Numerical Simulation of 3D Atmospheric Flow Around a Bluff Body of CAARC Standard High Rise Building Model

Based on Reynolds Averaged Navier Stokes Equations(RANS)standard k ε model, realizable k ε model, RNG k ε model and SST k ε model, the 3D steady wind flow field around standard high building CAARC in atmospheric boundary layer was numerically simulated with software Fluent 6.3. And upon the comparison with those from wind tunnel test, it was found that numerical simulation was a feasible way to study the wind flow around high building and the distribution of wind pressure in the building’s surface. The four proposed models can reach the accuracy from the actual demand. Furthermore, it was also shown that, the numerical results were approximate to those from wind tunnel tests in the windward while between those from NPL and TJ 2 tests in the side and leeward. The pressure on the windward surface was positive with the maximum at 2/3 height and the minimum on the sides and the bottom. The pressures on the leeward surface and two sides were negative. There were little differences among the results of the four models.     

Numerical Analysis on Bearing Capacity of Piles Subjected to Side Loads

Besides the loading applied by the upper building, the piles are often subjected to indirect loading such as side loads. These kinds of loads would cause the pile bear additional force (negative skin friction), which may be large enough to reduce the bearing capacity and cause structural failure of a pile. By establishing the numerical model of pile soil interaction, the bearing capability of pile under side load was analyzed. The joint effect of different magnitude and the distance of the side load on the skin friction were focused. The joint effect of length of the pile and the distance of side load on the skin friction was discussed. The expression of the two combination relationship was obtained. Meanwhile, by using the least square method, the expression of total skin friction on different side load combination was achieved. And based on the statistical analysis of the dispersion coefficient, the function expression was proved to be of high precision. The results show that when k, which indicates the relative relation of side load distance s and the side load magnitude Q, increases to 32, the value of negative skin friction goes to zero. When c, indicating the relative relation between pile length L and side load distance s, increases to 0.5, the value of negative skin friction goes to zero. Beyond limit value of these two relative relationships, the bearing capability of the pile will not be affected by side loads.     

Luminance Calculation Model and Modified Coefficient of Building Nightscape

The illumination computational formula recommended by the International Commission on Illumination (CIE) does not adapt to the modern construction materials with mixed reflection characters. In order to find a new luminance computational method adapting to the modern construction materials and to save building energy and control urban nightscape luminance, 30 frequently-used construction materials with respect to various directions in photometric laboratory were measured. Then the luminance modified coefficient K(i,β) was figured out, and analysed the connection of reflection luminance and atmospheric attenuation in the process of divergence of light. The K(i,β) and viewing distance, light kinds, luminaire use, material cleanliness, maintenance condition of lighting system as modified coefficient was adopted to amend the computational formula of CIE, and then a new calculation model is derived. Through calculating and comparing, the luminance value of the new calculation model is one-third as much as that of the traditional one.     

Numerical Simulation for Fire Smoke Flow in a High-rise Building with Patio Space

Characteristics of smoke flow and fire spread in a patio space of a high-rise building were studied to investigate their influences on fire compartment and safety evacuation.Fire development model was established and fire scenarios were designed to simulate fire and smoke spread by CFD software numerically based on concepts of fire performance-based design in a high-rise building with double patio space,whose height are 74.65 m and 55.95 m,respectively.Simulation results show that in all fire scenarios,performance targets for safety evacuation for people in each floor was satisfied,if smoke was extracted naturally using the patio space.Hang walls mounted in corridors around the patio space prevent smoke flowing out smoothly,shorten the coming of the risk time and increase fire danger.Using chimney effect,it is preferred to adopt natural smoke exhaust method in a high-rise building with patio space.     

Analysis of Yangtze River Water as a Potential Source for Developing a Water Source Heat Pump in Chongqing

Characteristics of smoke flow and fire spread in a patio space of a high-rise building were studied to investigate their influences on fire compartment and safety evacuation. Fire development model was established and fire scenarios were designed to simulate fire and smoke spread by CFD software numerically based on concepts of fire performance-based design in a high-rise building with double patio space, whose height are 74. 65 m and 55. 95 m, respectively. Simulation results show that in all fire scenarios, performance targets for safety evacuation for people in each floor was satisfied, if smoke was extracted naturally using the patio space. Hang walls mounted in corridors around the patio space prevent smoke flowing out smoothly, shorten the coming of the risk time and increase fire danger. Using chimney effect, it is preferred to adopt natural smoke exhaust method in a high rise building with patio space.     

Opening Flow Coefficient and its Effect on Fire Smoke Flow

The flow coefficient of the typical doors and windows in different states between opening and closing was tested in a high rise experimental fire tower. It can be used for the prediction calculation of the fire smoke flow and the calculation of the positive air supply as well as for the ventilation. Using the prediction software of the fire smoke flow properties in the building, the effect of the flow coefficient on the fire smoke flow was also studied.     

Wind Vibration Characteristics of High-rise Building of RC Frame Structures

For high-rise building of RC Frame Structures, its security problems with wind load is more important, in this paper the mechanical model is established to simulate the atmospheric flow field around high-rise building, and the modal analysis is carried on for the structure. The simulation results show that velocity contour of wind field and pressure change contour describe the wind field characteristics. Wind velocity and pressure change near frontwall and backwall will affect obviously the vibration characteristics of high-rise building. Natural frequency and vibration mode can be obtained though modal analysis of high-rise building with wind load action, and necessary measures will be taken to avoid unnecessary losses due to resonance factors. And harmonic response is analyzed for high-rise building with load action to avoid resonance.     

Influence numerical analysis of combustion chamber thermal boundary conditions on unsteady combustion characteristics in micro ICE

To research the influence of combustion chamber thermal boundary conditions on micro combustion characteristics in micro ICE, the laminar flow finite rate model is adopted to simulate the micro combustion process. Firstly, the influence of grid scale, the time step length and the maximum iterations per time step on accuracy of simulation results are explored. The results show that simulation results agree well with experimental results. And then, the influences of heat transfer coefficient, wall thickness and material on combustion characteristics are discussed. The results indicate that heat transfer coefficient has obvious influence on combustion characteristics. The pressure rise rate decreases, the ignition delays and the highest pressure value drops 2 atmospheres as heat transfer coefficient increases from 0 to 55 W/(m 2·K). The wall thickness and material have a little effect on combustion characteristics. This is because that the main heat transfer resistance in the heat flow path from cylinder to external environment lies between the outer wall and environment.     

Investigations of the particle motion characteristics in the gas solid two phase wake of leeward side circular cylinder

This paper investigates the characteristics of the particle motion in circular cylinder wake flow of leeward side by simulating the micro particle flow around circular cylinder using Euler two fluid model combined with Reynolds stress model. It compares the particle velocity and concentration of different particle size in the leeward area. The results show that the vortex is formed after the gas flowed passing the cylinder, and the concentration and velocity of particles are affected by the turbulent intensity in the leeward side. Gas entrainment vortex and particles own inertia decide the flow form of fine particle around the cylinder. Both effects impact the particle concentration distribution of different size particles in the leeward area. With the increase of particle size, the particle concentration increases at the beginning and then decreases in the leeward area.     

An Improved Grey Relation Model of Safety Evaluations of Evacuation from High rise Building Fires

Based on a study of the time process of individual evacuees in high rise building fires, we found that the low security influencing factor will affect the possibility of successful evacuation severely. The traditional grey relational grade cannot reflect the effect of the grey relational coefficient fluctuation. Moreover, the single weight calculation with a subjective or objective weight will also directly affect the evaluation result of safe evacuation during high rise building fires. Based on these analyses, the grey Euclid relative grade was applied to indicate the effect of the grey relational coefficient fluctuation. The Spearman correlative rating coefficient was used to combine the subjective and objective weights to eliminate the deficiency of the single weight case. We discuss the possibility of applying the improved grey relational evaluation. Comparing the evaluation results, we found that the weight combination and grey Euclid relation applied in a safety evaluation model can improve evaluation result accuracy. The evaluation model thus corresponds to the characteristics of high rise building fires and the weight set substantially affects the evaluation result.     

Numerical Model of Hot Smoke Flow in Residential Fire

Based on the characteristics of spatial structure of residential units, the law of indoor hot smoke flow was investigated by experimental research on a platform model with multiple floors and rooms in a residential building. Three factors exerting influence on hot smoke flow in residential construction were mainly analyzed, including the relationship between the height of space and the area of single room, the size of doorway opening, and the hub space. Based on basic concepts of thermodynamics and fluid mechanics, the geometric relational model of the height of space and the area of single room impacted on filling speed of hot smoke in room was presented by conservation of mass. Moreover, under the influence of hot smoke flow, the formula of doorway opening size was developed by conservation of momentum. The results show that the fire safety of residential building should take full account of the impact of spatial structural. The indoor temperature distribution and hot smoke flow path will be controlled effectively by the design of single room size and room connectivity.     

A Three Dimensional Simplified Method for Analysis of Soil Arching Effect in the Pile-supported Embankments

To improve the understanding of the soil aching effect in the embankment fill, a series of model tests and finite element analysis were carried out. It is found that for low fill height relative to the net pile spacing, H/s－a≤1, the failure surface is vertical or slightly inclined which starts from the pile edge and goes through the whole fill height. For H/s－a≥1.5, the developed bulb shaped rupture surface is located near the pile head and can be approximated as a logarithmic spiral surface. By using the failure surface shape determined from the model test and FEM analyses, a three dimensional simplified method to evaluate the soil arching effect was proposed. The computed results were compared with FEM results and the experimental data collected from literatures, it is found that the present simplified method can predict reliable results.     

Shear Capacity Calculation Analysis of Reinforced Concrete Beams Based on Truss-arch Model

According to the theory of truss-arch model, the shear mechanism of reinforced concrete beam was analyzed, and formula of shear bearing capacity was proposed. In this formula, softening effect of concrete and the arch function were taken into account, and the coefficients in the formula were amended with experimental data. When the performance difference between the structural material and the original material is huge, the code formula of shear bearing capacity calculation is inapplicable. After the computation, the ratio of the results calculated by truss-arch model theory formula and the results calculated by the current code formula was close to 1, and the standard deviation coefficient and coefficient of variation were smaller than those of standard formula results, and the results calculated by truss-arch model formula were in good agreement with the experimental results. The collected experimental data was calculated with the shear capacity formula in ACI318-08, and the calculation results showed that United States building code was more conservative than the standard of China. The results indicate that the shear bearing capacity formula based on truss-arch model can be used for computation of shear bearing capacity of reinforced concrete beams.     

Experimental Study of Flow and Heat Transfer in Heat Exchanger with Small Channels

The experimental study of the flow resistance and heat transfer characteristics are conducted for water and ethylene glycol solution (66% Wt) flowing in the heat exchanger with small rectangular microchannels . The heat exchanger having the channels of 0.4 mm in width, 2.0 mm in height, and 20 mm in length is heated by a hearing rod at the bottom surface, the upper and two side surfaces are adiabatic. During experiments, the Reynolds number are ranged from 2 to 2 500. The experimental results show that the flow friction factor decreases and Nusselt number increases with increasing Reynolds number for water and ethylene glycol solution. At a fixed Reynolds number, the Nusselt number for ethylene glycol solution with larger Prandtl number is greater than that for water. Meanwhile, the correlations of flow resistance and heat transfer in the heat exchanger with small channels are obtained for engineering application.     

Numerical Simulation of Turbulent Flow Flow Over a Tiny Rearward facing Step on Circular Cylinder

Results of numerical simulation for viscous incompressible turbulent flow field over a tiny rearward facing step on circular cylinder are presented.The Domain Subdividing and Matching method and the Simplified SOLA solution are engaged in the simulation. The effects of the step's height,installed position and Reynolds number on the flow field are obtained and discussed. The results show that, if the rearward facing step is installed on the cylinder surface at a suitable point, a reattached boundary layer will be produced at the downstream of the step lagged in a small distance on the cylinder s surface and will re separate from the cylinder s surface.The reattachment point and the re separated point will exchange as the step's height and installed point exchanging.There is an effective reattachment region. If the fluid flow separated from the sharp edge of the rearward step reattaches in the effective region, the re separated point will occur at the downstream of the cross section of the cylinder and the drag will be reduced. This pattern is not directly connected with the flow in laminar nor in turbulent.[WT5HZ]     

Error Analysis for In-situ Measurement of Heat-transfer Coefficient of Building Envelope

The in-situ measurement of heat-transfer coefficient of external wall is the major content of building energy efficient measurement. A new test method and error assessment function were put forward. Computer simulation was conducted to analysis the influence of hot-box size, air temperature in hot box, structure and thickness of external wall on the result error to provide the theoretical guidance for test apparatus development. The results show that, size of hot-box and thickness of external wall is the major factors which decide the error in test. In-situ measurements were conducted according to the computer simulation results and show fine accuracy.     

Reynolds Number Effect on Wind-induced Vibration of Stay-cables

In order to analyze the large amplitude vibration mechanism of cables based on Reynolds number effect, wind forces measurement and free vibration tests were carried out on cable models with/without artificial water rivulet. In the tests, the cable models without artificial water rivulet were in different surface roughness and those with artificial water rivulet attached were in smooth surface, and artificial water rivulet was attached in different positions respectively. Wind force coefficients, Den Hartog galloping coefficients and free vibration amplitudes were obtained. It is shown that in critical Reynolds number range, there is the possibility that the special wind force coefficient characteristics and flow pattern induce vibration, and this is the possible mechanism for dry cable galloping. The roughness of cable surface can change the intensity of critical Reynolds number effect and the range of critical Reynolds number. The existence of water rivulet can change the critical Reynolds number effect. For some water rivulet positions, in certain Reynolds number range, dCF/dα＜0, vibration happens, which agrees with the Den Hartog galloping criterion. In high Reynolds number range, besides Den Hartog galloping, vibrations are relevant to significant decrease of wind force coefficients and unstable flow pattern.     

Subway Station Plate Evaporative Cooler Heat and Mass Transfer of Falling Film under Gas liquid Cross flow Condition

With the influence of the different gas Reynolds number and liquid Reynolds number on falling film heat and mass transfer of subway station plate evaporative cooler, the experiment was carried out by non contact infrared thermal imaging technology under gas liquid cross flow condition. The results indicated that during the increasing of liquid Reynolds number the thickness of liquid film increased and the temperature difference between liquid film inlet and outlet decreased in determined heating water temperature which weakened the heat transfer of liquid film. However, the increase of liquid Reynolds number strengthened the liquid film turbulence that enhanced heat transfer. Under the synergistic effect of these two factors, there was an optimal liquid Reynolds number which minimize thermal resistance and maximize heat and mass transfer coefficient of liquid film.     

Elastic-Perfectly Plastic Solution of Tunnel Surrounding Rocks Using Mogi-Coulomb Strength Criterion

Reasonable choice of rock strength criteria is crucial for stress and displacement prediction and support design in tunnel engineering. Based on Mogi-Coulomb strength criterion and elastic-perfectly plastic model, analytical solutions of stress and displacement for surrounding rocks around a circular tunnel were derived The intermediate principal stress coefficient was used to present the intermediate principal stress effect. The results in this study were compared with the current solutions in the literatures and the influence of intermediate principal stress and shear strength parameters of surrounding rocks was discussed. The results showed extensive applicability and the Mohr-Coulomb strength criterion and Matsuoka-Nakai criterion are two special cases; when the intermediate principal stress coefficient b was equals to 0.5, the results indicated that the intermediate principal stress effect and its range for rock strength; the influence of cohesion and internal friction angle on the plastic radius and tunnel wall displacement was significant; Care should be taken to the effects of intermediate principal stress and shear strength parameter variations of surrounding rocks on tunnel design and construction.     

Effects of Air Temperature and Humidity on Particle Deposition in a Ventilation Duct

Particle deposition in a fully developed turbulent flow of ventilation duct with a rectangular cross section of 0.3 m×0.2 m and 3 m in length was investigated. The effects of thermophoretic force and air humidity were also considered. Trajectories of 3 000 particles were tracked on the basis of the random walk model from Lagrangian approach. The profile of dimensionless deposition velocity with relaxation time was achieved and the comparison with the previous studies was made with particle size range of 0.01 50 μm and air flow velocity of 5 m/s. It is found that the trend of dimensionless deposition velocity is in agreement with the previous studies and the profile of dimensionless deposition velocity showed a V shaped curve. The effects of temperature and air humidity were also investigated with particle size of 1 μm. Thermophoretic force caused by temperature gradient between air flow and wall surface accelerated particle deposition. Meanwhile, it is also found that the deposition velocity increases with the increase of air relative humidity.