PREDICTING MOISTURE-CONTENT CHANGES OF WOOD EXPOSED TO DAILY TEMPERATURE AND HUMIDITY CHANGES

Because wood is a hygroscopic material, its moisture content and thus its dimensions change with those of temperature and humidity in an env ironment where the wood is exposed. In this paper a method of computer simulation based on a numerical method with finite differences is des cribed to estimate the moisture content changes of wood with daily osc illations. For the simulation process, Fick's diffusion equation with a surface emission layer is applied. A moisture-content dependent diff usion-coefficient and two types of hygroscopic ithotherms also are use d in the simulation. To obtain the parameters for the simulation, the moisture content changes of wooden plates of four species with differe nt thicknesses were measured for one week. Consistency between the mea sured and calculated moisture contents was investigated by use of a ro ot mean square error of calculated values, a correlation coefficient a nd the gradient of a regression line between measured and calculated v alues, and the ratio of the moisture content fluctuation ranges for me asured to calculated values. The calculated moisture content changes f or a week well-agreed with the measured values. The range of moisture content fluctuations caused by the daily oscillation of atmospheric co nditions is affected by the thicknesses of the wooden plates. It is su ggested that one can estimate the moisture content changes of wood and thus the dimensional changes accompanying the weather, and that seaso nal changes of atmosphere can be estimated by use of the simulation me thod.