Low-Order Modeling For A Small-Scale Flybarless Helicopter UAV A Grey-Box Time-Domain Approach

2012 ◽  
Author(s):  
Skander Taamallah
Keyword(s):  
Time Domain ◽  
Small Scale ◽  
Low Order

A Critical Analysis on Low-Order Simulation Models for Darrieus VAWTs: How Much Do They Pertain to the Real Flow?

2018 ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
Giovanni Ferrara ◽  
Giacomo Persico ◽  
Vincenzo Dossena ◽  
...  
Keyword(s):  
Flow Field ◽  
Incidence Angle ◽  
Computational Cost ◽  
Simulation Models ◽  
Small Scale ◽  
Critical Issues ◽  
Overall Performance ◽  
Lift And Drag ◽  
Real Flow ◽  
Low Order

To improve the efficiency of Darrieus wind turbines, which still lacks from that of horizontal-axis rotors, Computational Fluid Dynamics (CFD) techniques are now extensively applied, since they only provide a detailed and comprehensive flow representation. Their computational cost makes them, however, still prohibitive for routine application in the industrial context, which still makes large use of low-order simulation models like the Blade Element Momentum (BEM) theory. These models have been shown to provide relatively accurate estimations of the overall turbine performance; conversely, the description of the flow field suffers from the strong approximations introduced in the modelling of the flow physics. In the present study, the effectiveness of the simplified BEM approach was critically benchmarked against a comprehensive description of the flow field past the rotating blades coming from the combination of a two-dimensional unsteady CFD model and experimental wind tunnel tests; for both data sets, the overall performance and the wake characteristics on the mid plane of a small-scale H-shaped Darrieus turbine were available. Upon examination of the flow field, the validity of the ubiquitous use of induction factors is discussed, together with the resulting velocity profiles upstream and downstream the rotor. Particular attention is paid on the actual flow conditions (i.e. incidence angle and relative speed) experienced by the airfoils in motion at different azimuthal angles, for which a new procedure for the post-processing of CFD data is here proposed. Based on this model, the actual lift and drag coefficients produced by the airfoils in motion are analyzed and discussed, with particular focus on dynamic stall. The analysis highlights the main critical issues and flaws of the low-order BEM approach, but also sheds new light on the physical reasons why the overall performance prediction of these models is often acceptable for a first-design analysis.

Angle Sensor Based on Golden Spiral–Shaped Tapered Ring Resonator Using Finite Difference Time-Domain Method

2015 ◽  
Vol 781 ◽  
pp. 462-465 ◽  
Author(s):  
S. Harnsoongnoen ◽  
U. Charoen-In ◽  
S. Pattitanang ◽  
C. Auntarin ◽  
N. Angkawisittpan
Keyword(s):  
Finite Difference ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Dynamic Range ◽  
Time Domain Method ◽  
Ring Resonators ◽  
Small Scale ◽  
Angle Sensor ◽  
Domain Method ◽  
Difference Time

In this paper, an angle sensor based on coplanar waveguides (CPWs) loaded with golden spiral–shaped tapered ring resonators (GS-RRs) is proposed. The E-fields and H-fields of the GS-RRs were simulated and analyzed using finite difference time-domain method (FDTD). It is shown that the proposed sensor has a high dynamic range and linearity for rotation sensing. The proposed sensor can be operated at a single fixed resonant frequency (6.32 GHz) which is inexpensive and probably for superior interest in a small scale structure using MEMS technology.

Vortex-Induced Vibrations on Flexible Cylindrical Structures Coupled With Non-Linear Oscillators

2009 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Kazuo Nishimoto ◽  
Jaap de Wilde
Keyword(s):  
Time Domain ◽  
Lift Coefficient ◽  
Domain Model ◽  
Scale Model ◽  
Small Scale ◽  
Current Profile ◽  
Flexible Cylinder ◽  
Vortex Induced Vibrations ◽  
Offshore Industry ◽  
New Time

The recent escalade of the oil prices encourages the search and exploration of new oil fields. This represents a challenge to engineers, due to more difficult conditions of operation in harsh environments and deeper reservoirs. The offshore industry faces, in the edge of technology with new necessities and limiting conditions imposed by the environment, an increase in the cost of production. It is, therefore, of vital importance to have the equipments operating at the most optimized conditions in order to reduce these costs. VIV software developed in the frequency domain was successful in designing risers and pipelines using large safety factors and making conservative assumptions. These tools only predict single-mode vibrations. In this perspective, the present paper describes the results obtained from a new time-domain code developed to assess the vortex-induced vibrations of a long flexible cylinder. A time-domain analysis was chosen because this suits the problem well, since it is able to predict and calculate different modes of vibrations. In the model, a cylinder is divided into elements that can be exposed to an arbitrary current profile. Each of these elements is free to oscillate parallel and transversely to the flow, and is coupled to a pair of van der Pol’s wake oscillators. This simulates the vortex shedding and, therefore, the fluctuating nature of drag and lift coefficient during the occurrence of VIV. The governing equations are solved by 4th-Order Runge-Kutta schemes in time domain. The new time-domain model is compared with small scale model test data from benchmarking.

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