Research On The Analyzing And Calculating Methods Of Road Tunnel Ventilation Network

Abstract:In recent years, the road tunnels in China are growing both in length and scale, which makes it more possible for the contamination to accumulate to a high concentration and result in a disaster, and the tunnel ventilation and smoke extraction technology becomes the key guarantee for the tunnel security. So, in this paper, a systematic research on ventilation and smoke extraction modes of tunnel is carried out, and method is proposed based on the network model for calculation and design of tunnel ventilation and smoke exhaust system. And then, it is applied to a practical engineering, and the results calculated by ventilation network model are validated through fire model tests. The main work of the paper are as follows:(1) The ventilation network theory is introduced into the calculation of road tunnel ventilation systems, the flow characteristics and compositions of ventilation power are analyzed respectively under longitudinal ventilation mode, semi-transverse ventilation mode, transverse ventilation mode and combination ventilation mode, network graphs of the tunnel ventilation systems are drawn, and calculation models based on network and how to configure fans in normal operation condition under different tunnel ventilation modes are proposed.(2) Calculation models based on ventilation network in fire operation condition are proposed, and the method for calculating central technical parameters, the air flux and pressure of fans in need under different tunnel fire ventilation modes are provided.(3) A road tunnel ventilation network calculation procedure with the air flux expressed by mass flux is developed. The procedure can realize the calculation of mass flow rate, wind pressure, wind speed, ventilation resistance and number of fans in need.(4) The dynamic variations of wind resistance coefficient attached to smoke vent and smoke duct branches with the different smoke vent design schemes under central exhaust mode are studied in this paper. In different smoke vent design scenarios, the smoke temperature distributions along tunnel ceiling and smoke duct, the smoke flow velocity distributions along the duct and through the vent are acquired. Finally, the two key parameters, wind density and wind resistance coefficient of network branches are determined.(5) The calculation procedure is applied to the research of smoke extraction technology in Cangling tunnel with central exhaust mode, the rule how the smoke vent design schemes, smoke exhaust modes, exhaust volume and air leakage influence the smoke flow velocity distributions along the duct and through the vent is gained, and proper vent design scheme is proposed. In the end, the reliability of the network procedure is approved by comparing the calculation results of procedure in fire operation condition with reduced-scale model fire tests.(6) A bayesian network model is established to reliability analysis of fire ventilation system devices based on bayes theory, and the formulae for calculating the possibility of ventilation system devices in working state and in failure state are provided, respectively.Based on the systematic research of ventilation and smoke extraction modes in tunnel, network models are established for the tunnel ventilation calculation in normal operation condition and in fire operation condition, and the mass flow rate, wind pressure, wind speed, ventilation resistance and number of fans in need can be solved, which has a reference meaning to future road tunnel ventilation system design and calculation.