In modem manufacturing, a new type of sheet metal part with step cross-section in both inner hole and outer edge is proposed. The traditional stamping separating processes can only produce sheet metal part with vertic...In modem manufacturing, a new type of sheet metal part with step cross-section in both inner hole and outer edge is proposed. The traditional stamping separating processes can only produce sheet metal part with vertical cross-section. According to the latest developing theory and potential of cold pressure forming： combination of pressure and cold forging, a new flow control forming of sheet metal（FCF） is excogitated based on blanking process of general stamping and combined with cold forging processes such as extrusion and coining, etc, which is aiming at the above-mentioned new type of sheet metal part. With utilization of this new process, the new type of sheet metal parts can be manufactured. In order to shorten the testing period, the numerical simulation was carried out by using DEFORM-3D software, and both deformation and mechanics rules were analyzed. Based on the simulation, both punching part and blanked parts of this new type were successfully developed. Then a new conception of optimal distance between the step walls of inner hole and outside edge was proposed and the design principle for its numerical value was inferred. Furthermore, a mold set for combination of stamping ＆ cold forging was designed and manufactured, by which the technologic experiments were taken for validation with Aluminum plate of thickness 2.35 mm for power battery cover board, which verified the principle of the distance between the step walls. The research of cold pressure forming of thin sheet metal with step cross-section is significant, not only to the development of modem mechanical manufacture, but also to metal plastic forming science.展开更多
Computations of wall distances still play a key role in modern turbulence modeling. Motivated by the expense involved in the computation, an approach solving partial differential equations is considered. An Euler-like...Computations of wall distances still play a key role in modern turbulence modeling. Motivated by the expense involved in the computation, an approach solving partial differential equations is considered. An Euler-like transport equation is proposed based on the Eikonal equation. Thus, the efficient algorithms and code components developed for solving transport equations such as Euler and Navier-Stokes equations can be reused. This article provides a detailed implementation of the transport equation in the Cartesian coordinates based on the code of computational fluid dynamics for missiles （MI- CFD） of Beihang University. The transport equation is robust and rapidly convergent by the implicit lower-upper symmetric Gauss-Seidel （LUSGS） time advancement and upwind spatial discretization. Geometric derivatives must also be upwind determined to ensure accuracy. Special treatments on initial and boundary conditions are discussed. This distance solving approach is successfully applied on several complex geometries with 1-1 blocking or overset grids.展开更多
Root-mean-square distance Drms with characteristic of weighted-average is introduced in this article firstly. Drms can be used to capture the general proximity of a site to a dipping fault plane comparing with the rup...Root-mean-square distance Drms with characteristic of weighted-average is introduced in this article firstly. Drms can be used to capture the general proximity of a site to a dipping fault plane comparing with the rupture distance Drup and the seismogenic distance Dseis. Then, using Drup, Dseis and Drms, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Chi-Chi earthquake are evaluated by regression analysis. The logarithm residual shows that the PGA on hanging wall is much greater than that on footwall at the same Drup or Dseis when the Drup or Dseis is used as site-to-source distance measure. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same Drms when Drms is used. This result confirms that the hanging wall/footwall effect is mainly a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if the root-mean-square distance Drms is used as the site-to-source distance measure.展开更多
Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent.However,majority of studies on blast walls have some shortcomings.The exp...Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent.However,majority of studies on blast walls have some shortcomings.The explosion test data are few.Most exsiting studies focus on the propagation of shock wave and the influence of blast wall on the propagation of shock wave.Discussion on the main parameters of blast wall design is meagre,such as the design of safety distance,the distance from the blast wall to the protective building,height and width of the blast wall.This paper uses the finite element programme LS-DYNA to design the blast wall.To analyze the convergence of the finite element model and to determine the mesh size of the model,this paper establishes several finite element models with different sizes of meshes to verify the model.Then,the overpressure distribution of the shock wave on the protective building is simulated to implement the blast wall design.The geometric parameters of the blast wall are preliminarily determined.And the influence of the safety distance on the overpressure of the building surface is mainly discussed,so as to determine the final design parameters.When the overpressure is less than 2 kPa,it is considered that there will be no damage to people caused by flying fragments.Eventually,the blast wall height is 3 m,the thickness is 1 m,and the safety distance is 35 m.The proposed method is used to demonstrate the design method,and the final design parameters of the blast wall can thus be used for reference.展开更多
The hazard caused by the fragments of damaged structures is usually significant in acci-dental explosions or hostile blast events.A reliable and efficient method to estimate probable fragment size,velocity and launch ...The hazard caused by the fragments of damaged structures is usually significant in acci-dental explosions or hostile blast events.A reliable and efficient method to estimate probable fragment size,velocity and launch distance will be useful to assess and design countermeasures to mitigate the possible fragment hazards.This paper presents a numerical method for predicting the size and launch distance of the fragments caused by explosive damage of masonry wall.Numerical simulations with different scaled distances are carried out,and the statistical distribution functions of the fragment size and launch distance in terms of the scaled distance are derived.展开更多
文摘In modem manufacturing, a new type of sheet metal part with step cross-section in both inner hole and outer edge is proposed. The traditional stamping separating processes can only produce sheet metal part with vertical cross-section. According to the latest developing theory and potential of cold pressure forming： combination of pressure and cold forging, a new flow control forming of sheet metal（FCF） is excogitated based on blanking process of general stamping and combined with cold forging processes such as extrusion and coining, etc, which is aiming at the above-mentioned new type of sheet metal part. With utilization of this new process, the new type of sheet metal parts can be manufactured. In order to shorten the testing period, the numerical simulation was carried out by using DEFORM-3D software, and both deformation and mechanics rules were analyzed. Based on the simulation, both punching part and blanked parts of this new type were successfully developed. Then a new conception of optimal distance between the step walls of inner hole and outside edge was proposed and the design principle for its numerical value was inferred. Furthermore, a mold set for combination of stamping ＆ cold forging was designed and manufactured, by which the technologic experiments were taken for validation with Aluminum plate of thickness 2.35 mm for power battery cover board, which verified the principle of the distance between the step walls. The research of cold pressure forming of thin sheet metal with step cross-section is significant, not only to the development of modem mechanical manufacture, but also to metal plastic forming science.
基金supported by the National Basic Research Programme of China (No.2009CB724104)the Post-Doctoral Science Foundation of China (No.20090450285)
文摘Computations of wall distances still play a key role in modern turbulence modeling. Motivated by the expense involved in the computation, an approach solving partial differential equations is considered. An Euler-like transport equation is proposed based on the Eikonal equation. Thus, the efficient algorithms and code components developed for solving transport equations such as Euler and Navier-Stokes equations can be reused. This article provides a detailed implementation of the transport equation in the Cartesian coordinates based on the code of computational fluid dynamics for missiles （MI- CFD） of Beihang University. The transport equation is robust and rapidly convergent by the implicit lower-upper symmetric Gauss-Seidel （LUSGS） time advancement and upwind spatial discretization. Geometric derivatives must also be upwind determined to ensure accuracy. Special treatments on initial and boundary conditions are discussed. This distance solving approach is successfully applied on several complex geometries with 1-1 blocking or overset grids.
基金Basic Science Research Foundation of Institute of Engineering Mechanics, China Earthquake Administration (2006B07) Natural Science Foundation of Heilongjiang Province (E2007-13)Joint Seismological Science Foundation of China (C07025)
文摘Root-mean-square distance Drms with characteristic of weighted-average is introduced in this article firstly. Drms can be used to capture the general proximity of a site to a dipping fault plane comparing with the rupture distance Drup and the seismogenic distance Dseis. Then, using Drup, Dseis and Drms, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Chi-Chi earthquake are evaluated by regression analysis. The logarithm residual shows that the PGA on hanging wall is much greater than that on footwall at the same Drup or Dseis when the Drup or Dseis is used as site-to-source distance measure. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same Drms when Drms is used. This result confirms that the hanging wall/footwall effect is mainly a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if the root-mean-square distance Drms is used as the site-to-source distance measure.
基金This work was supported by the National Natural Science Foundation of China(No.51878507).
文摘Blast wall can prevent vehicles from approaching the protective building and can reduce the destructive power of shock wave to a certain extent.However,majority of studies on blast walls have some shortcomings.The explosion test data are few.Most exsiting studies focus on the propagation of shock wave and the influence of blast wall on the propagation of shock wave.Discussion on the main parameters of blast wall design is meagre,such as the design of safety distance,the distance from the blast wall to the protective building,height and width of the blast wall.This paper uses the finite element programme LS-DYNA to design the blast wall.To analyze the convergence of the finite element model and to determine the mesh size of the model,this paper establishes several finite element models with different sizes of meshes to verify the model.Then,the overpressure distribution of the shock wave on the protective building is simulated to implement the blast wall design.The geometric parameters of the blast wall are preliminarily determined.And the influence of the safety distance on the overpressure of the building surface is mainly discussed,so as to determine the final design parameters.When the overpressure is less than 2 kPa,it is considered that there will be no damage to people caused by flying fragments.Eventually,the blast wall height is 3 m,the thickness is 1 m,and the safety distance is 35 m.The proposed method is used to demonstrate the design method,and the final design parameters of the blast wall can thus be used for reference.
基金Supported by the Australian Research Council (ARC,No.DP0774061)National Natural Science Foundation of China (No.50638030 and 50528808).
文摘The hazard caused by the fragments of damaged structures is usually significant in acci-dental explosions or hostile blast events.A reliable and efficient method to estimate probable fragment size,velocity and launch distance will be useful to assess and design countermeasures to mitigate the possible fragment hazards.This paper presents a numerical method for predicting the size and launch distance of the fragments caused by explosive damage of masonry wall.Numerical simulations with different scaled distances are carried out,and the statistical distribution functions of the fragment size and launch distance in terms of the scaled distance are derived.
