Robust detection, isolation and accommodation for sensor failures

The objective is to extend the recent advances in robust control system design of multivariable systems to sensor failure detection, isolation, and accommodation (DIA), and estimator design. This effort provides analysis tools to quantify the trade-off between performance robustness and DIA sensitivity, which are to be used to achieve higher levels of performance robustness for given levels of DIA sensitivity. An innovations-based DIA scheme is used. Estimators, which depend upon a model of the process and process inputs and outputs, are used to generate these innovations. Thresholds used to determine failure detection are computed based on bounds on modeling errors, noise properties, and the class of failures. The applicability of the newly developed tools are demonstrated on a multivariable aircraft turbojet engine example. A new concept call the threshold selector was developed. It represents a significant and innovative tool for the analysis and synthesis of DiA algorithms. The estimators were made robust by introduction of an internal model and by frequency shaping. The internal mode provides asymptotically unbiased filter estimates.The incorporation of frequency shaping of the Linear Quadratic Gaussian cost functional modifies the estimator design to make it suitable for sensor failure DIA. The results are compared with previous studies which used thresholds that were selcted empirically. Comparison of these two techniques on a nonlinear dynamic engine simulation shows improved performance of the new method compared to previous technique

Finding RR Lyrae Stars with SkyMapper: an Observational Test

One of the major science goals of the SkyMapper Survey of the Southern Hemisphere sky is the determination of the shape and extent of the halo of the Galaxy. In this paper we quantify the likely efficiency and completeness of the survey as regards the detection of RR Lyrae variable stars, which are excellent tracers of the halo stellar population. We have accomplished this via observations of the RR Lyrae-rich globular cluster NGC 3201. We find that for single epoch uvgri observations followed by two further epochs of g, r imaging, as per the intended three-epoch survey strategy, we recover known RR Lyraes with a completeness exceeding 90%. We also investigate boundaries in the gravity-sensitive single-epoch two-color diagram that yield high completeness and high efficiency (i.e., minimal contamination by non-RR Lyraes) and the general usefulness of this diagram in separating populations.Comment: 10 pages, 5 figures, to appear in the Publications of the Astronomical Society of Australia (PASA), published by Cambridge University Pres

Self modulated dynamics of a relativistic charged particle beam in plasma wake field excitation

Self modulated dynamics of a relativistic charged particle beam is reviewed within the context of the theory of plasma wake field excitation. The self-consistent description of the beam dynamics is provided by coupling the Vlasov equation with a Poisson-type equation relating the plasma wake potential to the beam density. An analysis of the beam envelope self-modulation is then carried out and the criteria for the occurrence of the instability are discussed thereby.Comment: This is a 10 pages manuscript which contain 4 figures. This manuscript is recently submitted in 'Nuclear Instruments and Methods in Physics Research Section A' as a proceeding of the conference 'EAAC 2015

Groundwater Modelling of Dhaka City and Surrounding Areas and Evaluation of the Effect of Artificial Recharge to Aquifers

Dhaka city lies on the Madhupur Clay overlying the Plio-Pliestocene Dupi Tila Formation which forms the principal aquifer. Massive withdrawal of water from this aquifer caused fall of water table at an alarming rate which might provoke subsidence, ecological and environmental hazards [1]. It has been found that the aquifer system of the study area can be divided in to four aquifers and four aquitards up to a depth of 400m. The long term hydrographs for the observation wells within the Dhaka City shows a sharp decline of water level with little or even no fluctuation which indicates over exploitation of aquifers [2]. The water table contour maps of wet and dry season show a pointed cone of depression in the central part of the study area. The research work has been carried out to predict the future response of groundwater level after 20 years for increasing abstraction and assessment of the USAbility of the artificial recharge of aquifers of the Dhaka City using groundwater modelling technique. An eight layer transient groundwater flow model was set up with time steps of a month using MODFLOW. Two model scenarios were considered for model prediction. For the first scenario it has been found that after 20 years the elevation of groundwater level will decline to about -120m in the central part of the Dhaka City, and the mega cone of depression will spread over an area of about 1962 km2. For the second scenario substantial water is injected into the aquifer for recharging the aquifer artificially. The quantity of artificially recharged water was equal to the abstraction of water in Dhaka City. The model predicted that the elevation of the groundwater level after 20 years of pumping will not decline anymore and will be fixed at 70m which is the present minimum groundwater level. The area of the mega cone of depression around Dhaka city will reduce by 945km2 for the next 20 years. As a consequence of artificial recharge predicted environmental degradation in and around Dhaka City can be prevented

Sensor failure detection for jet engines

Revisions to the advanced sensor failure detection, isolation, and accommodation (DIA) algorithm, developed under the sensor failure detection system program were studied to eliminate the steady state errors due to estimation filter biases. Three algorithm revisions were formulated and one revision for detailed evaluation was chosen. The selected version modifies the DIA algorithm to feedback the actual sensor outputs to the integral portion of the control for the nofailure case. In case of a failure, the estimates of the failed sensor output is fed back to the integral portion. The estimator outputs are fed back to the linear regulator portion of the control all the time. The revised algorithm is evaluated and compared to the baseline algorithm developed previously

Micellization Behavior of Ionic Surfactants in Presence of Butanol Isomers in Non-aqueous Solutions

Electrical conductivity and surface tension measurements of various surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate micellar solution,  containing  1-butanol  (1-BuOH),  2-butanol  (2-BuOH)  and tertiary butanol (t-BuOH) in n,n-dimethyl acetamide have been determined at various temperatures. Both methods show that micelles are formed in n,n-dimethyl acetamide  (DMA) solution in the presence of butanol isomers. Critical micelle concentration (cmc) has been determined for each of the surfactants. Critical micelle concentrations have also been measured as a function of temperatures and concentration of butanol isomers added. It is suggested that the addition of alcohol leads to an increase in n,n-dimethyl acetamide penetration into the micellar interface that depends on the alkyl chain configuration for three isomeric alcohols. Thermodynamic parameters of micellization, enthalpy  (ÄH0m,  entropy  (ÄS0m),  and free energy  (ÄG0m)  were determined from the temperature  dependence of  CMC.  The solvent composition dependence of these thermodynamic parameters is determined in terms of the effect of additives on the micellization of ionic surfactants. It is observed that both ÄH0m and ÄS0m bear out not only the observed order of decrease in cmc but also account reasonably the effects produced by differences in alkyl chain configuration for these isomeric alcohols. In all cases ÄG0m < 0, and remained practically constant over the entire solvent composition range studied.  It is suggested that due to different structural consequences of intermolecular interactions,  both enthalpy and entropy must differ in a  mutually compensating manner so that G0m is not significantly affected

Thermodynamics of Dissociation and Micellization of Sodium Surfactant Solutions in Formamide

Electrical conductivity and surface tension measurement of sodium surfactants, such as sodium caprylate, sodium laurate, sodium palmitate and sodium stearate, in formamide has been determined at different temperatures. The methods show that micelles are formed in formamide solution. Critical micelle concentration (CMC) has been determined for each of the sodium surfactants. The result show that these surfactants behave as a weak electrolyte in dilute solution of formamide below the critical micellar concentration, and the conductance result can be explained on the basis of Ostwald’s formula and Debye–Huckle’s theory of weak electrolytes. The dissociation constant and thermodynamic parameters for dissociation and micellization processes of these surfactants are also evaluated. The micellization process has been found to be predominant over the dissociation process. Keywords: Critical Micelle Concentration (CMC), Micellization, Conductivity, Dissociation, Thermodynamics, Surface Tensio