A CSP model for simple non-reversible and parallel repair plans

Thiswork presents a constraint satisfaction problem (CSP) model for the planning and scheduling of disassembly and assembly tasks when repairing or substituting faulty parts. The problem involves not only the ordering of assembly and disassembly tasks, but also the selection of them from a set of alternatives. The goal of the plan is the minimization of the total repairing time, and the model considers, apart from the durations and resources used for the assembly and disassembly tasks, the necessary delays due to the change of configuration in the machines, and to the transportation of intermediate subassemblies between different machines. The problem considers that sub-assemblies that do not contain the faulty part are nor further disassembled, but allows non-reversible and parallel repair plans. The set of all feasible repair plans are represented by an extended And/Or graph. This extended representation embodies all of the constraints of the problem, such as temporal and resource constraints and those related to the selection of tasks for obtaining a correct plan.Ministerio de Educación y Ciencia DIP2006-15476-C02-0

A Constraint-based Model for Multi-objective Repair Planning

This work presents a constraint based model for the planning and scheduling of disconnection and connection tasks when repairing faulty components in a system. Since multi-mode operations are considered, the problem involves the ordering and the selection of the tasks and modes from a set of alternatives, using the shared resources efficiently. Additionally, delays due to change of configurations and transportation are considered. The goal is the minimization of two objective functions: makespan and cost. The set of all feasible plans are represented by an extended And/Or graph, that embodies all of the constraints of the problem, allowing non reversible and parallel plans. A simple branch-and-bound algorithm has been used for testing the model with different combinations of the functions to minimize using the weighted-sum approach.Ministerio de Educación y Ciencia DIP2006-15476-C02-0

Automated Hierarchical, Forward-Chaining Temporal Planner for Planetary Robots Exploring Unknown Environments

The transition of mobile robots from a controlled environment towards the real-world represents a major leap in terms of complexity coming primarily from three different factors: partial observability, nondeterminism and dynamic events. To cope with them, robots must achieve some intelligence behaviours to be cost and operationally effective. Two particularly interesting examples of highly complex robotic scenarios are Mars rover missions and the Darpa Robotic Challenge (DRC). In spite of the important differences they present in terms of constraints and requirements, they both have adopted certain level of autonomy to overcome some specific problems. For instance, Mars rovers have been endowed with multiple systems to enable autonomous payload operations and consequently increase science return. In the case of DRC, most teams have autonomous footstep planning or arm trajectory calculation. Even though some specific problems can be addressed with dedicated tools, the general problem remains unsolved: to deploy on-board a reliable reasoning system able to operate robots without human intervention even in complex environments. This is precisely the goal of an automated mission planner. The scientific community has provided plenty of planners able to provide very fast solutions for classical problems, typically characterized by the lack of time and resources representation. Moreover, there are also a handful of applied planners with higher levels of expressiveness at the price of lowest performance. However, a fast, expressive and robust planner has never been used in complex robotic missions. These three properties represent the main drivers for the outcomes of the thesis. To bridge the gap between classical and applied planning, a novel formalism named Hierarchical TimeLine Networks (HTLN) combining Timeline and HTN planning has been proposed. HTLN has been implemented on a mission planner named QuijoteExpress, the first forward-chaining timeline planner to the best of our knowledge. The main idea is to benefit from the great performance of forward-chaining search to resolve temporal problems on the state-space. In addition, QuijoteExpress includes search enhancements such as parallel planning by division of the problem in sub-problems or advanced heuristics management. Regarding expressiveness, the planner incorporates HTN techniques that allow to define hierarchical models and solutions. Finally, plan robustness in uncertain scenarios has been addressed by means of sufficient plans that allow to leave parts of valid plans undefined. To test the planner, a novel lightweight, timeline and ROS-based executive named SanchoExpress has been designed to translate the plans into actions understandable by the different robot subsystems. The entire approach has been tested in two realistic and complementary domains. A cooperative multirover Mars mission and an urban search and rescue mission. The results were extremely positive and opens new promising ways in the field of automated planning applied to robotics

Study of Hybrid Solar Gas Turbine System: T100 Modeling and Dynamic Analysis of Thermal Energy Storage

Concentrated Solar Power (CSP) hybrid gas turbine systems particularly based on the micro Gas Turbines (mGT) will be of great importance in future power infrastructure where energy security, economic feasibility and clean and efficient power generation are the key concerns. Integration of Thermal Energy Storage (TES) in CSP hybrid gas turbine systems could be a viable solution to overcome the intermittent nature of solar power, and increase the dispatchability. Based on this perception, a comprehensive analysis of both mGT cycle and TES technology should be undertaken, in order to achieve a better understanding of the behavior of TES and its interaction with other components in a hybrid gas turbine system. The present work intends to contribute to this analysis through mGT and TES system modeling and testing. This thesis is framed in two main parts: first part deals with T100 mGT modeling and second part focuses on the study of thermal storage systems. Regarding TES, detailed dynamic analysis of sensible heat storage is provided, while a preliminary study of thermochemical storage is conducted. The mGT performance diagnosis involves the development for steady-state simulation of T100, model validation, and application in real operating conditions at the Ansaldo Energia AE-T100 test rig. Furthermore, diagnostic application of the AE-T100 model for whole mGT cycle is discussed with the help of two case studies at AE-T100 test rig. AE-T100 model has also been applied in the real operating conditions of micro Humid Air Turbine (mHAT) system located at Vrije Universiteit Brussel (VUB), to highlight the modeling capability of AE-T100 tool as well as monitoring the recuperator performance in the VUB-mHAT cycle. The second part of this work concerns the dynamic modeling and experimental validation of a sensible TES system at laboratory scale, which is part of the Hybrid Solar Gas Turbine (HSGT) system developed at the University of Genova. TES is modeled with the help of a two-dimensional CFD model based on the ANSYS-FLUENT code, and a one-dimensional TRANSEO model employing software designed by the Thermochemical Power Group (TPG) at the University of Genova. The experimental validation, modeling capability to present the actual thermal stratification and State of Charge (SoC) of the TES, and scope of each model are also discussed. This study also highlighted the potential of TES system based on the monolithic structures for hybrid gas turbine systems i.e. low pressure drop across the TES which are acceptable for the whole gas turbine hybrid system, modular structure of the storage and very low thermal losses. In addition to the sensible heat storage system, ThermoChemical Storage (TCS) based on the redox cycle of cobalt oxides pair Co3O4\CoO was finally studied by the candidate during research period at Zhejiang University, China. The mathematical model which has been developed in MATLAB is based on the mass and energy conservation and reaction kinetics of the redox cycle, and has been validated against the experimental data available from literature. This work was aimed to study the process of thermochemical storage and understand the reaction kinetics of cobalt oxides with less computational effort. This analysis will help in design and optimization of the actual TCS system at the Zhejiang University, China. Overall, the knowledge and modelling capabilities developed for mGT cycle and TES systems in this study will be merged to develop a single simulation tool for mGT based CSP hybrid systems, in the future

Performance and Cost Analysis of a Structured Concrete Thermocline Thermal Energy Storage System

Increasing global energy demands and diminishing fossil fuel resources have raised increased interest in harvesting renewable energy resources. Solar energy is a promising candidate, as sufficient irradiance is incident to the Earth to supply the energy demands of all of its inhabitants. At the utility scale, concentrating solar power (CSP) plants provide the most cost-efficient method of harnessing solar energy for conversion to electrical energy. A major roadblock to the large-scale implementation of CSP plants is the lack of thermal energy storage (TES) that would allow the continued production of electricity during the absence of constant irradiance. Sensible heat TES has been suggested as the most viable form of TES for CSP plants. Two-tank fluid TES systems have been incorporated at several CSP plants, significantly enhancing the performance of the plants. A single-tank thermocline TES system, requiring a reduced liquid media volume, has been suggested as a cost-reducing alternative. Unfortunately, the packed-aggregate bed of such TES system introduces the issue of thermal ratcheting and rupture of the tank\u27s walls. To address this issue, it has been suggested that structured concrete be used in place of the aggregate bed. Potential concrete mix designs have been developed and tested for this application. Finite-difference-based numeric models are used to study the performance of packed-bed and structured concrete thermocline TES systems. Optimized models are developed for both thermocline configurations. The packed-bed thermocline model is used to determine whether or not assuming constant fluid properties over a temperature range is an acceptable assumption. A procedure is developed by which the cost of two-tank and single-tank thermocline TES systems in the capacity range of 100-3000 MWhe can be calculated. System Advisory Model is used to perform life-cycle cost and performance analysis of a central receiver plant incorporating four TES scenarios: no TES, two-tank TES, packed-bed thermocline TES, and structured concrete thermocline TES. Conclusions are drawn as to which form of TES provides the most viable option. Finally, concrete specimens cast from the aforementioned mix designs are tested in the presence of molten solar salt, and their applicability as structured filler material is assessed

Salt Dependence of Thermodynamic Stability of a Cold-Active DNA Polymerase I Fragment

P. ingrahamii is a halo-psychrophilic bacterium isolated from Arctic sea ice. We have cloned and purified the large fragment of the cold-active DNA polymerase I from P. ingrahamii, named Klenpin. The objective of this project is to directly compare the thermodynamic stability of Klenpin, and the salt dependence of that stability, with Klenow and Klentaq; two homologous polymerases from a mesophile (E. coli) and a thermophile (Thermus aquaticus). We first examined the effects of salts on the thermal stability (Tm) of Klenpin and Klenow across the Hofmeister series. Significantly different trends were observed on the melting temperature changes for Klenpin versus Klenow, even in chaotropic salts such as guanidine hydrochloride at low concentrations. Klenow responded to Hofmeister stabilizing salts and destabilizing salts as expected, while Klenpin was stabilized by all salts, even those that normally destabilize proteins. We further examined the salt effect on the structure of Klenpin and Klenow using CD spectra, Trp fluorescence quenching, and dynamic light scattering. The results show that salt alters the structure of Klenpin to a more compact conformation, whereas no significant influence is observed in Klenow. Salt also alters the unfolding process of Klenpin. In chemical denaturation, an intermediate is observed in the presence of salt, whereas Klenpin folds following a two-state model without salt. An increase in free energy of unfolding of Klenpin is also seen upon the addition of NaCl, and this improvement is mainly from the additional unfolding transition introduced due to the intermediate. We hypothesize that non-specific screening of unfavorable electrostatic interactions on the surface of Klenpin may be responsible for many of the observed salt effects and several computational comparisons were conducted to test this hypothesis. Unlike those typically found for archaebacterial halophilic proteins, no significant difference is observed in the comparison of amino acid preference between Klenpin and Klenow. But the electrostatic surface potential maps of Klenpin, Klenow, and Klentaq show larger clusters of acidic and basic residues on the Klenpin surface, supporting our hypothesis that salts modify Klenpin through the nonspecific screening of unfavorable electrostatic interactions on the surface