130 research outputs found
Friction Stir Welding of Copper Canisters Using Power and Temperature Control
This thesis presents the development to reliably seal 50 mm thick copper canisters containing the Swedish nuclear waste using friction stir welding. To avoid defects and welding tool fractures, it is important to control the tool temperature within a process window of approximately 790 to 910°C. The welding procedure requires variable power input throughout the 45 minute long weld cycle to keep the tool temperature within its process window. This is due to variable thermal boundary conditions throughout the weld cycle. The tool rotation rate is the input parameter used to control the power input and tool temperature, since studies have shown that it is the most influential parameter, which makes sense since the product of tool rotation rate and spindle torque is power input. In addition to the derived control method, the reliability of the welding procedure was optimized by other improvements. The weld cycle starts in the lid above the joint line between the lid and the canister to be able to abort a weld during the initial phase without rejecting the canister. The tool shoulder geometry was modified to a convex scroll design that has shown a self-stabilizing effect on the power input. The use of argon shielding gas reduced power input fluctuations i.e. process disturbances, and the tool probe was strengthened against fracture by adding surface treatment and reducing stress concentrations through geometry adjustments. In the study, a clear relationship was shown between power input and tool temperature. This relationship can be used to more accurately control the process within the process window, not only for this application but for other applications where a slow responding tool temperature needs to be kept within a specified range. Similarly, the potential of the convex scroll shoulder geometry in force-controlled welding mode for use in applications with other metals and thicknesses is evident. The variable thermal boundary conditions throughout the weld cycle, together with the risk of fast disturbances in the spindle torque, requires control of both the power input and the tool temperature to achieve a stable, robust and repeatable process. A cascade controller is used to efficiently suppress fast power input disturbances reducing their impact on the tool temperature. The controller is tuned using a recently presented method for robust PID control. Results show that the controller keeps the temperature within ±10°C of the desired value during the 360º long joint line sequence. Apart from the cascaded control structure, good process knowledge and control strategies adapted to different weld sequences i.e. different thermal boundary conditions have contributed to the successful results
A cryogenic liquid-mirror telescope on the moon to study the early universe
We have studied the feasibility and scientific potential of zenith observing
liquid mirror telescopes having 20 to 100 m diameters located on the moon. They
would carry out deep infrared surveys to study the distant universe and follow
up discoveries made with the 6 m James Webb Space Telescope (JWST), with more
detailed images and spectroscopic studies. They could detect objects 100 times
fainter than JWST, observing the first, high-red shift stars in the early
universe and their assembly into galaxies. We explored the scientific
opportunities, key technologies and optimum location of such telescopes. We
have demonstrated critical technologies. For example, the primary mirror would
necessitate a high-reflectivity liquid that does not evaporate in the lunar
vacuum and remains liquid at less than 100K: We have made a crucial
demonstration by successfully coating an ionic liquid that has negligible vapor
pressure. We also successfully experimented with a liquid mirror spinning on a
superconducting bearing, as will be needed for the cryogenic, vacuum
environment of the telescope. We have investigated issues related to lunar
locations, concluding that locations within a few km of a pole are ideal for
deep sky cover and long integration times. We have located ridges and crater
rims within 0.5 degrees of the North Pole that are illuminated for at least
some sun angles during lunar winter, providing power and temperature control.
We also have identified potential problems, like lunar dust. Issues raised by
our preliminary study demand additional in-depth analyses. These issues must be
fully examined as part of a scientific debate we hope to start with the present
article.Comment: 35 pages, 11 figures. To appear in Astrophysical Journal June 20 200
Temperature Regulation in Multicore Processors Using Adjustable-Gain Integral Controllers
This paper considers the problem of temperature regulation in multicore
processors by dynamic voltage-frequency scaling. We propose a feedback law that
is based on an integral controller with adjustable gain, designed for fast
tracking convergence in the face of model uncertainties, time-varying plants,
and tight computing-timing constraints. Moreover, unlike prior works we
consider a nonlinear, time-varying plant model that trades off precision for
simple and efficient on-line computations. Cycle-level, full system simulator
implementation and evaluation illustrates fast and accurate tracking of given
temperature reference values, and compares favorably with fixed-gain
controllers.Comment: 8 pages, 6 figures, IEEE Conference on Control Applications 2015,
Accepted Versio
A 1.2-V 10- µW NPN-Based Temperature Sensor in 65-nm CMOS With an Inaccuracy of 0.2 °C (3σ) From 70 °C to 125 °C
An NPN-based temperature sensor with digital output transistors has been realized in a 65-nm CMOS process. It achieves a batch-calibrated inaccuracy of ±0.5 ◦C (3¾) and a trimmed inaccuracy of ±0.2 ◦C (3¾) over the temperature range from −70 ◦C to 125 ◦C. This performance is obtained by the use of NPN transistors as sensing elements, the use of dynamic techniques, i.e. correlated double sampling and dynamic element matching, and a single room-temperature trim. The sensor draws 8.3 μA from a 1.2-V supply and occupies an area of 0.1 mm2
Modeling the Temperature Bias of Power Consumption for Nanometer-Scale CPUs in Application Processors
We introduce and experimentally validate a new macro-level model of the CPU
temperature/power relationship within nanometer-scale application processors or
system-on-chips. By adopting a holistic view, this model is able to take into
account many of the physical effects that occur within such systems. Together
with two algorithms described in the paper, our results can be used, for
instance by engineers designing power or thermal management units, to cancel
the temperature-induced bias on power measurements. This will help them gather
temperature-neutral power data while running multiple instance of their
benchmarks. Also power requirements and system failure rates can be decreased
by controlling the CPU's thermal behavior.
Even though it is usually assumed that the temperature/power relationship is
exponentially related, there is however a lack of publicly available physical
temperature/power measurements to back up this assumption, something our paper
corrects. Via measurements on two pertinent platforms sporting nanometer-scale
application processors, we show that the power/temperature relationship is
indeed very likely exponential over a 20{\deg}C to 85{\deg}C temperature range.
Our data suggest that, for application processors operating between 20{\deg}C
and 50{\deg}C, a quadratic model is still accurate and a linear approximation
is acceptable.Comment: Submitted to SAMOS 2014; International Conference on Embedded
Computer Systems: Architectures, Modeling, and Simulation (SAMOS XIV
Operating Point Optimization of a Hydrogen Fueled Hybrid Solid Oxide Fuel Cell-Steam Turbine (SOFC-ST) Plant
This paper presents a hydrogen powered hybrid solid oxide fuel cell-steam turbine (SOFC-ST) system and studies its optimal operating conditions. This type of installation can be very appropriate to complement the intermittent generation of renewable energies, such as wind generation. A dynamic model of an alternative hybrid SOFC-ST configuration that is especially suited to work with hydrogen is developed. The proposed system recuperates the waste heat of the high temperature fuel cell, to feed a bottoming cycle (BC) based on a steam turbine (ST). In order to optimize the behavior and performance of the system, a two-level control structure is proposed. Two controllers have been implemented for the stack temperature and fuel utilization factor. An upper supervisor generates optimal set-points in order to reach a maximal hydrogen efficiency. The simulation results obtained show that the proposed system allows one to reach high efficiencies at rated power levels.This work has been carried out in the Intelligent Systems and Energy research group of the University of the Basque Country (UPV/EHU) and has been supported by the UFI11/28 research grant of the UPV/EHU and by the IT677-13 research grant of the Basque Government (Spain) and by DPI2012-37363-CO2-01 research grant of the Spanish Ministry of Economy and Competitiveness
Testing Lorentz and CPT symmetry with hydrogen masers
We present details from a recent test of Lorentz and CPT symmetry using
hydrogen masers. We have placed a new limit on Lorentz and CPT violation of the
proton in terms of a recent standard model extension by placing a bound on
sidereal variation of the F = 1 Zeeman frequency in hydrogen. Here, the
theoretical standard model extension is reviewed. The operating principles of
the maser and the double resonance technique used to measure the Zeeman
frequency are discussed. The characterization of systematic effects is
described, and the method of data analysis is presented. We compare our result
to other recent experiments, and discuss potential steps to improve our
measurement.Comment: 26 pages, 16 figure
Nonlinear Fuzzy Model Predictive Control for a PWR Nuclear Power Plant
Reliable power and temperature control in pressurized water reactor (PWR) nuclear power plant is necessary to guarantee high efficiency and plant safety. Since the nuclear plants are quite nonlinear, the paper presents nonlinear fuzzy model predictive control (MPC), by incorporating the realistic constraints, to realize the plant optimization. T-S fuzzy modeling on nuclear power plant is utilized to approximate the nonlinear plant, based on which the nonlinear MPC controller is devised via parallel distributed compensation (PDC) scheme in order to solve the nonlinear constraint optimization problem. Improved performance compared to the traditional PID controller for a TMI-type PWR is obtained in the simulation
Report of the Seasat Failure Review Board
The Seasat spacecraft failed on October 9, 1978, after satisfactory operation in orbit for 105 days, as a result of a loss of electrical power in the Agena bus that was used as a part of the spacecraft. The loss of power was caused by a massive and progressive short in one of the slip ring assemblies that was used to connect the rotating solar arrays into the power subsystem. The most likely cause of this short was the initiation of an arc between adjacent slip ring brush assemblies. The triggering mechanism of this arc could have been either a wire-to-brush assembly contact, a brush-to-brush contact, or a momentary short caused by a contaminant that bridged internal components of opposite electrical polarity
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