Estimation Method of Loss Coefficient for Wind-Induced Internal Pressure Fluctuations

Abstract

As the importance of wind-induced internal pressure for building safety has continually been highlighted, increasing attentions have been paid to numerical methods for estimating fluctuating internal pressures, leading to the emergence of numerous second order nonlinear governing equations with two ill-defined parameters, namely inertial coefficient (CI) and loss coefficient (CL). Because resonance frequency and damping ratio of fluctuating internal pressures are susceptible to the values of inertial and loss coefficients, respectively, a correct understanding, and reasonable estimates, of these two parameters are required before using the governing equations to predict internal pressure responses. Compared with the inertial coefficient, which can be easily obtained from the Helmholtz frequency, a wider range of values of loss coefficient is in use, therefore this study focuses on the more uncertain parameter CL and presents an alternative method to identify loss coefficients of measured internal pressures without the onerous fitting works required by the current method. The reliability of this method is then verified using both wind tunnel tests and random excitation experiments using a loudspeaker specially designed for internal pressure studies. Potential influence factors for loss coefficient CL including opening size, opening shape, and magnitude of external pressure at the opening are investigated. The results indicate that (1) loss coefficient increases with opening area and depth, but decreases when external pressure strengthens; (2) the opening shape has a limited effect on the loss coefficient; and (3) CL is estimated to be in the range of 19–234 for varying opening sizes.