Parameters Of Numerical Model Research Articles

The Chemical Kinetic Numerical Computation and Kinetic Model Parameters Estimating of Parallel Reactions with Different Reaction Orders

Abstract. Parallel reaction is a common reaction of chemical kinetics, and there are two types of parallel reactions according to the reaction orders equivalence: parallel reactions with same reaction orders and parallel reactions with different reaction orders. For the reason that the reaction orders are different, the chemical kinetic numerical computation and kinetic model parameters estimating of parallel reactions with different reaction orders is more complicated than parallel reactions with same reaction orders. In this paper, the 4th order Runge-Kutta method was employed to solve the numerical computation problems of complex ordinary differential equations, which was the chemical kinetic governing equations of parallel reactions with different reaction orders, and also, the Richardson extrapolation and Least Square Estimate were employed to estimate the kinetic model parameters of parallel reactions with different reaction orders. A C++ program has been processed to solve the problem and has been tested by an example of parallel reactions with different reaction orders.

Lumped parameter model of sintered heat pipe: Transient numerical analysis and validation

This paper describes a lumped parameter numerical model which is able to simulate the transient as well as the steady-state operation of a sintered heat pipe. The main objective of the work is to build a simple, engineering-approach simulation tool to define the HP characteristics of small HPs, which are now in the market with doubtful specifications. The code has been validated by comparisons with numerical and experimental results readily available from the open literature and an extensive numerical simulation campaign has been carried out in order to characterize the thermal–hydraulic behavior of mini heat pipes. This analysis focuses particularly on the effects of wick thickness, porosity, grain structure and void fraction level in the evaporator on thermal performance and working limits. Mini HPs with different dimensions (8, 5 and 3 mm outer diameter, 1 mm wall thickness, sintered copper wick, water as filling fluid) have been considered. It was found that there is an optimum wick thickness which minimizes the thermal resistance with no remarkable grain radius effect, while, as expected, the grain size affects the evaporator wick dryness.

Spatial distribution of tissue level properties in a human femoral cortical bone

The mechanical properties of cortical bone are determined by a combination bone tissue composition, and structure at several hierarchical length scales. In this study the spatial distribution of tissue level properties within a human femoral shaft has been investigated. Cylindrically shaped samples (diameter: 4.4mm, N=56) were prepared from cortical regions along the entire length (20–85% of the total femur length), and around the periphery (anterior, medial, posterior and lateral quadrants). The samples were analyzed using scanning acoustic microscopy (SAM) at 50MHz and synchrotron radiation micro computed tomography (SRμCT). For all samples the average cortical porosity (Ct.Po), tissue elastic coefficients (cij) and the average tissue degree of mineralization (DMB) were determined. The smallest coefficient of variation was observed for DMB (1.8%), followed by BV/TV (5.4%), cij (8.2–45.5%), and Ct.Po (47.5%). Different variations with respect to the anatomical position were found for DMB, Ct.Po and cij. These data address the anatomical variations in anisotropic elastic properties and link them to tissue mineralization and porosity, which are important input parameters for numerical multi-scale bone models.

PEMFC application for aviation: Experimental and numerical study of sensitivity to altitude

Proton Exchange Membrane Fuel Cells are more and more considered as energy converters for mobile applications, such as road vehicles, boats and airplanes. The feasibility of PEMFC integration to aircraft raises several difficulties such as the loss of performance due to altitude and ambient pressure decrease.An aerobic PEMFC system is experimentally investigated at three different altitudes representative of aircraft cruise (200 m, 1200 m and 2200 m), and at different air stoichiometric factors (from 1.5 to 2.5). The experimental results are employed to perform fitting of PEMFC numerical model parameters and validation of the model. A least square method is implemented in a Matlab® code to determine one set of model parameters for all experimental data sets. The model based on literature is modified in order to better represent the effect of ambient pressure on voltage response. Comparisons of experimental and numerical results are presented and show good agreement. Fuel cell performance is found to decrease drastically as altitude increases, as well as air stoichiometric factor decreases. The air pressure in cathode gas channels is measured and analysed. The decline of PEMFC performances in altitude is due to ambient pressure decrease, to air compressor efficiency drop and to flooding in the gas channels. This PEMFC loss of performances is attenuated by high cathode stoichiometric factors.

Short-Distance Undercrossing of Shield Tunneling on Existent Tunnel in Soft Soil Area

In urban environment, short-distance undercrossing of shield tunneling to an existent tunnel is an unloading process and can cause adverse effect on the existent tunnel. This kind of effect should be controlled. To analysis and control this effect, numerical simulation, field monitoring and optimization of construction parameter are used. To get reasonable calculation parameters for numerical models, field monitoring is conducted. The numerical simulation is utilized to study the process of short-distance undercrossing. The simulation result revealed that the deformation of the existent tunnel can be beyond the tolerable value unless some measure is adopted, but the deformation can be reduced significantly by improving the ground under the existent tunnel with cement deep mixing method. Construction measures are adopted, such as the strict controlling of synchronized grouting, secondary grouting, rotation speed of cutter head and driving speed. As a result, the deformation of the existent tunnel is controlled in the tolerable value.

Design and experiment of a cradle truss type floating raft system

In this paper, a new design concept of an isolated cradle trusslike structure to support vibrating machinery is proposed. The acoustic and vibratory energy transmission in this isolation system is investigated to improve the vibration isolation performance of conventional floating raft system. The finite element method and experimental measurements are used to understand the dynamic behavior of this cradle truss. In conjunction with experiments, a vectorial four pole parameter numerical model is used to identify power flow of the floating raft isolation system. The proposed floating raft design achieved a vibration reduction of 30–40dB in the frequency range of 20–600Hz. It is also shown that the loss factors of the cradle truss configured floating raft are up to 4dB than conventional floating flat raft.

Design rules for composite sandwich wakeboards

Wakeboarding is a water sport born in the mid 1980s that derives from surfing and water skiing. The objective of this work is to understand the failure mechanism and evaluate the maximum hydroelastic loads during the slamming phenomena of the board used in this sport, in order to provide reliable design rules to follow during the design process. Wakeboards are usually built as a composite sandwich structure, with plastic foam core and CFRP (carbon fibre reinforced plastics) or GFRP (glass fibre reinforced plastics) faces. Several specimens were extracted from a real board and tested in three point bending to investigate the major failure mechanisms. These data are later used in a parametric full-scale SPH numerical model investigation of the water-entry event. The numerical results show that, due to the fluid–structure interaction, there is a maximum deformation that the board cannot overreach even for very high impact energies. This limits the maximum impact stresses reached during the water entry of wakeboards. From these numerical results, mathematical relations between design variables are drawn by using analytical formulas based on classical sandwich theory. As result of this research, practical guidelines (formulas, tables and graphs) on the effects of total mass, initial impact velocity, board curvature and core and face strength and thickness are outlined to give reliable design rules.

Functional grading in hierarchical honeycombs: Density specific elastic performance

The introduction of hierarchy into structures has been credited with improving their elastic and other properties. Similarly, functional grading has been demonstrated to increase the damage tolerance of honeycomb structures, although with the penalty of reduced Young’s modulus or increased density. The combination of both hierarchy and functional grading has not been reported for honeycomb structures, although it is known in natural materials. A parametric numerical modelling study has been made of the in-plane elastic properties of honeycombs and how they are affected by functional grading and hierarchy, and importantly to establish whether it is possible to avoid reductions in Young’s modulus. A set of analytical models has been developed to describe functional grading and hierarchy in honeycombs, based upon beam mechanics and the transform section method. The conditions for transition of a hierarchical honeycomb in behaviour from that of a discrete structure to that of a continuum are established. Furthermore, conditions are established for which hierarchical honeycombs, uniform or functionally graded, can surpass in-plane Young’s moduli of conventional honeycombs a by factor of up to 2, on an equal density basis.

Direct comparison of measured and calculated total knee replacement force envelopes during walking in the presence of normal and abnormal gait patterns

Knee joint forces measured from instrumented implants provide important information for testing the validity of computational models that predict knee joint forces. The purpose of this study was to validate a parametric numerical model for predicting knee joint contact forces against measurements from four subjects with instrumented TKRs during the stance phase of gait. Model sensitivity to abnormal gait patterns was also investigated. The results demonstrated good agreement for three subjects with relatively normal gait patterns, where the difference between the mean measured and calculated forces ranged from 0.05 to 0.45 body weights, and the envelopes of measured and calculated forces (from three walking trials) overlapped. The fourth subject, who had a “quadriceps avoidance” external moment pattern, initially had little overlap between the measured and calculated force envelopes. When additional constraints were added, tailored to the subject’s gait pattern, the model predictions improved to complete force envelope overlap. Coefficient of multiple determination analysis indicated that the shape of the measured and calculated force waveforms were similar for all subjects (adjusted coefficient of multiple correlation values between 0.88 and 0.92). The parametric model was accurate in predicting both the magnitude and waveform of the contact force, and the accuracy of model predictions was affected by deviations from normal gait patterns. Equally important, the envelope of forces generated by the range of solutions substantially overlapped with the corresponding measured envelope from multiple gait trials for a given subject, suggesting that the variable strategic processes of in vivo force generation are covered by the solution range of this parametric model.

Experiments and numerical simulations of single particle foreign object damage-like impacts of thermal barrier coatings

The thermal barrier coatings (TBCs) used on the hot section components of many aero-turbines face a variety of compromising conditions while in service. One condition of particular concern on high-pressure turbine (HPT) blades is foreign object damage (FOD) wherein hard foreign particles, often found in the gas path of operating aero-turbines, are struck by the leading edge of the HPT blades. Even single impacts of this kind can cause complete spallation of the local TBC, removing thermal protection on one of the hottest component surfaces in the entire engine. We present here the first experimental FOD study we know of where the impacting particle size, geometry, and velocity, as well as TBC temperature, are well known at each impact site. We then quantitatively compare the experimental impact crater profiles with numerical simulations of equivalent impact scenarios, finding excellent agreement and thereby validating the numerical modeling techniques and parameters. Finally, we present a numerical parameter study of particle and TBC material properties using the validated model.

Robust Sliding Mode Control for Tokamaks

Nuclear fusion has arisen as an alternative energy to avoid carbon dioxide emissions, being the tokamak a promising nuclear fusion reactor that uses a magnetic field to confine plasma in the shape of a torus. However, different kinds of magnetohydrodynamic instabilities may affect tokamak plasma equilibrium, causing severe reduction of particle confinement and leading to plasma disruptions. In this sense, numerous efforts and resources have been devoted to seeking solutions for the different plasma control problems so as to avoid energy confinement time decrements in these devices. In particular, since the growth rate of the vertical instability increases with the internal inductance, lowering the internal inductance is a fundamental issue to address for the elongated plasmas employed within the advanced tokamaks currently under development. In this sense, this paper introduces a lumped parameter numerical model of the tokamak in order to design a novel robust sliding mode controller for the internal inductance using the transformer primary coil as actuator.

Towards clinical applicability of the diffusion-based DT-MRI visualization algorithm

For the purpose of DT-MRI data visualization, an algorithm based on a numerical model of texture diffusion is proposed. As a prerequisite of entering clinical use, its parameters need to be adjusted properly so that the procedure gives satisfactory results with limited computational resources and time available. This contribution introduces the principles of the method and reports on the results of extensive computational studies aimed at finding optimal settings of the numerical scheme and model parameters with respect to visualization purposes. Total variation is used as a measure of visual quality of the produced images. Further, we provide evidence that using the algorithm is fully feasible on state of the art hardware. Finally, high resolution visualizations based on real data are demonstrated.

Tensile and bending behaviour of a strain hardening cement-based composite: Experimental and numerical analysis

Abstract IFSTTAR has developed a Multi-Scale Cement Based Composite (MSCC). This composite material is strain hardening in tension and exhibits ultra-high strengths as well in both compression and tension. The main research objectives for the present paper are the determination of the strain hardening properties of the material: using a newly developed tensile test in conjunction with a finite-element-based inverse analysis, the input parameters of an (adapted) numerical model can be identified. Therefore, numerical simulations can be performed to describe the bending behaviour of a thin slab having a thickness representative of the corresponding industrial application. The main conclusions of this study are: – The studied material clearly exhibits strain hardening in tension with a uniaxial tensile strength of about 20 MPa and a modulus of rupture of about 50 MPa. – Elasto-plastic behaviour with strain hardening is a relevant mechanical model (for the studied material) for designing (by the finite element method) structural elements behaving principally in bending.

3-D Model for Intra-Cavity Frequency Doubled ${\rm Nd{:}YVO}_{4}/{\rm MgO{:}PPLN}$ Green Lasers

A 3-D numerical model is developed for a continuous wave, intra-cavity frequency doubled Nd:YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> /MgO:PPLN green laser. A fast Fourier transform beam propagation method is employed to solve the 3-D coupled-wave equations in the laser cavity. Both analytical solution and experimental results are made to validate the 3-D numerical model. By employing the developed numerical model, key material and device parameters that affect the device performance, such as nonlinear crystal length and loss, pump beam spot size and cavity length are investigated.

이산화탄소 주입공 그라우팅 시멘트의 역학적 물성 및 파괴 거동

이산화탄소 지중저항을 위한 주입공의 안정성 및 누출제어에 주요 영향을 미치는 그라우팅 시멘트의 물리, 역학적 물성과 파괴 거동 특성을 실내실험을 통해 규명하였다. 물과 조강 3종 포틀랜드 시멘트를 네 종류의 질량비(각각 0.4, 1, 2, 3)로 배합한 시편을 제작하여 시험하였다. 그라우팅재의 제반 물리, 역학적 물성은 물/시멘트 배합비 0.4와 1 사이에서 급격하게 변화하며 전체적으로 물/시멘트 배합비가 증가함에 따라 공극률은 증가, 탄성파속도, 탄성계수, 압축, 인장강도 등은 감소하는 체계적인 변화양상을 보였다. 특히 일련의 삼축압축실험에서는 시편 성형시 물/시멘트 배합비와 시편에 작용하는 구속압 조건에 따라 취성파괴와 연성변형의 경계가 명확히 구분되었다. 규명된 물성 및 파괴거동은 이산화탄소 주입공 주변의 암반응력과 주입압 조건에 따라 발생할 수 있는 그라우팅재의 일차적 변형, 파괴, 균열 등의 모델분석에 주요 입력인자로 활용될 수 있을 것으로 기대한다. We conducted laboratory experiments to determine the physical and mechanical properties, and the failure behaviors, of cements for use as grouting material in a <TEX>$CO_2$</TEX>-injection borehole. Samples with lour different ratios of water to cement mass (0.4, 1, 2, and 3) were tested. The analyzed properties (porosity, sonic velocity, modulus, and compressive and tensile strengths) varied systematically as a function of the ratio of water to cement (w/c), showing a sharp change between w/c ratios of 0.4 and 1. Triaxial compression tests revealed a clear boundary between brittle and ductile failure depending on the w/c ratio and confining pressure. The present results can be utilized as input parameters for numerical models to understand the initial deformation and failure behavior of grouting cements in a <TEX>$CO_2$</TEX>-injection borehole.

The Numerical Simulation of the Triaxial Test of Cemented Coarse-Grained Soils

Cemented coarse-grained soils have both the properties of coarse-grained soils and concrete. This paper used discrete element method (DEM) to simulate of the drained monotonic load triaxial tests of coarse-grained soils and cemented coarse-grained soils respectively, the microscopic parameters of numerical models were calibrated based on the tests. The characteristics of the cemented coarse-grained soils and the microscopic mechanism were analyzed. The results showed that, the cemented coarse-grained soils have the higher modulus and strength compared with coarse-grained with adding the 3% cement in the specimens and appear the significant strain softening after the stress reaches the peak value; the deformation of the soil particles,the friction between soil particles and the crack of the cement bond are the mainly internal factors.

Numerical investigation into the stiffness anisotropy of asphalt concrete from a microstructural perspective

A micromechanical model was built in this paper to investigate the stiffness anisotropy of asphalt concrete (AC) using the discrete element method. Four three-dimensional cubic AC digital samples with different aggregate particle orientations were built using discrete element software PFC3D. The aggregate gradation and shape, air voids and mastic included in the digital samples were modeled using different contact models, with due consideration of the volumetric fractions of the different phases. Laboratory uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. Simulation of the uniaxial cyclic compressive tests was performed on the four cubic samples loaded in three different directions. Dynamic stiffness in different directions was calculated from the compression stress–strain responses. Results show that the AC stiffness is significantly dependent on preferential orientation of aggregate particles. The AC stiffness in the long-axis direction of aggregate particles is shown to be up to 43% higher than the stiffness in the particle short-axis direction. The stiffness anisotropy of AC decreases as the mixture temperature drops.

Shape Design of Lifting body Based on Genetic Algorithm

This paper briefly introduces the concept and history of lifting body, and puts forward a new method for the optimization of lifting body. This method has drawn lessons from the die line design of airplane is used to parametric numerical modeling for the lifting body, and extract the characterization of shape parameters as design variables, a combination of lifting body reentry vehicle aerodynamic conditions, aerodynamic heating, volumetric Rate and the stability of performance. Multi-objective hybrid genetic algorithm is adopted to complete the aerodynamic shape optimization and design of hypersonic lifting body vehicle when under more variable and constrained condition in order to obtain the Pareto optimal solution of Common Aero Vehicle shape.

Large-Eddy Simulation for an Axisymmetric Piston-Cylinder Assembly With and Without Swirl

Large-eddy simulation (LES) has been performed for an axisymmetric piston-cylinder assembly with and without swirl. For both cases, the LES mean and rms velocity profiles show better agreement with experimental data than profiles obtained using a Reynolds-averaged Navier–Stokes (RANS) approach with a standard k − e turbulence model. The sum of the resolved and modeled contributions to turbulence kinetic energy (TKE) approaches grid independence for the meshes used in this study. The sensitivity of LES to key numerical and physical model parameters has been investigated. Results are especially sensitive to mesh and to the subfilter-scale (SFS) turbulence models. Satisfactory results can be obtained using simple viscosity-based SFS turbulence models, although there is room for improvement. No single model gives uniformly best agreement between model and measurements at all spatial locations and at all times. The strong sensitivity of computed mean and rms velocity profiles to variations in the SFS turbulence model suggests that better results might be obtained using more sophisticated models.

Effects of Soil Water Salinity on Field Soil Hydraulic Functions

Unsaturated soil hydraulic parameters and functions used in numerical models to simulate water flow and solute transport in the unsaturated zone are generally considered invariant of soil water salinity levels. This study uses 5 years of field soil water salinity levels at three observation sites from the Land Retirement Demonstration Project (LRDP) (2006) located in western Fresno County, California, to test the hypothesis that field unsaturated soil hydraulic properties are also a function of soil water salinity level. The HYDRUS-1D software package for simulating one-dimensional (1D) movement of water, heat, and multiple solutes in variably saturated media, and Parameter Estimation (PEST), a model-independent parameter optimizer, is used to optimize the soil hydraulic parameters and downward bottom flux corresponding to three different average soil salinity levels at each site. The results show that at the same pressure head, soil water content is less with higher soil water salinity as compared with lower soil water salinity. It is thus concluded that the use of soil water salinity invariant soil water hydraulic parameters in numerical modeling can seriously compromise predictions, especially for a variable soil water salinity environment.