The hygrothermal performance of a ventilated roof cavity is greatly affected by the airflow passing through it.This ventilation flow is mainly driven by the wind pressure difference between openings and the thermal-in...The hygrothermal performance of a ventilated roof cavity is greatly affected by the airflow passing through it.This ventilation flow is mainly driven by the wind pressure difference between openings and the thermal-induced buoyancy.However,the wind effect is not well understood as it is often neglected in previous studies.The present study investigates the properties of such airflows,including the flow pattern,flow regime,and flow rate,using a CFD method.The target building is a large-span commercial building with a low-pitched roof.To study the wind-induced airflows,the onset atmospheric boundary layer wind flow was modelled,and the results were compared with the site-measured data recorded in the literature.To study the thermal-induced buoyancy effects,a roof cavity model found in the literature with experimental data was adopted.The findings show that the flow pattern in the roof cavity varied with the airflow driven factors.The flow separation at the windward eave inlet of the thermally induced flows are more pronounced compared with those of the wind-induced flows.Furthermore,the wind-induced airflows can generate around two times more ventilation flow rate through the roof cavity compared to the thermal-induced airflow.The findings indicate that wind-induced ventilation flows are the dominant factor of the roof cavity ventilation in a large-span,low-pitched building.展开更多
Understanding roof behaviour and immediate roof failure patterns of longwall face is a prerequisite for establishing correct roof control theory and appplying effective roof control measures. Roof behaviour and immedi...Understanding roof behaviour and immediate roof failure patterns of longwall face is a prerequisite for establishing correct roof control theory and appplying effective roof control measures. Roof behaviour and immediate roof failure pattern have a close relationship with upper mining boundary conditions of longwall face. According to actual situation of Datong Mining Area,upper mining boundary conditions of longwall face have been classified into 5 types in this paper.Roof behaviour and immediate roof failure pattern under each upper mining boundary condition are discussed in details.展开更多
Due to the high accuracy and fast acquisition speed offered by airborne Light Detection and Ranging(LiDAR)technology,airborne LiDAR point clouds have been widely used in three-dimensional building model reconstruction...Due to the high accuracy and fast acquisition speed offered by airborne Light Detection and Ranging(LiDAR)technology,airborne LiDAR point clouds have been widely used in three-dimensional building model reconstruction.This paper presents a novel approach to segment building roofs from point clouds using a Gaussian mixture model in which buildings are represented by a mixture of Gaussians(MoG).The Expectation-Maximization(EM)algorithm with the minimum description length(MDL)principle is employed to obtain the optimal parameters of the MoG model for separating building roofs.To separate complete planar building roofs,coplanar Gaussian components are merged according to their distances to the corresponding planes.In addition,shape analysis is utilized to remove nonplanar objects caused by trees and irregular artifacts.Building models are obtained by combining segmented planar roofs,topological relationships,and regularized building boundaries.Roof intersection segments and points are derived by the segmentation results,and a rasterbased regularization method is employed to obtain geometrically correct and regular building models.Experimental results suggest that the segmentation method is able to separate building roofs with high accuracy while maintaining correct topological relationships among roofs.展开更多
文摘The hygrothermal performance of a ventilated roof cavity is greatly affected by the airflow passing through it.This ventilation flow is mainly driven by the wind pressure difference between openings and the thermal-induced buoyancy.However,the wind effect is not well understood as it is often neglected in previous studies.The present study investigates the properties of such airflows,including the flow pattern,flow regime,and flow rate,using a CFD method.The target building is a large-span commercial building with a low-pitched roof.To study the wind-induced airflows,the onset atmospheric boundary layer wind flow was modelled,and the results were compared with the site-measured data recorded in the literature.To study the thermal-induced buoyancy effects,a roof cavity model found in the literature with experimental data was adopted.The findings show that the flow pattern in the roof cavity varied with the airflow driven factors.The flow separation at the windward eave inlet of the thermally induced flows are more pronounced compared with those of the wind-induced flows.Furthermore,the wind-induced airflows can generate around two times more ventilation flow rate through the roof cavity compared to the thermal-induced airflow.The findings indicate that wind-induced ventilation flows are the dominant factor of the roof cavity ventilation in a large-span,low-pitched building.
文摘Understanding roof behaviour and immediate roof failure patterns of longwall face is a prerequisite for establishing correct roof control theory and appplying effective roof control measures. Roof behaviour and immediate roof failure pattern have a close relationship with upper mining boundary conditions of longwall face. According to actual situation of Datong Mining Area,upper mining boundary conditions of longwall face have been classified into 5 types in this paper.Roof behaviour and immediate roof failure pattern under each upper mining boundary condition are discussed in details.
基金This work was supported by the National Key Scientific Instrument and Equipment Development Projects of China[grant number 2013YQ120343]the National Natural Science Foundation of China[grant numbers 41171265 and 41101436]the 100 Talents Program of the Chinese Academy of Sciences.
文摘Due to the high accuracy and fast acquisition speed offered by airborne Light Detection and Ranging(LiDAR)technology,airborne LiDAR point clouds have been widely used in three-dimensional building model reconstruction.This paper presents a novel approach to segment building roofs from point clouds using a Gaussian mixture model in which buildings are represented by a mixture of Gaussians(MoG).The Expectation-Maximization(EM)algorithm with the minimum description length(MDL)principle is employed to obtain the optimal parameters of the MoG model for separating building roofs.To separate complete planar building roofs,coplanar Gaussian components are merged according to their distances to the corresponding planes.In addition,shape analysis is utilized to remove nonplanar objects caused by trees and irregular artifacts.Building models are obtained by combining segmented planar roofs,topological relationships,and regularized building boundaries.Roof intersection segments and points are derived by the segmentation results,and a rasterbased regularization method is employed to obtain geometrically correct and regular building models.Experimental results suggest that the segmentation method is able to separate building roofs with high accuracy while maintaining correct topological relationships among roofs.
