Wind tunnel investigations on aerodynamics of a 2:1 rectangular section for various angles of wind incidence

M. Keerthana,P. Harikrishna 한국풍공학회 2017 Wind and Structures, An International Journal (WAS Vol.25 No.3

Multivariate fluctuating pressures acting on a 2:1 rectangular section (2-D) with dimensions of 9 cm by 4.5 cm has been studied using wind tunnel experiments under uniform and smooth flow condition for various angles of wind incidence. Based on the variation of mean pressure coefficient distributions along the circumference of the rectangular section with angle of wind incidence, and with the aid of skin friction coefficients, three distinct flow regimes with two transition regimes have been identified. Further, variations of mean drag and lift coefficients, Strouhal number with angles of wind incidence have been studied. The applicability of Universal Strouhal number based on vortex street similarity of wakes in bluff bodies to the 2:1 rectangular section has been studied for different angles of wind incidence. The spatio-temporal correlation features of the measured pressure data have been studied using Proper Orthogonal Decomposition (POD) technique. The contribution of individual POD modes to the aerodynamic force components, viz, drag and lift, have been studied. It has been demonstrated that individual POD modes can be associated to different physical phenomena, which contribute to the overall aerodynamic forces.

Numerical investigations on the effect of mean incident wind on flutter onset of bridge deck sections

M. Keerthana,P. Harikrishna 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.82 No.4

The effect of mean angle of wind attack on the flutter critical wind speed of two generic bridge deck cross-sections, viz, one closed box type streamlined section (deck-1) and closed box trapezoidal bluff type section with extended flanges/overhangs (deck-2) type of section have been studied using Computational Fluid Dynamics (CFD) based forced vibration simulation method. Owing to the importance of the effect of the amplitude of forcing oscillation on the flutter onset, its effect on the flutter derivatives and flutter onset have been studied, especially at non-zero mean angles of wind attack. The flutter derivatives obtained have been used to evaluate flutter critical wind speeds and flutter index of the deck sections at non-zero mean angles of wind attack studied and the same have been validated with those based on experimental results reported in literature. The value of amplitude of forcing oscillation in torsional degree of freedom for CFD based simulations is suggested to be in the range of 0.5° to 2°, especially for bluff bridge deck sections. Early onset of flutter from numerical simulations, thereby conservative estimate of occurrence of instability has been observed from numerical simulations in case of bluff bridge deck section. The study aids in gaining confidence and the extent of applicability of CFD during early stages of bridge design, especially towards carrying out studies on mean incident wind effects.

Wind tunnel investigations on aerodynamics of a 2:1 rectangular section for various angles of wind incidence

Keerthana, M.,Harikrishna, P. Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.25 No.3

Multivariate fluctuating pressures acting on a 2:1 rectangular section (2-D) with dimensions of 9 cm by 4.5 cm has been studied using wind tunnel experiments under uniform and smooth flow condition for various angles of wind incidence. Based on the variation of mean pressure coefficient distributions along the circumference of the rectangular section with angle of wind incidence, and with the aid of skin friction coefficients, three distinct flow regimes with two transition regimes have been identified. Further, variations of mean drag and lift coefficients, Strouhal number with angles of wind incidence have been studied. The applicability of Universal Strouhal number based on vortex street similarity of wakes in bluff bodies to the 2:1 rectangular section has been studied for different angles of wind incidence. The spatio-temporal correlation features of the measured pressure data have been studied using Proper Orthogonal Decomposition (POD) technique. The contribution of individual POD modes to the aerodynamic force components, viz, drag and lift, have been studied. It has been demonstrated that individual POD modes can be associated to different physical phenomena, which contribute to the overall aerodynamic forces.

Segmentation Analysis of Domestic Tourists – A Case Study

Rajat Rastogi,Harikrishna M.,Ajit Patil 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.5

This paper presents the segmentation analysis of domestic leisure tourists in India. Samples were taken from visitors to 6 cities categorised by ‘leisure value’ and the population was further segmented based on ‘household income’ and ‘trip frequency’. Key salient features were substantial numbers of tourists belonging to middle-income group, and major share going to train. Logit analysis was carried out. NL structure was justified for seven categorisations out of nine. The proposed sub-categorisation was found to be significant and statically different then the parent population. Factors like household income, comfort and convenience of use of a travel mode, service levels in travel modes, budgetary constraints, presence of children and older persons in a family and affordability of travel mode were found to be influencing the leisure travel. Consideration set got influenced by user and destination connectivity. Frequency of travel was affected by economic affordability and status of the tourist. Value of travel time kept shifting judiciously across the sub-categories. The tourists valued their time highly if visiting spiritual locations or made less number of leisure trips in a year. Middle income group was found aspiring to avail higher facilities on leisure travel and was willing to pay more for the same. Policy initiatives are proposed based on the work. The approach is applicable to any city across the countries, which has either cultural, religious or waterfront value.

Prediction of negative peak wind pressures on roofs of low-rise building

Rao, K. Balaji,Anoop, M.B.,Harikrishna, P.,Rajan, S. Selvi,Iyer, Nagesh R. Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.6

In this paper, a probability distribution which is consistent with the observed phenomenon at the roof corner and, also on other portions of the roof, of a low-rise building is proposed. The model is consistent with the choice of probability density function suggested by the statistical thermodynamics of open systems and turbulence modelling in fluid mechanics. After presenting the justification based on physical phenomenon and based on statistical arguments, the fit of alpha-stable distribution for prediction of extreme negative wind pressure coefficients is explored. The predictions are compared with those actually observed during wind tunnel experiments (using wind tunnel experimental data obtained from the aerodynamic database of Tokyo Polytechnic University), and those predicted by using Gumbel minimum and Hermite polynomial model. The predictions are also compared with those estimated using a recently proposed non-parametric model in regions where stability criterion (in skewness-kurtosis space) is satisfied. From the comparisons, it is noted that the proposed model can be used to estimate the extreme peak negative wind pressure coefficients. The model has an advantage that it is consistent with the physical processes proposed in the literature for explaining large fluctuations at the roof corners.

Prediction of negative peak wind pressures on roofs of low-rise building

K. Balaji Rao,M.B. Anoop,P. Harikrishna,S. Selvi Rajan,Nagesh R. Iyer 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.6

In this paper, a probability distribution which is consistent with the observed phenomenon at the roof corner and, also on other portions of the roof, of a low-rise building is proposed. The model is consistent with the choice of probability density function suggested by the statistical thermodynamics of open systems and turbulence modelling in fluid mechanics. After presenting the justification based on physical phenomenon and based on statistical arguments, the fit of alpha-stable distribution for prediction of extreme negative wind pressure coefficients is explored. The predictions are compared with those actually observed during wind tunnel experiments (using wind tunnel experimental data obtained from the aerodynamic database of Tokyo Polytechnic University), and those predicted by using Gumbel minimum and Hermite polynomial model. The predictions are also compared with those estimated using a recently proposed non-parametric model in regions where stability criterion (in skewness-kurtosis space) is satisfied. From the comparisons, it is noted that the proposed model can be used to estimate the extreme peak negative wind pressure coefficients. The model has an advantage that it is consistent with the physical processes proposed in the literature for explaining large fluctuations at the roof corners.

Epicardial Ablation of Ventricular Tachycardia: a Review

Rhanderson Cardoso,Arash Aryana,Sheldon M. Singh,Harikrishna Tandri,Andre d'Avila 대한심장학회 2018 Korean Circulation Journal Vol.48 No.9

For over 3 decades, it has been known that reentry circuits for ventricular tachycardia (VT) are not limited to the subendocardial myocardium. Rather, intramural or subepicardial substrates may also give rise to VT, particularly in those with non-ischemic cardiomyopathy. Percutaneous epicardial mapping and ablation has been successfully introduced for the treatment of such subepicardial VT. Herein, we review the indications for epicardial ablation and the identification of epicardial VT by electrocardiographic and imaging modalities. We also discuss the optimal technique for epicardial access and the implications of epicardial fat which has the potential to mimic scar, decreasing the specificity of electrogram morphology and impeding energy delivery to the tissue. Finally, we also report on possible complications of the procedure and strategies to mitigate adverse events.