26,586 research outputs found
Model-based Aeroservoelastic Design and Load Alleviation of Large Wind Turbine Blades
This paper presents an aeroservoelastic modeling approach for dynamic load alleviation
in large wind turbines with trailing-edge aerodynamic surfaces. The tower, potentially on a
moving base, and the rotating blades are modeled using geometrically non-linear composite
beams, which are linearized around reference conditions with arbitrarily-large structural
displacements. Time-domain aerodynamics are given by a linearized 3-D unsteady vortexlattice
method and the resulting dynamic aeroelastic model is written in a state-space
formulation suitable for model reductions and control synthesis. A linear model of a single
blade is used to design a Linear-Quadratic-Gaussian regulator on its root-bending moments,
which is finally shown to provide load reductions of about 20% in closed-loop on the full
wind turbine non-linear aeroelastic model
Accelerator Design for the CHESS-U Upgrade
During the summer and fall of 2018 the Cornell High Energy Synchrotron Source
(CHESS) is undergoing an upgrade to increase high-energy flux for x-ray users.
The upgrade requires replacing one-sixth of the Cornell Electron Storage Ring
(CESR), inverting the polarity of half of the CHESS beam lines, and switching
to single-beam on-axis operation. The new sextant is comprised of six
double-bend achromats (DBAs) with combined-function dipole-quadrupoles.
Although the DBA design is widely utilized and well understood, the constraints
for the CESR modifications make the CHESS-U lattice unique. This paper
describes the design objectives, constraints, and implementation for the CESR
accelerator upgrade for CHESS-U
BICEP2 II: Experiment and Three-Year Data Set
We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
(=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales.Comment: 30 pages, 24 figure
Modeling and analysis of nonlinear rotordynamics due to higher order deformations in bending
A mathematical model incorporating the higher order deformations in bending is devel- oped and analyzed to investigate the nonlinear dynamics of rotors. The rotor system con- sidered for the present work consists of a flexible shaft and a rigid disk. The shaft is modeled as a beam with a circular cross section and the Euler Bernoulli beam theory is applied with added effects such as rotary inertia, gyroscopic effect, higher order large deformations, rotor mass unbalance and dynamic axial force. The kinetic and strain (defor- mation) energies of the rotor system are derived and the RayleighâRitz method is used to discretize these energy expressions. Hamiltonâs principle is then applied to obtain the mathematical model consisting of second order coupled nonlinear differential equations of motion. In order to solve these equations and hence obtain the nonlinear dynamic response of the rotor system, the method of multiple scales is applied. Furthermore, this response is examined for different possible resonant conditions and resonant curves are plotted and discussed. It is concluded that nonlinearity due to higher order deformations significantly affects the dynamic behavior of the rotor system leading to resonant hard spring type curves. It is also observed that variations in the values of different parameters like mass unbalance and shaft diameter greatly influence dynamic response. These influences are also presented graphically and discussed
Aeroelastic effects in multirotor vehicles. Part 2: Methods of solution and results illustrating coupled rotor/body aeromechanical stability
This report is a sequel to the earlier report titled, Aeroelastic Effects in Multi-Rotor Vehicles with Application to Hybrid Heavy Lift System, Part 1: Formulation of Equations of Motion (NASA CR-3822). The trim and stability equations are presented for a twin rotor system with a buoyant envelope and an underslung load attached to a flexible supporting structure. These equations are specialized for the case of hovering flight. A stability analysis, for such a vehicle with 31 degrees of freedom, yields a total of 62 eigenvalues. A careful parametric study is performed to identify the various blade and vehicle modes, as well as the coupling between various modes. Finally, it is shown that the coupled rotor/vehicle stability analysis provides information on both the aeroelastic stability as well as complete vehicle dynamic stability. Also presented are the results of an analytical study aimed at predicting the aeromechanical stability of a single rotor helicopter in ground resonance. The theoretical results are found to be in good agreement with the experimental results, thereby validating the analytical model for the dynamics of the coupled rotor/support system
The strain-based beam finite elements in multibody dynamics
We present a strain-based finite-element formulation for the dynamic analysis of flexible elastic planar multibody systems, composed of planar beams. We consider finite displacements, rotations and strains. The discrete dynamic equations of motion are obtained by the collocation method. The strains are the basic interpolated variables, which makes the formulation different from other formulations. The further speciality of the formulation is the strong satisfaction of the cross-sectional constitutive conditions at collocation points. In order to avoid the nested integrations, a special algorithm for the numerical integration over the length of the finite element is proposed. The midpoint scheme is used for the time integration. The performance of the formulation is illustrated via numerical examples, including a stiff multibody system. (c) 2007 Elsevier Ltd. All rights reserved
Chiral microstructures (spirals) fabrication by holographic lithography
We present an optical interference model to create chiral microstructures
(spirals) and its realization in photoresist using holographic lithography. The
model is based on the interference of six equally-spaced circumpolar linear
polarized side beams and a circular polarized central beam. The pitch and
separation of the spirals can be varied by changing the angle between the side
beams and the central beam. The realization of the model is carried out using
the 325 nm line of a He-Cd laser and spirals of sub-micron size are fabricated
in photoresist.Comment: 6 page
Aeronautical Engineering: A continuing bibliography, supplement 120
This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980
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Finite element for the analysis of rotor-dynamic systems that include gyroscopic effects
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents new finite element formulations for the analysis of rotor-dynamic systems that include the effects of gyroscopic influence. Euler-Bernoulli finite elements have been created for both shaft and propeller descriptions. In addition to the gyroscopic effects, centrifugal stiffening has been considered for the propeller elements. The principle of virtual work has been used to determine the equations of motion and formulate element matrices. The proposed element matrices have been incorporated in the VIBRATIO suite of vibration analysis software in order to test the formulations. The software uses an innovative hybrid modelling technique that enables the user to analyse various dynamic problems including rotating beam elements with rigid body attachments. A model of a ship's drive shaft has been created in VIBRATIO for comparison against a verified ANSYS model. Results for forced vibration shaft analysis show excellent correlation between VIBRATIO's Euler shaft formulation and ANSYS's Timoshenko formulation. Incremental analyses of propeller systems using the novel gyroscopic formulation show gyroscopic effects of flexible blade attachments, and also the changing mode shapes and frequencies due to centrifugal stiffening. Results show gyroscopic and centrifugal stiffening effects must not be ignored for an accurate propeller analysis.This work was financially supported by Brunel University
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