Effect of Hinge Stiffness on Flutter Characteristics of Flat Plate Wing with Flap

Pratik Shrestha,Min-Soo Jeong,In Lee 한국항공우주학회 2012 한국항공우주학회 학술발표회 논문집 Vol.2012 No.4

Flutter of flight vehicle structure can lead to catastrophic structural failure of aircraft. For this reason, aeroelastic simulation should be performed to understand flutter characteristics and to avoid any disastrous event which may occur due to such dynamic aeroelastic phenomenon. In this paper, the stiffness of the hinge, connecting the lifting surface to the control surface, is examined to see its effect on flutter characteristics by performing aeroelastic analysis. Flat plate wing with flap is modeled using MSC. Patran Flight Loads. Modal and flutter analysis of the wing for varying hinge stiffness is conducted using MSC.NASTRAN solver. P-k method is used for carrying out flutter analysis in MSC.NASTRAN solver. Results obtained from the analysis shows improved flutter characteristics with increase in hinge stiffness.

Effect of Inboard and Outboard Folding Angles on Aeroelastic Characteristics of a Folding Wing

Pratik Shrestha,Min-Soo Jeong,Eun-Ho Kim,In Lee,Jae-Sung Bae 한국항공우주학회 2012 한국항공우주학회 학술발표회 논문집 Vol.2012 No.11

Morphing aircrafts such as folding wing can fly efficiently at varying flight conditions and therefore they have the potential to replace existing fixed wing aircrafts. Structural changes in aircrafts wing form can have vast effect on the structural and aerodynamic characteristics of folding wing. Dynamic aeroelastic instability such as flutter of flight vehicle structure can lead to catastrophic structural failure of aircraft. For this reason, flutter characteristics should be thoroughly investigated and research needs to be performed to determine possible means of improving flutter characteristics of morphing wings. In this paper, flutter characteristics of baseline folding wing with varying inboard folding angle is investigated and validated, then parametric study is carried out by varying outboard folding angle. Folding wing is modeled using MSC. Patran Flight Loads. Flutter analysis of the flat plate folding wing is performed using P-k method in MSC.NASTRAN solver. Results obtained from the flutter analysis demonstrates that up to certain inboard folding angle flutter speed improves with the increase of inboard wing folding angle and through combination of inboard and outboard folding angle optimal flutter speed can be achieved.

Flutter Characteristics of a Morphing Flight Vehicle with Varying Inboard and Outboard Folding Angles

Shrestha, Pratik,Jeong, Min-Soo,Lee, In,Bae, Jae-Sung,Koo, Kyo-Nam The Korean Society for Aeronautical and Space Scie 2013 International Journal of Aeronautical and Space Sc Vol.14 No.2

Morphing aircraft capable of varying their wing form can operate efficiently at various flight conditions. However, radical morphing of the aircraft leads to increased structural complexities, resulting in occurrence of dynamic instabilities such as flutter, which can lead to catastrophic events. Therefore, it is of utmost importance to investigate and understand the changes in flutter characteristics of morphing wings, to ensure uncompromised safety and maximum reliability. In this paper, a study on the flutter characteristics of the folding wing type morphing concept is conducted, to examine the effect of changes in folding angles on the flutter speed and flutter frequency. The subsonic aerodynamic theory Doublet Lattice Method (DLM) and p-k method are used, to perform the flutter analysis in MSC.NASTRAN. The present baseline flutter characteristics correspond well with the results from previous study. Furthermore, enhancement of the flutter characteristics of an aluminum folding wing is proposed, by varying the outboard wing folding angle independently of the inboard wing folding angle. It is clearly found that the flutter characteristics are strongly influenced by changes in the inboard/outboard folding angles, and significant improvement in the flutter characteristics of a folding wing can be achieved, by varying its outboard wing folding angle.

Impact Localization on Composite Structure Through Use of FBG Sensors and Reference Database Impact Localization Algorithm

Pratik Shrestha,Jin-Hyuk Kim,Yurim Park,Chun-Gon Kim 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.4

Composite materials are widely being used as an alternative to conventional materials for their superior material properties. However, these material have damage mechanism significantly differing from the conventional materials, which makes it considerably challenging to inspect for damages though traditional structural maintenance approach. Low velocity impacts on composite materials can cause barely visible impact damages, hence continuous structural health monitoring (SHM) of the composite structure is needed to identify such impacts. Therefore, in this paper impact localization on composite plate is investigated using fiber Bragg grating (FBG) sensors. A high speed FBG interrogator is used to sample the impact signals at 100 kHz and reference database impact localization algorithm is used to localize the impact point. Moreover, through the present study it is demonstrated that using FBG sensors can effectively localize the impact location on the composite specimen with maximum localization error limited to within 28 mm of the actual impact location.

Impact Localization on Composite Structure under Simulated Operational Noise using FBG Sensors and Reference Database Algorithm

Pratik Shrestha,Jin-Hyuk Kim,Yurim Park,Chun-Gon Kim 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11

Low velocity impacts can cause barely visible impact damages on composite structure which are difficult to detect through conventional non-destructive inspection approach. Therefore continuous structural health monitoring (SHM) of the composite structure is needed to identify such impacts. In this paper, impact localization on composite plate is investigated using fiber Bragg grating (FBG) sensors while the structure is being excited using a shaker to simulate operational noise conditions. A high speed FBG interrogator is used to sample the impact signals at 100 kHz and reference database impact localization algorithm is used for estimating the location of the impact point. Moreover, through the present study it is demonstrated that even under simulated noise conditions the use of FBG sensors together with reference database algorithm can effectively localize the impact location on the composite specimen with maximum localization error of less than 35 mm from the actual impact location.

Composite Structure Damage Detection Using FBG Sensor and Reference Database Algorithm

Pratik Shrestha,Jin-Hyuk Kim,Yurim Park,Chun-Gon Kim 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.4

Continuous structural health monitoring (SHM) instead of conventional non-destructive inspection (NDI) of the composite structure is needed to detect and localize low velocity impacts which can cause barely visible impact damages (BVID). Furthermore, SHM system to identify occurrence of damage due to such low velocity impact is highly desirable. In this paper, damage detection on composite plate is investigated using fiber Bragg grating (FBG) sensors. A high speed FBG interrogator is used to sample the response signals from the FBG sensor at 100 kHz and a damage detection algorithm based on similarity comparing reference database method is used for identifying undamaged or damaged state of the composite specimen. Moreover, through the present study it is demonstrated that FBG sensors together with reference database algorithm are suitable not only for localizing the impact location on the composite specimen but also for detecting damage on the composite specimen.

Impact localization on composite structure using FBG sensors and novel impact localization technique based on error outliers

Shrestha, Pratik,Kim, Jin-Hyuk,Park, Yurim,Kim, Chun-Gon Elsevier 2016 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.142 No.-

<P><B>Abstract</B></P> <P>Structural health monitoring of composite structures is essential for timely detection and localization of low velocity impacts. In this paper, a novel method for localizing impacts using an error outlier based impact localization algorithm is proposed. The outlier method for impact localization was developed and implemented by localizing several impact points on a quasi-isotropic composite structure. Multiplexed FBG sensors were attached to the composite structure to monitor low velocity impacts, sampled at a frequency of 100kHz using a high speed FBG interrogator. Localization results for the error outlier based localization method were compared with the RMS and correlation based impact localization results. The novel localization technique presented in this paper demonstrates an effective means of estimating impact locations. Furthermore, overall improvement in the localization performance was obtained using the outlier based impact localization algorithm: impact points on the composite plate were localized with an average error of 10.7mm.</P>

Error outlier with weighted Median Absolute Deviation threshold algorithm and FBG sensor based impact localization on composite wing structure

Shrestha, Pratik,Park, Yurim,Kwon, Hyunseok,Kim, Chun-Gon Elsevier 2017 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.180 No.-

<P><B>Abstract</B></P> <P>In this paper, a low velocity impact localization algorithm based on an error outlier assessment technique with weighted Median Absolute Deviation (MAD) threshold was developed to localize impact on complex composite structures. The error outlier with MAD threshold algorithm was used to localize impacts on a 1000mm×1400mm area of the upper and lower surfaces of a Jabiru UL-D composite wing. Impact monitoring was performed with three multiplexed FBG sensors and the data acquisition was done using SFI-710 high speed interrogator to obtain the impact response signal at a frequency of 100kHz. The weighted MAD threshold used to filter the likely impact locations from a set of detected locations, and the proposed algorithm was able to localize impacts with consistent overall performance for a varying number of allowed detected locations. A parametric study was also performed to determine the possibility of localizing impact using a single sensor. The feasibility of utilizing the error outlier with weighted MAD threshold algorithm to localize impact with a single sensor was effectively demonstrated. Overall, impacts on the upper and lower surface of the composite wing were predicted and the localization results for three and one FBG sensors were comparable.</P>

Flutter Characteristics of a Morphing Flight Vehicle with Varying Inboard and Outboard Folding Angles

Pratik Shrestha,Min-Soo Jeong,In Lee,Jae-Sung Bae,Kyo-Nam Koo 한국항공우주학회 2013 International Journal of Aeronautical and Space Sc Vol.14 No.2

Morphing aircraft capable of varying their wing form can operate efficiently at various flight conditions. However, radical morphing of the aircraft leads to increased structural complexities, resulting in occurrence of dynamic instabilities such as flutter, which can lead to catastrophic events. Therefore, it is of utmost importance to investigate and understand the changes in flutter characteristics of morphing wings, to ensure uncompromised safety and maximum reliability. In this paper, a study on the flutter characteristics of the folding wing type morphing concept is conducted, to examine the effect of changes in folding angles on the flutter speed and flutter frequency. The subsonic aerodynamic theory Doublet Lattice Method (DLM) and p-k method are used, to perform the flutter analysis in MSC.NASTRAN. The present baseline flutter characteristics correspond well with the results from previous study. Furthermore, enhancement of the flutter characteristics of an aluminum folding wing is proposed, by varying the outboard wing folding angle independently of the inboard wing folding angle. It is clearly found that the flutter characteristics are strongly influenced by changes in the inboard/outboard folding angles, and significant improvement in the flutter characteristics of a folding wing can be achieved, by varying its outboard wing folding angle.

Low velocity impact localization on composite wing structure using error outlier based algorithm and FBG sensors

Shrestha, Pratik,Park, Yurim,Kim, Chun-Gon Elsevier Science Ltd 2017 Composites Part B, Engineering Vol.116 No.-

<P><B>Abstract</B></P> <P>In this paper, localization of low velocity impacts was conducted on a composite wing structure using an error outlier based impact localization algorithm. Composite wing impact monitoring was performed using multiplexed FBG sensors attached to the upper surface of the wing and a high speed interrogator was used to sample the impact response signals at a frequency of 100 kHz. The error threshold parameter and Number of Additional Outliers parameter were found to have a significant effect on the localization performance of the error outlier based impact localization algorithm. Furthermore, the present research shows that, for complex composite structures, a lower error threshold is required than those required for the simple composite plate case. Additionally, using an error outlier with a limited number of selected location ‘k’ based impact localization algorithm, with increasing Number of Additional Outliers parameter, improves the overall localization performance. The error outlier with a limited number of selected location ‘k’ based impact localization algorithm successfully localized low velocity impacts on the wing structure with an average localization error of 7.8 mm and a maximum localization error of 24.6 mm.</P>