Publications of Pablo Alarcon Soto
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See detailTopology optimization in OpenFOAM: how to define the maximum inverse permeability to consider manufacturing constraint
Alarcon Soto, Pablo ULiege; Duysinx, Pierre ULiege

Conference (2021, June)

Topology optimization in OpenFOAM: how to define the maximum inverse permeability to consider manufacturing constraint Proton-Exchange Membrane Fuel Cells (PEMFC) are systems that directly convert ... [more ▼]

Topology optimization in OpenFOAM: how to define the maximum inverse permeability to consider manufacturing constraint Proton-Exchange Membrane Fuel Cells (PEMFC) are systems that directly convert chemicals into electricity by means of an electro-chemical reaction between hydrogen and oxygen. Following the concerns related to climate change, Hydrogen PEMFC are a promising option to contribute to a decarbonized society. Nevertheless, to rival the Internal Combustion Engine (ICE), PEMFC shall decrease their manufacturing cost, increase their lifetime and their efficiency, among others. The INOXYPEM research project explores new designs of bipolar plates made of stamped coated steel. This work aims at increasing the efficiency of PEMFC by defining the channel network layout of bipolar plates using Fluid Flow Topology Optimization (FFTO) techniques, while simultaneously accounting for the manufacturing restrictions of the sheet metal forming process. We developed an in-house design environment that couples fluid simulations from OpenFOAM with Optimization Algorithms. The flow is simulated using the Incompressible Navier Stokes equations in steady-state condition. These equations are combined with Darcy’s law by means of a Brinkman penalization, resulting in a density-based method to perform the Topology Optimization. Our research addresses two of the main difficulties found in the topology optimization for fluid-based problems: Firstly, the vast majority of the related publications is performed using the finite element method (76% of all publications), whilst the number of publications that use the finite volume method (the preferred for computational fluid dynamics) reach a surprisingly low level of use of only 7% (the other 16% goes to the lattice Boltzmann method and 1% to particle-based methods). Our research is developed using the finite volume method with a continuous adjoint formulation for the sensitivity analysis. Secondly, when solving the modified Navier-Stokes equations, it’s necessary to define a maximum value for the inverse permeability that comes from the Brinkman penalization, which is the design variable in the problem (0 in the fluid zones and a large value in solid zone). This large value should be big enough to correctly penalize the velocity inside the solid regions, but not too big in order to avoid numerical problems. It’s common practice to either define a really big number by intuition or to define a value based on the Darcy number. However, when using the Darcy number, numerical simulations have shown that this method leads to highly-problem-dependent designs. Thus, our research proposes a new way of defining the maximum value of the inverse permeability based on the Reynolds number, principally because this is the main dimensionless number when working with the Incompressible Navier Stokes equations in steady-state condition. In summary, our in-house developed solver performs the minimization of the total pressure loss considering constraints over the volume. In order to reflect manufacturing restrictions of the steel forming process, constraints on the maximum size of the channels and the separation between them are also implemented. The main contributions brings closer the world of the topology optimization to the computational fluid dynamics by considering the nature of the working fluid (using the Reynolds number to define the inverse permeability) and also by using the finite volume method. [less ▲]

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See detailImposing minimum and maximum member size, minimum cavity size, and minimum separation distance between solid members in topology optimization
Fernandez Sanchez, Eduardo Felipe ULiege; Yang, Kai-ke; Koppen, Stijn et al

in Computer Methods in Applied Mechanics and Engineering (2020), 368

This paper focuses on density-based topology optimization and proposes a combined method to simultaneously impose Minimum length scale in the Solid phase (MinSolid), Minimum length scale in the Void phase ... [more ▼]

This paper focuses on density-based topology optimization and proposes a combined method to simultaneously impose Minimum length scale in the Solid phase (MinSolid), Minimum length scale in the Void phase (MinVoid) and Maximum length scale in the Solid phase (MaxSolid). MinSolid and MinVoid mean that the size of solid parts and cavities must be greater than the size of a prescribed circle or sphere. This is ensured through the robust design approach based on eroded, intermediate and dilated designs. MaxSolid seeks to restrict the formation of solid parts larger than a prescribed size, which is imposed through local volume restrictions. In the first part of this article, we show that by proportionally restricting the maximum size of the eroded, intermediate and dilated designs, it is possible to obtain optimized designs satisfying, simultaneously, MinSolid, MinVoid and MaxSolid. However, in spite of obtaining designs with crisp boundaries, some results can be difficult to manufacture due to the presence of multiple rounded cavities, which are introduced by the maximum size restriction with the sole purpose of avoiding thick solid members in the structure. To address this issue, in the second part of this article we propose a new geometric constraint that seeks to control the minimum separation distance between two solid members, also called the Minimum Gap (MinGap). Differently from MinVoid, MinGap introduces large void areas that do not necessarily have to be round. 2D and 3D test cases show that simultaneous control of MinSolid, MinVoid, MaxSolid and MinGap can be useful to improve the manufacturability of maximum size constrained designs. [less ▲]

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See detailMisalignment topology optimization with manufacturing constraints
Bauduin, Simon ULiege; Alarcon Soto, Pablo ULiege; Fernandez Sanchez, Eduardo Felipe ULiege et al

in Structural and Multidisciplinary Optimization (2020), 61(6), 2467-2480

This work aims at introducing misalignment response in the design of mechanical transmission components using topology optimization. Misalignment considerations can be of high importance for various ... [more ▼]

This work aims at introducing misalignment response in the design of mechanical transmission components using topology optimization. Misalignment considerations can be of high importance for various industrial applications as in gearbox or differential, where aligned axes are to be ensured during the usage of the part. Nevertheless, to the authors’ knowledge, no work so far implements such response in a topology optimization framework. In this contribution, misalignment between two spatial vectors is evaluated in various ways using trigonometry and vector functions. The misalignment is formulated through the spatial displacements of the constituent nodes of the objective vectors. The authors choose a formulation among other and implement the later in a 2D topology framework for further investigation on test cases. Issues such as material disconnection, non-discrete solutions or lack of engineering meaning are tackled along this work by the introduction of constraints and parametric studies. A performance test is achieved on a simplified gearbox transmission system to assess the performance between designs with or without misalignment considerations.Manufacturing constraints are introduced to improve the manufacturability of the optimized solution. Subsequently a 3D test case further highlights the usefulness of this contribution. [less ▲]

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See detailAn aggregation strategy of maximum size constraints in density-based topology optimization
Fernandez Sanchez, Eduardo Felipe ULiege; Collet, Maxime; Alarcon Soto, Pablo ULiege et al

in Structural and Multidisciplinary Optimization (2019)

The maximum size constraint restricts the amount of material within a test region in each point of the design domain, leading to a highly constrained problem. In this work, the local constraints are ... [more ▼]

The maximum size constraint restricts the amount of material within a test region in each point of the design domain, leading to a highly constrained problem. In this work, the local constraints are gathered into a single one using aggregation functions. The challenge of this task is presented in detail, as well as the proposed strategy to address it. The latter is validated on different test problems as the compliance minimization, the minimum thermal compliance, and the compliant mechanism design. These are implemented in the MATLAB software for 2D design domains. As final validation, a 3D compliance minimization problem is also shown. The study includes two well-known aggregation functions, p-mean and p-norm. The comparison of these functions allows a deeper understanding about their behavior. For example, it is shown that they are strongly dependent on the distribution and amount of data. In addition, a new test region is proposed for the maximum size constraint which, in 2D, is a ring instead of a circle around the element under analysis. This slightly change reduces the introduction of holes in the optimized designs, which can contribute to improve manufacturability of maximum size–constrained components. [less ▲]

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See detailAn overhang constraint adaptable to a proper building orientation
Fernandez Sanchez, Eduardo Felipe ULiege; Yang, Kaike; Koutla, Ioanna ULiege et al

in World Congress of Structural and Multidisciplinary Optimization (WCSMO13), May 20-24, 2019, Beijing, China. (2019, May 20)

In additive manufacturing processes, the critical overhang angle of downward facing surfaces limits printability of parts. To consider this limitation of the process in topology optimization, several ... [more ▼]

In additive manufacturing processes, the critical overhang angle of downward facing surfaces limits printability of parts. To consider this limitation of the process in topology optimization, several approaches have been proposed in the literature. Most of them operate with a user-defined building direction, thus, if the orientation is not appropriate, structural performance could be drastically compromised. This work aims to reduce the dependence of the user on the definition of the building direction. We make use of a gradient-based constraint due to the low computation cost it demands in comparison to layer-by-layer approaches. The method is demonstrated on 2D and 3D examples. [less ▲]

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See detailImposing Manufacturing Constraints in Topological Optimization of 2D Fuel Cell flow problems using OpenFOAM
Alarcon Soto, Pablo ULiege; Fernandez Sanchez, Eduardo Felipe ULiege; Bauduin, Simon ULiege et al

in Proceedings of the 13th World Congress of Structural and Multidisciplinary Optimization (WCSMO-13) (2019, May)

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See detailMisalignment topology optimization with manufacturing constraints
Bauduin, Simon ULiege; Alarcon Soto, Pablo ULiege; Fernandez Sanchez, Eduardo Felipe ULiege et al

Conference (2019, May)

Topology optimization design problems aims at the minimization of an objective function while satisfying various constraints. Since Bendsøe and Kikuchi (1988) topology optimization has mostly been based ... [more ▼]

Topology optimization design problems aims at the minimization of an objective function while satisfying various constraints. Since Bendsøe and Kikuchi (1988) topology optimization has mostly been based on “compliance formulation” as it provides solutions where the displacements are globally controlled. However, this formulation doesn’t take into account special design requirements over local displacements or even relative displacements such as the misalignment between two gear axes. This point is of paramount importance to achieve the best efficiency in many mechanical transmission devices. Although critical in practical engineering designs, this question is especially challenging as very few contributions exist on the subject. Coupling topology optimization with the misalignment minimization can provide promising results once right formulation can be identified. At first, the misalignment can be expressed in various ways. A few formulations have been tested on a simple case study composed of two gear axes to be align. This allowed us to choose a promising expression for the misalignment and furthermore to investigate its efficiency on 2D test cases consisting of a simplified one-stage-reduction box and a simplified differential. The objective is to minimize the misalignment between two beams representing the gears engaged with each other. The formulations have been implemented in our in-house MATLAB code. Different issues have been highlighted and solved. The first basic implementation leads to unclear optimized material distributions as well as non-converged solutions. Optimization results have been investigated and new design formulations have been elaborated to tackle the various issues. We have showed that imposing a constraint on the measure of non-discreteness is able to enforce black-and-white solution with actual engineering meaning. The second issue is a possible disconnection of the structure coming from an ill-posed nature of the optimization problem as only local constraints are taken into account and no global performance of the problem is required. This issue is partly tackled by imposing a constraint on the measure of discreteness, but another natural way is to introduce an additional constraint on the global compliance of the component. According to our numerical experiments, the proposed formulation is able to yield optimized solutions that make sense from an engineering point of view in 2D but also in 3D applications. Presently we are also introducing manufacturing constraints such as minimum/maximum size and minimum gap to further improve the manufacturability of the optimized solutions. The 3D academic torsion problem (see below) illustrates the effectiveness of the proposed formulation including misalignment in a 3D case. The presentation will be illustrated with several industrial applications. [less ▲]

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See detailCritical Plane approach for fatigue resistance using stress-based topology optimization
Collet, Maxime ULiege; Bauduin, Simon ULiege; Fernandez Sanchez, Eduardo Felipe ULiege et al

Conference (2018, September 17)

Fatigue is responsible for almost 80% of the overall breakages in mechanical components (Oest(2017)). Such a failure phenomenon must be prevented as soon as the early stage of design. Since the seminal ... [more ▼]

Fatigue is responsible for almost 80% of the overall breakages in mechanical components (Oest(2017)). Such a failure phenomenon must be prevented as soon as the early stage of design. Since the seminal works by Augut Wöhler, see Schültz(1996), the literature counts various methods able to prevent fatigue failure (Schijve(2003)). In the automotive industry, the components undergo a high number of cycles leading to consider the stresses as variables into the fatigue criteria. Topology optimization has become a valuable tool used to propose preliminary designs as attested by several commercial software on the market. Combining fatigue design with a stress-based topology optimization procedure is therefore natural. In this work, the coupling of the Dang Van criterion (Dang Van et al(1989), Dang Van(2010)) within a topology optimization code is investigated to provide fatigue resistant layouts. The choice of the Dang Van criterion is encouraged by its wide usage in the automotive industry (Koutiri(2011)). The former is based on the concept of critical plane in the vicinity of which plastic yielding occurs. With the hypothesis of reaching the elastic shakedown state, the criterion establishes that crack initiation is prevented if the microscopic stress state remains below a prescribed threshold. Following the framework proposed by Dang Van (Dang Van(1989)), the fatigue failure procedure is introduced into a density-based topology optimization code embedding stress constraints. The first step of the procedure is to construct the microscopic stress using a regular finite element analysis and evaluate a damage value in the sense of Dang Van. A sub-optimization routine is necessary to solve a min-max problem in order to find the residual stress tensor to construct the microscopic stresses (Mandel et al(1977), Bernasconi(2002)). This sub-optimization might be time consuming and must be dealt with care. In a second step, this work shows how the fatigue resistance procedure is implemented into a density-based topology optimization using stress constraints and in particular how the sensitivity analysis is performed using the adjoint approach (Tortorelli and Michaleris(1994)). The optimization process is carried out with the Method of Moving Assymptotes (Svanberg(1987)) along the qp-relaxation (Bruggi(2008)) to overcome the singularity phenomenon of the stress constraints. The proposed optimization framework is evaluated in terms of its numerical performances and is compared to classical results obtained by a regular stress-based topology optimization on several benchmarks. [less ▲]

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See detailConstraints Aggregation in Topology Optimization
Fernandez Sanchez, Eduardo Felipe ULiege; Collet, Maxime ULiege; Bauduin, Simon ULiege et al

Scientific conference (2018, September 17)

A vast amount of the methods that address local design requirements introduce a wide set of constraints within the optimization problem. This local formulation calls for the use of aggregation functions ... [more ▼]

A vast amount of the methods that address local design requirements introduce a wide set of constraints within the optimization problem. This local formulation calls for the use of aggregation functions in order to avoid the computational burden on the optimizer. This step of collecting the constraints within a few representative ones seems as a simple implementation detail coming at the final stage of the formulation. Therefore it is often neglected in the discussion. However if this aggregation step is not well treated the success of the whole method may be compromised, and in many cases the simplest part of the constraint becomes time-consuming or even, the hardest point of the formulation. Aggregation functions are built to be smooth and differentiable approximations of the max function. In addition their sensitivity information should be smooth in order to be used in efficient continuous optimization algorithms. They have also to catch accurately the most critical constraints to mimic the locally constrained problem. The classical application is in the field of stress constraints, where a large amount of contributions have been made on the subject. Most of the research contributes with new aggregation techniques, which are adapted to the context of topology optimization with stress constraints. However, to tailor high quality global manufacturing constraints, we need to make further progress in the understanding of the aggregation functions when used in the topology optimization. To this end, we perform a deep theoretical investigation and a quantitative numerical assessment of the behavior of these functions when being used in different formulations of manufacturing and mechanical constraints. Specifically, we focus the study on p-mean and p–norm functions within the framework of density methods. We include in the analysis methods to introduce: i) maximum size control, ii) minimum gap between solid members, iii) minimum size, iii) overhang control for additive manufacturing and iv) stress constraints. Some important observations obtained from this study are: p-norm depends on the amount of data that is being aggregated, making it more unstable under mesh refinement. On the other hand, p-mean is less dependent on mesh modifications but it is likely to produce results that do not satisfy every local constraint. In addition, by looking at the sensitivities it is possible to have an insight of the nonlinearity of a method. [less ▲]

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See detailImposing minimum gap distance in topology optimization through maximum size constraints
Fernandez Sanchez, Eduardo Felipe ULiege; Collet, Maxime ULiege; Bauduin, Simon ULiege et al

Conference (2018, May 02)

Maximum size constraints in topology optimization increase the complexity of the designs. It introduces extra channels and cavities that hinder the manufacturability of the component. In this work the ... [more ▼]

Maximum size constraints in topology optimization increase the complexity of the designs. It introduces extra channels and cavities that hinder the manufacturability of the component. In this work the show some contributions to improve the manufacturability of designs that include a maximum size control in topology optimization. [less ▲]

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See detailOVERHANGING CONSTRAINTS IN ADDITIVE MANUFACTURINGUSING TWODIFFERENT TOOLS
Bauduin, Simon ULiege; Collet, Maxime; Fernandez Sanchez, Eduardo Felipe ULiege et al

Poster (2018)

As the manufacturing methods undergo huge evolution thanks to the emergence of additive manufacturing techniques, the interest of a coupling with the topology optimization problem is highly demanded by ... [more ▼]

As the manufacturing methods undergo huge evolution thanks to the emergence of additive manufacturing techniques, the interest of a coupling with the topology optimization problem is highly demanded by industries (such as automotive and aerospace). The challenges are still numerous around such coupling and this work focuses on the overhanging problem related to the metalic additive manufacturing technics(LBM and EBM). To tackle the problem various research directions are investigated and compared to another. [less ▲]

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See detailMISALIGNMENT TOPOLOGY OPTMIZATION
Bauduin, Simon ULiege; Alarcon Soto, Pablo ULiege; Fernandez Sanchez, Eduardo Felipe ULiege et al

Conference (2018)

Topology optimization problems aims at the minimization of an objective function while satisfying various constraints. This objective function has been based on “compliance formulation” since Bendsøe and ... [more ▼]

Topology optimization problems aims at the minimization of an objective function while satisfying various constraints. This objective function has been based on “compliance formulation” since Bendsøe and Kikuchi (1988) as it provides solutions where the displacements are globally controlled. However, this formulation doesn’t take into account special needs over local displacements or even relative displacements such as the misalignment between two gears. This point is of paramount importance to achieve the best efficiency. Although critical, this domain is especially challenging as very few contributions exist on the subject. Coupling topology optimization with the misalignment minimization can provide promising results once chosen the right formulation. The misalignment can be expressed in various ways. In this work a small amount of formulations were tested on a simple case study composed of two axes to be align. This allowed us to choose a promising expression for the misalignment and furthermore to investigate its efficiency on a 2D problem. The former consists of a box clamped on both sides where a load is applied in its center. The objective is to minimize the misalignment between two horizontal bars located at the middle of each clamped edges. This optimization problem was implemented in our in-house MATLAB code. Different issues were already highlighted during this simple test. The first one was an unclear optimized material distribution as well as a non-converged solution. This typical result of topology optimization has been investigated throughout the years and interesting methods were developed to tackle this issue. For our case study we have chosen to impose a constraint on the measure of discreteness in our optimization formulation to impose a more black-and-white solution with actual engineering meaning. The second issue was a disconnection of the structure coming from an ill-posed optimization formulation as only local constraints are taken into account and no global performance of the problem is required. This issue is furthermore emphasized by imposing a constraint on the measure of discreteness. Thusly a natural way to deal with it is to introduce a constraint on the global compliance of the solution. According to our tests we obtained interesting and engineering meaningful solutions on a 2D case. Our formulation of misalignment and our side constraints were furthermore also tested on a 3D torsion problem. [less ▲]

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See detailTopology optimization of mechanical components fabricated by additive manufacturing for a Shell Eco Marathon vehicle
Alarcon Soto, Pablo ULiege; Collet, Maxime ULiege; Bauduin, Simon ULiege et al

Conference (2017, June 07)

Since 2004, a team of students and researchers of University of Liege takes part to the Shell Eco Marathon race with a lightweight electric vehicle. The goal of this pedagogical project is to design ... [more ▼]

Since 2004, a team of students and researchers of University of Liege takes part to the Shell Eco Marathon race with a lightweight electric vehicle. The goal of this pedagogical project is to design, fabricate and operate a vehicle exhibiting the least energy consumption. A key factor to reduce the energy consumption is to minimize the vehicle mass. Besides the body structure made of CRFP, engineers have also to focus on the weight reduction of any mechanical parts of the powertrain, transmission and of rolling gear. The combination of topology optimization with additive manufacturing techniques allows to propose innovative designs exhibiting a high performance to weight ratio. Topology optimized designs are often characterized by a high geometrical complexity that is not possible to manufacture without 3D printing. This work presents the CAE design methodology that was developed to combine topology and shape optimization with 3d printing manufacturing. Novel developments both in shape and topology optimization have also been realized for the specific character of these components. The design methodology is illustrated with several applications of components of our new Eco Marathon prototype. They include a support for electric traction motors and different torque arms of the steering mechanism to be implemented in the new 2017 vehicle. The presentation is going to show the different design steps from the specifications and the formulation of the design problem to the 3D-printing of the parts: the topology optimization, interpretation and CAD reconstruction, shape optimization and detailed finite element verification of the solution. The optimization is performed thanks to the commercial software NX-TOPOL and the final CAD design is reconstructed in the CATIA environment software after a smoothing procedure in the NX-CAD environment. We show that the final design can be 3D-printed and a comparison with a design produced using traditional design approach is provided. [less ▲]

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