Approximation of Distributed Aerodynamic Force to a Few Concentrated Forces for Studying Supersonic Panel Flutter

Kailash Dhital(카일라시 디탈),Jae-Hung Han(한재흥),Yoon-Kyu Lee(이윤규) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.4

The present study considers the usage of concentrated force to simulate panel flutter. This idea has been validated for studying the flutter of wing structure in subsonic flow, yet its application in the supersonic region remained to be explored. In that context, a simply supported panel subjected to forces, equivalent to aerodynamic force is used for studying supersonic panel flutter. The distributed aerodynamic force is approximated to few concentrated forces by taking numerical integration. The aeroelastic equation is formulated using classical small-deflection theory and piston theory in linear panel flutter whereas for emulated panel flutter the flutter equation is derived by replacing the pressure due to aerodynamic loading with pressure from concentrated loading. Finally, critical flutter frequency, critical dynamic pressure, and corresponding mode shape are found for emulated panel flutter and compared with linear panel flutter. Two important parameters, the number of concentrated forces and their location are discussed through numerical examples and optimization process respectively. So far, the flutter results acquired in this study are reasonable to explain the feasibility of reproducing panel flutter using concentrated forces.

Approximation of Distributed Aerodynamic Force to a Few Concentrated Forces for Studying Supersonic Panel Flutter

Kailash Dhital(디탈 카일라스),Jae-Hung Han(한재흥),Yoon-Kyu Lee(이윤규) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.5

The present study considers the usage of concentrated forces to simulate real panel flutter. The concept of using concentrated forces have been validated for studying the flutter of wing structure in subsonic flow, yet its application in the supersonic region remained to be explored. Hence, a simply supported panel subjected to forces, equivalent to aerodynamic force is considered for studying supersonic panel flutter. The distributed aerodynamic forces are approximated to few concentrated forces by taking numerical integration. The aeroelastic equation is formulated using the classical small-deflection theory and the piston theory for linear panel flutter whereas for emulated panel flutter the flutter equation is derived by replacing the pressure due to aerodynamic loading with pressure from concentrated loading. Finally, flutter frequency, flutter dynamic pressure, and corresponding mode shape are found for emulated panel flutter and compared with linear panel flutter. Two important parameters, the number of concentrated forces and their location are discussed through numerical examples and optimization process respectively. So far, the flutter results acquired in this study are reasonable to suggest the feasibility of reproducing panel flutter using concentrated forces.

Aerodynamic and aeroelastic flutters driven triboelectric nanogenerators for harvesting broadband airflow energy

Phan, Hai,Shin, Dong-Myeong,Heon Jeon, Sang,Young Kang, Tae,Han, Pyunghwa,Han Kim, Gyu,Kook Kim, Hyung,Kim, Kyujung,Hwang, Yoon-Hwae,Won Hong, Suck Elsevier 2017 Nano energy Vol.33 No.-

<P><B>Abstract</B></P> <P>Aerodynamic and aeroelastic flutter-driven triboelectric nanogenerators are successfully used to harvest broadband airflow energy. The unit component of the flutter membrane consists of thin, free-standing Al foil electrodes covered on both sides with electrospun poly(vinyl chloride) nanofiber-structured mats, which provide advantageous tribo-surfaces specifically to increase the friction area. The airflow-induced triboelectric power generation from a single unit of the flutter-membrane-based triboelectric nanogenerator (FM-TENG) was up to 0.33 μW under a mild airflow condition. The use of a multi-layered triboelectric nanogenerator, fabricated by simply stacking the single units, can improve the output performance of the device. In a separate configuration, we designed a novel FM-TENG structure by mounting an aeroelastic flutter-belt adapted for use with a flutter-membrane energy-harvester. A rubber belt, which was sandwiched between the flutter membranes, created a rapid periodic vibrational mode via aeroelastic fluttering, synergistically harvesting triboelectric energy with the application of a constant air stream through the closed channel of the FM-TENG. Thus, our flutter-membrane-based approach creates a sustainable and cost-efficient energy harvesting system for collecting broadband airflow energy. Furthermore, the aerodynamic and aeroelastic FM-TENG have great potential to be used in numerous areas of self-powered electronic systems and in-situ wireless sensor applications for automobiles or aircraft.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Aerodynamic and aeroelastic flutter-driven triboelectric nanogenerators. </LI> <LI> Multi-layered triboelectric nanogenerators. </LI> <LI> Adapting an aeroelastic flutter to synergistically combine aerodynamic and aeroelastic movement. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The harvest of broadband airflow energy is accomplished using aerodynamic and aeroelastic flutter-driven triboelectric nanogenerators. Multi-layered triboelectric nanogenerators are made by simply stacking single units and can improve the output performance of the device. Adapting an aeroelastic flutter to synergistically combine aerodynamic and aeroelastic movement enables dramatic improvements in the electrical output of the triboelectric nanogenerator.</P> <P>[DISPLAY OMISSION]</P>

Prediction of bridge flutter under a crosswind flow

Tan-Van Vu,이학은,이호엽,최병호 한국풍공학회 2013 한국풍공학회지 Vol.17 No.3

This paper presents a number of approximated analytical formulations for the flutter analysis of long-span bridges using the so-called uncoupled flutter derivatives. The formulae have been developed from the simplified framework of a bimodal coupled flutter problem. As a result, the proposed method represents an extension of Selberg’s empirical formula to generic bridge sections, which may be prone to one of the aeroelastic instability such as coupled-mode or single-mode (either dominated by torsion or heaving mode) flutter. Two approximated expressions for the flutter derivatives are required so that only the experimental flutter derivatives of (*2*1,AH) are measured to calculate the onset flutter. Based on asymptotic expansions of the flutter derivatives, a further simplified formula was derived to predict the critical wind speed of the cross section, which is prone to the coupled-mode flutter at large reduced wind speeds. The numerical results produced by the proposed formulas have been compared with results obtained by complex eigenvalue analysis and available approximated methods show that they seem to give satisfactory results for a wide range of study cases. Thus, these formulas can be used in the assessment of bridge flutter performance at the preliminary design stage.

Prediction of bridge flutter under a crosswind flow

Vu, Tan-Van,Lee, Ho-Yeop,Choi, Byung-Ho,Lee, Hak-Eun Techno-Press 2013 Wind and Structures, An International Journal (WAS Vol.17 No.3

This paper presents a number of approximated analytical formulations for the flutter analysis of long-span bridges using the so-called uncoupled flutter derivatives. The formulae have been developed from the simplified framework of a bimodal coupled flutter problem. As a result, the proposed method represents an extension of Selberg's empirical formula to generic bridge sections, which may be prone to one of the aeroelastic instability such as coupled-mode or single-mode (either dominated by torsion or heaving mode) flutter. Two approximated expressions for the flutter derivatives are required so that only the experimental flutter derivatives of ($H_1^*$, $A_2^*$) are measured to calculate the onset flutter. Based on asymptotic expansions of the flutter derivatives, a further simplified formula was derived to predict the critical wind speed of the cross section, which is prone to the coupled-mode flutter at large reduced wind speeds. The numerical results produced by the proposed formulas have been compared with results obtained by complex eigenvalue analysis and available approximated methods show that they seem to give satisfactory results for a wide range of study cases. Thus, these formulas can be used in the assessment of bridge flutter performance at the preliminary design stage.

Identification of eighteen flutter derivatives of an airfoil and a bridge deck

Chowdhury, Arindam Gan,Sarkar, Partha P. Techno-Press 2004 Wind and Structures, An International Journal (WAS Vol.7 No.3

Wind tunnel experiments are often performed for the identification of aeroelastic parameters known as flutter derivatives that are necessary for the prediction of flutter instability for flexible structures. Experimental determination of all the eighteen flutter derivatives for a section model facilitates complete understanding of the physical mechanism of flutter. However, work in the field of identifying all the eighteen flutter derivatives using section models with all three degree-of-freedom (DOF) has been limited. In the current paper, all eighteen flutter derivatives for a streamlined bridge deck and an airfoil section model were identified by using a new system identification technique, namely, Iterative Least Squares (ILS) approach. Flutter derivatives of the current bridge and the Tsurumi bridge are compared. Flutter derivatives related to the lateral DOF have been emphasized. Pseudo-steady theory for predicting some of the flutter derivatives is verified by comparing with experimental data. The three-DOF suspension system and the electromagnetic system for providing the initial conditions for free-vibration of the section model are also discussed.

Coupled Flutter Analysis of Long-span Bridges Using Full Set of Flutter Derivatives

Tan-Van Vu,김영민,이학은 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.4

A convenient and effective finite element-based method for coupled flutter analysis of long-span bridges is presented. The exact formulation of the aerodynamic self-excited forces with eighteen flutter derivatives utilized by complex notation is proposed. The predictions of the flutter wind speed and the critical frequency are compared with those either given by existing methods or the wind tunnel test showing the effectiveness and accuracy of the present approach. Numerical flutter analysis for an asymmetric bridge is the application for engineering practice, and its obtained results highlight the important role of the first lateral bending and torsional mode in generating the coupled flutter. Multi-mode analyses that are based on only the symmetrical modes can predict accurately the bridge flutter onset. The consistent self-excited aerodynamic force formulations produce the flutter velocity that is closer to the experimental one of full-bridge model in the wind tunnel.

Panel Flutter Emulation Using a Few Concentrated Forces

Kailash Dhital,한재흥 한국항공우주학회 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

The objective of this paper is to study the feasibility of panel flutter emulation using a fewconcentrated forces. The concentrated forces are considered to be equivalent to aerodynamic forces. The equivalence is carried out using surface spline method and principle of virtual work. The structural modeling of the plate is based on the classical plate theory and the aerodynamic modeling is based on the piston theory. The present approach differs to the linear panel flutter analysis in scheming the modal aerodynamics forces with unchanged structural properties. The solutions for the flutter problem are obtained numerically using the standard eigenvalue procedure. A few concentrated forces were considered with an optimization effort to decide their optimal locations. The optimization process is based on minimizing the error between the flutter bounds from emulated and linear flutter analysis method. The emulated flutter results for the square plate of four different boundary conditions using six concentrated forces are obtained with minimal error to the reference value. The results demonstrated the workability and viability of using concentrated forces in emulating real panel flutter. In addition, the paper includes the parametric studies of linear panel flutter whose proper literatures are not available.

The Difference of Left Atrial Volume Index : Can It Predict the Occurrence of Atrial Fibrillation after Radiofrequency Ablation of Atrial Flutter?

Kim, Ung,Kim, Young Jo,Kang, Sang Wook,Song, In Wook,Jo, Jung Hwan,Lee, Sang Hee,Hong, Geu Ru,Park, Jong Seon,Shin, Dong Gu 영남대학교 의과대학 2007 Yeungnam University Journal of Medicine Vol.24 No.2

Background : The occurrence of atrial fibrillation after ablation of atrial flutter is clinically important. We investigated variables predicting this evolution in ablated patients without a previous atrial fibrillation history. Materials and Methods : Thirty-six patients (Ma1e=28) who were diagnosed as atrial flutter without previous atrial fibrillation history were enrolled in this study. Group 1 (n=11) was defined as those who developed atrial fibrillation after atrial flutter ablation during 1 year follow-up. Group 2 (n=25) was defined as those who has not occurred atrial fibrillation during same follow-up term. Echocardiogram was performed to all patients. We measured left atrial size, left ventricle end diastolic and systolic dimension, ejection fraction and left atrial volume index before and after ablation of atrial flutter. The differences of each variables were compared and analyzed between two groups. Results : The preablation left ventricular ejection fraction (preLVEF) and postablation left ventricular ejection fraction (postLVEF) are 54±14%, 56±13% in group 1 and 47±16%, 52±13% in group 2. The differences between each two groups are statistically insignificant (2.2±1.5 in group 1 vs 5.4±9.8 in group 2, p=0.53). The preablation left atrial size (preLA) and postablation left atrial size (postLA) are 40±4 mm, 41±4 mm in group1 and 44±8 mm, 41±4 mm in group 2. The atrial sizes of both groups were increased but, the differences of left atrial size between two groups before and after flutter ablation were statistically insignificant (0.6±0.9 mm in group 1 vs -3.8±7.4 mm in group 2, p=0.149). The left atrial volume index before flutter ablation was significantly reduced in group 1 than group 2 (32±10 mm³/m², 35±10 mm³/m² in group 1 and 32±10 mm³/m², 29±8 mm³/m² in group 2, p<0.05). Conclusion : The difference between left atrial volume index before and after atrial flutter ablation is the robust predictor of occurrence of atrial fibrillation after atrial flutter ablation without previous atrial fibrillation.

Panel Flutter Emulation Using a Few Concentrated Forces

Dhital, Kailash,Han, Jae-Hung The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

The objective of this paper is to study the feasibility of panel flutter emulation using a few concentrated forces. The concentrated forces are considered to be equivalent to aerodynamic forces. The equivalence is carried out using surface spline method and principle of virtual work. The structural modeling of the plate is based on the classical plate theory and the aerodynamic modeling is based on the piston theory. The present approach differs from the linear panel flutter analysis in scheming the modal aerodynamics forces with unchanged structural properties. The solutions for the flutter problem are obtained numerically using the standard eigenvalue procedure. A few concentrated forces were considered with an optimization effort to decide their optimal locations. The optimization process is based on minimizing the error between the flutter bounds from emulated and linear flutter analysis method. The emulated flutter results for the square plate of four different boundary conditions using six concentrated forces are obtained with minimal error to the reference value. The results demonstrated the workability and viability of using concentrated forces in emulating real panel flutter. In addition, the paper includes the parametric studies of linear panel flutter whose proper literatures are not available.