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
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
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
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
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.
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.
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.
