Finite Element Simulation Techniques Research Articles

Thermomechanical Simulation of the Splashing of Ceramic Droplets on a Rigid Substrate

Finite element simulation techniques have been applied to the spreading process of single ceramic liquid droplets impacting on a flat cold surface under plasma-spraying conditions. The goal of the present investigation is to predict the geometrical form of the splat as a function of technological process parameters, such as initial temperature and velocity, and to follow the thermal field developing in the droplet up to solidification. A non-linear finite element programming system has been utilized in order to model the complex physical phenomena involved in the present impact process. The Lagrangean description of the motion of the viscous melt in the drops, as constrained by surface tension and the developing contact with the target, has been coupled to an analysis of transient thermal phenomena accounting also for the solidification of the material. The present study refers to a parameter spectrum as from experimental data of technological relevance. The significance of process parameters for the most pronounced physical phenomena is discussed as are also the consequences of modelling. We consider the issue of solidification as well and touch on the effect of partially unmelted material.

Simulating turbulent flow over thin element and flat valley V-shaped riblets

The time-dependent flow over riblets of various shapes is calculated using a control volume finite element simulation technique and assuming a model of the near-wall viscous flow region of a turbulent boundary layer. The cross-sectional shapes considered include thin element blade riblets and saw-toothed riblets (but with flat valleys), which are similar to the more common continuous V-shaped riblets. Turbulence statistics derived from the calculations include skewness and flatness factors. It is concluded that to achieve maximum drag reduction, riblets not only need to ensure a thicker than usual viscous laminar-like flow in their grooves, but also the transient momentum exchange must be minimized between this inner region and the larger-scale outer motions associated with quasistreamwise vortices.

Finite element simulation (FES): A computer modeling technique for studies of chemical modification of the ionosphere

A numerical modeling code for ionospheric modification experiments has been developed using finite element simulation (FES) techniques. The FES approach to multi-component diffusion and chemistry is described in the context of chemical release “active experiments” in the F-region ionosphere. Comparisons of simulation results matched to cases for which analytical solutions exist, as well as with actual experimental observations, point to a successful and versatile capability for predicting and interpreting chemical induced ionospheric modifications.

Calculation of non-Newtonian flow of colloidal dispersions: Finite elements and Brownian dynamics

We present a novel method for the numerical calculation of the flow of particulate fluid systems and apply it to the flow of a colloidal dispersion. This method is based on the CONNFFESSIT (Calculation Of Non-Newtonian Flow: Finite Element and Stochastic Simulation Technique) [Laso and Ottinger, J. Non-Newtonian Fluid Mech., 47 (1993) 1]. It couples microscopic dynamic simulations (Brownian Dynamics, BD) with macroscopic Finite Element (FE) methods as traditionally used in the calculation of viscoelastic flow. The standard continuum-mechanical form of the momentum transport equation is closed by microscopic BD simulations. The coupling between the macroscopic FE formulation for the velocity field and the microscopic simulation is effected through the stress tensor, which is obtained as an ensemble average over BD trajectories. This combination of microscopic simulations with macroscopic FE methods obviates the need for a rheological constitutive equation (strain history-stress relationship) to describe the fluid system. It is therefore possible to solve flow problems for very general fluid systems, for which no exact constitutive equation can be derived.

Study on a method for direct optical measurement of the nonlinear fracture parameter T* integral. 2nd Report. Hybrid numerical-experimental method on the T* integral caustic measurement.

This paper presents a methodology of direct experimental measurement of the T* integral which has great potential as a nonlinear (elastoplastic) fracture mechanics parameter. A hybrid numerical-experimental method was developed to measure the T* integral by the maximum size of reflected caustic patterns. To this end, the formation process of the caustic pattern for an elastoplastic crack-tip in a compact tension specimen was simulated by the previously developed finite element simulation technique aided by computerized symbolic manipulation. Experimental measurement of·the caustic pattern in the compact tension specimen was also carried out. Both simulated and actual caustic patterns agreed very well. The relations between the T* integral and the size of causticpattern were obtained f or various optical setups.

Numerical solution methods for electroheat problems

This paper reviews the use of numerical methods in simulating and solving problems that arise in the electroheat industry. Particular attention is given to the coupled electrothermal and induction stirring problems that are typical of this industry. Following a brief review of the nature of electrothermal problems, the Finite Difference, Volume Integral Equation and Finite Element simulation techniques are critically examined. It is shown that each technique has a definite role and each is illustrated with practical examples. A brief discussion of unsolved problems is presented.

Measurement and simulation of thermistor response time in the millisecond range

The Finite Element Simulation Technique (FEST) has been applied to the design of hermetically-sealed thermistors with millisecond response times. These thermistors are used in stopped-flow calorimeters developed especially for investigations of biological reactions. FEST is also used to reconstruct the reaction kinetics obtained with these thermistors by correcting for their finite sensor response times and temperature loss.

Fast stopped-flow microcalorimeter

A fast stopped-flow microcalorimeter using a thermistor and an a.c. bridge is described. Time resolution, limited by the response of the thermistor, is 3 ms for t 1 2 while sensitivity is 100 μ°C in this bandpass. A reaction requires 0.3 ml of each reactant. The microcalorimeter is adiabatic to within 2% for 2 s and mixing may be repeated every 5 min. Computer finite element simulation techniques (FEST) are used to correct for the thermistor response time and heat losses. Results of tests with reactions of NaOH and HCl, NaHCO 3 and HCl, and glycylglycine and CO 2 agree with published kinetic and thermodynamic values to within an experimental error of less than 2%.

Block iterative finite element preprocessed scheme for simulation of large non‐linear problems

AbstractThe ‘Block Iterative Finite Element Preprocessed Scheme’ (BIFEPS) for finite element simulation combines two independent steps. In the ‘finite element preporcessing step’, spatial information about the finite element mesh is analysed and all integrals arising from the application of the Galerkin method are evaluated and stored on a permanent sequential storage unit (such as tape or disk). In the ‘block iterative step’, the preprocessed information is retrieved from permanent storage and the matrix equation is assembled and solved in an efficient manner according to a generalization of the block successive over‐relaxation iterative method. Significant advantages over common finite element simulation techniques are achieved in terms of both computer core requirements and execution time. Numerical experiments show that the advantages of BIFEPS are greatest for large, non‐linear simulation problems.