15 research outputs found
Low intrusive coupling of implicit and explicit integration schemes for structural dynamics: application to low energy impacts on composite structures
Simulation of low energy impacts on composite structures is a key feature in
aeronautics. Unfortunately they are very expensive: on the one side, the structures of
interest have large dimensions and need fine volumic meshes (at least locally) in order to
capture damages. On the other side small time steps are required to ensure the explicit
algorithms stability which are commonly used in these kind of simulations [4]. Implicit
algorithms are in fact rarely used in this situation because of the roughness of the solutions
that leads to prohibitive expensive time steps or even to non convergence of Newtonlike
iterative processes. It is also observed that rough phenomenons are localized in
space and time (near the impacted zone). It may therefore be advantageous to adopt
a multiscale space/time approach by splitting the structure into several substructures
owning there own space/time discretization and their own integration schemes. The
purpose of this decomposition is to take advantage of the specificities of both algorithms
families: explicit scheme focuses on rough areas while smoother (actually linear) parts of
the solutions are computed with larger time steps with an implicit scheme. We propose
here an implementation of the Gravouil-Combescure method (GC) [1] by the mean of low
intrusive coupling between the implicit finite element analysis (FEA) code Z-set and the
explicit FEA code Europlexus. Simulations of low energy impacts on composite stiffened
panels are presented. It is shown on this application that time step ratios up to 5000 can be reached. However, computations related to the explicit domain still remain a
bottleneck in terms of cpu time
Approche multiéchelle en espace et en temps pour la prévision des endommagements dans les structures composites soumises à un impact de faible énergie
The composite laminates are increasingly used in aircraft structural parts which lead to new issues such as the Low Energy Impacts (LEI). Indeed, although they have well mechanical properties relative to their mass, small shocks may be very harmfull for laminates. Controlling such situations is essential for manufacturers that why lot of testing campaigns are currently performed. Yet, they are time consuming and expensive considering the many influential parameters (energy, speed, layup...). Numerical simulations of this phenomenon by practicing the so called âvirtual testingâ process could be really helpfull to rationalize testing campaigns in order to save money. Yet, this practice remain currently hard to do at the industrial scale due to the excessive CPU time required for fine simulation of damages induced by the LEI. Based on this observation, this work has consisted in taking advantage of the spatial and temporal location of delamination, matrix cracking and fiber breakage that can occur during impact in order to reduce the computational cost. Thus, a space and time multiscale method has been put in place. The impacted structure is split into two areas. One is located around the impacted point, it contains all the non-regularities of the problem (contact, softening law, cohesive zone model). This domain is treated with the explicit dynamics code Europlexus. The other one corresponds to the complementary part. The mechanical problem is much more regular and it is treated with the implicit dynamics code Zset / Zebulon. A low intrusive coupling based on the GC method is carried out between these two codes. It allows to use an adapted model in both regions different time step are in particular used. A time step ratio upper to 1000 can be reach between the one of the explicit code set by the stability condition and the one used in the complementary part. As a results, significant CPU time is saved. This is confirmed by the simulation of a stiffened composite panel impacted. It is also shown that the implicit / explicit allocation can change over the calculation. To do that, a switch mechanism has been established. It thus makes it possible to transit the resolution of a portion of the structure initially solved in the code Zebulon to Europlexus. As a results, further gain is obtained.Les stratifiĂ©s composites sont de plus en plus utilisĂ©s dans les piĂšces de structures des aĂ©ronefs ce qui fait Ă©merger de nouvelles problĂ©matiques comme celle des Impacts de Faible Energie (IFE). En effet, bien quâils possĂšdent des propriĂ©tĂ©s rapportĂ©es Ă leur masse trĂšs intĂ©ressantes ces matĂ©riaux peuvent ĂȘtre vulnĂ©rables aux petits chocs. Or, compte tenu des nombreux paramĂštres influents lors dâun tel impact (Ă©nergie, vitesse, stratification...), les essais actuellement majoritairement privilĂ©giĂ©s Ă lâĂ©chelle industrielle sont long et coĂ»teux. Ainsi, lâapport de la simulation numĂ©rique pourrait ĂȘtre dâune grande aide pour les constructeurs. La pratique du « virtual testing », en particulier, permettrait dâaller dans cette direction ce qui aurait pour effet de rationaliser les campagnes dâessais et les coĂ»ts financier qui en dĂ©coulent. Cependant, elle peine Ă ĂȘtre mise en place ici car le temps CPU nĂ©cessaire pour la simulation fine des ndommagements induits par les IFE est trop important avec les mĂ©thodes actuelles. Partant de ce constat, ce travail a consistĂ© Ă tirer avantageusement partie de la localisation spatiale et temporelle des dĂ©laminages, fissurations matricielles et ruptures de fibres qui peuvent apparaĂźtre pendant lâimpact pour diminuer le coĂ»t de calcul. Ainsi une mĂ©thode multiĂ©chelle en espace et en temps a Ă©tĂ© mise en place. Elle consiste Ă dĂ©couper la structure impactĂ©e en deux zones. Lâune est situĂ©e autour du point dâimpact, elle contient lâensemble des non-rĂ©gularitĂ©s du problĂšme (contact, loi adoucissante, modĂšle de zone cohĂ©sive). Elle est traitĂ©e avec le code de dynamique explicite Europlexus. Lâautre correspond Ă la partie complĂ©mentaire. Le problĂšme mĂ©canique y est beaucoup plus rĂ©gulier et il est traitĂ© avec le code de dynamique implicite Zset/ZĂ©bulon. Un couplage peu intrusif basĂ© sur la mĂ©thode GC est donc rĂ©alisĂ© entre ces deux codes. Il permet dâutiliser une modĂ©lisation adaptĂ©e dans chacune des deux rĂ©gions ce qui permet en particulier dâutiliser des pas de temps diffĂ©rents. Un rapport supĂ©rieur Ă 1000 peut ainsi ĂȘtre obtenu entre celui du code explicite fixĂ© par la condition de stabilitĂ© et celui utilisĂ© dans la partie complĂ©mentaire. Un gain de temps CPU significatif confirmĂ© par la simulation dâun impact rĂ©alisĂ© sur un panneau composite raidi est ainsi obtenu. Il est Ă©galement montrĂ© que la rĂ©partition implicite/explicite peut Ă©voluer au cours du calcul. Pour cela un mĂ©canisme de bascule a Ă©tĂ© mis en place. Il permet ainsi de faire transiter la rĂ©solution dâune partie de la structure initialement traitĂ©e dans le code Zebulon dans Europlexus. Un gain de temps supplĂ©mentaire est alors obtenu grĂące Ă cette mĂ©thode sur le mĂȘme cas dâapplication
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A multiscale space time approche to simulate damages in composite structures subjected to a low energy impact
Les stratifiĂ©s composites sont de plus en plus utilisĂ©s dans les piĂšces de structures des aĂ©ronefs ce qui fait Ă©merger de nouvelles problĂ©matiques comme celle des Impacts de Faible Energie (IFE). En effet, bien quâils possĂšdent des propriĂ©tĂ©s rapportĂ©es Ă leur masse trĂšs intĂ©ressantes ces matĂ©riaux peuvent ĂȘtre vulnĂ©rables aux petits chocs. Or, compte tenu des nombreux paramĂštres influents lors dâun tel impact (Ă©nergie, vitesse, stratification...), les essais actuellement majoritairement privilĂ©giĂ©s Ă lâĂ©chelle industrielle sont long et coĂ»teux. Ainsi, lâapport de la simulation numĂ©rique pourrait ĂȘtre dâune grande aide pour les constructeurs. La pratique du « virtual testing », en particulier, permettrait dâaller dans cette direction ce qui aurait pour effet de rationaliser les campagnes dâessais et les coĂ»ts financier qui en dĂ©coulent. Cependant, elle peine Ă ĂȘtre mise en place ici car le temps CPU nĂ©cessaire pour la simulation fine des ndommagements induits par les IFE est trop important avec les mĂ©thodes actuelles. Partant de ce constat, ce travail a consistĂ© Ă tirer avantageusement partie de la localisation spatiale et temporelle des dĂ©laminages, fissurations matricielles et ruptures de fibres qui peuvent apparaĂźtre pendant lâimpact pour diminuer le coĂ»t de calcul. Ainsi une mĂ©thode multiĂ©chelle en espace et en temps a Ă©tĂ© mise en place. Elle consiste Ă dĂ©couper la structure impactĂ©e en deux zones. Lâune est situĂ©e autour du point dâimpact, elle contient lâensemble des non-rĂ©gularitĂ©s du problĂšme (contact, loi adoucissante, modĂšle de zone cohĂ©sive). Elle est traitĂ©e avec le code de dynamique explicite Europlexus. Lâautre correspond Ă la partie complĂ©mentaire. Le problĂšme mĂ©canique y est beaucoup plus rĂ©gulier et il est traitĂ© avec le code de dynamique implicite Zset/ZĂ©bulon. Un couplage peu intrusif basĂ© sur la mĂ©thode GC est donc rĂ©alisĂ© entre ces deux codes. Il permet dâutiliser une modĂ©lisation adaptĂ©e dans chacune des deux rĂ©gions ce qui permet en particulier dâutiliser des pas de temps diffĂ©rents. Un rapport supĂ©rieur Ă 1000 peut ainsi ĂȘtre obtenu entre celui du code explicite fixĂ© par la condition de stabilitĂ© et celui utilisĂ© dans la partie complĂ©mentaire. Un gain de temps CPU significatif confirmĂ© par la simulation dâun impact rĂ©alisĂ© sur un panneau composite raidi est ainsi obtenu. Il est Ă©galement montrĂ© que la rĂ©partition implicite/explicite peut Ă©voluer au cours du calcul. Pour cela un mĂ©canisme de bascule a Ă©tĂ© mis en place. Il permet ainsi de faire transiter la rĂ©solution dâune partie de la structure initialement traitĂ©e dans le code Zebulon dans Europlexus. Un gain de temps supplĂ©mentaire est alors obtenu grĂące Ă cette mĂ©thode sur le mĂȘme cas dâapplication.The composite laminates are increasingly used in aircraft structural parts which lead to new issues such as the Low Energy Impacts (LEI). Indeed, although they have well mechanical properties relative to their mass, small shocks may be very harmfull for laminates. Controlling such situations is essential for manufacturers that why lot of testing campaigns are currently performed. Yet, they are time consuming and expensive considering the many influential parameters (energy, speed, layup...). Numerical simulations of this phenomenon by practicing the so called âvirtual testingâ process could be really helpfull to rationalize testing campaigns in order to save money. Yet, this practice remain currently hard to do at the industrial scale due to the excessive CPU time required for fine simulation of damages induced by the LEI. Based on this observation, this work has consisted in taking advantage of the spatial and temporal location of delamination, matrix cracking and fiber breakage that can occur during impact in order to reduce the computational cost. Thus, a space and time multiscale method has been put in place. The impacted structure is split into two areas. One is located around the impacted point, it contains all the non-regularities of the problem (contact, softening law, cohesive zone model). This domain is treated with the explicit dynamics code Europlexus. The other one corresponds to the complementary part. The mechanical problem is much more regular and it is treated with the implicit dynamics code Zset / Zebulon. A low intrusive coupling based on the GC method is carried out between these two codes. It allows to use an adapted model in both regions different time step are in particular used. A time step ratio upper to 1000 can be reach between the one of the explicit code set by the stability condition and the one used in the complementary part. As a results, significant CPU time is saved. This is confirmed by the simulation of a stiffened composite panel impacted. It is also shown that the implicit / explicit allocation can change over the calculation. To do that, a switch mechanism has been established. It thus makes it possible to transit the resolution of a portion of the structure initially solved in the code Zebulon to Europlexus. As a results, further gain is obtained
Low intrusive coupling of implicit and explicit integration schemes for structural dynamics: application to low energy impacts on composite structures
Simulation of low energy impacts on composite structures is a key feature in
aeronautics. Unfortunately they are very expensive: on the one side, the structures of
interest have large dimensions and need fine volumic meshes (at least locally) in order to
capture damages. On the other side small time steps are required to ensure the explicit
algorithms stability which are commonly used in these kind of simulations [4]. Implicit
algorithms are in fact rarely used in this situation because of the roughness of the solutions
that leads to prohibitive expensive time steps or even to non convergence of Newtonlike
iterative processes. It is also observed that rough phenomenons are localized in
space and time (near the impacted zone). It may therefore be advantageous to adopt
a multiscale space/time approach by splitting the structure into several substructures
owning there own space/time discretization and their own integration schemes. The
purpose of this decomposition is to take advantage of the specificities of both algorithms
families: explicit scheme focuses on rough areas while smoother (actually linear) parts of
the solutions are computed with larger time steps with an implicit scheme. We propose
here an implementation of the Gravouil-Combescure method (GC) [1] by the mean of low
intrusive coupling between the implicit finite element analysis (FEA) code Z-set and the
explicit FEA code Europlexus. Simulations of low energy impacts on composite stiffened
panels are presented. It is shown on this application that time step ratios up to 5000 can be reached. However, computations related to the explicit domain still remain a
bottleneck in terms of cpu time