Huilin Xing

Numerical analysis and design for tubular hydroforming

Abstract To get an optimum deformation path for tubular hydroforming, the hydroforming limit of isotropic and anisotropic tubes subjected to internal hydraulic pressure, independent axial load or torque is firstly proposed based on the Hills general theory for the uniqueness to the boundary value problem and compared with those of the conventional sheet forming. The influences of the deformation path, the material properties and the active length–diameter ratio on the nucleation and the development of wrinkling during the free tubular hydroforming are also investigated. The above theory is used as a criterion and implemented with some new functions in our ITAS3D, an in-house finite element code for simulating the sheet forming, to control the materials flow and to prevent the final failure modes from occurring. Finally, the tubular hydroforming of an automobile differential gear box is taken as an example to show the efficiency and usefulness of the algorithm.

Three dimensional finite element modeling of thermomechanical frictional contact between finite deformation bodies using R-minimum strategy

An algorithm for analyzing the transient thermal coupling with the frictional contact between the multiple elastic-plastic bodies in finite deformation is presented using the R-minimum strategy. An arbitrarily shaped contact element strategy, named as node-to-point contact element strategy, is proposed to handle the thermomechanical frictional contact between finite deformation bodies. Assuming the material properties to be temperature dependent, the constitutive equations for both the thermomechanical frictional contact and the thermal-elastic-plastic materials are deduced respectively and applied in our finite element code. Finally, two examples are presented to show the efficiency and usefulness of this algorithm

Three-dimensional finite element simulation of large-scale nonlinear contact friction problems in deformable rocks

A three-dimensional finite element method is proposed and used to deal with large-scale nonlinear contact friction problems in deformable rocks. Together with the use of the node-to-point contact element strategy, the corresponding three-dimensional finite element algorithm is presented to simulate the nonlinear contact friction behaviour between deformable rock blocks. In order to ensure the correctness and accuracy of the resulting numerical solutions, the proposed finite element formulation for a three-dimensional nonlinear contact friction problem is verified using a benchmark problem, for which the analytical solution is available. As an application example, the proposed three-dimensional finite element method is used to investigate the plate behaviour of a subduction fault model, which simulates a region around Northeast Japan. Due to the general nature of the methodology, the proposed three-dimensional finite element algorithm can be also used to simulate many nonlinear contact friction problems associated with the slope instability process and the sliding failure mechanism between a gravity dam and its foundation in the engineering field.

Finite-element analysis and design of thin sheet superplastic forming

Abstract A 3-dimensional finite-element method using a constant strain triangular membrane element for modeling non-Newtonian sheet flow has been developed. Meanwhile, microstructure variation (such as grain growth and cavity growth) during superplastic forming is considered. An adaptive algorithm is presented for the calculation of the back pressure and the bulging pressure to control cavity growth and distribution and to maintain the optimum deformation mode. Then a simple and effective pre-forming design method is presented and applied to control the sheet forming and to obtain components with a more reasonable wall-thickness distribution. Finally, examples are presented for the forming of a square box and the cover of an electric device, with pre-forming design.

Lattice Boltzmann modeling and evaluation of fluid flow in heterogeneous porous media involving multiple matrix constituents

Geomaterials are typical heterogeneous porous media involving multiple types of matrix constituents which dominate the subsurface flow behavior. An improved lattice Boltzmann method (LBM) approach is developed for analyzing the detailed flow characteristics through multiple matrix constituents, investigating sample size effects on the permeability variation, and evaluating characteristic information at the representative elementary volume (REV) scale for the macroscale reference. Applications are conducted in both 2D and 3D to numerically investigate the impact of geometric topology and matrix property on the detailed velocity field, and effects of sample sizes on the permeability for evaluating effective REV scale fluid flow parameters. The simulation results demonstrate that the improved LBM approach is able to quantitatively describe and simulate complex fluid flow through multiple-matrix constructed heterogeneous porous media, which provides more realistic simulation results for up-scaled research and engineering. Quantitative modeling of detailed heterogeneous porous media flow involving multiple permeable minerals.Investigating sample size effects on the permeability variation and the flow flux.Evaluating characteristic information at the representative element volume (REV) scale for the macroscale reference.Providing meaningful REV scale parameters for relative up-scaling research.2D/3D applications in porous flows involving quartz, clay, feldspar and cavities.

Finite-element modeling of multibody contact and its application to active faults

Earthquakes have been recognized as resulting from a stick–slip frictional instability along the faults between deformable rocks. An arbitrarily‐shaped contact element strategy, named the node‐to‐point contact element strategy, is proposed, applied with the static‐explicit characters to handle the friction contact between deformable bodies with stick and finite frictional slip and extended here to simulate the active faults in the crust with a more general nonlinear friction law. An efficient contact search algorithm for contact problems among multiple small and finite deformation bodies is also introduced. Moreover, the efficiency of the parallel sparse solver for the nonlinear friction contact problem is investigated. Finally, a model for the plate movement in the north‐east zone of Japan under gravitation is taken as an example to be analyzed with different friction behaviors. Copyright

Recent development in numerical simulation of enhanced geothermal reservoirs

This paper briefly introduces the current state in computer modelling of geothermal reservoir system and then focuses on our research efforts in high performance simulation of enhanced geothermal reservoir system. A novel supercomputer simulation tool has been developing towards simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involving heterogeneously fractured geomaterials at different spatial and temporal scales. It is applied here to simulate and visualise the enhanced geothermal system (EGS), such as (1) visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e., the permeability) for the further numerical analysis and evaluation of the enhanced geothermal reservoir; (2) converting the available fractured rock image/fracture data as well as the reservoir geological geometry to suitable meshes/grids and further simulating the fluid flow in the complicated fractures involving the detailed description of fracture dimension and geometry by the lattice Boltzmann method and/or finite element method; (3) interacting fault system simulation to determine the relevant complicated rupture process for evaluating the geological setting and the in-situ reservoir properties; (4) coupled thermo-fluid flow analysis of a geothermal reservoir system for an optimised geothermal reservoir design and management. A few of application examples are presented to show its usefulness in simulating the enhanced geothermal reservoir system.

Ejection landslide at northern terminus of beichuan rupture triggered by the 2008 Mw 7.9 Wenchuan earthquake

On 12 May 2008, the Mw 7.9 Wenchuan earthquake triggered wide- spread damaging landslides in many parts of the Longmen Shan area. Among these landslides, the Donghekou ejection landslide is quite special. It is located at the north- east end of the Beichuan rupture, and it has caused a great loss of life at the villages of Donghekou, Qinchuan, and Sichuan Provinces. Because of its special location, this ejection landslide differs from landslides caused by gravity or rainstorms only; the sliding surface is not uniformly continuous. Instead, two sections can be distin- guished: an upper section with a step sliding surface and a lower section more gently dipping. The landslide started with material ejection caused by large local seismic acceleration, throwing rocks into the air with a parabolic trajectory before they fell back to the ground. In this paper, we analyze geologic and geomorphologic conditions that favored the occurrence of this landslide, and we introduce a simple tectonic- geomorphology model to explain the mechanism that led to the ejection landslide. We find that the location of the landslide zone, along with the domino-like ground tension cracks observed on both sides of the Beichuan rupture, is controlled by the propagation of the rupture. Our result also suggests that, in addition to local seismic shaking intensity, horizontal acceleration, and geomorphologic and geologic condi- tions, the vertical acceleration and the style of faulting could also play an important role in the occurrence of earthquake-triggered landslides.

FE modeling of thermo‐elasto‐plastic finite deformation and its application in sheet warm forming

In this paper, a strategy for analyzing a problem of the transient thermal coupling with the elastoplastic finite deformation is presented. A general constitutive equation is deduced by assuming the material properties to be temperature‐dependent. The thermal and mechanical coupling problem is solved with a staggered algorithm, which partitions the coupled problem into an elasto‐plastic problem at the known temperature field and a pure heat transfer problem at the fixed configuration. In this procedure, the elasto‐plastic mechanical analysis is based on the static‐explicit solution algorithm, which applies the finite deformation theory to describe the nonlinear behavior of the deformation body and its contact interaction with the tools during the forming process induced by the ordinary external loading and the “thermal loading”. In addition, both the ordinary heat transfer boundary conditions and the mechanical terms are taken into account in the implicit finite element analysis of the heat transfer. A special method based on the R‐minimum strategy is presented to solve the interaction problem between the static‐explicit mechanical analysis and the implicit thermal analysis. Furthermore, as examples, the analyses of sheet warm forming processes are demonstrated.

A unified friction description and its application to the simulation of frictional instability using the finite element method

This article first summarizes some available experimental results on the frictional behaviour of contact interfaces, and briefly recalls typical frictional experiments and relationships, which are applicable for rock mechanics, and then a unified description is obtained to describe the entire frictional behaviour. It is formulated based on the experimental results and applied with a stick and slip decomposition algorithm to describe the stick--slip instability phenomena, which can describe the effects observed in rock experiments without using the so-called state variable, thus avoiding related numerical difficulties. This has been implemented to our finite element code, which uses the node-to-point contact element strategy proposed by the authors to handle the frictional contact between multiple finite-deformation bodies with stick and finite frictional slip, and applied here to simulate the frictional behaviour of rocks to show its usefulness and efficiency.