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Vol. 9, No. 3 (1953)

1953-02-05
Topics
CONTENT
THEORY OF ATTENUATION OF SOUND IN FOGGY AIR DUE TO EVAPORATION AND CONDESATION PROCESSES
WEI YUNG-CHIO
1953, 21 (3): 149-169. doi: 10.7498/aps.9.149
Abstract +
As sound waves traverse in clouds or foggy air the temperature change, which accompanies the pressure variation, would make the water molecules at the droplet's surface to evaporate or those in its close surroundings to condense according as there is condensation or rarefaction respectively. In general, the pressure waves always pro-pagate ahead of the density waives since a finite time is required for this process to take place. However at very high frequencies, the periodic pressure varies too fast for this process to follow, the situation is essentially "dry adiabatic". Only at very low frequencies is the term "relaxation time" of any significance, so the "dispersion" and "absorption".This problem has been handled, in the present paper, in some respect in an analogous way to that in the collision theory of molecular absorption of sound. The previous calculations due to Oswatitsch have been found to be erroneus, and special attention has been given to each of the following:(1) Relation between air density and particle concentration;(2) Relation between the change of the amount of liquid water and the amount of vapor;(3) Derivation of the equation of growth of droplet; and(4) Diffusion and heat conduction coefficients.
CONTINUOUS BEAMS WITH NON-UNIFORM STIFFNESS
CHIEN WEI-ZANG
1953, 21 (3): 170-182. doi: 10.7498/aps.9.170
Abstract +
In this paper, the method of continued fraction is used for the determination of the bending moments of a continuous beam with non-uniform stiffness.
ON THE MATRIX THEORY OF CONTINUOUS BEAMS ON ELASTIC FOUNDATION
HU HAI-CHANG
1953, 21 (3): 183-191. doi: 10.7498/aps.9.183
Abstract +
In this paper, we employ the theory of matrices and continued fractions for the solution of the bending problem of continuous beams on elastic foundation with unyielding supports. End moments are obtained in explicit expressions. Accurate numerical results may be calculated from these expressions directly without salving simultaneous equations.
ELECTRIC CIRCUIT ANALYSIS BY THE NETHOD OF DIFFERENCE EQUATION
YEH KAI-YUAN
1953, 21 (3): 192-200. doi: 10.7498/aps.9.192
Abstract +
The method of difference equation recently employed by Prof. Chien Wei-zang in his treatment of continuous beams is applied here to the solution of electric circuit problem. The superiority of this method over the customary ones-viz. (1) classical method, (2) Heaviside transformation, (3) Fourier transformation, and (4) Laplace transformation,-lies in the fact that the tedious work of solving a large number of simultaneous equations in the customary methods is avoided. The present paper is confined to the problem of the continuous network. The investigation is divided into two parts: (1) the continuous net-work in steady state, (2) in transient state. In the first part, the chief result is
ON THE DECAY OF TURBULENCE
CHUANG FENG-KAN
1953, 21 (3): 201-214. doi: 10.7498/aps.9.201
Abstract +
This paper consists of two parts. The first part gives a description of the motion of large eddies in a turbulent flow. The non-stationary character of the large eddies is emphasized. Up to present, there appears to be some confusion regarding the law of turbulence decay, especially the variation of the microscale with time. This paper introduces a new characteristic length for large eddies which leads to a new decay law valid at the initial period. The apparent discrepancies between Kolmogoroffs decay law and Lin's decay law are seen to be due to different expansions of the present one. It is hoped that the physical picture described herein would give some further insight into the structure of turbulence. In the second part, an analysis similar to that adopted iby Sedov for the correlation coefficients is applied to the turbulent spectrum. New results are obtained, in particular the transition of the decay law from the initial period to the final period.