Predicting air pressure in drainage stack of high-rise building

It is necessary to understand the features of air pressure in a drainage stack of a high-rise building for properly designing and operating a drainage system. This paper presents a mathematical model for predicting the stack performance. A step function is used to describe the effect of the air entrainment caused by the water discharged from branch pipes. An additional source term is introduced to reflect the gas-liquid interphase interaction （GLII） and stack base effect. The drainage stack is divided into upper and base parts. The air pressure in the upper part is predicted by a total variation diminishing （TVD） scheme, while in the base part, it is predicted by a characteristic line method （CLM）. The predicted results are compared with the data measured in a real-scale high- rise test building. It is found that the additional source term in the present model is effective. It intensively influences the air pressure distribution in the stack. The air pressure is also sensitive to the velocity-adjusting parameter （VAP）, the branch pipe air entrainment, and the conditions on the stack bottom.

Spatial and Time Structure of a Gravity Wave in Horizontal Atmosphere of Heterogeneous Stratification

By the use of the WKBJ method combined with the characteristic line method, the asymptotic solution of a gravity wave envelope in the atmosphere of horizontal heterogeneous stratification and time-varying stratification is obtained. The solution shows that not only the variation of amplitude of the gravity wave but also the variation of wavelength and the width of the envelope are affected by the horizontal heterogeneity. As the wave envelope moves from a region, of strong stratification to a weak one, the horizontal wavelength will become shorter, the width of the envelope will narrow and its amplitude will increase. The variation of stratification with time cannot lead to the variation of wavelength and envelope width, but the amplitude of the wave envelope will increase while the amplitude of the wave decreases in time.

Dynamic modeling of thermal conditions for hot-water district-heating networks

To investigate the dynamic characteristics of the thermal conditions of hot-water district-heating networks, a dynamic modeling method is proposed with consideration of the heat dissipations in pipes and the characteristic line method is adopted to solve it. Besides, the influences of different errors, space steps and initial values on the convergence of the dynamic model results are analyzed for a model network. Finally, a part of a certain city district-heating system is simulated and the results are compared with the actual operation data in half an hour from 6 secondary heat stations. The results indicate that the relative errors for the supply pressure and temperature in 5 stations are all within 2%, except in one station, where the relative error approaches 4%. So the proposed model and algorithm are validated.

Size Effect on Onset and Subsequent Evolution of Adiabatic Shear Band:Theoretical and Numerical Analysis

The adiabatic shear instability of ductile materials has attracted more and more attentions of researchers and groups,who have been sparing no effort in further understanding of the underlying mechanism since the first experimental depiction of adiabatic shear instability by Zener and Hollomon.As for the adiabatic shear instability,many factors account for its occurrence,including heat conduction,inertia effect,microstructure effect and so on.However,lots of experimental evidence has shown that metal materials display a strong size effect when the characteristic length scale is in the order of microns.The size effect has also been observed in the analysis of shear band in the ductile materials because the order of the bandwidth stays within the microscale range.However,a comprehensive understanding of the whole process of adiabatic shear banding(ASB),including the early onset and the subsequent evolution,is still lacking.In this work,a gradient plasticity model based on the Taylor-based nonlocal theory feasible for the linear perturbation analysis and convenient for numerical calculation is proposed to investigate the strain gradient on the onset of ASB and the coupling effect of heat conduction,inertia effect and strain gradient at the early stage,as well as on the subsequent evolution process at later stages.As for the onset of ASB,the linear perturbation method is used to consider the effect on the initial formation of ASB.After the investigation of the onset of ASB.the characteristic line method is applied to describe the subsequent nonlinear evolution process of ASB.Three stages of ASB evolution are clearly depicted during the evolution process,and the significance of size effect on the ASB nonlinear evolution process of ASB at different stages is analyzed.With the help of linear perturbation analysis and characteristic line method,a comprehensive description of the role of strain gradient in the ASB from the early onset to the end of the evolution is provided.