Physical and numerical simulation of two-phase flow in the area of mini-channel

Platform structures are commonly utilized for various purposes including offshore drilling, processing, and support of offshore operations. A jacket is a supporting structure for deck facilities, stabilized by piles driven through it to the seabed. In a jacket design, operational and environmental loads are very important and must be intensively investigated to secure the stability of structures during their service life, as well as installation phase. The main purpose of this research is to evaluate the results of physical modeling for the launch operation of jackets from barge into the sea, as the most hazardous stage in the installation of a platform, and compare them to those of numerical modeling. Both physical and numerical modeling parameters are described and they are examined on a prototype platform, i.e., Balal oil field production and living quarter platform that is a 1700 tone, eight-legged jacket located in the center of Persian Gulf, some 100km distance from Iranian Lavan Island. It is found that both numerical and physical methods can describe the motion of the barge similarly well, but some differences are traced in the motion of jacket. The inequalities are, then, appeared to be due to the Froude-type parameters applied for modeling purpose. One notable fact investigated in this research is the necessity for choosing Reynolds–Froude type in the physical modeling of the launch, instead of Froude type. This is because, in addition to the importance of gravitational and inertial forces, the viscosity affects the drag hydrodynamic force, as well. It should be noted that viscosity and consequently drag coefficient in Froude type modeling cannot be quite applicable and this causes the difference observed between the results of physical and numerical modeling. Although there have been so many jacket launching designed and probably their physical models have been tested, but to the best of our knowledge from the literature, there was found no study on Reynolds–Froude physical modeling of jacket launch phenomenon. If one is interested in practicing a Reynolds-Froude physical modeling, it could be done either in a centrifuge test or by using a fluid with lower viscosity dependent on the scale of model, or even by finding a fluid (with new viscosity and new density) and a new gravity to have simultaneously the Froude and the Reynolds similarity laws satisfied.

The Zuppinger water wheel, developed in the 1850s, is one of the most efficient water wheels and is commonly used for low-head hydropower generation. The high efficiencies of the wheel over a wide operating range, its simplicity in design and slow rotational speed offer a low-cost and environmentally friendly low-head hydropower solution. A physical and numerical model study of a wheel is presented in this paper. Three-dimensional numerical simulations were performed using the computational fluid dynamics (CFD) code Flow-3D. The influence of grid size on the results of the numerical model was assessed using a systematic grid refinement study. Grid convergence indices (GCIs) were calculated for two grid sets each, with three different grid sizes, using a constant grid refinement ratio. The GCIs were reduced to levels below 5% for the selected quantities of interest. The CFD model results were compared with physical model results at different operating points of the wheel. The maximum differences in power output and efficiency between the physical and numerical model results were 2.5% and 8%, respectively.

The Joule-heated ceramic-lined melter is an integral part of the high level waste immobilization process under development by the US Department of Energy. Scaleup and design of this waste glass melting furnace requires an understanding of the relationships between melting cavity design parameters and the furnace performance characteristics such as mixing, heat transfer, and electrical requirements. Developing empirical models of these relationships through actual melter testing with numerous designs would be a very costly and time consuming task. Additionally, the Pacific Northwest Laboratory (PNL) has been developing numerical models that simulate a Joule-heated melter for analyzing melter performance. This report documents the method used and results of this modeling effort. Numerical modeling results are compared with the more conventional, physical modeling results to validate the approach. Also included are the results of numerically simulating an operating research melter at PNL. Physical Joule-heated melters modeling results used for qualiying the simulation capabilities of the melter code included: (1) a melter with a single pair of electrodes and (2) a melter with a dual pair (two pairs) of electrodes. The physical model of the melter having two electrode pairs utilized a configuration with primary and secondary electrodes. The principal melter parameters (themore » ratio of power applied to each electrode pair, modeling fluid depth, electrode spacing) were varied in nine tests of the physical model during FY85. Code predictions were made for five of these tests. Voltage drops, temperature field data, and electric field data varied in their agreement with the physical modeling results, but in general were judged acceptable. 14 refs., 79 figs., 17 tabs.« less

Statistical analysis of bimslope stability using physical and numerical models

Platform structures are commonly utilized for various purposes including offshore drilling, processing and support of offshore operations. A jacket is a supporting structure for deck facilities stabilized by leg piles through the seabed. In a jacket design, operational and environmental loads are very important and must be investigated intensively to secure the stability of structures during their operational life, as well as installation phase. The main purpose of this research is to evaluate and compare the results of physical and numerical modeling for the launch operation of jackets from barge into the sea, as the most hazardous stage in the installation of a platform. Both physical & numerical modeling basics are described and they are performed on Balal PLQ (Production and Living Quarter) platform that is one 8-legged, 1700-tone main jacket of Balal oil field, located in the center of Persian Gulf, some 100 kms distance from Iranian Lavan Island. It is found that both methods can describe the motion of the barge similarly well, but some differences are traced in the motion of jacket. Then, the inequalities are evaluated to be due to the Froude-type parameters chosen for modeling purpose. The most important result achieved in this research is the necessity of choosing Reinolds-Froude type for physical modeling of launching, instead of Froude-type. This is due to the effect of viscosity in drag hydrodynamic force in addition to the importance of gravitational and inertial forces. It should be noted that viscosity and consequently drag coefficient in Froude type modeling is not quite correct and causes the difference between the results of physical and numerical modeling. To our knowledge, based on the surveyed done in the literature, although there was no results found on the physical modeling of jacket launch to be addressed, but it seems that Reynolds-Froude modeling could be done either in a centrifuge test or by using a fluid with lower viscosity dependent on the scale of model.

The article deals with problems of using of measurement method Particle Image Velocimetry (PIV) to measure velocity fields in the flowing water in front, above and behind drowned titling weir gate. The aim was to obtain information about the distribution of speed in the area of interest for the verification or calibration of the numerical model. Experiments were carried out in inclinable channel connected to the hydraulic circuit with a pump and storage tank at the Water Management Research Laboratory (LVV) of Institute of Water Structures at the Faculty of Civil Engineering in Brno University of Technology. Hydraulic inclinable channel has cross-section with dimensions of 0.4x0.4m and length of 12.5m. The measured area has cross-section approximately 0.2m wide and 0.4m high and its length is 1m. The results of physical modelling allowed a comparison of experimental data with numerical simulation results of this type of flow in the commercial software ANSYS CFX-12.0. In the foreground interest in the field of water management still more are getting and applying options of numeric modeling, mainly based on very rapid development of the performance of personal computers. Using the numerical simulations of fluid flow, we are today able to obtain detailed information about all characteristics of the flow required for optimal design of waterwork. However, a significant disadvantage of numerical simulation is the necessity to obtain initial and marginal (boundary) conditions that must be entered as input data into the computer calculation program. These input data is in most cases can be obtained only on the basis of physical modeling, so measurements characteristics of flow on the physical model. The results of numerical simulations must be compared with the results of physical modelling and on the base it calibrated the numerical model. To determine the characteristics of liquid flow respectively velocity field on the physical model appears to be an ideal method of PIV (Particle Image Velocimetry), which allows us a sufficiently accurate measurement velocity field of fluid flow in the selected area.

Effects of T-shape groin parameters on beach accretion

Introduction. The distorted scale method is often used to develop physical models of hydraulic structures. Notably, scientific researches concerning the methodology of distortions are quite rare, especially those that are focused on the modeling of wind waves. In the modern practice, scale distortions only affect the underwater topography and hydraulic structures. In this case, initial waves remain unchanged, and this can lead to errors in the wave mode at the control points of a model. Given the data on errors, the author considers the changes in the parameters of initial waves, if the scale of a physical model is distorted. Materials and methods. The author used methods of physical and numerical modeling. Experimental studies were conducted in a wave flume and a wave pool that had a wavemaker. In the course of the experiments, the initial wave mode was changed and the parameters of waves were measured at the control points of distorted physical models. Numerical mode­ling was employed to analyze the computational patterns similar to the physical models. Results. The author used physical models featuring varying degrees of distortion to obtain a collection of the wave mode data under the conditions of the wave transformation and diffraction. Physical and numerical modeling results are compared. The author provides an assessment of the results attained by changing the parameters of initial waves and distorted physical models. Conclusions. The scale distortion triggers changes in the wave mode that may not be easy to control and correct. This fact must be taken into account when distorted hydraulic models are developed. This approach demonstrates varying efficiency if applied to different physical models featuring characteristic processes.

Comparison of experimental data and numerical simulation of two-phase flow pattern in vertical minichannel The aim of the study was the implementation of a numerical simulation of the air-water two-phase flow in the minichannel and comparing results obtained with the values obtained experimentally. To perform the numerical simulations commercial software ANSYS FLUENT 12 was used. The first step of the study was to reproduce the actual research installation as a three-dimensional model with appropriate and possible simplifications - future computational domain. The next step was discretisation of the computational domain and determination of the types of boundary conditions. ANSYS FLUENT 12 has three built-in basic models with which a two-phase flow can be described. However, in this work Volume-of-Fluid (VOF) model was selected as it meets the established requirements of research. Preliminary calculations were performed for a simplified geometry. The calculations were later verified whether or not the simplifications of geometry were chosen correctly and if they affected the calculation. The next stage was validation of the chosen model. After positive verification, a series of calculations was performed, in which the boundary conditions were the same as the starting conditions in laboratory experiments. A satisfactory description of the experimental data accuracy was attained.

This paper describes the modelling of seiching in an exposed new marina using the combination of numerical and physical modelling. The new Western Marina is part of the Beirut Central District reclamation scheme (Lebanon). Due to the rapidly changing shallow water bathymetry near the harbour entrance, hydraulic design studies paid particular attention to the potential for seiching in the new marina. Both models show that the long-period wave energy is concentrated around frequencies corresponding to wave periods of 50-80s (fundamental natural mode) and 67 minutes (Helmholtz mode). The non-linear Boussinesq type model is applied to understand the seiching phenomena, for calculation of the spatial variation of the long wave amplification, screening of alternative harbour configurations and to investigate possible model effects in the physical model. The physical model is interactively applied to investigate in detail the most promising layouts, especially for incident wave conditions associated with strong wave breaking, where the numerical model is not yet feasible. Comparison between physical and numerical model results is shown to be in excellent agreement supporting this strong approach in future studies of low frequency oscillations in ports and harbours forced by wind-waves and swell.

Wave refraction and diffraction effects resulting from bathymetric depressions (a dredged borrow pit and a dredged entrance channel to a port) were investigated for a major port expansion project. Due to the complex bathymetry and port configuration, a combination of physical and numerical modeling was developed. A third generation, phase-averaged, spectral wind-wave model was developed for this study using an unstructured mesh. The model was used to transform offshore wave conditions to provide the extreme nearshore wave design conditions of significant wave height, peak period, and mean wave direction (Hm0, Tp, MWD). A time-domain, Boussinesq-type wave model was also established to simulate the propagation of waves traveling from deep water to shallow water involving the primary wave motion as well as the bound and free long waves. This model is capable of reproducing the combined effects of most of the wave phenomena of interest to the harbor engineer, including shoaling, refraction, diffraction and partial reflection of irregular, finite amplitude waves propagating over complex bathymetry (i.e., borrow pits, dredged channel). The results of the study indicate that the surface interactions with the deep-draft and wide navigation channels significantly influence the incident waves and manifest themselves into both amplification and attenuation of the incident wave field. Both of these effects in-turn critically influence inputs to design, planning of port infrastructure, as well as assessment of harbor agitation and vessel downtime. While in recent years port designers have typically relied upon numerical wave models to perform most of the initial studies, in our study a combination of physical and numerical modeling was used. Based on the combined observations from the physical and numerical modeling results, conclusions and recommendations from this work show that both models compared well. Wave heights observed in the physical model were similar to or slightly higher than the numerical predictions.

Hydrogen is an essential energy carrier to ensure energy security. The alkaline water electrolysis is one of the methods of hydrogen production and large-scale hydrogen production can be achieved with this method. Since the energy efficiency on a present water electrolysis plant is only 60% [1], improving the efficiency is required for high energy efficiency hydrogen energy system. The energy loss in water electrolysis with high current density comes from a lack of the ion on the electrode, therefore promoting the ion transportation can improve the electrolysis efficiency. The reason of the decrease in the water electrolysis efficiency have been studied; Qian [2] showed generated gas bubbles sticking to the electrodes decrease effective surface area, and Jassen [3] revealed the presence of gas bubbles prevents ion transportation in the electrolyte. Whereas, Vogt [4] reported that mass transportation phenomena are classified into three types of convections induced by gas bubbles, which can encourage ion transportation. These results indicate the dynamics of bubbles play a significant role on the ion transportation and the efficiency. As the investigation with experiments have a limitation, numerical simulations have also been carried out. Mat [5] investigated an effect of gas evolution on a vertical electrochemical cell with two-phase flow model simulating void fraction in the cell. Hreiz [6] simulated two-phase flow induced by electrogenerated bubbles using the two-way momentum coupling Euler-Lagrange CFD approach. Nevertheless, there are only a few studies that dealt with both two-phase flow and electrochemical reaction. Furthermore, no previous study has analyzed an effect of gas bubble dynamics on the electrolysis with taking bubble-induced micro-convection into consideration. From the background mentioned above, in this study, we conducted three-dimensional coupling numerical simulation of two-phase flow and electrochemical phenomena and analyze influence of the convection with micro bubbles on the ion transportation and a cell overpotential. Moreover, we discuss the influence of the bubble atomization on the efficiency under various bubble conditions. Two-phase flow is simulated with lattice kinetic scheme (LKS) including a phase-field model proposed by Inamuro [7]. The rate of electrochemical reaction is calculated given by Butler-Volmer equation. The ion mass transportation in the electrolyte is simulated with Nernst-Planck equation. The electrical field generated by applying a voltage on the electrodes is governed by Maxwell’s equation. We use a nickel for both electrodes and 6 mol/L KOH solution for the electrolyte. The cell temperature is 298 K, and bubble size is less than 1 mm. The water electrolysis is simulated under constant current; the average of current density is 820 mA/cm2. Time variations of the cell overpotential is shown in Fig.1. The flow is generated by bubble rising and the cell overpotential is suppressed. The overpotential suppression by the flow overcomes an overpotential increase by the presence of gas bubbles preventing ion transportation in the electrolyte. Moreover, this overpotential suppression is enhanced by bubble atomization. The overpotential suppression can be separated into two types of an overpotential; one is an ohmic loss, the other is an anodic concentration overpotential. Fig.2 illustrates time variations of drop in ohmic loss and anodic concentration overpotential. Both of the overpotential constantly decreases with time. The anodic concentration is suppressed by promoting ion transportation to the anode surface and ohmic loss is suppressed by mixing the electrolyte. Fig.3 shows three-dimensional concentration distribution, and the 2 mol/L iso-surface is also illustrated in this figure. The iso-surface shifts to the anode side with increases in the number of bubbles, and smaller bubble accelerates ion transportation to the electrode and decreases the anodic overpotential and ohmic loss. This result can be explained by the result reported by Guan [8] that a smaller bubble lowers the lift force against a wall and approaches closer to the wall. [1] Pletcher, D. & Li, X. Int. J. Hydrogen Energy 36, 15089–15104 (2011). [2] Qian, K., Chen, Z. D. & Chen. J. J. J, J. Appl. Electrochem. 28, 1141–1145 (1998). [3] Janssen, L. J. J. J. Appl. Electrochem. 30, 507–509 (2000). [4] H, Vogt. Electrochim. Acta 38, 1421–1426 (1993). [5] Mat, M. D. & Aldas, K. Int. J. Hydrog. Energyn 30, 411–420 (2005). [6] Hreiz, R., Abdelouahed, L., Fünfschilling, D. & Lapicque, F. Chem. Eng. Reseach Des. 100, 268–281 (2015). [7] Inamuro, T., Yokoyama, T., Tanaka, K. & Taniguchi, M. Comput. Fluids 137, 55–69 (2016). [8] GUAN, C., YANASE, S., MATSUURA, K., KOUCHI, T. & NAGATA, Y. Japan Soc. Fluid Mech. 37, 281–289 (2018). Figure 1

Study of the numerical instabilities in Lagrangian tracking of bubbles and particles in two-phase flow

At present both primary and secondary aluminium needs to be refined before further treatment. This can be done by barbotage process, so blowing small bubbles of inert gas into liquid metal. This way harmful impurities especially hydrogen can be removed. Barbotage is very complex taking into consideration hydrodynamics of this process. Therefore modelling research is carried out to get to know the phenomena that take place during the process better. Two different modelling research can be applied: physical and numerical. Physical modelling gives possibility to determine the level of gas dispersion in the liquid metal. Whereas, numerical modelling shows the velocity field distribution, turbulent intensity and volume fraction of gas. The paper presents results of physical and numerical modelling of the refining process taking place in the bath reactor URO-200. Physical modelling was carried out for three different flow rate of refining gas: 5, 10 and 15 dm3/min and three different rotary impeller speeds: 0, 300, 500 rpm Commercial program in Computational Fluid Dynamics was used for numerical calculation. Model VOF (Volume of Fluid) was applied for modelling the multiphase flow. Obtained results were compared in order to verify the numerical settings and correctness of the choice.

The article discusses the features and results of physical and mathematical modeling of filtration experiments on terrigenous and carbonate rock core samples at different crimping pressures. Such studies are necessary to understand the effect of rock pressure on the reservoir properties and relative phase permeability (RP) of reservoir rocks, including from the standpoint of the Digital Core technology, since core tomography is usually performed under atmospheric conditions and data on rock properties are required for reservoir conditions. The article discusses the features and results of physical and mathematical modeling of filtration experiments on terrigenous and carbonate rock core samples at different crimping pressures. Such studies are necessary to understand the effect of rock pressure on the reservoir properties and relative phase permeability (RP) of reservoir rocks, including from the standpoint of the Digital Core technology, since core tomography is usually performed under atmospheric conditions and data on rock properties are required for reservoir conditions. The laboratory study of the relative permeability was carried out on composite core models by the method of stationary filtration at crimping pressures of 10 and 20 MPa. Mathematical modeling of filtration experiments was performed in the Eclipse simulator. The distribution of porosity in the hydrodynamic models of the core was set based on data from computed tomography of the core. The distribution of other rock properties (permeability, residual saturations, RPP values at residual saturations) was calculated using generalized dependencies. It is shown that for terrigenous and carbonate rocks, an increase in pressure leads to different behavior of the RPP functions and fluid mobility. The results of laboratory studies are interpreted from the point of view of processes at the micro level, based on the formation of the nature of the flow and the associated water saturation during deformation of the void space. It is also shown that filtration experiments on core at different rock pressures can be simulated on a hydrodynamic simulator, but at the same time, the study of patterns in the change in model parameters with a change in pressure depends on the presence of patterns in the behavior of rock properties based on the results of physical modeling.