scholarly journals Nonlinear Analysis and Bifurcation Characteristics of Whirl Flutter in Unmanned Aerial Systems

Drones ◽  
2021 ◽  
Vol 5 (4) ◽  
pp. 122
Author(s):  
Anthony Quintana ◽  
Rui Vasconcellos ◽  
Glen Throneberry ◽  
Abdessattar Abdelkefi
Keyword(s):  
Degrees Of Freedom ◽  
Structural Characteristics ◽  
Nonlinear Effects ◽  
Unmanned Aerial Systems ◽  
Reduced Order ◽  
Structural Nonlinearities ◽  
Whirl Flutter ◽  
Aerial Systems ◽  
Fifth Order ◽  
Dangerous Behaviors

Aerial drones have improved significantly over the recent decades with stronger and smaller motors, more powerful propellers, and overall optimization of systems. These improvements have consequently increased top speeds and improved a variety of performance aspects, along with introducing new structural challenges, such as whirl flutter. Whirl flutter is an aeroelastic instability that can be affected by structural or aerodynamic nonlinearities. This instability may affect the prediction of potentially dangerous behaviors. In this work, a nonlinear reduced-order model for a nacelle-rotor system, considering quasi-steady aerodynamics, is implemented. First, a parametric study for the linear system is performed to determine the main aerodynamic and structural characteristics that affect the onset of instability. Multiple polynomial nonlinearities in the two degrees of freedom nacelle-rotor model are tested to simulate possible structural nonlinear effects including symmetric cubic hardening nonlinearities for the pitch and yaw degrees of freedom; purely yaw nonlinearity; purely pitch nonlinearity; and a combination of quadratic, cubic, and fifth-order nonlinearities for both degrees of freedom. Results show that the presence of hardening structural nonlinearities introduces limit cycle oscillations to the system in the post-flutter regime. Moreover, it is demonstrated that the inclusion of quadratic nonlinearity introduces asymmetric oscillations and subcritical behavior, where large and potentially dangerous deformations can be reached before the predicted linear flutter speed.

Guidance of Multi-Agent Fixed-Wing Aircraft Using a Moving Mesh Method

2016 ◽  
Vol 04 (03) ◽  
pp. 227-244 ◽  
Author(s):  
A Ram Kim ◽  
Shawn Keshmiri ◽  
Weizhang Huang ◽  
Gonzalo Garcia
Keyword(s):  
Degrees Of Freedom ◽  
Moving Mesh ◽  
Unmanned Aerial Systems ◽  
Moving Mesh Method ◽  
Large Solution ◽  
Mesh Method ◽  
Spatial Dimensions ◽  
Multi Agent ◽  
Aerial Systems ◽  
Mesh Technique

This paper presents a novel guidance logic for multi-agent fixed-wing unmanned aerial systems using a moving mesh method. The moving mesh method is originally designed for use in the adaptive numerical solution of partial differential equations, where a high proportion of mesh points are placed in the regions of large solution variations and few points in the rest of the domain. In this work, the positions of the aircraft are considered as mesh nodes connected to form a triangular mesh in two spatial dimensions. The outer aircraft positions are planned with the reference point algorithm. This logic provides the outer agents moving point positions that are relative to a virtual point position with the desired heading angle and velocity. The inner agents, or interior mesh nodes, are moved with a moving mesh technique to keep the whole mesh as uniform as possible. The moving mesh technique has built-in mechanisms to keep the mesh as uniform as possible and prevent nodes from crossing over or tangling. This property can be seen as an automatic internal collision avoidance mechanism. It also has explicit formulas for nodal velocities, making the technique easy to implement on computer. The mesh nodes are replaced by unmanned aerial systems with nonlinear six degrees of freedom dynamics. The centralized moving mesh guidance is complimented by a decentralized nonlinear predictive controller to control each aircraft. To validate flexibility and coherency of agents and formation, the moving point concept is used in the simulation to follow an arbitrary, linear, sinewave-like, or curvature shaped flight segments. Robustness of the algorithm is also verified where agents were affected by external wind.

scholarly journals DIGITAL STORAGE AND THE DATA COLLECTION FOR THE SEISMIC PREVENTION: A COMPARISON FROM THE ITALIAN RECENT EXPERIENCES

2019 ◽  
Vol XLII-2/W11 ◽  
pp. 325-329
Author(s):  
E. Brusa
Keyword(s):  
Structural Characteristics ◽  
Unmanned Aerial Systems ◽  
The Public ◽  
Fire Brigade ◽  
Built Heritage ◽  
Digital Storage ◽  
Laser Scanners ◽  
Remotely Piloted Aircraft ◽  
Public Archives ◽  
Aerial Systems

<p><strong>Abstract.</strong> Concerning the care of our Built Heritage, one of the most important problem that was observed after an earthquake is the speed in the reaction, aiming to minimize the damages provoked by the shakes. As a matter of fact, the necessary time for the reaction of the rescue teams should be not too long, in order to avoid further damages provoked by the future shakes. Thus, the best way to minimize this type of damage is to design appropriate shoring systems that replace the lack of stiffness provoked by earthquake as soon as possible. In this sense, it’s necessary to know many information of a damaged monument, such as: the geometry, the materials and the structural characteristics, the presence of previous alterations and/or restorations, etc. Unfortunately, the accessibility to this kind of information is not always available after an earthquake, due to the possible damages provoked to the buildings, where the public archives and the documentation are normally stored (L’Aquila 2009, Amatrice 2016).</p><p>The awareness of this problem started immediately after the serious earthquake that hit the city of L’Aquila in 2009. Then, it became more urgent after 2016, when the extended and continued earthquake in the Centre of Italy provoked increasing damages to buildings and monuments. In particular, an important role in the churches’ collapses that had occurred during this last earthquake was due to the difficulty in finding the necessary information to design proper shoring systems.</p><p>Nowadays, starting from the experience of L’Aquila, teams composed by functionaries of the Ministry of Culture, engineers from different universities and special members of the Fire Brigade have developed and improved various models for the management of the emergency phases. Using the modern geomatics tools (i.e. Unmanned Aerial Systems (UAS), Terrestrial Laser Scanners (TLS), Remotely Piloted Aircraft Systems (RPAS)), it’s possible to achieve the digital acquisition of many building’s data and characteristics (i.e. through the 3D Object recognition and reconstruction, the point cloud analysis, etc.).</p><p>This article examines some of the most interesting solutions that were adopted after the recent Italian earthquakes (L’Aquila 2009, Emilia-Lombardia 2012, Centre of Italy 2016) by some of the major public Entities (Superintendences, Italian Fire Brigade). Moreover, it evaluates the possibility to enhance both the competences and the tools that have been until now developed, with the purpose to use them for an effective Built Heritage prevention, without having to wait a new emergency phase to adopt them.</p>

LIGHTER-THAN-AIR (LTA) UNMANNED AERIAL SYSTEM (UAS) CARRIER CONCEPT FOR SURVAILLANCE AND DISASTER MANAGEMENT

2019 ◽  
Vol 3 ◽  
pp. 1255
Author(s):  
Ahmad Salahuddin Mohd Harithuddin ◽  
Mohd Fazri Sedan ◽  
Syaril Azrad Md Ali ◽  
Shattri Mansor ◽  
Hamid Reza Jifroudi ◽  
...  
Keyword(s):  
Unmanned Aerial Vehicles ◽  
Disaster Management ◽  
Unmanned Aerial Systems ◽  
Unmanned Aerial System ◽  
Border Control ◽  
Aerial Vehicles ◽  
Operational Safety ◽  
In Situ Methods ◽  
Aerial Systems

Unmanned aerial systems (UAS) has many advantages in the fields of SURVAILLANCE and disaster management compared to space-borne observation, manned missions and in situ methods. The reasons include cost effectiveness, operational safety, and mission efficiency. This has in turn underlined the importance of UAS technology and highlighted a growing need in a more robust and efficient unmanned aerial vehicles to serve specific needs in SURVAILLANCE and disaster management. This paper first gives an overview on the framework for SURVAILLANCE particularly in applications of border control and disaster management and lists several phases of SURVAILLANCE and service descriptions. Based on this overview and SURVAILLANCE phases descriptions, we show the areas and services in which UAS can have significant advantage over traditional methods.

Beach and dune impacts due to Hurricane Florence in Dare County, North Carolina

Shore & Beach ◽  
2019 ◽  
pp. 44-49 ◽  
Author(s):  
Elizabeth Sciaudone ◽  
Liliana Velasquez-Montoya
Keyword(s):  
North Carolina ◽  
Prior Knowledge ◽  
Unmanned Aerial Systems ◽  
State University ◽  
National Wildlife Refuge ◽  
Sediment Samples ◽  
Wildlife Refuge ◽  
Full Report ◽  
Aerial Systems

Less than two weeks after Hurricane Florence made landfall in North Carolina (NC), a team of researchers from NC State University traveled to Dare County to investigate the storm’s effects on beaches and dunes. Using available post-storm imagery and prior knowledge of vulnerabilities in the system, the team identified several locations to visit in the towns of Kitty Hawk, Nags Head, Rodanthe, Buxton, and Hatteras, as well as a number of locations within the Pea Island National Wildlife Refuge (Figure 1). Data collected included topographic profiles, still imagery and video from unmanned aerial systems, sediment samples, and geo-located photography. This Coastal Observations piece presents some of the data and photos collected; the full report is available online (Sciaudone et al. 2019), and data collected will be made available to interested researchers upon request.

A Comparative Economic Study on the Use of Unmanned Aerial Systems versus Motorcycles to Transport Laboratory Samples in Liberia

2019 ◽  
Author(s):  
Walter Ochieng ◽  
Tun Ye ◽  
Christina M. Scheel ◽  
Aun Lor ◽  
John M. Saindon ◽  
...  
Keyword(s):  
Unmanned Aerial Systems ◽  
Economic Study ◽  
Aerial Systems
Sign in / Sign up

Export Citation Format

Share Document