【正文】 復(fù)雜的通氣系統(tǒng)需要大量費用且于空間有密切聯(lián)系[8]。文章通過四根立管提出一種模擬實驗，說明了瞬時產(chǎn)生和加強(qiáng)的氣壓在排水管中的流動機(jī)制。s onwards, the AAV on pipe 12 opens fully and an increased airflow from this source may be identified. The flutter stage is replaced by a fully open period from to s vertical stacks. This paper presents a simulation based on a fourstack network that illustrates flow mechanisms within the pipework following both appliance discharge generated, and sewer imposed, transients. This simulation identifies the role of the active air pressure control devices in maintaining system pressures at levels that do not deplete trap seals. Further simulation exercises would be necessary to provide proof of concept, and it would be advantageous to parallel these with laboratory, and possibly site, trials for validation purposes. Despite this caution the initial results are highly encouraging and are sufficient to confirm the potential to provide definite benefits in terms of enhanced system security as well as increased reliability and reduced installation and material costs. Keywords: Active control。mm. In addition, the simulation replicates local appliance trap seal oscillations and the operation of active control devices, thereby yielding data on network airflows and identifying system failures and consequences. While the simulation has been extensively validated [10], its use to independently confirm the mechanism of SARS virus spread within the Amoy Gardens outbreak in 2003 has provided further confidence in its predictions [12]. Air pressure transient propagation depends upon the rate of change of the system conditions. Increasing annular downflow generates an enhanced entrained airflow and lowers the system pressure. Retarding the entrained airflow generates positive transients. External events may also propagate both positive and negative transients into the network. The annular water flow in the ‘wet’ stack entrains an airflow due to the condition of ‘no slip’ established between the annular water and air core surfaces and generates the expected pressure variation down a vertical stack. Pressure falls from atmospheric above the stack entry due to friction and the effects of drawing air through the water curtains formed at discharging branch junctions. In the lower wet stack the pressure recovers to above atmospheric due to the traction forces exerted on the airflow prior to falling across the water curtain at the stack base. The application of the method of characteristics to the modelling of unsteady flows was first recognized in the 1960s [13]. The relationships defined by Jack [14] allows the simulation to model the traction force exerted on the entrained air. Extensive experimental data allowed the definition of a ‘pseudofriction factor’ applicable in the wet stack and operable across the water annular flow/entrained air core interface to allow bined discharge flows and their effect on air entrainment to be modelled. The propagation of air pressure transients in building drainage and vent systems is defined by the St Venant equations of continuity and momentum [9],(1)(2)These quasilinear hyperbolic partial differential equations are amenable to finite difference solution once transformed via the Method of Characteristics into finite difference relationships, Eqs. (3)–(6), that link conditions at a node one time step in the future to current conditions at adjacent upstream and downstream nodes, Fig. 2.. St Venant equations of continuity and momentum allow airflow velocity and wave speed to be predicted on an xt grid as shown. Note , . For the C+ characteristic:(3)when(4)and the C characteristic:(5)when(6)where the wave speed c is given byc=(γp/ρ).(7)These equations involve the air mean flow velocity, u, and the local wave speed, c, due to the interdependence of air pressure and density. Local pressure is calculated as(8)Suitable equations link local pressure to airflow or to the interface oscillation of trap seals.The case of the appliance trap seal is of particular importance. The trap seal water column oscillates under the action of the applied pressure differential between the transients in the network and the room air pressure. The equation of motion for the Ubend trap seal water column may be written at any time as(9)It should be recognized that while the water column may rise on the appliance side, conversely on the system side it can never exceed a datum level drawn at the branch connection.In practical terms trap seals are set at 75 or 50s, airflow is driven up stack 1 towards the PAPA connection. However, as the base of the other stacks have not a yet had positive sewer pressure levels imposed, a secondary airflow path is established downwards to the sewer connection in each of stacks 2–4, as shown by the negative airflows in Fig. 8. As the imposed transient abates so the reversed flow reduces and the PAPA discharges air to the network, again demonstrated by the simulation, Fig. 8. This pattern repeats as each of the stacks is subjected to a sewer transient. Fig. 9 illustrates typical air pressure profiles in stacks 1 and 2. The pressure gradient in stack 2 confirms the airflow direction up the stack towards the AAV/PAPA junction. It will be seen that pressure continues to decrease down stack 1 until it recovers, pipes 1 and 3, due to the effect of the continuing waterflow in those pipes.The PAPA installation reacts to the sewer transients by absorbing airflow, Fig. 10. The PAPA will expand until the accumulated air inflow reaches its assumed 406．排入管網(wǎng)的水7．立管1底部排水8．瞬時氣壓強(qiáng)加于污水管9．水封的振動和保持——密封建筑排水和通氣系統(tǒng)的可行性――瞬時氣壓的控制和抑制作為系統(tǒng)操作的自然結(jié)果，建筑排水系統(tǒng)和通氣系統(tǒng)內(nèi)部產(chǎn)生的氣壓瞬變對于水封破壞和交叉污染的可居住空間來說也是可靠的。然而，吸氣閥不能解決建筑排水系統(tǒng)和通氣系統(tǒng)中瞬時正壓傳播的問題，污水管網(wǎng)中自由水流或遠(yuǎn)處產(chǎn)生的瞬時正壓的到達(dá)通路間歇的關(guān)閉，有可能順。關(guān)鍵詞：活性氣壓控制，存水彎保持，瞬變傳播。s. The entrained airflow in pipe 1 reduces to zero at the stack base and a pressure transient is generated within that stack, Fig. 6. The impact of this