Waterjet penetration simulation by hybrid code of SPH and FEA

The creativity of this work is combining finite element analysis (FEA) and smoothed particle hydrodynamics (SPH) methods to simulate the waterjet (WJ) penetration process. In WJ penetration, the waterjet undergoing extremely large deformation will introduce the distortion of mesh in FEA. To overcome this difficulty, the coupled method of SPH and FEA was developed, in which the waterjet was modeled by SPH particles and the target material was modeled by finite elements. The two parts interacted by contact algorithm of “nodes-to-surface”. Utilizing this hybrid model, waterjet with high velocity penetrating the target materials was calculated and the mechanism of erosion was depicted. The computation result gives the relationship between the jet velocity and the erosion capacity, including the depth of penetration and mass removal, which was compared with the experimental data.     

Comparison study of MPM and SPH in modeling hypervelocity impact problems

Due to the high nonlinearities and extreme large deformation, the hypervelocity impact simulation is a challenging task for numerical methods. Meshfree particle methods, such as the smoothed particle hydrodynamics (SPH) and material point method (MPM), are promising for the simulation of hypervelocity impact problems. In this paper, the material point method is applied to the simulation of hypervelocity impact problems, and a three-dimensional MPM computer code, MPM3D, is developed. The Johnson–Cook material model and Mie–Grüneisen equation of state are implemented. Furthermore, the basic formulations of MPM are compared with SPH, and their performances are compared numerically by using MPM3D and LS-DYNA SPH module.     

典型民机机身段水上冲击数值模拟方法及其耐撞性研究

为了改善民机在紧急迫降情况下的安全性能,对典型机身段水上冲击数值模拟方法及其冲击特性进行了研究。通过合理的简化建立了机身段有限元模型,对有限元方法(FEM)、任意拉格朗日/欧拉方法(ALE)和光滑粒子方法(SPH)水体模型进行了研究,探讨了水体材料模型对机身段结构动态响应特性的影响。在7 m/s垂向冲击速度下,对比分析了水面和刚性地面情况下的机身段结构的耐撞性能。结果表明ALE方法具有最佳计算精度和计算效率。由于忽略了偏应力,采用空材料得到的机身结构响应与弹性流体和弹塑性水体材料有明显不同。在水上冲击过程中,由于水体耗散了大量冲击动能,因此机身加强框变形较小。机身底部蒙皮结构承受较大的均布载荷,因此蒙皮吸能结构吸收了较多的冲击动能,是最重要的吸能结构之一。相对于刚性地面,水面冲击情况下机身具有更小的加速度过载。在紧急迫降情况下,选择湖泊或者江河等水域作为迫降地点可以减小乘员承受加速度过载。     

Experimental and numerical study on the orthogonal and oblique impact on water filled pipes

A 300 mm long piece of copper (ASTM B280) pipe with an outer diameter of 35 mm and 0.7 mm wall thickness was subjected to a rigid steel pipe impact under a drop weight loading configuration where the pipe was simply supported at its ends. Differences in deformation features for a pipe filled with water and an empty pipe were investigated for two configurations namely orthogonal and oblique impact. Compared to orthogonal pipe impact the oblique pipe impact has not been reported in the literature. It is hoped that current work would serve as a first step in this direction. Finite Element Method coupled with Smooth Particle Hydrodynamics (SPH) available in LS-DYNA was used to simulate the empty and water filled pipe impacts under orthogonal and oblique configurations respectively. Fluid structure interaction (FSI) during the water filled pipe impact was successfully modeled using SPH which is a simple method for predicting the short duration FSI events. Experimental results of the effect of varying D/T ratio on the empty and water filled pipes have been reported.     

An ellipsoidal particle–finite element method for hypervelocity impact simulation

A number of coupled particle–element and hybrid particle–element methods have been developed for the simulation of hypervelocity impact problems to avoid certain disadvantages associated with the use of pure continuum‐based or pure particle‐based methods. To date these methods have employed spherical particles. In recent work a hybrid formulation has been extended to the ellipsoidal particle case. A model formulation approach based on Lagrange's equations, with particle entropies serving as generalized coordinates, avoids the angular momentum conservation problems which have been reported with ellipsoidal smooth particle hydrodynamics models. Copyright © 2003 John Wiley & Sons, Ltd.     

A kernel free particle‐finite element method for hypervelocity impact simulation

An improved hybrid particle‐finite element method has been developed for the simulation of hypervelocity impact problems. Unlike alternative methods, the revised formulation computes the density without reference to any kernel or interpolation functions, for either the density or the rate of dilatation. This simplifies the state space model and leads to a significant reduction in computational cost. The improved method introduces internal energy variables as generalized co‐ordinates in a new formulation of the thermomechanical Lagrange equations. Example problems show good agreement with exact solutions in one dimension and good agreement with experimental data in a three‐dimensional simulation. Copyright © 2005 John Wiley & Sons, Ltd.     

Impact analysis of arbitrarily‐shaped bodies using a finite element method and a smoothed particle hydrodynamics method

We propose a new method to obtain contact forces under a non‐smoothed contact problem between arbitrarily‐shaped bodies which are discretized by finite element method. Contact forces are calculated by the specific contact algorithm between two particles of smoothed particle hydrodynamics, which is a meshfree method, and that are applied to each colliding body. This approach has advantages that accurate contact forces can be obtained within an accelerated collision without a jump problem in a discrete time increment. Also, this can be simply applied into any contact problems like a point‐to‐point, a point‐to‐line, and a point‐to‐surface contact for complex shaped and deformable bodies. In order to describe this method, an impulse based method, a unilateral contact method and smoothed particle hydrodynamics method are firstly introduced in this paper. Then, a procedure about the proposed method is handled in great detail. Finally, accuracy of the proposed method is verified by a conservation of momentum through three contact examples. Copyright © 2016 John Wiley & Sons, Ltd.     

Modelling of Bird Strike on an Aircraft Wing Leading Edge Made from Fibre Metal Laminates – Part 2: Modelling of Impact with SPH Bird Model

Fibre Metal Laminates with layers of aluminium alloy and high strength glass fibre composite have been reported to possess excellent impact properties and be suitable for aircraft parts likely to be subjected to impacts such as runway debris or bird strikes. In a collaborative research project, aircraft wing leading edge structures with a glass-based FML skin have been designed, built, and subjected to bird strike tests that have been modelled with finite element analysis. In this second part of a two-part paper, a finite element model is developed for simulating the bird strike tests, using Smooth Particle Hydrodynamics (SPH) for modelling the bird and the material model developed in Part 1 of the paper for modelling the leading edge skin. The bird parameters are obtained from a system identification analysis of strikes on flat plates. Pre-test simulations correctly predicted that the bird did not penetrate the leading edge skin, and correctly forecast that one FML lay-up would deform more than the other. Post test simulations included a model of the structure supporting the test article, and the predicted loads transferred to the supporting structure were in good agreement with the experimental values. The SPH bird model showed no signs of instability and correctly modelled the break-up of the bird into particles. The rivets connecting the skin to the ribs were found to have a profound effect on the performance of the structure.     

An experimental and numerical investigation on tyre impact

A key issue in the design of tyres is their capability to sustain intense impact loads. Hence, the development of a reliable experimental data basis is important, against which numerical models can be compared. Experimental data on tyre impact in the open literature is somewhat rare. In this article, a specially design rig was developed for tyre impact tests. It holds the test piece in a given position, allowing a drop mass with a round indenter to hit pressurised tyres with different impact energies. A high-speed camera and a laser velocimeter were used to track the impact event. From the laser measurement it was possible to obtain the impact force and the local indentation. A finite element study was then conducted using material properties from the open literature. By comparing the experimental measurements with the numerical results, it became evident that the model was capable of predicting the major features of the impact of a mass on a tyre. This model is therefore of value for the assessment of the performance of a tyre in extreme cases of mass impact.     

A discrete splitting finite element method for numerical simulations of incompressible Navier–Stokes flows

The presence of the pressure and the convection terms in incompressible Navier–Stokes equations makes their numerical simulation a challenging task. The indefinite system as a consequence of the absence of the pressure in continuity equation is ill‐conditioned. This difficulty has been overcome by various splitting techniques, but these techniques incur the ambiguity of numerical boundary conditions for the pressure as well as for the intermediate velocity (whenever introduced). We present a new and straightforward discrete splitting technique which never resorts to numerical boundary conditions. The non‐linear convection term can be treated by four different approaches, and here we present a new linear implicit time scheme. These two new techniques are implemented with a finite element method and numerical verifications are made. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamic analysis of instrumented CHARPY impact tests using specimen deflection measurement and mass-spring models

A new experimental procedure is proposed which allows the determination of parameters of mass-spring models used to analyse the CHARPY impact test. It is based on the measurement of the tup load and the specimen deflection during the impact test. The contact stiffness between the tup and the specimen is derived from the ratio of the specimen deflection over the tup displacement. The model predictions are compared with experimental results obtained from impact tests performed on PMMA specimens. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of contact fatigue crack growth using twin-disc tests and numerical evaluations

The contact fatigue damages on the rail surface, such as head check, squats are one of the growing problems. Fracture of rail can be prevented by removing the crack before it reaches the critical length. Therefore, the crack growth rate needs to be estimated precisely according to the conditions of the track and load. In this study, we have investigated the crack growth behavior on rail surface by using the twin-disc tests and the finite element analysis. We have verified the relationship between the crack growth rate and the variety of parameters as cracks grow from the initiation stage.     

Finite element analysis (FEA) applied to polyethylene foam cushions in package drop tests

Two designs of polyethylene (PE) foam cushions were compared, using a rigid ‘product’ of mass 5.6 kg, and an outer corrugated fibreboard box. The acceleration–time history for the product was measured when the box was dropped flat from 1 m onto a rigid floor. The data was processed to calculate the impact force as a function of the packaging deformation. Finite element analysis (FEA) predictions of the impact force vs. package deflection were accurate for end‐cap designs using Ethafoam, but underestimated the slope of the experimental force vs. deflection relation for corner‐cap designs. The corner‐cap design is more efficient in reducing the peak product acceleration for multiple impacts. The contribution of the corrugated board box to the impact response appears to be small. The FEA results were compared with those from the cushion curve design method and were found to better predict the performance of complex shaped cushions. Copyright © 2004 John Wiley & Sons, Ltd.     

基于有限元与光滑粒子耦合的弹丸挤进过程分析

基于有限元（FEM）与光滑粒子（SPH）耦合算法,建立弹丸身管耦合系统动力学模型。通过对某大口径火炮弹丸挤进过程进行数值模拟,弥补弹丸挤进过程有限元分析方法无法有效模拟弹带大变形缺陷,成功模拟出弹丸挤进阶段弹带塑性流动过程,在此基础上深入研究弹带的应力应变变化规律。分析弹丸初始装填角、弹炮间隙、弹丸装填不到位等因素对挤进过程中弹丸动力响应影响。结果表明,仿真与实弹射击的弹带变形一致性较好。     

Failure analysis of low velocity impact on thin composite laminates: Experimental and numerical approaches

The dynamic behavior of composite laminates is very complex because there are many concurrent phenomena during composite laminate failure under impact load. Fiber breakage, delaminations, matrix cracking, plastic deformations due to contact and large displacements are some effects which should be considered when a structure made from composite material is impacted by a foreign object. Thus, an investigation of the low velocity impact on laminated composite thin disks of epoxy resin reinforced by carbon fiber is presented. The influence of stacking sequence and energy impact was investigated using load–time histories, displacement–time histories and energy–time histories as well as images from NDE. Indentation tests results were compared to dynamic results, verifying the inertia effects when thin composite laminate was impacted by foreign object with low velocity. Finite element analysis (FEA) was developed, using Hill’s model and material models implemented by UMAT (User Material Subroutine) into software ABAQUS™, in order to simulate the failure mechanisms under indentation tests.     

A robust and efficient numerical finite element method for cables

Numerical simulation of cable systems remain delicate due to their geometrical nonlinearity and also to their intrinsic unilateral constitutive law. Indeed Finite Element approaches (if not implemented carefully) fail to predict accurate equilibrium for cable structures. The major issue to be addressed is the ill-conditioning, starting configuration and wrong choice of descent direction during iterative methods. An iterative scheme based on Finite Element Method is presented to overcome this issue, even with large number of elements.     

Post-impact behaviour of aerospace composites for high-temperature applications: experiments and simulations

The post-impact performance of different carbon-fabric-reinforced composite materials were studied experimentally and analytically. Three types of thermosetting matrix were considered: conventional epoxy, high-temperature curing epoxy and epoxy-isocyanate. Experimental testing consisted of impacting rectangular specimens at different energy levels by using a spring-driven impact apparatus that was able to impart velocities of up to 5 m s⁻¹ to masses of 0.5, 1.0, 2.5 and 5.0 kg travelling horizontally. After impact, coupons were non-destructively inspected by means of opaque-enhanced dye-penetrant X-radiography and tested in static compression to correlate impact energy, damage extent and residual strength. Epoxy composites contain damage within a narrow region, while epoxy-isocyanate materials propagate the damage far away from impact point. Epoxy composites show an asymptotically decreasing failure strength with impact energy up to a lower threshold (0.3–0.4 times that of the undamaged material), while epoxy-isocyanate material shows a trend of ever decreasing residual strength. An analytical study was performed by means of the finite element code PAM-FISS, used to simulate the compression-after-impact (CAI) tests. Type, size and location of damage, as well as the mechanisms leading to final failure, were reproduced quite well by the finite element analysis (FEA), while some discrepancies between FEA and experimental CAI residual strength tests were found (7% for undamaged specimens and 10% for blister-delaminated specimens); higher errors were found in the case of completely delaminated specimens, mainly owing to the inability of the present software and hardware to conveniently model the complete state of damage.     

Improved fractional step method for simulating fluid‐structure interaction using the PFEM

Numerical difficulties are present in the particle finite element method even though it has been shown to be a powerful and effective approach to simulating fluid‐structure interaction. To overcome problems of mass loss on the free surface and the added‐mass effect, an improved fractional step method (FSM) that handles added‐mass terms in a mathematically exact way is developed. A further benefit is that no assumptions regarding the structural response are made in handling added‐mass terms, thus it is straightforward to incorporate material nonlinearity in fluid‐structure interaction (FSI) under this approach. Patch tests and comparisons with experimental data are presented in order to verify and validate the improved FSM for FSI applications. The computational cost of this approach is shown to be negligible compared with the other aspects of the FSM, particularly when the size of the structure and the fluid‐structure interface is small relative to the volume of fluid. Copyright © 2014 John Wiley & Sons, Ltd.     

Multi-objective optimization design using amended particle swarm optimization and Taguchi method for a six-phase copper rotor induction motor

A multi-objective optimization design technique for a six-phase copper rotor induction motor is proposed. The amended particle swarm optimization (PSO) and Taguchi methods combined with finite element analysis are used in this design technique. The objectives in the first-stage optimization are the minimization of manufacturing cost and starting current. In the second-stage optimization, the objectives are the maximization of efficiency, power factor and output torque. The Taguchi method can optimize the machine parameters of performance characteristics in electrical discharge machining. The experimental results are further transformed into the signal-to-noise ratios and amended PSO coefficients based on amended PSO analysis with regard to multiple performance characteristics index values. The results of the optimizations showed significant reduction in terms of the use of magnets as well as improvement in the machine performance. Finally, the experimental results confirm the validity of the proposed optimization design approach.