Mesh Deformation Research Articles

Multi-view Performance Capture of Surface Details

This paper presents a novel approach to recover true fine surface detail of deforming meshes reconstructed from multi-view video. Template-based methods for performance capture usually produce a coarse-to-medium scale detail 4D surface reconstruction which does not contain the real high-frequency geometric detail present in the original video footage. Fine scale deformation is often incorporated in a second pass by using stereo constraints, features, or shading-based refinement. In this paper, we propose an alternative solution to this second stage by formulating dense dynamic surface reconstruction as a global optimization problem of the densely deforming surface. Our main contribution is an implicit representation of a deformable mesh that uses a set of Gaussian functions on the surface to represent the initial coarse mesh, and a set of Gaussians for the images to represent the original captured multi-view images. We effectively find the fine scale deformations for all mesh vertices, which maximize photo-temporal-consistency, by densely optimizing our model-to-image consistency energy on all vertex positions. Our formulation yields a smooth closed form energy with implicit occlusion handling and analytic derivatives. Furthermore, it does not require error-prone correspondence finding or discrete sampling of surface displacement values. We demonstrate our approach on a variety of datasets of human subjects wearing loose clothing and performing different motions. We qualitatively and quantitatively demonstrate that our technique successfully reproduces finer detail than the input baseline geometry.

Automatic optimization design of a feeder extrusion die with response surface methodology and mesh deformation technique

During the extrusion process of aluminum alloy profiles, scientific and reasonable design of extrusion dies affects directly on the product qualified rate, production efficiency, and cost. In this work, for a 7N01 aluminum alloy beam profile used in high-speed train, the response surface method (RSM) and mesh deformation technique (MDT) are applied to automatically optimize the feeder chamber of the extrusion die. With implanted material physical properties and constitutive model of this alloy, the numerical simulation of the extrusion process is firstly carried out and verified experimentally. Then, RSM is used to optimize seven different geometric variables of the feeder chamber and to narrow the variables’ ranges. On the basis of above optimization, MDT is finally applied to automatically optimize the feeder chamber. After optimization, the velocity distribution in the cross section of the profile tends to more uniform. The standard deviation of the velocity field decreases from 7.83 to 2.47 mm/s with the reducing rate of 68.46%. More importantly, the automatic optimization process with mesh deformation technique is explored in this work, which could provide an effective and potential means for the automatic optimization design of three-dimensional dies or products in other fields.

A fast and robust hybrid method for block‐structured mesh deformation with emphasis on FSI‐LES applications

SummaryThe present work introduces an efficient technique for the deformation of block‐structured grids occurring in simulations of fluid–structure interaction (FSI) problems relying on large‐eddy simulation (LES). The proposed hybrid approach combines the advantages of the inverse distance weighting (IDW) interpolation with the simplicity and low computational effort of transfinite interpolation (TFI), while preserving the mesh quality in boundary layers. It is an improvement over the state‐of‐the‐art currently in use. To reach this objective, in a first step, three elementary mesh deformation methods (TFI, IDW, and radial basis functions) are investigated based on several test cases of different complexities analyzing not only their capabilities but also their computational costs. That not only allows to point out the advantages of each method but also demonstrates their drawbacks. Based on these specific properties of the different methods, a hybrid methodology is suggested that splits the entire grid deformation into two steps: first, the movement of the block‐boundaries of the block‐structured grid and second, the deformation of each block of the grid. Both steps rely on different methodologies, which allows to work out the most appropriate method for each step leading to a reasonable compromise between the grid quality achieved and the computational effort required. Finally, a hybrid IDW‐TFI methodology is suggested that best fits to the specific requirements of coupled FSI‐LES applications. This hybrid procedure is then applied to a real‐life FSI‐LES case. Copyright © 2016 John Wiley & Sons, Ltd.

Investigation of Blood Flow Modeling in Artery Using ALE Formulation

The aim of the paper is to use Arbitrary Lagrangian Eulerian (ALE) formulation for fluid–structure interaction for modeling blood flow in artery. Predicting blood flow and its effects on arteries requires simulation of fluid–structure coupling with deformable mesh. For fluid simulation velocity–pressure formulation is used, we present the algorithm which allows to compute fluid velocity and pressure using explicit time integration. This method has been applied successfully for several applications including sloshing tank analysis. For the structure shell type elements with five points integration through the thickness to accurately represent bending effects, are modeled. Since the structure is deformable, to prevent high mesh distortion an elasticity material model for the mesh is used for mesh deformation. For fluid–structure coupling, explicit contact algorithm based on penalty method. Such a model can be used to study the profile of the flow and pressure waves as they propagate along the arteries. In the paper, the onset of a pressure pulse was simulated at the entrance of a three dimension straight artery blood vessel and the resulting dynamic response in the form of a propagating pulse wave through the wall was analyzed and compared. Good agreement was found between the numerical results and the theoretical description of an idealized artery. Work has also been done on implementing the material constitutive models specific for vascular applications.

3D Numerical Calculations of Tangent Leakages in Scroll Compressor During Unsteady Process

A continuous increase in computing power brought progress in a scroll compressor modelling. The early simplified models now can be supplemented with a significantly more detailed CFD models. These models require a high resolution meshes due to the characteristics of the positive displacement machines. The working chambers geometries are evolving in time due to the vanes movement. For that reason, a moving boundary conditions have to be applied to the numerical model. This entails it is necessary to use a mesh deformation and to modify the solved equations so they are correct in the changing reference system. In order to remain a high mesh quality, a procedure for remeshing also has to be introduced. In return, the solution gives a better insight into the process compared to the simplified models. In the paper, a numerical spatial scroll compressor model with a mesh generation procedure is presented. The calculations were performed for different values of the radial clearances between scroll wraps. The clearance causes a leakage between higher and lower pressure chambers and affects their mass and energy balance. A comparison between the numerical and an analytical solution was used as a benchmark for the results.

3D numerical calculations of tangent leakages in scroll compressor during unsteady process

A continuous increase in computing power brought progress in a scroll compressor modelling. The early simplified models now can be supplemented with a significantly more detailed CFD models. These models require a high resolution meshes due to the characteristics of the positive displacement machines. The working chambers geometries are evolving in time due to the vanes movement. For that reason, a moving boundary conditions have to be applied to the numerical model. This entails it is necessary to use a mesh deformation and to modify the solved equations so they are correct in the changing reference system. In order to remain a high mesh quality, a procedure for remeshing also has to be introduced. In return, the solution gives a better insight into the process compared to the simplified models. In the paper, a numerical spatial scroll compressor model with a mesh generation procedure is presented. The calculations were performed for different values of the radial clearances between scroll wraps. The clearance causes a leakage between higher and lower pressure chambers and affects their mass and energy balance. A comparison between the numerical and an analytical solution was used as a benchmark for the results.

Research on Automatic Skinning of Articulated Characters Using Extended Position Based Dynamic

This paper proposes automatic skinning using extended position based dynamic in character animation, which adds energy conservation constraints based on the easy expandability of the position based dynamics. In the skeletal motion process, the deformation of surface mesh is divided into two stages. First stage: at each frame, the skeleton moves and both the surface and volumetric vertices are deformed by a standard LBS algorithm. Second stage: we use position based dynamics to update both the tetrahedral mesh and surface mesh automatically by solving the constraints. Lastly, self-collision and Laplacian smoothing are used to refine the deformation locally and output the result. In order to verify the feasibility and effectiveness of the mentioned algorithm, this paper experiment with different models and obtain the desired results.

Comparison of the fracture resistances of glass fiber mesh- and metal mesh-reinforced maxillary complete denture under dynamic fatigue loading.

PURPOSEThe aim of this study was to investigate the effect of reinforcing materials on the fracture resistances of glass fiber mesh- and Cr–Co metal mesh-reinforced maxillary complete dentures under fatigue loading.MATERIALS AND METHODSGlass fiber mesh- and Cr–Co mesh-reinforced maxillary complete dentures were fabricated using silicone molds and acrylic resin. A control group was prepared with no reinforcement (n = 15 per group). After fatigue loading was applied using a chewing simulator, fracture resistance was measured by a universal testing machine. The fracture patterns were analyzed and the fractured surfaces were observed by scanning electron microscopy.RESULTSAfter cyclic loading, none of the dentures showed cracks or fractures. During fracture resistance testing, all unreinforced dentures experienced complete fracture. The mesh-reinforced dentures primarily showed posterior framework fracture. Deformation of the all-metal framework caused the metal mesh-reinforced denture to exhibit the highest fracture resistance, followed by the glass fiber mesh-reinforced denture (P<.05) and the control group (P<.05). The glass fiber mesh-reinforced denture primarily maintained its original shape with unbroken fibers. River line pattern of the control group, dimples and interdendritic fractures of the metal mesh group, and radial fracture lines of the glass fiber group were observed on the fractured surfaces.CONCLUSIONThe glass fiber mesh-reinforced denture exhibits a fracture resistance higher than that of the unreinforced denture, but lower than that of the metal mesh-reinforced denture because of the deformation of the metal mesh. The glass fiber mesh-reinforced denture maintains its shape even after fracture, indicating the possibility of easier repair.

An Iterative Mesh Untangling Algorithm Using Edge Flip

Existing mesh untangling algorithms are unable to untangle highly tangled meshes. In this study, we address this problem by proposing an iterative mesh untangling algorithm using edge flip. Our goal is to produce meshes with no inverted elements and good element qualities when inverted elements with poor element qualities are produced during mesh generation or mesh deformation process. Our proposed algorithm is composed of three steps: first, we iteratively perform edge flip; subsequently, optimization-based mesh untangling is conducted until all inverted elements are eliminated; finally, we perform mesh smoothing for generating high-quality meshes. Numerical results show that the proposed algorithm is able to successfully generate high-quality meshes with no inverted elements for highly tangled meshes.

Feature moving operation of hexahedral mesh

In the product design process, the finite element mesh regeneration is an inevitable step, but it is time consuming. The mesh editing is a kind of an effective mesh regeneration technique. In this paper, a method for widely moving features of hexahedral mesh is proposed to satisfy application requirement. After the feature moving operation is applied to CAD model, the mesh deformation based on the mean value coordinates is carried out in the corresponding deformed region of the hex mesh to decrease the possible inverted elements caused by a wide range deformation. Then, the parameters of generating the density field are extracted from the initial hexahedral mesh, and used to calculate the local target density field by considering the geometric and topological information on the deformed region. Finally, based on difference between current density field and target density field of deformed region, the local refining and coarsening operations are devised and conducted to make the deformed region compatible with the target density field. Experimental results for the mechanical parts verify the effectiveness of proposed method.

CFD simulations of transient load change on a high head Francis turbine

Motivated by the importance of better understanding the structural integrity of high-head hydraulic turbines operating at intermittent conditions, complete 360º steady-state and transient simulations of a Francis turbine are presented in this paper. The main target of the work has been to investigate different numerical approaches such as mesh deformation for different operating conditions. Steady-state simulations were performed at the best efficiency point (BEP) and used as initial conditions for the transient simulations considering load rejection from BEP to part load (BEP2PL) and during load acceptance from BEP to high load (BEP2HL). Simulation results were compared with experimental data available for the Francis-99 project where close agreement was found for the mesh independent solution. The transient load analyses showed general trends in accordance with the measurement reports, especially for the pressure in vaneless space that is of high importance regarding RSI effects. Some deviations were identified for the net head at load rejection for which further investigations will be conducted. All CFD simulations were performed at model scale with ANSYS CFX v. 17 at either 96 or 120 cores (2.60 GHz). The immersed boundary technique was tested during the initial stages of the project, but had to be abandoned due to severe memory requirements. Pressure amplitudes and other instantaneous results were not considered.

A novel surface mesh deformation method for handling wing-fuselage intersections

This paper describes a method for mesh adaptation in the presence of intersections, such as wing-fuselage. Automatic optimization tools, using Computational Fluid Dynamics (CFD) simulations, face the problem to adapt the computational grid upon deformations of the boundary surface. When mesh regeneration is not feasible, due to the high cost to build up the computational grid, mesh deformation techniques are considered a cheap approach to adapt the mesh to changes on the geometry. Mesh adaptation is a well-known subject in the literature; however, there is very little work which deals with moving intersections. Without a proper treatment of the intersections, the use of automatic optimization methods for aircraft design is limited to individual components. The proposed method takes advantage of the CAD description, which usually comes in the form of Non-Uniform Rational B-Splines (NURBS) patches. This paper describes an algorithm to recalculate the intersection line between two parametric surfaces. Then, the surface mesh is adapted to the moving intersection in parametric coordinates. Finally, the deformation is propagated through the volumetric mesh. The proposed method is tested with the DLR F6 wing-body configuration.

A mesh deformation technique based on two-step solution of the elasticity equations

In the computation of fluid mechanics problems with moving boundaries, including fluid-structure interaction, fluid mesh deformation is a common problem to be solved. An automatic mesh deformation technique for large deformations of the fluid mesh is presented on the basis of a pseudo-solid method in which the fluid mesh motion is governed by the equations of elasticity. A two-dimensional mathematical model of a linear elastic body is built by using the finite element method. The numerical result shows that the proposed method has a better performance in moving the fluid mesh without producing distorted elements than that of the classic one-step methods.

Efficient mesh deformation based on Cartesian background mesh

Moving mesh is widely used in the simulation of aerodynamic shape optimization, multibody relative motion, aircraft icing and aeroelasticity. The efficient and high quality mesh deformation is the key technology of moving mesh. This paper presented a new Mesh Deformation method based on Cartesian Background Mesh (MDCBM). First, the Cartesian background mesh is deformed with radial basis functions (RBF). Second, the displacement of Cartesian background mesh is algebraically interpolated onto all meshes in the computing domain. Since the background mesh is coarse, the background mesh deformation can be finished fast. Because the background mesh of MDCBM is regular, the mapping relationship between background mesh and the computing mesh is simple. So the time spent on mapping search is substantially reduced. The examples including NACA0012 airfoil, multi-element airfoil with structured, unstructured mesh and DLR-F4 wing–body show the good performance of MDCBM. We highlight the advantages of MDCBM with respect to its computational efficiency and high quality of deformed mesh.

A combined registration and finite element analysis method for fast estimation of intraoperative brain shift; phantom and animal model study.

Finite element models for estimation of intraoperative brain shift suffer from huge computational cost. In these models, image registration and finite element analysis are two time-consuming processes. The proposed method is an improved version of our previously developed Finite Element Drift (FED) registration algorithm. In this work the registration process is combined with the finite element analysis. In the Combined FED (CFED), the deformation of whole brain mesh is iteratively calculated by geometrical extension of a local load vector which is computed by FED. While the processing time of the FED-based method including registration and finite element analysis was about 70s, the computation time of the CFED was about 3.2s. The computational cost of CFED is almost 50% less than similar state of the art brain shift estimators based on finite element models. The proposed combination of registration and structural analysis can make the calculation of brain deformation much faster.

Experiments and transient simulation on spring-loaded pressure relief valve under high temperature and high pressure steam conditions

Reliable performances of high temperature and high pressure operating steam pressure relief valves (HTHP PRVs) are extremely important for the safety of nuclear power plants. It is still a challenge to accurately describe the dynamic performance of HTHP PRVs. In this study, the accuracy of computational fluid dynamics (CFD) based modelling of the transient processes is examined. For one of the HTHP PRVs named DWPRV, the effects of different parameters on the dynamic performance were investigated by combining CFD simulation and experiments. In the simulation, the domain decomposition method (DDM) and the Grid Pre-deformation Method (GPM) were adopted to handle the moving disk geometry and the large mesh deformation. The effect of damping was also studied. It is confirmed that the use of CFD simulation can improve the design and settings of a HTHP PRV in a highly energetic service that is difficult to test due to safety reasons. For the DWPRV, it was found that the maximum flow rate occurs when the curtain area is 1.18 times the throat area. The degree of superheat ranging from 0 °C to 100 °C has a negligible effect on the performance of DWPRV regardless of the changes in the material mechanical properties with operating temperatures. The reseating pressure increases linearly with the rise in the distance between the upper adjusting ring and the sealing face. The lower adjusting ring exhibits a weak effect on the reseating pressure. For the ratios of rated lift to throat diameter equaling to 0.3 and 0.35, the DWPRV exhibits the higher blowdown for the ratio of 0.35.

Extended ALE Method for fluid–structure interaction problems with large structural displacements

Standard Arbitrary Lagrangian–Eulerian (ALE) methods for the simulation of fluid–structure interaction (FSI) problems fail due to excessive mesh deformations when the structural displacement is large. We propose a method that successfully deals with this problem, keeping the same mesh connectivity while enforcing mesh alignment with the structure. The proposed Extended ALE Method relies on a variational mesh optimization technique, where mesh alignment with the structure is achieved via a constraint. This gives rise to a constrained optimization problem for mesh optimization, which is solved whenever the mesh quality deteriorates. The performance of the proposed Extended ALE Method is demonstrated on a series of numerical examples involving 2D FSI problems with large displacements. Two-way coupling between the fluid and structure is considered in all the examples. The FSI problems are solved using either a Dirichlet–Neumann algorithm, or a Robin–Neumann algorithm. The Dirichlet–Neumann algorithm is enhanced by an adaptive relaxation procedure based on Aitken's acceleration. We show that the proposed method has excellent performance in problems with large displacements, and that it agrees well with a standard ALE method in problems with mild displacement.

Rapid generation of human femur models based on morphological parameters and mesh deformation

ABSTRACTIn this paper a new method for generating human femur models was presented, which combined parametric technology and deformation technology. The main target of our proposed method was to quickly generate a three-dimensional model which would best suit the patient's femur bone, even if a part of the bone was damaged or only partial data about the bone shape is available. First, all femur sample models were remeshed so as to have the same topology as the template, which enabled them to achieve compatible mesh segmentation quickly. Then, complete morphological parameters of all femur samples were calculated effectively and thereby a parameter set was got, which served as both reference and a constraint for generating new femur models. Next, according to partial known parameters, the best matching sample and the average model were selected to create a rough femur model through global interpolation. Finally, the rough model was further deformed locally to modify details until the desired femur model was obtained. Experimental results showed that the proposed method could efficiently generate anatomically suitable femur models, of which both the parameter error and the shape error were clinically acceptable.

Discontinuous Cell Method (DCM) for the simulation of cohesive fracture and fragmentation of continuous media

In this paper, the Discontinuous Cell Method (DCM) is formulated with the objective of simulating cohesive fracture propagation and fragmentation in homogeneous solids without issues relevant to excessive mesh deformation typical of available Finite Element formulations. DCM discretizes solids by using the Delaunay triangulation and its associated Voronoi tessellation giving rise to a system of discrete cells interacting through shared facets. For each Voronoi cell, the displacement field is approximated on the basis of rigid body kinematics, which is used to compute a strain vector at the centroid of the Voronoi facets. Such strain vector is demonstrated to be the projection of the strain tensor at that location. At the same point stress tractions are computed through vectorial constitutive equations derived on the basis of classical continuum tensorial theories. Results of analysis of a cantilever beam are used to perform convergence studies and comparison with classical finite element formulations in the elastic regime. Furthermore, cohesive fracture and fragmentation of homogeneous solids are studied under quasi-static and dynamic loading conditions. The mesh dependency problem, typically encountered upon adopting softening constitutive equations, is tackled through the crack band approach. This study demonstrates the capabilities of DCM by solving multiple benchmark problems relevant to cohesive crack propagation. The simulations show that DCM can handle effectively a wide range of problems from the simulation of a single propagating fracture to crack branching and fragmentation.

Comparison of Acceleration Data Structures for High Quality Fast Reflections of Static and Deformable Models in Walkthrough Animations

In order to render realistic images, the reflectance of surfaces must be simulated accurately. Generally, the ray tracing rendering technique is used to make a material reflect its surroundings, since it represents with great fidelity the behavior of light. However, ray tracing is still a very costly algorithm, so far mostly indicated in offline rendering scenarios. This situation is even more challenging for scenes containing 3D deformable meshes, since their geometry and, thus, the acceleration structures used, need to be updated in each frame of the animation. In this paper, we present an extended version of our hybrid algorithm that combines rasterization and a pure ray tracing through the NVIDIA OptiX to render high quality fast reflections, including scenes with deformable models. Additionally, we analyze and compare the performances of different NVIDIA OptiX acceleration data structures for generating reflections of static and deformable models in walkthrough animations. The results show that NVIDIA OptiX acceleration structures reach high frames per second for static objects. However, there is a performance decay in terms of frames per second when dealing with deformable models, since it becomes necessary to update the acceleration structures to cope with changing geometry, but even under these restrictions, we were able to achieve interactive frame rates.