Krzysztof Wiśniewski and Robert L. Taylor
Numerical aspects of initial stability analysis of a cylindrical shell of non‐constant parameters along the generator and under non‐symmetrical loads are considered. A variational…
Abstract
Numerical aspects of initial stability analysis of a cylindrical shell of non‐constant parameters along the generator and under non‐symmetrical loads are considered. A variational approach based on Sanders' and Donnell's non‐linear equations of thin, elastic shells is applied. The problem is decomposed to determine: the stability vectors in the axial direction in the first step, and the critical load and the stability vector in the circumferential direction in the second step. The discretization is based on finite Fourier representations and the finite difference method. To find the approximate stability vector in the axial direction an auxiliary problem for axisymmetric loads is solved. The error of the method is defined and the effectiveness of the method is estimated. The decomposition leads to small and fast algorithms suitable for personal computers. Shells with constant and stepped thicknesses under wind loads are calculated as examples. Tested algorithms show considerable effectiveness and good accuracy of results.
KATSUMORI HATANAKA and MUTSUTO KAWAHARA
A new fractional step method in conjunction with the finite element method is proposed for the analysis of the thermal convection and conduction in a fluid region expressed by the…
Abstract
A new fractional step method in conjunction with the finite element method is proposed for the analysis of the thermal convection and conduction in a fluid region expressed by the momentum equations, the equation of continuity and the energy equation. This paper focuses on the features of the present finite element method which gives a simple way of treating the Neumann boundary condition for the pressure Poisson equation. The applicability and effectiveness of the proposed scheme are illustrated through the numerical examples of the two‐dimensional natural convection flow in enclosures with several Rayleigh numbers.
Details
Keywords
The purpose of this paper is to present a new method of measuring thermal resistance of power light-emitting diodes (LEDs). Properties of power LEDs strongly depend on their…
Abstract
Purpose
The purpose of this paper is to present a new method of measuring thermal resistance of power light-emitting diodes (LEDs). Properties of power LEDs strongly depend on their internal temperature. The value of this temperature depends on the cooling conditions characterized by thermal resistance.
Design/methodology/approach
The new method of measuring the value of this parameter belongs to the group of electric methods. In this method, the problem of estimating the value of electrical power converted into light is solved. By comparing the values of the case temperature obtained for the LED operating in the forward mode and the reverse-breakdown mode, the thermal power is estimated. On the basis of the measured value of the thermally sensitive parameter (the LED forward voltage) and the estimated value of the thermal power, thermal resistance is calculated.
Findings
The elaborated method was used to measure thermal resistance of the selected types of power LEDs operating at different cooling conditions. The correctness of the elaborated measurement method was proved by comparing the results of measurements obtained with the use of the new method and the infrared method.
Research limitations/implications
On the basis of the obtained results of measurements and the catalog data of the tested diodes, the dependence of the measurement error of thermal resistance of the LED on its luminous efficiency is discussed.
Originality/value
The new measurement method is easy to use and more accurate than the classical method of thermal resistance measurement of the diode.