Computational simulation of flow over stepped spillways

Numerical simulations of water flow over stepped spillways with different step configurations are presented. The finite element computational fluid dynamics module of the ADINA software was used to predict the main characteristics of the flow. This included the determination of the water surface, the development of skimming flow over corner vortices, and the determination of energy dissipation. Since the actual flow is turbulent, the k-ε flow model was used. A two-phase solution process was adopted in order to optimize the overall simulation efficiency. In the first phase, a simple yet reasonable water surface consisting of three straight lines was used as an initial guess and was treated as a fixed wall. In the second phase, the results from the first phase were used as initial conditions and the water surface was treated as a free surface that evolved to attain a steady state configuration. For all the cases considered, the predicted water surface profile over the entire length of the spillway was in close agreement with the experimentally measured water surface profile. The predicted energy dissipation was also comparable to the experimentally attained values.     

Computational simulation of transient blast loading on three-dimensional structures

A computing technique is described for the numerical solution of three-dimensional, time-dependent fluid dynamic problems with irregularly shaped and movable boundaries (or internal obstacles) confining the flow. This paper presents in detail the method used in treating the three-dimensional boundary conditions. The numerical solution technique for the full nonlinear Navier-Stokes equations has been presented elsewhere. The general method is illustrated here through comparison of computed surface pressure time histories with the corresponding experimental data for a plane-shock wave (5 psi overpressure) passing over a rectangular parallelepiped.     

Biomechanics of manual material handling through simulation: Computational aspects

Computerized human motion simulation allows generation of dynamic human motions on computers. Biomechanical stresses can be estimated using the motions generated on a computer without actually collecting joint coordinate data. A two-dimensional whole-body lifting simulation model is presented in this paper. The model assumes that humans perform lifting activities based on minimization of physical work, subject to various constraints. The simulation method contains three major computation units: trajectory formation unit, dynamics of motion unit, and nonlinear optimization unit. The trajectory formation unit generates smooth polynomials representing motion characteristics of human lifting. Kinematics and kinetics are calculated in the dynamics unit. Objective and constraint functions are evaluated in the optimization unit. Optimal motions are generated by minimizing the objective function, subject to the constraints. Computation methods of the three units and simulation results are presented.     

Computer-aided simulation for bone surgery

A system for evaluating bone deformities using a 3-D model directly recovered from 2-D images and for simulating surgery is described. It derives a 3-D object representation from only two X-ray images. It also offers user-friendly simulation of bone surgery with low-cost hardware and software. The system exhibits satisfactory behavior for reconstructing the bone shape, providing suitable data for the simulation and evaluation of bone surgery. Although the spline interpolation of the bone surface does not produce a realistic 3-D visualization of the tibia, which is used as an example, the reconstruction is useful in solving problems inherent in the pathology considered     

Optimal bone density distributions: Numerical analysis of the osteocyte spatial influence in bone remodeling

In this paper a control and optimization procedure for bone remodeling simulations was adopted to study the effect of the osteocyte influence range on the predicted density distribution. In order to reach this goal, the osteocyte network regulating bone remodeling process in a 2-D bone sample was numerically simulated. The assumed proportional-integral-derivative (PID) bone remodeling rule was related to the error signal between the strain energy density and a selected target. Furthermore the control parameters and the target were optimally determined minimizing a suitable cost index: the goal was to minimize the final mass and the energy thus maximizing the stiffness. The continuum model results show that the developed and adapted trabecular structure was consistent with the applied loads and only depended on the external forces, the value of the cost index, the maximum attainable elastic modulus value (hence, the maximum density value) and the value of the energy target. The remodeling phenomenon determined the number and thickness of the trabeculae which are formed from a uniform distribution of mass density in the considered domain; this number and these thicknesses are controlled by the values assigned to the parameters of the model. In particular, the osteocyte decay distance (D) of the influence range affected the trabecular patterns formation, showing an important effect in the adaptive capacity of the optimization numerical model.     

Computational challenges in cell simulation: a software engineering approach

Molecular biology's advent in the 20th century has exponentially increased our knowledge about the inner workings of life. We have dozens of completed genomes and an array of high-throughput methods to characterize gene encodings and gene product operation. The question now is how we will assemble the various pieces. In other words, given sufficient information about a living cell's molecular components, can we predict its behavior? We introduce the major classes of cellular processes relevant to modeling, discuss software engineering's role in cell simulation, and identify cell simulation requirements. Our E-Cell project aims to develop the theories, techniques, and software platforms necessary for whole-cell-scale modeling, simulation, and analysis. Since the project's launch in 1996, we have built a variety of cell models, and we are currently developing new models that vary with respect to species, target subsystem, and overall scale.     

Computational design of V-CoCrFeMnNi high-entropy alloys: An atomistic simulation study

In the high-entropy alloy (HEA) community, many researchers have been trying to improve the strength of the CoCrFeMnNi HEA by generating a transformation-induced-plasticity (TRIP) effect and/or maximizing the solid solution hardening effect. Adding vanadium (V) to the CoCrFeMnNi HEAs could be an effective way to improve strength, because vanadium stabilizes the body-centered cubic (bcc) phase and its atomic size is larger than Co, Cr, Fe, Mn, and Ni. To design high strength V-added HEAs, we investigated the effect of vanadium on the critical resolved shear stress (CRSS) by utilizing an atomistic simulation, proposing an empirical equation to estimate the relative effect of alloying elements on the CRSS. For this, we first developed the Co-Cr-Fe-Mn-Ni-V hexanary interatomic potential by newly developing the Cr-V, Fe-V, and Mn-V binary interatomic potentials. As a result, two novel V-added HEAs were designed and the designed HEAs show higher strength than the previously developed non-equiatomic CoCrFeMnNi HEAs, as predicted from the empirical equation.     

Computational simulation and analysis of double-swept blade in BVI noise reduction

The TURNS computational fluid dynamics (CFD) code with the Beddoes prescribed wake and the WOPWOP computational acoustics code is used to study blade-sweep blade–vortex interaction (BVI) noise reduction design. The CFD three-dimensional unsteady solutions of blade surface pressure distributions are used as the input to WOPWOP acoustics computational code to produce the overall sound pressure level (OASPL) on a 3-rotor radiation observer hemisphere around the helicopter rotor. To study the effects of blade sweep on BVI noise reduction, computations are performed on a baseline rectangular blade and a corresponding double-swept blade to better understand the impact of blade sweep on BVI noise reduction in relation to the interaction angle between blade leading edge and the shed tip-vortex. The present study indicates that tip-region blade forward sweep produces favorable BVI angles for dominate BVIs to reduce the maximum BVI noise level on the advancing side, while increasing noise level on the retreating side. Increasing in the noise level on the retreating side as a trade-off for decreasing in the maximum noise level on the advancing side results favorably in the reduction of the overall maximum noise level and in changing the ‘hot’ noise spots into a more desirable ‘less hot’ noise region.     

Simplifying biochemical tumorous bone remodeling models through variable order derivatives

Bone is a living tissue that is constantly being renewed, where different cell types can induce a remodeling action to its structure. These mechanisms are typically represented through differential equations, accounting for the biochemical coupling between osteoclastic and osteoblastic cells. Remodeling models have also been extended to include the effects of tumorous disruptive pathologies in the bone dynamics.This article provides a novel approach to existing biochemical models, acting on two different stages. First, the models are said to physiologically better explain an osteolytic metastatic disease to the bone than the multiple myeloma previously considered. Second, and most importantly, variable order derivatives were introduced, for the first time in biochemical bone remodeling models. This resulted in a set of equations with less parameters that describe tumorous remodeling, and provide similar results to those of the original formulation. A more compact model, that promptly highlights tumorous bone interactions, is then achieved. Comparison of simulations and parameters is provided.Such results are a one-step-closer insight to, in a near future, easily provide clinical decision systems ensuring tailored personalized therapy schemes, for more efficient and targeted therapies.     

Computational model of mesoscopic structure of concrete for simulation of fracture processes

This paper describes mathematical modelling and computational tool for simulation of fracture processes of cementitious composites at the mesoscopic level. The tool relies on highly realistic 3D- and 2D-representations of the heterogeneous internal structure of concrete for understanding the micromechanics of aggregate–matrix interactions. The generation mechanism allows control of aggregate volume content, shape and size distribution. The allocation procedure proved capable to produce numerical concrete with aggregate distributions comparable to real concrete. The continuum was discretised into lattices of linear elements, for structural analyses. Compression, direct tension and wedge-splitting tests were simulated. Parametrical study was carried out to investigate effects of different material properties and proportions in concrete admixtures.     

Computational technologies for simulation of complex near-wall turbulent flows using unstructured meshes

The work is devoted to the peculiarities of the implementation of hybrid Reynolds’ Averaged Navier-Stokes equations-Large Eddy Simulation (RANS-LES) approaches of the Detached Eddy Simulation (DES) family for simulation of complex near-wall turbulent flows using unstructured meshes. The problems of determining required geometric characteristics in the mesh nodes and adaptation of hybrid approaches to the used accurate numerical approximation scheme in space are considered. The classic benchmark problem of the decay of homogeneous isotropic turbulence and the results of the computation of a complex turbulent flow near the wall with the presence of flow separation and reattachment are considered to verify the implemented technique and to demonstrate its efficiency.     

催化柴油管式液相加氢脱硫数值模拟

采用计算流体力学(CFD)软件FLUENT,以用户自定义函数(UDF)添加化学反应和反应热,对实验室带有陶瓷膜管分散器的催化柴油管式液相加氢脱硫反应器进行模拟计算,得出反应床层不同部位的硫化物含量分布和温度分布状况。从反应床层的入口到出口,催化柴油的硫化物含量逐渐下降,且下降速度趋缓。在压力6.5 MPa、混氢量0.84%(m)、空速2 h~(-1)、进口温度633 K的条件下,位于床层高度0.15 m处出现最高温度点643.8 K,径向温差最大2.1 K,表明催化柴油管式液相加氢脱硫反应器催化剂装填合适的高径比为4~6。工艺条件的模拟结果表明:随着进口温度上升、混氢量增加、空速减小脱硫率提高,与实验数据吻合程度较好,说明模拟研究过程中采用的模型和控制方程准确性较高。     

Dynamical systems,SIMP, bone remodeling and time dependent loads

The dynamical systems approach to sizing and SIMP topology optimization, introduced in a previous paper, is extended to the case of time-varying loads. A general dynamical system, satisfying a Lyaponov-type descent condition, is derived and specialized to a goal function combining stiffness and mass. For a cyclic time-dependent load it is indicated how, in the limit of short cycles compared to the overall time scale, this can be handled by multiple load cases. Numerical examples, both for a convex and a non-convex case, illustrates the theory.     

Computational complexity for a class of multipoint iterative procedures without or with internal memory

In a preceding paper we studied multipoint iterative procedures with and without memory in order to calculate an approximation of the simple root of the equationf(x)=0; in this paper we shall study the computational complexity for an optimal class of, the procedures.

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Sommario In un precedente articolo abbiamo studiato i procedimenti iterativi a più punti con e senza memoria per calcolare una approssimazione di una radice semplice della equazionef(x)=0. In questo articolo studieremo la complessità di calcolo per una classe ottimale di tali procedimenti.

     

Computational error-analysis of a discontinuous Galerkin discretization applied to large-eddy simulation of homogeneous turbulence

A computational error-assessment of large-eddy simulation (LES) in combination with a discontinuous Galerkin finite element method is presented for homogeneous, isotropic, decaying turbulence. The error-landscape database approach is used to quantify the total simulation error that arises from the use of the Smagorinsky eddy-viscosity model in combination with the Galerkin discretization. We adopt a modified HLLC flux, allowing an explicit control over the dissipative component of the numerical flux. The optimal dependence of the Smagorinsky parameter on the spatial resolution is determined for second and third order accurate Galerkin methods. In particular, the role of the numerical dissipation relative to the contribution from the Smagorinsky dissipation is investigated. We observed an ‘exchange of dissipation’ principle in the sense that an increased numerical dissipation implied a reduction in the optimal Smagorinsky parameter. The predictions based on Galerkin discretization with fully stabilized HLLC flux were found to be less accurate than when a central discretization with (mainly) Smagorinsky dissipation was used. This was observed for both the second and third order Galerkin discretization, suggesting to emphasize central discretization of the convective nonlinearity and stabilization that mimics eddy-viscosity as sub-filter dissipation.     

Computational simulation of model and full scale Class 8 trucks with drag reduction devices

Numerical solutions of the unsteady Reynolds-averaged Navier–Stokes equations using a parallel implicit flow solver are given to investigate unsteady aerodynamic flows affecting the fuel economy of Class 8 trucks. Both compressible and incompressible forms of the equations are solved using a finite-volume discretization for unstructured grids and using Riemann-based interfacial fluxes and characteristic-variable numerical boundary conditions. A preconditioned primitive-variable formulation is used for compressible solutions, and the incompressible solutions employ artificial compressibility. Detached eddy simulation (DES) versions of the one-equation Menter SAS and the two-equation k − ?/k − ω hybrid turbulence models are used. A fully nonlinear implicit backward-time approximation is solved using a parallel Newton-iterative algorithm with numerically computed flux Jacobians. Unsteady three-dimensional aerodynamic simulations with grids of 18–20 million points and 50,000 time steps are given for the Generic Conventional Model (GCM), a 1:8 scale tractor–trailer model that was tested in the NASA Ames 7 × 10 tunnel. Computed pressure coefficients and drag force are in good agreement with measurements for a zero-incidence case. Similar computations for a case with 10° yaw gave reasonable agreement for drag force, while the pressure distributions suggested the need for tighter grid resolution or possibly improved turbulence models. Unsteady incompressible flow simulations were performed for a modified full scale version of the GCM geometry to evaluate drag reduction devices. All of these simulations were performed with a moving ground plane and rotating rear wheels. A simulation with trailer base flaps is compared with drag reduction data from wind tunnels and track and road tests. A front spoiler and three mud-flap designs with modest drag reduction potential are also evaluated.     

Computer modeling approach for a novel internal architecture of artificial bone

A computer-aided modeling approach for constructing a novel 3D concentric microstructure in artificial bone is presented. Concentric structure has the gradient porosity, which could mimic the microstructures in native bone. The mathematical foundation behind the concentric structure model was described in detail and a special software to construct the unique structures was developed. The constructed model is based on a unified mathematical model and possesses structural extensionality, which could facilitate the further optimization. The artificial bone model with certain porosity and different concentric fiber structures could be constructed and visualized in the special software. By incorporating the concentric fiber structures into the calcium phosphate cement (CPC) matrix, the fiber-reinforced CPC composite artificial bone with controlled fiber structure and desired porosity could be fabricated.     

内循环厌氧反应器的气-液-固三相流数值模拟研究

利用计算流体动力学(CFD)方法对内循环厌氧反应器气-液-固三相流进行了三维非稳态数值模拟研究,探索了迭代时间对内循环形成过程的影响,并重点考察了反应器内Z方向上流体力学特性及三相分离器对颗粒的截留作用。结果表明,反应器内液相及固相内循环均成功形成,CFD技术能够很好地应用于IC反应器的研究;且Z方向上,一级反应室及二级反应室内固相及气相体积分率随轴向高度增大变化不大,而在径向上存在较大波动;一级提气管内液相、固相及气相轴向速度均比二级提气管内大,气含率及固含率也较大,一级厌氧反应室起到主要的水处理作用;三相分离器及气液分离器的设计对于反应器效率影响较大。     

Computational simulation of gas flow and heat transfer near an immersed object in fluidized beds

To improve the understanding of the heat transfer mechanism and to find a reliable and simple heat-transfer model, the gas flow and heat transfer between fluidized beds and the surfaces of an immersed object is numerically simulated based on a double particle-layer and porous medium model. The velocity field and temperature distribution of the gas and particles are analysed during the heat transfer process. The simulation shows that the change of gas velocity with the distance from immersed surface is consistent with the variation of bed voidage, and is used to validate approximately dimensional analysing result that the gas velocity between immersed surface and particles is 4.6U_mf/ε_mf. The effects of particle size and particle residence time on the thermal penetration depth and the heat-transfer coefficients are also discussed.