Tyler Reid

Vibrations and stability of axially traveling laminated beams

Abstract In this paper, vibrations and stability of an axially traveling laminated composite beam are investigated analytically via the method of multiple scales. Based on classical laminated beam theory, the governing equations of motion for a time-variant axial speed are obtained using Newton’s second law of motion and constitutive relations. The method of multiple scales, an approximate analytical method, is applied directly to the gyroscopic governing equations of motion and complex eigenfunctions and natural frequencies of the system are obtained. The stability boundaries of the system near resonance are determined via the Routh–Hurwitz criterion. Finally, a parametric study is conducted which considers the effects of laminate type and configuration as well as the mean speed and amplitude of speed fluctuations on the vibration response, natural frequencies and stability boundaries of the system.

Orbital representations for the next generation of satellite-based augmentation systems

The landscape of the Global Navigation Satellite System (GNSS) is changing. New constellations are coming online, and a diversity of new signals are coming to the user space. Multi-frequency adds a means for ionospheric correction as well as robustness to jamming. Multi-constellation gives rise to better geometry and robustness to satellite failures. Systems which require a high degree of safety such as aviation require Satellite-Based Augmentation Systems (SBAS) to be used in conjunction with GNSS. As such, SBAS standards must be modernized to reflect the evolving GNSS environment. SBAS will deliver additional service on a new frequency at L5, giving the ideal opportunity to modernize the SBAS Minimum Operational Performance Standards (MOPS). Geostationary (GEO) satellites currently comprise the space segment of SBAS. However, GEOs remain at the equator limiting their visibility at the Poles. As activity in the Arctic is increasing, SBAS service in this region is of utmost importance to ensure safety. As such, it is desired that the next-generation L5 MOPS allow for orbit classes other than GEO. Orbital diversity for the delivery of SBAS corrections will allow for better visibility of this service on all places on earth. Here, we discuss the design and qualification of the L5 MOPS orbit messages, namely the ephemeris and almanac. These will support a multitude of orbit classes including all of those used today by both GNSS and SBAS.

GNSS Integrity in The Arctic: GNSS Integrity in The Arctic

Growing activity in the Arctic calls for high integrity navigation in this region. This can be achieved using Global Navigation Satellite Systems (GNSS) in conjunction with Satellite Based Augmentation Systems (SBAS) or Advanced Receiver Autonomous Integrity Monitoring (ARAIM). Single frequency GPS-only SBAS is in service in some regions today and is reliant on ground and space infrastructure. ARAIM will be more autonomous and will rely on the multitude of signals and core constellations coming in the future. Here, we examine both SBAS and ARAIM in the context of aviation and maritime requirements in the Arctic. Results demonstrate that the introduction of multi-frequency and multi-constellation to these systems enables navigation safety in the Arctic. SBAS brings aircraft precision approach as well as precise maritime operations such as mapping. ARAIM also supports precision approach in addition to autonomous ice navigation at sea but falls short of precision maritime requirements.

The Potential Role of Objective Activity Monitoring in Off-Site Follow-Ups Post-Bariatric Surgery

Title: The Potential Role of Objective Activity Monitoring in Off-Site Follow-Ups Post-Bariatric Surgery. Background: Weight gain and attendance at follow-up visits after bariatric surgery are of great concern for the multidisciplinary care team. Geography and schedules make attending follow-up visits increasingly difficult as time after surgery goes on. Recently, inexpensive commercially available activity monitors have become more common place, making information concerning physical activity and sedentary behaviours deliverable online, allowing for important patient lifestyle information to be transmitted to the multidisciplinary care team. The purpose of this study was to determine if off-site objectively monitored physical activity and sedentary time can describe health measures such as total body fat, abdominal adipose tissue (AAT), and weight maintenance long-term post-bariatric surgery. Methods and findings: 59 individuals who had undergone bariatric surgery wore an ActivPAL for seven consecutive days, monitoring physical activity and sedentary time and underwent one DXA scan to determine body composition. Linear regression shows that (moderate-to-vigorous physical activity (MVPA) explained 18.8% of variance in body fat (p=0.019) and 11.3% of the variance in AAT (p=0.033). Conclusions: Objective monitoring could offer beneficial information concerning patients’ health at post-surgical follow-up visits.

Using Traffic Information Services Broadcast (TIS-B) signals for aviation navigation

Airspaces around the world are introducing capabilities and infrastructure to handle higher traffic densities. Highly capable satellite based navigation is being adopted to help aircraft operate more efficiently in the future. Furthermore, Automatic Dependent Surveillance Broadcast (ADS-B), where aircraft and other users broadcast their precise position, velocity and intent, is being introduced to help manage these airspaces. This allows air traffic and other aircraft to have excellent awareness of the airspace users. Adoption of new systems and technologies will only intensify as future airspaces will have to handle more varied traffic such as unmanned aerial vehicles (UAV). GNSS is critical to both future air navigation and ADS-B. Many of improvements in future airspace are primarily achieved with GNSS. This makes a robust, accurate terrestrial alternate essential should GNSS be unavailable. This paper examines using the Traffic Information Services Broadcast (TIS-B) service that is part of ADS-B implementation to provide terrestrial navigation. TIS-B would broadcast an aircraft position report generated using radar measurements. Conceptually, an aircraft may be able to use the reception of its own TIS-B report to provide knowledge of its position. This paper provides an overview of the concept and of the potential capabilities of the system.

Arctic Sea Ice Extent Forecasting Using Support Vector Regression

The summer minimum Arctic sea ice extent has long been used as a measure of climate change, with record lows being reported in recent years. Understanding the dynamics of the Arctic sea ice extent is of utmost importance in understanding the timescales associated with this change. Complex global climate models are typically employed to gain insights about the future of Arctic sea ice, however, these models are typically very computationally expensive to solve and the results are often controversial. Here, we use historical data from remote sensing satellites along with machine learning algorithms in the forecasting of the Arctic sea ice extent. Support Vector Regression is employed in the learning of a dynamic model to represent this system. Validation results demonstrate the ability of the method to successfully forecast both the seasonal and long-term trends in Arctic sea ice coverage.