Pub Date : 2021-10-07DOI: 10.23967/WCCM-ECCOMAS.2020.133
N. Valle, F. Trias, J. Castro
The numerical simulation of multiphase flows presents several challenges, namely the transport of different phases within de domain and the inclusion of capillary effects. Here, these are approached by enforcing a discrete physics-compatible solution. Extending our previous work on the discretization of surface tension [N. Valle, F. X. Trias, and J. Castro. An energy-preserving level set method for multiphase flows. J. Comput. Phys., 400:108991, 2020] with a consistent mass and momentum transfer a fully energy-preserving multiphase flow method is presented. This numerical technique is showcased within the simulation of a falling film under several working conditions related to the normal operation of LiBr absorption chillers. Keywords— Multiphase flows, Symmetry-preserving, Computational Methods, Falling films
多相流的数值模拟面临着几个挑战，即不同相在区域内的输运和毛细效应的包含。在这里，这些都是通过执行一个离散的物理兼容解决方案来实现的。扩展了我们先前关于表面张力离散化的研究[N]。Valle, F. X. Trias和J. Castro。多相流的保能水平集方法。j .第一版。理论物理。[j]，[400:108991, 2020]在质量和动量传递一致的情况下，提出了一种完全守恒的多相流方法。该数值技术在与溴化锂吸收式制冷机正常运行有关的几种工作条件下的落膜模拟中得到了展示。关键词:多相流，对称性保持，计算方法，落膜
{"title":"Energy Preserving Multiphase Flows: Application to Falling Films","authors":"N. Valle, F. Trias, J. Castro","doi":"10.23967/WCCM-ECCOMAS.2020.133","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.133","url":null,"abstract":"The numerical simulation of multiphase flows presents several challenges, namely the transport of different phases within de domain and the inclusion of capillary effects. Here, these are approached by enforcing a discrete physics-compatible solution. Extending our previous work on the discretization of surface tension [N. Valle, F. X. Trias, and J. Castro. An energy-preserving level set method for multiphase flows. J. Comput. Phys., 400:108991, 2020] with a consistent mass and momentum transfer a fully energy-preserving multiphase flow method is presented. This numerical technique is showcased within the simulation of a falling film under several working conditions related to the normal operation of LiBr absorption chillers. Keywords— Multiphase flows, Symmetry-preserving, Computational Methods, Falling films","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126169131","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-25DOI: 10.23967/wccm-eccomas.2020.260
J. Bect, S. Zio, G. Perrin, C. Cannamela, E. Vázquez
Numerical models based on partial differential equations (PDE), or integro-differential equations, are ubiquitous in engineering and science, making it possible to understand or design systems for which physical experiments would be expensive-sometimes impossible-to carry out. Such models usually construct an approximate solution of the underlying continuous equations, using discretization methods such as finite differences or the finite elements method. The resulting discretization error introduces a form of uncertainty on the exact but unknown value of any quantity of interest (QoI), which affects the predictions of the numerical model alongside other sources of uncertainty such as parametric uncertainty or model inadequacy. The present article deals with the quantification of this discretization uncertainty.A first approach to this problem, now standard in the V&V (Verification and Validation) literature, uses the grid convergence index (GCI) originally proposed by P. Roache in the field of computational fluid dynamics (CFD), which is based on the Richardson extrapolation technique. Another approach, based on Bayesian inference with Gaussian process models, was more recently introduced in the statistical literature. In this work we present and compare these two paradigms for the quantification of discretization uncertainty, which have been developped in different scientific communities, and assess the potential of the-younger-Bayesian approach to provide a replacement for the well-established GCI-based approach, with better probabilistic foundations. The methods are illustrated and evaluated on two standard test cases from the literature (lid-driven cavity and Timoshenko beam).
{"title":"On the Quantification of Discretization Uncertainty: Comparison of Two Paradigms","authors":"J. Bect, S. Zio, G. Perrin, C. Cannamela, E. Vázquez","doi":"10.23967/wccm-eccomas.2020.260","DOIUrl":"https://doi.org/10.23967/wccm-eccomas.2020.260","url":null,"abstract":"Numerical models based on partial differential equations (PDE), or integro-differential equations, are ubiquitous in engineering and science, making it possible to understand or design systems for which physical experiments would be expensive-sometimes impossible-to carry out. Such models usually construct an approximate solution of the underlying continuous equations, using discretization methods such as finite differences or the finite elements method. The resulting discretization error introduces a form of uncertainty on the exact but unknown value of any quantity of interest (QoI), which affects the predictions of the numerical model alongside other sources of uncertainty such as parametric uncertainty or model inadequacy. The present article deals with the quantification of this discretization uncertainty.A first approach to this problem, now standard in the V&V (Verification and Validation) literature, uses the grid convergence index (GCI) originally proposed by P. Roache in the field of computational fluid dynamics (CFD), which is based on the Richardson extrapolation technique. Another approach, based on Bayesian inference with Gaussian process models, was more recently introduced in the statistical literature. In this work we present and compare these two paradigms for the quantification of discretization uncertainty, which have been developped in different scientific communities, and assess the potential of the-younger-Bayesian approach to provide a replacement for the well-established GCI-based approach, with better probabilistic foundations. The methods are illustrated and evaluated on two standard test cases from the literature (lid-driven cavity and Timoshenko beam).","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"146 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115474007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-12DOI: 10.23967/WCCM-ECCOMAS.2020.213
A. Ferrero, F. Masseni, L. Muscarà, D. Pastrone
Hybrid rocket engines (HREs) present interesting advantages over liquid rocket engines (LREs) and solid rocket motors (SRMs). In order to appreciate these advantages, one should look into the different combustion characteristics; in the hybrid engines the combustion occurs in a macrodiffusion flame and the oxidizer to fuel ratio changes along the combustion chamber. In solid rockets the oxidizer and fuel are mechanically or chemically bound in a single solid phase and they burn with a microdiffusion flame while, in the liquid engines, the combustion results from a premixed flame. Thus, unlike hybrids, both these engines have an uniform mixture ratio. On the other hand, in hybrid engines it is possible to throttle by modulating only the liquid flow rate, which is simpler than in a liquid engine where two flow rates must be synchronized. Furthermore, the European Union is pushing to proscribe some dangerous liquid propellants such as the hydrazine derivatives. As a consequence, there is a huge interest for the “green” propellants and also in this case the HREs present an optimum choice since they employ low toxicity propellants. Indeed, most hybrid propellants and additives are essentially nontoxic, resulting in minimal local environmental impact. The physical separation of fuel and oxidizer serves also to reduce the probability of an accident, which could lead to propellant release in the environment. An interesting feature is that the HREs seem viable for the lift-off from Mars because the typical solid fuels employed in HREs, contrary from the ones used for SRMs, do not develop cracks when subjected to wide temperature ranges [1]. From an economical point of view the operational cost for hybrid systems is affordable thanks to their safety features and inert propellant [2]. Despite the several advantages of hybrid systems compared to liquid and solid systems, the hybrids have not seen yet a mass production unlike heritage propulsion systems. In fact, the
{"title":"Multiphysics Modelling of a Hybrid Rocket Engine","authors":"A. Ferrero, F. Masseni, L. Muscarà, D. Pastrone","doi":"10.23967/WCCM-ECCOMAS.2020.213","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.213","url":null,"abstract":"Hybrid rocket engines (HREs) present interesting advantages over liquid rocket engines (LREs) and solid rocket motors (SRMs). In order to appreciate these advantages, one should look into the different combustion characteristics; in the hybrid engines the combustion occurs in a macrodiffusion flame and the oxidizer to fuel ratio changes along the combustion chamber. In solid rockets the oxidizer and fuel are mechanically or chemically bound in a single solid phase and they burn with a microdiffusion flame while, in the liquid engines, the combustion results from a premixed flame. Thus, unlike hybrids, both these engines have an uniform mixture ratio. On the other hand, in hybrid engines it is possible to throttle by modulating only the liquid flow rate, which is simpler than in a liquid engine where two flow rates must be synchronized. Furthermore, the European Union is pushing to proscribe some dangerous liquid propellants such as the hydrazine derivatives. As a consequence, there is a huge interest for the “green” propellants and also in this case the HREs present an optimum choice since they employ low toxicity propellants. Indeed, most hybrid propellants and additives are essentially nontoxic, resulting in minimal local environmental impact. The physical separation of fuel and oxidizer serves also to reduce the probability of an accident, which could lead to propellant release in the environment. An interesting feature is that the HREs seem viable for the lift-off from Mars because the typical solid fuels employed in HREs, contrary from the ones used for SRMs, do not develop cracks when subjected to wide temperature ranges [1]. From an economical point of view the operational cost for hybrid systems is affordable thanks to their safety features and inert propellant [2]. Despite the several advantages of hybrid systems compared to liquid and solid systems, the hybrids have not seen yet a mass production unlike heritage propulsion systems. In fact, the","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130424520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.134
M. Franke, R. Ortigosa, Amparo Gil, M. Hille
. The present contribution aims at the consistent discretisation of nonlinear, coupled thermo-electro-elastodynamics. In that regard, a new one-step implicit and thermodynamically consistent energy-momentum integration scheme for the simulation of thermo-electro-elastic processes undergoing large deformations will be presented. The consideration is based upon polyconvexity inspired, constitutive models and a new tensor cross product algebra, which facilitate the design of the so-called discrete derivatives (for more information it is referred to the pioneering works [3, 2]). The discrete derivatives are fundamental for the algorithmic evaluation of stresses and other derived variables like entropy density or the absolute temperature leading to a structure preserving integration scheme. In particu-lar, recently published works of the authors concerning consistent time integration of large deformation thermo-elastodynamics
{"title":"Energy-Momentum Scheme For Nonlinear Thermo-Electro-Elastodynamics","authors":"M. Franke, R. Ortigosa, Amparo Gil, M. Hille","doi":"10.23967/WCCM-ECCOMAS.2020.134","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.134","url":null,"abstract":". The present contribution aims at the consistent discretisation of nonlinear, coupled thermo-electro-elastodynamics. In that regard, a new one-step implicit and thermodynamically consistent energy-momentum integration scheme for the simulation of thermo-electro-elastic processes undergoing large deformations will be presented. The consideration is based upon polyconvexity inspired, constitutive models and a new tensor cross product algebra, which facilitate the design of the so-called discrete derivatives (for more information it is referred to the pioneering works [3, 2]). The discrete derivatives are fundamental for the algorithmic evaluation of stresses and other derived variables like entropy density or the absolute temperature leading to a structure preserving integration scheme. In particu-lar, recently published works of the authors concerning consistent time integration of large deformation thermo-elastodynamics","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126859367","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.343
A. Amani, J. Castro, A. Oliva
Three-dimensional numerical simulation of Taylor gas bubbles as primary unites of slug flow patterns rising in non-Newtonian environments is performed in the context of Direct Numerical Simulation (DNS) of the governing equations, where the whole physics of fluid motions will be taken into account. State-of-the-art numerical tools are proposed to tackle the numerical challenges in the DNS study of this problem. E.g. a coupled level-set volume-of-fluid (CLSVOF) interface capturing method is used to solve the topological changes of the interface. Physical formulations are integrated with moving-mesh (MM) technique to decrease the computational cost of 3D simulations and adaptivemesh-refinement (AMR) technique to increase the local accuracy around the interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. To the best of the authors’ knowledge, this is the first work dealing with three-dimensional direct numerical simulation of Taylor bubbles rising in non-Newtonian environments.
{"title":"Three-Dimensional Direct Numerical Simulation (DNS) of Taylor Bubbles Rising in Non-Newtonian Environments","authors":"A. Amani, J. Castro, A. Oliva","doi":"10.23967/WCCM-ECCOMAS.2020.343","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.343","url":null,"abstract":"Three-dimensional numerical simulation of Taylor gas bubbles as primary unites of slug flow patterns rising in non-Newtonian environments is performed in the context of Direct Numerical Simulation (DNS) of the governing equations, where the whole physics of fluid motions will be taken into account. State-of-the-art numerical tools are proposed to tackle the numerical challenges in the DNS study of this problem. E.g. a coupled level-set volume-of-fluid (CLSVOF) interface capturing method is used to solve the topological changes of the interface. Physical formulations are integrated with moving-mesh (MM) technique to decrease the computational cost of 3D simulations and adaptivemesh-refinement (AMR) technique to increase the local accuracy around the interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. To the best of the authors’ knowledge, this is the first work dealing with three-dimensional direct numerical simulation of Taylor bubbles rising in non-Newtonian environments.","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122678967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.079
R. Jesudasan, J. Mueller
. Non-Uniform Rational B-Splines (NURBS) have become the industrial standard to represent and exchange a CAD geometry between CAD/CAE systems. CAD-based shape parameterisation uses parameters of a CAD model to modify the shape which allows to integrate a CAD model into the design loop. However, feature-trees of typical commercial CAD systems are not open and obtaining exact derivatives for gradient-based optimisation methods is not possible. Using the CAD-based NSPCC approach a designer can deform multiple NURBS patches in the design loop without violating geometric and/or thickness constraints. The NSPCC approach takes CAD descriptions as input and perturbs the control points of the NURBS boundary representation to modify the shape. In this work, an adaptive NSPCC method is proposed where the optimisation begins with a coarser design space and adapts to finer parametrisation during the design process where more shape control is needed. The refinement sensor is based on a comparison of smoothed node-based sensitivity compared to its projection onto the shape modes of the current parametrisation. Both static and adaptive parametrisation methods are coupled in the adjoint-based shape optimisation process to reduce the total pressure loss of a turbine blade internal cooling channel. The discrete adjoint flow solver STAMPS is used to compute the flow fields and their derivatives w.r.t. surface node displacements. The shape derivatives for gradient-based optimisation are obtained by application of reverse mode AD to the NSPCC
{"title":"Cad-Based Adaptive Shape Parametrisation for Aerodynamic Shape Optimisation","authors":"R. Jesudasan, J. Mueller","doi":"10.23967/WCCM-ECCOMAS.2020.079","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.079","url":null,"abstract":". Non-Uniform Rational B-Splines (NURBS) have become the industrial standard to represent and exchange a CAD geometry between CAD/CAE systems. CAD-based shape parameterisation uses parameters of a CAD model to modify the shape which allows to integrate a CAD model into the design loop. However, feature-trees of typical commercial CAD systems are not open and obtaining exact derivatives for gradient-based optimisation methods is not possible. Using the CAD-based NSPCC approach a designer can deform multiple NURBS patches in the design loop without violating geometric and/or thickness constraints. The NSPCC approach takes CAD descriptions as input and perturbs the control points of the NURBS boundary representation to modify the shape. In this work, an adaptive NSPCC method is proposed where the optimisation begins with a coarser design space and adapts to finer parametrisation during the design process where more shape control is needed. The refinement sensor is based on a comparison of smoothed node-based sensitivity compared to its projection onto the shape modes of the current parametrisation. Both static and adaptive parametrisation methods are coupled in the adjoint-based shape optimisation process to reduce the total pressure loss of a turbine blade internal cooling channel. The discrete adjoint flow solver STAMPS is used to compute the flow fields and their derivatives w.r.t. surface node displacements. The shape derivatives for gradient-based optimisation are obtained by application of reverse mode AD to the NSPCC","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129053818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.066
A. V. Alexandrov, L. Dorodnicyn, A. Duben, D. Kolyukhin
. A method for the numerical generation of anisotropic turbulent velocity fields is presented. The proposed technique is based on the spectral method (SM) [1]. The traditional adaptation of isotropic field generated with spectral methods uses a Cholesky decomposition of Reynolds stresses tensor. After this adaptation the resulted field loses the property of incompressibility provided in the isotropic case. We have modified this method to use it in the anisotropic case and guarantee the incompressibility of generated turbulent field. Comparison of the results of IDDES simulation of canonical turbulent flow using inlet boundary conditions based on modified and non modified spectral methods are presented.
{"title":"Modified Spectral Method of Anisotropic Turbulent Velocity Field Generation Preserving Incompressibility","authors":"A. V. Alexandrov, L. Dorodnicyn, A. Duben, D. Kolyukhin","doi":"10.23967/WCCM-ECCOMAS.2020.066","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.066","url":null,"abstract":". A method for the numerical generation of anisotropic turbulent velocity fields is presented. The proposed technique is based on the spectral method (SM) [1]. The traditional adaptation of isotropic field generated with spectral methods uses a Cholesky decomposition of Reynolds stresses tensor. After this adaptation the resulted field loses the property of incompressibility provided in the isotropic case. We have modified this method to use it in the anisotropic case and guarantee the incompressibility of generated turbulent field. Comparison of the results of IDDES simulation of canonical turbulent flow using inlet boundary conditions based on modified and non modified spectral methods are presented.","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121535547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.055
A. Chierici, L. Chirco, V. Giovacchini, S. Manservisi
. In recent years, the optimal control in fluid dynamics has gained attention for the design and the optimization of engineering devices. One of the main challenges concerns the application of the optimal control theory to turbulent flows modeled by the Reynolds averaging Navier-Stokes equations. In this work we propose the implementation of an optimal boundary control problem for the Reynolds-Averaged Navier-Stokes system closed with a two-equations turbulence model. The optimal boundary velocity is sought in order to achieve several objectives such as the enhancement of turbulence or the matching of the velocity field over a well defined domain region. The boundary where the control acts can be the main inlet section or additional injection holes placed along the domain. By minimizing the augmented Lagrangian functional we obtain the optimality system comprising the state, the adjoint, and the control equations. Furthermore, we propose numerical strategies that allow to solve the optimality system in a robust way for such a large number of unknowns.
． 近年来，流体动力学中的最优控制在工程装置的设计和优化中得到了广泛的关注。其中一个主要的挑战是如何将最优控制理论应用于由Reynolds平均Navier-Stokes方程模拟的湍流。在这项工作中，我们提出了用两方程湍流模型封闭的reynolds - average Navier-Stokes系统的最优边界控制问题的实现。寻找最优边界速度是为了实现几个目标，如增强湍流或匹配速度场在一个明确的区域。控制作用的边界可以是主入口部分或沿区域放置的附加注射孔。通过最小化增广拉格朗日泛函，得到由状态方程、伴随方程和控制方程组成的最优系统。此外，我们提出了数值策略，允许以鲁棒的方式解决如此大量的未知数的最优性系统。
{"title":"An Adjoint Method for the Optimal Boundary Control of Turbulent Flows Modeled with the Rans System","authors":"A. Chierici, L. Chirco, V. Giovacchini, S. Manservisi","doi":"10.23967/WCCM-ECCOMAS.2020.055","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.055","url":null,"abstract":". In recent years, the optimal control in fluid dynamics has gained attention for the design and the optimization of engineering devices. One of the main challenges concerns the application of the optimal control theory to turbulent flows modeled by the Reynolds averaging Navier-Stokes equations. In this work we propose the implementation of an optimal boundary control problem for the Reynolds-Averaged Navier-Stokes system closed with a two-equations turbulence model. The optimal boundary velocity is sought in order to achieve several objectives such as the enhancement of turbulence or the matching of the velocity field over a well defined domain region. The boundary where the control acts can be the main inlet section or additional injection holes placed along the domain. By minimizing the augmented Lagrangian functional we obtain the optimality system comprising the state, the adjoint, and the control equations. Furthermore, we propose numerical strategies that allow to solve the optimality system in a robust way for such a large number of unknowns.","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131025825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.289
Tulio Honoro, S. A. Dandachli, Alexandra Bourdot
. The stability of ettringite under sorption and the conversion into metaettringite are studied using hybrid Grand Canonical Monte Carlo (GCMC) and (classical) Molecular Dynamics (MD) simulations sampling the osmotic ensemble. The desorption branch obtained from simulation and the associated volume changes are in agreement with the experimental evidence. We pay special attention to the structural changes at low RH, which is associated with metaettringite conversion, which is recognized as a disordered polymorph of ettringite with an unknown structure to date. We show that the conversion of ettringite into metaettringite is associated with an increase in entropy. The adsorption branch obtained from simulations is reversible in the ettringite domain in agreement with experiments. The reversibility in the conversion of metaettringite into ettringite, which is observed experimentally, is not captured by the simulation approach adopted. The large deformations associated with ettringite desorption make it difficult to capture reversibility with a direct sampling of the osmotic ensemble. Further, we discuss the role of hydrogen bonds on the hysteresis observed in sorption cycles in ettringite.
{"title":"Reversible Order-Disorder Transition in Ettringite-Metaettringite Conversion","authors":"Tulio Honoro, S. A. Dandachli, Alexandra Bourdot","doi":"10.23967/WCCM-ECCOMAS.2020.289","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.289","url":null,"abstract":". The stability of ettringite under sorption and the conversion into metaettringite are studied using hybrid Grand Canonical Monte Carlo (GCMC) and (classical) Molecular Dynamics (MD) simulations sampling the osmotic ensemble. The desorption branch obtained from simulation and the associated volume changes are in agreement with the experimental evidence. We pay special attention to the structural changes at low RH, which is associated with metaettringite conversion, which is recognized as a disordered polymorph of ettringite with an unknown structure to date. We show that the conversion of ettringite into metaettringite is associated with an increase in entropy. The adsorption branch obtained from simulations is reversible in the ettringite domain in agreement with experiments. The reversibility in the conversion of metaettringite into ettringite, which is observed experimentally, is not captured by the simulation approach adopted. The large deformations associated with ettringite desorption make it difficult to capture reversibility with a direct sampling of the osmotic ensemble. Further, we discuss the role of hydrogen bonds on the hysteresis observed in sorption cycles in ettringite.","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127803662","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-11DOI: 10.23967/WCCM-ECCOMAS.2020.231
A. A. Al-Shabab, D. Vitlaris, Zhonglu Lin, B. Grenko, Panagiotis Tsoutsanis, A. Antoniadis, M. Skote
. The simulation of an oleo-pneumatic shock absorber is discussed focusing on the solver validation and high fidelity case setup. The multi-physics nature of the problem is tackled by conducting a range of validation cases in the base areas expected to be of relevance. A dynamic system model of the shock absorber is used to generate physically consistent boundary conditions. In addition, steady RANS simulations provide a preliminary insight into the internal flow development and to assist in the design of higher resolution grids.
{"title":"Numerical Investigation of Oleo-Pneumatic Shock Absorber: Setup and Validation","authors":"A. A. Al-Shabab, D. Vitlaris, Zhonglu Lin, B. Grenko, Panagiotis Tsoutsanis, A. Antoniadis, M. Skote","doi":"10.23967/WCCM-ECCOMAS.2020.231","DOIUrl":"https://doi.org/10.23967/WCCM-ECCOMAS.2020.231","url":null,"abstract":". The simulation of an oleo-pneumatic shock absorber is discussed focusing on the solver validation and high fidelity case setup. The multi-physics nature of the problem is tackled by conducting a range of validation cases in the base areas expected to be of relevance. A dynamic system model of the shock absorber is used to generate physically consistent boundary conditions. In addition, steady RANS simulations provide a preliminary insight into the internal flow development and to assist in the design of higher resolution grids.","PeriodicalId":148883,"journal":{"name":"14th WCCM-ECCOMAS Congress","volume":"573 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120877627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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