In vivo structural dynamic analysis of the dragonfly wing: the effect of stigma as its modulator

2019 ◽  
Vol 377 (2150) ◽  
pp. 20190132 ◽  
Author(s):  
Amit Kumar ◽  
Navin Kumar ◽  
Rakesh Das ◽  
Piyush Lakhani ◽  
Bharat Bhushan
Keyword(s):  
Drag Coefficient ◽  
Natural Frequencies ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Active Role ◽  
Image Correlation ◽  
Mode Shapes ◽  
Correlation Technique ◽  
Structural Dynamic

The flapping of the dragonfly forewing under in vivo condition has been analysed by image correlation technique to get an insight of its structural dynamics. The modal parameters such as flapping frequency, natural frequencies, mode shapes and modal strain have been obtained that will facilitate the biomimetic design of wings for micro air vehicles. The stigma, which is a pigmented spot at the leading edge of the wing near the tip having heavier mass, takes an active role in the real-time flapping by shaping its trajectory as eight-shaped, which enhances the drag coefficient and stroke efficiency. The extra mass on it and its removal transformed the trajectory into two different elliptical and oval shapes, respectively, which reduced the drag coefficient and stroke efficiency of the flapping wing by altering the flapping kinematics. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 2)’.

scholarly journals Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4705
Author(s):  
Julian Lich ◽  
Tino Wollmann ◽  
Angelos Filippatos ◽  
Maik Gude ◽  
Juergen Czarske ◽  
...  
Keyword(s):  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fiber Reinforced ◽  
Structural Dynamic ◽  
Spatially Resolved ◽  
Glass Fiber Reinforced ◽  
Vibration Responses ◽  
And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

scholarly journals Impact of Geometrical Imperfections on Estimation of Buckling and Limit Loads in a Silo Segment Using the Vibration Correlation Technique

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 567
Author(s):  
Łukasz Żmuda-Trzebiatowski ◽  
Piotr Iwicki
Keyword(s):  
Natural Frequencies ◽  
Vibration Mode ◽  
Mode Shapes ◽  
Correlation Technique ◽  
Limit Loads ◽  
Linear Buckling ◽  
Geometrical Imperfections ◽  
Linear Problems ◽  
Formed Channel ◽  
Corrugated Wall

The paper examines effectiveness of the vibration correlation technique which allows determining the buckling or limit loads by means of measured natural frequencies of structures. A steel silo segment with a corrugated wall, stiffened with cold-formed channel section columns was analysed. The investigations included numerical analyses of: linear buckling, dynamic eigenvalue and geometrically static non-linear problems. Both perfect and imperfect geometries were considered. Initial geometrical imperfections included first and second buckling and vibration mode shapes with three amplitudes. The vibration correlation technique proved to be useful in estimating limit or buckling loads. It was very efficient in the case of small and medium imperfection magnitudes. The significant deviations between the predicted and calculated buckling and limit loads occurred when large imperfections were considered.

Mode shape–aided cable force determination using digital image correlation

2020 ◽  
pp. 147592172095216
Author(s):  
Banfu Yan ◽  
Derui Li ◽  
Wenbing Chen ◽  
Lu Deng ◽  
Xiaomo Jiang
Keyword(s):  
Digital Image Correlation ◽  
Mode Shape ◽  
Digital Image ◽  
Image Correlation ◽  
Effective Length ◽  
Estimation Methods ◽  
Mode Shapes ◽  
Correlation Technique ◽  
Remote Measurement ◽  
Cable Force

Assuming the distance between two nodal points of a specific cable vibration mode as the effective length of a pinned–pinned cable, mode shape–aided cable tension estimation methods are employed to estimate the cable force. This article proposes a framework based on digital image correlation technique for remote measurement of the dynamic displacement time history of cables in cable structures. Frequency domain decomposition technique is then used to extract the cable natural frequencies and mode shapes. Identified cable mode shapes are used along with a tensioned pinned–pinned cable model to estimate the cable force. Accuracy of the proposed methodology is investigated using the experimental data coming from a laboratory-scale test setup and hanger cables of a real-world arch bridge.

scholarly journals Model Updating of Friction Stir Welding for Aluminium and Magnesium Plate Structure

2018 ◽  
Vol 150 ◽  
pp. 04004 ◽  
Author(s):  
Nazrotul Afina Nazri ◽  
Mohd Shahrir Mohd Sani ◽  
Muhammad Nasiruddin Mansor ◽  
Siti Norazila Zahari
Keyword(s):  
Friction Stir Welding ◽  
Natural Frequencies ◽  
Model Updating ◽  
Mode Shapes ◽  
Average Error ◽  
Element Analysis ◽  
Structural Dynamic ◽  
Friction Stir ◽  
Dissimilar Friction Stir Welding ◽  
Al 7075

Friction stir welding (FSW) of aluminium and magnesium alloys face high demands in automotive and aerospace application due to its advanced and lightweight properties. FSW is an emerging solid state joining process in which the material that is being welded does not melt and recast. The main objectives of this project are to perform model updating based on finite element analysis (FEA) and experimental modal analysis (EMA) of dissimilar material of aluminium alloy AL 7075 and magnesium alloy AZ 31B. Modal properties such as natural frequencies, mode shapes are obtained and compared between FEA and EMA. The discrepancies of first five modes natural frequencies are below than 10% and the model updating have been conducted to minimize the error between two methods. This model updating are based on sensitivity analysis in order to make sure which parameters are given more influence in this structural dynamic analysis. Young’s modulus and Poisson’s ratio both materials are selected in the model updating process. After perform model updating, total average error of the natural frequencies of dissimilar friction stir welding plate is improved significantly.

scholarly journals Vibration Analysis of Radial Compressor Impellers

1983 ◽  
Author(s):  
J. Wachter ◽  
H. Celikbudak
Keyword(s):  
Dynamic Behavior ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Design Parameters ◽  
Centrifugal Impeller ◽  
Structural Dynamic ◽  
Experimental Procedure ◽  
Radial Compressor ◽  
Comparison Of The Results ◽  
Important Design

There are many problems facing the designers of turbomachines with the demand for ever increasing capabilities and reliability. One problem that requires considerable attention is the vibration characteristics of some components. It is object of this work to determine the dynamic behavior, namely natural frequencies, mode shapes of a centrifugal impeller which are being important design parameters in order to avoid costly failures in the development phase. This work divides into three sections. First, a Finite Element structural dynamic analysis is presented. Then experimental procedure used to determine the natural frequencies and mode shapes is described together with the comparison of the results obtained both theoretically through FEM and experimentally. Finally, interferometric holography technique is used as a means for obtaining the dynamic behavior of the impeller.

scholarly journals Comparisons of Differential Filtering and Homography Transformation in Modal Parameter Identification from UAV Measurement

Sensors ◽  
2021 ◽  
Vol 21 (16) ◽  
pp. 5664
Author(s):  
Jiqiao Zhang ◽  
Zhihua Wu ◽  
Gongfa Chen ◽  
Qiang Liang
Keyword(s):  
Modal Analysis ◽  
Natural Frequencies ◽  
Time History ◽  
Reference Points ◽  
Image Correlation ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Modal Parameter ◽  
Filtering Method ◽  
Homography Transformation

This paper proposes a differential filtering method for the identification of modal parameters of bridges from unmanned aerial vehicle (UAV) measurement. The determination of the modal parameters of bridges is a key issue in bridge damage detection. Accelerometers and fixed cameras have disadvantages of deployment difficulty. Hence, the actual displacement of a bridge may be obtained by using the digital image correlation (DIC) technology from the images collected by a UAV. As drone movement introduces false displacement into the collected images, the homography transformation is commonly used to achieve geometric correction of the images and obtain the true displacement of the bridge. The homography transformation is not always applicable as it is based on at least four static reference points on the plane of target points. The proposed differential filtering method does not request any reference points and will greatly accelerate the identification of the modal parameters. The displacement of the points of interest is tracked by the DIC technology, and the obtained time history curves are processed by differential filtering. The filtered signals are input into the modal analysis system, and the basic modal parameters of the bridge model are obtained by the operational modal analysis (OMA) method. In this paper, the power spectral density (PSD) is used to identify the natural frequencies; the mode shapes are determined by the ratio of the PSD transmissibility (PSDT). The identification results of three types of signals are compared: UAV measurement with differential filtering, UAV measurement with homography transformation, and accelerometer-based measurement. It is found that the natural frequencies recognized by these three methods are almost the same. This paper demonstrates the feasibility of UAV-differential filtering method in obtaining the bridge modal parameters; the problems and challenges in UAV measurement are also discussed.

Structural Dynamic Behavior of Axial Compressor Rotor

2017 ◽  
Author(s):  
Subramani Satish Kumar ◽  
Ranjan Ganguli ◽  
Siddanagouda Basanagouda Kandagal ◽  
Soumendu Jana
Keyword(s):  
Natural Frequencies ◽  
Axial Compressor ◽  
Axial Flow ◽  
Rotating Stall ◽  
Modal Identification ◽  
Mode Shapes ◽  
Stationary Condition ◽  
Structural Dynamic ◽  
Modal Characteristics ◽  
Compressor Rotor

The vibrations involved in a typical axial compressor rotor in an aircraft engine are complex. Generally, the compressor blades are arranged in a cantilever type configuration. It is also known that the amplitude of vibration is highest near the tip section of the shroudless blade. Compressors are limited by aerodynamic instabilities such as rotating stall and surge. Rotating stall generally initiates near the tip region of the compressor. Blade vibrations coupled with aerodynamic instabilities will lead to a catastrophic scenario of flutter that is asynchronous to the rotor speed. This aeroelastic interaction is detrimental if not taken into consideration. Knowledge of vibration characteristics of the compressor rotor will help in mapping the flutter zone for safe operation. The modal characteristics of the transonic axial compressor rotor available at the Axial Flow Compressor Research (AFCR) facility of National Aerospace Laboratories (NAL) are established in this study. A cyclic-symmetric pre-stressed modal analysis is performed on a single sector of the compressor rotor consisting of a shroudless blade connected to the disk with a pin type dovetail arrangement for different speeds. The main diagnostic charts for turbomachinery vibration i.e., Campbell and Interference diagrams are generated for various speeds and harmonic indices/ nodal diameters of the compressor rotor. The critical crossings of the engine order excitation lines over the natural frequencies of the blade are highlighted. Experimental modal investigations and analysis are carried out on the compressor rotor at the stationary condition and for two different boundary conditions. First, the blade alone modal characteristics under the free-free condition are established. Later, the complete blade-disk assembly mounted on a base test-stand is used to investigate the cantilever fixed-free boundary condition of the chosen blade. The modal characteristics are established by performing impact hammer experiments. Blade excitation is provided by a calibrated Dytran make impact hammer and the response is measured using a calibrated accelerometer. The structural dynamic data acquisition hardware and software from OROS is used for determining the natural frequencies, mode shapes and structural damping for each mode of the compressor rotor. There is a good agreement in the natural frequencies and mode shapes established using experiment and numerical methods for the first three modes investigated. Modal Assurance Criteria (MAC) analysis is carried out for two different modal identification algorithms to compare the mode shapes.

An Investigation of the Temperature Influence on a Shift of Natural Frequencies Using Digital Image Correlation

2014 ◽  
Vol 611 ◽  
pp. 506-510 ◽  
Author(s):  
Martin Hagara ◽  
Martin Schrötter ◽  
Pavol Lengvarský
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Natural Frequencies ◽  
Damping Ratio ◽  
Indicator Function ◽  
Image Correlation ◽  
Mode Shapes ◽  
Temperature Influence ◽  
Air Gun

The contribution describes an original optical measuring technique serving for the investigation of temperature influence on the shift of investigated objects natural frequencies. The mentioned method uses a modified high-speed digital image correlation system with original program Modan 3D created in Matlab, by which it is possible to non-contactly determine the natural frequencies using complex mode indicator function (CMIF) or normal mode indicator function (NMIF), the mode shapes as well as the damping ratio. Influence of the temperature on the shift of natural frequencies was analyzed at the planar steel specimen of circular shape with three holes. To the excitation a modal hammer was used. The specimen heating was realized by a hot-air gun, whereby the influence of the elevated temperature on the shift of natural frequencies was investigated by three temperatures distinguishing the room temperature 50° C, 75° C and 100° C.

Structural Modification of a Pipe Under Harmonic Excitation Using an Hybrid Numerical/Experimental Method

2011 ◽  
Author(s):  
Charles Bodel
Keyword(s):  
Modal Analysis ◽  
Nuclear Power ◽  
Natural Frequencies ◽  
Harmonic Excitation ◽  
Experimental Modal Analysis ◽  
Point Of View ◽  
Mode Shapes ◽  
Design Stage ◽  
Centrifugal Pumps ◽  
Structural Dynamic

Vibrations generated by centrifugal pumps are difficult to predict at the design stage, for it is hardly possible to accurately determine the natural frequencies of pipes and to avoid coincidences with the blade pass frequency of the pump and its harmonics. One is often led to modify the existing structure, by adding stiffness, mass or damping. This paper illustrates this point on a pipe connected to a pump in a nuclear power plant operated by EDF (E´lectricite´ de France). In October 2010, abnormal vibrations were measured on a thin pipe at the outlet of a pump in a powerplant in France. The French nuclear regulatory commission asked EDF to perform a diagnosis and to define solutions within a few months. EDF/R&D division has used an original method developed in 2004 based on hybrid data, and called LMME-SDM (for Local Model Mode-shapes Expansion Structural Dynamic Modification). The main objective is to define a structure modification able to remove all natural frequencies close to the harmonic excitation. For the purpose of the study, we need a numerical model, which should be fairly correct from a static point of view, but which is not necessarily updated from a dynamic point of view, and an experimental modal analysis carried out under real conditions on the pipe. During the experimental modal analysis, a test of added mass has been carried out so that the method can be validated by comparing the predicted and the observed frequency. This method has already been used in industrial cases in former studies [3], however the study presented here has reached a higher level in complexity. Even if this method is able to give reasonable results compared to measurements, it is close to its limits.

scholarly journals Structural Dynamic Analysis of the Chenderoh Dam Sector Gate Section

2018 ◽  
Vol 217 ◽  
pp. 02002 ◽  
Author(s):  
Mohamad Hazwan Mohd Ghazali ◽  
Mohd Hafiz Zawawi ◽  
Nurul Husna Hassan ◽  
Mohd Rashid Mohd Radzi ◽  
Ahmad Zhafran Ahmad Mazlan ◽  
...  
Keyword(s):  
Dynamic Analysis ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Fe Model ◽  
Ansys Software ◽  
Structural Dynamic ◽  
The Real ◽  
Reference Information ◽  
Real Scale ◽  
Operational Methods

The dynamic characteristics such as natural frequencies, mode shapes and frequency response function (FRF) are the important characteristics to be investigated to access the level of durability of any dam structures. These characteristics are important since it will be the reference information for any operational methods to be used for the dam structures. In this study, one of the real dam (i.e., Chenderoh Dam) that available in Malaysia is taken into consideration, where the dynamic analysis of the sector gate section of the dam structure is investigated. the real scale of the sector gate section is measured on site and modelled into the CAD software with the consideration of real build-in materials. Then, the finite element (FE) model is constructed in ANSYS software with the required boundary condition and meshing sensitivity analysis. From the result of modal analysis, 30 natural frequencies are determined in the range of 0.5904 Hz to 8.471 Hz together with the mode shapes but only the most significant natural frequencies will be shown in this paper. In addition, all three axes of the FRF graphs show an agreement for the highest natural frequency value at 7.95 Hz, where the maximum deflection occurred in x axis direction with 2.03 × 10-7 m.

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