Two-dimensional Test Research Articles

ASAM v2.7: a compressible atmospheric model with a Cartesian cut cell approach

Abstract. In this work, the fully compressible, three-dimensional, nonhydrostatic atmospheric model called All Scale Atmospheric Model (ASAM) is presented. A cut cell approach is used to include obstacles and orography into the Cartesian grid. Discretization is realized by a mixture of finite differences and finite volumes and a state limiting is applied. Necessary shifting and interpolation techniques are outlined. The method can be generalized to any other orthogonal grids, e.g., a lat–long grid. A linear implicit Rosenbrock time integration scheme ensures numerical stability in the presence of fast sound waves and around small cells. Analyses of five two-dimensional benchmark test cases from the literature are carried out to show that the described method produces meaningful results with respect to conservation properties and model accuracy. The test cases are partly modified in a way that the flow field or scalars interact with cut cells. To make the model applicable for atmospheric problems, physical parameterizations like a Smagorinsky subgrid-scale model, a two-moment bulk microphysics scheme, and precipitation and surface fluxes using a sophisticated multi-layer soil model are implemented and described. Results of an idealized three-dimensional simulation are shown, where the flow field around an idealized mountain with subsequent gravity wave generation, latent heat release, orographic clouds and precipitation are modeled.

A low diffusion flux splitting method for inviscid compressible flows

A low diffusion flux splitting method capable of capturing crisp shock profile and exact contact surface is presented. Here, the flux vector of the Euler equations is split into convective and pressure parts following Toro–Vázquez formulation. The low diffusive property of the present scheme is brought about by adding an anti-diffusion term to the pressure parts. This numerical method can be regarded as an improved version of Toro and Vázquez’s flux splitting schemes (i.e. TV and TV-AWS) which are found to produce shock instabilities and carbuncle phenomena. Numerical results for several carefully chosen one- and two-dimensional test problems are investigated to demonstrate the accuracy and robustness of the proposed scheme.

Microscopic modeling of the creep behavior of rockfills with a delayed particle breakage model

The aim of this study was to develop a practical way of modeling the time-dependent behavior of rockfill materials and to provide useful information that is difficult to obtain from physical tests. Because the micro-mechanism governing the time-dependent rockfill behavior is delayed particle breakage, an updated rock aging model is implemented in an existing code. Particle breakage is represented by the failure of zero-thickness cohesive interface elements that are pre-inserted into the finite element discretization associated with each particle. With only three additional parameters together with temporal integration, we can account for the aging of rock blocks under various stress states and climatic conditions. A series of two-dimensional simulated creep tests were performed on a dense assembly of polygonal particles. By varying rock aging parameters, we can reproduce the typical creep behaviors. The effects of weathering and cyclic loading are investigated by performing five comparative creep tests. The influences of the stress level on the creep deformation are in agreement with experimental observations. A multi-stage creep test is also conducted to verify that the creep behavior has stress history dependence.

Chebyshev collocation spectral lattice Boltzmann method for simulation of low-speed flows.

In this study, the Chebyshev collocation spectral lattice Boltzmann method (CCSLBM) is developed and assessed for the computation of low-speed flows. Both steady and unsteady flows are considered here. The discrete Boltzmann equation with the Bhatnagar-Gross-Krook approximation based on the pressure distribution function is considered and the space discretization is performed by the Chebyshev collocation spectral method to achieve a highly accurate flow solver. To provide accurate unsteady solutions, the time integration of the temporal term in the lattice Boltzmann equation is made by the fourth-order Runge-Kutta scheme. To achieve numerical stability and accuracy, physical boundary conditions based on the spectral solution of the governing equations implemented on the boundaries are used. An iterative procedure is applied to provide consistent initial conditions for the distribution function and the pressure field for the simulation of unsteady flows. The main advantage of using the CCSLBM over other high-order accurate lattice Boltzmann method (LBM)-based flow solvers is the decay of the error at exponential rather than at polynomial rates. Note also that the CCSLBM applied does not need any numerical dissipation or filtering for the solution to be stable, leading to highly accurate solutions. Three two-dimensional (2D) test cases are simulated herein that are a regularized cavity, the Taylor vortex problem, and doubly periodic shear layers. The results obtained for these test cases are thoroughly compared with the analytical and available numerical results and show excellent agreement. The computational efficiency of the proposed solution methodology based on the CCSLBM is also examined by comparison with those of the standard streaming-collision (classical) LBM and two finite-difference LBM solvers. The study indicates that the CCSLBM provides more accurate and efficient solutions than these LBM solvers in terms of CPU and memory usage and an exponential convergence is achieved rather than polynomial rates. The solution methodology proposed, the CCSLBM, is also extended to three dimensions and a 3D regularized cavity is simulated; the corresponding results are presented and validated. Indications are that the CCSLBM developed and applied herein is robust, efficient, and accurate for computing 2D and 3D low-speed flows. Note also that high-accuracy solutions obtained by applying the CCSLBM can be used as benchmark solutions for the assessment of other LBM-based flow solvers.

Shock Attenuation Properties and Deformation Behavior of Sports Surfaces by Two-dimensional Impact Test

This study focused on two-dimensional deformation behavior of sports surfaces. Shock attenuation tests and friction tests are generally performed to assess the vertical and horizontal properties of the sports surfaces, respectively. Although the diagonal impacts are often observed in human activities, these tests treat only the vertical impact test. Therefore two-dimensional impact test device were developed for examining the two-dimensional properties of sport surfaces. In previous studies, we evaluated two-dimensional shock attenuation properties of sports surfaces with the VFR (Vertical Force Reduction) and HFR (Horizontal Force Reduction) values. Additionally, we evaluated vertical and horizontal displacement by two-dimensional impact tests with high-speed video analysis in this study.

B-8 2方向衝撃試験によるスポーツサーフェスの変形および緩衝特性(反発・発射,衝撃・緩衝)

Shock attenuation property of sports surfaces is especially important not only for the athlete's performance but also for injury prevention. To evaluate the properties of the sports surfaces, some sports governing bodies often adopt friction tests and shock attenuation tests to determine the horizontal and vertical characteristics, respectively. Although the diagonal impacts are often observed in athletic sports, shock attenuation test only treats the vertical impact test. Therefore we developed a two-dimensional impact test device for examining the two-dimensional cushioning characteristics of sports surfaces in previous studies. To produce a simultaneous two-dimensional force against a test specimen, we incorporated a parallelogram linkage in the measuring system. In previous study, three different hardness of surfaces were examined for calculating the FR (Force Reduction) values not only the vertical component but also the horizontal component. As the results, Vertical FR values were increased with increasing the initial angle and impact intensity in all surfaces. And the different patterns of horizontal FR values were observed in these surfaces. In this study, we evaluated vertical and horizontal displacement by two-dimensional impact tests with high-speed video analysis. And we evaluated hysteresis properties of sports surfaces. As the results, horizontal properties of sports surfaces might depend on not only the material but also the structure of the specimen.

A method to improve fluence resolution derived from two-dimensional detector array measurements for patient-specific IMRT verification using the information collected in dynalog files.

This paper proposes a method for improving the resolution of the fluence derived from detector array measurement using the information collected in dynalog files. From dynalog information, a file is generated with the actual multileaf collimator (MLC) positions and used as input to the treatment planning system (TPS) to obtain the dynalog-derived fluence and the theoretical response over the detector array. In contrast with the measured response, this theoretical response allows for correction of the dynalog-derived fluence and translation into the reconstructed fluence. This fluence is again introduced into the planning system to verify the treatment using clinical tools. Initially, more than 98% of the points passed the two-dimensional (2D) phantom gamma test (3% local dose - 3 mm) for all of the treatment verifications, but in some dose–volume histogram (DVH) comparisons, we note sensitive differences for the planning target volume (PTV) coverage and for the maximum doses in at-risk organs (up to 3.5%). In dose–distribution evaluations, we found differences of up to 5% in the PTV edges in certain cases due to detector array measurement errors. This work improves the resolution of the fluence derived from detector array measurements based on the treatment information, in contrast with the current commercial proposals based on planned data.

Analysis on the Mechanical Behaviors of Soil-rock Mixtures Using Discrete Element Method

Two-dimensional numerical direct shear tests were carried out using the Discrete Element Method (DEM) to study the effects of rock content on the mechanical behaviors of soil-rock mixtures (SRM).The mixtures were made from particles of contrasting size and stiffness. The DEM simulation captured the behaviors of SRM as observed in previous experiments, showing that the peak shear stress and the dilation increased with an increasing rock content. Moreover, it also found that the peak friction angle and dilation angle increased while cohesion decreased with an increasing rock content. On the other hand, the DEM provided insight to the distribution of contact force chains, the magnitude and orientation of the principal stresses, and the rotation of particles experience as the shearing progressed which could not be revealed in the physical experiments. The results indicated that the rock content also had a meaningful effect on these micromechanical observations. At last, how the rock content influenced the shear strength of SRM was discussed according to Taylor's theory. It was concluded that the shear strength of SRM increased for higher rock content mainly because of the contribution of the interlocking, while the contribution of the contact friction was demonstrated to be very small.

DiceDesignandDiceEval: TwoRPackages for Design and Analysis of Computer Experiments

This paper introduces two R packages available on the Comprehensive R Archive network. The main application concerns the study of computer code output. Package DiceDesign is dedicated to numerical design of experiments, from the construction to the study of the design properties. Package DiceEval deals with the fit, the validation and the comparison of metamodels. After a brief presentation of the context, we focus on the architecture of these two packages. A two-dimensional test function will be a running example to illustrate the main functionalities of these packages and an industrial case study in five dimensions will also be detailed.

Isogeometric Methods for CFD and FSI-Simulation of Flow around Turbine Blades

Coupled fluid-structure interaction simulations of wind turbines have traditionally been considered computationally too expensive to carry out. However, more powerful computers and better solution techniques based on IsoGeometric Analysis (IGA) can make such simulations viable. Literature indicates that the smoothness of IGA approximations generally yield higher accuracy per- degree-of-freedom. We consider a two-dimensional test case prototypical of wake-vortex analyses and strip-theory approaches used in the numerical simulation of wind turbine.

Boundary conditions for simulations of oscillating bubbles using the non-linear acoustic approximation

We have developed a new boundary condition for finite volume simulations of oscillating bubbles. Our method uses an approximation to the motion outside the domain, based on the solution at the domain boundary. We then use this approximation to apply boundary conditions by defining incoming characteristic waves at the domain boundary. Our boundary condition is applicable in regions where the motion is close to spherically symmetric. We have tested our method on a range of one- and two-dimensional test cases. Results show good agreement with previous studies. The method allows simulations of oscillating bubbles for long run times (5×105 time steps with a CFL number of 0.8) on highly truncated domains, in which the boundary condition may be applied within 0.1% of the maximum bubble radius. Conservation errors due to the boundary conditions are found to be of the order of 0.1% after 105 time steps. The method significantly reduces the computational cost of fixed grid finite volume simulations of oscillating bubbles. Two-dimensional results demonstrate that highly asymmetric bubble features, such as surface instabilities and the formation of jets, may be captured on a small domain using this boundary condition.

Parallel Navier–Stokes simulations for high speed compressible flow past arbitrary geometries using FLASH

We report extensions to the FLASH code to enable high-speed compressible viscous flow simulation past arbitrary two- and three-dimensional stationary bodies. The body shape is embedded in a block-structured Cartesian adaptive mesh refinement grid by implementing appropriate computer graphics algorithms. A high mesh refinement level is required for an accurate body shape representation which results in large grid sizes especially for three-dimensional simulations. Simulations are done in parallel on IBM Blue Gene/Q computing system on which the code performance has been assessed in both pure MPI and hybrid MPI-OpenMP modes. We also implement appropriate wall boundary conditions in FLASH to model viscous-wall effects. Navier–Stokes (NS) solutions for various two-dimensional test cases like a shock–boundary layer interaction problem as well as for hypersonic flow past blunted cone–cylinder–flare and double-cone geometries are shown. Three dimensional NS simulations of micro vortex generators employed in hypersonic flow control have also been carried out and the computed results have been found to be consistent with experimental results.

Wake oscillator model for assessment of vortex-induced vibration of flexible structures under wind action

The wake oscillator model is considered to be the most proper semi-empirical model for qualitatively or even quantitively assessing the vortex-induced vibration of a structure in the design stage. However, the complexities in parameter determination limit its usage in real engineering fields. Moreover, this kind of model is traditionally used to describe the experimental phenomena of two-dimensional cross-section models, the gaps between the results of two-dimensional cross-section model tests and the prototype responses of the three-dimensional real structures should be filled up. In this paper, a detailed study of the wake oscillator model is firstly presented, which demonstrates the influences of model parameters on the VIV features described by the wake oscillator model. Then, a new method for conveniently identifying the model parameters in the wake oscillator model is proposed. Besides, a new procedure, based on the wake oscillator model, for interpreting the wind tunnel test results into real structures is also proposed. The results are validated by wind tunnel tests and compared with field measurements.

An adaptive metamodel-based global optimization algorithm for black-box type problems

In this article, an adaptive metamodel-based global optimization (AMGO) algorithm is presented to solve unconstrained black-box problems. In the AMGO algorithm, a type of hybrid model composed of kriging and augmented radial basis function (RBF) is used as the surrogate model. The weight factors of hybrid model are adaptively selected in the optimization process. To balance the local and global search, a sub-optimization problem is constructed during each iteration to determine the new iterative points. As numerical experiments, six standard two-dimensional test functions are selected to show the distributions of iterative points. The AMGO algorithm is also tested on seven well-known benchmark optimization problems and contrasted with three representative metamodel-based optimization methods: efficient global optimization (EGO), GutmannRBF and hybrid and adaptive metamodel (HAM). The test results demonstrate the efficiency and robustness of the proposed method. The AMGO algorithm is finally applied to the structural design of the import and export chamber of a cycloid gear pump, achieving satisfactory results.

Modelling of transient heat conduction with diffuse interface methods

We present a survey on different numerical interpolation schemes used for two-phase transient heat conduction problems in the context of interface capturing phase-field methods. Examples are general transport problems in the context of diffuse interface methods with a non-equal heat conductivity in normal and tangential directions to the interface. We extend the tonsorial approach recently published by Nicoli M et al (2011 Phys. Rev. E 84 1–6) to the general three-dimensional (3D) transient evolution equations. Validations for one-dimensional, two-dimensional and 3D transient test cases are provided, and the results are in good agreement with analytical and numerical reference solutions.

Optimal design of groundwater remediation system using a probabilistic multi-objective fast harmony search algorithm under uncertainty

This study develops a new probabilistic multi-objective fast harmony search algorithm (PMOFHS) for optimal design of groundwater remediation systems under uncertainty associated with the hydraulic conductivity (K) of aquifers. The PMOFHS integrates the previously developed deterministic multi-objective optimization method, namely multi-objective fast harmony search algorithm (MOFHS) with a probabilistic sorting technique to search for Pareto-optimal solutions to multi-objective optimization problems in a noisy hydrogeological environment arising from insufficient K data. The PMOFHS is then coupled with the commonly used flow and transport codes, MODFLOW and MT3DMS, to identify the optimal design of groundwater remediation systems for a two-dimensional hypothetical test problem and a three-dimensional Indiana field application involving two objectives: (i) minimization of the total remediation cost through the engineering planning horizon, and (ii) minimization of the mass remaining in the aquifer at the end of the operational period, whereby the pump-and-treat (PAT) technology is used to clean up contaminated groundwater. Also, Monte Carlo (MC) analysis is employed to evaluate the effectiveness of the proposed methodology. Comprehensive analysis indicates that the proposed PMOFHS can find Pareto-optimal solutions with low variability and high reliability and is a potentially effective tool for optimizing multi-objective groundwater remediation problems under uncertainty.

Adaptive mesh refinement for compressible thermal flow in porous media

We present the implementation of a detailed model for compositional flow in porous media into an adaptive mesh refinement (AMR) framework. This model is applicable to a number of thermal problems. The basic numerical approach is an efficient shock-capturing method designed to minimise the number of expensive phase equilibrium calculations needed per time step. This is implemented in an AMR framework, using a multigrid method for general parabolic equations. The AMR method is applicable to a general class of hyperbolic–parabolic problems which includes the porous media model. We test the method on one-dimensional and two-dimensional thermal gas injection test cases, including non-uniform propagation in a heterogeneous medium.

A new parallel algorithm for constructing Voronoi tessellations from distributed input data

We present a new parallel algorithm for generating consistent Voronoi diagrams from distributed input data for the purposes of simulation and visualization. The algorithm functions by building upon any serial Voronoi tessellation algorithm. The output of such a serial tessellator is used to determine the connectivity of the distributed domains without any assumptions about how points are distributed across those domains, and then in turn to build the portion of the global tessellation local to each domain using information from that domains neighbors. The result is a generalized methodology for adding distributed capabilities to serial tessellation packages. Results from several two-dimensional tests are presented, including strong and weak scaling of its current implementation.

Quasi-a priori mesh adaptation and extrapolation to higher order using τ-estimation

Improving the balance between cost and accuracy of computational fluid dynamics solvers by local mesh adaptation has become a topic of increasing interest. Numerical error based adaptation sensors proved to be robust and converge faster than sensors simply based on features of the flow field. However, this family of sensors known as residual-based sensors usually suffer from a high computational cost, e.g. the adjoint or Richardson extrapolation and are a posteriori indicators, which thus implies an initial solution to the problem. In this paper, we develop a mesh adaptation indicator accurate in the early stages of the iteration procedure, based on the τ-estimation technique. τ-estimation allows for an accurate truncation error estimation and can therefore be used to correct the discretized equations through the so-called τ-extrapolation methodology. We introduce the τ-estimation technique for non-converged solutions and derive all the necessary conditions to be used in the context of mesh adaptation and extrapolation of practical problems. Then, we apply this methodology to two-dimensional test cases, Euler flow past a NACA0012 airfoil in different Mach regimes, with a special focus on computational time. We demonstrate that quasi-a priori τ-estimation can substantially reduce the cost when combined with mesh adaptation or τ-extrapolation in comparison to classic adaptation sensors.

Study of Flow Transitions during Air Sparging Using the Geotechnical Centrifuge

AbstractAir sparging (AS) is an in-situ groundwater remediation technique for volatile organic compounds (VOCs) in contaminated sites. Knowledge of effect of the injected air on air flow patterns and extent of the zone known as zone of influence (ZOI) is crucial for design of in situ air sparging. The two main objectives of this research are to study transition of air flow patterns and characteristics of ZOI under different air injection pressures during centrifugal tests and to find the scaling factors for centrifugal tests under different gravitational levels (N times gravitational force). In this research, the modeling of models test was first performed to validate centrifugal technique for simulating air sparging. Then, a set of two-dimensional (2D) centrifugal modeling tests were performed under various gravitational levels to study the transition of air flow patterns and characteristics of ZOI during air sparging. The centrifugal model tests showed that the observed 2D ZOI was truncated-cone under v...