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To provide an approach to active vibration reduction of flexible spacecraft actuated by on‐off thrusters during attitude control for spacecraft designers, which can help them analysis and design the attitude control system.

The new approach includes attitude controller acting on the rigid hub, designed by using pulse‐width pulse‐frequency modulation integrated with component command technique, and the piezoelectric material elements as sensors/actuators bonded on the surface of the beam appendages for active vibration suppression of flexible appendages, designed by optimal positive position feedback (OPPF) control technique. The OPPF compensator is devised by setting up a cost function to be minimized by feedback gains, which are subject to the stability criterion at the same time, and an extension to the conventional positive position feedback control design approach is investigated.

Numerical simulations for the flexible spacecraft show that the precise attitude control and vibration suppression can be accomplished using the derived vibration attenuator and attitude control controller.

Studies on how to control the on‐off actuated system under impulse disturbances are left for future work.

An effective method is proposed for the spacecraft engineers planning to design attitude control system for actively suppressing the vibration and at the same time quickly and precisely responding to the attitude control command.

The advantage in this scheme is that the controllers are designed separately, allowing the two objectives to be satisfied independently of one another. It fulfils a useful source of theoretical analysis for the attitude control system design and offers practical help for the spacecraft designers.

This paper presents the analysis of a nonlinear on/off control system including a filter of a second order in the closed loop. The proposed system is capable of generating a pulse width modulation which is used to design and built up a PWM (Pulse Width Modulation) chopper dedicated to regulate fluctuating power supplies such as photovoltaic, wind turbine systems; etc. The use of the second order filter aims to compensate the output against the fluctuations of irradiation as well as the variation of the load. The study essentially focuses on determining the relationship between the pulse durations with respect to system parameters and technological requirements. The theoretical study is followed by a simulation of a DC-DC chopper.

This paper aims to study the minimizing of energy consumption in air cooled-heat exchanger through a convenient control system. Thus, the performance of a given air cooler has been considered in different weather conditions for both ideal and non ideal operations.

The minimum number of fans in service has been calculated and used for the study and assessment of a proper controlling system with the purpose of energy saving in air coolers. On-Off controlling has been compared to variable speed drivers controlling to determine a feasible method for the process control of this cooling equipment.

Economical parameters show that installing variable speed drivers could be rational, as the payback period, the net present values of investment and the internal rate of return are completely persuading. The internal rate of return (IRR) for installation of variable speed driver (VSD) controls is 69 per cent. According to the results, there is a possibility of 0.45 and 0.33 MWh energy consumption reduction for VSD control under ideal and non-ideal conditions and consequently reduces annually 318 and 237 ton equivalent CO₂.

Air cooled heat exchangers are used as one of the energy consumption equipment in most plants, but before the emergence of serious problems, not enough attention was given to their operation.

This paper aims to show the current situation and additional requirements for the aircraft automation systems based on the lessons learned from the two 737 MAX crashes.

In this study, the Swiss cheese model was used to find the real root causes of the 737 MAX accidents. Then, the results have been compared with the actions taken by the manufacturers and authorities. Based on the comparison, the necessary improvements to prevent such accidents are defined. Regarding the faulty sensor that forms the accidents, a synthetic sensor was developed using an aerodynamic model.

It has been proven that the safety-critical automation systems should not be designed by relying on a single set of sensor data. Automation levels should be defined in a standard way. Depending on the defined automation level, the system must be designed as either fail-safe or fail-operational system. When designing backup systems, it should be decided by looking at not only whether it has power but also the accuracy of the incoming signals.

Aviation certification requirements related to automation systems need to be revised and improved. With this context, it was revealed that the certification processes for automation systems should be re-evaluated and updated by aviation authorities, especially Federal Aviation Administration and European Union Aviation Safety Agency.

Task sharing between automation system and pilot based on the classification of automation levels and determining certification requirements accordingly has been brought to the agenda. A synthetic Angle of Attack sensor was developed by using an aerodynamic model for fault detection and diagnosis.

This paper initially presents the results of the analysis of a non linear on/off control system which is capable of generating a pulse width modulation (PWM). This technique can be used to design PWM choppers that can be dedicated to regulate fluctuating power supplies (photovoltaic, wind turbines, etc.). However, since the PWM losses mainly depend on the switching frequency, thus, the determination of an optimal frequency is required. Indeed, on the one hand, we seek to operate at high frequencies to reduce the residual noise by filtering. On the other hand, there is a limitation of the switching frequency due to the physical switching elements properties. Therefore, a compromise has to be made in order to determine an optimal switching frequency that minimizes the switching power losses. The main objective of this work is to present a technique that enables to sizing the chopper parameters based on the minimizing of the switching losses. An illustrative example of the proposed technique for sizing a PWM chopper is presented.

This paper initially presents the results of the analysis of a non linear on/off control system which is capable of generating a pulse width modulation (PWM). This technique can be used to design PWM choppers that can be dedicated to regulate fluctuating power supplies (photovoltaic, wind turbines, etc.). However, since the PWM losses mainly depend on the switching frequency, thus, the determination of an optimal frequency is required. Indeed, on the one hand, we seek to operate at high frequencies to reduce the residual noise by filtering. On the other hand, there is a limitation of the switching frequency due to the physical switching elements properties. Therefore, a compromise has to be made in order to determine an optimal switching frequency that minimizes the switching power losses. The main objective of this work is to present a technique that enables to sizing the chopper parameters based on the minimizing of the switching losses. An illustrative example of the proposed technique for sizing a PWM chopper is presented.

The purpose of this study was to examine lighting systems at 77 laboratories located within one building to save energy and associated costs.

Field measurements of illumination were conducted and compared to lighting standards and industry recommendations.

For energy and cost saving, de-lamping all four-lamp luminaires down to two-lamp luminaires and installing occupancy sensors in all laboratories were recommended.

The research team’s project working hours and study period were limited. This study begins to fill the gap in the literature regarding lighting field studies.

By carefully considering light level recommendations, industry standards and installation budgets, existing facilities can install appropriate retrofits to save energy and money without sacrificing illumination levels. Recommended retrofits are anticipated to significantly curtail annual federal energy consumption practices at the labs.

The retrofits recommended in this study will reduce US federal government’s energy-related expenditures and greenhouse gas emissions in support of the 2010 Presidential Mandate. The proposed occupancy sensors are anticipated to compensate for humans’ failure to manually control lighting.

This field study adds value by documenting cost-effective methods to measure, record and manage laboratory lighting, and it calls for the implementation of social, economic and ecological interventions. The recommended retrofits will reduce US federal government’s energy-related expenditures and greenhouse gas emissions in support of the 2010 Presidential Mandate.

When electricity was cheap, manual block light switching on a first‐in, last‐out basis was acceptable, with the result that many buildings were lit for up to 15 hours a day irrespective of the contribution of daylight or even of the presence of people. Behavioural studies at the Building Research Establishment (BRE) have shown that switching on occurs at the start of occupancy if the daylight is judged to be insufficient, but switching off only occurs when the space becomes empty. In other words, while people are very good at turning lights on when they feel they need them, they are very forgetful when it comes to switching them off when they are no longer required.

FOLLOWING its acquisition by BTR the aerospace activities of Dunlop have been reorganised and now include the Aviation Division in Coventry the Aircraft Tyres Division in Birmingham, the Precision Rubber Division and Serek Aviation. All manner of design and development work can be undertaken relating to tyres, wheels, brakes, brake management systems and the many hydraulic, pneumatic and electronically controlled systems manufactured by the company. This work is greatly helped by the comprehensive range of testing facilities available and the instrumentation and analysis equipment for a wide variety of aircraft components.

THE Hawk is a low cost/low‐cost‐of‐ownership, close air support/ground attack aircraft designed for world‐wide operation. Having a gross take‐off mass of about 16,000 lb and powered by the Rolls‐Royce Turboméca Ltd Adour Mk. 151 turbofan developing some 23,8 kN (5340 lb) sea‐level static thrust.