Seigo Sakai

Artificial Upwelling of Deep Seawater Using the Perpetual Salt Fountain for Cultivation of Ocean Desert

Deep seawater in the ocean contains a great deal of nutrients. Stommel et al. have proposed the notion of a “perpetual salt fountain” (Stommel et al., 1956). They noted the possibility of a permanent upwelling of deep seawater with no additional external energy source. If we can cause deep seawater to upwell extensively, we can achieve an ocean farm. We have succeeded in measuring the upwelling velocity by an experiment in the Mariana Trench area using a special measurement system. A 0.3 m diameter, 280 m long soft pipe made of PVC sheet was used in the experiment. The measured data, a verification experiment, and numerical simulation results, gave an estimate of upwelling velocity of 212 m/day.

Nongray radiative heat transfer analysis in the anisotropic scattering fog layer subjected to solar irradiation

Abstract Radiative heat transfer in the fog layer is analyzed. Direct and diffuse solar irradiation, and infrared sky flux are considered as incident radiation. Anisotropic scattering of radiation by water droplets is taken into account. Absorption and emission of radiation by water droplets and radiative gases are also considered. Furthermore, spectral dependences of radiative properties of irradiation, reflectivity, gas absorption and scattering and absorption of mist are considered. The radiation element method by ray emission model (REM2) is used for the nongray radiation analysis. Net downward radiative heat flux at the sea surface and radiative equilibrium temperature distribution in the fog layer are calculated for several conditions. Transmitted solar flux decreases as liquid water content (LWC) in the fog increases. However, the value does not become zero but has the value about 60 W / m 2 . The effect of humidity and mist on radiative cooling at night is investigated. Due to high temperature and humidity condition, the radiation cooling at night is not so large even in the clear sky. Furthermore, the radiative equilibrium temperature distribution in the fog layer in the daytime is higher as LWC increases, and the inversion layer of temperature occurs.

Radiative Heat Transfer Simulation Using Programmable Graphics Hardware

To analyze physical behaviors of a thermal environment, we have to simulate several heat transfer phenomena such as heat conduction, convection, and radiation. Among those phenomena, radiative heat transfer simulation is much time-consuming. In this paper, therefore, one of acceleration techniques developed in the graphics community that exploits a graphics processing unit (GPU) is applied to the basic radiative heat transfer simulation. Implementation of the simulation on GPU makes GPUs computing power available for the most time-consuming part of the simulation, calculation of form factors between surfaces. This paper improves the computational accuracy of the radiative heat transfer simulation running on GPU, and then examines its performance, in terms of the trade-off between the execution time and computational accuracy. The experimental results clearly show that GPU co-processing can significantly accelerate the form factor calculation. Therefore, the GPU implementation is a promising approach to acceleration of the radiative transfer simulation, especially in the case where the form factor matrix becomes too large to be stored in the main memory

Improvement of computational time in radiative heat transfer of three-dimensional participating media using the radiation element method

Abstract The radiation element method by ray emission model (REM2) has been improved by using the stabilized bi-conjugate gradient (BiCGSTAB) method and reduction of the size of equations in order to reduce computational time. This improved method was applied to analyze radiative heat transfer in arbitrary three-dimensional participating media and enclosures. The accuracy of the improved method was evaluated by comparing its predictions with the Monte Carlo and the YIX solutions. And the method was used to calculate radiative heat transfer in the boiler furnace. Total CPU time to calculate the radiative heat transfer for a model comprised of 3211 elements was reduced to 1/22 of that by the previous numerical method using a decomposition method.

Description of the adhesive crystal growth under normal and micro-gravity conditions employing experimental and numerical approaches

Investigation of the crystal growth in solutions is closely related to effective and high quality production of medicine, food and new materials. In the present study, experiments and numerical simulations were performed to explain the mechanism of crystal growth from an aqueous solution. In the experiment, transient double diffusion fields were observed by using an accurate optical measuring system. In the numerical simulation, transient double diffusion fields were calculated by a numerical simulation code, applying initial and boundary conditions obtained by experiment. The results of numerical simulation show good agreement with experimental results. Taking these two approaches into consideration, it was considered that adhesive crystal growth was dominated by the temperature dependence of the solutal diffusion coefficient. The microscopic mechanism of adhesive crystal growth is almost the same between micro-gravity and normal gravity conditions; nevertheless, the macroscopic growth rate is different in each situation. Simulation of adhesive crystal growth can be performed easily using appropriate boundary conditions obtained by the present experiments.

A fast approximated method of radiative exchange for combined heat transfer simulation

The radiation element method (REM) was improved by using view factor approximation instead of the ray-tracing method to estimate the view factors. This improved method was applied to analyze radiative exchange between arbitrary three-dimensional bodies comprised of diffuse surfaces. The view factor approximation required one-sixth of the CPU time of the ray-tracing method to estimate the view factors for a model comprising of 7,344 surface elements. The total CPU time by the incomplete Cholesky conjugate gradient (ICCG) method plus the view factor approximation was reduced to one-fifth of that of the ICCG plus ray-tracing method.

Radiative Heat Transfer Analysis within Three-Dimensional Clouds Subjected to Solar and Sky Irradiation

Abstract A three-dimensional radiative heat transfer analysis of an arbitrary-shaped modeled cloud subjected to solar and sky irradiation has been performed. The Radiation Element Method by Ray Emission Model (REM2) was used for numerical simulation. Nongray, anisotropic scattering, absorbing, and emitting are taken into account in calculating the three-dimensional cloud. The modeled cloud is considered to be a low-level fair-weather cumulus in a tropical atmosphere. The cloud is modeled by unstructured mesh elements in order to investigate the curvature of cloud shape. Radiative cooling occurs in the thin layer below the cloud surface, and the thickness is approximately 20–40 m. Radiative cooling is enhanced at the swelled top of the cloud with a convex shape, which can cause a downward forcing and enhance the entrainment instability. On the other hand, radiative cooling close to the root of the swelled top is relatively weak. The solar heating does not affect the temperature change in the cloud compared...

Numerical Study of Interaction Between Natural Convection Flow and Horizontal Wind

When a large-scale fire, such as a town area fire by an earthquake disaster and forest fire, happens, there can be a fire whirlwind, which is a strong flow including strong flame and sparks. It is sometimes called a firestorm. Fire whirlwind is exposed to high heat, and possesses high heat itself. Therefore, the fire whirlwind is very dangerous. The whirlwind moves and promotes spread of a fire and may enlarge the damage rapidly. Various studies are performed about fire whirlwind, but the property and outbreak mechanism of the whirlwind are not elucidated enough till now. Therefore, in this study, we pay our attention to the flow that is a basic phenomenon of fire whirlwind, and examine the influence that a natural convection gives to outbreak and behavior of fire whirlwind by numerical computation. The numerical analysis performed three-dimensional calculation with analysis software FLUENT6.1. Firstly, a model of the fire domain is constructed. The model is referred from an example of large-scale fire at the Great Kanto Earthquake (1923 in Japan), and natural convection is observed for different heat flux. Then, it is analyzed in a similar model whether a whirlwind occurs or not, after natural convection is fully-developed with changing velocity of the air flow from the side. Furthermore, it is analyzed in a model in which a fire occurs at random whether a whirlwind occurs or not after natural convection is fully-developed with changing velocity of the air flow from the side. As a result of analysis, a whirlwind occurs. The whirlwind sometimes moves and extinct. Then, the influence that a natural convection gives outbreak of the whirlwind is evaluated with changing heat flux and velocity of wind.© 2007 ASME

Numerical Prediction of Fire Whirlwind Outbreak and Scale Effect of Whirlwind Behavior

Our Japanese, especially the residents in east area of Japan, have experienced a large earthquake on March 11, 2011, i.e. East Japan great earthquake disaster (Takewaki et al., 2011). There were a lot of fires in the northeast area of Japan, for example in Kesen-numa City. Despite of a number of town area fires, a fire whirlwind was never observed in this disaster. However, fire whirlwind is still one of the concerned accidents in the earthquake (Hough & Bilham; 2005).

Numerical study of fire whirlwind taking into account radiative heat transfer

The fire whirlwind is a strong swirling flow with flame and spark, which may occur in the case of, widespread fire in the urban region by an earthquake disaster or an air raid, and a large-scale fire such as a forest fire. Fire whirlwind moves and promotes spread of fire and may extend serious damage rapidly. In this study, performing the numerical analysis of fire whirlwind with respect to scale effect, it is examined whether a relationship exists between a real phenomenon and the phenomenon in the reduction model with taking into account radiative heat transfer. Three dimensional analyses are performed to investigate the thermal and flow fields by using the analytical software FLUENT6.3. It is analyzed that those swirling flow in original scale, 1/10 scale, 1/50 scale, 1/100 scale from the original brake out to vanish. As an analytical condition, parameter calculation is repeated to get the velocity of a parallel flow which is the easiest to occur the swirling flow for each reduction model, and then scale effect is discussed by comparing the velocity of the natural convection, the velocity of the parallel flow, the center pressure of the whirlwind and the continuance time of the swirling flow. The analysis model of C-character heat source model is performed as well as the analysis in L-character model, which is one of the representative example of the fire whirlwind occurred at Tokyo in the Great Kanto Earthquake (1923). The result of the numerical analysis shows that there is a scale effect to the speed of the parallel flow to generate the swirling flow.