References of "Boman, Romain"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailOn the use of rhodium mirrors for optical diagnostics in ITER
Mertens, P.; Boman, Romain ULiege; Dickheuer, S. et al

in Fusion Engineering and Design (in press)

The first mirrors of optical diagnostics in ITER are exposed to high radiation and fluxes of particles which escape the plasma, in the order of 10 20 m −2 s −1 . At the position of the mirror, the flux ... [more ▼]

The first mirrors of optical diagnostics in ITER are exposed to high radiation and fluxes of particles which escape the plasma, in the order of 10 20 m −2 s −1 . At the position of the mirror, the flux may still reach about 10 18 m −2 s −1 . First mirrors are thus the most vulnerable in-vessel optical components, being subject to erosion, esp. by fast charge-exchange neutrals, or to deposition of impurities at flux rates which can reach 0.05 nm/s. The material selected for the reflecting surface must combine a high optical reflectivity in a wide spectral range and a sufficient resistance to physical sputtering during normal operation and during mirror cleaning discharges, if any is installed. Rhodium ( 103 Rh) was identified early as a possible or even promising candidate. It combines several attractive properties, for instance a mass which leads in most cases to low sputtering yields together with an optical reflectance (R Rh ≈75%) which is much higher than of some other options. R Rh is insensitive to large temperature changes. Rhodium is fairly inert and its low oxidation is an appreciable advantage in case of steam ingress events. The core-plasma CXRS diagnostic in ITER (UPP 3) have now turned to Rh as a baseline. The aim is to procure monocrystalline rhodium (SC-Rh) to mitigate the increase of the diffuse reflection with the damage due to physical sputtering. © 2019 Elsevier B.V. [less ▲]

Detailed reference viewed: 35 (9 ULiège)
Full Text
See detailElement activation strategy for Additive Manufacturing, based on the element deletion algorithm
Laruelle, Cédric ULiege; Boman, Romain ULiege; Papeleux, Luc ULiege et al

Poster (2019, May 27)

With the rise of Additive Manufacturing (AM) technologies in the industry, it is becoming more and more crucial to have a good understanding of those processes. This leads to a high need for the ... [more ▼]

With the rise of Additive Manufacturing (AM) technologies in the industry, it is becoming more and more crucial to have a good understanding of those processes. This leads to a high need for the implementation of a model that can accurately simulate such a process. The difficulties of simulating AM can come from multiple sources. Firstly, from the nature of the process. Indeed, it requires a large deformation thermo-mechanical simulation. Secondly, the modeling of the material law is complex. Lastly, the geometry of the process imposes a very fine discretization (layers can be as small as a few μm). This creates models that are very computationally costly. Moreover, the process requires altering the geometry of the model during simulations to model the addition of matter, which is a computational challenge by itself. This poster presents the implementation of a three-dimensional thermal Finite Element Analysis (FEA) of AM in the fully implicit in-house Finite Element code “Metafor”. The main focus of the work is on mesh management techniques. The method to activate elements during a simulation is adapted from the element deletion algorithm (erosion method) implemented in Metafor in the scope of crack propagation. The final model is compared against literature results with a good agreement. [less ▲]

Detailed reference viewed: 21 (0 ULiège)
Full Text
See detailEfficient parametric computations using ensemble propagation for high dimensional finite element models
Liegeois, Kim ULiege; Boman, Romain ULiege; Phipps, Eric et al

Conference (2019, April 25)

Detailed reference viewed: 15 (2 ULiège)
Full Text
See detailEnsemble Propagation for Efficient Uncertainty Quantification of Mechanical Contact Problems
Liegeois, Kim ULiege; Boman, Romain ULiege; Phipps, Eric et al

Conference (2019, February 28)

Detailed reference viewed: 12 (4 ULiège)
See detailAdvances in cold rolling modeling at ULiège
Boemer, Dominik ULiege; Carretta, Yves; Boman, Romain ULiege et al

Scientific conference (2019, February 13)

Detailed reference viewed: 48 (12 ULiège)
Full Text
Peer Reviewed
See detailCUPyDO - An integrated Python environment for coupled fluid-structure simulations
Thomas, David ULiege; Cerquaglia, Marco Lucio ULiege; Boman, Romain ULiege et al

in Advances in Engineering Software (2019)

CUPyDO, a fluid-structure interaction (FSI) tool that couples existing independent fluid and solid solvers into a single synchronization and communication framework based on the Python language is ... [more ▼]

CUPyDO, a fluid-structure interaction (FSI) tool that couples existing independent fluid and solid solvers into a single synchronization and communication framework based on the Python language is presented. Each coupled solver has to be wrapped in a Python layer in order to embed their functionalities (usually written in a compiled language) into a Python object, that is called and used by the coupler. Thus a staggered strong coupling can be achieved for time-dependent FSI problems such as aeroelastic flutter, vortex-induced vibrations (VIV) or conjugate heat transfer (CHT). The synchronization between the solvers is performed with the predictive block-Gauss-Seidel algorithm with dynamic under-relaxation. The tool is capable of treating non-matching meshes between the fluid and structure domains and is optimized to work in parallel using Message Passing Interface (MPI). The implementation of CUPyDO is described and its capabilities are demonstrated on typical validation cases. The open-source code SU2 is used to solve the fluid equations while the solid equations are solved either by a simple rigid body integrator or by in-house linear/nonlinear Finite Element codes (GetDP/Metafor). First, the modularity of the coupling as well as its ease of use is highlighted and then the accuracy of the results is demonstrated. [less ▲]

Detailed reference viewed: 427 (109 ULiège)
Full Text
Peer Reviewed
See detailComputational methods in welding and additive manufacturing
Bruchon, Julien; Bergheau, Jean-Michel; Boman, Romain ULiege

in Comptes Rendus Mécanique (2018), 346(11), 997-1122

Detailed reference viewed: 29 (4 ULiège)
Full Text
See detailEffective development of a finite-element solver at the University
Boman, Romain ULiege; Papeleux, Luc ULiege; Ponthot, Jean-Philippe ULiege

Conference (2018, August 29)

Software development is usually neglected by academic researchers in the field of computational solid mechanics. This lack of long-term strategy often leads to the loss of valuable numerical models and ... [more ▼]

Software development is usually neglected by academic researchers in the field of computational solid mechanics. This lack of long-term strategy often leads to the loss of valuable numerical models and algorithms. In the first part of this talk, the key ideas behind the management of the source code of METAFOR, a nonlinear finite-element solver developed at the University of Liège, are presented in detail. The primary goal is to continuously integrate all the developments into a single application so that future projects can safely rely on the results from the past. The second part of the talk exhibits several applications of metal forming processes computed with METAFOR and based on the Arbitrary Lagrangian Eulerian formalism. [less ▲]

Detailed reference viewed: 41 (10 ULiège)
Full Text
Peer Reviewed
See detailComparison of stochastic and interval methods for uncertainty quantification of metal forming processes
Arnst, Maarten ULiege; Ponthot, Jean-Philippe ULiege; Boman, Romain ULiege

in Comptes Rendus Mécanique (2018), 346(8), 634-646

Various sources of uncertainty can arise in metal forming processes, or their numerical simulation, or both, such as uncertainty in material behavior, process conditions, and geometry. Methods from the ... [more ▼]

Various sources of uncertainty can arise in metal forming processes, or their numerical simulation, or both, such as uncertainty in material behavior, process conditions, and geometry. Methods from the domain of uncertainty quantification can help assess the impact of such uncertainty on metal forming processes and their numerical simulation, and they can thus help improve robustness and predictive accuracy. In this paper, we compare stochastic methods and interval methods, two classes of methods receiving broad attention in the domain of uncertainty quantification, through their application to a numerical simulation of a sheet metal forming process. [less ▲]

Detailed reference viewed: 51 (10 ULiège)
Full Text
Peer Reviewed
See detailFinite element modelling of cold drawing for high-precision tubes
Boutenel, Florian; Delhomme, Myriam; Velay, Vincent et al

in Comptes Rendus Mécanique (2018), 346(8), 665-677

Cold tube drawing is a metal forming process that allows manufacturers to produce high-precision tubes. The dimensions of the tube are reduced by pulling it through a conical converging die with or ... [more ▼]

Cold tube drawing is a metal forming process that allows manufacturers to produce high-precision tubes. The dimensions of the tube are reduced by pulling it through a conical converging die with or without inner tool. In this study, finite element modelling has been used to give a better understanding of the process. This paper presents a model that predicts the final dimensions of the tube with very high accuracy. It is validated thanks to experimental tests. Moreover, five studies are performed with this model, such as investigating the influence of the die angle on the drawing force or the influence of relative thickness on tube deformation. [less ▲]

Detailed reference viewed: 27 (8 ULiège)
Full Text
See detailFinite Element activation strategy in the numerical simulation of Additive Manufacturing Processes
Laruelle, Cédric ULiege; Boman, Romain ULiege; Papeleux, Luc ULiege et al

Poster (2018, May 28)

Additive Manufacturing (AM) is currently enjoying a tremendous boom. However, there is still a crucial lack of fundamental knowledge regarding AM. Hence, there is a high demand for the implementation of a ... [more ▼]

Additive Manufacturing (AM) is currently enjoying a tremendous boom. However, there is still a crucial lack of fundamental knowledge regarding AM. Hence, there is a high demand for the implementation of a model to accurately simulate an AM process. The complexity of such a simulation comes from multiple sources. Firstly, from the nature of the process. Indeed, it requires a large deformation thermo-mechanical simulation. Secondly, the modeling of the material law is complex. Lastly, the geometry of the process imposes a very fine discretization (layers can be as small as a few µm). This creates models that are computationally costly. Moreover, the process requires altering the geometry of the model during the simulation to model the addition of matter, which is a computational challenge by itself. This work presents a first implementation of a three-dimensional thermal Finite Element Analysis (FEA) of AM in the fully implicit in-house Finite Element code “Metafor”. The main focus of the work is on mesh management. The method to activate elements and to activate and deactivate boundary conditions during a simulation is adapted from the element deletion algorithm (erosion method) implemented in Metafor in the scope of crack propagation. The final model is compared against literature results, in particular to numerical and experimental results from a thermal experimental calibration of blown powder laser solid forming of Ti-6Al-4V. The model shows a reasonable agreement between the simulations. [less ▲]

Detailed reference viewed: 82 (23 ULiège)
Full Text
See detailOn the Ensemble Propagation for Efficient Uncertainty Quantification of Mechanical Contact Problems
Liegeois, Kim ULiege; Boman, Romain ULiege; Phipps, Eric et al

Conference (2018, April 17)

A new approach called embedded ensemble propagation has recently been proposed to improve the efficiency of sampling-based uncertainty quantification methods on emerging architectures. It consists of ... [more ▼]

A new approach called embedded ensemble propagation has recently been proposed to improve the efficiency of sampling-based uncertainty quantification methods on emerging architectures. It consists of simultaneously evaluating a subset of samples of the model, instead of evaluating them individually. This method improves memory access patterns, enables sharing of information from sample to sample, reduces message passing latency, and improves opportunities for vectorization. However, the impact of these improvements on the efficiency of the code depends on its code divergence, whereby individual samples within an ensemble must follow different code execution paths. In this presentation we will show the feasibility of propagating an ensemble through mechanical contact problems, discuss some of the code divergence issues arising in mechanical contact problems where each sample within an ensemble can give rise to a different contact configuration, discuss strategies to manage them, and illustrate them with numerical examples. At the end we will extend these notions to more general non-linear problems. [less ▲]

Detailed reference viewed: 83 (40 ULiège)
Full Text
Peer Reviewed
See detailContinuous roll forming including in-line welding and post-cut within an ALE formalism
Crutzen, Yanick ULiege; Boman, Romain ULiege; Papeleux, Luc ULiege et al

in Finite Elements in Analysis and Design (2018), 143

Cold roll forming is a rather old process for which there is a renewed interest due to its capacity to form ultra high-strength steels. For the first time ever in the literature, the manufacturing chain ... [more ▼]

Cold roll forming is a rather old process for which there is a renewed interest due to its capacity to form ultra high-strength steels. For the first time ever in the literature, the manufacturing chain involving both the continuous cold roll-forming process, the in-line welding operation for closed sections and the post-cut operation is numerically modelled. The first phase of this process sequence consists in computing the hopefully steady state configuration of the strip for the total length of the roll-forming mill, including the in-line welding phase. For addressing this problem, the Arbitrary Lagrangian Eulerian (ALE) formalism is used. Once the ALE steady state is reached, the computation is pursued with a second Lagrangian phase which is aimed at simulating the post-cut operation that releases the formed section from the rolling tools of the mill, enabling to determine the final geometry of the product. In this paper, the computational modelling framework employed within the in-house finite element code METAFOR is described. In particular, the proposed techniques — which are definitely original within an ALE formalism — for modelling the in-line welding operation and the post-cut operation are extensively detailed. The welding is considered with three different methods: (1) symmetry boundary conditions coupled with a well-suited node relocation procedure, (2) a closed mesh of the closed section coupled with a well-suited node relocation procedure, and (3) sticking elements based on a spring constitutive formulation. A set of simple numerical examples demonstrates the confidence in all the proposed modelling methods. Finally, these methods are successfully applied in the cases of two complex roll-forming mills of closed tubular sections. [less ▲]

Detailed reference viewed: 52 (13 ULiège)
Full Text
Peer Reviewed
See detailThermomechanical simulations of blanking process operated over a wide range of punch velocities
Canales Cardenas, Cristian ULiege; Boman, Romain ULiege; Ponthot, Jean-Philippe ULiege

in Journal of Physics. Conference Series (2018), 1063

numerical model based on the finite element method has been developed to simulate the blanking process. Thanks to this model we analyse the influence of punch velocities during blanking on the quality of ... [more ▼]

numerical model based on the finite element method has been developed to simulate the blanking process. Thanks to this model we analyse the influence of punch velocities during blanking on the quality of the sheared edge and the characteristic parameters governing the process (maximum punch force and displacement, temperature increase). In this model, inertia, viscous and thermal effects are properly considered by means of a unified thermomechanical framework. A full remeshing approach is adopted to overcome the high distortion of elements due to large deformations, prior to fracture. The material strain-rate sensitivity is introduced by means of an extension of elasto-viscoplastic constitutive equations for the large strain regime. The inertial effects are considered thanks to an implicit time integration scheme. Crack propagation during the process is tracked using the element deletion method driven by an uncoupled damage criterion. Finally, the coupled thermomechanical problem is solved by an isothermal staggered scheme. Experimental and numerical results are compared for the entire range of punch velocities under consideration. Good agreement between both results has been found. [less ▲]

Detailed reference viewed: 38 (5 ULiège)
Full Text
Peer Reviewed
See detailUltrasonic roll bite measurements in cold rolling: Contact length and strip thickness
Carretta, Yves; Hunter, Andrew; Boman, Romain ULiege et al

in Proceedings of the Institution of Mechanical Engineers. Part J, Journal of Engineering Tribology (2018), 232(2), 179-192

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip ... [more ▼]

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip flatness defects and thickness inhomogeneity. To control the process, online process measurements are usually carried out; such as the rolling load, forward slip and strip tensions at each stand. Shape defects of the strip are usually evaluated after the last stand of a rolling mill thanks to a flatness measuring roll. However, none of these measurements is made within the roll bite itself due to the harsh conditions taking place in that area. This paper presents a sensor capable of monitoring strip thickness variations as well as roll bite length in situ and in real time. The sensor emits ultrasonic pulses that reflect from the interface between the roll and the strip. Both the time-of-flight of the pulses and the reflection coefficient (the ratio of the amplitude of the reflected signal to that of the incident signal) are recorded. The sensor system was incorporated into a work roll and tested on a pilot rolling mill. Measurements were taken as steel strips were rolled under several lubrication conditions. Strip thickness variation and roll-bite length obtained from the experimental data agree well with numerical results computed with a cold rolling model in the mixed lubrication regime. [less ▲]

Detailed reference viewed: 65 (10 ULiège)
Full Text
Peer Reviewed
See detailItô-SDE MCMC method for Bayesian characterization of errors associated with data limitations in stochastic expansion methods for uncertainty quantification
Arnst, Maarten ULiege; Abello Álvarez, Belén; Ponthot, Jean-Philippe ULiege et al

in Journal of Computational Physics (2017), 349

This paper is concerned with the characterization and the propagation of errors associated with data limitations in polynomial-chaos-based stochastic methods for uncertainty quantification. Such an issue ... [more ▼]

This paper is concerned with the characterization and the propagation of errors associated with data limitations in polynomial-chaos-based stochastic methods for uncertainty quantification. Such an issue can arise in uncertainty quantification when only a limited amount of data is available. When the available information does not suffice to accurately determine the probability distributions that must be assigned to the uncertain variables, the Bayesian method for assigning these probability distributions becomes attractive because it allows the stochastic model to account explicitly for insufficiency of the available information. In previous work, such applications of the Bayesian method had already been implemented by using the Metropolis–Hastings and Gibbs Markov Chain Monte Carlo (MCMC) methods. In this paper, we present an alternative implementation, which uses an alternative MCMC method built around an Itô stochastic differential equation (SDE) that is ergodic for the Bayesian posterior. We draw together from the mathematics literature a number of formal properties of this Itô SDE that lend support to its use in the implementation of the Bayesian method, and we describe its discretization, including the choice of the free parameters, by using the implicit Euler method. We demonstrate the proposed methodology on a problem of uncertainty quantification in a complex nonlinear engineering application relevant to metal forming. [less ▲]

Detailed reference viewed: 49 (17 ULiège)
Full Text
Peer Reviewed
See detailUltrasonic roll bite measurements in cold rolling - roll stress and deformation
Carretta, Yves; Hunter, Andrew; Boman, Romain ULiege et al

in Journal of Materials Processing Technology (2017), 249

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip ... [more ▼]

In cold rolling of thin metal strip, contact conditions between the work rolls and the strip are of great importance: roll deformations and their effect on strip thickness variation may lead to strip flatness defects and thickness inhomogeneity. To control the process, several online measurements are usually carried out such as the rolling load, forward slip and strip tensions at each stand. Shape defects of the strip are usually evaluated after the last stand of a rolling mill thanks to a flatness measuring roll. However, none of these measurements is made within the roll bite itself due to the harsh conditions taking place in that area. This paper presents a sensor capable of monitoring roll deformations as well as roll radial stresses in situ and in real time. The sensor emits ultrasonic pulses that reflect from the roll surface. The time-of-flight (ToF) of the pulses is recorded during the testing. The sensor system was incorporated into a work roll and tested on a pilot rolling mill. Measurements were taken as steel strips were rolled under different strip elongation. Roll deformation and radial stresses obtained from the experimental data are in good agreement with numerical results computed with a cold rolling model developed in non-linear Finite Element software. [less ▲]

Detailed reference viewed: 55 (15 ULiège)