2,378 research outputs found
Prototype 9.7 m Schwarzschild-Couder telescope for the Cherenkov Telescope Array: status of the optical system
The Cherenkov Telescope Array (CTA) is an international project for a
next-generation ground-based gamma ray observatory, aiming to improve on the
sensitivity of current-generation experiments by an order of magnitude and
provide energy coverage from 30 GeV to more than 300 TeV. The 9.7m
Schwarzschild-Couder (SC) candidate medium-size telescope for CTA exploits a
novel aplanatic two-mirror optical design that provides a large field of view
of 8 degrees and substantially improves the off-axis performance giving better
angular resolution across all of the field of view with respect to
single-mirror telescopes. The realization of the SC optical design implies the
challenging production of large aspherical mirrors accompanied by a
submillimeter-precision custom alignment system. In this contribution we report
on the status of the implementation of the optical system on a prototype 9.7 m
SC telescope located at the Fred Lawrence Whipple Observatory in southern
Arizona.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Busan, Korea. All CTA contributions at arXiv:1709.0348
A Large-Diameter Hollow-Shaft Cryogenic Motor Based on a Superconducting Magnetic Bearing for Millimeter-Wave Polarimetry
In this paper we present the design and measured performance of a novel
cryogenic motor based on a superconducting magnetic bearing (SMB). The motor is
tailored for use in millimeter-wave half-wave plate (HWP) polarimeters, where a
HWP is rapidly rotated in front of a polarization analyzer or
polarization-sensitive detector. This polarimetry technique is commonly used in
cosmic microwave background (CMB) polarization studies. The SMB we use is
composed of fourteen yttrium barium copper oxide (YBCO) disks and a contiguous
neodymium iron boron (NdFeB) ring magnet. The motor is a hollow-shaft motor
because the HWP is ultimately installed in the rotor. The motor presented here
has a 100 mm diameter rotor aperture. However, the design can be scaled up to
rotor aperture diameters of approximately 500 mm. Our motor system is composed
of four primary subsystems: (i) the rotor assembly, which includes the NdFeB
ring magnet, (ii) the stator assembly, which includes the YBCO disks, (iii) an
incremental encoder, and (iv) the drive electronics. While the YBCO is cooling
through its superconducting transition, the rotor is held above the stator by a
novel hold and release mechanism (HRM). The encoder subsystem consists of a
custom-built encoder disk read out by two fiber optic readout sensors. For the
demonstration described in this paper, we ran the motor at 50 K and tested
rotation frequencies up to approximately 10 Hz. The feedback system was able to
stabilize the the rotation speed to approximately 0.4%, and the measured rotor
orientation angle uncertainty is less than 0.15 deg. Lower temperature
operation will require additional development activities, which we will
discuss
Integrating the RTO in the MPC: an adaptive gradient-based approach
Model Predictive Control (MPC) is the most used advanced control technique in process industries, since it ensures stability, constraints satisfaction and convergence to the setpoint. The optimal setpoint is calculated by the Real Time Optimizer (RTO), minimizing the economic objective taking into account the operational limits of the plant. Since RTO employs complex stationary nonlinear models to perform the optimization and a larger sampling time than the controller, the economic setpoints calculated by the RTO may be inconsistent for the MPC layer and the economic performance of the overall
controller may be worse than expected. The aim of this work is to propose an MPC controller that explicitly integrates the RTO into the MPC control layer. The proposed strategy is based on
the MPC for tracking; the optimization problem to be solved only requires one evaluation of the gradient of the economic cost function at each sampling time. Based on this gradient, a second
order approximation of the economic function is obtained and used in the MPC optimization problem resulting in a convex optimization problem. Recursive feasibility and convergence to the optimal equilibrium point is ensured
Nonlinear model predictive control-based guidance law for path following of unmanned surface vehicles
This work proposes a nonlinear model predictive control-based guidance
strategy for unmanned surface vehicles, focused on path following. The
application of this strategy, in addition to overcome drawbacks of previous
line-of-sight-based guidance laws, intends to enable the application of
predictive strategies also to the low-level control, responsible for tracking
the references provided by the guidance strategy. The stability and robustness
of the proposed strategy are theoretically discussed. Furthermore, given the
non-negligible computational cost of such nonlinear predictive guidance
strategy, a practical nonlinear model predictive control strategy is also
applied in order to reduce the computational cost to a great extent. The
effectiveness and advantages of both proposed strategies over other nonlinear
guidance laws are illustrated through a complete set of simulations.Comment: 21 pages, 15 figures. Postprint of the final published wor
Economic MPC for the management of drinking water networks
Trabajo presentado a la European Control Conference (ECC) celebrada en Estrasburgo (Francia) del 24 al 27 de junio de 2014.This paper addresses the management of drinking water networks (DWNs) regarding a multi-objective cost function by means of economically-oriented model predictive control (EMPC) strategies. Specifically, assuming the water demand and the energy price as periodically time-varying signals, this paper shows that the EMPC framework is flexible to enhance the control of DWNs without relying on hierarchical control schemes that require the use of real-time optimisers (RTO) or steady-state target optimisers (SSTO) in an upper layer. Four different MPC strategies are discussed in this paper: a hierarchical two-layer approach, a standard EMPC where the multi-objective cost function is optimised directly, and two different modifications of the latter, which are meant to overcome possible feasibility losses in the presence of changing operating patterns. The discussed schemes are tested andcompared by means of a case study taken from a part of the Barcelona DWN.This work has been partially funded by the EU Project EFFINET (FP7-ICT-2011-8-31855) and the DGR of Generalitat de Catalunya (SAC group Ref. 2009/SGR/1491).Peer Reviewe
The MAP Satellite Feed Horns
We present the design, manufacturing methods, and characterization of 20
microwave feed horns currently in use on the Microwave Anisotropy Probe (MAP)
satellite. The nature of the cosmic microwave background (CMB) anisotropy
requires a detailed understanding of the properties of every optical component
of a microwave telescope. In particular, the properties of the feeds must be
known so that the forward gain and sidelobe response of the telescope can be
modeled and so that potential systematic effects may be computed. MAP requires
low emissivity, azimuthally symmetric, low-sidelobe feeds in five microwave
bands (K, Ka, Q, V, and W) that fit within a constrained geometry. The beam
pattern of each feed is modeled and compared with measurements; the agreement
is generally excellent to the -60 dB level (80 degrees from the beam peak).
This agreement verifies the beam-predicting software and the manufacturing
process. The feeds also affect the properties and modeling of the microwave
receivers. To this end, we show that the reflection from the feeds is less than
-25 dB over most of each band and that their emissivity is acceptable. The
feeds meet their multiple requirements.Comment: 9 pages with 7 figures, of which 2 are in low-resolution versions;
paper is available with higher quality figures at
http://map.gsfc.nasa.gov/m_mm/tp_links.htm
Performance of Sensitivity based NMPC Updates in Automotive Applications
In this work we consider a half car model which is subject to unknown but
measurable disturbances. To control this system, we impose a combination of
model predictive control without stabilizing terminal constraints or cost to
generate a nominal solution and sensitivity updates to handle the disturbances.
For this approach, stability of the resulting closed loop can be guaranteed
using a relaxed Lyapunov argument on the nominal system and Lipschitz
conditions on the open loop change of the optimal value function and the stage
costs. For the considered example, the proposed approach is realtime applicable
and corresponding results show significant performance improvements of the
updated solution with respect to comfort and handling properties.Comment: 6 pages, 2 figure
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