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2024 | Book

Sensors & Instrumentation and Aircraft/Aerospace Testing Techniques, Volume 8

Proceedings of the 41st IMAC, A Conference and Exposition on Structural Dynamics 2023


About this book

Sensors & Instrumentation and Aircraft/Aerospace Testing Techniques, Volume 8: Proceedings of the 41st IMAC, A Conference and Exposition on Structural Dynamics, 2023, the eighth volume of ten from the Conference brings together contributions to this important area of research and engineering. The collection presents early findings and case studies on fundamental and applied aspects of Shock & Vibration, Aircraft/Aerospace Testing Techniques including papers on:

Alternative Sensing & AcquisitionActive ControlsInstrumentation

Table of Contents

Chapter 1. Modal Analysis of a BattleBot Blade
In this chapter, the dynamic characteristics of a BattleBot blade is studied. To optimize the design and improve the structural behavior of a test object, modal analysis is a crucial process. Obtaining modal parameters, namely, the natural frequencies, damping, and mode shapes of the unit under test, facilitates in adjusting the dynamic properties and in improving performance. In this case, a heavyweight BattleBot blade that is designed for combat competitions is tested and analyzed. The results are further used to tweak the design of the BattleBot to make it more resistant to damage or breaking of crucial components. Furthermore, these dimensional changes can also help improve the impact force of the BattleBot’s blades when it strikes the opponent. Using a new material for the fabrication can also assist in making the robot lighter and stiffer. Hence, a modal test can help make the BattleBot more efficient for the competitions. This work focuses on the experimental setup and discusses the workflow of modal analysis of the BattleBot blade. A modal hammer is used to excite the blade and a uni-axial accelerometer is used to obtain the vibration characteristics. The short pulse induced with a modal hammer excites a wide range of frequencies. To avoid the mass loading effect that is induced with a roving response measurement, the modal test is carried out with a roving excitation method. The test measurements and results are presented in this chapter.
Aakash Umesh Mange, Chad Walber
Chapter 2. Test Data Measurement Uncertainty Analysis
The Structural Validation Branch (AFRL/RQVV) is a research and development test organization that supports internal (Air Force) and external customers. The calculation of test data uncertainty is a necessary capability for a test organization. Test data uncertainty analysis provides error limit values based on the combined effects of random and systematic error sources. The measurement uncertainty calculations provide a means to characterize the measurement methods and understand what the test data represent. This allows engineers to make informed decisions based on the quality of the test data. Error source examination can also be used to determine if corrective actions are necessary and/or possible to eliminate or reduce measurement errors. AFRL/RQVV has completed a project to develop the procedures and tools to calculate and document test data measurement uncertainty values.
David T. Buck
Chapter 3. Carbon Nanotube (CNT) Elastomers for Sensing Applications: A Narrative Review
Elastomers are traditionally considered materials with low tensile strength and minimal electrical conductivity. Carbon nanotubes (CNT) are classified as fullerenes, or carbon-based materials forming a molecular mesh, that assume a cylindrical shape and display remarkable properties, such as high tensile strength and enhanced electrical conductivity as compared to other carbon allotropes. Elastomers doped with carbon nanotubes form CNT elastomers, which act as semi-conductors and can be formulated to exhibit many useful characteristics for the design of various sensors, such as strain gages. While CNT elastomers have been studied for more than 20 years, there are relatively few, if any, commercial sensor products utilizing this innovative technology. In this chapter, we survey selected portions of the CNT literature, explore the operation and characteristics of CNT elastomers, and consider some CNT elastomer requirements of potential interest for the design of sensors.
Hannah Loukusa, Eric Little
Chapter 4. Magnetoelastic Vibration Sensors
In this work, we explore the application of magnetoelasticity towards the realization of vibration transducers. Such sensors have unique and complementary properties when compared against more conventional transduction schemes. The sensors can be constructed to have a native response to jerk, the time derivative of acceleration. Acceleration causes force on an internal mass, the force induces strain on a magnetoelastic material, and the strain produces a magnetic field. The time derivative of magnetic flux through a voice coil results in a measurable voltage, consistent with Faraday’s law. Taken together, the generated voltage is directly proportional to applied jerk. Because of this native jerk response, the transducer’s frequency response has a 6 dB/octave slope compared to accelerometers and a 12 dB/octave slope compared to geophones. A second noteworthy feature is that, like geophones, magnetoelastic sensors have low output impedance and can, therefore, be used without amplification electronics in many applications. This may be ideal for applications requiring large networks of sensors.
Ehsan Vatankhah, Connor Hodges, Xiaoyu Niu, Zihuan Liu, Yuqi Meng, Askold S. Belyakov, Neal A. Hall
Chapter 5. Implementation of Shaft-Mounted Accelerometer in the Local Fault Diagnosis of Geared Systems
The goal of this chapter is to implement a wireless shaft-mounted accelerometer to provide a robust signal processing tool able to detect, localize, and assess mechanical irregularities in rotary machineries. For the purpose of experimental studies, a gear testing apparatus is designed and built to acquire vibration signal via both a traditional bearing-mounted accelerometer and the shaft-mounted accelerometer. First, a comparative analysis is outlined to compare the capability of the shaft-mounted and bearing-mounted accelerometers to the feature extraction of the damage. Then the quality of the vibration signal measured by the shaft-mounted accelerometer in different location and directions of the shaft is studied. Afterward, the sensitivity of the shaft-mounted accelerometer to the severity and location of the damage is evaluated by considering different size of one broken tooth and choosing different locations for the fault with respect to the transducer. Finally, the shaft-mounted accelerometer is used to obtain the same experimental results, while the speed is changing, which suggests the proposed approach is also effective towards condition monitoring of the gears under fluctuating load-speed condition.
Mohsen Azimi, Eniko T. Enikov, Wyatt Pena
Chapter 6. Methodologies to Distinguish Locomotive Types Based on the Measured Geometry
This chapter presents methods to sort locomotives and other certain types of vehicles by types using geometry measured by a measurement station. The approach is implemented using a series of artificial locomotives created by adding normally distributed noise to each distance between adjustment wheels of locomotives that are in exploitation in Norway. Two approaches are studied. The first approach, Gaussian Mixture Clustering, is presented and shown to be suitable to obtain geometries of the main locomotives in the set. The second approach, based on the comparison of norms of differences between geometries of measured and known locomotives, is found quite accurate to use for sorting measured locomotives by the predefined types. The methods are presented on geometries of locomotives, but they also can be used for distinguishing different types of wagons and multiple units.
Mariia Zakharenko, Gunnstein T. Frøseth, Anders Rönnquist
Chapter 7. Feedback Active Noise Cancellation Using Single Sensor with Deep Learning
Constructive measures should be taken immediately to tackle urban noise pollution, which is an omnipresent but neglected threat to human health. Many attempts have been made by researchers during recent decades to alleviate this issue; however, due to the nature of linear filters, conventional active noise control (ANC) methods, for example, filtered-x least mean square (FxLMS) algorithm, are useful just for attenuating narrowband linear or tonal noises. To deal with environmentally complex ANC applications, we developed a new deep learning-based artificial intelligence algorithm, which is able to model the intrinsic nonlinear behavior of various noises and produce anti-noise, which destructively interferes with unwanted noise to neutralize it. The proposed algorithm as a feedback controller significantly outperformed the traditional feedback FxLMS method in terms of noise attenuation metric.
Alireza Mostafavi, Young-Jin Cha
Chapter 8. Govan-Partick Pedestrian Bridge: Piezoelectric Energy Harvesting from Footfall-Induced Vibrations
The Govan-Partick pedestrian bridge is an under-construction footbridge that aims to reconnect the less developed Govan region of Glasgow to the neighboring Partick region, which contains cultural, economic, and educational landmarks, such as the University of Glasgow. This chapter aims to simulate the total energy that can be harvested via footfall-induced vibrations by people and cycles travelling on the bridge and display the data to the public to encourage active travel. This is done in accordance with the University’s GALLANT (Glasgow as a Living Lab Accelerating Novel Transformation) Project, which aims to increase active travel, such as walking and cycling, within Glasgow and aim for low carbon energy solutions.
Piezoelectric energy harvesting is a growing field that utilizes mechanical vibrations and stresses to derive electric energy. Using piezo patches installed on cantilever beams, the vibrations induced from footfall are harvested to generate an electric potential, which can then be stored or used to charge sensors used to monitor the activity on the bridge. The data will be displayed in real time to promote active travelling.
By modelling the bridge in a Finite Element Analysis Software, this work aims to derive the modal measurements of the bridge and import them into a simulation program to obtain the potential energy that can be generated under different parametric conditions. This information is core to correctly dimension the sensor network and the visualization device. Preliminary energy estimations will be driven by data obtained from observation of the footfall on already existing footbridges across the river Clyde.
Venkatsubramaniam Shashank, Falcone Gioia, Cammarano Andrea
Chapter 9. OASIS: Open Acquisition System for IEPE Sensors: For Academic Research and Teaching Purposes
Expensive measurement equipment often inhibits students from gaining practical experience with vibration measurements. The commercially available, proprietary hardware and software additionally does not grant insight into the used algorithms or allow modification and expansion. Both issues are overcome with the use of community developed open-source designs. This chapter discusses the requirements for vibration measurements in an academic context, like sampling frequency or resolution and especially synchronicity. These requirements are derived and incorporated into the design of an open-source data acquisition board for IEPE sensors (OASIS). The design is focused on the use of commonly available parts and a broadly community supported micro-controller (ESP32 family), with the costs bounded below 100 euro.
The built acquisition system offers four channels for IEPE signals, which can be sampled with up to 20 kHz and 16-bit resolution continuously. Additionally, wireless synchronization of multiple data acquisition boards is provided. This allows for use cases on systems with partly rotating structures, e.g., wind turbines, where synchronous measurements of stationary and rotating parts are necessary. The here-proposed approach does not rely on external clocks, like GPS or network services. An experimental validation shows that it is possible to synchronize two systems using this approach with a delay that is less than 100 µs.
Oliver M. Zobel, Johannes Maierhofer, Daniel J. Rixen
Chapter 10. Design of a Variable Stiffness Impact Damper Using Magnetorheological Elastomers
The suppression and control of mechanical vibrations, shock, and impacts is a subject of great interest for different areas of engineering, due to their potential negative effects, such as noise, fatigue, and mechanical failure in general. This is particularly important for the aerospace and automotive industries where in addition weight reduction is paramount. Usually, isolation and suppression methods are used either in the form of resilient isolators intended to absorb and dissipate the energy or in the form of tuned mass dampers. However, recently the applications where nonlinear elements are implemented have become more relevant. A particular nonlinear strategy for vibration and shock suppression is the impact dampers. These devices work on the principle of transferring momentum from the vibrating structure to the damper through impacts between them. There are several proposed designs of impact dampers, either configured as an end stop, also called vibro-impact attachments, or particle impact dampers, where small particles are contained into a vibrating structure or attached to it, and the collisions between the particles and the confinement result in energy dissipation and thus vibration suppression. In this work, the design of a variable stiffness impact damper is proposed. By controlling the stiffness of the damper, the amount of energy absorption and dissipation can be enhanced during impacts. To build the impact damper, a magnetorheological elastomer (MRE) is considered. These elastomers are manufactured using silicone rubber with embedded ferromagnetic particles, achieving stiffness variation through the application of a magnetic field. The design and modeling of the damper using a nonlinear geometry is introduced, and then prototypes are manufactured and experimentally quantified in terms of their capacity to change stiffness when a magnetic field is applied, as well as the energy absorption and vibration suppression capabilities. The advantages and limitation of the proposed design are then presented and discussed. It is found how the impact damper with variable stiffness can improve the vibration suppression under certain conditions depending on the level of the impact and the stiffness change obtained. Discussion about further control strategies and implementation are presented.
Diego Francisco Ledezma-Ramírez, Emiliano Rustighi, Pablo Ernesto Tapia-González
Chapter 11. Realization of a Virtual Acoustic Black Hole with Piezoelectric Patches
Reducing the mechanical vibration is of the utmost importance to lower mechanical stress and thus extend the life of a structure. This work proposes a novel concept to achieve this through an acoustic black hole (ABH) effect implemented via a digital controller. An ABH is a device that localizes the vibrational energy, which is in turn dissipated using damping layers. Its practical realization consists of a tapered wedge beam whose thickness follows a power-law profile. Its efficiency usually starts beyond a cut-on frequency, which is inversely proportional to its length. Obtaining the ABH effect on slender structures is thus very challenging: to achieve vibration reduction at low frequencies, the tapered wedge beam must be very long and thin. We propose herein to circumvent this problem by using a digital controller connected to piezoelectric transducers which are bonded to the host structure. Digital controllers have the significant advantage of being able to reproduce virtually any desired mechanical impedance function and, in particular, that of an ABH. We verify the soundness of the approach through detailed numerical simulations. Those are conducted on a one-dimensional slender beam modeled by the finite element method. The simulations show promising results, and the practical realization of the virtual acoustic black hole (VABH) is discussed eventually.
Samuel Quaegebeur, Ghislain Raze, Li Cheng, Gaëtan Kerschen
Chapter 12. A Portable Fixed Base Support for Modal Survey Tests
Fixed base (FB) correction methods (FBCMs) have been increasingly used to transform flexible or dynamically active boundary conditions into fixed boundaries in modal tests. This chapter documents the development of a portable test setup to conduct an FB modal survey test that can be integrated into other environmental testing configurations to accelerate testing schedules. The test article is attached to a T-slot table via an adapter plate that is bolted at multiple locations via T-slot bolts. During testing, inflatable airbags are used to raise the T-slot table off the supports, thus creating a soft boundary condition. Using 11 electrodynamic modal shakers, nine constraint shapes were measured and used to remove the dynamics of the T-slot table via the FBCM. Overall, there was excellent agreement between the FB target modes and the extracted FB modes. With this deployable setup, FB modal tests can easily be integrated into existing testing schedules, providing the ability to correlate FB models of flight hardware.
Peter A. Kerrian, Kevin Napolitano, Gregory Less
Chapter 13. Characterization of Nonlinear Joint Stiffness Using Dynamic and Static Experimental Methods
An experimental study was conducted to characterize the nonlinear rotational stiffness of a missile fin control actuation system testbed. Dynamic testing was used to measure the acceleration response of the fin to a sine-sweep input at various force levels. The modal frequency and damping of the rotation mode were tracked as a function of applied force to determine the converged control surface rotation mode. Frequency response functions were generated in order to estimate the dynamic stiffness of the control actuation system joint. Static freeplay and rigidity data were also collected using an applied quasi-static load and measuring the resultant displacements at multiple locations around the fin. The freeplay and rigidity data were used to characterize the degree of nonlinearity in the joint stiffness with respect to applied load.
Benjamin L. Martins, Caleb R. Heitkamp, Joseph M. Jaeckels
Chapter 14. Dynamic Characterization of Aircraft Shock Cords Used for Free-Free Boundary Conditions for Ground Vibration Testing
In ground vibration tests (GVT), it is often critical to separate rigid body modes from flexible body modes to simulate a free-free boundary condition. This is often done by chaining several aircraft shock cords in series and parallel to achieve a stiffness that results in a sufficiently isolated rigid body bounce mode for the test article. Thus, the stiffness values of these aircraft shock cords are critical in estimating the rigid body bounce frequency. However, the stiffness of these aircraft shock cords are often uncharacterized by the manufacturer or are presented as an elongation percentage at a given static load. One approach to characterizing the stiffness of these shock cords is to measure deflection as a function of an applied static load. Using this approach has typically resulted in significant underestimation of the measured rigid body bounce frequency, potentially leading to less than desirable separation between rigid body modes and flexible body modes. In response to this discrepancy, ATA performed an in-depth study to better characterize the dynamic stiffness of these aircraft shock cords to better estimate rigid body isolation frequencies. This chapter presents the methodology used to characterize the dynamic stiffness of these shock cords and the results of this study, which has significantly reduced bounce mode frequency estimation error.
Joseph M. Jaeckels, Arthur J. Nguyen, Douglas J. Osterholt
Chapter 15. Flight Worthiness Evaluation of Small Unmanned Aircraft Using Acoustic Testing
A study on the ability to evaluate flight worthiness of a popular small unmanned aircraft systems (sUAS) using acoustic methods is presented. The ability to detect propeller and other potential damage that may be present in an autonomous operations environment is of great interest. SUAS are increasingly being designed to operate autonomously, however prior to flight there must be a flight worthiness evaluation to help ensure safe operations. To accomplish this, an evaluation of the effects of prop damage in the acoustic signature provides meaningful insight using a noninvasive evaluation tool. This study provides data obtained by experimentally measuring the acoustic noise levels produced, as well as the vibration levels on the host airframe and at the base. The data are analyzed to gain further understanding of the acoustic and vibration responses to accurately make predictions on flight worthiness. The experiments utilize an airframe that is commonly used in the UAS community with props with and without damage. The data are obtained from an aircraft powered in a stowed configuration, as would be occurring at a remote UAS launch station. This detailed study on the acoustic responses help enable the development of noninvasive damage detection algorithms. These systems would be part of robust and economical safety assessment procedures and protocols for preflight testing to ensure flight worthiness of remote autonomous sUAS operations that are planned.
William Semke, Djedje-Kossu Zahui
Chapter 16. Low-Order Mechanical Modeling of Liquid Fuel Sloshing
Since the space launch vehicle undergoes not only external disturbances such as aerodynamic force or solar wind pressure but also internal dynamic influences such as the bending mode vibration of the vehicle and the sloshing of the liquid propellant, it is essential to reflect these disturbances when designing a precise flight controller. The sloshing phenomenon refers to the vibration of a fluid having a free surface and occurs in the liquid fuel and oxidant tanks due to the accelerated motion of the vehicle. Since the propellant’s sloshing natural frequencies may overlap with the frequency band of the attitude control device. For this reason, the sloshing mode of the propellant may resonate with the actuation of the TVC (thrust vector control) device or the bending mode of the vehicle, which can cause severe damage of the vehicle or instability of the attitude control (Healy, Development of the Rocket Engine for the Jupiter Missile. Rocketdyne, 1958). Among the solutions to mitigate the sloshing problem, there is a method of installing baffles that provides damping in the sloshing, but in the case of a space vehicle, the baffle design causes an increase in mass and cost, so there is a limit to its use. Therefore, it is necessary to accurately capture the dynamic characteristics of the sloshing and to apply the low-order equivalent mechanical model to the attitude controller using a simple mechanical mass-spring model or pendulum model as shown in Fig. 16.1.
Morgan Choi, Huinam Rhee
Chapter 17. Development of Steering Law for Thrust Vector Control Using Clustered Thrusters
Space launch vehicles often require large thrust engines depending on their mission. However, as the size of the engine increases, combustion instability problems may become severer and the reverse-thrust control, which is one of the key re-landing technologies required for the development of reusable rockets, becomes more difficult. Therefore, use of clustered low thrust engines in Fig. 17.1 has advantages compared to a single large thrust engine. In addition, use of the clustered engines makes it possible to control the yawing of the rocket, which is the spin motion about the longitudinal axis.
Jiwoong Kim, Morgan Choi, Huinam Rhee
Chapter 18. Fiducial Marker–Based Localization of Autonomous UAV for Structural Health Monitoring
This chapter presents an autonomous navigation system based on computer vision for unmanned aerial vehicles (UAVs). The emerging area of autonomous UAV has shown rapid development in the field of structural health monitoring (SHM) for the collection of important structural data from civil infrastructure. Much of previous research has been focused on the use of magnetic compass sensor-based methods for control and localization of UAV in GPS-denied environments. However, these methods are vulnerable to magnetic interference of the surrounding environment and result in poor control of UAV with dangerous levels of path deviations. Therefore, this chapter suggests the use of unique small fiducial markers that are unsusceptible to magnetic interference and can be permanently attached to walls or ceilings of structures to enable robust autonomous flight of UAVs. A pseudo markers map is created where the location of each marker is stored in a marker’s library. The markers are detected by the UAV during the flight and the prebuilt library information is used to localize UAV’s position in the whole structure. It has been shown through various experiments that the use of computer vision-based technique can significantly improve the control of UAV in challenging indoor and outdoor GPS-denied environments. This marker-based localization method is a low-cost, flexible, and practical solution to realize true autonomous UAVs in civil structures such as bridges, parkade, and buildings.
Ali Waqas, Young-Jin Cha
Chapter 19. Obstacle Avoidance Method for Autonomous UAV for Structural Health Monitoring
This chapter presents an obstacle avoidance method (OAM) to realize an autonomous collision-avoiding unmanned aerial vehicle (UAV) for the collection of structural data from civil infrastructure. OAM is of high importance to avoid serious accidents during autonomous flights of UAVs for monitoring purposes. A collision must be avoided to avert the loss of human and financial loss. Therefore, this chapter provides a new unique real-time OAM that consists of four steps: obstacle detection, obstacle clustering, distance estimation, and generation of new waypoints. For obstacle detection, deep learning algorithm YOLOv3 is implemented, which can detect obstacles at 10 frames per second during the flight. Obstacles are detected in the form of bounding boxes in the image stream of the UAV. Next, if more than one obstacle is detected, the k-means clustering algorithm is used to group the obstacles based on their relative position and the nearest obstacle group is selected to be avoided first. Then the distance from the nearest obstacle to the UAV is estimated using monocular depth estimation and a pinhole camera model. If the obstacle is dangerously close to the UAV, it must be avoided. For this purpose, a new obstacle avoidance waypoint is generated based on the obstacle position and flight path of the UAV. Experimentally, it has been shown that our obstacle avoidance method has real-time and robust performance compared to existing state-of-the-art OAM methods.
Ali Waqas, Young-Jin Cha
Chapter 20. Modal Characterization of 3D Printed Compliant Mechanisms for Space Exploration
The moon’s surface is covered with dust (regolith) and microscopic particles created by numerous meteorite impacts (lunar meteoric gardening). The lack of the smoothening actions of hydrological and aeolian process and the interaction with cosmic radiation have made regolith abrasive and electrostatically charged. Due to these characteristics, regolith has been identified as a major issue to lunar (and other planets) exploration, being responsible for clogging and wearing in the exposed hinges of the tools used in extravehicular activities.
Compliant mechanisms permit to eliminate the use of hinges and, therefore, of sliding motions between adjacent surfaces, because they use elastic deformation to supply the desired kinematic behavior. Due to their design, these mechanisms present areas that undergo large deformations and alternating stress concentrations and, therefore, fatigue effects. In this work, we examine the dynamic behavior of a compliant mechanism designed for extravehicular space exploration using additive manufacturing. The vibration mode-shapes and the corresponding natural frequencies will be identified, with particular focus on the equivalent structural characteristics and their linearity.
Dorota Budzyń, Hossein Zare-Behtash, Andrea Cammarano
Sensors & Instrumentation and Aircraft/Aerospace Testing Techniques, Volume 8
Chad Walber
Matthew Stefanski
Stephen Seidlitz
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