Novel Approaches for Structural Health Monitoring

The thirty-plus years of progress in the field of structural health monitoring (SHM) have left a paramount impact on our everyday lives. Be it for the monitoring of fixed- and rotary-wing aircrafts, for the preservation of the cultural and architectural heritage, or for the predictive maintenance of long-span bridges or wind farms, SHM has shaped the framework of many engineering fields. Given the current state of quantitative and principled methodologies, it is nowadays possible to rapidly and consistently evaluate the structural safety of industrial machines, modern concrete buildings, historical masonry complexes, etc., to test their capability and to serve their intended purpose. However, old unsolved problematics as well as new challenges exist. Furthermore, unprecedented conditions, such as stricter safety requirements and ageing civil infrastructure, pose new challenges for confrontation. Therefore, this Special Issue gathers the main contributions of academics and practitioners in civil, aerospace, and mechanical engineering to provide a common ground for structural health monitoring in dealing with old and new aspects of this ever-growing research field

資源に制約のある小型衛星における自由空間光通信に関する研究

Presently, the farthest CubeSats have gone into deep space was via a piggy-back ride to the orbit of planet Mars where a twin-6U CubeSats (MarCO-A & B) in formation provided X-band (8.425GHz) radio-frequency (RF) communication relay support between the Insight Lander spacecraft and the NASA Deep Space Network (DSN) receiving system on Earth at about 8Kbps data rate. Subsequent planned interplanetary CubeSat missions (such as the ESA Asteroid Impact and Deflection Assessment collaborative mission) seeks to leverage on and improve the capacity. The increasing demand for higher network bandwidth and system data-throughput has led to the utilization of higher frequency bands in the electromagnetic spectrum and increase in transmitter power for long range scenarios. Operating at higher frequencies (or shorter wavelengths) provides an expanded channel capacity and reduction in the transceiver components sizes comparable to the lower frequencies (VHF, UHF) counterparts. However, RF signals are highly susceptible to divergent spreading, atmospheric absorption and attenuation, severely limiting the communication system performance and efficiency. The RF spectrum is also fast becoming congested with severe signal interference problems especially in collocated and multi-node systems. On the contrary, the optical bands are currently underexplored, less regulated and without licensing complications. Free-space laser communication represents a paradigm shift in modern high-rate data link and information processing capability enhancement. Laser signals have very high directivity, significantly increasing the transmitter’s effective isotropic radiated power (EIRP) and improving the received signal to noise ratio in a long distance link such as direct deep-space satellite to ground communication system. Compactness of opto-electronic components is likewise attractive for very low-resource (size, weight and power) small satellite platforms, especially CubeSats. On the contrary, the suiting benefits of the narrow laser beamwidth simultaneously give rise to misalignment challenges, pointing and acquisition, tracking (PAT) problems, resulting to pointing errors between the communicating nodes. Platform disturbances and micro-vibrations from satellite onboard subsystems and deployable appendages also contribute to the laser signal pointing instability. A small satellite in deep space establishing an optical link with the ground will require a very strictly precise attitude determination and control system working together with a rapid response beam stabilization system having a high level of reliability and accuracy. Lean or small (commonly used interchangeably) satellite philosophy is gaining prominence in defining the current and future architecture of space exploration missions. In recognition of this, the International Academy of Astronautics constituted a Study Group to define the industry standards and requirements of small satellites. The lean satellite approach seeks cheaper, quick development and delivery of small satellite missions, utilizing commercial-off-the-shelf components, smaller human resource and faster mission turn-around time. CubeSats are getting more roles and are consistently been considered for demanding tasks which were once the domain of traditional satellites. However, there exists a number of technology gaps that must be filled before the full potentials of CubeSat applications for very high throughput missions and deep space exploration can be fully harnessed. Gigabytes rate communication transceivers, compact propulsion system, interplanetary guidance and navigation systems are a few of the current technological gaps. This research is focused on tackling the problems of laser communication adaptability on small satellites in considerable range with Earth-bound optical ground systems. To this end, the systematic design of an example theoretical mission described in this thesis adapts lean satellite initiative, use of COTS components and scalability. A new approach of utilizing Photodiode Array (PDA) as an optical feedback sensor applicable to a MEMS Fine Steering Mirror (FSM) based laser beam fine pointing and control system is introduced in this thesis. Analyses and experiments demonstrated that the PDA have a much improved frame rate, eliminating the feedback delay experienced in the use of CCD cameras for laser beam position control. This presents a useful improvement in the performance of optical beacon tracking and fine pointing systems for laser communication modules in small satellites. Experiments on characterization of platform jitter spectrum and beam steering system mitigating the jitter effects in a 6U CubeSat platform is also presented in this thesis. CubeSats and Unmanned Aerial Vehicles (UAV) are identical in terms of “leanness” or “scarcity” of onboard resources and are both considered as viable host platforms for laser communication devices in a ubiquitous optical communication regime. As a derivation of this research, the activities of the Japanese’ National Institute of Information and Communications Technology, NICT-Kyutech collaboration on the development of a Drone 40Gbps lasercom fine pointing system is discussed. The Drone lasercom project sought to advance the state-of-the-art in UAV communication capabilities, with the agile optical coarse tracking, acquisition and fine pointing system playing a very critical role. In conclusion, the work done and reported in this thesis contributes to the advancement of free-space laser communication technology on small satellites in both near-Earth and deep space scenarios.九州工業大学博士学位論文 学位記番号：工博甲第537号 学位授与年月日：令和3年12月27日1. Introduction |2. Background and Literature Review |3. Lunar Cubesat Lasercom Design Reference Mission |4. Photodiode Array Aided Laser Beam Steering Experiment |5. Cubesat Jitter Effects on Lasercom Beam Pointing Stability |6. Drone 40gbps Lasercom Project |7. Conclusion and Recommendations九州工業大学令和3年

Selected Papers from the 5th International Electronic Conference on Sensors and Applications

This Special Issue comprises selected papers from the proceedings of the 5th International Electronic Conference on Sensors and Applications, held on 15–30 November 2018, on sciforum.net, an online platform for hosting scholarly e-conferences and discussion groups. In this 5th edition of the electronic conference, contributors were invited to provide papers and presentations from the field of sensors and applications at large, resulting in a wide variety of excellent submissions and topic areas. Papers which attracted the most interest on the web or that provided a particularly innovative contribution were selected for publication in this collection. These peer-reviewed papers are published with the aim of rapid and wide dissemination of research results, developments, and applications. We hope this conference series will grow rapidly in the future and become recognized as a new way and venue by which to (electronically) present new developments related to the field of sensors and their applications

Modeling, Simulation and Control of Very Flexible Unmanned Aerial Vehicle

This dissertation presents research on modeling, simulation and control of very flexible aircraft. This work includes theoretical and numerical developments, as well as experimental validations. On the theoretical front, new kinematic equations for modeling sensors are derived. This formulation uses geometrically nonlinear strain-based finite elements developed as part of University of Michigan Nonlinear Aeroelastic Simulation Toolbox (UM/NAST). Numerical linearizations of both the flexible vehicle and the sensor measurements are developed, allowing a linear time invariant model to be extracted for control analysis and design. Two different algorithms to perform sensor fusion from different sensor sources to extract elastic deformation are investigated. Nonlinear least square method uses geometry and nonlinear beam strain-displacement kinematics to reconstruct the wing shape. Detailed information such as material properties or loading conditions are not required. The second method is the Kalman filter, implemented in a multi-rate form. This method requires a dynamical system representation to be available. However, it is more robust to noise corruption in sensor measurements. In order to control maneuver loads, Model Predictive Control is applied to maneuver load alleviation of a representative very flexible aircraft (X-HALE). Numerical studies are performed in UM/NAST for pitch up and roll maneuvers. Both control and state constraints are successfully enforced, while reference commands are still being tracked. MPC execution is also timed and current implementation is capable of almost real-time operation. On the experimental front, two aeroelastic testbed vehicles (ATV-6B and RRV-6B) are instrumented with sensors. On ATV-6B, an extensive set of sensors measuring structural, flight dynamic, and aerodynamic information are integrated on-board. A novel stereo-vision measurement system mounted on the body center looking towards the wing tip measures wing deformation. High brightness LEDs are used as target markers for easy detection and to allow each view to be captured with fast camera shutter speed. Experimental benchmarks are conducted to verify the accuracy of this methodology. RRV-6B flight test results are presented. System identification is applied to the experimental data to generate a SISO description of the flexible aircraft. System identification results indicate that the UM/NAST X-HALE model requires some tuning to match observed dynamics. However, the general trends predicted by the numerical model are in agreement with flight test results. Finally, using this identified plant, a stability augmentation autopilot is designed and flight tested. This augmentation autopilot utilizes a cascaded two-loop proportional integral control design, with the inner loop regulating angular rates and outer loop regulating attitude. Each of the three axes is assumed to be decoupled and designed using SISO methodology. This stabilization system demonstrates significant improvements in the RRV-6B handling qualities. This dissertation ends with a summary of the results and conclusions, and its main contribution to the field. Suggestions for future work are also presented.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144019/1/pziyang_1.pd

Phase-advanced attitude sensing and control for fixed-wing micro aerial vehicles in turbulence

The scale of fixed-wing Micro Aerial Vehicles (MAVs) lend them to many unique applications. These applications often require low speed flights close to the ground, in the vicinity of large obstacles and in the wake of buildings. A particular challenge for MAVs is attitude control in the presence of high turbulence. Such flights pose a challenging operational environment for MAVs, and in particular, ensuring sufficient attitude control in the presence of significant turbulence. Low-level flight in the atmospheric boundary layer without sufficient attitude control is hazardous, mainly due to the high levels of turbulence intensity close to the ground. MAV accidents have occurred due to the lack of a reliable attitude control system in turbulent conditions as reported in the literature. Challenges associated with flight control of fixed-wing MAVs operating in complex environments are significantly different to any larger scale vehicle. The scale of MAVs makes them particularly sensitive to atmospheric disturbances thus limiting their operation. A review of the literature revealed that rolling inputs from turbulence were the most challenging whereby conventional inertial-based attitude control systems lack the responsiveness for roll control in high turbulence environments. The solution might lie with flying animals, which have adapted to flight within turbulence. The literature survey identified bio-inspired phase-advanced sensors as a promising sensory solution for complementing current reactive attitude sensors. The development of a novel bio-inspired phase-advanced sensor and associated control system, which can sense the flow disturbances before an attitude perturbation, is the focus of this research. The development of such a system required an in-depth understanding of the features of the disturbing phenomena; turbulence. Correlation studies were conducted between the oncoming turbulence and wing-surface pressure variations. It was found that the highest correlation exists between upstream flow pitch angle variation and the wing-surface pressure fluctuations. However, due to the insufficient time-forward advantage, surface pressure sensing was not used for attitude control. A second sensing approach was explored to cater for the control system’s time-lags. Multi-hole pressure probes were embedded in the wings of the MAV to sense flow pitch angle and magnitude variation upstream of the wing. The sensors provide an estimate of the disturbing turbulence. This approach caters for the time-lags of the system providing sufficient time to counteract the gust before it results in an inertial response. Statistical analysis was used to assess the disturbance rejection performance of the phase-advanced sensory system, which was benchmarked against a conventional inertial-based sensory system in a range of turbulence conditions. Unconstrained but controlled test flights were conducted inside the turbulence environment of two wind-tunnels, in addition to outdoor flight testing in the atmosphere. These three different turbulence conditions enabled testing of a wide range of turbulence spectra believed to be most detrimental to the MAV. A significant improvement in disturbance rejection performance was observed in relation to conventional inertial-based sensory systems. It can be concluded that sensory systems providing time-forward estimates of turbulence can complement conventional inertial-based sensors to improve the attitude stability performance

The Public Service Media and Public Service Internet Manifesto

This book presents the collectively authored Public Service Media and Public Service Internet Manifesto and accompanying materials.The Internet and the media landscape are broken. The dominant commercial Internet platforms endanger democracy. They have created a communications landscape overwhelmed by surveillance, advertising, fake news, hate speech, conspiracy theories, and algorithmic politics. Commercial Internet platforms have harmed citizens, users, everyday life, and society. Democracy and digital democracy require Public Service Media. A democracy-enhancing Internet requires Public Service Media becoming Public Service Internet platforms – an Internet of the public, by the public, and for the public; an Internet that advances instead of threatens democracy and the public sphere. The Public Service Internet is based on Internet platforms operated by a variety of Public Service Media, taking the public service remit into the digital age. The Public Service Internet provides opportunities for public debate, participation, and the advancement of social cohesion. Accompanying the Manifesto are materials that informed its creation: Christian Fuchs’ report of the results of the Public Service Media/Internet Survey, the written version of Graham Murdock’s online talk on public service media today, and a summary of an ecomitee.com discussion of the Manifesto’s foundations

Ultrasonic sensor platforms for non-destructive evaluation

Robotic vehicles are receiving increasing attention for use in Non-Destructive Evaluation (NDE), due to their attractiveness in terms of cost, safety and their accessibility to areas where manual inspection is not practical. A reconfigurable Lamb wave scanner, using autonomous robotic platforms is presented. The scanner is built from a fleet of wireless miniature robotic vehicles, each with a non-contact ultrasonic payload capable of generating the A0 Lamb wave mode in plate specimens. An embedded Kalman filter gives the robots a positional accuracy of 10mm. A computer simulator, to facilitate the design and assessment of the reconfigurable scanner, is also presented. Transducer behaviour has been simulated using a Linear Systems approximation (LS), with wave propagation in the structure modelled using the Local Interaction Simulation Approach (LISA). Integration of the LS and LISA approaches were validated for use in Lamb wave scanning by comparison with both analytical techniques and more computationally intensive commercial finite element/diference codes. Starting with fundamental dispersion data, the work goes on to describe the simulation of wave propagation and the subsequent interaction with artificial defects and plate boundaries. The computer simulator was used to evaluate several imaging techniques, including local inspection of the area under the robot and an extended method that emits an ultrasonic wave and listens for echos (B-Scan). These algorithms were implemented in the robotic platform and experimental results are presented. The Synthetic Aperture Focusing Technique (SAFT) was evaluated as a means of improving the fidelity of B-Scan data. It was found that a SAFT is only effective for transducers with reasonably wide beam divergence, necessitating small transducers with a width of approximately 5mm. Finally, an algorithm for robot localisation relative to plate sections was proposed and experimentally validated

NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 43)

Abstracts are provided for 128 patents and patent applications entered into the NASA scientific and technical information system during the period Jan. 1993 through Jun. 1993. Each entry consists of a citation, an abstract, and in most cases, a key illustration selected from the patent or patent application