Air entrainment into balcony spill plumes

New plume formulations have been developed for assessing air entrainment into thermal plumes that spill over a balcony edge into an atrium void.     

窗口火作用下外保温系统温度分布特性

采用真实尺度的3层建筑进行窗口火实体火灾实验,研究模塑聚苯乙烯(EPS)、挤塑聚苯乙烯(XPS)、聚氨酯(PUR)和酚醛(PF)等4种典型保温泡沫层的外墙外保温系统温度及室内温度的分布特性.研究结果表明:XPS和PF系统表面在横向立面上维持较高温度,EPS和PUR系统远离角落的区域表面温度较低且随着横向距离增大明显降低；热塑性外保温系统的内部温度明显高于热固性外保温系统；第2层和第3层距楼板高度0.9m以下的室内区域烟气温度暴露风险较小,但2层0.9m高度以上、3层1.8m高度以上的区域以及窗户区域均存在较高温度暴露风险.     

Experimental study of the effects of a thermal plume entrainment mode on the flow structure: Application to fire

The aim of this work is to experimentally simulate two heat sources of fire, one placed at ground level, the other at a height above the ground, in order to determine the effect of source air entrainment on the resulting flow structure. The development of a free thermal plume was examined by generating a plume produced from an electrically heated disk at a constant temperature. We first studied the behavior of a thermal plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the plume. The analysis of the average fields as well as the axial evolution of velocity and temperature showed an important widening of the profiles that encouraged a faster spread of the plume. We then determined the structure of the thermal plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting plume.     

Physical modelling of fire spread in Grasslands

The propagation of grassland fires is simulated using a fully physical based model, partially developed during the FIRESTAR European Union programme. This approach, based on a multiphase formulation, includes the calculation of the degradation of the vegetation (by dehydration and pyrolysis) and the turbulent/reactive flow resulting from the mixing between the ambient gas (wind flow) and the pyrolizate. The solid fuel is simulated as homogeneous distribution of solid particles forming a porous media, interacting with the gas flow using a continuous distribution of drag forces. Other source terms representing the interactions between the vegetation and the gas flow are also taken into account, such as the production of water vapour and gaseous fuel, the radiation of soot particles and ashes, and the convective exchange in the energy balance. The model was validated from preliminary calculations carried out at small scale, for a homogeneous fuel bed (pine needles, excelsior, sticks) and compared with experimental results obtained in a wind tunnel. Calculations are then extended to study the propagation of fires through a flat grassland, for various wind speed conditions. The numerical results are compared to empirical and semi-empirical predictions obtained in similar conditions.     

Knowledge entrainment and project management: The case of large-scale transformation projects

An increasing number of change processes and initiatives are organized and implemented as projects, often through the formation of ‘large-scale transformation projects’ (LST), involving a great number of specialists, departments, partners, development work, and knowledge bases. The theoretical foundation that supports the choice of managing change as projects and, in effect, the role of project management has received surprisingly little attention in the current literature. In this paper, we present a model where the success of change initiatives is explained by the quality of project management, which in turn is determined by the quality of knowledge integration. The outlined model highlights knowledge integration as a process determined by the scope and speed of change, which typically result in problems with synchronization of activities within an LST project. Our model draws on the idea of ‘knowledge entrainment’ to explain the fact that different parts (organizations, teams, individuals) tend to develop different time orientations and hence rely on different cycles of knowledge processes. This has important effects on the absorptive capacity of the involved parts of the project and the amount of information and knowledge that the project can digest. This paper discusses different knowledge-entrainment mechanisms and their effects on the role and practice of project management. Empirical data from an LST project in Posten, one of Northern Europe’s largest messaging and logistics operators, illustrate the model. The paper contributes to the analysis of the relationships between knowledge integration and time, particularly in LST projects.     

On the extrapolation of CFD results for smoke and heat control in reduced-scale set-ups to full scale: Atrium configuration

It is a common practice to use reduced-scale experiments to develop formulae for the design of smoke and heat exhaust ventilation systems. Implicitly, up-scaling of results is assumed justified. A similar approach can be adopted with numerical simulations, i.e. a reduced-scale setup can be up-scaled to compare results to full-scale observations. However, both in numerical simulations and in experiments, scaling must be done in a proper way. The classical method for up-scaling results obtained in fire related experiments is based on preservation of the Froude number only. The present paper, focusing on the up-scaling of results by means of a series of CFD simulations of fire-induced flows in an atrium configuration, confirms this to be justified as long as the flows in both the reduced-scale and full-scale configurations are sufficiently turbulent. If this is not the case, it is illustrated that other dimensionless numbers must also be preserved in scaling, in addition to the Froude number.     

滑坡冲击铲刮效应物理模型试验及机制探讨

 滑坡–碎屑流在高速运动过程中对基底物质存在明显的冲击铲刮作用,从而造成滑坡体积不断增大,扩大其致灾影响范围。通过开展物理模型试验研究滑坡物质的颗粒粒径和体积以及基底物质的粒径和堆积厚度对铲刮效应的影响,同时采用MotionPro-Y3–S1高速摄像机观察冲击铲刮过程。试验结果表明：滑坡物质在运动过程中强烈地冲击铲刮基底物质,使其高速飞溅及剪切运动;铲刮距离随滑坡物质体积、粒径以及基底物质颗粒粒径的增大和可侵蚀基底厚度的减小而增大。结合试验现象以及前人的研究成果对滑坡冲击铲刮机制进行探讨：滑坡–碎屑流的冲击铲刮作用在前缘主要表现为冲切破坏,它以撞击力的形式使基底物质发生破坏而铲刮,而在中后部主要表现为运动剪切作用,以剪切力的形式使基底物质发生剪切破坏而被铲刮。     

Experimental simulations of fire-induced smoke control in tunnels using an “air–helium reduced scale model”: Principle, limitations, results and future

When a fire occurs in a long tunnel, smoke control is crucial for obvious reasons of safety. Ventilation and extraction systems have to be designed with accuracy in order to control the longitudinal motion of the fire-induced smoke and to extract it efficiently in a zone close to the fire source. This paper presents experimental investigations carried out on a small scale tunnel model (scale reduction is 1:20) to study the fire-induced smoke control by longitudinal and transverse ventilation systems. The experimental model is non-thermal and a buoyant release (a mixing of air and helium) is used to represent the fire smoke plume. The main objective of this model is to represent, as well as make possible, the duality between inertial forces (due to ventilation) and buoyant forces. Radiation and heat losses at the walls are not taken into account in this model. At first, the principle of the simulation is widely described. Then, some results are presented for both longitudinal and transverse smoke control by a mechanical ventilation. Finally, perspectives for future investigations are proposed.     

High resolution three-dimensional numerical modelling of rockfalls

Accurate prediction of rockfalls is a major need in mountain areas, both for hazard assessment and the design of countermeasures. In this paper, the performance of an original simulation code, initially developed for regional-scale analysis, is tested at the local scale by using high-resolution input data, in order to show its application to site-specific problems. The code is based on a kinematic algorithm and allows to run detailed, spatially distributed simulations of rockfall on a three-dimensional topography described by a Digital Elevation Model. Two examples from the Central Italian Alps, both characterised by the occurrence of frequent historical events, valuable elements at risk (urban areas, corridors) and countermeasures (barriers and retaining walls) are presented. The suggested approach proves to effectively account for rockfall dynamics when used with high-resolution data. Model calibration issues are discussed and model results are compared to available experimental data. The scale dependency of the results is also discussed.     

Physical and analytical modelling of geosynthetic strip pull-out behaviour

The design methods used for soil mass structures, such as mechanically stabilised earth (MSE) structures, are based on soil/reinforcement anchorage models which require the knowledge of the soil/reinforcement interface friction capacity. However, different types of reinforcements are used in these structures and present different behaviour. This study concerns two types of strips reinforcements. The first one is metallic and is classically designed using elasto-plastic models (21 and 22). The second type is geosynthetic. The classical anchorage models do not take into account the extensibility of this materiel and do not reproduce its complex behaviour.     

The advantages of information management through building information modelling

As building information modelling (BIM) is positioned by governments and construction professionals as a solution to the problems in the construction industry, research is needed into the benefits BIM actually confers. The focus here is on the effectiveness of BIM as a medium for communicating information within a construction team. A case study of an offsite precast concrete fabrication facility was conducted. At the time of the study, the facility was supplying precast units for four public sector projects, and using four information management systems: e-mail, a construction project extranet tool, an Enterprise Resource Planning system and a new BIM-based system. The flow of information through the four media was measured and visualized as the projects progressed. This quantitative measurement of information flow was combined with qualitative data from interviews with facility staff. It was found that the introduction of the BIM-based system diverted information flow through the building model and away from the extranet system. The use of e-mail was largely unaffected. BIM allowed considerably more accurate, on-time and appropriate exchange of information. It is concluded it is possible to quantify some of the benefits of BIM to information management. This research paves the way for future research into the management of more construction project information linked more closely to building models.     

Physical and numerical modelling of strip footing on geogrid reinforced transparent sand

This paper presents the results of laboratory scale plate load tests on transparent soils reinforced with biaxial polypropylene geogrids. The influence of reinforcement length and number of reinforcement layers on the load-settlement response of the reinforced soil foundation was assessed by varying the reinforcement length and the number of geogrid layers, each spaced at 25% of footing width. The deformations of the reinforcement layers and soil under strip loading were examined with the aid of laser transmitters (to illuminate the geogrid reinforcement) and digital camera. A two-dimensional finite difference program was used to study the fracture of geogrid under strip loading considering the geometry of the model tests. The bearing capacity and stiffness of the reinforced soil foundation has increased with the increase in the reinforcement length and number of reinforcement layers, but the increase is more prominent by increasing number of reinforcement layers. The results from the physical and numerical modelling on reinforced soil foundation reveal that fracture of geogrid could initiate in the bottom layer of reinforcement and progress to subsequent upper layers. The displacement and stress contours along with the mobilized tensile force distribution obtained from the numerical simulations have complimented the observations made from the experiments.     

Dynamics and dynamic modelling of H2S production in sewer systems

Accurate and reliable predictions of sulfide production in a sewer system greatly benefit formulation of appropriate strategies for optimal sewer management. Sewer systems, rising main systems in particular, are highly dynamic in terms of both flow and wastewater composition. In order to get an insight in sulfide production as a response to the dynamic changes in sewer conditions, several measurement campaigns were conducted in two rising mains in Gold Coast, Australia. The levels of various sulfur species and volatile fatty acids (VFAs) were monitored through hourly sampling for periods ranging from 8 to 29 h. The results of these field studies showed large temporal as well as spatial variations in sulfide generation. A dynamic sewer model taking into account the hydraulics and the biochemical transformation processes was formulated and calibrated and validated using the data collected during the four measurement campaigns at the two sites. The model was demonstrated to reasonably well describe the temporal and spatial variations in sulfide, sulfate and VFA concentrations. Application of the model was illustrated with a case study aimed to optimize oxygen injection to one of the two mains studied, which is being used as a means to control sulfide production on this site. The model predicted that, moving the current oxygen injection point to a location close to the end of the sewer line could achieve the same degree of sulfide control with only 50% of the current oxygen use. This study highlighted that the location at which oxygen is injected plays a major role in sulfide control and a dynamic model could be used to make a proper choice of the location.     

The reliability of inverse modelling for the wide scale characterization of the thermal properties of buildings

The reduction of energy use in buildings is a major component of greenhouse gas mitigation policy and requires knowledge of the fabric and the occupant behaviour. Hence there has been a longstanding desire to use automatic means to identify these. Smart metres and the internet-of-things have the potential to do this. This paper describes a study where the ability of inverse modelling to identify building parameters is evaluated for 6 monitored real and 1000 simulated buildings. It was found that low-order models provide good estimates of heat transfer coefficients and internal temperatures if heating, electricity use and CO₂ concentration are measured during the winter period. This implies that the method could be used with a small number of cheap sensors and enable the accurate assessment of buildings’ thermal properties, and therefore the impact of any suggested retrofit. This has the potential to be transformative for the energy efficiency industry.     

节理密度对围岩变形及破坏影响的试验研究

采用相似模型试验和岩土工程数字照相变形量测软件,研究了深埋应力场中不同断续节理密度的岩体在开挖条件下巷道围岩破裂区的产生与扩展机理,分析了围岩破坏和碎胀变形的发展规律及其对巷道稳定性的影响。研究表明:岩体中节理密度对岩体的承载能力影响很大。与节理岩体相比,完整岩体在破裂前可以承受较大的弹性变形;节理岩体即使与完整岩体具有相同的承载能力,但其稳定性及变形量却有区别,完整岩体的变形量更小、稳定性更好。产生相同的围岩破裂区,岩体中节理越密集需要的应力越低,反之亦然;在相同的应力作用下,岩体中节理越密集,表明岩体越破碎,产生的围岩破裂区就越大,围岩碎胀变形也越大,导致工程的稳定性越差;因此,岩体中断续节理的密度控制着围岩的稳定性。     

Deterioration modelling of small-diameter water pipes under limited data availability

Low value and high volume buried infrastructure assets in the water distribution network are typically less well understood and often sub-optimally managed in comparison to more critical or higher value assets. This is despite attracting an estimated yearly expenditure from water utilities operating in the developed world in excess of £4.42 billion per annum. To address this problem the authors have developed a novel deterioration modelling framework founded on latest geospatial technologies and statistical analysis. The modelling framework is specifically applied to truly small diameter water distribution assets of 25–50 mm diameter. Reliability curves are developed from failure data provided by two UK Water Companies that have captured communication pipe failure records since 2001. Failure projections based on deterioration modelling curves are compared and contrasted to demonstrate the robustness of this modelling approach. A high degree of accuracy is observed for all pipe materials achieving an R² values greater than 0.96.     

Intelligence in buildings: the potential of advanced modelling

“Intelligence” in buildings usually implies facilities management via building automation systems (BAS). However, present-day commercial BAS adopt a rudimentary approach to data handling, control and fault detection, and there is much scope for improvement. This paper describes a model-based technique for raising the level of sophistication at which BAS currently operate. Using stochastic multivariable identification, models are derived which describe the behaviour of air temperature and relative humidity in a full-scale office zone equipped with a dedicated heating, ventilating and air-conditioning (HVAC) plant. The models are of good quality, giving prediction accuracies of ±0.25 °C in 19.2 °C and of ±0.6% rh in 53% rh when forecasting up to 15 minutes ahead. For forecasts up to 3 days ahead, accuracies are ±0.65 °C and ±1.25% rh, respectively.

The utility of the models for facilities management is investigated. The “temperature model” was employed within a predictive on/off control strategy for the office zone, and was shown to substantially improve temperature regulation and to reduce energy consumption in comparison with conventional on/off control. Comparison of prediction accuracies for two different situations, that is, the office with and without furniture plus carpet, showed that some level of furnishing is essential during the commissioning phase if model-based control of relative humidity is contemplated.

The prospects are assessed for wide-scale replication of the model-based technique, and it is shown that deterministic simulation has potential to be used as a means of initialising a model structure and hence of selecting the sensors for a BAS for any building at the design stage. It is concluded that advanced model-based methods offer significant promise for improving BAS performance, and that proving trials in full-scale everyday situations are now needed prior to commercial development and installation.     

The relevance of sewer deterioration modelling to support asset management strategies

Deterioration modelling can be a powerful tool to support utilities in planning efficient sewer rehabilitation strategies. However, the benefits of using deterioration models are still to be demonstrated to increase the confidence of utilities toward simulation results. This study aims at assessing the performance of a statistical deterioration model to estimate the current condition and predict the future deterioration of a sewer network. The prediction quality of the deterioration model GompitZ has been assessed using the extensive data-set of 35,826 inspections performed in the city of Braunschweig, Germany. The performance of the statistical model has been compared with the performance of a simple model based only on the condition of observed sewers. Results show that the statistical model performs much better than the simple model for simulating the deterioration of the network. The findings highlight the relevance of using modelling tools to simulate sewer deterioration and support strategic asset management.     

Petri net modelling of bridge asset management using maintenance-related state conditions

Bridge structures are an important part of the UK transportation network. They are also experiencing increasing rates of deterioration due to the increasing traffic volume and load intensity. Available bridge models have many restrictions due to the assumptions of the analytical method used and the means by which the model states are defined to represent the condition of the structure. These models also lack the complexity to allow detailed maintenance and renewal options to be explored. This paper presents a bridge model developed based on the Petri net (PN) approach. The method allows for detailed modelling of the individual components in the structure whilst maintaining the size of the analytical problem to a manageable size and resulting in an efficient analysis. The bridge model is formed from sub-models of each of the bridge components and takes into consideration the component deterioration process, the interaction and dependency between different component deterioration processes, along with the inspection and maintenance processes. The model states are defined based on actual degraded component conditions which they experience. It is therefore easy to relate these to the appropriate maintenance options. This gives a considerable advantage over those models based on the condition scores or ratings. The state residence times between changes in state resulting from deterioration and maintenance are governed by appropriate Weibull distributions. Thus, avoiding the restriction of constant failure rates used in Markov approaches which are rarely appropriate to model deteriorating asset conditions. The application of the model is demonstrated on a typical bridge structure where the PN model is solved using Monte Carlo simulation, the model results are also presented and discussed.     

Computational fluid dynamics modelling of different detention pond configurations in the interest of sustainable flow regimes and gravity sedimentation potential

This study presents the results of the flow regime evaluation, by means of computational fluid dynamics (CFD), of a vegetated detention pond located at Waterlooville, Hampshire, UK. Alternative pond layouts were assessed for the same flow conditions on the basis of recommendations made in the literature. The results were validated by comparing the maximum computational velocities for the same case using different numbers of mesh elements. It was found that the development of a CFD model of detention ponds is intricate but feasible. The main findings were: (i) The present design performed well in terms of flood risk management, but the flow patterns could result in questionable treatment efficiency; (ii) vegetation seems to promote horizontal recirculation and turbulence; (iii) triangular and elliptical pond designs showed very poor performance; (iv) the most appropriate design for the given location and hydrological regime is an elliptical pond with a central emergent/submerged island.