Bottom Rim Research Articles

A study on the dynamic characteristics of the Korean Yi-dynasty bell type structure

The dynamic characteristics of the Korean Yi-dynasty bell type structure, including the acoustic effects, are analyzed both theoretically and experimentally. The numerical solutions of natural frequencies and mode shape for membrane and flexural behavior are obtained by using the NASTRAN program for the finite element method with plate shell elements of triangular and quadrilateral types. Test bells, A and B types similar to the Kap-Sa bell in Kong-Ju chosen among typical Korean Yi-dynasty bells, are manufactured on different scales to the original bell. To consider the effects of the variation of the structural dimension on the dynamic response, these bells are analyzed with respect to the variation of the thickness of the wall and the bottom rim and the asymmetric Dang-Jwas. The impact method with the Fast Fourier Transform Analyzer is adopted to experimentally assess the dynamic response. Results are in good agreement with the numerical solutions.

Tube-in-Basket burner for rice husk. II: Performance of TiB burners

Three working models, TiB MK II, MK IIK and III, capable of continuous combustion, are described. It is shown that these burners can be operated continuously in a stable pseudo-steady-state manner by means of intermittent charging of husk from the top and discharging of ash from the bottom. Mass and heat balance data, flame temperatures, combustion efficiencies and heat transfer efficiencies for heating water in a vessel are included. Combustion efficiency of about 72% was achieved in TiB MK II by making a significant change in the basket design, the lower half being made conical. The efficiency was boosted further to roughly 82% in MK IIK by extending the bottom rim of the cone straight down by an additional 7·5 cm and replacing the upper basket cylinder by a fully enclosed box. A water heating jacket was also incorporated in this model around the upper end of its burner tube. This modification resulted in a highly efficient water heating or steam raising device. Comparison with step-grate furnaces shows that TiB burners have similar or superior performance characteristics with additional advantages of simplicity, compactness and low cost.

Presa de Djatiluhur, Indonesia

This dam is located in Java, close to Djakarta, on the Tjitarum river. The dam consists of a stone dyke and an internal watertight screen, of suitably chosen and compacted soil. The width of the dyke at the base is 600 m, and the dam rises 100 m above its foundations. The reservoir that will be formed will hold 3,000 X 10 6 m 3 of water, at 107 m height. A special feature of this project is that the power station and spillway are related to a concrete cylindrical body, of 90 m diameter and 110 m height. At the top of this is the surface spillway, and on the outside are the water intakes for each of the 6 generator groups located along the inner bottom rim of the concrete cylinder.

The Moving Flame Experiment

When a flame is rotated around the outside bottom rim of a cylindrical pan of water initially at rest, D. Fultz has observed that the fluid acquires a net vertical component of angular momentum opposite to the rotation of the heat source. We have repeated this experiment in a cylindrical annulus in order to restrict the radial motions and have found that the same phenomenon occurs. Using a simple model based on the latter experiment we investigate the mechanism by which a fluid can acquire and maintain this momentum, considering that friction is the only force which can exert a net torque about the vertical.
 The effects of the heat source are replaced by a forced temperature field which has sinusoidal variations in the circumferential direction and which rotates about the vertical axis at a constant rate. The correlation between vertical and horizontal velocity components in the equilibrium state has been computed from the linearized two-dimensional vorticity equation. It is shown that when the viscosity is small or when the speed of the heat source is large there is a convergence of horizontal momentum towards the center of the channel which is balanced by the viscous stress of the induced mean motion. The total momentum of the fluid is computed from the conservation principle and is found to vary inversely as the square root of the molecular viscosity and inversely as the 5/2 power of the speed of the heat source.

A modification of the Baermann funnel technique for the collection of nematodes from plant material.

The Baermann funnel technique is now well known to nematologists, but the modification here described was devised to facilitate the collection of large numbers of nematodes in a small volume of water with the minimum of plant debris present. The method has proved very satisfactory in obtaining nematodes for toxicity tests, for example, from “tulip-rooted” oats infested with stem eelworm. It is often a lengthy procedure to remove nematodes from a relatively large bulk of water such as is contained in a full watch-glass, particularly if much fine plant debris is also present. By means of the modification described an almost “pure culture” of nematodes is obtained, the amount of water being very little greater in volume than the nematodes.The apparatus is shown diagrammatically in Fig. 1:—The funnel, f, has resting in it a small metal sieve, s, which may easily be made by cutting off a section about ¾-in. deep from a piece of copper pipe of from 2½–8-in. diameter. Fine copper wire mesh, wm, is then soldered on to the bottom rim. This wire mesh need not be fine enough to retain all fragments of plant material, since a circle of fine bolting silk, bs, is laid within the sieve on top of the wire mesh, so that it fits exactly within the inside of the sieve. No bolting silk has yet been found which will retain living nematodes. The bolting silk, however, retains all plant material and is easily removed and cleaned.