Wind turbine drives — Test results from the ‘falcon’

A wind turbine drive has been designed and built for full scale trials in order to assess the use of this type of propulsion for commercial craft. This wind turbine rig is fitted to the 5.6m long Blackwater sloop ‘Falcon’.

Test results from this boat are presented over a range of operating wind conditions up to Beaufort force 6 (11.5m/s) for two different wind turbine rotors. Maximum boatspeeds reached were 3.5 knots upwind (in 7.2m/s wind), 5.0 knots across the wind (9.8m/s wind) and 5.2 knots downwind (8m/s wind). The ‘hull speed’ of this boat is around 5.0 knots.     

Use of meteorological/constructional statistics to estimate building heat needs

Building heat needs over a month or a year are often estimated on the basis of the relevant degree day value, in which some crude account is taken of solar and other casual gains in the choice of the base temperature. A more realistic assessment of building heat needs including the effects of passive gain (through a window or glazed wall) can be made using the ‘empirical’ approach of Davies. In this article a statistical approach is developed in which use is made of degree day type data, and measures of days which are ‘disadvantageous’ and ‘advantageous’ from the point of view of saving back-up heating, together with the first four moments of the distribution of advantageous days (7 statistics in all). From five of these statistics a curve can be fitted to the distribution. After suitable integration of the fitted curves another estimate of building heat needs is obtained (the ‘curve fitting’ value). The heat needs as obtained empirically and by curve fitting agree closely. The 7 statistics are easily handled by a mini computer. They thus provide a convenient and accurate extension to degree day methods when local meteorological information has been processed in conjunction with passive solar collector characteristics. Window area, or glazed wall resistance, and assumptions about ventilation rate are only needed in the final stage of computing heat needs.     

Wind action on glass and Brown''s integral

The action of fluctuating wind pressure on glass panels is considered, making use of ‘Brown's integral’ formulation of glass damage accumulation. A probability distribution for wind pressures, with nonzero skewness is used to compute the expected damage during a wind storm of given duration. The damage accumulation rate is found to be strongly dependent on the intensity and skewness of the probability distribution. The contributions of various amplitude ranges to the damage integral are examined. The major contributions to the damage are found to come from isolated peaks occurring at infrequent intervals during a storm. Current design practices are examined making use of the ‘design coefficient’ concept.     

Prestressed membrane structures — The ultimate thin-walled structure

Whilst for normal thin-gauge materials such as steel and aluminium, buckling is a problem when the ratio of unsupported width to thickness is perhaps in the order of 200 or so, membrane roof structures may behave satisfactorily with ratios of up to 50 000 and thus might be termed the ‘ultimate thin-walled structure’. All modern architectural membrane structures are prestressed to maintain a tensile state and to reduce deflections under applied loadings such as from wind. These forms of ‘soft shells’ are in two broad categories — the air-supported type and the tension type. This paper discusses the general design principles which are used to achieve exciting, visual and technologically intriguing forms with such high slenderness ratios.     

Long-term performance of geocomposites used as highway edge drains

Prefabricated highway edge drains have been widely used in the USA since 1985. Laboratory testing and initial on-site evaluations have been generally positive, however long-term performance is an unknown. The major areas of concern are ‘blinding’ of the filter fabric that would prevent water from entering into the geocomposite and the ‘clogging’ of the core with fines. This paper presents the results of 72 randomly selected sites that were excavated in 3 states representing a total of 900 000 m (3 000 000 ft) of installed geocomposite edge drain.     

Aesthetics of thin-walled structures

Thin-walled structures are assumed to include all ‘surface-acting’ structures. This is a brief review of the factors generally considered to influence our emotional and intellectual response to built forms. General problems arising from the strong forms and large plain surfaces of thin-walled structures are considered. A number of specific types are then treated under the headings of ‘bridges’, ‘shells’, ‘silos’, ‘tents’ and ‘air-supported structures’.     

Interrupted interface on the cybernetics of digital design process

From the viewpoint of Batesonian cybernetics, ‘conscious purpose’ and ‘artistic process’ are distinct ends of a spectrum of the functioning of ‘self’. The conceptual stage of the design process is essentially an artistic activity unencumbered with accuracy, dimensionality, scale, program or even tectonics, albeit all of these maybe tacitly present at the ‘back of a designer's mind’. Artistic activities involve broad mental processes that are beneath the stratum of consciousness. By definition, consciousness is selective awareness; it is linear in execution and limited in its capability to synthesize complex parameters. One of the central questions of this paper is “if artistic process requires one to abandon, or relinquish conscious purpose at the time of the generation of the work of art, and if the early stages of artistic process is a result of a vast number of ‘unconscious’ forces and impulses, then how can the computer, which demands (and thus propagates) geometric precision, focused operation and rational execution, be part of that process?” This paper will explore how, cybernetically, the computer can be ‘coupled’ with ‘self’ (via a visual interface) and the artistic process. Three specially devised conceptual design exercises—namely BlurrDesign, BlinDesign and BlitzDesign—and three corresponding “interruptive” computer interface modifications were deployed in an introduction to digital media course. The results of this study are now under consideration for their effectiveness in promoting conceptual design using the computer, and how the ‘self’ might form a cybernetic whole with the machine. The findings could have implications in design pedagogy, informatics and interface design.     

Wind tunnel tests and manoeuvre simulator tests with different types of sails and ships

The present paper describes how wind tunnel tests combined with manoeuvring simulator tests and wind statistics can be used to estimate the mean reduction in power consumption for larger ships equipped with sail systems for auxiliary propulsion purposes. The results presented is based on wind tunnel tests with a 60, 000 tdw bulk carrier carried out for the Burmeister & Wain Ship Design in Denmark.     

An assessment of the sensitivity of lattice towers to fatigue induced by wind gusts

The dynamic properties of lattice towers are closely constrained by practical economic design. It is thus possible to generalize the prediction of dynamic response, using the stochastic wind gust model, with details as outlined in the seminar ‘Wind engineering in the eighties’ (CIRIA, London, 1980). An approximation to the combined effect of resonant and non-resonant components of the response is presented, as a factor to be applied to the effective stress range based on the dynamic response alone, computed at a single ‘reference wind speed’.

Results are presented for a range of practical structures, which indicate that good detailing can generally ensure that fatigue damage caused by wind gusts does not seriously limit design. The sensitivity of the normalized results to changes of location and of tower function and geometry is shown to be relatively small.     

Influence of lips on thin-walled sections

Turning the free edge of an unstiffened flange inwards or outwards to form a ‘lip’, can substantially improve the local buckling resistance of a member. The lip is the most common type of edge stiffener used in cold-rolled, thin-walled sections. In this paper the behaviour of plate elements of thin-walled sections stiffened by compound lips (i.e. lips which are folded twice to form ‘lips on the lips’) is examined both theoretically and experimentally. An outline of a series of tests on compound edge-stiffened thin-walled sections of various geometries is given and some load-end compression displacement paths are compared with the theoretical predictions. Reasonably good agreement is obtained between the experimental and theoretical results. Comparisons of the theoretical predictions with experimental results of other researchers are also presented in this paper.     

Understanding imperfection-sensitivity in the buckling of thin-walled shells

The buckling of thin-walled shell structures under load is still imperfectly understood, in spite of much research over the past 50 years. In this paper the author traces the history of the ideas which have been deployed in order to shed light on what is often referred to as ‘imperfection-sensitive’ buckling behaviour of shells. The ideas, which recur in various combinations, involve interaction of competing buckling modes, nonlinear behaviour, the growth of initial geometric imperfections under load and the alteration of the distribution of membrane stress as imperfections grow. The author claims that there are strong grounds for supposing that ‘locked in’ initial stresses on account of imperfect initial geometry and the static indeterminacy of boundary conditions of real shells have a pronounced effect on the buckling performance. This effect has been ignored in the past, and is the subject of a current experimental study.     

On the upward movement of smoke and related shopping mall problems

The data of Morgan and his co-workers for the movement of smoke in 1/10 scale shopping malls are re-examined. This has been done to see how far a simple theoretical treatment based on plume theory and virtual sources (a basis for many calculation methods) can be exploited instead of the more complicated theory of sources of finite sizes. The work follows and extends the work of Law.

A number of theoretical relationships are used to correlate data and, in particular, they confirm Law's view that the data can be used to give plausible values for the positions of the virtual sources. Some of the complexities of the theory for finite strip sources may be bypassed if experiments are used for estimating the position of effective virtual sources. Experiments to locate the effective virtual source and the limiting asymptotic form of the theory (appropriate to line sources) can correlate and scale data to an accuracy satisfactory for fire engineering purposes. Various aspects of theory are discussed including the method of allowing for the ‘ends’ of finite strip sources, and the use of the theory of weak plumes for strong plumes.

There remains however a problem in reconciling the ‘near’ field of the plume rising around the balcony edge to the ‘far field’, but it is shown that the introduction of an exceptionally high local entrainment could — for these data — be avoided if: (a) the mass at any level in the plume is about 45% larger than expected from other laboratory experiments on plumes; or (b) there is extra entrainment due to the deflection and consequent disturbance as the plume strikes the ceiling; or (c) there is extra upward flow owing to radiation heating up the lower walls and floor as suggested by recent investigations. These matters await further investigation.     

Tangible virtuality—perceptions of computer-aided and physical modelling

Designing—giving form to new objects or environments—is largely a question of anticipating the workings of spatial and material environments, which can become ‘reality’ only by being built. Until ‘realized’, a design is essentially a figment of the designer's imagination, although his or her ideas may be laid down and conveyed to others via specialized design media. In this way, impressions of the design may be shared with clients, colleagues or other ‘actors’ in the design process.

Such products of the designer's imaging process can be relatively abstract or begin to approach future reality. Form & Media research can be ‘revealing’, stimulating insights concerning preferences, working processes and the effects of products of the designer's imagination. In the past 10 years, we have gained considerable practical experience with both virtual and tangible (scale) models. We have compared different techniques in conference workshops, within educational settings and in our Form & Media research laboratory. The research projects ranged from the development of practical techniques and working methods to protocol analyses of designing architects.

This contribution draws comparisons between different computer-aided modelling techniques, with an indication of their perspectives, making use of the experience gained from various experiments in an educational context, and will highlight the potentials for different combinations of digital and physical modelling techniques.     

Coupled dynamics of tensioned buoyant platforms and mooring tethers

A mathematical model is presented of the coupled dynamics of a tensioned buoyant surface platform and the lateral dynamics of its taut mooring tethers. A finite element model of the lateral mooring tether dynamics is extended to take account of nonlinear square law fluid damping by a simple global ‘whole tether’ linearization and an alternative computationally more expensive ‘element-by-element’ linearization scheme. The resultant finite element model is combined with the surface platform dynamic analysis and the coupled dynamic model is used to investigate the effects of water depth, surface platform mass and tether mass per unit length on the tether displacements and bending stresses as well as the resultant surface platform displacements. The results show that the bending stresses induced in the tethers due to their dynamic motions are quite small and that the tether dynamics only affect the motion response of the platform appreciably if the tethers are long (1500 m or more), have a large mass per unit length and have a relatively low tension; or if the platform mass is relatively small. It was also found that the additional computing time required for the local ‘element-by-element’ equivalent linearization was not matched by the small improvement in accuracy obtained over the global ‘whole tether’ technique.     

An instrumented steep reinforced soil embankment at Åndalsnes, Norway

The design and construction of an instrumented steep reinforced soil embankment built over a competent foundation is described. The embankment, which is intended to act as a snow avalanche barrier, was constructed from a uniformly graded medium sand and ‘Tensar’ SR2 geogrid was used as the primary reinforcement. Reinforcement strains were measured using ‘Bison’ strain coils and measurements were also made of stresses and lateral displacements occurring in the soil. The measured values of reinforcement strain are shown to be substantially less than those obtained from a limit equilibrium analysis of the embankment in which the mobilized friction angle is based on pressure cell measurements of vertical and horizontal total stress. This result is consistent with other published field trials and indicates an excessive conservatism in the limit equilibrium methods currently used for design.     

Seismic response of multi-storey steel buildings with flexible connections

In the limit states design of steel building frames, usually simplifying assumptions are made with regard to the behaviour of beam-to-column connections. The Canadian standard for steel buildings recognizes three such sets of assumptions. One of them is the ‘special simple construction’ in which the beam-to-column connections are assumed to be completely free (pinned) to resist gravity loads and are assumed to be ‘rigid’ to resist the lateral loads due to earthquake or wind. Such connections are then designed for moments due to lateral loads only, and thus they are usually flexible. This paper is concerned with the influence of the connection flexibility and the strength on the overall strength and stiffness of steel building frames. The study considers 10 storey and 20 storey office buildings. The first part of the paper illustrates the analysis and design of the 10 storey building on the basis of ‘special simple construction’. By using realistic connection behaviour, the frames were subjected to equivalent static loads due to wind or earthquake and El Centro, 1940 earthquake excitation. In the nonlinear static analysis the building frames were subjected to specified gravity loads and incremental lateral loads until failure. In the nonlinear dynamic analysis the buildings were subjected to specified gravity loads and 70% of El Centro, 1940 earthquake excitation. For comparison purposes the frames were analysed twice, first assuming rigid connections and then with flexible connections. The static analyses results show that the connection flexibility increases the building deflections at specified loads, but the strength is only marginally affected. The dynamic analyses results show an increase in deflections and also generally an increase in column bending moments due to connection flexibility and the associated strength.     

Thermal response of sprinklers part II. Characteristics and test methods

This paper presents an introduction to the measurement of the thermal response characteristics of sprinklers and aspects of testing which are relevant to performance requirements for specific applications, e.g., for life safety and for protecting high-rack storage. Comparisons are made between test results and ranking orders derived from two methods; the ‘rate-of-rise’ test developed in the U.K. and the ‘plunge’ test as developed in the U.S.A. This paper describes the background to both tests and presents explanations for the differences in the results obtained from each method. The rate-of-rise test is suggested for sprinkler classification; the plunge test for measuring consistency in operation.     

A computational intelligent fuzzy model approach for excavator cycle time simulation

The tracked hydraulic excavator is one of the most versatile and widely utilised piece of earthmoving equipment. In many instances, the ‘excavator’ represents the first choice of earthmoving plant for both construction managers and estimators, since when properly employed (i.e. with a competent operator and in an appropriate working environment), it offers high production rates at economical cost. Nonetheless, predicting machine production performance is difficult; given the typical multiple operational parameters (e.g. machine weight, machine configuration, ground conditions, operator ability) that can apply. Consequently, determination of accurate cost estimates and predicted contract durations are subject to considerable inaccuracy, especially where a significant amount of site work is needed.

To address this inadequacy, this paper presents a computational intelligent ‘fuzzy’ model with the ability to forecast excavator cycle time. In this context, a cycle is defined as one complete revolution, from ‘place empty bucket in dig material’ through ‘fill bucket’, ‘move charged bucket to target’, ‘empty charged bucket’ and ‘return bucket to dig material’. The developed model is based upon 70 separate cycle time observations obtained from four plant manufacturers. These data provide a representative spread of machine cycle times since they include a range on a continuum from optimum to adverse operational parameters. Tests on the derived model identified that its accuracy was acceptable; but the accuracy could be improved using larger samples and a more comprehensive and exhaustive range of variables to predict machine cycle time.     

Adaptive architecture: integrating low-energy technologies for climate control in the desert

The article describes a ‘climatically adaptive’ approach to intelligent building in which a variety of technologies are integrated in the architectural design to provide thermal comfort with a minimal expenditure of energy. This concept is illustrated by the design of the Blaustein International Center for Desert Studies, a multi-use complex completed recently at the Sede-Boker Campus of Ben-Gurion University of the Negev. In response to the local climate of this desert region, a number of strategies were developed by the authors to exploit natural energy for heating and cooling: earth berming of major parts of the building, ‘selective glazing’ for seasonal shading and energy collection, a down-draft ‘cool-tower’ for evaporative cooling and a hybrid mechanism for hot-air supply are several of the unique systems whose performance and feasibility are analyzed within the context of the overall building design.