Numerical Model Agrees Research Articles

Internal‐Wave Dissipation Mechanisms and Vertical Structure in a High‐Resolution Regional Ocean Model

AbstractMotivated by the importance of mixing arising from dissipating internal waves (IWs), vertical profiles of internal‐wave dissipation from a high‐resolution regional ocean model are compared with finestructure estimates made from observations. A horizontal viscosity scheme restricted to only act on horizontally rotational modes (such as eddies) is introduced and tested. At lower resolutions with horizontal grid spacings of 2 km, the modeled IW dissipation from numerical model agrees reasonably well with observations in some cases when the restricted form of horizontal viscosity is used. This suggests the possibility that if restricted forms of horizontal viscosity are adopted by global models with similar resolutions, they could be used to diagnose and map IW dissipation distributions. At higher resolutions with horizontal grid spacings of ∼250 m, the dissipation from vertical shear and horizontal viscosity act much more strongly resulting in dissipation overestimates; however, the vertical‐shear dissipation itself is found to agree well with observations.

Influence of input variables on the unitary deformation experienced in pipes subjected to the action of lateral loads

The hydrocarbon transportation industry uses extensive pipeline networks subject to complex loading conditions. The finite element analysis (FEA) has proven to be effective in simulating the deformation behavior in these pipelines, which assists in the assessment of their integrity and risks. In this work, a model developed using finite elements is proposed to analyze the behavior of API 5L Gr B carbon steel pipes, subject to internal pressure and lateral loads. The model is validated through uniaxial tensile and four-point bending tests. In addition, parametric analysis is carried out considering variables such as diameter, lateral load, and distance between supports. The objective is to identify which one of these variables has the most influence in the unit strain. The results indicate that the unit strain obtained from the numerical model agrees with the experimental tests. Furthermore, it is concluded that the diameter is the influential parameter.

Numerical Investigation of Sulfate Diffusion Characteristics in Recycled Aggregate Concrete Based on Mesoscale Multiphase Analysis

Sulfate-induced deterioration can reduce the service life of recycled aggregate concrete (RAC). To demonstrate the transport behavior of sulfate ions in RAC, a two-dimensional, six-phase numerical model of RAC is proposed in this study. Sulfate ion diffusion coefficients were defined for different phases [attached mortar, new mortar, interfacial transition zone (ITZ) between attached mortar and original aggregate, ITZ between the new mortar and original aggregate, and ITZ between the new mortar and attached mortar] of RAC. The effects of ITZ width and porosity on ion transport behavior in RAC were analyzed. The results show that the numerical model agrees with the experimental data. Numerical results indicate that the six-phase model of RAC provides more-accurate simulation results because tortuosity is reflected in the model. The width and porosity of ITZs both affect the diffusion of sulfate ions in concrete. However, due to the low volume fraction of ITZ in concrete, just improving ITZ performance has no significant effect on ion attack resistance of concrete. The ITZ is a crucial zone where damage may originate and develop.

Variation of Lubricant Distribution Across the Radial Direction in a Journal Bearing

Abstract A computational fluid dynamics analysis of two-phase flow was used to obtain the distribution of lubricant in a journal bearing, including inlet tube and groove. It was found that for an incomplete starting film, the oil spread-length varies along the groove depth and film thickness. The magnitude of variation was found to be independent of the inlet mass flowrate. Numerical simulations of the proposed model show that in the cavitation region, the streamlets do not fill the entire film thickness. The present numerical model agrees with experimental observations.

Numerical Modeling of Equal and Differentiated Gas Injection in Ladles: Effect on Mixing Time and Slag Eye

Ladle refining plays a crucial role in the steelmaking process, in which a gas stream is bubbled through molten steel to improve the rate of removal of impurities and enhance the transport phenomena that occur in a metallurgical reactor. In this study, the effect of dual gas injection using equal (50%:50%) and differentiated (75%:25%) flows was studied through numerical modeling, using computational fluid dynamics (CFD). The effect of gas flow rate and slag thickness on mixing time and slag eye area were studied numerically and compared with the physical model. The numerical model agrees with the physical model, showing that for optimal performance the ladle must be operated using differentiated flows. Although the numerical model can predict well the hydrodynamic behavior (velocity and turbulent kinetic energy) of the ladle, there is a deviation from the experimental mixing time when using both equal and differentiated gas injection at a high gas flow rate and a high slag thickness. This is probably due to the insufficient capture of the velocity field near the water–oil (steel–slag) interface and slag emulsification by the numerical model, as well as the complicated nature of correctly simulating the interaction between both gas plumes.

Numerical investigation of parametric resonance due to hydrodynamic coupling in a realistic wave energy converter

Representative models of the nonlinear behavior of floating platforms are essential for their successful design, especially in the emerging field of wave energy conversion where nonlinear dynamics can have substantially detrimental effects on the converter efficiency. The spar buoy, commonly used for deep-water drilling, oil and natural gas extraction and storage, as well as offshore wind and wave energy generation, is known to be prone to experience parametric resonance. In the vast majority of cases, parametric resonance is studied by means of simplified analytical models, considering only two degrees of freedom (DoFs) of archetypical geometries, while neglecting collateral complexity of ancillary systems. On the contrary, this paper implements a representative 7-DoF nonlinear hydrodynamic model of the full complexity of a realistic spar buoy wave energy converter, which is used to verify the likelihood of parametric instability, quantify the severity of the parametrically excited response and evaluate its consequences on power conversion efficiency. It is found that the numerical model agrees with expected conditions for parametric instability from simplified analytical models. The model is then used as a design tool to determine the best ballast configuration, limiting detrimental effects of parametric resonance while maximizing power conversion efficiency.

Numerical modeling of a regional groundwater flow system to assess groundwater storage loss, capture and sustainable exploitation of the transboundary Milk River Aquifer (Canada – USA)

Groundwater capture and storage loss play a major role in the sustainable exploitation of a regional aquifer. This study aimed to identify the impact of major and long-term groundwater exploitation on a regional aquifer system to understand the processes controlling the sustainable exploitation of the transboundary Milk River Aquifer (MRA). The MRA extends over 26,300 km2, being a major water resource across southern Alberta (Canada) and northern Montana (USA). Concerns about the sustainability of the MRA were raised as the century-old exploitation has led to important drawdowns and the local loss of historical artesian conditions. A steady-state numerical model of the regional flow system was developed and calibrated against hydraulic heads, groundwater fluxes, and the area with flowing artesian wells. Four groundwater abstraction scenarios were simulated: 1) natural flow conditions without exploitation; 2) the mean abstraction rate over the last 108 years; 3) the historical maximum global abstraction rate of the MRA; and 4) a theoretical high abstraction rate based on the maximum rate estimated for each MRA exploitation zone. The numerical model agrees with the previously formulated conceptual model and supports its hydraulic plausibility. Results show that MRA exploitation has led to a major change in flow patterns to sustain groundwater abstraction. The MRA water balance under exploitation indicates that more recharge and reduced seepage to bedrock valleys compensate groundwater withdrawals. Based on its impact on regional discharge and the reduction in MRA storage, the mean historical level of exploitation of the MRA appears sustainable. Larger exploitation rates would significantly reduce groundwater discharge to surface seepage locations and lead to a larger reduction in groundwater storage in the MRA. Modeling also illustrates that the MRA is an internationally shared resource. This situation would justify a joint management of the aquifer system between Canada and USA; especially in the area comprised between the recharge area in Montana and the Canadian reach of the Milk River.

Wave breaking in undular bores generated by a moving weir

If a weir is dragged through a wave flume, the upstream flow takes the form of an undular bore propagating ahead of the weir. It was found previously in the work of Wilkinson and Banner (“Undular bores,” in 6th Australian Hydraulics and Fluid Mechanics Conference, Adelaide, Australia, 1977) that the leading wave of the undular bore will break if the bore strength given by the ratio of downstream to upstream flow depth exceeds a certain value. In the present work, a Boussinesq system is used to study the situation in a numerical wave tank. It is found that if a convective breaking criterion is used to indicate wave breaking, then the critical bore strength of the numerical model agrees with the experimental value of Wilkinson and Banner up to an error of less than 2%.

Simulation of Angular Flow in a Shallow Basin Triggered by a Rotating Vertical Cylinder by SPH Method

A simple numerical model has been generated for developing a code of Smoothed Particle Hydrodynamics (SPH) method. Those will be modified and used for future research. In this computational research domain is a square that consists of a real particle and virtual particle as the boundary treatment. In the initial condition, particle occupies a certain position. Circular flow has been generated by a rotating vertical cylinder to produce shear velocity to the real particle. The particles movement has been observed during time integration. A physical model has been constructed to compare the numerical model. The movement of real particles on the numerical model agrees with the movement of water particles on the physical model.

Simulating Temporal Organization of Histogenesis

The paper discusses a discrete model of hepatic plate histogenesis based on the dissymmetry distribution times of cell cycles. The model is based on the assumption of the finality of cell time as an internal parameter of a single cycle of biological spacetime. Another assumption is the divisibility of maternal cell time in half between daughter cells, which makes it possible to consider the stem cell macrocycle in histogenesis as a system of nested cell cycles with progressively decreasing time. In addition, it was expected that at each step of cell division in homogeneous histogenesis, a asymmetric distribution of reference of cell time management by mitosis, which is related to the intron region of the genome. The obtained numerical model agrees with the characteristics of the architectonics of the liver, the limited number of cell divisions, and the frequency distribution of mitosis and aging as the extinction process of cells with short cycles.

Failure behavior of annealed glass for building windows

The failure strength of annealed float glass is difficult to predict accurately due to several factors that influence the glass’ mechanical behavior, including stress rate, environmental conditions, fabrication process, glass thickness and the presence of surface flaws. Some of these parameters strongly depend on the construction practices of each country. This study aimed to assess the failure strength of annealed glass commonly used in the construction industry in Mexico, based on experimental tests. It is also determined experimental data dispersion as function of the glass thickness. The approach employs destructive tests on annealed glass plates subjected to out-of-plane loading in a coaxial double ring (CDR) test setup and analytical linear and a geometric non-linear finite element analyses. The mechanical behavior determined by the numerical model agrees with the failure strength and deflection obtained experimentally. The results show the mean failure strength of glass specimens with several thicknesses typically used in Mexico, and the analysis of data dispersion is also presented. The statistical analyses of glass failure strengths with thickness range 3–19mm indicate that all samples cannot be considered coming from the same population and data dispersion depended on glass thickness. Finally, the use of the experimental results for evaluating mean failure strength of glass panels and a comparison with expected wind-induced pressure in buildings located in two sites in Mexico is exposed.

Numerical Simulations of the Flame of a Single Coaxial Injector

The processes of mixing and combustion in the jet of a shear-coaxial injector are investigated. Two test cases (nonreacting and reacting) are simulated using the commercial computational fluid dynamics code ANSYS CFX. The first test case is an experiment on the mixing in a nonreacting coaxial jet carried out with the use of planar laser induced fluorescence (PLIF). The second test case is an experiment on the visualization of hydrogen-oxygen flame using PLIF of OH in a single injector combustion chamber at pressure of 53 bar. In the first test case, the two-dimensional axisymmetric simulations are performed using the shear-stress turbulence (SST) model. Due to the dominant flow unsteadiness in the second test case, the turbulence is modeled using transient SAS (Scale-Adaptive Simulation) model. The combustion is modeled using the burning velocity model (BVM) while both two- and three-dimensional simulations are carried out. The numerical model agrees with the experimental data very well in the first test case and adequately in the second test case.

NUMERICAL STUDY ON AERODYNAMIC CHARACTERISTICS OF BUNDLE CONDUCTOR FOR UHV BASED ON ALE METHOD

The bundle conductor is often threatened by the wind-excited or wake-induced vibration generated by vortex shedding. So as to simulate the common fluid–structure nonlinear interaction problems in Ultra-High Voltage (UHV) transmission lines, the N-S equations of incompressible viscous fluid with the ALE description has been adopted to formulate the fluid-solid governing equations in the analogue computation and the 2-bundle and 6bundle sectional models, as well as the deduced finite element discretization scheme of conductor displacement are introduced in the algorithm. Wind tunnel experimental studies are carried out based on the single stranded model, 6-bundle stranded and 6bundle circle model for the focus of aerodynamic characteristics and the difference between stranded cable and circle cable. Results show that solution of numerical model agrees favorably with experimental results. The aerodynamic coefficients decrease significantly within the expected critical range of wind speed or Reynolds numbers and the cables roughness is not the principle factor to the aerodynamic coefficient when the Reynolds numbers belong to the critical region. However, the interference effect of the bundle conductor widely influenced the wind load applied on the surface of each cable.

Numerical model of a small-scale liquid-to-air membrane energy exchanger: Parametric study of membrane resistance and air side convective heat transfer coefficient

A small-scale single-panel liquid-to-air membrane energy exchanger (LAMEE) is a novel membrane based energy exchanger that allows heat and moisture transfer between a supply air stream and a salt solution flow through a semi-permeable membrane. In this paper, the steady-state effectiveness of the small-scale single-panel LAMEE is experimentally measured and numerically modeled. The numerical model is compared with the experimental data for summer and winter test conditions. Parameters those are investigated using the numerical model include membrane vapor diffusion resistance (VDR) and air side convective heat transfer coefficient. The membrane VDR in the small-scale LAMEE is measured and the effect of this parameter is studied for the steady-state effectiveness. Decreasing the membrane VDR from 56 s/m to 24 s/m increases the LAMEE latent effectiveness by 11%, and as expected, it doesn't have any effect on the LAMEE sensible effectiveness. Enhanced convective heat transfer coefficient in the air flow of the small-scale LAMEE is calculated, and the effect of this parameter on the LAMEE effectiveness is investigated. The results show 138% improvement in the convective heat transfer coefficient in the air channel of the LAMEE with an air screen at Reair = 1570 which results in 11% improvement in the LAMEE effectiveness. Finally, the modified numerical model is validated by the experimental data for the steady-state effectiveness of the small-scale LAMEE under summer test conditions at four different values of the thermal capacity ratio (Cr* = 1, 3, 5 and 7) and NTU = 3.8. Moreover, the numerical model is used for winter test conditions, and the results are compared with the experimental data. The results show that the numerical model agrees with the experimental data for the latent and total effectiveness of the LAMEE under the air heating and humidifying and air heating and dehumidifying test conditions.

A numerical and experimental friction analysis of reciprocating hydraulic ‘U’ rod seals

This article is focused on the comparison between experimental and numerical friction forces obtained for a typical hydraulic ‘U’ rod seal. The numerical results are obtained by the inverse hydrodynamic lubrication method. The experimental results have been obtained on an original experimental device capable of measuring the friction force between a rod and two seals. The reciprocating rod speed, the temperature and pressure in the test cell are controlled. Despite the fact that the numerical results correspond to an idealized hydrodynamic problem for smooth surfaces, it was found that the numerical model agrees with experimental data when the predicted film thickness is higher than the rod roughness but largely lower than the seal roughness. This suggests that the roughness of the seal disappears under the pressure in the sealed contact and do not play an essential role in the lubrication mechanisms. However, it is clear that for very small film thickness, the full film lubrication theory for smooth surfaces is not convenient. This may imply that in these conditions mixed lubrication cannot be ignored or that adhesion phenomena, not taken into account by the lubrication theory, can appear in the contact areas.

Behavior of Sheet Pile Quay Wall Stabilized by Sea-Side Ground Improvement in Dynamic Centrifuge Tests

Sea-side ground improvement is one of the techniques used for increasing seismic stability of sheet pile quay wall. A series of centrifuge shaking table test is conducted to investigate the seismic behavior of sheet pile quay wall stabilized with sea-side cement deep mixing (CDM). At 50 g centrifugal acceleration, the clay ground is consolidated and four to five stages of shaking are applied to the quay wall. The recorded input-output accelerations, deflection of the quay wall, earth pressures along depth and pore pressures were used to evaluate the behavior of the stabilized sheet pile quay wall. The results indicated that an improved area provides significant resistance against seismic loading. The ground improvement can reduce 30% to 60% bending moment during the seismic loading. The horizontal deflection of the quay wall decreases rapidly with increase in area of the CDM until it reaches a certain limit. Prediction by the numerical model agrees fairly well with the results of centrifuge model tests.

Propagation of sound in long enclosures

The propagation of sound in long enclosures is addressed theoretically and experimentally. In many previous studies, the image source method is frequently used. However, these early theoretical models are somewhat inadequate because the effect of multiple reflections in long enclosures is often modeled by the incoherent summation of contributions from all image sources. Ignoring the phase effect, these numerical models are unlikely to be satisfactory for use in predicting intricate patterns of interference due to contributions from each image source. In the present paper, the effect of interference is incorporated by coherently summing the contributions from the image sources. To develop a simple numerical model, the walls of long rectangular enclosures are represented by either geometrically reflecting or impedance boundaries. Measurements in a one-tenth-scale model are conducted to validate the numerical model. In some of the scale-model experiments, the enclosure walls are lined with a carpet to simulate the impedance boundary condition. It has been shown that the proposed numerical model agrees reasonably well with experimental data.

The propagation of sound in tunnels

The sound propagation in tunnels is addressed theoretically and experimentally. In many previous studies, the image source method is frequently used. However, these early theoretical models are somewhat inadequate because the effect of multiple reflections in long enclosures is often modeled by the incoherent summation of contributions from all image sources. Ignoring the phase effect, these numerical models are unlikely to be satisfactory for predicting the intricate interference patterns due to contributions from each image source. In the present paper, the interference effect is incorporated by summing the contributions from the image sources coherently. To develop a simple numerical model, tunnels are represented by long rectangular enclosures with either geometrically reflecting or impedance boundaries. Scale model experiments are conducted for the validation of the numerical model. In some of the scale model experiments, the enclosure walls are lined with a carpet for simulating the impedance boundary condition. Large-scale outdoor measurements have also been conducted in two tunnels designed originally for road traffic use. It has been shown that the proposed numerical model agrees reasonably well with experimental data. [Work supported by the Research Grants Council, The Industry Department, NAP Acoustics (Far East) Ltd., and The Hong Kong Polytechnic University.]