Numerical simulation of a direct shear test on a rock joint using a bonded-particle model

Rock joints were numerically simulated, and an extensive series of direct shear tests were carried out using the code PFC3D. The feasibility of reproducing a rock joint using the contact bond model was demonstrated, and the effects of the geometrical features and the micro-properties of a joint on its shear behavior were examined. Asperity failure was observed from the micro-cracks and contact force distribution, as well as the stresses and displacements in shear and normal directions. A rough joint with a joint roughness coefficient (JRC) value ranging from 10 to 20 was produced in an intact sample by defining the joint-contacts along a predefined joint surface. To simulate a decrease in joint wall strength (JCS) caused by weathering and alterations, the bond strength between particles involved in the joint-contacts was reduced by up to 70%. The shear behavior and failure progress at a given stress corresponded well to those observed in laboratory tests. The friction coefficient was the most important factor governing the shear strength and dilation angle. The variation in joint roughness and contact bond strength had a larger effect on the cohesion than peak friction angle. In addition, a new approach to represent JRC and JCS values of a joint was proposed for practical use. A numerical 3D-profile scanning technique was developed to evaluate the actual JRC of the simulated joint, and the relationship between the JCS and the contact bond strength was investigated.     

A study of a fire on a diesel railcar

A fire broke out on a diesel railcar while running on a line of the Japan Railways Group. After an exhaustive investigation into the cause of the fire, it was found that the origin had been the lubricating oil of the engine. The lubricating oil vaporized from a long idling engine while the car was standing and accumulated in the exhaust silencer in considerable amounts. When the car was climbing up a long slope, the oil was exposed to a high-temperature exhaust gas and ignited. The flame attacked and melted the exhaust funnel, and eventually caused a fire.     

Prediction of thermal comfort in a building during a cold spell

The comfort diagrams and the so-called PMV-PPD values are already used today directly and indirectly in a wide field in technical practice, even at a standard level. This theory is known also in Hungary, and the PMV-PPD values have been used by us for the solution of a design problem. The task was to elaborate a calculation method, an index number suitable for the determination of the thermal confort effect in the case of occasional underheating of residential and communal buildings in winter.The results of this work are presented in this paper.     

Case study of a rainwater recovery system in a commercial building with a large roof

This paper describes a prototype rainwater recovery system that has been fitted within a supermarket. In this system, rainwater is recovered from the roof structure, collected and then used to satisfy part of the domestic cold water requirements of the supermarket (for toilet flushing). The design and commissioning of the system installed is first described. The system has been fitted with a monitoring system, which has been used to record the water usage and to estimate the rainwater recovered for use in the supermarket over approximately an 8-month period. The results are used to calculate the collection efficiency of the system compared to potential gains determined from local rainfall data. This data has also been used to calculate the revenue cost savings for this system. The additional capital cost of this system has been estimated and this has been used to calculate a payback period of 12 years, based upon a collection efficiency of 57.4%. Alternative payback periods for different locations in the UK are also discussed. Finally, this paper considers the effects of alternative roof and tank sizes on system economics. This shows that tank size is critical and that different configurations may be used to achieve payback periods approaching 4 years.     

Damage around a cylindrical opening in a brittle rock mass

This paper presents an application of the sliding/wing crack model to the problem of a cylindrical opening in a brittle rock mass subjected to a hydrostatic stress field. The rock mass is assumed to contain a uniform initial distribution of microcracks. These microcracks serve as sources of stress concentration, and can propagate tensile wing cracks at their tips in a compressive stress field. It is shown that the sliding/wing crack model can essentially reproduce the complex stress–strain response obtained in laboratory experiments. The stress and displacement field induced by excavation of a tunnel in such a brittle rock mass is determined using the Biot Hodograph Method. The condition for instability of the tunnel can be inferred from the wing crack density, which characterizes the degree of rock damage around the tunnel.     

大断面下穿铁路地道桥顶拉法施工技术

以孝义市北景观大道大断面下穿铁路地道桥顶拉法施工为例,详细介绍施工方案比选、顶拉法施工工艺和顶力力学状态,确定了分节长度选择原则及其参数,并开展了工程的现场施工实践。结果表明:顶拉法施工中具有施工场地小等优点,成功克服了场地受限条件下长距离、大断面地道桥施工难题。     

Helmholtz evolution of a semi-infinite aquifer drained by a circular tunnel

The evolution equation of a drained aquifer during the consolidation process when time is transformed into the Laplace variable is the modified Helmholtz equation. The governing equation of the steady state of a heterogeneous aquifer which hydraulic conductivity when plotted against depth in a semi-log graph has a constant slope is also the modified Helmhotlz equation. The same equation comes out when the slopes of the hydraulic conductivity plotted against depth and against the hydraulic potential in a semi-log graph are constants. The modified Helmholtz equation will be solved exactly considering a semi-infinite aquifer drained by a circular tunnel. A unique state function, which according to the case considered has different interpretations, is obtained in closed form as an infinite sum involving modified Bessel functions. The amount of water that flows into the tunnel contrarily to the state function may change from case to case and will be calculated exactly and in closed form for the different cited cases. The analytic solution has a wide range of application, is valid for different cases, and within every case needs being adapted to the particular problem to be solved. An illustrative application will show an adaptation of the solution to rock masses when the hydraulic conductivity plotted against the effective stress in a semi-log graph has a constant slope. This will allow estimating the relative precision of approximated formulae for the water inflow in fissured rock masses such as the Zhang and Franklin equation and the first order approximation.     

Study of a passive scalar transport in a pipeline x-junction

The transport processes of a passive scalar generated in the mixing of two fluids in a pipeline x-junction are analysed in this paper. The turbulent flow field is computed for the merging of streams using a method of computational fluid dynamics. Two- and three-dimensional simulations are achieved employing both Cartesian and BFC co-ordinates. The numerical model is validated from an experimental set-up. Different parameters are measured for various operating conditions. The influence of the angle between pipe inlets is studied, to establish the optimal condition where the passive scalar concentration in both outlets is similar.     

Selecting a suitable procurement method for a building project

Building procurement has become a fashionable term with industry practitioners and researchers. It determines the overall framework and structure of responsibilities and authorities for participants within the building process. It is a key factor contributing to overall client satisfaction and project success. The selection of the most suitable procurement method consequently is critical for both clients and project participants, and is becoming an important and contemporary issue within the building industry. The problem, nevertheless, lies in the fact that there has been limited empirical research in this field of study. Postal questionnaire surveys of 41 clients and 35 consultants were carried out, and were used to obtain experience of and attitudes to a variety of procurement methods and the criteria used for selection. The findings indicate that a simple set of the criteria generally is adequate and sufficient for procurement path selection, and that there is a reasonable consensus on the appropriate weighting for each path. Moreover, it is shown that, contrary to expectations, similar clients generally do not have similar procurement needs.     

层状场地中二维沉积谷地对弹性波的三维散射

为研究层状场地中二维沉积谷地对斜入射弹性波的三维散射问题,建立了求解问题的移动间接边界元方法。方法通过沿二维沉积谷地轴线方向的傅里叶变换将三维问题降为二维问题,进而在沉积谷地截面内进行边界单元的离散和求解,求得截面内的三维动力响应,然后将截面内的计算结果沿沉积谷地轴线方向进行波数展开即可求得任意位置动力响应。文中通过与前人结果的比较验证了方法的正确性,并以均匀半空间场地和基岩上单一土层场地为例进行了数值计算和分析,给出了一些有益的结论。     

Removal of soluble COD by a biofilm formed on a membrane in a jet loop type membrane bioreactor

The soluble chemical oxygen demand (COD) removal efficiency through a cake layer (biofilm) deposited on the surfaces of a membrane was investigated as a function of biofilm thickness in a jet loop type membrane bioreactor (JL-MBR). The mechanisms for the removal were investigated based on the microbial characteristics of the biofilm. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was used to identify the microbial community and a Specific oxygen uptake rate (SOUR) analysis was applied to determine the activities of microbial communities in a biofilm. Both the activities and community of microbial communities in the biofilm were similar to those found in a mixed liquor since, in JL-MBR all the substrates, dissolved oxygen, and nutrients are forced to flow through the biofilm, which differs from the biofilms grown on a non-permeable substratum in conventional biofilm process. The removal efficiency of soluble COD in a reactor through the active biofilm increased, reaching a constant value of approximately 92% despite the continuous increase in the thickness of active biofilm with the operation time. This might be attributed to (i) the presence of soluble COD that is not readily biodegraded, (ii) the presence of small and non-biodegradable organic molecules that could easily pass through the biofilm as well as the membrane, and (iii) too short a contact time of soluble solutes with the active microorganisms in the biofilm.     

风力涡轮钢结构塔楼的优化设计

为了使用于安装风力涡轮机的钢结构塔楼设计成本最小化,该塔楼结构形式为一个微锥形的焊接环肋壳体钢结构。用3个柱形壳单元组件来模拟45m高的钢壳,每个单元都有15m高,并且都有恒定的平均直径和厚度。根据欧洲规范1第2～第4章(Eurocode1,Part2～4)计算风荷载。设计中考虑壳体屈曲和环肋的局部屈曲。环肋非常必要,它可以阻止塔楼变成椭圆形。为计算生产成本,要考虑将这些钢壳加工为接近圆柱形状的加工成本和组装焊接部件的成本。成本最小化包括材料和生产成本最小化。最适宜的壳厚度、环肋的个数和直径采用Rosenbrock法直接计算。结果表明,采用环肋的数量越少,成本就越低。这个方法可以被用来预测微锥形塔楼的最小设计成本,满足细长型结构的需要,这种结构以动力荷载导致的弯曲为结构的主要荷载。     

Betons a hautes performances,a granulats artificiels actifs

High strength concretes, in particular at early ages (more than 40 MPa at 3 days and up to 80 MPa at 7 days), are obtained by replacement of certain granular size ranges of sand or gravel by cement-active artificial aggregates in a given concrete composition elaborated with a local supply of aggregates and cement. The strengthening of the paste-aggregate bond by chemical reactions between the artificial aggregates and the cement also involves an improvement of other concrete performances and not only of mechanical strengths. The cracking ability is decreased, the wear strength is higher, and water permeability is low or even nil for certain compositions. The laboratory results are confirmed by tests on the site and show the possibility of achieving high strength concretes without any particular selection of cement and natural aggregates.     

Cooling water discharges into a sea with a sloping bed

Analytical solutions for the rise in background water temperatures due to the discharge of cooling water from a power station are developed. Previous work has taken account of the cooling water flow rate and temperature increase through the station, the tidal excursion and residual drift, cross-tide dispersion and heat exchange between the water and atmosphere in a sea with constant depth. The treatment in the present paper incorporates the slope of the sea bed.The mathematical feature of the analysis is that a closed form for the background (or far-field) temperature distribution is obtained in terms of confluent hypergeometric functions. The parameters which define these functions involve the site hydrographic feature and cooling water system parameters.Results are presented which indicate the sensitivity of the temperature rise to bed slope and the position of the discharge. The temperature at the shore, which may be an important ecological indicator and station design parameter, decreases as the distance of the outlet from the shore increases; the effect of the bed slope on the rate of decrease is quantified.     

Extinction limit of a pool fire with a water mist

This work describes an experimental investigation of fire extinction limit and enhancement for a gasoline pool fire interacting with a water mist. A downward-directed nozzle produces a fine water spray over a small-scale opposed pool fire. The fire extinction limit is obtained from minimum nozzle injection pressure measured when the fire extinguish takes place. The burning rate of the fuel is also measured using a verified technique. For the conditions tested, it is shown that there are two distinct regions in the relationship between the distance from the nozzle to the fuel pan and the injection pressure, i.e. a fire extinction region and a fire enhanced region. The effective water flux is shown to be a more useful parameter than the injection pressure for the fire extinction limit. It is also revealed that the larger the spray thrust the larger the burning rate is in the fire enhanced region.     

Identification of Key Sectors in a region of a developed economy

This paper attacks the problem of selection of a proper weighting system for a choice of Key Sectors to be emphasized by development policy for a region within a developed nation. The basic concept of the Rasmussen model is utilized and three weighting methods-unweighted (Rasmussen), weighted by shares of final demand (Hazari) and weighted by shares of output (Rao-Harmston)-are tested using models of the Missouri economy.The results indicate that, if planners are to be allowed to influence policy in a developed country, a weighting system based upon sectoral shares in total output is preferable to one which uses sectoral shares in final demand.The authors are grateful to Stanley Johnson for assistance with statistical method used, and to Geetha Rao, for computer help.     

Fluid-structure interaction of a two-dimensional membrane in a flow with a pressure gradient with application to convertible car roofs

The flow-induced deformation of a membrane in a flow with a pressure gradient is studied. The investigation focuses on the deformation of aerodynamically loaded convertible car roofs. A computational methodology is developed with a line-element structural model that incorporates initial slackness of the flexible roof material. The computed flow-structure interaction yields stable solutions, the flexible roof settling into static equilibrium. The interaction converges to a static deformation within 1% difference in the displacement variable after three iterations between fluid and structural codes. Reasonably accurate predictions, to within 7%, are possible using only a single iteration between the fluid and the structural codes for the model problem studied herein. However, the deformation results are shown to be highly dependent on the physical parameters that are used in the calculation. Accurate representation of initial geometry, material properties and slackness should be found before the predictive benefits of the fluid-structure computations are sought. The iterative methodology overcomplicates the computation of deformation for the relatively small displacements encountered for the model problem studied herein. Such an approach would be better suited to applications with large amplitude displacements such as those encountered in sail design or deployment of a parachute.     

On underfloor air-conditioning of a room containing a distributed heat source and a localised heat source

This paper studies air flow in an air-conditioned room containing a distributed heat source and a localised heat source, into which cool air is supplied at low momentum through openings at a low level, and from which old air is extracted from a high level. This situation may be analogous to an auditorium containing a distributed audience and a localised group of actors and lighting on a stage, into which cool air is distributed from underneath the seating, and from which old air is removed through a ceiling, for example. Using a combination of a theoretical model and laboratory experiments, the paper shows that, in such conditions, if the localised heating is sufficiently strong compared to the distributed heating, the room will become stratified into two layers at steady state. A layer of warm air lies atop a cooler layer that attains a temperature above that of the supply air. This temperature structure depends primarily on the supply air flow rate and the ratio of the distributed heating to the total heat flux. For a room with fixed heating, increasing the supply air flow rate raises the interface between the upper and lower layers, while cooling both layers. The temperature in the upper layer depends on the total heat flux, but the temperature in the lower layer depends on the flux of distributed heating. For a room with a fixed supply air flow rate and a fixed total heat flux, increasing the strength of distributed heating warms the lower layer, but does not affect the temperature in the upper layer. Such increase in the strength of distributed heating also raises the interface. To achieve sufficient ventilation and thermal comfort in an occupied lower zone while keeping any pocket of uncomfortably warm air well above it, cool air needs to be supplied within an appropriate range of flow rates, which depends on the ratio of the distributed heating to the total heat flux. The paper shows how to determine such appropriate ranges of flow rates for different heating ratios, using the model.     

Performance validation of a hybrid ventilation strategy comprising longitudinal and point ventilation by a fire experiment using a model-scale tunnel

We examined the exhaust performance of a hybrid ventilation strategy for maintaining a safe evacuation environment for tunnel users in a tunnel fire. The hybrid ventilation strategy combines the longitudinal ventilation strategy with the point ventilation strategy which is a type of transverse ventilation strategy. The model tunnel developed by this study was scaled to 1/5 the size of a full-scale tunnel. The model-scale experiment was performed taking into consideration Froude's law of similarity. Measurement items were the distribution of temperature and concentration of smoke inside the tunnel, longitudinal wind velocity, mass flow of smoke in the point ventilation duct, and the heat release rate of the fire source. The following main conclusions were obtained. The smoke height was constant even when varying the extraction rate of smoke from the ceiling vent. The backlayering length and critical velocity of the smoke flow in the hybrid strategy could be predicted by the methodology developed by using the longitudinal strategy. The hybrid strategy maintained a safe evacuation environment on both sides of the tunnel fire.     

Imposing a rigidly coded master plan on a generated organic context: a case in Damascus,Syria

This paper illustrates the underlying Islamic guidelines and principles which dictated the building process in the Middle Eastern traditional built environment. It analyses a cluster of traditional houses in a residential quarter in Damascus, with the objectives of exploring the reciprocal effect between the physical form of the cluster and the social life that existed within it. It explores to what degree the settlement supports the social interactions of its residents and how the social life shaped the built environment. The second part of the paper studies several cases of new buildings replacing the traditional houses in the same quarter, with the objective of demonstrating the relationships between the building code, the new physical built environment and its influence on the social life within it. The goal of this paper is to establish a guideline for a new building code in Damascus, a sensitive approach with respect to physical and social requirements.