• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 204
  • 44
  • 43
  • 20
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 480
  • 293
  • 100
  • 91
  • 91
  • 91
  • 69
  • 61
  • 59
  • 59
  • 40
  • 39
  • 39
  • 38
  • 36
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
211

Flight Testing Small UAVs for Aerodynamic Parameter Estimation

Chase, Adam Thomas 01 June 2014 (has links)
A flight data acquisition system was developed to aid unmanned vehicle designers in verifying the vehicle's design performance. The system is reconfigurable and allows the designer to choose the correct combination of complexity, risk, and cost for a given flight test. The designer can also reconfigure the system to meet packaging and integration requirements. System functionality, repeatbility, and accuracy was validated by collecting data during multiple flights of a radio-controlled aircraft. Future work includes sensor fusion, thrust prediction methods, stability and control derivative estimation, and growing Cal Poly's small-scale component aerodynamic database.
212

Modeling and Testing Powerplant Subsystems of a Solar UAS

Bughman, Luke J. 01 October 2019 (has links)
In order to accurately conduct the preliminary and detailed design of solar powered Unmanned Aerial Systems (UAS), it is necessary to have a thorough understanding of the systems involved. In particular, it is desirable to have mathematical models and analysis tools describing the energy income and expenditure of the vehicle. Solar energy income models may include available solar irradiance, photovoltaic array power output, and maximum power point tracker efficiency. Energy expenditure models include battery charging and discharging characteristics, propulsion system efficiency, and aerodynamic efficiency. In this thesis, a series of mathematical models were developed that characterize the performance of these systems. Several of these models were then validated against test data. Testing was conducted on specific components used by a solar UAS designed and built by students at the California Polytechnic State University, San Luis Obispo, which completed a six-hour flight relying only on solar energy in May 2019. Results indicate that, while some models accurately predicted test outcomes, others still need further improvement. While these models may be useful during the preliminary and detailed design phases of a solar powered UAS, specific component testing should be conducted to converge on the most desired design solution.
213

Design Methods for Remotely Powered Unmanned Aerial Vehicles

Howe, William Beaman 01 March 2015 (has links) (PDF)
A method for sizing remotely powered unmanned aerial vehicles is presented to augment the conventional design process. This method allows for unconventionally powered aircraft to become options in trade studies during the initial design phase. A design matrix is created that shows where, and if, a remotely powered vehicle fits within the design space. For given range and power requirements, the design matrix uses historical data to determine whether an internal combustion or electrical system would be most appropriate. Trends in the historical data show that the break in the design space between the two systems is around 30 miles and 1 kW. Electrical systems are broken into subcategories of onboard energy sources and remote power sources. For this work, only batteries were considered as an onboard energy source, but both lasers and microwaves were considered for remote power transmission methods. The conventional sizing method is adjusted to so that it is based on energy consumption, instead of fuel consumption. Using the manner in which microwaves and laser propagate through the atmosphere, the weight fraction of a receiving apparatus is estimated. This is then used with the sizing method to determine the gross takeoff weight of the vehicle. This new sizing method is used to compare battery systems, microwave systems, and laser systems.
214

Enabling Rapid Conceptual Design Using Geometry-Based Multi-Fidelity Models in Vsp

Belben, Joel Brian 01 April 2013 (has links) (PDF)
The purpose of this work is to help bridge the gap between aircraft conceptual design and analysis. Much work is needed, but distilling essential characteristics from a design and collecting them in an easily accessible format that is amenable to use by inexpensive analysis tools is a significant contribution to this goal. Toward that end, four types of reduced-fidelity or degenerate geometric representations have been defined and implemented in VSP, a parametric geometry modeler. The four types are degenerate surface, degenerate plate, degenerate stick, and degenerate point, corresponding to three-, two-, one-, and zero- dimensional representations of underlying geometry, respectively. The information contained in these representations was targeted specifically at lifting line, vortex lattice, equivalent beam, and equivalent plate theories, with the idea that suitability for interface with these methods would imply suitability for use with many other analysis techniques. The ability to output this information in two plain text formats— comma separated value and Matlab script—has also been implemented in VSP, making it readily available for use. A modified Cessna 182 wing created in VSP was used to test the suitability of degenerate geometry to interface with the four target analysis techniques. All four test cases were easily completed using the information contained in the degenerate geometric types, and similar techniques utilizing different degenerate geometries produced similar results. The following work outlines the theoretical underpinnings of degenerate geometry and the fidelity-reduction process. It also describes in detail how the routines that create degenerate geometry were implemented in VSP and concludes with the analysis test cases, stating their results and comparing results among different techniques.
215

A realization of integrated satellite-terrestrial communication networks for aeronautical services via joint radio resource management

Cheng, Yongqiang, Xu, Kai J., Pillai, Anju, Pillai, Prashant, Hu, Yim Fun, Ali, Muhammad, Ahmed, Adeel January 2013 (has links)
Despite air travel has not grown as predicted, air travel is still expected to rise to just less than doubling the current figure by 2030. This creates an urging need to develop more efficient Air Traffic Management (ATM) solutions. Around the globe, research and development initiatives have been launched to modernize the air traffic control infrastructures. These modernized infrastructures will be built around continuous information gathering, sharing and transferring of data between aircraft and air navigation service providers and airports ground infrastructure, which will be difficult for current aeronautical communications systems to handle. As a result, new communication infrastructures are required to manage future aeronautical communication traffic demand. This paper proposes an integrated aeronautical communication architecture consisting of four radio access technologies for communications between aircrafts and ground Aeronautical Telecommunication Network (ATN). The design and implementation of a Joint Radio Resource Management (JRRM) framework to manage these radio resources are discussed. The design is verified by a proof-of-concept JRRM prototype which is developed for the management of radio resource between the Inmarsat Broadband Global Area Network (BGAN) and the Aeronautical Mobile Airport Communication System (AeroMACS).
216

Optimal datalink selection for future aeronautical telecommunication networks

Alam, Atm S., Hu, Yim Fun, Pillai, Prashant, Xu, K., Baddoo, J. 08 May 2017 (has links)
Yes / Modern aeronautical telecommunication networks (ATN) make use of different simultaneous datalinks to deliver robust, secure and efficient ATN services. This paper proposes a Multiple Attribute Decision Making based optimal datalink selection algorithm which considers different attributes including safety, QoS, costs and user/operator preferences. An intelligent TRigger-based aUtomatic Subjective weighTing (i-TRUST) method is also proposed for computing subjective weights necessary to provide user flexibility. Simulation results demonstrate that the proposed algorithm significantly improves the performance of the ATN system. / Innovate U.K. Project SINCBAC-Secure Integrated Network Communications for Broadband and ATM Connectivity: Application number 18650-134196.
217

Space-Time Coding for the Advanced Range Telemetry Continuous Phase Modulation

Leatham, Robert L 08 April 2020 (has links)
Aeronautical telemetry systems that transmit the same signal through multiple antennas from the flight vehicle suffer from severe link dropouts when the signals destructively interfere one with another at receiver. The underlying issue is a transmit array with element spacing far greater than the wavelength producing a transmit antenna pattern with significant and deep nulls. Recently, space-time coding techniques have been proven to resolve the issue for systems using linear modulations and shaped-offset quadrature shift keying (SOQPSK) modulation, a non-linear continuous phase modulation (CPM). This thesis examines application of space-time coding techniques to resolve the self-interference issue for another CPM modulation, the advanced range telemetry (ARTM) CPM. It is shown in this thesis among the two branches of space-time coding, space-time block coding (STBC) and space-time trellis coding (STTC), only the latter offers a solution for a full rate, low complexity, no hardware modification implementation. Various candidate STTCs are identified via simulation using the pair-wise error probability as a performance metric. One STTC is identified with trivial implementation costs and an error performance that is a function of code length.
218

Network coding for multicast communications over satellite networks

Jaff, Esua K., Susanto, Misfa, Ali, Muhammad, Pillai, Prashant, Hu, Yim Fun January 2015 (has links)
No / Random packet errors and erasures are common in satellite communications. These types of packet losses could become significant in mobile satellite scenarios like satellite-based aeronautical communications where mobility at very high speeds is a routine. The current adaptive coding and modulation (ACM) schemes used in new satellite systems like the DVBRCS2 might offer some solutions to the problems posed by random packet errors but very little or no solution to the problems of packet erasures where packets are completely lost in transmission. The use of the current ACM schemes to combat packet losses in a high random packet errors and erasures environment like the satellite-based aeronautical communications will result in very low throughput. Network coding (NC) has proved to significantly improve throughput and thus saves bandwidth resources in such an environment. This paper focuses on establishing how in random linear network coding (RLNC) the satellite bandwidth utilization is affected by changing values of the generation size, rate of packet loss and number of receivers in a satellite-based aeronautical reliable IP multicast communication. From the simulation results, it shows that the bandwidth utilization generally increases with increasing generation size, rate of packet loss and number of receivers.
219

Parametric Optimization Of A Wing-Fuselage System Using A Vorticity-Based Panel Solver

Cruz, Chino 01 December 2023 (has links) (PDF)
Aerodynamic topology optimization is a useful tool in the aerodynamic design pro-cess, especially when looking for marginal gains within a design. One example isa turboprop racer concept aircraft that is designed with the goal of breaking worldspeed records. An optimization framework was developed with the intention of laterbeing applied to this design. In the early design stages, the optimization frameworkmust focus on quicker methods of drag estimation, such as a panel codes. The largenumber of design variables in topology optimization can exponentially increase func-tion evaluations and thus computational cost. A vorticity-based panel solver wasproven out for this application to reduce the computational cost while keeping theaccuracy of the results similar to that of traditional CFD solvers in conditions with-out prominent flow separation. The framework developed here includes geometryparameterization, function evaluation scripting, and post-processing, which are allrun within the optimization algorithm. The designs used to validate the solver arewing-fuselage systems of various sailplane configurations with existing experimentaldata. These sailplane designs were also used as the initial geometry to demonstratethe framework. A parametric optimum was found to reduce drag by 9%, but it mustbe noted that this method does have certain trade offs and limitations.
220

A redundancy software design for joint radio resource management system in a satellite-terrestrial based aeronautical communication network

Cheng, Yongqiang, Xu, Kai J., Hu, Yim Fun January 2013 (has links)
No / This paper presents a Master/Slave redundancy mechanism for the airborne Integrated Modular Radio to improve the reliability of the joint radio resource management (JRRM) system. The proposed mechanism adopts keep-alive heart beat messages and real time information synchronization to ensure a smooth switchover in the event of a platform failure. To enhance the scalability and decoupling of the system, the proposed hot swap solution makes the JRRM switchover transparent to both the higher layers and the lower layers. The experiment results and the performance obtained from the test-bed has proved the validity of the solution.

Page generated in 0.0667 seconds