Person-borne improvised explosive devices(PBIEDs)are often used in terrorist attacks in Western countries.This study aims to predict the trajectories of PBIED fragments and the subsequent safety risks for people expos...Person-borne improvised explosive devices(PBIEDs)are often used in terrorist attacks in Western countries.This study aims to predict the trajectories of PBIED fragments and the subsequent safety risks for people exposed to this hazard.An explosive field test with a typical PBIED composed of a plastic explosive charge and steel nut enhancements was performed to record initial fragment behaviour,including positions,velocity,and trajectory angles.These data were used to predict the full trajectory of PBIED fragments using a probabilistic analysis.In the probabilistic analyses a probability of fatality or serious injury was computed.Based on the results presented,many practical conclusions can be drawn,for instance,regarding safe evacuation distances if a person were exposed to a suspected PBIED.展开更多
The analysis of the dynamics of surface girders is of great importance in the design of engineering structures such as steel welded bridge plane girders or concrete plate-column structures.This work is an extension of...The analysis of the dynamics of surface girders is of great importance in the design of engineering structures such as steel welded bridge plane girders or concrete plate-column structures.This work is an extension of the classical deterministic problem of free vibrations of thin(Kirchhoff)plates.Themain aim of this work is the study of stochastic eigenvibrations of thin(Kirchhoff)elastic plates resting on internal continuous and column supports by the Boundary Element Method(BEM).This work is a continuation of previous research related to the random approach in plate analysis using the BEM.The static fundamental solution(Green’s function)is applied,coupled with a nonsingular formulation of the boundary and domain integral equations.These are derived using a modified and simplified formulation of the boundary conditions,inwhich there is no need to introduce theKirchhoff forces on a plate boundary.The role of the Kirchhoff corner forces is played by the boundary elements placed close to a single corner.Internal column or linear continuous supports are introduced using the Bezine technique,where the additional collocation points are introduced inside a plate domain.This allows for significant simplification of the BEM computational algorithm.An application of the polynomial approximations in the Least Squares Method(LSM)recovery of the structural response is done.The probabilistic analysis will employ three independent computational approaches:semi-analytical method(SAM),stochastic perturbation technique(SPT),and Monte-Carlo simulations.Numerical investigations include the fundamental eigenfrequencies of an elastic,thin,homogeneous,and isotropic plate.展开更多
Mechanical engineering structures and structural components are often subjected to cyclic thermomechanical loading which stresses their material beyond its elastic limits well inside the inelastic regime.Depending on ...Mechanical engineering structures and structural components are often subjected to cyclic thermomechanical loading which stresses their material beyond its elastic limits well inside the inelastic regime.Depending on the level of loading inelastic strains may lead either to failure,due to low cycle fatigue or ratcheting,or to safety,through elastic shakedown.Thus,it is important to estimate the asymptotic stress state of such structures.This state may be determined by cumbersome incremental time-stepping calculations.Direct methods,alternatively,have big computational advantages as they focus on the characteristics of these states and try to establish them,in a direct way,right from the beginning of the calculations.Among the very few such general-purpose direct methods,a powerful direct method which has been called RSDM has appeared in the literature.The method may directly predict any asymptotic state when the exact time history of the loading is known.The advantage of the method is due to the fact that it addresses the physics of the asymptotic cycle and exploits the cyclic nature of its expected residual stress distribution.Based on RSDM a method for the shakedown analysis of structures,called RSDM-S has also been developed.Despite most direct methods for shakedown,RSDM-S does not need an optimization algorithm for its implementation.Both RSDM and RSDM-S may be implemented in any Finite Element Code.A thorough review of both these methods,together with examples of implementation are presented herein.展开更多
The sand-steel interface(SSI)behavior is crucial for the stability of offshore structures in marine environments.A series of cyclic and post-cyclic shear tests were conducted using a modified direct shear apparatus(MD...The sand-steel interface(SSI)behavior is crucial for the stability of offshore structures in marine environments.A series of cyclic and post-cyclic shear tests were conducted using a modified direct shear apparatus(MDSA),to examine both global and local SSI behaviors.Experimental visualization and image processing improvements enabled a comprehensive investigation of the influences of material properties and loading characteristics.Cyclic loading induced significant dilation-contraction alternations,with overall contraction predominating.Boundary conditions influenced the trends of cyclic shear stress,which stabilized after a specific loading cycles.Post-cyclic SSI exhibited notable dilation and stress-softening.Sands with improved gradation showed poor SSI strength development and more pronounced cyclic contraction.An optimal surface roughness for SSI strength develop-ment was identified.Dilation state lines,reflecting cyclic deformation,displayed a downward trend with pro-gressive loading cycles.Friction angles,affected by displacement amplitude,underwent a weakeningstrengthingstabilizing process with cumulated shear displacement.Shear band thicknesses,sensitive to normal stress,surface roughness,and displacement amplitude,gradually stabilized with increased shear displacement.Grain microstructure evolution during cyclic shearing depended on the initial sand fabric.Fine grains migrated and collapsed during cyclic loading,combined with grains lying down,lubricating sand-sand friction.Insignificant macro-micro changes in SSI with a smooth plate indicated only sliding motion occurring.展开更多
基金This work was supported by the Poland National Center for Research and Development,under the grant DOB-BIO10/01/02/2019 within the Defence and Security Programme.
文摘Person-borne improvised explosive devices(PBIEDs)are often used in terrorist attacks in Western countries.This study aims to predict the trajectories of PBIED fragments and the subsequent safety risks for people exposed to this hazard.An explosive field test with a typical PBIED composed of a plastic explosive charge and steel nut enhancements was performed to record initial fragment behaviour,including positions,velocity,and trajectory angles.These data were used to predict the full trajectory of PBIED fragments using a probabilistic analysis.In the probabilistic analyses a probability of fatality or serious injury was computed.Based on the results presented,many practical conclusions can be drawn,for instance,regarding safe evacuation distances if a person were exposed to a suspected PBIED.
基金funded by research grant OPUS no.2021/41/B/ST8/02432 entitled Probabilistic entropy in engineering computations sponsored by The National Science Center in Polandthe Institute of Structural Analysis of Poznan University of Technology in the framework of the internal research grant 0411/SBAD/0010.
文摘The analysis of the dynamics of surface girders is of great importance in the design of engineering structures such as steel welded bridge plane girders or concrete plate-column structures.This work is an extension of the classical deterministic problem of free vibrations of thin(Kirchhoff)plates.Themain aim of this work is the study of stochastic eigenvibrations of thin(Kirchhoff)elastic plates resting on internal continuous and column supports by the Boundary Element Method(BEM).This work is a continuation of previous research related to the random approach in plate analysis using the BEM.The static fundamental solution(Green’s function)is applied,coupled with a nonsingular formulation of the boundary and domain integral equations.These are derived using a modified and simplified formulation of the boundary conditions,inwhich there is no need to introduce theKirchhoff forces on a plate boundary.The role of the Kirchhoff corner forces is played by the boundary elements placed close to a single corner.Internal column or linear continuous supports are introduced using the Bezine technique,where the additional collocation points are introduced inside a plate domain.This allows for significant simplification of the BEM computational algorithm.An application of the polynomial approximations in the Least Squares Method(LSM)recovery of the structural response is done.The probabilistic analysis will employ three independent computational approaches:semi-analytical method(SAM),stochastic perturbation technique(SPT),and Monte-Carlo simulations.Numerical investigations include the fundamental eigenfrequencies of an elastic,thin,homogeneous,and isotropic plate.
文摘Mechanical engineering structures and structural components are often subjected to cyclic thermomechanical loading which stresses their material beyond its elastic limits well inside the inelastic regime.Depending on the level of loading inelastic strains may lead either to failure,due to low cycle fatigue or ratcheting,or to safety,through elastic shakedown.Thus,it is important to estimate the asymptotic stress state of such structures.This state may be determined by cumbersome incremental time-stepping calculations.Direct methods,alternatively,have big computational advantages as they focus on the characteristics of these states and try to establish them,in a direct way,right from the beginning of the calculations.Among the very few such general-purpose direct methods,a powerful direct method which has been called RSDM has appeared in the literature.The method may directly predict any asymptotic state when the exact time history of the loading is known.The advantage of the method is due to the fact that it addresses the physics of the asymptotic cycle and exploits the cyclic nature of its expected residual stress distribution.Based on RSDM a method for the shakedown analysis of structures,called RSDM-S has also been developed.Despite most direct methods for shakedown,RSDM-S does not need an optimization algorithm for its implementation.Both RSDM and RSDM-S may be implemented in any Finite Element Code.A thorough review of both these methods,together with examples of implementation are presented herein.
基金the Natural Science of Jiangsu Province under Grant No BK20241527the Fundamental Research Funds for the Central Universities under Grant No B250201025the National Natural Science Foundation of China under Grant No 52309129.
文摘The sand-steel interface(SSI)behavior is crucial for the stability of offshore structures in marine environments.A series of cyclic and post-cyclic shear tests were conducted using a modified direct shear apparatus(MDSA),to examine both global and local SSI behaviors.Experimental visualization and image processing improvements enabled a comprehensive investigation of the influences of material properties and loading characteristics.Cyclic loading induced significant dilation-contraction alternations,with overall contraction predominating.Boundary conditions influenced the trends of cyclic shear stress,which stabilized after a specific loading cycles.Post-cyclic SSI exhibited notable dilation and stress-softening.Sands with improved gradation showed poor SSI strength development and more pronounced cyclic contraction.An optimal surface roughness for SSI strength develop-ment was identified.Dilation state lines,reflecting cyclic deformation,displayed a downward trend with pro-gressive loading cycles.Friction angles,affected by displacement amplitude,underwent a weakeningstrengthingstabilizing process with cumulated shear displacement.Shear band thicknesses,sensitive to normal stress,surface roughness,and displacement amplitude,gradually stabilized with increased shear displacement.Grain microstructure evolution during cyclic shearing depended on the initial sand fabric.Fine grains migrated and collapsed during cyclic loading,combined with grains lying down,lubricating sand-sand friction.Insignificant macro-micro changes in SSI with a smooth plate indicated only sliding motion occurring.
