Present Numerical Model Research Articles

Development and validation of an open-source CFD model for the efficiency assessment of data centers

In this study, an open-source computational fluid dynamics (CFD) model was developed based on OpenFOAM libraries for the accurate and robust simulation of thermal distribution in a data center. Two boundary conditions were developed for the temperature field in the black-box modeling of server components. The numerical model was first validated by comparing numerical results with the experimental measurements for three benchmark problems in the field of thermal engineering. Then, thermal distribution in an open-aisle data center was simulated using the proposed numerical model and results were compared with the experimental measurements. The consistency between numerical results and previous experimental measurements indicates that the present numerical model can be reliably used for the efficiency assessment of air-cooled data centers. Efficiency of the data center can be evaluated with respect to four metrics in the proposed numerical model. In addition to the determination of the overall efficiency, distribution of the efficiency can be monitored over the racks to capture thermal zones where the efficiency decreases due to the recirculation effects and cold air by-pass.

Meshless Generalized Finite Difference Method for the Propagation of Nonlinear Water Waves under Complex Wave Conditions

The propagation of nonlinear water waves under complex wave conditions is the key issue of hydrodynamics both in coastal and ocean engineering, which is significant in the prediction of strongly nonlinear phenomena regarding wave–structure interactions. In the present study, the meshless generalized finite difference method (GFDM) together with the second-order Runge–Kutta method (RKM2) is employed to construct a fully three-dimensional (3D) meshless numerical wave flume (NWF). Three numerical examples, i.e., the propagation of freak waves, irregular waves and focused waves, are implemented to verify the accuracy and stability of the developed 3D GFDM model. The results show that the present numerical model possesses good performance in the simulation of nonlinear water waves and suggest that the 3D “RKM2-GFDM” meshless scheme can be adopted to further simulate more complex nonlinear problems regarding wave–structure interactions in ocean engineering.

Numerical study of wave effect on water entry of a three-dimensional symmetric wedge

Marine and aerospace structures are frequently subject to impact loads on wave surface. The primary aim of this paper is to obtain a fundamental understanding of wave effect on wedge entry problem. A three-dimensional (3D) full-scale symmetric wedge with three degrees of freedom (3DOF) is numerically modeled in the incompressible air–water two phase flows. The numerical implementation and regular wave surface are realized in Reynolds-averaged Navier–Stokes equations (RANS) framework (STAR-CCM+ 2020.1) by combining with volume of fluid (VOF) and velocity-inlet wavemaking methods. The accuracy of the present numerical model is validated by the experimental tests. Various case studies are then carried out to investigate the difference between calm water and wave crest entries, and to analyze the mechanisms of the wave position and wave height effects through several physical results, including acceleration, velocity, pressure, displacement, rotation and free surface. Results indicate that the process of water entry can be divided into early, vertical-down and bounce-up stages. Further, the wave effect on the water entry problem can be explained as that the incident wave particle velocities and the surface slope result in the variations of effective impacting velocity and entry type of the wedge, and thus remarkably influence the hydrodynamic loads and rotating motion of the wedge. The parametric study reveals that the wave height has no significant effect on the vertical force but positively affects the horizontal impact force and rotating motion of the wedge.

Numerical simulation of ballistic impact on multilayer ceramic backed fibre reinforced composite target plate

Fibre reinforced polymer composites have been established as potential materials for making body armours. The present work depicts estimation of ballistic resistance of multilayer ceramic backed fibre reinforced composite target through 3D numerical simulation using Ansys/Autodyn software. The present numerical and material models have been validated against the results available in the literature. After that, the velocity–time history of the projectile is examined for impact velocities ranging between 330 to 1200 m/s. Here, the study has been focused on predicting the progressive damage and failure modes of the ceramic-composites target plate under impact. Also, the variation in residual velocities, time of penetration/perforation with different incident velocities, damage pattern in the deformable projectile and the kinetic energy of the impactor is studied. Finally, the trend of variation of ballistic limit velocity with different masses and diameter of the impactor has also been investigated.

Comparison of inelastic moment resistances of rolled steel beams based on different specifications and a numerical study

The inelastic buckling resistances of wide flange beams are strongly influenced by residual stresses and initial imperfections. However, the resistances as evaluated from simple solutions presented in several popular design specifications are found to be considerably different. The present study thus develop a numerical solution in ABAQUS software to investigate the inelastic buckling moment resistances of rolled steel beams with compact sections and subjected to the effects of residual stresses and initial imperfections. The residual stresses are taken as provided in AISC, CSA S16, EC 3 specifications, while the initial imperfections are taken as the first lateral-torsional buckling mode with a magnitude limited in AISC, CSA specifications. Through comparisons between the specifications and the numerical solutions, one observes a significant difference between the moment resistances predicted by the specifications, in which the AISC predicts the highest values, while the EC 3 predicts the lowest moments. The moment resistances based on the present numerical models lie between the EC 3 and CSA solutions and they are relatively close to EC 3 solutions. Effects of load height positions on the inelastic buckling moment resistances are significant, as investigated in the present study

POD analysis of the wake behind a circular cylinder with splitter plate

Flow past a circular cylinder is a widely studied phenomenon which finds application in a wide array of real life scenarios, like flow past cables, poles, building protrusions, automobile parts etc. The present study aims at analysing the vortex shedding phenomenon occurring in the wake of a circular cylinder and observing the effect of a splitter plate, attached to the rear stagnation point, on this flow. Finite volume method has been utilized via commercial CFD software, ANSYS Fluent, to solve transient, laminar, incompressible, isothermal flow. The study has been carried out in the low Reynolds number regime with Re = 100, 125 and 150, where the flow remains two-dimensional. The effect of splitter plate on the flow properties, such as coefficient of lift and drag, have been studied. Validation shows that the present numerical model is in good agreement with available literature. Proper Orthogonal Decomposition (POD) technique has been employed on vorticity field in order to study the dominant modes and their corresponding enstrophies along with the time coefficients. It is found that the first six modes contribute more than 95% of the total enstrophy in all the cases studied.

Non-linear periodic long waves based on Boussinesq equation for shallow water waves: A coupled FEM modeling

A coupled mathematical model is developed based on the non-linear Boussinesq equation (BE) for shallow water waves to investigate the influence of the periodic non – linear long waves inside the irregular domain. A coupled numerical model based on the solution of the BE in a bounded region with the incorporation of the effects of viscous dissipation, dispersion, convective non-linearities, and variable bathymetry is obtained by using Galerkin Finite Element Method (GFEM), and an analytical approach based on Fourier-Bessel series solution for the scattered waves in unbounded region. The current coupled numerical model is validated by comparing the simulation results with existing studies. Moreover, the accuracy of the current scheme is also examined using convergence analysis for the rectangular domain. The present numerical model is applied on T and TT–shaped harbors to investigate the role of geometry to induce the amplification. In addition, the current approach implemented on the realistic Paradip port, Odisha, India, and Pohang New Harbor (PNH), South Korea at six record stations for practical implication. Therefore, the present numerical model can be utilized to construct/redesign an artificial port in the coastal region including variable bathymetry considering the effect of partial reflection, dissipation, and convective non – linearities.

Finite element modeling of extreme wave analysis with dissipation in arbitrary shaped domain

A finite element numerical model is presented considering the effect of refraction, diffraction, and energy dissipation by breakwater. As wave move from deep to shallow water coastal regions, wave parameter changes as a result of depth variations, presence of irregular shore boundaries, and wave reflections from the coastline. Therefore, to understand the wave transformation phenomenon near the coastal region, mild slope equation is solved using the finite element method. The numerical model is validated against the experimental and numerical results available for the rectangular domain and is applied to a real coastal Paradip port, situated in Odissa (India). The wave height is computed at the selected key stations in the port. From the simulated results, it is observed that the present numerical model with dissipation parameter is an efficient and useful tool for the analysis of water surface wave problem in realistic domains.

Turbulent structures and characteristics of flows past a vertical surface-piercing finite circular cylinder

The flows past a vertical surface-piercing finite circular cylinder at Re = 2.7 × 105 and Fr = 1.1 are investigated numerically by means of delayed detached-eddy simulation and a geometric volume-of-fluid method based on piecewise-linear interface calculation. Good agreement with experimental data is achieved in various aspects, thereby demonstrating the reliability and accuracy of the present numerical model. On this basis, the characteristics of typical turbulent structures are analyzed thoroughly, as is the spanwise variation of the flow field caused by complex interactions. Because of the effects of the free surface and the free end, the velocity profile, separation angle, vorticity, and turbulent kinematic energy at different spanwise positions exhibit strong three-dimensionality, including the outward-spreading trend at the interface and the fluctuation induced by the upwash flow near the free end. By using the modified Omega–Liutex method Ω̃R, instantaneous and time-averaged primary turbulent structures are identified well with the iso-surfaces of proper thresholds. A complete necklace vortex and a pair of wave-induced vortices are observed below the free surface, while a pair of large-scale arch vortices and two pairs of tip vortices are generated near the free end. The Liutex lines and streamlines are then used to analyze the spatial formations and developments of these structures. Furthermore, by performing spectral analysis at different probes on the cylinder surface and in the wake region, the dominant frequencies for each primary turbulent structure are determined.

Thermo elasto-plastic contact analyzis for high temperature applications

This study presents the development of a thermo-mechanical simulation model for an elastic-plastic contact problem between a half cylinder and a plane plate. The set of equations was solved using direct coupling method by ANSYS mechanical. The results obtained from the present numerical model of the structural contact without heat transfer are compared with those of analytical, experimental and other numerical models. Then, the contact problem was solved using a coupled thermo-mechanical model. Computational results showed significant effects of thermal consideration in the elastic-plastic contact problem. Large deformations of structure due to high temperature are predicted using the thermo-mechanical model with elastic-plastic deformations. This model is useful to predict deformations on the structural components due to contact at high temperature situation.

Parametric study of bow slamming for a KRISO container ship

A systematic parametric study is performed in the present work to investigate the influence of various physical and geometrical parameters, such as wave steepness, wavelength, vessel speed, relative velocity on bow slamming load. For this purpose, a CFD-based one way coupled method is used. The ship's heave and pitch motions are determined using a standard potential theory-based method. Subsequently, the estimated values are used as input to a finite volume-based commercial CFD solver for computing slamming pressure. A scaled KRISO container ship (KCS) model is chosen for the analysis. Initially, the present numerical model is compared with state-of-the-art numerical and theoretical results to establish the correctness of the proposed model. A series of cases is then taken to check the dependency of bow slamming pressure on various physical and geometric parameters. In the final part of the paper, an empirical formula is developed based on this parametric study and with the help of the curve fitting method. It is observed that the developed analytical formulation corroborates well with CFD results and classification society rules and can be used for the quick prediction of bow slamming pressure for estimating design slamming load.

Investigation of local scour around two vertical piles by using numerical method

Local scour around two vertical piles is investigated numerically. A three-dimensional finite element solver is used to conduct the numerical study. The flow model is based on the three-dimensional Reynolds Averaged Navier-Stokes (RANS) equation by using the SST k-ω turbulence model closure. As for the scour model, both suspended load transport and bed load transport are considered. The numerical model is validated against (1) flow over smooth bed (2) local scour around one vertical pile by comparing with published data. In order to add weight of evidence on the effectiveness of present numerical model, two experimental tests are carried out. Present numerical model works well to predict the velocity and local scour around piles by comparing with published data and present experiment. Then the numerical model is used to study local scour around two vertical piles in tandem, side by side and staggered arrangements. The dependence of scour depth at the upstream side of the piles on gap ratio is discussed. Moreover, the time scale of scour under various gap ratios is investigated.

Numerical Simulation of Local Scour around Three Cylindrical Piles in a Tandem Arrangement

Scouring is one of the most common potential causes of bridge pile foundation failure with loss of life, economic and environmental impacts. Comprehensive studies on the numerical simulation of local scour around pile groups are still limited. This paper presents a numerical simulation using Flow-3D software to calculate the maximum sediment scour depth and investigate the mechanism around the groups of three cylinders in a tandem arrangement. A validation using the experimental study was carried out to confirm the reliability of the present numerical model. By using the Van Rijn transport rate equation and RNG k-ε turbulence model, the results of time evolution of scour depth and bed elevation contour show good agreement with the experimental study. The numerical simulation of three cylinders in a tandem arrangement were conducted with pile spacing ratios, G/D of 2 and 3. The local scour is affected by the horseshoe vortex from the downflow driven by the downward pressure gradient and rotates in front of the pile and the high bed shear stress, triggered by flow acceleration. The deepest maximum local scour depth is always obtained by the front pile as a shield pile, followed by the piles behind. The trend of the maximum local scour depth in a tandem arrangement is in accordance with the experimental studies and has a better agreement than previous numerical studies with the same model setup. This means that the numerical model used to simulate pile groups is accurate and capable of calculating the depth of sediment scour.

Alternating current losses in superconducting circular/stacked coils used in energy storage systems

Large transient currents and magnetic intensities are generally encountered by the superconducting magnetic energy storage systems thereby resulting in AC losses that occur during the charging/discharging durations thus, estimation of such heat loads must be known before the actual designing of cooling arrangements. Various analytical methods are accessible to approximate such losses however, not adequate to predict the same accurately. In this work, an extensive numerical model has been established to estimate AC losses among the stacked/circular coils used in superconducting magnetic energy storage applications under various transport currents (150 A to 225 A) and strong fields (1e5 A/m to 4e5 A/m). A homogenization method has been incorporated into the model stacks of high-temperature superconducting tapes (Ic=330 A @ 0 T self-field) instead of an actual multi-turned coil. The modeling has been done to achieve an anisotropic bulk equivalent for the stack keeping the overall electromagnetic identity of the model the same as that of the original multi-turned stacked geometry such that it eliminates the multiple boundaries among the geometrical layout consisting of metallic, insulating, superconducting, and substrate layers. In the present numerical model, E-J power law has been used which has considered the overcritical current densities. The results showed that transport currents affect AC losses significantly and as it approaches critical current, the AC losses increased abruptly. The novelty of the work is in the consideration of external fields which are present beforehand the actual current transportation through the coils using the homogenization approach. It has been concluded that perpendicular fields have a significant effect on AC losses compared to parallel fields. Considering the fact of high computational speed, this model can further be extended to solve more complex transient characteristics of HTS motors or generators. It has been concluded that the homogenized model can estimate average AC loss two orders faster than the original stacked model.

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.

Conjugate modeling of flow and simultaneous heat and mass transfer in convective drying of porous substances

An in-depth understanding of the convective drying mechanism is significant for improving industrial production efficiency and reducing available energy consumption. In this research, a conjugate numerical model appropriate for representing the convective drying is developed and incorporated into the computational fluid dynamics framework, which adopts a non-equilibrium approach to depict the thermal transfer between the hot air and wet porous substances. The thermophysical properties of wet porous substances are formulated to change dynamically in response to the variation of moisture content. A concept of two-resistance dynamic equilibrium is introduced to characterize the interstitial mass exchange between phases, in which the void surfaces of wet porous substances are treated as phase interfaces. That numerical model is then validated by simulating the convective drying of apple slices for different airflow conditions. Calculation results show that the numerical model is capable of accurately predicting the time history of moisture content. The simulative results are in excellent agreement with experimental data as well. The flow distribution of field variables, the non-equilibrium thermal transfer, and the interstitial mass exchanges are also effectively captured. It indicates that the present conjugate numerical model can predict the pivotal physical phenomena involved in convective drying.

Numerical Bichromatic Wave Generation Using Designed Mass Source Function

A mass source wave-maker method is generalized as the two-wave-source wave-maker method to generate bichromatic waves in the numerical model, whose governing equations are Navier–Stokes equations with the continuity equation. The Fluent software is taken as the calculation platform. In the numerical model, the waves at both the left and right ends of the numerical wave flume are absorbed with the momentum sources added in Navier–Stokes equations. The numerical simulation of bichromatic waves propagation with different frequencies in uniform deep, intermediate, and shallow water has been conducted. The numerical solutions are compared with the theoretical solutions obtained on the basis of Stokes waves theory. The frequency spectrum analyses of the results are conducted and discussed, and the differences between the weakly nonlinear theoretical solutions and the fully nonlinear numerical results are investigated in detail. It is found that the numerical model can effectively simulate the nonlinear effect of bichromatic waves in water with different depths, and the theoretical solutions only adapt the deep and intermediate water. The results indicate that the present numerical model is valuable in the aspect of practical application.

Numerical research on the performance of solid fuel rocket scramjet combustor

Combustion efficiency is the main factor affecting the performance of solid fuel rocket scramjet. To reveal the influence of combustor configuration on performance and further improve combustion efficiency, the influence of the width-height ratio of the rectangle-section combustor on the performance of solid fuel rocket scramjet is investigated numerically in this article. Three-dimensional compressible Reynolds-averaged Navier-Stokes equations coupled with shear stress transport k– ω turbulence model are employed to simulate the aerodynamics. The Euler–Lagrange approach is used to calculate the multiphase flow. Combustion of carbon particles is modeled by the improved Moving Flame Front model. Accuracy of the present numerical model is validated by the experimental data of a rectangle-section combustor from literature. Results show that as the width-height ratio increases, the combustion efficiency increases first and then decreases. The influence of cavity and its position on the performance are also investigated. Results show that cavity can significantly improve combustion efficiency. The effect of cavity position on performance is related to the distribution of particles.

A fixed grid based accurate phase-field method for dendritic solidification in complex geometries

In this paper, an easily implementable immersed interface method based high-resolution phase-field model is proposed for simulating dendritic growth related problems in complicated geometries. At first, resolution issues of different Fourier Pseudo-spectral based dealiasing schemes are shown for the anisotropic phase field equations at high thermal undercooling conditions using just adequate spatial grid resolution. The problems of aliasing error and spectral leakage are studied using high-order based exponential smoothing spectral filters, which generally occur at low sampling rate situations. A fully dealiased zero padding scheme based anisotropic phase-field method is also developed in conjunction with an optimal third order strong stability preserving Runge–Kutta (SSPRK3) time integration scheme for obtaining more accurate and stable numerical solutions. In the later part, a modified phase-field method is implemented with the indicator function which simulates different crystal growth problems in complex geometries without using non-trivial mesh refinement algorithm. Effect of non-interacting obstacles present in the computational domain can also be readily incorporated in the present numerical model by using the single order parameter based phase-field equations.

Moored ship motion under the resonance conditions with breakwaters: A coupled numerical approach

A hybrid element model has been formulated to understand the wave interaction with moored ship motion using mild slope equation (MSE) including the influence of breakwaters and wave absorbers, under resonance conditions for variable bathymetry. In a hybrid element formulation, a combined approach with the finite element method (FEM) in an interior domain (port region) including moored ship region and an analytical approximation in the unbounded region (open sea) is utilized to determine the wave response of moored ship motion. Especially, in this approach, a FEM and analytical approximation are firstly utilized to solve MSE with the consideration of permeable breakwaters for moored ship motion under the resonance conditions. The non-uniform discretization pattern enhanced the numerical accuracy of the coupled numerical approach and is verified by using convergence analysis. Further, the simulation results are compared with existing studies to validate the applicability of the present numerical model. Wave absorbers and permeable breakwaters are employed to determine the incident wave response over moored ship motion inside the realistic Paradip port, Odisha, India. In addition, the efficacy of permeable breakwaters and wave absorbers on moored ship motion is investigated. It is shown that breakwaters and wave absorbers at appropriate locations play a significant role to induce/reduce the resonance inside the port. Therefore, the current numerical model provides the countermeasures tactics such as installing breakwaters, wave absorbers to mitigate the resonance in arbitrarily shaped ports for safe moorings.