Attitude control without angular velocity measurement: a passivityapproach

It is well known that the linear feedback of the quaternion of the attitude error and the angular velocity globally stabilizes the attitude of a rigid body. In this note, we show that the angular velocity feedback can be replaced by a nonlinear filter of the quaternion, thus removing the need for direct angular velocity measurement. In contrast to other approaches, this design exploits the inherent passivity of the system; a model-based observer reconstructing the velocity is not needed. An application of the proposed scheme is illustrated for the robot control problem. Simulation results are included to illustrate the theoretical results     

Water network cost optimization in a paper mill based on a new library of mathematical models

The increasing costs associated with water supply and the disposal of wastewater has stimulated industries to seek more efficient water management systems. Mathematical modelling and simulation can be a very valuable tool for the study of the multiple alternatives available whilst assessing optimum solutions for water management in industry. This study introduces a new steady state model library able to reproduce industrial water circuits. It has been implemented in a novel software framework for the representation, simulation and optimization of industrial water networks. A water circuit representing a paper mill has been modelled and simulated showing the capability to reproduce real case studies. Alternative scenarios for the water network have also been tested to assess the capability of the models to optimize water circuits minimizing total cost.     

Challenges for integrated design (ID) in sustainable buildings

It is often argued that integrated design (ID) is a powerful way to enhance collaboration in construction projects. This collaboration is seen as a way of improving innovation to create more sustainable buildings. Contrary to the traditional silo-type and linear design process, ID is based on upfront stakeholder involvement and a holistic approach to project decision-making. Although ID’s premises are theoretically-founded, a close empirical look at its practices shows that numerous challenges compromise its results and efficiency. This study examines the ID process through an iterative process that includes the construction of a conceptual framework and its empirical validation. We examine three green construction projects in Canada. Based on the analysis of 26 interviews with key project stakeholders and more than 198 construction documents, the study assembles – and ultimately applies – a multi-lens framework based on four themes: the fragmented nature of construction; risk perception; stakeholders’ commitment; and efficiency in the design process. Results show that three tensions arise in ID practices: between collaboration and process efficiency, between short-term and long-term goals, and between integrated methods and traditional ones. The study sheds light on ID limits and reveals how stakeholders can improve their interactions to design more sustainable buildings.     

Practical Application of New Simulation Methods for the Elimination of Geometric Instabilities in Centerless Grinding

Elimination of geometric lobing in centerless grinding has been extensively investigated. Several models have been successfully developed, but no practical tool has been implemented on machines to ease the setting up of the machine to ensure stable conditions. This paper describes a software tool which has been developed for setting up and optimization of centerless plunge grinding processes to avoid geometric instabilities. The software generates stability maps showing the stable and non-stable geometric configurations and the number of lobes generated in non-stable conditions. Complementary time domain models quantitatively predict the evolution of the profile error for each geometric configuration.     

A systems view of temporary housing projects in post‐disaster reconstruction

Natural cataclysms (earthquakes, hurricanes and so forth) become natural disasters when they coincide with vulnerabilities; unfortunately, informal settlements in developing countries are only too often highly vulnerable – a reality amply and unhappily confirmed by available statistics. In this context, reconstruction projects are sandwiched between the short‐term necessity to act promptly and the long‐term requirements of sustainable community development – a situation that is currently reflected in alternative and conflicting paradigms at the policy level.

Adopting a case‐study approach, we explore the use of temporary housing within two post‐disaster environments, where the impact of different organizational designs leads to fundamentally different solutions to the short‐term housing problem.

Our research adopts a dynamic systems approach, associating strategic organizational team design with the development of tactical technical proposals. Two case studies from Turkey and Colombia show that a coherent approach to the sequential stages of providing immediate shelter, temporary housing and permanent reconstruction is not always obtained. The research results emphasize that the performance of reconstruction projects is directly linked to the design and management of the project team.     

Global tracking sliding mode control for a class of nonlinear systems via variable gain observer

A novel output‐feedback sliding mode control strategy is proposed for a class of single‐input single‐output (SISO) uncertain time‐varying nonlinear systems for which a norm state estimator can be implemented. Such a class encompasses minimum‐phase systems with nonlinearities affinely norm bounded by unmeasured states with growth rate depending nonlinearly on the measured system output and on the internal states related with the zero‐dynamics. The sliding surface is generated by using the state of a high gain observer (HGO) whereas a peaking free control amplitude is obtained via a norm observer. In contrast to the existing semi‐global sliding mode control solutions available in the literature for the class of plants considered here, the proposed scheme is free of peaking and achieves global tracking with respect to a small residual set. The key idea is to design a time‐varying HGO gain implementable from measurable signals. Copyright © 2010 John Wiley & Sons, Ltd.     

Understanding differences in construction project governance between developed and developing countries

Whereas most experts recognize the substantial differences in the construction sector between developed and developing countries, very little is known about how and to what extent construction project governance actually differs between the two contexts. In order to shed light on these differences, a suitable definition of project governance must be adopted and identical variables must be assessed in developed and developing contexts. Three characteristics of temporary multi-organizations that conduct construction projects (used here as categories of analysis) help identify these differences: formal structuring, informal structuring, and the role and participation of stakeholders. Based on three case studies, a survey, and semi-directed interviews, significant differences are found in how power and authority are exercised (and leadership styles applied), in the use of informality and in the roles assumed by stakeholders. Although the analysis of such differences is often considered a diagnosis of problems to be ‘fixed’ in projects in developing countries, we believe that these differences should be read as project governance mechanisms of adaptation to different environmental conditions, and therefore key elements that need to be fully understood by professionals working in developing countries.     

New results on output-feedback variable structure model-referenceadaptive control: design and stability analysis

The variable structure model-reference adaptive control(VS-MRAC) redesign and stability analysis, presented previously by the authors (1993) for the case of plants with relative degree n*⩽2, is generalized to the case of arbitrary n*⩾1. This paper presents a complete stability analysis in the general case. The redesign is based on the explicit consideration of input disturbances which may include the disturbance originated by the uncertainty of the plant high-frequency gain. This leads to a considerably simpler and less restrictive stability analysis as well as to a systematic controller design for external disturbance rejection. The overall error system is globally exponentially stable with respect to a small residual set. Robustness to unmodeled dynamics is also discussed     

A variable structure model reference robust control without a prior knowledge of high frequency gain sign

The design of a variable structure model reference robust control without a prior knowledge of high frequency gain sign is presented. Based on an appropriate monitoring function, a switching scheme for some control signals is proposed. It is shown that after a finite number of switching, the tracking error converges to zero at least exponentially for plants with relative degree one or converges exponentially to a small residual set for plants with higher relative degree, and the input disturbance can be completely rejected without affecting the tracking performance.