Experimental and Numerical Investigation of Wind Induced Pressure on C-shaped Building Models

Wind induced forces are significant for buildings and therefore their impact on such structures is essientally required during their design and analysis. For analytical solution of the wind load, estimations of the wind pressure coefficients on its faces are the pre requisite. Generally, there are three primary methods which are used to estimate pressure coefficient: full-scale building tests, model test in wind tunnel and parametric equations derived from experiments. Buildings shapes are changing with emerging demands of several aesthetical features. Developments of new building materials and construction techniques have enabled us to build new building, which are tall and unsymmetrical (irregular) but unfortunately such structures are susceptible to more complex wind loads. Thus, it becomes necessary to estimate the wind loads with higher degree of confidence. Although ample information regarding wind load on symmetrical and regular structure is available in various international codes, but they lack the study of wind forces on unsymmetrical structures. Literature provides some information on L, T, E, Y, N, Plus (+) and also on U-shaped building plans with flat surface only i.e., without curvature. Although, there are many C-shaped buildings that exist in real practice, no work has been reported for C-shaped building models with variation in curvature. Wind pressure on the structures is affected by its geometry, the nature of the corner (with or without curvature), incidence angle of wind and flow features. The present work focuses on the outcome of experimental investigation of mean pressure coefficients on different faces of C-shaped building models. Distribution of wind pressure coefficient on the surfaces of C-shaped buildings models (irregular plan) through numerical and physical modelling are attempted. Experiments have been carried out on the different C-shaped building models with and without corner curvature along considering some other variables such as the angle of incidence, side ratio, frontal ratio and aspect ratio in a subsonic open circuit wind tunnel. All the experiments have been carried out at the Aerodynamics laboratory of the Department of Aerospace Engineering, Indian Institute of Technology Kharagpur (IITKGP), India. One way to accurately estimate the wind pressure coefficients on the surfaces of C-shaped building is their model testings in a wind tunnel. The building models were made of 5 mm thick Perspex sheets. Recorded data of pressure at the located pressure taping points enabled to determine the pressure coefficient variation on the surfaces with wind angles and corner curvature. It has been observed that the pressure coefficient at a location on a surface varies significantly with the angle of incidence and the curvature of the surfaces. Also, the extent of (xii) maximum and minimum pressure zones, and their locations have been observed to change with the curvature and the wind direction. This work also presents numerical analysis through Computational Fluid Dynamics (CFD) technique to calculate wind effect used C-shaped buildings with varying aspect ratio and its optimization caused by the alteration of angle of incidence of the wind forces ranging from 00 to 1800 at an interval of 300. Further, results obtained through numerical simulation have been validated with the corresponding experimental results. Numerical analysis has been carried out using ANSYS Fluent with k-ε model of turbulence. This suggests the applicability of this technique to predict the wind pressures on the surfaces of the prototype building more accurately. Further, analytical equations are developed for determining surface mean pressure coefficient (̅̅̅) on the face of the building structures using relevant experimental data obtained from laboratoary experiments. Various data driven techniques or artificial intelligence techniques such as group method of data handling neural network (GMDH-NN), multivariate adaptive regression spline (MARS) and gene-expression programming (GEP) approach are used to develop model equations of surface mean pressure coefficient (̅̅̅) using the non-dimensional parameters such as the side ratio, height ratio, curvature ratio, and wind incidence angle. Influence of each parameter for predicting the surface mean pressure coefficient on the surfaces of different C-shaped building models by the developed equations are tested through sensitivity analysis. Performance of all the developed models are evaluated by means of various statistical measures such as coefficient of determination (R2), root-mean-square-error (RMSE), mean absolute error (MAE), the mean absolute percentage error (MAPE), coefficient of efficiency (E), Akaike Information Criterion (AIC), and Scatter index (SI) and uncertainty analysis to determine the best predictable model equation. These developed model equations through GMDH-NN, MARS and GEP approaches can be used as a practical tool for the prediction of surface mean pressure coefficient (̅̅̅) on the face of the prototype buildings

Modelling of Wind Pressure Coefficients on C-Shaped Building Models

Designs of buildings are changing with emerging demands of several aesthetical features and efficient design based on geometry. Development of new building materials and construction techniques have enabled us to build new buildings which are tall and unsymmetrical, but unfortunately such structures are more susceptible to wind loads. Thus it becomes necessary to estimate wind loads with higher degree of confidence. Although ample information regarding wind load on symmetrical and regular structure is available in various international codes, they lack the study of effect of wind forces on unsymmetrical structures. This paper presents experimental and numerical studies of the wind effect on commonly used C-shaped buildings with varying aspect ratio and its optimization caused by the alteration of angle of incidence. Furthermore, results obtained by numerical analysis have been validated with the experimental one. For this study, numerical analysis has been carried out using ANSYS Fluent with k-ε model of turbulence. Computational fluid dynamics (CFD) techniques is used to evaluate the surface pressure on various faces of the model for angle of attack of 0° to 180° at an interval of 30° in a subsonic open circuit wind tunnel. The results found by CFD technique are well compared with the experimental results which suggest the feasibility of using this technique of predicting wind pressures on building efficiently and accurately

A simple technique for direct, high power laser beam profile measurement using thermal imagers

Measuring the profile of a laser beam is of critical importance, especially for high power laser systems. Although different techniques exist to measure the beam profile, owing to the use of optoelectronic detectors or cameras, they primarily work at lower powers and require tapping and attenuating the beam. In this process, there is potential for the diagnostic system affecting the beam quality. In this work, we propose a simple technique which can measure the beam profile at full power using a thermal imager without the need for additional optical components. The method involves taking a thermal image of the beam while it is incident on an absorptive surface such as a thermopile head which is used to measure optical power. In addition, a second image is taken using a focused incidence on the surface at low powers. The second image which is reused provides the point spread function. We then make use of the linearity of the heat equation which allows the deconvolution of the point spread function from the original image to obtain the actual beam profile. In this work, we utilized the technique to directly analyze the beam profile at full power of a 100 W class fiber laser and analyzed deviations from single-modedness. In addition, we utilized offset splices to few-mode fibers to launch higher order modes at the 100W level and demonstrate their direct characterization of multimode nature of the profile. This technique provides a simple alternative, using instruments present in most laser labs for direct, high power laser beam profiling

Preserved lignin structures in early eocene Surat lignites, Cambay Basin, Western India

Lignite samples from Vastan and Tadkeshwar lignite mines, Cambay Basin have been analysed to elucidate lignin precursor using thermochemolysis-gas chromatography-mass spectrometry. The thermochemolysis products of lignites are characterized by monomethoxy-, dimethoxy-, and trimethoxybenzene derivatives originated from -hydroxyphenyl, guaiacyl, and syringyl units of lignin polymer, respectively. The other compounds obtained in thermochemolysates of studied lignites are some resin derived C-15 sesquiterpenoids, with a series of fatty acid methyl esters and -alkanes/alkenes. The methylated guaiacyl and syringyl derivatives originate from the cleavage of beta-O-4 linkages and subsequent methylation of acidic hydroxyl groups of preserved lignin. Gymnosperm lignin is characterized mainly by guaiacyl derivatives whereas angiosperm lignin yields some syringyl-type compounds in addition to guaiacyl-type compounds. By analogy with the lignin structure of modern trees, the abundant occurrences of syringyl derivatives in the thermochemolysis products of Surat lignites clearly demonstrate that the palaeofloral community was dominated by angiosperms during the deposition of these lignites