Martin Widden

The spring-and-lever balancing mechanism, George Carwardine and the Anglepoise lamp

Abstract Two short and direct methods of exact analysis of the spring-and-lever balancing mechanism are presented. It is shown that perfect balance can be achieved by the use of a close-coiled spring whose free length is effectively zero and whose stiffness is chosen appropriately. The two-degree-of-freedom balancing mechanism, commonly seen in desk lamps but useful in many other situations, is then analysed. The treatment is extended to allow for the weight of the components of the mechanism itself. The originator of these devices was George Carwardine, whose patents over the period 1931–35 show the evolution of his ideas on this subject. A short biographical note is included as an appendix.

Experimental and computed natural frequencies of square pultruded GRP plates: effects of anisotropy, hole size ratio and edge support conditions

Experiments have been carried out to determine the free vibration frequencies and mode shapes of 3.2 mm thick, pultruded GRP, square plates with six combinations of clamped (C), simply supported (S) and free (F) edge supports. Comparison of experimental and theoretical/numerical frequencies confirms that thin homogeneous orthotropic/anisotropic plate theory provides a reasonable model for predicting the free vibration response of pultruded GRP plates. Additional vibration experiments were carried out on plates with central circular cutouts. The hole size ratios were varied from about 0.1 to 0.4 for three combinations of clamped (C) and simply supported (S) edge conditions. Finite-element (FE) frequency and mode shape predictions based on orthotropic plate theory were again shown to be in reasonable agreement with the experimental frequencies and modes.

Calculation of the performance of resonant wave energy converters in real seas

It is well known that the performance of point-absorber wave energy converters (WECs) depends upon resonance with the wave frequency. Indeed, the ideal performance of a resonating point-absorber WEC in a regular sea that can be represented by a simple sinusoid is well known, provided all motions are small and remain in the linear region. However, the performance of such a device in a more realistic, irregular sea that is not represented by a simple sinusoid cannot be so readily calculated. The first difficulty lies in modelling the hydrodynamic behaviour of the device. Recent developments in representing the hydrodynamic diffraction and radiation forces have enabled relatively simple simulation models to be developed, such as those presented and used in this paper. The second difficulty lies in the design of the device itself. In a regular sea with a known wave frequency, the settings of the power take-off system can be defined at well-known optimum values. It is shown in the present paper that, even when the wave frequency is not constant, the local wave frequency can be estimated, and this estimate can be used to adjust the power take-off system settings to maintain quasiresonance and, hence, approach the level of performance in a comparable regular sea. In this manner, for irregular seas it is possible to identify a dominant wave frequency over a relatively short time period and to use this frequency continuously to adjust the power take-off system settings, so as to adapt to the current sea conditions. This is likely, in some sea conditions, to involve the power take-off supplying power over part of the cycle, rather than absorbing it. This will increase the demands placed on the power take-off - particularly on its efficiency when the direction of power flow has to be reversible. The relative performance of such a tuneable point-absorber WEC is assessed in the paper. It is shown that the power converted in irregular seas could be as much as 50 per cent of the rated power, where the latter estimate is equivalent to the power converted in a corresponding regular sea.

The exploitation of low-head hydropower by pressure interchange with air, using siphons

Abstract The paper describes and analyses a hydropower system based on siphons in which the pressure of low-head water is converted into air pressure. The analysis suggests that, with careful design of the flow passages to minimize losses, air-pumping efficiencies of 70 per cent or more should be achievable; the overall efficiency of the hydropower system should be better than 60 per cent. Although such values of efficiency are lower than usually found in hydro plant, the economics of the system are likely to be attractive owing to the low capital cost of the system compared with conventional water turbine systems. It is shown that a siphon plant is suitable, in single-stage from, for heads up to about 1.7m. For higher heads the system can be used in two or more stages.

Design–build–test of model aerofoils for engineering education using FDM

A practical project undertaken by many first-year Engineering students at Lancaster University is to design, build and test a model wind turbine. Until recently it was difficult to produce convincing aerofoil shapes at small scale, but the recent acquisition of a fused-deposition modeller (FDM) has provided an opportunity to improve the accuracy of the model aerofoils that students can produce. This paper discusses the design method and tools used by the students, and the production of test blades. Particular note is made of the effects of the FDM construction on the blades, including the orientation of build and resulting surface finish, structural issues, and cost. Samples of graphics from student reports are presented, including some results for the efficiency of the turbines.

Analysis of a pitching-and-surging wave-energy converter that reacts against an internal mass, when operating in regular sinusoidal waves

The paper examines the behaviour of a pitching-and-surging wave-energy converter driven by unidirectional waves that exert harmonically varying forces on its hull. The power take-off (PTO) is by means of an inertia that moves either on a straight horizontal rail or on an arm that turns about a horizontal axis. Angular displacements are taken to be small, so that linear analysis is appropriate; these are idealized conditions, but any wave-energy converter must be able to operate effectively in ideal conditions. For good power capture with the least engineering difficulties, it is found that the power take-off inertia should be centred as high as possible above the overall centre of mass G. It is shown that power is captured from the waves by motion of the centre of pressure P relative to the overall centre of mass G. This can only result from motion in pitch and is dependent on the fact that there is a large vertical distance between points P and G. It is found in practical cases that the added mass of water generally brings G closer to P, and this limits the power that can be captured.

The development of a rapid-prototyping technique for mechatronic-augmented heavy plant

Abstract Telechiric, semi-autonomous and autonomous heavy plant is finding an increasing role in applications such as construction, sub-sea work and decommissioning. There is a need for improved operator interfaces for such plant, and hence for rapid-prototyping tools which link the development of the operator interface with control and operational strategies and with machine geometries. The paper sets out a strategy by which different operator interfaces can be readily evaluated while at the same time generating the requisite information structure for the control of real items of plant. The proposed system is based on the use of interconnected PCs, one to simulate the operator interface and another to provide a kinematic representation of the machine using an appropriate “desk-top reality” environment. This system offers a safe, practical, rapid and cost-effective means of assessing proposed operator interfaces, as well as facilitating the development of machine kinematic structures and the associated operational and control strategies.

Function Cost of Pressure Vessels and Rolling Element Bearings

The aim of function costing is to provide designers with a technique for estimating costs directly from the specification of a product or system. This paper provides function cost information for pressure vessels and rolling element bearings. It is shown that the cheapest pressure vessels are much longer and thinner than vessels in common use, i.e. pipes. The costs of both roller and ball bearings are approximately proportional to their load capacities. For bearings selected on the basis of their fatigue performance, i.e. when the dynamic load rating is used for selection, the most economic bearing is that with the greatest value for the ratio D/d. The effect of not achieving this optimum ratio of D/d is also shown.

A BASIC DESIGN-BUILD-TEST EXPERIENCE: MODEL WIND TURBINE USING ADDITIVE MANUFACTURE

This paper describes a project undertaken by most first-year Engineering undergraduates at Lancaster University in which they are set the task to design, build and test a scale-model wind turbine.

Use of Virtual Reality in Automation Development for Construction Plant

Abstract This paper is concerned with the design and implementation of user interfaces associated with construction plant and equipment and proposes some future developments that the technology under investigation offers to the control engineer in developing algorithms in parallel with the machine which they are seeking to control. Research at Lancaster University has achieved significant progress in the field of advanced large mobile robots for a number of years, in particular with LUCIE (Lancaster University Computerised Intelligent Excavator). For such developments the work has often been conducted either using scale models of actual plant, or computer simulations that produce predictions, generally as graphs, of the performance of the new techniques. The output of this offers an understanding of the control requirements of large complex machines operating in unstructured environments.