Unified Numerical Model Research Articles

Three-dimensional stochastic assimilation of gravity data in Lalor volcanogenic massive sulphide, Manitoba, Canada

We propose a new numerical workflow based on stochastic data integration where we merge a conceptual geological model, drillhole geophysical and geological logs, and surface geophysical data to compute a unified numerical model of a volcanogenic massive sulphide (VMS) deposit. The first step of the workflow consists in building a three-dimensional (3D) numerical conceptual model of the geology. This conceptual model, as well as geological logs, is then used to generate multiple equiprobable scenarios of the geology by means of multiple-point simulation (MPS). The MPS method studies high-order statistics in the space of a numerical conceptual model, making it possible to reproduce complex geological structures. We then use conventional conditional sequential Gaussian simulation, which is a method based on a node-by-node sequential process, to stochastically populate the geological grid with densities. For this purpose we use available density logs to simulate multiple equiprobable spatial distributions of the density at high spatial resolution within each geological unit separately. The stochastic high-resolution density models are iteratively combined by the gradual deformation method to minimize the difference between measured Bouguer anomaly data and the data computed on the combined realizations of density. Application of the proposed method to the Lalor deposit, a VMS deposit in Manitoba, Canada, produces a density model that honours the geology of the deposit and the Bouguer anomaly data. This unified model has the advantage to include all the available information (geological and density logs and surface geophysics) at scales appropriate for mining applications.

A Unified Three-Dimensional Numerical Model for Boiling Curve in a Temperature Controlled Mode1

In the present study, level set method is used to simulate the entire boiling curve in a temperature-controlled mode spanning all the three regimes viz., nucleate, transition, and film boiling with a unified numerical model supplemented with correlations specifying nucleation site density and waiting time between successive nucleations. In order to improve the performance of the code, parallel computing has also been implemented. Vapor evolution process along with temporal- and spatial-averaged wall heat flux and wall void fraction are computed for a uniform wall superheat case. Wall void fraction is found to increase with increase in wall superheat nonlinearly as different regimes of boiling were traversed. Energy partitioning from wall into liquid, interface, and microlayer has also been examined where it is found that as the wall void fraction increases, the percent energy going into liquid decreases while the microlayer contribution peaks around critical heat flux (CHF). Numerical simulations are carried out in 3D with water as test liquid and contact angle of 38 deg.

Numerical Simulation of Metal Vapour Behavior in Double Electrodes TIG Welding

Metal vapour from the weld pool in double electrodes tungsten inert gas welding is taken into account by a unified numerical model including the arc plasma and the weld pool. The thermodynamic properties and transport coefficients of the arc plasma are dependent on both the local temperature and the mass fraction of the metal vapour. A second viscosity approximation is used to describe the diffusion coefficient of the metal vapour in the arc plasma. The temperature and the flow fields of both the arc plasma and the weld pool are calculated together with the metal vapour concentration. The simulated results are presented for the cases of 3 and 9 mm electrode separation, respectively. It is shown that the metal vapour behavior is much different in these two cases. In the case of 3 mm electrode separation, the metal vapour above the mass fraction of 0.2% is concentrated just above the weld pool surface, while in the case of 9 mm electrode separation, the metal vapour is diffused to the most region of the arc plasma for the same range of mass fraction. In addition, the arc plasma temperature as well as the heat flux at the weld pool is constricted by the presence of the metal vapour. The constricted heat flux at the weld pool results in an increase in the temperature of the weld pool about 100 K or less but a slight shrinkage of the weld pool shape.

Numerical simulation of droplet transfer behavior in variable polarity gas metal arc welding

Gas metal arc welding (GMAW) using an alternating current waveform is usually termed as variable polarity GMAW (VP-GMAW), during which the electrode polarity switches between positive and negative periodically. The arc properties and the droplet transfer in VP-GMAW would be different from traditional direct current GMAW. In order to clarify the droplet transfer phenomena during a VP-GMAW process, a unified numerical model including the interaction between the arc plasma and the moving droplet is developed. The simulation results indicate that the arc plasma generated at electrode negative polarity shows a less constricted shape, a lower plasma temperature and velocity, compared to positive polarity. The resultant droplet is found to have a bigger size and a lower temperature than that of direct current gas metal arc welding with the same average welding current. Moreover, a quantitative analysis of the heat fluxes into the electrode is further conducted to explain the thermal mechanism for the differences in droplet properties between variable polarity and direct current gas metal arc welding. Finally, the simulated results are compared with the high-speed images, and the simulated and experiment results show good agreements.

A Unified Numerical Model for Typhoon Surge in the Northwestern Pacific

ABSTRACT Kang, S.K.; Seung, Y.H.; Kim, K.O.; Kim, E.J., and Jung, K.T., 2017. A unified numerical model for typhoon surge in the Northwestern Pacific. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 139–143. Coconut Creek (Florida), ISSN 0749-0208. A new finite difference modeling system with modified fetched variable grid technique has been developed in order to predict the typhoon induced surge over the Northwestern Pacific. The grid resolution ranges from 18.5 km (10 ′) in open ocean to 109 m (1/17 ′) near the coastal areas of interest, which is quite suitable for resolving the complicated coastal boundaries of the Korean coasts. The total grid number is about 1,350,000 points and the model computation can be effectively carried out with efficient time interval satisfying 1–30 Courant numbers. This system has various advantages over regular finite difference grid system, allowin...

Free vibrations of composite laminated doubly-curved shells and panels of revolution with general elastic restraints

A unified numerical analysis model is presented to solve the free vibration of composite laminated doubly-curved shells and panels of revolution with general elastic restraints by using the Fourier–Ritz method. The first-order shear deformation theory is adopted to conduct the analysis. The admissible function is acquired by using a modified Fourier series approach in which several auxiliary functions are added to a standard cosine Fourier series to eliminate all potential discontinuities of the displacement function and its derivatives at the edges. Furthermore, the general elastic restraint and kinematic compatibility and physical compatibility conditions are imitated by the boundary and coupling spring technique respectively when the composite laminated doubly-curved panels degenerate to the complete shells of revolution. Then, the desired results are solved by the variational operation. Large quantities of numerical examples are calculated about the free vibration of cross-ply and angle-ply composite laminated doubly-curved panels and shells with different geometric and material parameters. Through the sufficient conclusions obtained from the comparison, it can be seen that highly accurate solutions can be yielded with a little computational effort. To understand the influence of different boundary conditions, lamination schemes, material and geometrical parameters on the vibration characteristics, a series of parametric studies are carried out. Lastly, results for vibration of the composite laminated doubly-curved panels and shells subject to various kinds of boundary conditions and with different geometrical and material parameters are also presented firstly, which can provide the benchmark data for other studies conducted in the future.

ミグ溶接プロセスの統合数値シミュレーション

ミグ溶接プロセスの統合数値シミュレーション

Temperature Prediction in a Free-Burning Arc and Electrodes for Nanostructured Materials and Systems

Temperature in a free-burning arc used for synthesis of nanoparticles and nanostructured materials is generally around 20,000 K just below the cathode, falling to about 15,000 K just above the anode, and decreasing rapidly in the radial direction. Therefore, the electrode erosion is indispensable for these atmospheric plasma systems, as well as for switching devices, due to the high heat flux transferred from high temperature arcs to electrodes, but experimental and theoretical works have not identified the characteristic phenomena because of the complex physical processes. To the previous study, we have focused on the arc self-induced fluid flow in a free-burning arc using the computational fluid dynamics (CFD) technique. At this time, our investigation is concerned with the whole region of free-burning high-intensity arcs including the tungsten cathode, the arc plasma and the anode using a unified numerical model for applying synthesis of nanoparticles and nanostructured materials practically.

Integrated Simulation Challenges with the DeepWind Floating Vertical Axis Wind Turbine Concept

This paper presents the experiences and challenges with concurrently carrying out numerical model development, integrated simulations and design of a novel floating vertical axis wind turbine, the DeepWind concept. The floating VAWT modelling capabilities of the aero-hydro-elastic HAWC2 simulation tool are briefly described and the design approach adopted for such a challenging project was to independently design subsystems in parallel, apart from essential design specifications. Instability issues encountered when integrating all subsystems in the unified numerical model, in particular blade edgewise and controller instabilities, are presented and efforts to alleviate such issues are detailed. A multidisciplinary design and optimization approach is proposed to eliminate these issues and accelerate future design cycles.

Settling Suspensions Flow Modelling: A Review

In spite of the widespread application of settling suspensions, their inherent complexity has yet to be properly predicted by a unified numerical model or empirical correlation, and usually industries still possess customized charts or data for their particular suspension. This is, clearly, rather inefficient and can lead to oversized dimensioning, low energy efficiency and even operation limitations/difficulties. In this manuscript a review of empirical correlations, charts and numerical models that have been employed to predict the behaviour of settling suspensions is briefly described, providing information on the advantages and drawbacks of each method. Their evolution throughout the years: from Durand and Condolios correlations, to empirical models by Wasp, single phase simplifications with mixture properties by Shook and Roco, and to other Euler-Euler or Euler-Lagrangian numerical models, will be presented. Some considerations on recent particle migration and turbulence modification publications will be added. In addition, information about some current CFD application of Lattice-Boltzmann and Discrete Element Method (DEM) will be given. Lastly, data from CFD modelling employed by the authors that is able to predict turbulence attenuation in settling flows with medium sized particles for different concentrations is reported.

Convective Flows in Evaporating Sessile Droplets

The evaporation rate and internal convective flows of a sessile droplet with a pinned contact line were formulated and investigated numerically. We developed and analyzed a unified numerical model that includes the effects of temperature, droplet volume, and contact angle on evaporation rate and internal flows. The temperature gradient on the air/liquid interface causes an internal flow due to Marangoni stress, which provides good convective mixing within the droplet, depending upon Marangoni number. As the droplet volume decreases, the thermal gradient becomes smaller and the Marangoni flow becomes negligible. Simultaneously, as the droplet height decreases, evaporation-induced flow creates a large jet-like flow radially toward the contact line. For a droplet containing suspended particles, this jet-like convective flow carries particles toward the contact line and deposits them on the surface, forming the so-called "coffee ring stain". In addition, we reported a simple polynomial correlation for dimensionless evaporation time as a function of initial contact angle of the pinned sessile droplet which agrees well with the previous experimental and numerical results.

Simulation of the coupling of the upper and lower atmosphere

The coupling of the upper and lower atmosphere and the problem of developing a unified numerical model of the Earth’s gaseous envelope is considered. The existing models of the upper and lower atmosphere are analyzed and specific models for use as parts of a future metamodels of Earth’s atmosphere are selected. A general algorithm for combining these models is proposed.

Numerical modelling of the activity concentration measurements of beta-radioactive noble gases by absorption in polycarbonates and external beta-counting

This work presents a unified numerical model for detailed description of the measurement of activity concentrations of radioactive noble gases by absorption in polycarbonates and external beta-counting. The model combines the numerical description of the kinetics of sorption and desorption processes with Monte Carlo simulations and calculates the measurement efficiency. The numerical model is compared to experimental data for 85Kr and 222Rn and a very good agreement is found. The numerical and experimental results show that for plate polycarbonates the measurement efficiency depends on the sorption and desorption times. In the case of 85Kr measurements the numerical modelling shows that this dependence is pronounced for thick polycarbonates and short exposure durations. For large exposure times 85Kr concentration inside the polycarbonate reaches homogeneous distribution, hence the efficiency of the system stays constant with time. In the case of 222Rn measurements no homogeneous activity distribution inside the polycarbonate can be reached due to the short half-life of 222Rn. The measurement efficiency in the case of 222Rn depends slightly on the desorption time. It is also demonstrated that in the case of 222Rn the measurement efficiency could be influenced by registration of the alpha-particles of 222Rn and its progeny. This influence increases the time dependence of the efficiency on the sorption and desorption times. Therefore, this effect must always be checked for and taken into account if an accurate measurement result is necessary. The developed numerical model allows to optimize the measurements by choosing appropriate experimental conditions in terms of polycarbonate thickness and sorption and desorption times. Results from several scenarios are presented, which allow the experimenter to chose a priori the optimal exposure and measurement conditions. Finally, we present results from pilot experiments on slowing down the desorption of the radioactive noble gases from the polycarbonates. We demonstrate that cooling the exposed polycarbonates to liquid nitrogen temperature practically stops the desorption of 222Rn from the polycarbonate specimen.

Numerical analysis of AC tungsten inert gas welding of aluminum plate in consideration of oxide layer cleaning

A unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a result of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.

Time-dependent calculations of molten pool formation and thermal plasma with metal vapour in gas tungsten arc welding

A gas tungsten arc (GTA) was modelled taking into account the contamination of the plasma by metal vapour from the molten anode. The whole region of GTA atmosphere including the tungsten cathode, the arc plasma and the anode was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of the shielding gas and metal vapour. The transient two-dimensional distributions of temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the molten pool as a function of time for a 150 A arc current at atmospheric pressure, both for helium and argon gases. It was shown that the thermal plasma in the GTA was influenced by iron vapour from the molten pool surface and that the concentration of iron vapour in the plasma was dependent on the temperature of the molten pool.GTA on high sulfur stainless steel was calculated to discuss the differences between a low sulfur and a high sulfur stainless steel anode. Helium was selected as the shielding gas because a helium GTA produces more metal vapour than an argon GTA. In the GTA on a high sulfur stainless steel anode, iron vapour and current path were constricted. Radiative emission density in the GTA on high sulfur stainless steel was also concentrated in the centre area of the arc plasma together with the iron vapour although the temperature distributions were almost the same as that in the case of a low sulfur stainless steel anode.

Magnetic levitation of large liquid volume

It is well known from experiments and industrial applications of cold crucible melting that an intense AC magnetic field can be used to levitate large volumes of liquid metal in the terrestrial conditions. The levitation confinement mechanism for large volumes of fluid is considerably different from the case of a small droplet, where surface tension plays a key role in constraining the liquid outflow at the critical bottom point. The dynamic interaction between the oscillatory motion of the free surface and the effects of turbulent flow is analysed using a unified numerical model, which describes the time dependent behaviour of the liquid metal and the magnetic field. The MHD modified k-? turbulence model is used to describe the mixing and damping properties at smaller scales not resolved by the macro model. The numerical multiphysics simulations suggest that it is possible to levitate a few kilograms of liquid metal in a cold crucible without requiring mechanical support from the container walls. Possible applications to the processing of reactive metals are discussed.

Metal Vapor Behavior in GTA Welding of a Stainless Steel Considering the Marangoni Effect

AbstractA gas tungsten arc in helium was modeled taking into account the contamination of the plasma by metal vapor from the weld pool. The whole region of gas tungsten arc atmosphere including the tungsten cathode, arc plasma and weld pool was treated using a unified numerical model. The anode was of a low sulfur stainless steel or a high sulfur stainless steel. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of shielding gas and metal vapor. The transient two‐dimensional distributions of the temperature, velocity of plasma flow and iron vapor concentration were predicted, together with the weld penetration at the atmospheric pressure. The distribution of the iron vapor is obviously different between the case of a low sulfur stainless steel anode and the case of a high sulfur stainless steel anode. © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Modelling compressible gas flow near the nozzle of a gas atomiser using a new unified model

In this paper, a unified numerical model is used to simulate the compressible gas flow, during the process of atomisation of liquid, near the atomiser nozzle in gas-only case studies. The flow of the under-expanded gas jets is studied, by analyzing the pressure field, density field and the spatial distribution of Mach number of the gas. The simulated predictions of gas status at the nozzle exit, the radial profile of Pitot pressure, aspiration pressure, and the spatial distribution of the density gradient, are compared with relevant experimental results and an analytical correlation, in order to validate and verify the application of this unified model in the numerical simulation of the gas dynamic behavior during gas atomisation. The simulation results show that the compressible gas flow near the nozzle of a discrete jet atomiser is different from that in a typical annular slit atomiser. Unlike existing models, this new formulation has the potential to be used in future to simulate the simultaneous flow of compressible gas and a weakly compressible liquid metal stream.

Metal Vapour Behaviour in Gas Tungsten Arc Thermal Plasma during Welding

The present modelling of a gas tungsten arc in helium or argon accounts for metal vapour contamination from the weld pool as an anode. The whole region of gas tungsten arc welding, namely, tungsten cathode, arc plasma and weld pool is treated in a unified numerical model. A viscosity approximation is used to express the diffusion coefficient in terms of the viscosities of shielding gas and iron vapour. The time dependent two-dimensional distributions of temperature, velocity and iron vapour concentration are predicted, together with the weld penetration as function of time for a 150 A arc at atmospheric pressure. It is shown that the thermal plasma in a gas tungsten arc is markedly influenced by iron vapour from the weld pool surface and the concentration of iron vapour in the plasma is dependent on the temperature of the weld pool surface.

Metal vapour behaviour in thermal plasma of gas tungsten arcs during welding

A gas tungsten arc in helium and argon was modelled taking into account the contamination of the plasma by metal vapour from the weld pool. The whole region of gas tungsten arc atmosphere including the tungsten cathode, arc plasma and weld pool was treated using a unified numerical model. A viscosity approximation was used to express the diffusion coefficient in terms of viscosity of shielding gas and metal vapour. The transient two-dimensional distributions of the temperature, velocity of plasma flow and iron vapour concentration were predicted, together with the weld penetration as a function of time for a 150 A arc current at the atmospheric pressure, both for helium and argon welding gases.It was shown that the thermal plasma in gas tungsten arcs is influenced by iron vapour from the weld pool surface and that the concentration of iron vapour in plasma is dependent on the temperature of the weld pool.