Papers by Keyword: Source Identification

Abstract: A systematic iterative dynamic programming procedure is proposed for on-line motion planning of mobile sensor network nodes in a specified spatial domain in such a way as to maximize the identification accuracy of an unknown contamination source. The design criterion is a general scalar measure defined on the Fisher information matrix associated with the estimated coordinates of the contamination source. The approach converts the problem to an optimal control one in which the control forces of the sensors are optimized using iterative dynamic programming.

Abstract: China has to confront the groundwater resources crisis and the deterioration of groundwater environment. Reinforcing the studies on groundwater pollution source identification (GPSI) could be an important support to contamination removing, groundwater protecting, drinking water security, and development of society and economy. Exploring the new theory and method on GPSI could push the studies on ill-posed problems, and improve the techniques of contamination remediation. GPSI has been studied for thirty years, and a brief review is given to conclude the characteristics of GPSI problems. The mathematical simulation method can be classified into four types: optimization method, analytical and regression method, direct method, and stochastic method. A specific review of optimization approaches is given in this paper. The configuration, simulation procedures, common optimization algorithms used by the optimization methods are discussed in detail. Both non-heuristic and heuristic algorithm can be used to solve the PSI problem. The heuristic algorithm is more suitable for complex numerical and field cases, but it is time-consuming. The non-heuristic algorithm, especially the algorithm combined with analytical method, is time-economical, but is not suitable for complicated numerical and field tests. Further researches may focus on more complex GPSI problems, expressing physical chemistry and biological process, improving efficiency and model uncertainty of GPSI modeling.

Abstract: Thirty-eight groundwater samples from three deep seated aquifers (the Quaternary, the Coal bearing and the Taiyuan Fm aquifers) had been collected from three coal mines in northern Anhui Province, China for analyzing their major ions, and the statistical methods (correlation, cluster and discriminant analysis) had been processed for evaluating the source of ions and relationship between aquifers. The results suggest that: (1) the chemical signatures of the groundwater are mainly controlled by dissolution of plagioclase, K-feldspar and calcite; (2) the aquifers had been mixed with each other, especially the mixing between the Quaternary aquifer and the Taiyuan Fm aquifer. Discriminant analysis has produced two functions and a diagram, which can be used for water source discrimination.

Abstract: Oil spill; Source identification; δ15N; Nitrogen isotope profile; biodegradation Abstract. A preliminary evaluation of nitrogen isotope analysis as a novel, alternative method for identifying spilled oils is presented. The nitrogen isotopic compositions of crude oil from different oilfields in China may be significantly different, which provides a way of screening possible sources for spilled oil of unknown origin, especially in areas of heavy tanker traffic carrying oils from different geographical regions. The value of δ15N increases gradually with the degree of biodegradation. This findings can be applied for correlation and differentiation of spilled oils at their lightly to moderately weathered stages.

Abstract: When a metal or composite structure begins to fail, for example due to high cycle fatigue, acoustic emissions caused by the propagation of cracks give rise to bursts of ultrasonic waves travelling through the structure. The health of a structure can be monitored by means of sensors which detect these waves. Acoustic emissions are often generated in experiments by breaking a pencil lead against the surface of the structure in a standardised way but the forces that this imparts are not well understood at present. A Local Interaction Simulation Approach (LISA) algorithm has been implemented to simulate the propagation of ultrasonic waves. This code has been validated against experiments in previous work and has been shown to accurately reproduce the propagation of Lamb waves (including reflections and dispersion etc.) within thin-plate like structures. This paper deals with the use of the LISA code to characterise the forces associated with standard pencil lead breaks. The displacement due to waves emanating from a break is measured and a Differential Evolution (DE) optimisation scheme is used to find the optimal profile of forcing to match the simulation with experiment.

Abstract: Ultra-precision raster milling is one of the most significant techniques for the fabrication of high precision components with the surface roughness less than 10nm and form errors less than 0.2 um, without the need for any subsequent polishing. However, no matter how well a machine may be designed, there is a limit to the accuracy that can be achieved. This paper studies the machining errors caused by the diamond tool and the axis motions using Freeform 705G. With an empirical approach, the error sources are separated based on their effects on the surface finish. The main source leading to poor surface finish is identified. This establishes a basis for subsequent error compensation and equipment maintenance.