Computational mechanics

Vol. 63, num. 5, p. 821-833

DOI: 10.1007/s00466-018-1624-3

Date of publication: 2019-05

Abstract:

Potential flow solvers represent an appealing alternative for the simulation of non-viscous subsonic flows. In order to deliver accurate results, such techniques require prescribing explicitly the so called Kutta condition, as well as adding a special treatment on the “wake” of the body. The wake is traditionally modelled by introducing a gap in the CFD mesh, which requires an often laborious meshing work. The novelty of the proposed work is to embed the wake within the CFD domain. The approach has obvious advantages in the context of aeroelastic optimization, where the position of the wake may change due to evolutionary steps of the geometry. This work presents a simple, yet effective, method for the imposition of the embedded wake boundary condition. The presented method preserves the possibility of employing iterative techniques in the solution of the linear problems which stem out of the discretization. Validation and verification of the solver are performed for a NACA 0012 airfoil.

The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-018-1624-3]]>

Advanced modeling and simulation in engineering sciences

Vol. 5, num. 1, p. 1-40

DOI: 10.1186/s40323-018-0113-8

Date of publication: 2018-12

Abstract:

The paper presents a robust algorithm, which allows to implicitly describe and track immersed geometries within a background mesh. The background mesh is assumed to be unstructured and discretized by tetrahedrons. The contained geometry is assumed to be given as triangulated surface. Within the background mesh, the immersed geometry is described implicitly using a discontinuous distance function based on a level-set approach. This distance function allows to consider both, “double-sided” geometries like membrane or shell structures, and “single-sided” objects for which an enclosed volume is univocally defined. For the second case, the discontinuous distance function is complemented by a continuous signed distance function, whereas ray casting is applied to identify the closed volume regions. Furthermore, adaptive mesh refinement is employed to provide the necessary resolution of the background mesh. The proposed algorithm can handle arbitrarily complicated geometries, possibly containing modeling errors (i.e., gaps, overlaps or a non-unique orientation of surface normals). Another important advantage of the algorithm is the embarrassingly parallel nature of its operations. This characteristic allows for a straightforward parallelization using MPI. All developments were implemented within the open source framework “KratosMultiphysics” and are available under the BSD license. The capabilities of the implementation are demonstrated with various application examples involving practice-oriented geometries. The results finally show, that the algorithm is able to describe most complicated geometries within a background mesh, whereas the approximation quality may be directly controlled by mesh refinement.]]>

Virtual Physiological Human Conference

p. 38

Presentation's date: 2018-09-06

Computational mechanics

Vol. 59, num. 6, p. 1003-1030

DOI: 10.1007/s00466-017-1382-7

Date of publication: 2017-06

Abstract:

The present paper explores the solution of a heat conduction problem considering discontinuities embedded within the mesh and aligned at arbitrary angles with respect to the mesh edges. Three alternative approaches are proposed as solutions to the problem. The difference between these approaches compared to alternatives, such as the eXtended Finite Element Method (X-FEM), is that the current proposal attempts to preserve the global matrix graph in order to improve performance. The first two alternatives comprise an enrichment of the Finite Element (FE) space obtained through the addition of some new local degrees of freedom to allow capturing discontinuities within the element. The new degrees of freedom are statically condensed prior to assembly, so that the graph of the final system is not changed. The third approach is based on the use of modified FE-shape functions that substitute the standard ones on the cut elements. The imposition of both Neumann and Dirichlet boundary conditions is considered at the embedded interface. The results of all the proposed methods are then compared with a reference solution obtained using the standard FE on a mesh containing the actual discontinuity.

The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-017-1382-7]]>

DOI: 10.13140/RG.2.1.1079.8561

Date of publication: 2015

Abstract:

Designing large ultra-lightweight structures within a fluid flow, such as inflatable hangars in an atmospheric environment, requires an analysis of the naturally occurring fluid-structure interaction (FSI). To this end multidisciplinary simulation techniques may be used. The latter, though, have to be capable of dealing with complex shapes and large deformations as well as challenging phenomena like wrinkling or folding of the structure. To overcome such problems the method of embedded domains may be used. In this work we discuss a new solution procedure for FSI analyses based on the method of embedded domains. In doing so, we are in particular answering the questions: How to track the interface in the embedded approach, how does the subsequent solution procedure look like and how does both compare to the well-known Arbitrary-Lagrangian-Eulerian (ALE) approach? In this context a level set technique as well as different mapping and mesh-updating strategies are developed and evaluated. Furthermore the solution procedure of a completely embedded FSI analysis is established and tested using different small- and large-scale examples. All results are finally compared to results from an ALE approach. It is shown that the embedded approach offers a powerful and robust alternative in terms of the FSI analysis of ultra-lightweight structures with complex shapes and large deformations. With regard to the solution accuracy, however, clear restrictions are elaborated.]]>

International Conference on Computacional Methods for Coupled Problems in Science and Engineering

p. 1

Presentation's date: 2015

Abstract:

The simulation of Fluid Structure Interaction (FSI) problems requires by its very nature taking into account relevant displacements of solids within a fluid domain. While “small” deformations can be conveniently represented by Arbitrary Lagrangian Eulerian (ALE) techniques, such approaches fail when facing large deformations. One possible solution is the use of “Embedded Solvers” which essentially consist in embedding an approximation of the geometry within the fluid discretization so that such information can be taken into account while solving the fluid problem. Current work focuses on the implementation of one of such Embedded approaches in the context of Variational Multi Scale (VMS) techniques. We will show how this technique can be employed to perform effectively fully coupled LES-like simulations. The method is completed by the use of the parallel adaptive refinement strategy described in [1]. The method is evaluated in application to a real deformable structure for which experimental results are available.]]>

Abstract:

The importance of advanced simulation to the competitiveness of both large and small companies is well established. The principal objective of Fortissimo is to enable European manufacturing, particularly small to medium enterprises (SMEs), to benefit from the efficiency and competitive advantage inherent in the use of simulation. However, the simulation of, for example, high-pressure gas cylinders, the moulding of plastics or the thermodynamic properties of hazardous materials requires enormous computing power and specialised software tools and services. Generally, large companies, which have a greater pool of skills and resources, find access to advanced simulation easier than SMEs which can neither afford expensive High Performance Computing equipment nor the licensing cost for the relevant tools. This means that SMEs are not able to take advantage of advanced simulation, even though it can clearly make them more competitive. The goal of Fortissimo is to overcome this impasse through the provision of simulation services running on a cloud infrastructure making use of High Performance Computing systems also making appropriate skills and tools available in a distributed, internet-based environment.\n\nFortissimo will make advanced simulation more easily accessible, particularly to SMEs, through the realisation of a 'one-stop shop' where hardware, expertise, applications, visualisation and tools will be easily available and affordable on a pay-per-use basis. In doing this it will create and demonstrate a sustainable commercial ecosystem where actors at all levels in the value chain can realise sufficient commercial benefit to enable that ecosystem to persist independently of EU funding and continue to provide affordable services to manufacturing industry, particularly SMEs.\n\nFortissimo will be driven by end-user requirements where (~50) business-relevant application experiments will be used to develop, test and demonstrate both the infrastructure and the 'one-stop pay-per-use shop'. The project participants represent all actors in the value chain. Not only will Fortissimo contribute to the increased competitiveness of European manufacturing industry through the innovative infrastructure that it will develop and test, but it will create commercial opportunities for European Independent Software Vendors, as well as for service and High Performance Computing infrastructure providers, through the creation of a new market for their products and services. Fortissimo places considerable emphasis on the exploitation of opportunities at all levels of the value chain ranging from the end-user to the High Performance Computing infrastructure provider.\n\nFortissimo involves 1,132 months of effort, a total cost of €21.7m and EC funding of €16m over a duration of three years, commensurate with achieving its ambitious goals.]]>

World Congress on Computational Mechanics, European Congress on Computational Mechanics, European Congress on Computational Fluid Dynamics

p. 1

Presentation's date: 2014-07

Abstract:

The industrial simulation is observing a considerable increment in the size and complexity of the problems. This trend demands more computational resource and also more robustness of the algorithms. The first issue requires an efficient use of hardware and parallelization and the latter can be address by embedded methods. In this work we present efficient parallel algorithms for searching the embedded objects, assigning the in and out color, calculating the distance function and interpolate variables. The first part of the work is dedicated to the data structures which are used to find the intersected elements and interpolating the results. The efficiency of the embedded method depends highly to this selection especially when the structure moves and so the cut elements and distances are changing. In the second part the coloring algorithm which is used to define the inside and outside for the embedded elements is described. This part is completed with the parallelization of the method. The algorithm is based on ray casting [1] technique which is customized for using with embedding methods and also especial cases like shells and memberanes. Finally the calculation of the distance will be described. The proposed algorithm comes as an extension to the coloring algorithm which propagates the exact distances through the fluid while performing the ray casting process. In this way the algorithm reduces considerably its computational task.]]>

European Conference on Computational Mechanics

Presentation's date: 2014-07

World Congress on Computational Mechanics, European Congress on Computational Mechanics, European Congress on Computational Fluid Dynamics

p. 1-2

Presentation's date: 2014-07

International Symposium on Computational Wind Engineering

p. 354-355

Presentation's date: 2014-06

DOI: 10.1007/978-3-319-06136-8

Date of publication: 2014

Abstract:

This book presents and discusses mathematical models, numerical methods and computational techniques used for solving coupled problems in science and engineering. It takes a step forward in the formulation and solution of real-life problems with a multidisciplinary vision, accounting for all of the complex couplings involved in the physical description. Simulation of multifaceted physics problems is a common task in applied research and industry. Often a suitable solver is built by connecting together several single-aspect solvers into a network. In this book, research in various fields was selected for consideration: adaptive methodology for multi-physics solvers, multi-physics phenomena and coupled-field solutions, leading to computationally intensive structural analysis. The strategies which are used to keep these problems computationally affordable are of special interest, and make this an essential book.]]>

Computers and fluids

Vol. 80, num. 1, p. 301-309

DOI: 10.1016/j.compfluid.2012.02.004

Date of publication: 2013-07-10

Abstract:

Creating a highly parallelizable code is a challenge specially for Distributed Memory Machines (DMMs). Moreover, algorithms and data structures suitable for these platforms can be very different from the ones used in serial code. For this reason, many programmers in the field prefer to start their own code from scratch. However, for an already existing framework supported by a long-time expertise the idea of transformation becomes attractive in order to reuse the effort done during years of development. In this presentation we explain how a relatively complex framework but with modular structure can be prepared for high performance computing with minimum modification. Kratos Multi-Physics [1] is an open source generic multi-disciplinary platform for solution of coupled problems consist of fluid, structure, thermal and electromagnetic fields. The parallelization of this framework is performed with objective of enforcing the less possible changes to its different solver modules and encapsulate the changes as much as possible in its common kernel. This objective is achieved thanks to the Kratos design and also innovative way of dealing with data transfers for a multi-disciplinary code. This work is completed by the migration of the framework from the 86× architecture to the Marenostrum Supercomputing platform. The migration has been verified by a set of benchmarks which show high scalability, from which we present the Telescope problem in this paper.

Creating a highly parallelizable code is a challenge specially for distributed memory machines (DMMs). Moreover, algorithms and data structures suitable for these platforms can be very different from the ones used in serial code. For this reason, many programmers in the field prefer to start their own code from scratch. However, for an already existing framework supported by a long-time expertise the idea of transformation becomes attractive in order to reuse the effort done during years of development. In this presentation we explain how a relatively complex framework but with modular structure can be prepared for high performance computing with minimum modification. Kratos Multi-Physics [1] is an open source generic multi-disciplinary platform for solution of coupled problems consist of fluid, structure, thermal and electromagnetic fields. The parallelization of this framework is performed with objective of enforcing the less possible changes to its different solver modules and encapsulate the changes as much as possible in its common kernel. This objective is achieved thanks to the Kratos design and also innovative way of dealing with data transfers for a multi-disciplinary code. This work is completed by the migration of the framework from the x86 architecture to the Marenostrum Supercomputing platform. The migration has been verified by a set of benchmarks which show high scalability, from which we present the Telescope problem in this paper.]]>

Computers and fluids

Vol. 80, p. 342-355

DOI: 10.1016/j.compfluid.2012.01.023

Date of publication: 2013-07

Abstract:

The present article describes a simple element-driven strategy for the conforming refinement of simplicial finite element meshes in a distributed environment. The proposed algorithm is effective both for local adaptive refinement and for the division of all the elements within an existing mesh. We aim to provide sufficient detail to allow the practical implementation of the algorithm, which can be coded with minimal effort provided that a distributed linear algebra library is available. The proposed refinement strategy is composed of three basic components: a global splitting strategy, an elemental splitting procedure and an error estimation technique, which are combined so to guarantee obtaining a conformant refined mesh. A number of benchmark examples show the capabilities of the proposed method. Error is estimated for the incompressible fluid-flow benchmarks using a novel indicator based on the computation of the sub-scale velocity.

The present article describes a simple element-driven strategy for the conforming refinement of simplicial finite element meshes in a distributed environment. The proposed algorithm is effective both for local adaptive refinement and for the division of all the elements within an existing mesh. We aim to provide sufficient detail to allow the practical implementation of the algorithm, which can be coded with minimal effort provided that a distributed linear algebra library is available. The proposed refinement strategy is composed of three basic components: a global splitting strategy, an elemental splitting procedure and an error estimation technique, which are combined so to guarantee obtaining a conformant refined mesh. A number of benchmark examples show the capabilities of the proposed method. Error is estimated for the incompressible fluid-flow benchmarks using a novel indicator based on the computation of the sub-scale velocity.]]>

International journal for numerical methods in fluids

Vol. 71, num. 6, p. 687-716

DOI: 10.1002/fld.3680

Date of publication: 2013-02

Abstract:

We present an efficient technique for the solution of free surface flow problems using level set and a parallel edge-based finite elementmethod. An unstructured semi-explicit solution scheme is proposed. A custom data structure, obtained by blending node-based and edge-based approaches is presented so to allow a good parallel performance. In addition to standard velocity extrapolation (for the convection of the level set function), an explicit extrapolation of the pressure field is performed in order to impose both the pressure boundary condition and the volume conservation. The latter is also improved with a modification of the divergence free constrain. The method is shown to allow an efficient solution of both simple benchmark cases and complex industrial examples.]]>

International Workshop on Statistical Atlases and Computational Models of the Heart

p. 26-33

DOI: 10.1007/978-3-642-36961-2_4

Presentation's date: 2012-10

Abstract:

Aortic Coarctation is a congenital constriction of the aorta that increases blood pressure above the constriction and hinders the flow below it. Based on a 3D surface mesh of a moderate thoracic coarctation, a high quality volume mesh is created using an optimal tetrahedral aspect ratio for whole domain. In order to quantify the severity of this constriction, a coupled 1D lumped-parameter/3D CFD approach is used to calculate the pressure drop through the coarctation. The CFD computation is performed assuming that the arterial wall is rigid and the blood is considered a homogeneous Newtonian fluid with density r = 0.001 gr/mm3 and a dynamic viscosity m = 0.004 gr/mm/sec in laminar flow. The boundary conditions of the 3D model (inlet and outlet conditions) have been calculated using a 1D model. Parallelization procedures will be used in order to increase the performance of the CFD calculations

Aortic Coarctation is a congenital constriction of the aorta that increases blood pressure above the constriction and hinders the flow below it. Based on a 3D surface mesh of a moderate thoracic coarctation, a high quality volume mesh is created using an optimal tetrahedral aspect ratio for whole domain. In order to quantify the severity of this constriction, a coupled 1D lumped-parameter/3D CFD approach is used to calculate the pressure drop through the coarctation. The CFD computation is performed assuming that the arterial wall is rigid and the blood is considered a homogeneous Newtonian fluid with density r = 0.001 gr/mm3 and a dynamic viscosity m = 0.004 gr/mm/sec in laminar flow. The boundary conditions of the 3D model (inlet and outlet conditions) have been calculated using a 1D model. Parallelization procedures will be used in order to increase the performance of the CFD calculations.]]>

European Congress on Computational Methods in Applied Sciences and Engineering

Presentation's date: 2012-09-12

International journal for numerical methods in engineering

Vol. 89, num. 13, p. 1635-1651

DOI: 10.1002/nme.3302

Date of publication: 2012-03

International Conference on Textile Composites and Inflatable Structures

p. 1

Presentation's date: 2011-10-06

International Conference on Parallel Computational Fluid Dynamics

p. 1-5

Presentation's date: 2011-05-17

Abstract:

Creating a highly parallelizable code is a challenge and development for distributed memory machines (DMMs) can be very different form developing a serial code in term of algorithms and structure. For this reason, many developers in the field prefer to develop their own code from scratch. However, for an already existing framework with large development background the idea of transformation becomes attractive in order to reuse the effort done during years of development. In this presentation we explain how a relatively complex framework but with modular structure can be prepared for high performance computing with minimum modification. Kratos Multi-Physics [1] is an open source generic multi-disciplinary platform for solution of coupled problems consist of fluid, structure, thermal and electromagnetic fields. The parallelization of this framework is performed with objective of enforcing the less possible changes to its different solver modules and encapsulate the changes as much as possible in its common kernel. This objective is achieved thanks to the Kratos design and also innovative way of dealing with data transfers for a multi-disciplinary code. This work is completed by the migration of the framework from the x86 architecture to the Marenostrum Supercomputing platform. The migration has been verified by a set of benchmarks which show very good scalability, from which we present the Telescope problem in this paper.]]>

International Conference on Parallel Computational Fluid Dynamics

p. 1-5

Presentation's date: 2011-05

Abstract:

Dealing with large simulation is a growing challenge. Ideally for the wellparallelized software prepared for high performance, the problem solving capability depends on the available hardware resources. But in practice there are several technical details which reduce the scalability of the system and prevent the effective use of such a software for large problems. In this work we describe solutions implemented in order to obtain a scalable system to solve and visualize large scale problems. The present work is based on Kratos MutliPhysics [1] framework in combination with GiD [2] pre and post processor. The applied techniques are verified by CFD simulation and visualization of a wind tunnel problem with more than 100 millions of elements in our in-hose cluster in CIMNE.

Dealing with large simulation is a growing challenge. Ideally for the wellparallelized software prepared for high performance, the problem solving capability depends on the available hardware resources. But in practice there are several technical details which reduce the scalability of the system and prevent the effective use of such a software for large problems. In this work we describe solutions implemented in order to obtain a scalable system to solve and visualize large scale problems. The present work is based on Kratos MutliPhysics [1] framework in combination with GiD [2] pre and post processor. The applied techniques are verified by CFD simulation and visualization of a wind tunnel problem with more than 100 millions of elements in our in-hose cluster in CIMNE.]]>

International Conference on Parallel, Distributed, Grid and Cloud Computing for Engineering

DOI: 10.4203/ccp.95.56

Presentation's date: 2011-04

Abstract:

In this paper, we implement a parallel solver for the incompressible Navier-Stokes equations using the finite element method. We compare two different parallel programming strategies, OpenMP, which is based on a shared memory model, and MPI, which uses a distributed memory model. The incompressible Navier-Stokes equations constitute a transient, non-linear system which has well-known stability issues when the standard Galerkin finite element discretization is used. This means that some treatment will be required before we can implement their solution. We implement a solution strategy based on algebraic subgrid scale stabilization and a generalized Newmark method for iteration in time. This results in a linear system which, unfortunately, can be poorly scaled, as it involves both velocity and pressure degrees of freedom. As a result, the system is difficult to solve using iterative methods, which are preferable for large problems. To avoid this situation, we have used an uncoupling approach based on a Schur complement formulation for the pressure, which results in a scheme similar to that of fractional step methods. Two different implementations of this method, one using OpenMP and another based on MPI through the Trilinos library, have been used to solve Ahmed's body, a standard benchmark problem in turbulence which simulates the flow around a bus-like object. Both implementations are compared with each other and with a scalar run of the same example, with emphasis on performance gains provided by the parallelization. In this sense, we have found that the time benefit obtained from the parallelization is affected by the hardware where the simulations are run. In our case, this imposes us two clear restrictions: OpenMP is limited to processors that can access some shared memory, and in general the performance is affected by competition between the processes for memory access, which seems to be an important bottleneck in our test system. In general, it can be said that, when choosing an approach to parallelization, it is important to take into account the available hardware.]]>

Archives of computational methods in engineering

Vol. 17, num. 3, p. 253-297

DOI: 10.1007/s11831-010-9045-2

Date of publication: 2010-09

Abstract:

The objective of this work is to describe the design and implementation of a framework for building multi-disciplinary finite element programs. The main goals are generality, reusability, extendibility, good performance and memory efficiency. Another objective is preparing the code structure for team development to ensure the easy collaboration of experts in different fields in the development of multi-disciplinary applications. Kratos, the framework described in this work, contains several tools for the easy implementation of finite element applications and also provides a common platform for the natural interaction of different applications. To achieve this, an innovative variable base interface is designed and implemented. This interface is used at different levels of abstraction and showed to be very clear and extendible. A very efficient and flexible data structure and an extensible IO are created to overcome difficulties in dealing with multi-disciplinary problems. Several other concepts in existing works are also collected and adapted to coupled problems. The use of an interpreter, of different data layouts and variable number of dofs per node are examples of such approach. In order to minimize the possible conflicts arising in the development, a kernel and application approach is used. The code is structured in layers to reflect the working space of developers with different fields of expertise. Details are given on the approach chosen to increase performance and efficiency. Examples of application of Kratos to different multidisciplinary problems are presented in order to demonstrate the applicability and efficiency of the new object oriented environment.]]>

Archives of computational methods in engineering

Vol. 17, num. 3, p. 253-297

DOI: 10.1007/s11831-010-9045-2

Date of publication: 2010-09

Abstract:

'The simultaneous presence of several different fluids in external or internal flows is found in daily life, environment and numerous industrial processes. These types of flows are termed multi-fluid flows. Examples are gas-liquid transport, crude oil recovery, spray cans, sediment transport in rivers, pollutant transport in the atmosphere, cloud formation, fuel injection in engines, bubble column reactors and spray driers for food processing, to name only a few. Real time computational mechanics (RTCM) aims to developing computational systems to solve problems which must produce their results within short time intervals. Examples of real-time systems include flight control programs, patient monitoring; nuclear plants controls, industrial processing and prevention of risk. RTCM systems are having an ever increasing impact on the quality of human life. The objective of the project is to develop new formal approaches and computational methods based on innovative RTCM procedures for building accurate and robust quasi-real time computer codes applicable to solve multi-fluid engineering problems. In the project we will develop and validate new computational fluid dynamic techniques based on innovative particle methods, new time integration schemes allowing large time steps, reduction methods, GPUs and parallel processing to reach acceptable results for multi-fluid problems in quasi-real time. The main outcome of the REALTIME project will be a collection of methods and codes to predict and control in quasi-real time different problems involving natural and human induced hazards such as risky industrial processes, fire spread, critical atmospheric situations or patients monitoring situations in which the security or human life depends of a response in real time.']]>

World Congress on Computational Mechanis and European Congres on Computational Methods in Applied Sciences and Engineering

p. 1

Presentation's date: 2008-06

World Congress on Computational Mechanis and European Congres on Computational Methods in Applied Sciences and Engineering

p. 1

Presentation's date: 2008-06

Abstract:

The simulation of the interaction between light-weight structure and the flow around them is a typical challenge in FSI. The range of application spans from large civil engineering structures to biological membranes interacting with the blood. Recent advances in the solver technology allow the defintion of partition strongly coupled approaches which retain the computational efficiency of the single field solvers preserving the stability of the overall problem. Current paper focuses on the application of a Fractional Step type approach to FSI and its application to light-weight membrane systems. The method, implemented in the multi-physic solver “Kratos” is validated on different “standard” test cases.]]>