Deviation of a needle from its intended path can be minimized by using a robotic device to steer the needle towards its target. Such a device requires information about the interactions between the needle and soft tissue, and this information can be obtained using finite element (FE) analysis. In this study, we present an FE analysis that integrates the Johnson–Cook damage model for a linear elastic material with an element deletion-based method. The FE analysis is used to model a bevel-tipped needle interacting with gel. The constants for the damage model are obtained using a compression test. We compare simulation results with experimental data that include tip–gel interaction forces and torques, and three-dimensional (3D) in situ images of the gel rupture obtained using a laser scanning confocal microscope. We quantitatively show that the percentage errors between simulation and experimental results for force along the insertion axis and torque about the bevel edge are 3% and 5%, respectively. Furthermore, it is also shown qualitatively that tip compression is observed at the same locations in both experimental and simulation results. This study demonstrates the potential of using an FE analysis with a damage model and an element deletion-based method to accurately simulate 3D gel rupture, and tip–gel interaction forces and torques.
The design of extrusion dies depends on the experience of the designer. After the die has been manufactured, it is tested during an extrusion process and machined several times until it works properly. The die is designed by a trial and error method which is expensive interms of time consumption and the amount of scrap. Research is going on to replace the trial pressing with finite element simulations that concentrate on material and tool analysis. In order to validate the tool simulations, an experiment is required for measuring the deformation of the die. Measuring the deformation of the die is faced with two main obstacles: high temperature and little free space. To overcome these obstacles a method is tried, which works by applying a laser beam on a reflecting surface. This cheap method is simple, robust and gives good results. This paper describes measuring the deformation of a flat die used to extrude a single U shape profile. In addition, finite element calculation of the die is performed. Finally, a comparison is performed between experimental and numerical results.
Finite element analysis in aluminum extrusion is faced by several problems such as number of degrees of freedom, calculation time, large deformation and flow conservation. The problem of large deformation is overcome by applying the Eulerian formulation. The problems concerning number of degrees of freedom, calculation time can be overcome by simplifying the model especially at the bearing corner. On the one hand, detailed modeling of the bearing corner will increase the complexity of the analysis. On the other hand, simplified modeling of the bearing corner will face problems such as locking of the bearing corner node and loss of flow conservation. A sharp corner and modified corner geometry are examples of the simplified modeling. Moreover, boundary conditions will be applied at the bearing corner node in order to solve the problem of its locking and to satisfy the flow conservation condition. These boundary conditions include specifying a normal or formulating a constraint equation. This paper focuses on the calculation of the normal or constraint equation that can be applied either at a sharp corner or after modifying the corner geometry. Different elements are checked in this study such as plane strain, axisymmetric and tetrahedron elements. Finally, the extrusion force and average exit velocity are investigated and compared with a reference model. In the reference model a round corner with 0.5mm radius is built, contact boundary condition is applied between the die and aluminum, and Arbitrary Lagrangian Eulerian formulation is applied. The finite element analysis is performed in the in-house implicit finite element code "DiekA".
Abstract. The design of extrusion dies depends on the experience of the designer. After the die has been manufactured, it is tested during an extrusion trial and machined several times until it works properly. The die is designed by a trial and error method which is an expensive process in terms of time and the amount of scrap. In order to decrease the time and the amount of scrap, research is going on to replace the trial pressing with finite element simulations. The goal of these simulations is to predict the material flow through the die. In these simulations, it is required to calculate the material flow and the tool deformation simultaneously. Solving the system of equations concerning the material flow and the tool deformation becomes more difficult with increasing the complexity of the die. For example the total number of degrees of freedom can reach a value of 500,000 for a flat die. Therefore, actions must be taken to solve the material flow and the tool deformation simultaneously and faster. This paper describes the calculation of a flat die deformation used in the production of a U-shape profile with a coupled method. In this calculation an Arbitrary Lagrangian Eulerian and Updated Lagrangian formulation are applied for the aluminum and the tool finite element models respectively. In addition, for decreasing the total number of degrees of freedom, the stiffness matrix of the tool is condensed to the contact nodes between the aluminum and the tool finite element models. Finally, the numerical results are compared with experiment results in terms of extrusion force and the angular deflection of the tongue.
This paper presents a method of modelling surge pressures and wave propagation that can occur during well execution. The surge pressures have an impact on formations i.e. formation fracture resulting in mud losses and non-productive time. Knowing the amplitude of pressure surges in advance can lead to operation redesign to avoid losses. Pressure waves can occur at numerous points during well execution. For example, during liner operations, pressure waves can occur dart landing or plug shearing, liner hanger setting or clearing a plugged shoetrack component. It is possible that these pressure waves can create fractures in shale and sand layers i.e. when pressure wave amplitude exceeds formation fracturing limit. A physical model is built to compute pressure wave propagation through drill string, casing and open hole, to predict amplitude of pressure wave and to warn when a fracture may occur in formation to avoid mud losses and non-productive time. In the model, the continuity and energy partial differential equations are built for a cylindrical fluid element contained in an elastic hollow cylinder. Method of characteristic is applied to transfer the partial differential equations into ordinary differential equations. The ordinary differential equations are solved numerically to compute pressure distribution along well depth and in time. The physical model is implemented as a Graphical User Interface (GUI) tool to be used by drilling engineers at design phase of well to avoid losses. To date it has been used for cementing and perforating operations. Pressure wave computations are performed with the model for a field in Gulf of Mexico where mud losses have occurred, and results are presented in this paper.
Summary In this paper, we present a method of modeling surge pressures and wave propagation that can occur during well execution. The surge pressures have an effect on formations [i.e., formation fracture resulting in mud losses and nonproductive time (NPT)]. Knowing the amplitude of surge pressure in advance can lead to operation redesign to avoid losses. Swab- and surge-pressure waves can occur at numerous events during well execution. For example, during liner operations, pressure waves can occur at dart landing or plug shearing, liner-hanger setting, or clearing a plugged shoe-track component. It is possible for surge-pressure waves to create fractures in shale and sand layers (i.e., when surge-pressure-wave amplitude exceeds formation fracturing resistance). A transient-state physical model is built to compute pressure-wave propagation through drillstring, casing, and open hole to predict the amplitude of a surge-pressure wave and to warn when a fracture might occur in the formation, to avoid mud losses and NPT. In the model, continuity and energy partial-differential equations (PDEs) are built for a cylindrical fluid element contained in an elastic hollow cylinder. The method of characteristics is applied to convert the PDEs to ordinary-differential equations (ODEs). The ODEs are solved numerically to compute pressure distribution along well depth and in time. The model is implemented as a graphical-user-interface (GUI) tool to be used by drilling engineers at the design phase of a well to avoid losses. The GUI tool is targeted to address different scenarios that take place during the cementation process. To date, the transient-state physical model has been applied successfully in various applications, such as monodiameter technology, running casing, and perforating operations. Two cases are studied, one for a well in the Gulf of Mexico (GOM) where mud losses have been reported, and the other for a well in Malaysia where no mud losses have occurred. Pressure-wave computations are performed with the GUI tool for the two cases. The results of both cases are presented in this paper and show that formation fracture can be predicted by the GUI tool and subsequent losses can be avoided.
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