1,720,996 research outputs found
Fast moving horizon state estimation for discrete-time systems using single and multi iteration descent methods
No full textDescent algorithms based on the gradient,conjugate gradient, and Newton methods are investigated to perform optimization in moving horizon state estimation for discrete-time linear and nonlinear systems. Conditions that ensure the stability of the estimation error are established for single and multi iteration schemes with a least-squares cost function that takes into account only a batch of most recent information. Simulation results show the effectiveness of the proposed approaches also in comparison with techniques based on the Kalman filter
Experimental investigation on concentration profiles and fluctuations of dense gases in wind tunnel
No full textOne of the most frequent accident scenario following a loss of containment during HazMat transportation or processing is represented by the dispersion of a dense gas release. Several dispersion models are available to this purpose, more or less rigorously accounting for gravity slumping, air entrainment and possible heat transfer. Under confined geometry, the correct evaluation of possible concentration fluctuations represent an up-to-date research topic, both considering the process sector and a peculiar application represented by operating theaters for surgery. In this last context, the use of heavier than air gas is usually performed for anaesthetic application, while few validation data are available on the dispersion behavior following a fugitive emission and exposure of persons inside the enclosure. On these bases, the experimental phase of this paper was performed in a laboratory-scale wind tunnel of circular section, under different Reynolds number regimes, considering a continuous release scenario of two tracer gases, namely carbon dioxide and sulphur hexafluoride, at different low release rates. A detailed study on concentration fluctuations and time series is presented yielding reliable information on the influence of the different source types and flow rates. Conclusions are drawn on practical feasibility and application of the experimental results, in view of safe optimization of the design and mode of operation of ventilation systems in the considered settings
Piecewise linear approximations of multivariate functions: a multiresolution-based compression algorithm suitable for circuit implementation
No full textThis paper is concerned with a multiresolution approach to the piecewise-linear approximation of multivariate nonlinear continuous functions. The proposed technique has no restrictions on the number of variables the functions depend on, and is based on the use of piecewise-linear “hat” functions. The approximation levels are related to nested function spaces. The multiresolution approach allows one to define a simple model reduction strategy that is based on a proper error definition. The interest in the piecewise-linear approximations and in the hat functions is motivated by the simplicity of their circuit implementations. The efficiency of the method is tested via two benchmark examples, one of which concerns the approximation of the vector field of a nonlinear dynamical system
Multiresolution PWL approximations
No full textThis paper proposes a method to find multiresolution piecewise-linear (PWL) approximations of multivariate continuous nonlinear functions defined over limited compact domains. The method is derived from the context of PWL prewavelets on arbitrary triangulations and is aimed to the circuit implementations of the obtained approximations. Two illustrative examples are proposed in low-dimensional case studies
Optimal Control of Propagating Fronts by Using Level Set Methods and Neural Approximations
No full textWe address the optimal control of level sets associated with the solution of the normal flow equation. The problem consists in finding the normal velocity to the front described by a certain level set in such a way to minimize a given cost functional. First, the considered problem is shown to admit a solution on a suitable space of functions. Then, since in general it is difficult to solve it analytically, an approximation scheme that relies on the extended Ritz method is proposed to find suboptimal solutions. Specifically, the control law is forced to take on a neural structure depending nonlinearly on a finite number of parameters to be tuned, i.e., the neural weights. The selection of the optimal weights is performed with two different approaches. The first one employs classical line-search descent methods, while the second one is based on a quasi-Newton optimization that can be regarded as neural learning based on the extended Kalman filter. Compared with line-search methods, such an approach reveals to be successful with a reduced computational effort and an increased robustness with respect to the trapping into local minima, as confirmed by simulations in both two and three dimensions
Extended Kalman filtering to design optimal controllers of fronts generated by level set methods
No full textDynamic Programming and Value-Function Approximation in Sequential Decision Problems: Error Analysis and Numerical Results
No full textValue-function approximation is investigated for the solution via Dynamic Programming (DP) of continuous-state sequential N-stage decision problems, in which the reward to be maximized has an additive structure over a finite number of stages. Conditions that guarantee smoothness properties of the value function at each stage are derived. These properties are exploited to approximate such functions by means of certain nonlinear approximation schemes, which include splines of suitable order and Gaussian radial-basis networks with variable centers and widths. The accuracies of suboptimal solutions obtained by combining DP with these approximation tools are estimated. The results provide insights into the successful performances appeared in the literature about the use of value-function approximators in DP. The theoretical analysis is applied to a problem of optimal consumption, with simulation results illustrating the use of the proposed solution methodology. Numerical comparisons with classical linear approximators are presented
Seafarers' work exposure to tonal noise components
No full textThe requirement of better workers' psychophysical health and the wish to guarantee a correct comfort also during work activities, induce to consider the presence of significant pure tones also for the working spaces. However, the current European legislation regarding professional exposure to the noise of the workers, and namely the EU Directive 2003/10/CE, does not take into consideration the possible presence of pure tones in working noise. The same lack can be noticed in the standard ISO 1999:2013. As regards seafarers, the reference codes are the International Maritime Organization (IMO) Resolution A.468(XII) for ships built before 1 July 2014, and Resolution MSC.337(91) for newer ships. While tonal components are mentioned in the first one, stating that, if these are "obvious", the ISO noise rating (NR) number should be also determined, in the latter and most recent IMO Resolution no reference to tonal components is present. Tonal components cause annoyance and, at the same time, they induce hearing damage and can alter the behavior of workers, with a potential risk for the safety of ships. In this study, noise measurements taken onboard different ships are analyzed in order to determine seafarers' work exposure to tonal components. The survey includes different work spaces. To assess the presence of tonal components in crew's work environments the methodology of environmental noise analysis, defined in the Annex B of Italian Decree D.M. 16/3/98, has been used, making reference to ISO 226:2003 for determining normal equal-loudness level contours. The method used in order to evaluate tonal components is well established for the environmental noise annoyance and therefore it can be operatively extended to the workplace noise exposure. Results show that the presence of tonal disturbing components is not sporadic and therefore worthy of further analysis and regulation
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