Martin Crapper

h‐adaptive finite element solution of high Rayleigh number thermally driven cavity problem

An h‐adaptive finite element code for solving coupled Navier‐Stokes and energy equations is used to solve the thermally driven cavity problem. The buoyancy forces are represented using the Boussinesq approximation. The problem is characterised by very thin boundary layers at high values of Rayleigh number (>106). However, steady state solutions are achievable with adequate discretisation. This is where the auto‐adaptive finite element method provides a powerful means of achieving optimal solutions without having to pre‐define a mesh, which may be either inadequate or too expensive. Steady state and transient results are given for six different Rayleigh numbers in the range 103 to 108 for a Prandtl number of 0.71. The use of h‐adaptivity, based on a posteriori error estimation, is found to ensure a very accurate problem solution at a reasonable computational cost.

Flow field visualization of sediment-laden flow using ultrasonic imaging

This investigation concerns the application of particle image velocimetry (PIV) to ultrasonic images of sediment-laden flow in order to obtain accurate, quantitative, two dimensional vector maps of the flow field within the sediment suspension. Experiments were carried out using a medical ultrasound scanner to obtain ultrasonic images in a kaolin/salt water suspension of mean concentration 16 g/l and to compare results obtained with the ultrasound scanner in clear water with those from established measurement techniques. Measurements of mud were obtained, and the comparison with established methods indicated that the application of PIV to the analysis of ultrasound images yields velocity information accurate to within ±15%. This measurement technique will be of great value in furthering the understanding of the behavior of sediment-laden flows.

Simulation of biopile processes using a hydraulics approach

Biopiles are a common treatment for the ex-situ remediation of contaminated soil. Much research has been carried out on understanding and modelling microbial degradation, but hitherto no study has attempted to model the effect on a biopile of its ambient surroundings. A hydraulics-based approach to simulating a biopile in the context of its ambient surroundings is presented, taking into account processes within the pile, external conditions of wind and temperature, the location of aeration pipes and the venting pressure, and considering the distribution of treatment over various regions within the pile. A system of add-ons to a commercial CFD code has been developed, and various example simulations have been carried out to examine the potential of the hydraulics approach for practical application. Results show that the model produces reasonable results, with biodegradation related to the temperature within the pile and the temperature in turn related to wind speed and aeration details. A number of counter-intuitive results are described, indicating that simulation of the type carried out will produce valuable insight into the practical design of biopiling systems. The simulation system also allows the total environmental footprint of biopiling to be considered, examining not just degradation of contaminant but also its removal via volatilization and the energy used in heating air for venting.

h-adaptive finite element solution of unsteady thermally driven cavity problem

An h‐adaptive finite element code for solving coupled Navier‐Stokes and energy equations is used to solve the thermally driven cavity problem for Rayleigh numbers at which no steady state exists (greater than 1.9 × 108). This problem is characterised by sharp thermal and flow boundary layers and highly advection dominated transport, which normally requires special algorithms, such as streamline upwinding, to achieve stable and smooth solutions. It will be shown that h‐adaptivity provides a suitable solution to both of these problems (sharp gradients and advection dominated transport). Adaptivity is also very effective in resolving the flow physics, characterised by unsteady internal waves, are calculated for three Rayleigh numbers; 2 × 108, 3 × 108 and 4 × 108 using a Prandtl number of 0.71 and results are compared with other published results.

Experimental and Simulation Studies of Dilute Horizontal Pneumatic Conveying

Dilute horizontal pneumatic conveying has been the subject of this experimental and numerical study. Experiments were performed utilising a 6.5 m long, 0.075 m diameter horizontal pipe in conjunction with a laser-Doppler anemometry (LDA) system. Spherical glass beads with three different sizes 0.8–1 mm, 1.5 mm, and 2 mm were used. Simulations were carried out using the commercial discrete element method (DEM) software, EDEM, coupled with the computational fluid dynamics (CFD) package, FLUENT. Experimental results illustrated that, for mass solid loading ratios (SLRs) ranging from 2.3 to 3.5, the higher the particle diameter and solid loading ratio, the lower the particle velocity. From the simulation investigations it was concluded that the inclusion of the Magnus lift force had a crucial influence, with observed particle distributions in the upper part of the conveying line reproducible in the simulation only by implementing the Magnus lift force terms in the model equations.

Improving concrete placement simulation with a case-based reasoning input

Discrete-event simulation has been used extensively in the past to analyse construction operations and has been shown to be an effective tool for improving construction process planning. Unfortunately, the widespread application of simulation has been prevented, in part, by the requirement for the developer and user to understand the stochastic features of the process. Further, if the stochastic inputs are not representative of the real system, the simulation output will be misleading. This article proposes that case-based reasoning (CBR) could be used to: improve the input and output data of a simulation model and remove the requirement for a user to have specialist statistical knowledge of the process. Case-based reasoning works by solving new cases from knowledge stored in a case base. Two models are presented in this article: a discrete-event simulation model, MatSim, and a hybrid CBR-simulation model, CBRSim. Both models were developed using real construction data. The models were compared to measure any improvements in simulation output, by using a CBR suggested input. Data from an independent construction project were used to test both models, and the results indicate that CBRSim can achieve estimates of observed values that are more accurate and reliable than those from MatSim.

The health and safety implications of socio-cultural context for community construction projects in developing countries

Community participation in construction during rural infrastructure projects in developing countries is encouraged by many non-governmental organizations. The health and safety aspects of this type of development model have not previously been adequately researched, however. The aim is to identify the socio-cultural factors that motivate community members to participate in construction activities which they perceive as hazardous during a case study of a water and sanitation project in rural Ghana. This is a step towards understanding how health and safety can be more effectively managed during community development projects. A qualitative approach has been taken, using interview, observation and reflection. It was found that the communal culture of the local context resulted in community members feeling pressurized to participate in hazardous construction activities. Local customary laws further compelled individuals as they were concerned they could be fined or arrested should they not fulfil their communal obligations. Further work is required to determine the boundaries within which findings apply but it is likely that there are implications for others managing community construction projects both in Ghana and further afield.

Breakage functions of particles of four different materials subjected to uniaxial compression

ABSTRACT Particle breakage is a common problem in the conveying and handling of particulate solids. The phenomenon of particle breakage has been studied by experiments by a number of researchers in order to describe the process of breakage by mathematical functions. The development of comminution functions that can suitably describe the breakage behavior of granular materials can lead to a significant improvement in the design and efficiency of particulate solids handling equipment. The present study focuses on developing the strength distribution and the breakage functions of particles of four different materials subjected to uniaxial compressive loading. Single particles were compressed until fracture in order to determine their strength distribution and the fragments were investigated to determine their size distribution. The parameters of logistic function and breakage function were obtained by curve-fitting of the functions to the strength distribution and size distribution of the fragments, respectively. These functions were then implemented in the BGU-DEM code which was used to carry out discrete element method (DEM) simulations on single particle breakage by compression. The simulations produced a similar mass distribution of fragments to the breakage function obtained from the experimental data.

Safety and volunteer construction workers

The construction industry is dangerous, with 39 fatalities at work in the UK in 2012/13 and comparable and even larger figures reported worldwide. People also take part in construction on a voluntary basis; most volunteers have limited training and no technical qualification, whilst safety regulation frameworks range from being comparable to professional sectors to zero regulation in some international contexts. Unstructured interviews were undertaken with volunteer construction workers from two areas: those returning from international development projects and those regularly volunteering on UK heritage railways. Taking a social constructionist perspective, data was explored using discourse analysis to illuminate ‘safety’ within this unique construction ‘industry’. Those with engineering or technical backgrounds developed more tangible constructions of safety, around risks and hazards, within their activities, yet volunteers without this experience also acknowledged a wider context of danger. Volunteers on overseas projects developed discourses of ‘difference’ between safety at home and safety outside the UK, associated with negative practices overseas yet with acceptance of their inevitability as part of the voluntary experience. Further work is proposed to determine whether these insights can contribute to improved safety management within the voluntary construction context.

Modelling the failure modes in geobag revetments.

In recent years, sand filled geotextile bags (geobags) have been used as a means of long-term riverbank revetment stabilization. However, despite their deployment in a significant number of locations, the failure modes of such structures are not well understood. Three interactions influence the geobag performance, i.e. geobag-geobag, geobag-water flow and geobag-water flow-river bank. The aim of the research reported here is to develop a detailed understanding of the failure mechanisms in a geobag revetment using a discrete element model (DEM) validated by laboratory data. The laboratory measured velocity data were used for preparing a mapped velocity field for a coupled DEM simulation of geobag revetment failure. The validated DEM model could identify well the critical bag location in varying water depths. Toe scour, one of the major instability factors in revetments, and its influence on the bottom-most layer of the bags were also reasonably represented in this DEM model. It is envisaged that the use of a DEM model will provide more details on geobag revetment performance in riverbanks.