Dynamic condition monitoring of buried gas pipes

This paper describes a device which can be used to detect variation in the integrity of the surrounding medium which supports buried gas pipes. The method is also applicable to other kinds of pipe. Variation in pipe support condition leads to increased likelihood of pipe damage under vehicle loading. A vibrating 'pig' has been developed and tested on buried pipelines in Britain and the measured data obtained is compared with theoretical models. Certain features, such as voids, hard spots and joints, display characteristic responses to vibration and a library of such characteristics has been constructed both experimentally and from the theoretical models.

Identification of support conditions of buried pipes using a vibrating pig

This paper describes a method for monitoring the variation in support condition of pipelines using a vibration technique. The method is useful for detecting poor support of buried pipelines and for detecting spanning and depth of cover in sub-sea lines. Variation in the pipe support condition leads to increased likelihood of pipe damage. Under roadways, poorly supported pipe may be damaged by vehicle loading. At sea, spanned sections of pipe are vulnerable to ocean current loading and also to snagging by stray anchors in shallow waters. A vibrating `pig' has been developed and tested on buried pipelines. Certain features of pipe support, such as voids and hard spots, display characteristic responses to vibration, and these are measured by the vibrating pig. Post-processing of the measured vibration data is used to produce a graphical representation of the pipeline support and certain `feature characteristics' are identified. In field tests on a pipeline with deliberately constructed support faults, features detected by the vibrating pig are in good agreement with the known construction.

Investigation of anti-lock braking strategies for heavy goods vehicles

An articulated lorry was instrumented in order to measure its performance in straight-line braking. The trailer was fitted with two interchangeable tandem axle sub-chassis, one with an air suspension and the other with a steel monoleaf four-spring suspension. The brakes were only applied to the trailer axles, which were fitted with anti-lock braking systems (ABS), with the brake torque controlled in response to anticipated locking of the leading axle of the tandem. The vehicle with the air suspension was observed to have significantly better braking performance than the steel suspension, and to generate smaller inter-axle load transfer and smaller vertical dynamic tyre forces. Computer models of the two suspensions were developed, including their brakes and anti-lock systems. The models were found to reproduce most of the important features of the experimental results. It was concluded that the poor braking performance of the steel four-spring suspension was mainly due to interaction between the ABS and inter-axle load transfer effects. The effect of road roughness was investigated and it was found that vehicle stopping distances can increase significantly with increasing road roughness. Two alternative anti-lock braking control strategies were simulated. It was found that independent sensing and actuation of the ABS system on each wheel greatly reduced the difference in stopping distances between the air and steel suspensions. A control strategy based on limiting wheel slip was least susceptible to the effects of road roughness.

The effect of surface hardening on the elastic shakedown of elliptical contacts

The effect of varying both the aspect ratio and the coefficient of friction of contacts with elliptical geometry on their elastic shakedown performance has been examined theoretically for surfaces with two types of subsurface hardness or strength profiles. In stepwise hardening the hard layer is of uniform strength while in linear hardening its strength reduces from a maximum at the surface to that of the core at the base of the hardened layer. The shakedown load is expressed as the ratio of the maximum Hertzian pressure to the strength of the core material. As the depth of hardening, expressed as a multiple of the elliptical semi-axis, is increased so the potential shakedown load increases from a level that is appropriate to a uniform half-space of unhardened material to a value reflecting the hardness of the surface and near-surface material. In a step-hardened material, the shakedown limit for a surface 'pummelled' by the passage of a sequence of such loads reaches a cut-off or plateau value, which cannot be exceeded by further increases in hardening depth irrespective of the value of the friction coefficient. For a linear-hardened material the corresponding plateau is approached asymptotically. The work confirms earlier results on the upper bounds on shakedown of both point and line contacts and provides numerical values of shakedown loads for intermediate geometries. In general, the case depth required to achieve a given shakedown limit reduces in moving from a transversely moving nominal line load to an axisymmetric point load.

Influence of the state of the inlet endwall boundary layer on the interaction between pressure surface separation and endwall flows

This paper describes the effect of the state of the inlet boundary layer (laminar or turbulent) on the structure of the endwall flow on two different profiles of low-pressure (LP) turbine blades (solid thin and hollow thick). At present the state of the endwall boundary layer at the inlet of a real LP turbine is not known. The intention of this paper is to show that, for different designs of LP turbine, the state of the inlet boundary layer affects the performance of the blade in very different ways. The testing was completed at low speed in a linear cascade using area traversing, flow visualization and static pressure measurements. The paper shows that, for a laminar inlet boundary layer, the two profiles have a similar loss distribution and structure of endwall flow. However, for a turbulent inlet boundary layer the two profiles are shown to differ significantly in both the total loss and endwall flow structure. The pressure side separation bubble on the solid thin profile is shown to interact with the passage vortex, causing a higher endwall loss than that measured on the hollow thick profile.

A comparison of power losses for small (< 1 kW) induction motor drives adopting squarewave and sinusoidal PWM excitation

In this paper the influence of the form of motor excitation on the performance of a small (< 1 kW) induction motor drive is studied. Two forms of excitation, namely sine waves generated by pulse width modulation and simple square wave are explored. Sine wave excitation gives lower motor losses but increases inverter losses. Conversely, square wave excitation increases motor losses but decreases inverter losses. Losses have been measured directly by calorimetric means or, in the case of the inverter, predicted by a Pspice model that has been verified by calorimetric methods. The work shows that overall, the use of square wave excitation leads to a more efficient drive. © 2004 The Institution of Electrical Engineers.

Active roll control of an experimental articulated vehicle

A new experimental articulated vehicle with computer-controlled suspensions is used to investigate the benefits of active roll control for heavy vehicles. The mechanical hardware, the instrumentation, and the distributed control architecture are detailed. A simple roll-plane model is developed and validated against experimental data, and used to design a controller based on lateral acceleration feedback. The controller is implemented and tested on the experimental vehicle. By tilting both the tractor drive axle and the trailer inwards, substantial reductions in normalized lateral load transfer are obtained, both in steady state and transient conditions. Power requirements are also considered. © IMechE 2005.

Widening engineering horizons: Addressing the complexity of sustainable development

The complex, fragmented and diverse aspects of a sustainable development perspective are translated into an eight-point framework that defines a problem boundary larger than that traditionally adopted by civil engineers. This leads to practical questions intended to inform engineers who ask 'am I being sustainable?' during project implementation. The value of the questions is tested against a case history of a wastewater treatment project. This demonstrates the relevance of the questions to successive project delivery phases of defining the problem, choosing a solution and implementing that solution through design, construction and operation. The case history highlights that answers to several of the additional questions raised by considering this wider problem space are currently buried within government and clients' policies, regulations and standard practice; these answers may not be accessible to the professional engineer.

Implementation of semi-active damping on a tri-axle heavy-vehicle suspension

A semi-active truck damper was developed in conjunction with a commercial shock absorber manufacturer. A linearized damper model was developed for control system design purposes. Open- and closed-loop damper force tracking control was implemented, with tests showing that an open-loop approach gave the best compromise between response speed and accuracy. A hardware-in-the-loop test facility was used to investigate performance of the damper when combined with a simulated quarter-car model. The input to the vehicle model was a set of randomly generated road profiles, each profile traversed at an appropriate speed. Modified skyhook damping tests showed a simultaneous improvement over the optimum passive case of 13 per cent in vertical body acceleration and 8 per cent in dynamic tyre forces. Full-scale vehicle tests of the damper on a heavy tri-axle trailer were carried out. Implementation of modified skyhook damping yielded a simultaneous improvement over the optimum passive case of 8 per cent in vertical body acceleration and 8 per cent in dynamic tyre forces. © IMechE 2008.

The prediction of hot streak migration in a high-pressure turbine

Accurate predictions of combustor hot streak migration enable the turbine designer to identify high-temperature regions that can limit component life. It is therefore important that these predictions are achieved within the short time scales of a design process. This article compares temperature measurements of a circular hot streak through a turning duct and a research turbine with predictions using a three-dimensional Reynolds-averaged Navier-Stokes solver. It was found that the mixing length turbulence model did not predict the hot streak dissipation accurately. However, implementation of a very simple model of the free stream turbulence (FST) significantly improved the exit temperature predictions on both the duct and research turbine. One advantage of the simple FST model described over more complex alternatives is that no additional equations are solved. This makes the method attractive for design purposes, as it is not associated with any increase in computational time.

Stabilization of carbon nanotube field emitters

Carbon nanotubes (CNTs) have been determined to be field emitters of high quality, but CNTs produced by chemical vapour deposition can produce emission currents with high instability and noise. This work finds that adsorbates and amorphous carbon deposited during the growth process are the primary contributors to field emission instability, and shows that burning off the amorphous carbon in air at 450 °C removes the amorphous carbon, resulting in stabilities of better than 3 per cent over 1 h. This work removes one of the major barriers to the use of CNTs in field emission devices.

Dynamics of in-plane arch rocking: An energy approach

This study employs an analytical model to describe the rocking response of a masonry arch to in-plane seismic loading. Through evaluation of the rate of energy input to the system, the model reveals the ground motions that cause maximum rocking amplification. An experimental investigation of small-scale masonry arches subjected to past earthquake time histories is used to evaluate the analytical model and to explore arch rocking behaviour. The results demonstrate that rocking amplification can occur, but is highly sensitive to slight variations in the ground motion. Thus, the accuracy to which the arch response can be predicted is brought into perspective. The concept that the primary impulse of an expected ground motion is fundamentally important in predicting arch collapse is evaluated in light of the developed energy approach. Finally, a statistical method is proposed for predicting the probability of arch collapse during seismic loading.

Active steering of a tractor-semi-trailer

This paper develops a path-following steering control strategy for an articulated heavy goods vehicle. The controller steers the axles of the semi-trailer so that its rear end follows the path of the fifth wheel coupling: for all paths and all speeds. This substantially improves low-speed manoeuvrability, off-tracking, and tyre scrubbing (wear). It also increases high-speed stability, reduces 'rearward amplification', and reduces the propensity to roll over in high-speed transient manoeuvres. The design of a novel experimental heavy goods vehicle with three independent hydraulically actuated steering axles is presented. The path-following controller is tested on the experimental vehicle, at low and high speeds. The field test results are compared with vehicle simulations and found to agree well. The benefits of this steering control approach are quantified. In a low-speed 'roundabout' manoeuvre, low-speed off-tracking was reduced by 73 per cent, from 4.25 m for a conventional vehicle to 1.15 m for the experimental vehicle; swept-path width was reduced by 2 m (28 per cent); peak scrubbing tyre forces were reduced by 83 per cent; and entry tail-swing was eliminated. In an 80 km/h lane-change manoeuvre, peak path error for the experimental vehicle was 33 per cent less than for the conventional vehicle, and rearward amplification of the trailer was 35 per cent less. Increasing the bandwidth of the steering actuators improved the high-speed dynamic performance of the vehicle, but at the expense of increased oil flow.