Results Of Numerical Prediction Research Articles

432 動的き裂分岐現象の移動有限要素法による破壊経路予測シミュレーション

In actual fracture phenomena, branched cracks were often observed. The numerical simulation technique of dynamic crack bifurcation has not been established enough due to some numerical difficulties. The development of this simulation technique is very important to clarify the crack bifurcation mechanism. The authors have previously developed the moving finite element method with Delaunay triangulation for crack bifurcation analyses. In this study, the numerical path prediction is tried by using the moving FEM. For bifurcated cracks, crack propagation paths are predicted according to the maximum hoop stress. The results of numerical prediction agree with the experimental results and the results of generation phase simulation. In these simulations, the fracture mechanics parameters were accurately calculated by special form of the dynamic J integral.

Electromagnetic Control of Initial Solidification in Continuous Casting of Steel by Low Frequency Alternating Magnetic Field.

A marked improvement of the surface quality of casts and a break-through in casting speed in conventional continuous casting of steel require the introduction of new technology for initial solidification control. The authors have approached these problems by the use of electromagnetic shaping of the meniscus and demonstrated the possibility using simulation experiments. This paper describes the results of numerical prediction of the effect of electromagnetic field on the initial solidification of steel and the experimental results obtained by continuous casting of round austenite stainless steel billets of 180 mm diameter with solenoidal magnetic field with main frequency, 60 Hz. The numerical results concerned with magneto-hydrodynamics and heat transfer phenomena predicted improvement of the surface roughness of the cast billet and improvement of mold lubrication by decreasing the dynamic pressure due to the meniscus shaping effect. In the experimental casting, the surface of billets were smoothed and the mold friction force was reduced by imposing the magnetic field, which are in consistent with the numerical predictions.

The use of a one-dimensional depth-averaged moment of momentum equation for the nonhydrostatic pressure condition

A depth-averaged model formulated in the Cartesian coordinate system for curved open-channel flows is extended to solve problems where the effects of nonhydrostatic pressure distribution and nonuniform velocity distribution are significant. The nonhydrostatic pressure condition is added to the z-direction momentum equation assuming that the pressure deviation from the hydrostatic condition at the channel bed decreases linearly to the water surface. The pressure-effect terms are modified in both the moment of momentum and momentum equations. The resulting system of nonlinear equations is solved by a finite-element method. The derived model is then applied to four sophisticated nonuniform flow experiments from the literature. A comparison of the actual experimental results with their numerical prediction results, as calculated with the model, is presented. Generally speaking, a fairly good agreement for the depth-averaged velocities as well as reasonable perturbation profiles were obtained from this comparison. Therefore, it can be said that the depth-averaged model for open-channel flow is reasonably accurate under the given conditions. Key words: open-channel flow, depth-averaged method, finite-element method, nonhydrostatic pressure, nonuniform flow.

Prediction of Six-Stroke Diesel Engine Performance. 1st Report. Numerical Analysis by a Phenomenological Model.

The performance of a six-stroke diesel engine which has been proposed by the authers was numerically predicted using a phenomenological model developed in the previous study. Concentrations of nitric oxide and soot are calculated from the simple phenomenological relations of the spray formation, air entrainment, fuel vaporization, ignition and chemical reactions. Results of numerical prediction showed that the re-oxidation of soot occurred in the second compression stroke. It was confirmed that under various conditions, the ignition delay of the second combustion became shorter than that of first combustion. In the second combustion, the maximum heat release rate became lower compared with the first combustion because of the premixed combustion was restrained by a short ignition delay. From a comparative study of four- and six-stroke diesel engine performance, it was found that the six-stroke diesel engine has a potential to realize lower nitric oxide emission than the four-stroke diesel engine.

NUMERICAL PREDICTION OF A RECTANGULAR TURBULENT JET IN A CROSS FLOW

The trajectories and decay of the maximum velocity for turbulent jets in a cross flow were simulated by means of the κ — ϵ two-equation turbulence model in which differential equations were solved for the kinetic energy of turbulence and for the rate of its dissipation. The solution procedure employed an elliptic finite-difference scheme with the three velocity components and the pressure as the main dependent variables. The essential properties of the jet were discussed in the case of different ratios of the rectangular orifice length to the width H/B, ratios of the jet injected velocity to the main stream velocity R; and different injection angles α. The numerical prediction results were presented in the form of equivalent diameter. Lastly, two correlation equations were obtained and the numerical predictions are shown to agree well with the experimental data.

Prediction of the Trajectory of Triple Jets in a Uniform Crossflow

This paper describes the results of numerical prediction of the trajectories of turbulent triple jets issuing into a uniform crossflow. The prediction technique is based on the momentum integral equation and the law of conservation of momentum, together with the interference of the triple jets under the assumption of an axially symmetrical flow pattern for each of the jets. Results are presented for both triple buoyant and nonbuoyant jets, with the velocity ratio of jet flow to crossflow ranging from 3.0 to 10.6. The numerical predictions agree well with authors’ and other experimental data.

Numerical weather prediction for GATE

AbstractThe results of a few numerical weather prediction experiments that utilize GATE data are presented. Aside from some simple forecasts based on single‐level models, experiments with a multilevel model examine the roles of some of the physical processes. They include the influences of diurnally varying radiative effects, effects of cloud feedback on shortwave and longwave radiation, the heat balance of land surfaces, and the influence of West African orography in the 3‐ to 4‐day range of numerical weather prediction. Data sources for these experiments include surface and upper air observations from the World Weather Watch, GATE ships, upper winds from commercial aircraft, low‐ and high‐level cloud winds from geostationary satellites, winds from GATE research aircraft, and special surface observations from a ship data collection. The data analysis is based on a successive correction method where a subjective interface is also incorporated. The initial data are further subjected to a static as well as a dynamic initialization process.The major results are that single‐level forecasts are very promising with this data set if they are carried out at 700 mb. The multilevel adiabatic experiment produces very poor predictions due to lack of adequate vertical coupling between the lower and the upper troposphere and due to its inability to describe the broad‐scale monsoons. The diurnally varying heat balance of the earth's surface and cloudiness in radiative calculations appear to be important in the 3‐ to 4‐day range of prediction of African disturbances. In this paper we show some interesting vertical structure diagrams of African waves based on the results of numerical weather prediction, which exhibit a close similarity to the structures of composite GATE disturbances constructed by Professor R. J. Reed and his associates.

Numerical weather prediction for GATE

The results of a few numerical weather prediction experiments that utilize GATE data are presented. Aside from some simple forecasts based on single-level models, experiments with a multilevel model examine the roles of some of the physical processes. They include the influences of diurnally varying radiative effects, effects of cloud feedback on shortwave and longwave radiation, the heat balance of land surfaces, and the influence of West African orography in the 3- to 4-day range of numerical weather prediction. Data sources for these experiments include surface and upper air observations from the World Weather Watch, GATE ships, upper winds from commercial aircraft, low- and high-level cloud winds from geostationary satellites, winds from GATE research aircraft, and special surface observations from a ship data collection. The data analysis is based on a successive correction method where a subjective interface is also incorporated. The initial data are further subjected to a static as well as a dynamic initialization process. The major results are that single-level forecasts are very promising with this data set if they are carried out at 700 mb. The multilevel adiabatic experiment produces very poor predictions due to lack of adequate vertical coupling between the lower and the upper troposphere and due to its inability to describe the broad-scale monsoons. The diurnally varying heat balance of the earth's surface and cloudiness in radiative calculations appear to be important in the 3- to 4-day range of prediction of African disturbances. In this paper we show some interesting vertical structure diagrams of African waves based on the results of numerical weather prediction, which exhibit a close similarity to the structures of composite GATE disturbances constructed by Professor R. J. Reed and his associates.