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International audience; We present the Corotational Cut Finite Element Method for real-time surgical simulation. Users only need to provide a background mesh which is not necessarily conforming to the boundaries/interfaces of the simulated object. The details of the latter, represented by its surface or/and its internal interfaces, which can be directly obtained from binary images, are taken into account by a multilevel subelement embedding algorithm applied to elements of the background mesh that are cut by the surface/interfaces. To stabilize the system matrix when elements are cut by the surface/interfaces with very small intersections , we propose to move the background node(s) of the concerned cut elements by a distance proportional to the element size. This approach is simple but it can avoid the stability issues in such situations. Moreover, this approach does not include additional parameters as, e.g. ghost penalty method [1]. Dirichlet boundary conditions can be implicitly imposed on the surface using Lagrange multipliers, whereas traction or Neumann boundary conditions, which is/are applied on parts of the surface, can be distributed to the background nodes using shape functions. The implementation is verified by convergence studies with optimal rates. To verify the reliability of the method, it is applied to various needle insertion simulations (e.g. for biopsy or brachytherapy) into brain and liver models while considering frictional interactions between the needle and the tissue. Numerical results show that the present method can make the discretization independent from geometric description, and it can avoid the complexity of mesh generation of complex geometries while retaining the accuracy of the standard Finite Element Method. The proposed methodology is very suitable for real-time and patient specific simulations as it improves the simulation accuracy by automatically, and properly, taking the geometry of the simulated object into account.References[1] E. Burman et al, Int J Numer Meth Engg, vol. 104, no. 7, pp. 472-501, 2015.

Real-time simulations are becoming increasingly common for various applications, from geometric design to medical simulation. Two of the main factors concurrently involved in defining the accuracy of surgical simulations are: the modeling error and the discretization error. Most work in the area has been looking at the above sources of error as a compounded, lumped, overall error. Little or no work has been done to discriminate between modeling error (e.g. needle-tissue interaction, choice of constitutive models) and discretization error (use of approximation methods like FEM). However, it is impossible to validate the complete surgical simulation approach and, more importantly, to understand the sources of error, without evaluating both the discretization error and the modeling error. Our objective is thus to devise a robust and fast approach to measure the discretization error via a posteriori error estimates, which are then used for local remeshing in surgical simulations. To ensure that the approach can be used in clinical practice, the method should be robust enough to deal, as realistically as possible, with the interaction of surgical tools with the organ, and fast enough for real-time simulations. The approach should also lead to an improved convergence so that an economical mesh is obtained at each time step. The final goal is to achieve optimal convergence and the most economical mesh, which will be studied in our future work.

Sampling-while-drilling technology has quickly evolved into an established service and has been used in varied scenarios with object-oriented applications. This case study presents the application of fluid analysis and sampling while drilling a development well in the Te Giac Trang (TGT) field of Vietnam. The application of this technology contributed to accruing reserves, provided a deeper understanding of the production area, and avoided further drillstem testing, thereby saving numerous rig days. The principal challenge was to reduce the uncertainty in reservoir fluid type that remained after drillstem testing results from the exploration phase. The objectives included confirming the formation fluid type in two reservoir units, formation pressure regime and determining the pressure communication with the production area. The aim was also to avoid three more planned drillstem tests. Timing was critical, so two runs were planned strategically after the hole section was drilled. The first run performed was formation pressure testing with fluid identification and sampling from 11 prioritized depth stations. The mobility ranged between 29.3 and 128.1 mD/cP. The cleanup duration and volume ranged between 1 hour 14 minutes with 70.0 litres and 3 hours 7 minutes with 154.7 litres pumped respectively for the high- and low-mobility depth stations. A total of 1009.8 litres were pumped in 23.6 hours. The samples were sent immediately to the PVT laboratory for quick analysis. Despite the high levels of invasion expected during the cleanup and sampling operations, the contamination level was less than 10%; mostly between 4% and 8%; the lowest was 3%. Ten single-phase fluid samples were collected, out of which seven were oil and three were gas. As a result of the fast turnaround of the sampling results from the first run, the subsequent run performed was pressure testing only, with 61 depth stations. With a maximum overbalance of 1,381 psia (9,522 kPa) from both wiper trip runs, the sampling-while-drilling application provided excellent pressure repeatability with 100% sealing efficiency and representative formation pressure, mobility and fluid data. The planning of sequential runs with sampling to confirm fluid type followed by a run for additional pressure tests enabled the sampling-while-drilling technology to identify incremental reserves and avoid multiple drillstem tests, saving an estimated 35 rig days. The acquired pressure testing data added valuable information to the pressure communication dynamics between reservoir layers of the well and adjacent producing area of the field.

For problems in which discontinuities are dominant such as fracture of quasi-brittle materials or cutting of soft tissues, discrete approach is a more suitable than the continuum one since discontinuities can be represented naturally. Lattice models are the good candidate, especially when the mesostructure of the studied material needs to be modeled explicitly. Indeed, the outcome of cutting, tearing, needle insertion and similar operations on soft tissues is significantly affected by the microstructure of the material. In this contribution, a master/slave approach is used in order to couple finite elements and lattice approach in a multi-domain and multiscale framework.

Surgery is a complex practice whose positive outcome relies heavily on the experience of surgeons and therefore involves a number of risks. Computer-based simulation is a strong candidate for surgical training, guidance and surgical robotics. Cutting, tearing, needle insertion and similar operations which require topological changes, contact, and whose outcome is significantly affected by the microstructure of the material (discontinuities, holes, interfaces) remain some of the most difficult surgical gestures to simulate. One of the difficulties emanates from the requirement to handle propagating discontinuities as well as the micro or meso structure of the material being cut. We are interested in the development of a numerical tool capable of the interactive (50Hz) simulation of surgical cutting using a multi-domain lattice-continuum approach. Around the cutting region, a mesoscopic discrete lattice approach suitable for initiation of cuts and subsequent tears is used. The remaining regions can be modeled by a continuum approach or through model reduction approaches based on pre computations. The algorithms are implemented within the SOFA framework which is targets real-time computations, with an emphasis on medical simulation and the work is being performed in collaboration with the group of Dr Hadrien Courtecuisse and Stéphane Cotin.

For durability analysis and economic design (less material) of structures made of concrete-like materials, modeling of cracking process and failure is essential. In the framework of continuum mechanics, an internal length is introduced in nonlocal models to remedy the problem related to mesh sensitivity which is a pathology of classical damage models, when dealing with softening materials. However, the assessment of the internal length from heterogeneities of the material is still a difficult question, which makes an obscure issue in using nonlocal models. Our work concerns developing of a numerical tool based on the Lattice Element Method (LEM) which is a discrete model for simulating and predicting fracture in concrete(-like) material. Using the lattice model at the mesoscopic scale, there is no need to introduce any internal length in the constitutive law, as done in nonlocal models, and we can enfranchise this parameter by explicitly introducing the material mesotructure via geometric description. Based on the developed numerical tool, we studied, by performing numerical uniaxial tensile tests, the geometric influence of the material mesotructure as well as the influence of the boundary conditions and specimen sizes (that result in different stress gradient and material rotation field) on the size of the FPZ (Fracture Process Zone) and on the characteristic length of the homogenized quasi-brittle material. These studies provide recommendations/warnings when extracting an internal length required for nonlocal damage models from the material microstructure. Moreover, the studies contribute a direct insight into the mesoscale origin of the FPZ size and the material characteristic length, and consequently into the origin and nature of the nonlinear behavior of the material. Then, we implemented the lattice model into SOFA library developed by INRIA for realizing the coupling with the Finite Element Method (FEM) in order to deal with large-scale structures. We proposed a strong coupling algorithm between a macroscopic approach represented by FEM and a mesoscopic approach dealt by LEM within an adaptive manner. The coupling model is first used to validate the multiscale approach proposed on heuristic simulations. And in the long term, it provides a promising tool for simulations of large-scale structures made of quasi-brittle materials of real life.; Pour l'analyse de durabilité et la conception économique (moins de matériel) de structures en matériaux ressemblant à du béton, la modélisation de la rupture est essentielle. Dans le cadre de la mécanique des milieux continus, une longueur interne est introduite dans les modèles non locaux pour remédier au problème lié à la sensibilité du maillage qui est une pathologie des modèles d'endommagement classiques , lorsqu'il s'agit de matériaux adoucissantes. Toutefois, l'évaluation de la longueur interne de hétérogénéités du matériau est toujours une question difficile, ce qui rend un problème obscur en utilisant des modèles non locaux. Nos travaux portent sur le développement d'un outil numérique basée sur la méthode des éléments en treillis (LEM) qui est un modèle discret pour la simulation et la prévision de la rupture des structures en béton. En utilisant le modèle de réseau à l'échelle mésoscopique, il n'est pas nécessaire d'introduire une longueur interne dans la loi de comportement, comme cela se fait dans les modèles non locaux, et nous pouvons affranchir ce paramètre en introduisant explicitement la mesotructure matérielle via une description géométrique. Basé sur l'outil numérique développé, nous avons étudié, en effectuant des tests numériques de traction uniaxiale, l'influence géométrique de la mesotructure du matériau ainsi que l'influence des conditions aux limites et de tailles d'échantillons (qui se traduisent par le gradient de sollicitation et le champ de rotation de matériel différents) sur le taille de la FPZ (fracture process zone) et sur la longueur caractéristique du matériau quasi-fragile homogénéisé. Ces études fournissent des recommandations/avertissements lors de l'extraction d'une longueur interne nécessaire pour les modèles nonlocaux à partir de la microstructure du matériau. Par ailleurs, les études contribuent un aperçu direct de l'origine mésoscopic de la taille FPZ et la longueur de la caractéristique du matériau, et par conséquent sur l'origine et la nature du comportement non linéaire du matériau. Ensuite, nous avons implanté le modèle du treillis dans la bibliothèque de SOFA développé par l'INRIA pour réaliser le couplage avec la méthode des éléments finis (MEF) afin de faire face avec des structures à grande échelle. Nous avons proposé un algorithme de couplage entre une approche macroscopique représentée par MEF et une approche mésoscopique infligés par LEM au sein d'une manière adaptative. Le modèle de couplage est d'abord utilisée pour valider l'approche multi-échelle proposée sur des simulations heuristiques. Et à long terme, il fournit un outil prometteur pour des simulations de grandes structures en matériaux quasi-fragiles de la vie réelle.

For durability analysis and economic design (less material) of structures made of concrete-like materials, modeling of cracking process and failure is essential. In the framework of continuum mechanics, an internal length is introduced in nonlocal models to remedy the problem related to mesh sensitivity which is a pathology of classical damage models, when dealing with softening materials. However, the assessment of the internal length from heterogeneities of the material is still a difficult question, which makes an obscure issue in using nonlocal models. Our work concerns developing of a numerical tool based on the Lattice Element Method (LEM) which is a discrete model for simulating and predicting fracture in concrete(-like) material. Using the lattice model at the mesoscopic scale, there is no need to introduce any internal length in the constitutive law, as done in nonlocal models, and we can enfranchise this parameter by explicitly introducing the material mesotructure via geometric description. Based on the developed numerical tool, we studied, by performing numerical uniaxial tensile tests, the geometric influence of the material mesotructure as well as the influence of the boundary conditions and specimen sizes (that result in different stress gradient and material rotation field) on the size of the FPZ (Fracture Process Zone) and on the characteristic length of the homogenized quasi-brittle material. These studies provide recommendations/warnings when extracting an internal length required for nonlocal damage models from the material microstructure. Moreover, the studies contribute a direct insight into the mesoscale origin of the FPZ size and the material characteristic length, and consequently into the origin and nature of the nonlinear behavior of the material. Then, we implemented the lattice model into SOFA library developed by INRIA for realizing the coupling with the Finite Element Method (FEM) in order to deal with large-scale structures. We proposed a strong coupling algorithm between a macroscopic approach represented by FEM and a mesoscopic approach dealt by LEM within an adaptive manner. The coupling model is first used to validate the multiscale approach proposed on heuristic simulations. And in the long term, it provides a promising tool for simulations of large-scale structures made of quasi-brittle materials of real life., Pour l'analyse de durabilité et la conception économique (moins de matériel) de structures en matériaux ressemblant à du béton, la modélisation de la rupture est essentielle. Dans le cadre de la mécanique des milieux continus, une longueur interne est introduite dans les modèles non locaux pour remédier au problème lié à la sensibilité du maillage qui est une pathologie des modèles d'endommagement classiques , lorsqu'il s'agit de matériaux adoucissantes. Toutefois, l'évaluation de la longueur interne de hétérogénéités du matériau est toujours une question difficile, ce qui rend un problème obscur en utilisant des modèles non locaux. Nos travaux portent sur le développement d'un outil numérique basée sur la méthode des éléments en treillis (LEM) qui est un modèle discret pour la simulation et la prévision de la rupture des structures en béton. En utilisant le modèle de réseau à l'échelle mésoscopique, il n'est pas nécessaire d'introduire une longueur interne dans la loi de comportement, comme cela se fait dans les modèles non locaux, et nous pouvons affranchir ce paramètre en introduisant explicitement la mesotructure matérielle via une description géométrique. Basé sur l'outil numérique développé, nous avons étudié, en effectuant des tests numériques de traction uniaxiale, l'influence géométrique de la mesotructure du matériau ainsi que l'influence des conditions aux limites et de tailles d'échantillons (qui se traduisent par le gradient de sollicitation et le champ de rotation de matériel différents) sur le taille de la FPZ (fracture process zone) et sur la longueur caractéristique du matériau quasi-fragile homogénéisé. Ces études fournissent des recommandations/avertissements lors de l'extraction d'une longueur interne nécessaire pour les modèles nonlocaux à partir de la microstructure du matériau. Par ailleurs, les études contribuent un aperçu direct de l'origine mésoscopic de la taille FPZ et la longueur de la caractéristique du matériau, et par conséquent sur l'origine et la nature du comportement non linéaire du matériau. Ensuite, nous avons implanté le modèle du treillis dans la bibliothèque de SOFA développé par l'INRIA pour réaliser le couplage avec la méthode des éléments finis (MEF) afin de faire face avec des structures à grande échelle. Nous avons proposé un algorithme de couplage entre une approche macroscopique représentée par MEF et une approche mésoscopique infligés par LEM au sein d'une manière adaptative. Le modèle de couplage est d'abord utilisée pour valider l'approche multi-échelle proposée sur des simulations heuristiques. Et à long terme, il fournit un outil prometteur pour des simulations de grandes structures en matériaux quasi-fragiles de la vie réelle.

This paper presents the first real-time discretisation-error-driven adaptive finite element approach for corotational elasticity problems involving strain localisation. We propose a hexahedron-based finite element method combined with local oct-tree $h$-refinement, driven by a posteriori error estimation, for simulating soft tissue deformation. This enables to control the local error and global error level in the mechanical fields during the simulation. The local error level is used to refine the mesh only where it is needed, while maintaining a coarser mesh elsewhere. We investigate the convergence of the algorithm on academic examples, and demonstrate its practical usability on a percutaneous procedure involving needle insertion in a liver. For the latter case, we compare the force displacement curves obtained from the proposed adaptive algorithm with that obtained from a uniform refinement approach.