Modelling of the moisture concentration field due to cyclical hygrothermal conditions in thick laminated pipes

The paper presents a new method to calculate the moisture concentration field induced by cyclical environmental conditions in thick laminated pipes. The solution which is obtained is composed of a transient solution over the interior of the pipe wall and a fluctuating solution within two thin regions, close to the inner and outer lateral surfaces of the pipe wall. The thickness of these two regions is depending on both materials and frequency conditions. The transient solution is determined by using an analytical method based on the solving in average of the field equation. The fluctuating solution is derived from a finite difference scheme. It is shown that after some period of time the transient solution tends towards a permanent time independent solution. In that case, the fluctuating solution becomes a periodic solution which is conditioned by the cyclical boundary conditions. Finally, the effect of particular cyclical conditions on the moisture concentration in thick wall pipes will be tackled.