Influence Of Three-dimensional Effects Research Articles

Unsteady flow of gas at high pressure into a closed volume filled with liquid

Within the framework of 2D (two-dimensional, axisymmetric) and 3D (three-dimensional) formulations of the problem, this article presents a numerical simulation of the process of gas outflow under pressure into a closed container partially filled with liquid. The authors have performed the numerical modeling using the open platform OpenFOAM with the help of a solver based on the method of liquid volumes (VOF method) with a standard k-e turbulence model. A comparison is made with the one-dimensional (1D) asymptotic model, in which the oscillations of the fluid as a whole are determined by the enthalpy balance. A numerical study of the evolution of pressure during gas outflow is carried out. The results show that the physical properties of the fluid used affect the amplitude and frequency of the pulsations. The modeling has shown that gas flows into water in the form of a jet, and a projectile forms in liquid lead near the hole through which it flows out. The significant influence of three-dimensional effects on the evolution of gas outflow into liquid is demonstrated. Satisfactory agreement was obtained for both two-dimensional and three-dimensional calculations and the results obtained using the asymptotic model. For the “gas — water” system, the results of calculations by the asymptotic model give a significant difference from the results of numerical calculations.

The influence of three-dimensional effects on the performance of U-type oscillating water column wave energy harvesters

This paper studies the dynamics and power extraction of a U-Oscillating Water Column (U-OWC) device. A three-dimensional hydrodynamic model, based on the boundary integral equations method, is implemented. The U-OWC width and wave direction are analysed and compared with a two-dimensional model based on the eigen-function expansion method. Results show that as the device width increases, the power extraction per unit width tends to the two-dimensional value. For small converter widths, which are expected to be implemented in practical applications, three-dimensional effects are relevant and provide a systematic improvement in power output per unit width, due to their influence in the device hydrodynamic characteristics.

Modelling of three-dimensional crack patterns in deep reinforced concrete structures

The analysis of the crack width variation within the depth of a reinforced concrete structure is difficult to perform. No experimental measurement can give a non-intrusive, three-dimensional and quantitative description of cracking. Moreover, most of the design codes cannot give a predictive measurement of the full cracking pattern. This paper applies a global/local computational strategy in order to quantify the cracking behaviour of reinforced concrete structures. A continuous damage model is used to perform a full resolution at the global scale. Then a reanalysis of the damaged zones is performed at the local scale with a discrete element model. This strategy has proved its efficiency for the study of cracking of small laboratory specimens made in concrete. The extension to massive reinforced structures is achieved here and numerical results on the influence of three-dimensional effects and rebars on cracking are given.

Seepage flows instability in porous media

The goal of the present study is to investigate analytically, numerically and experimentally the instability of the displacement of viscous fluid by a less viscous one in two- and three-dimensional channels, and to determine characteristic size of entrapment zones. Experiments on miscible displacement of fluids in Hele–Shaw cells were conducted under microgravity conditions. Extensive direct numerical simulations allowed investigating the sensitivity of the displacement process to variation of values of the main governing parameters. The influence of three-dimensional effects (aspect ratio) on displacement instability was studied. One-dimensional model to simulate mixing flux due to frontal displacement instability was developed for engineering applications.

Three-dimensional theory of water impact. Part 1. Inverse Wagner problem

The three-dimensional problem of blunt-body impact onto the free surface of an ideal incompressible liquid is considered within the Wagner theory. The theory is formally valid during an initial stage of the impact. The problem has been extensively studied in both two-dimensional and axisymmetric cases. However, there are no exact truly three-dimensional solutions of the problem even within the Wagner theory. At present, three-dimensional effects in impact problems are mainly handled approximately by using a sequence of two-dimensional solutions and/or aspect-ratio correction factor. In this paper we present exact analytical rather than approximate solutions to the three-dimensional Wagner problem. The solutions are obtained by the inverse method. In this method the body velocity and the projection on the horizontal plane of the contact line between the liquid free surface and the surface of the entering body are assumed to be given at any time instant. The shape of the impacting body is determined from the Wagner condition. It is proved that an elliptic paraboloid entering calm water at a constant velocity has an elliptic contact line with the free surface. Most of the results are presented for elliptic contact lines, for which analytical solutions of the inverse Wagner problem are available. The results obtained can be helpful in testing other numerical approaches and studying the influence of three-dimensional effects on the liquid flow and the hydrodynamic loads.

Ground heat transfer: Some further insights into the influence of three-dimensional effects

The results of a numerical investigation of three-dimensional ground heat transfer are presented. In particular, the influence of varying floor slab geometry has been considered within an assessment of the importance of maintaining full three-dimensionality in the analysis of heat losses to the ground. A comparison is made between three-dimensional (3D) and two-dimensional (2D) representation of a particular series of test problems. The results obtained, for the specific problems analysed, suggest that two-dimensional simplification can lead to heat flux calculations that differ by at least 45% from the three-dimensional analysis of the problem. An analysis of the results is presented that can be used to aid the choice of analysis to be performed, estimate 3D behaviour from 2D analyses; and estimate the relative errors associated with 2D and 3D heat and flux calculations. The results achieved also help substantiate earlier findings that suggest that equations used to estimate heat flux should include reference to the area/perimeter ratio and not simply to the perimeter. One practical equation of this kind is suggested. Further work is required before more general conclusions can be made.

Heat Transfer Committee Best 1994 Paper Award: Experimental and Theoretical Investigations of Heat Transfer in Closed Gas-Filled Rotating Annuli II

Increasing the thermal efficiency by higher turbine inlet temperatures is one of the most important aims in the area of gas turbine development. Because of the high temperatures, the turbine vanes and blades have to be cooled, and also knowledge of the mechanically and thermally stressed parts in the hottest zones of the rotor is of great interest. The prediction of the temperature distribution in a gas turbine rotor containing closed, gas-filled cavities, for example, in between two disks, has to account for the heat transfer conditions encountered in these cavities. In an entirely closed annulus, forced convection is not present, but a strong natural convection flow exists, induced by a nonuniform density distribution in the centrifugal force field. In Bohn et al. (1994), experimental and numerical investigations on rotating cavities with pure centripetal heat flux had been carried out. The present paper deals with investigations on a pure axially directed heat flux. An experimental setup was designed to realize a wide range of Ra numbers (2·108< Ra < 5·1010) usually encountered in cavities of gas turbine rotors. Parallel to the experiments, numerical calculations have been conducted. The numerical results are compared with the experimental data. The numerical scheme is also used to account for the influence of Re on heat transfer without changing Ra. This influence could not be pointed out by experiments, because a variation of the Re–Ra characteristic of the employed annuli was not possible. It was found that the numerical and experimental data are in quite good agreement, with exception of high Ra, where the numerical scheme predicts higher heat transfer than the experiments show. One reason may be that in the experiments the inner and outer cylindrical walls were not really adiabatic, an assumption used in the numerical procedure. Moreover, the assumption of a two-dimensional flow pattern may become invalid for high Ra. The influence of three-dimensional effects was studied with the three-dimensional version of the numerical code. In contrast to the radial directed heat transfer, it was found that Nu is much smaller and depends strongly on Re, whereas the radial heat transfer is only weakly influenced by Re.

Magnetism in lowdimensional systems

Magnetism in lowdimensional systems is characterized by the importance of space and time dependent correlations with respect to static long range order which does not exist for finite temperatures in such systems except for the 2D-Ising model. Typical properties of these strongly fluctuating systems will be discussed and compared to the behaviour of normal magnets. Strongly nonlinear effects can be observed, like solitons and new quantum groundstates as in the 1D-Heisenberg antiferromagnet for S=1. As real crystals with quasi-lowdimensional magnetic behaviour can be obtained, experiments in this field have significantly advanced our understanding of collective processes in systems with strong correlations varying in space and time. All such crystals are threedimensional, thus the influence of threedimensional effects must be considered for a correct interpretation of experimental results. Due to the simple topology of the interactions in one dimension systematic studies of the energies involved, e.g. exchange and anisotrophy, are possible.

Estimate of the influence of three-dimensional effects on the development of unsteady natural concentration convection in a closed region

The problem of calculating unsteady natural concentration convection of a binary mixture of gases with arbitrary finite ratio of their densities in a closed rectangular thermally insulated region has been considered in the framework of the two-dimensional formulation by Nikulin and Strelets [1]. The present paper, which continues their work, is devoted to an analysis of the influence of the three-dimensional effects associated with the finite size of the region on the characteristics of the flow.

On the influence of three-dimensional effects and restricted water depth on ship hull vibration1

In this note a finite element method for the calculation of the three-dimensional added mass of a vibrating ship hull is presented. The hull is approximated by a cylinder of the same overall dimensions as the ship and the mode of vibration is approxi

Three-Dimensional Stripwise Damping Coefficients for Heave and Pitch of a Submerged Slender Spheroid

The distribution of the local damping force and moment along a submerged spheroid, oscillating in heave and pitch at zero forward speed, is found in this note. Two different methods of calculation (local energy radiation and the extended Lagally theorem) were used and they were shown to yield equivalent results. The influence of three-dimensional effects is shown to be important at all sections, including the mid-section, and this is not exhibited by ratios of total three-dimensional to two-dimensional damping. The importance of these findings for bending-moment calculations in waves is stressed.