have been developed to provide sufficient tension for the dissection plane and a good field of vision during the ESD procedure.However,traction direction is limited in most traction methods,resulting in insufficient effect in some cases.Although traction direction is considered important,there have been few investigations of its effect.In the first half of this review,important traction methods are discussed,including traction direction.In second half,appropriate traction methods for each organ are considered.Other important considerations for traction method,such as ability to adjust traction strength,interference between traction device and endoscope,and the need for specialized devices are also discussed.
文摘To solve the problem of temperature rise caused by the high power density of high-speed permanent magnet synchronous traction motors,the temperature rise of various components in the motor is analyzed by coupling the equivalent thermal circuit method and computational fluid dynamics.Also,a cooling strategy is proposed to solve the problem of temperature rise,which is expected to prolong the service life of these devices.First,the theoretical bases of the approaches used to study heat transfer and fluid mechanics are discussed,then the fluid flow for the considered motor is analyzed,and the equivalent thermal circuit method is introduced for the calculation of the temperature rise.Finally,the stator,rotor loss,motor temperature rise,and the proposed cooling method are also explored through experiments.According to the results,the stator temperature at 50,000 r/min and 60,000 r/min at no-load operation is 68℃ and 76℃,respectively.By monitoring the temperature of the air outlets inside and outside the motor at different speeds,it is also found that the motor reaches a stable temperature rise after 65 min of operation.Coupling of the thermal circuit method and computational fluid dynamics is a strategy that can provide the average temperature rise of each component and can also comprehensively calculate the temperature of each local point.We conclude that a hybrid cooling strategy based on axial air cooling of the inner air duct of the motor and water cooling of the stator can meet the design requirements for the ventilation and cooling of this type of motors.
基金This work was supported by The National Key R&D Program of China(Grant No.2017YFC0804601)the National Natural Science Foundation of China(No.51741410)Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.Z017017).
文摘This paper presents a direct traction boundary integral equation method(DTBIEM)for two-dimensional crack problems of materials.The traction boundary integral equation was collocated on both the external boundary and either side of the crack surfaces.The displacements and tractions were used as unknowns on the external boundary,while the relative crack opening displacement(RCOD)was chosen as unknowns on either side of crack surfaces to keep the single-domain merit.Only one side of the crack surfaces was concerned and needed to be discretized,thus the proposed method resulted in a smaller system of algebraic equations compared with the dual boundary element method(DBEM).A new set of crack-tip shape functions was constructed to represent the strain field singularity exactly,and the SIFs were evaluated by the extrapolation of the RCOD.Numerical examples for both straight and curved cracks are given to validate the accuracy and efficiency of the presented method.
基金supported by Guangdong Medical Scientific Research Funds(No.B2012304)Guangzhou Medical and Health Technology Projects(No.20141A011019)
文摘Background Animal models of myocardial infarction （MI） have been widely used to study the pathologi- cal and physiological changes that occur in MI, and to objectively evaluate the efficacy of new treatments. They are an important tool in this procedure. However, the mortality rate of MI animal models has so far been higher than in real-life situations. The aim of this study was to explore the use of a modified retrograde traction tracheal intubation （MRTI） method for increasing the success rate of MI models in rats. Methods Sixty male Sprague-Dawley rats were used in the experiment. Using the MRTI method of artificial airway generation, we established the MI model by ligation of the left anterior descending branch of the coronary artery. We analyzed the effects of MRTI, the use of lidocaine, operative details, nursing considerations during the operation, and post-operative factors on the success rate of the MI model in rats. Results The success rate of generating an MI model in rats can be significantly increased using the following methods： 1） Setting up the artificial airway through the use of MRTI by using a single-lumen central venous catheter; 2） Selecting a ligation site 2 mm be- low the midpoint of the connection between the left atrial appendage and the pulmonary cone; 3） Adding a drop of lidocaine to the surface of the heart to slow down the heart rate, make the operation easier to perform, and prevent arrhythmias postoperatively; 4） Clearing up airway secretions timely both intra and postoperative- ly; 5） Making sure that rats are in a warm state both intra and postoperatively; 6） Preventing wound infection. Conclusions Use of the MRTI method can quickly establish an artificial airway in rats. Intraoperative use of lidocaine, selecting a precise vascular ligation site, and appropriate care both intra and postoperatively can in- crease the success rate of MI model generation.
基金the National Natural Science Foundation of China (50075075)
文摘The mill roller bearing is made up of an internal ring, middlerolls and an external ring, the analysis of which is a multi-bodiescontact problem. In this paper, based on the three-dimensionalelastic contact BEM without friction, and using the structuralcharacteristics of roller bearings, middle rolls are de- scribed byelastic plate units of different shapes, which is placed on theinternal ring.
基金The present research workis financially supported by the National Natural Science Foundation of China (Grant No90510018)China Postdoctorial Science Foundation (Grant No20060390985)
文摘The stress intensity factors （SIF） considering arbitrarily distributed surface tractions are evaluated based on the sealed boundary finite element method （SBFEM）. The semi-analytical solving process for the stress intensity factors including the effects of surface tractions is presented. Provided are the numerical examples for the evaluation of mode I and Ⅱ stress intensity factors with linear and non-linear distributing forces loaded on the crack surfaces. The crack problems of anisotropy and bimaterial interface are also studied and the stress intensity factors of single-edge-cracked orthotropic material and bi-material interface problems with surface tractions are calculated. Comparisons with the analytical solutions show that the proposed approach is effective and possesses high accuracy.
基金supported by the National Natural Science Foundation of China under Grant 52107007the China Scholarship Council under Grant 202008120084the“Chunhui Plan”Collaborative Research Project of Chinese Ministry of Education under Grant HZKY20220604。
文摘This paper presents the design optimization of a self-circulated ventilation system for an enclosed permanent magnet(PM)traction motor utilized in the propulsion systems for subway trains.In order to analyze accurately the machine's inherent cooling capacity when the train is running,the ambient airflow and the related heat transfer coefficient(HTC)are numerically investigated considering synchronously the bogie installation structure.The machine is preliminary cooled with air ducts set on the motor shell,and the fluidic-thermal field distributions with only the shell air duct cooling are numerically calculated.During simulations,the HTC obtained in the former steps is applied to the external surface of the machine to model the inherent cooling characteristic caused by the train movement.To reduce the temperature rise and thus guarantee the motor's working reliability,an internal self-circulated air cooling system is proposed according to the machine temperature distribution.The air enclosed in the end-caps is driven by the blades mounted on both sides of the rotor core and forms two air circuits to bring the excessive power losses generated in the heating components to cool regions.The fluid flow and temperature rise distributions of the cooling system's structural parameters are further improved by the Taguchi method in order to confirm the efficacy of the internal air cooling system.
文摘Repeated Unit Cell（RUC）is a useful tool in micromechanical analysis of composites using Displacement-based Finite Element（DFE）method,and merely applying Periodic Displacement Boundary Conditions（PDBCs）to RUC is almost a standard practice to conduct such analysis.Two basic questions arising from this practice are whether Periodic Traction Boundary Conditions（PTBCs,also known as traction continuity conditions）are guaranteed and whether the solution is independent of selection of RUCs.This paper presents the theoretical aspects to tackle these questions,which unify the strong form,weak form and DFE method of the micromechanical problem together.Specifically,the solution’s independence of selection of RUCs is dealt with on the strong form side,PTBCs are derived from the weak form as natural boundary conditions,and the validity of merely applying PDBCs in micromechanical Finite Element（FE）analysis is proved by referring to its intrinsic connection to the strong form and weak form.Key points in the theoretical aspects are demonstrated by illustrative examples,and the merits of setting micromechanical FE analysis under the background of a clear theoretical framework are highlighted in the efficient selection of RUCs for Uni Directional（UD）fiber-reinforced composites.
文摘By using multi-grid method, the simultaneous Reynolds, elasticily, film-thickness,rheology, energy and thermal interface temperature equations are solved, and the numerical solution of line-ontact thermal EHL is successfully obtained and presented in this paper.In addition, the influence of sliding/rolling ratio on the distribution of temperature within the film and on the solid surface. minimum film thickness and traction coefficient are also studied. The results show that the influence of temperature on film thickness is significant and unnegligible, All mentioned above may provide a basis for further investigation of thermal EHL of helical gears.
文摘Although boundary displacement and traction are independent field variables in boundary conditions of an elasticity problem at a non-singular boundary point, there exist definite relations of singularity intensities between boundary displacement derivatives and tractions at a singular boundary point. The analytical forms of the relations at a singular smooth point for 2D isotropic elastic problems have been established in this work. By using the relations, positions of the singular boundary points and the corresponding singularity intensities of the unknown boundary field variables can be determined a priori. Therefore, more appropriate shape functions of the unknown boundary field variables in singular elements can be constructed. A numerical example shows that the accuracy of the BEM analysis using the developed theory is greatly increased.
