Experimental and numerical investigation of the airflow around a raised permeable panel

Analysis of the airflow around an elevated permeable panel is presented in this paper. The airflow was studied by both a 3D computational simulation and a full scale experiment using two kinds of cladding material, namely an impermeable plastic film and permeable nets. The air velocity at different locations around the panel was measured by rotary cup anemometers in order to investigate the airflow. A three-dimensional numerical simulation (CFD) was employed to analyze the edge effects. In the numerical model, the net was simulated as a porous medium obeying Forchheimer’s law. Both numerical results and full-scale experiments indicate important differences between the airflow around the panel covered by impermeable material (film) and the airflow around and through the permeable panels (nets). Airflow around the elevated experimental panel was found to become smoother when the plastic film is replaced by permeable nets. The numerical results derived by the 3D computational model show good qualitative and quantitative agreement with the full scale experimental data in the case of permeable (net-covered) panels.     

The field comparison of three measuring techniques for evaluation of the surface dust level in ventilation ducts

This paper reports the comparison of three measuring methods for quantifying the amount of dust on the inner surface of ventilation ducts: 1) a vacuum test method; 2) a gravimetric tape method; and 3) an optical method. Thirteen recently constructed buildings were selected for the field test in the Helsinki metropolitan area. The dust samples in each method were all taken from the same location in the duct. Most of the ducts sampled had no residual oil originating from the manufacturing process. The mean amount of dust measured with the vacuum test method was 1.3 g/m2 and the range was < 0.1-8.4 g/m2. The mean surface dust level measured using the gravimetric tape method was slightly lower, i.e. 1.2 g/m2 (< 0.1-5.0 g/m2). The mean cleanliness level of the ducts was 15% (2-41%) using the optical method. The wide variations and differences in the results of the different methods were caused by the unequal distribution of dust on the duct surfaces.     

A preliminary study of assimilating numerical weather prediction data into computational fluid dynamics models for wind prediction

The goal of this effort is to combine the strengths of Numerical Weather Prediction (NWP) with Computational Fluid Dynamics (CFD) to produce locale-specific flow patterns that could be used for micrositing wind power plants. We do this in two ways: (1) we use the mesoscale model data as inflow for the CFD model and (2) we assimilate vertical profiles of mesoscale model output into the CFD model as a body force. We study the impact of this technique with a case study in the rolling topography of central Pennsylvania. We compare wind profiles between the mesoscale model alone, the CFD model alone, and the fully assimilated mesoscale/CFD solution. In addition, we examine the impact of the mesoscale assimilation into the CFD model on the fine-scale flow structure. This preliminary approach of combining techniques in NWP and CFD through data assimilation provides a unique assessment of the utility of specific locations for wind power production as well as for improving simulations for other purposes.     

A second order turbulence model for the prediction of air movement and heat transfer in a ventilated room

A full-scale test room is used to investigate experimentally and numerically the velocity and temperature fields in the case of a mechanical ventilation. Detailed fields are measured for three cases of ventilation air temperature: an isothermal case, a hot case, and a cold case. The experimental data are used to test two turbulence models: a first order k-ε realizable turbulence model and a second order quadratic RSM (Reynolds Stress Model) turbulence model. The RSM model predicts the temperature and velocity fields better than the k-ε turbulence model. In particular, global values of velocity and temperature coming from experiments are in good agreement with the RSM turbulence model. This conclusion is confirmed using a turbulence analysis based on Lumley triangles.     

A calculation method for the floor surface temperature in radiant floor system

In this paper, a calculation method for the floor surface temperature in radiant floor heating/cooling system is proposed, a new formula is derived to estimate the floor surface temperature. The floor is divided into two layers. The correlation for the thermal conductivity of the lower layer is developed based on the numerical model of the radiant floor system built in this paper. The results show that the floor surface temperature values from the proposed method are in agreement with the experimental and numerical values.     

Experimental and numerical modelling of the three-dimensional incompressible flow behaviour in the near wake of circular cylinders

An experimental investigation was carried out to study the structure of the flow field around three-dimensional circular cylinders. The study of the flow field around an obstacle was performed in a wind tunnel using a particle image velocimetry (PIV) system. The flow of a fluid around an obstacle with a different velocity to the oncoming flow was examined. The results showed the dependence of the flow structure around the obstacle on its Reynolds number, and the spacing between a pair of obstacles. Detailed quantitative information of turbulence parameters in the vicinity of the obstacle was attained. Extensive wind tunnel experimental results are presented and compared with numerical simulation. A three-dimensional numerical model with Reynolds stress model (RSM) turbulence and a non-uniform grid system were used to examine the effects of a single cylinder and two cylinders in tandem on the flow. The principal objective was to analyse three-dimensional flow past a single cylinder and two circular cylinders placed in tandem by combining the application of a PIV experimental technique and an RSM turbulence model.For the case of two cylinders in tandem, the flow patterns are characterized in the gap region as a function of the distance between the cylinders. A good level of agreement was found between the experimental results of flow and numerical simulation.     

坑中坑对软土基坑变形影响的有限元分析

以福州某设有坑中坑的软土深基坑工程为研究对象,采用土工有限元分析技术,考虑桩土相互作用,建立基坑开挖模型,土体采用HS模型模拟,分析围护桩水平位移变化特性,研究坑中坑开挖对外坑基坑变形的影响。通过与实际监测资料的对比分析,表明了坑中坑的存在对外坑围护结构的变形有很大影响,数值模拟计算方法在坑中坑工程中有良好适用性,对于类似工程具有指导意义。     

Determination of the optimal parameters in regression models for the prediction of chlorophyll-a: A case study of the Yeongsan Reservoir, Korea

Statistical regression models involve linear equations, which often lead to significant prediction errors due to poor statistical stability and accuracy. This concern arises from multicollinearity in the models, which may drastically affect model performance in terms of a trade-off scenario for effective water resource management logistics. In this paper, we propose a new methodology for improving the statistical stability and accuracy of regression models, and then show how to cope with pitfalls in the models and determine optimal parameters with a decreased number of predictive variables. Here, a comparison of the predictive performance was made using four types of multiple linear regression (MLR) and principal component regression (PCR) models in the prediction of chlorophyll-a (chl-a) concentration in the Yeongsan (YS) Reservoir, Korea, an estuarine reservoir that historically suffers from high levels of nutrient input. During a 3-year water quality monitoring period, results showed that PCRs could be a compact solution for improving the accuracy of the models, as in each case MLR could not accurately produce reliable predictions due to a persistent collinearity problem. Furthermore, based on R² (goodness of fit) and F-overall number (confidence of regression), and the number of explanatory variables (R-F-N) curve, it was revealed that PCR-F(7) was the best model among the four regression models in predicting chl-a, having the fewest explanatory variables (seven) and the lowest uncertainty. Seven PCs were identified as significant variables, related to eight water quality parameters: pH, 5-day biochemical oxygen demand, total coliform, fecal indicator bacteria, chemical oxygen demand, ammonia-nitrogen, total nitrogen, and dissolved oxygen. Overall, the results not only demonstrated that the models employed successfully simulated chl-a in a reservoir in both the test and validation periods, but also suggested that the optimal parameters should cautiously be considered in the design of regression models.     

Use of numerical taxonomy for comparison of metal pollution in the environment

Numerical taxonomy has been applied to explain the behaviour of macroconstituents (Na, K, Ca, Mg) and heavy metals (Cr, Mn, Fe, Co, Ni, Pb, Cu, Zn, Cd) in different ecological sections (mollucs, plants, rain, drv deposition, soils, airborne dust, lixiviates through soils, springs) in the industrialized area near Bilbao (Spain). Distances based on correlation coefficients and mean Euclidean distances have been used for drawing dendrograms of metals and sections. Three types of effects may be distinguished, due to potassium, other macrocomponents (Na, Ca, Mg) and heavy metals as a result of the accumulation of these constituents in specific sections of the environment.     

A comparison of SWAT, HSPF and SHETRAN/GOPC for modelling phosphorus export from three catchments in Ireland

Recent extensive water quality surveys in Ireland revealed that diffuse phosphorus (P) pollution originating from agricultural land and transported by runoff and subsurface flows is the primary cause of the deterioration of surface water quality. P transport from land to water can be described by mathematical models that vary in modelling approach, complexity and scale (plot, field and catchment). Here, three mathematical models (soil water and analysis tools (SWAT), hydrological simulation program-FORTRAN (HSPF) and système hydrologique Européen TRANsport (SHETRAN)/grid oriented phosphorus component (GOPC)) of diffuse P pollution have been tested in three Irish catchments to explore their suitability in Irish conditions for future use in implementing the European Water Framework Directive. After calibrating the models, their daily flows and total phosphorus (TP) exports are compared and assessed. The HSPF model was the best at simulating the mean daily discharge while SWAT gave the best calibration results for daily TP loads. Annual TP exports for the three models and for two empirical models were compared with measured data. No single model is consistently better in estimating the annual TP export for all three catchments.     

An ANN-based model for the prediction of internal lighting conditions and user actions in non-residential buildings

This paper presents an Artificial Neural Network (ANN) based approach able to predict the internal lighting conditions in a working environment, taking into account the daylight entering the respective space as well as the special requirements of each user. The model training procedure is based both on real illuminance and occupancy data (measurements throughout a year) and on simulations, in order to integrate all possible conditions. User preferences in respect to lighting and blinds are expressed through probability curves. Illuminance due to the external daylight is calculated and predicted throughout the whole year, depending on the weather conditions, the time of the day, the location and the office orientation. The work plane distance from the window and the usage of blinds are also considered. The proposed model is further implemented for the prediction and evaluation of energy consumption for lighting in a working space based on the user preferences.     

The use of a double heat pipe heat exchanger system for reducing energy consumption of treating ventilation air in an operating theatre—A full year energy consumption model simulation

In two earlier papers [Y.H. Yau, Application of a heat pipe heat exchanger to dehumidification enhancement in tropical HVAC systems—a baseline performance characteristics study, International Journal of Thermal Sciences 46 (2) (2007) 164–171; Y.H. Yau, The analysis of enthalpy change with and without a heat pipe heat exchanger in a tropical air conditioning system, International Journal of Energy Research 30 (15) (2006) 1251–1263], two series of experiments were conducted under controlled conditions to establish the baseline performance characteristics of the heat pipe heat exchanger (HPHX). In the present paper, a complete empirical transient systems simulation program model is assembled to estimate the air states as well as the entire typical meteorological year energy consumption of an operating theatre located in Kuala Lumpur, Malaysia.     

Analysis of formation fracturing for the Maxi-HDD Qin River crossing project in China

A new irrigation pipeline was installed using the Horizontal Directional Drilling (HDD) method in order to alleviate the water shortage situation in Jiaozuo City, Henan Province, China. This pipe installation project included two parallel HDD crossings, with a pipe diameter of 1016 mm and a driven length of 1750 m for both of them. Based on the preliminary detailed geological survey report of the riverbed, hydro-fracturing control under high slurry pressure would be a big challenge for this project. This paper summarizes the prediction methods for the maximum allowable mud pressure in the borehole based on different mechanisms of formation fracturing. Based on the geological data of this crossing project, the Delft equation and another prediction method based on tensile failure (termed here the Xia method) were used to calculate the maximum allowable annular pressure. The real pumping pressure of this project was recorded by the contractor. By comparing the theoretical predictions of allowable pressure with the actual pressures for the horizontal section of the borehole, it indicated that the Xia method is conservative and the limits of the Delft equation could not be verified in this project. As a solution dealing with potential hydro-fracturing, finite element modeling shown that increasing the ground surface load would rise the borehole allowable pressure at which fracturing would occur. This solution was used to deal with a blow-out in the entry section of one pilot hole on this project. Under the guidance of the theoretical and numerical simulation results, the Qin River crossing project was successfully completed.     

A mine shaft case study on the accurate prediction of yield and displacements in stressed ground using lab-derived material properties

Continuum models provide a useful tool for the prediction of stress re-distribution due to excavation and induced yielding, and are used as a key analysis tool in the design of many underground excavations. Recent developments in the study of rock strength and post-yield behaviour have played a key role in improving our understanding of how plastic constitutive models can also be used to practically replicate observed phenomena in brittle rocks. In particular, new models for rock dilatancy can help to improve the applicability of plastic constitutive models as a predictive tool for excavation design. In this study, laboratory data for a heterogeneous, brittle, conglomerate unit from a mine shaft has been analysed. Using parameters from this analysis, brittle strength and dilatancy models have been implemented in a finite-difference code to predict not only stress re-distribution and yield around the shaft, but also to obtain realistic displacement values. Comparison of the modelling results to displacements measured using borehole extensometers show that the constitutive model and lab-derived parameters used were effective in predicting the rockmass behaviour. Parameters were further optimized through back analysis. One interesting finding of this analysis is that the in-situ rockmass dilation decay rate (as a function of plastic strain) appears to be faster than estimated based on laboratory data, which may be indicative of the influence of rockmass-scale natural fractures and other geological structures on the dilation decay process. It also appears possible to model the in-situ dilation decay rate using a single parameter, instead of separate parameters for unconfined and confined conditions. To conclude the study, more numerical results obtained using alternative dilatancy models are presented to illustrate the problem of non-uniqueness in plasticity back analyses.     

Evaluation of simplified models for predicting CO2 concentrations in small commercial buildings

Evaluation of a building for application of demand-controlled ventilation (DCV) typically involves the use of computer simulations to predict energy use/costs for both fixed ventilation and ventilation adjusted to maintain fixed CO₂ levels within the space. The simulation tools incorporate models for predicting CO₂ concentrations in response to internal sources (people), infiltration/exfiltration, and ventilation. This paper presents a detailed evaluation of different modeling approaches for predicting levels of CO₂ in occupied spaces for small, single-zone commercial buildings employing packaged air-conditioning equipment. Two-zone and three-zone transient models were compared with a quasi-static equilibrium model applied to three distinctly different building types. Baseline data were derived from computational fluid dynamic models that were developed for field sites. A complete building system simulation model was then used to compare the impact of the different modeling approaches on the predicted energy cost savings associated with application of DCV in each building type. The use of a transient CO₂ model did not have a significant impact on model prediction accuracy and energy cost savings predictions as compared with the quasi-static model. The difference in predicted annual energy costs between the various CO₂ modeling types were small and less than might result from errors introduced by factors such as CO₂ sensor uncertainty. Therefore, the use of an equilibrium model is sufficient for use in evaluating DCV for small commercial buildings.     

A model for the prediction of the air composition in pressure saturators

The paper deals with the air composition in pressure saturators used for dissolved air flotation. Two mathematical models are developed: a kinetic model for describing the change in saturator air composition with time from start-up to eventual equilibrium, and an abbreviated model for only predicting the saturator air composition once equilibrium is reached. Both derivations are based on mole balances for the two major components of atmospheric air, nitrogen and oxygen, and the equilibrium between saturator air and outflowing water as predicted by Henry's law. The models take factors into account which had hitherto been ignored, such as saturator efficiency, saturator pressure and the oxygen saturation level in the incoming water. The kinetic model gives a clear demonstration of the changes in air composition after saturator start-up and how different operating parameters affect the rate of change. It is demonstrated that laboratory saturators, operated at low hydraulic loading, could take many hours to attain equilibrium, which could explain anomalous measurements reported in the literature. Both mathematical models were tested with data collected from a laboratory saturator operated under conditions similar to those encountered at full-scale. The experimentally determined values agree well with the predicted results, with the exception that the actual saturator air composition converges towards an equilibrium concentration which is slightly less enriched in nitrogen than predicted by the theoretical models.     

A comparison of large Eddy simulations with a standard k-ε Reynolds-averaged Navier-Stokes model for the prediction of a fully developed turbulent flow over a matrix of cubes

A fully developed turbulent flow over a matrix of cubes has been studied using the large Eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) [more specifically, the standard k-ε model] approaches. The numerical method used in LES of an incompressible fluid flow was a second-order accurate, fully conservative discretization scheme. This scheme was used in conjunction with a dynamic semi-coarsening multigrid method applied on a staggered grid as proposed originally by Ham et al. (Proceedings of the Seventh Annual Conference of the Computational Fluid Dynamics Society of Canada, Halifax, Nova Scotia, Canada, 1999; J. Comput. Phys. 177 (2002) 117). The effects of the unresolved subgrid scales in LES are modeled using three different subgrid-scale models: namely, the standard Smagorinsky model; the dynamic model with time-averaging procedure (DMT); and, the localized dynamic model (LDM). To reduce the computational time, LES calculations were conducted on a Linux-based PC cluster using the message passing interface library. RANS calculations were performed using the STREAM code of Lien and Leschziner (Comp. Meth. Appl. Mech. Eng. 114 (1994) 123). The Reynolds number for the present flow simulations, based on the mean bulk velocity and the cube height, was 3800 which is in accordance with the experimental data of Meinders (Ph.D. Thesis, Faculty of Applied Sciences, Delft University of Technology, Delft, Netherlands, 1998). A comparison of predicted model results for mean flow and turbulence with the corresponding experimental data showed that both the LES and RANS approaches were able to predict the main characteristics of the mean flow in the array of cubes reasonably well. LES, particularly when used with LDM, was found to perform much better than RANS in terms of its predictions of the spanwise mean velocity and Reynolds stresses. Flow structures in the proximity of a cube, such as separation at the sharp leading top and side edges of the cube, recirculation in front of the cube, and the arch-type vortex in the wake are captured by both the LES and RANS approaches. However, LES was found to give a better overall quantitative agreement with the experimental data than RANS.     

Fracture model for the prediction of the electrical percolation threshold in CNTs/Polymer composites

In this paper, we propose a 3D stochastic model to predict the percolation threshold and the effective electric conductivity of CNTs/Polymer composites. We consider the tunneling effect in our model so that the unrealistic interpenetration can be avoided in the identification of the conductive paths between the CNTs inside the polymer. The results are shown to be in good agreement with reported experimental data.     

Numerical predictions of indoor climate in large industrial premises. A comparison between different k–ε models supported by field measurements

This paper explores the benefits of using computational fluid dynamics (CFD) as a tool for prediction of indoor environment in large and complex industrial premises, in this case a packaging facility. This paper also presents a comparison between three eddy-viscosity turbulence models, i.e. the standard k–ε, the RNG k–ε, and the realizable k–ε, used for predictions of the flow pattern and temperature distribution in this large industrial facility. The predictions are compared with field measurements and the RNG k–ε model has been found to be the one most concurrent with the measured values.     

储罐爆炸事故碎片抛射距离简易预测模型

摘 要：为合理确定液化石油气储罐爆炸事故中爆炸碎片的抛射范围,基于动力学原理和理论分析构建了爆炸碎片抛射距离预测模型,并借鉴某液化石油气爆炸事故案例有关数据进行数值模拟和验证分析。结果表明：模型预测值与事故数据及前人的Monte Carlo数值模拟结果较为吻合,模型对于球罐和柱形储罐爆炸事故都具有很好的适用性。该模型可快速便捷地预测爆炸碎片的危害范围,预测结果可为应急部门救援决策提供技术支持,同时也可为石油化工园区规划建设及风险管控提供理论依据。