The provision of well-designed tunnels and tunnel systems is only part of the story. Once the tunnel is in operation, it is equally important that it is operated in an effective manner. Early in his career, Alan Vardy was exposed to clear examples where operators misunderstood seriously the designer’s original intentions, leading to inefficient use in routine operation and sub-optimum safety during emergencies. These deficiencies were compounded by inconsistent planning about the balance between automatic control and direct human control. This was an important trigger for Vardy’s strong focus on the promotion of Tunnel Safety (beginning well before the series of disastrous fires that drew the matter to public attention). It also triggered interest in the development of automatic control systems with built-in intelligence.
Model-Based, Predictive Ventilation Control (MPVC)
The most powerful control system arising from Vardy’s research is a model-based, predictive method of controlling ventilation systems, using predictions from in-built simulators of the traffic and the airflows. The basis of the method, known by the acronym MPVC, was developed exclusively in Dundee, first in a simple form by Vardy & Javad Jafari and then in a more comprehensive form by Vardy, Jim Brown and Atsushi Ichikawa. For the particular cases of control during routine operation, the process is broadly as follows:
The ventilation simulator is given the following information:
• The current state of the ventilation fans
• The current state of the airflows and pollution everywhere in the tunnel
• Expected traffic conditions in the tunnel during the next control interval (20 minutes, say)
The simulator is then used to predict the conditions that will exist in the tunnel during the whole of the control interval. This is done for a large range of possible fan states during the interval and the most economical states are chosen by an optimisation routine that takes account of power costs, pollution levels and fan switching, etc.
A fundamental advantage of this approach is that control is based on expected future conditions, not on extrapolations of past conditions. The method is equally suited to implementation in either simple or complex tunnel networks. In its most simple form, it could notionally be used in tunnels with no instrumentation whatsoever although that is certainly not recommended. In part, this is because MPVC includes powerful reconciliation routines that ensure that the predictions do not vary greatly from actual measurements at tunnel sensors. These routines have the potential to warn operators about faulty sensors even when they are apparently behaving normally. They also help to ensure the validity of the information presented to the simulator at the start of each control interval (see above).
Following the development of the fundamental methodology in Dundee, Dr Ichikawa returned to Japan where he recommended MPVC to JHRI (now RI-NEXCO) (Japanese site, English site) and with Sohatsu Systems Laboratory Inc (Japanese site, English site), who already had a powerful traffic simulator. The method was then developed in a collaborative manner and it has been implemented in several road tunnels in Japan, including the Kan-Etsu Tunnel, which, at 11 km, is the longest in Japan.
Inverter-driven jet fans
In the case of tunnels ventilated longitudinally by jet fans, any control system (whether operated by humans or automatically) has to address a difficulty arising from the integer number of fans. If, for example, 3 fans are not quite sufficient to achieve the desired purpose, the next available option is 4 fans even though this might be more than necessary. In routine operation, this is wasteful. In emergencies, it can make it impossible to reduce air velocities - and hence smoke movement - as much as is theoretically possible. To overcome this problem, Sohatsu Systems Laboratory Inc, to which DTR acts as a Technical Advisor, has developed a method of driving jet fans through an inverter and hence using them as variable-speed fans.
Suppose that a tunnel has 5 jet fans and that, at some instant, the ideal thrust would be equivalent to using 3.6 fans. An obvious (but not optimum) way of using the variable speed capability would be to operate three fans at full speed and a fourth fan at approximately 60% speed. This method would be appropriate if only one fan were inverter driven. If all of the fans are inverter-driven, however, a much more efficient mode of operation is to use all five fans at approximately 72% of full speed. In routine operation, the key advantage is that this consumes less power. In emergency operation, the key advantages are that it is less noisy and that it is less sensitive to the failure of individual fans (through fire, say). It is also less sensitive to the consequences of reduced thrust when fans operate in heated air (smoke), but a good control system should compensate for this particular complication.
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Inverter control cabinet (37.5kW) |
Jet fan control - full scale test | With Fuji splendour |
Selected References
Azuma S, Nomura H, Ichikawa A, Kawashima S, Mitani A & Vardy AE (2011) Application of MPVC to the two longest road tunnels in Japan, Proc 14th int symp on Aerodynamics and Ventilation of Tunnels, Dundee, UK, 11-13 May 2011, BHR Group, 419-430
Dayman B, Vardy AE & Evans K (1991) Aerodynamic investigations of the ventilation system of the Tyne Tunnel.Proc 7th int symp on the Aerodynamics and Ventilation of Vehicle Tunnels, Brighton, UK, 27-29 Nov, BHR Group, 583-627
Hagenah B, Reinke P & Vardy AE (2006) Effectiveness of pressure relief shafts - full-scale assessment, Proc 12th int symp on the Aerodynamics and Ventilation of Vehicle Tunnels, Portoroz, Slovenia, 11-13 Jul, BHR Group, 379-391
Ichikawa A, Vardy AE & Brown JMB (2001) Model-based predictive control using genetic algorithms, Proc IMechE, J Power & Energy, 215, Part A, 623-638
Nakahori I, Ato T, Murakami K, Araki D, Kanatani T & Vardy AE (2009) The use of inverter-driven jet-fans to reduce tunnel ventilation costs, Proc 13th int symp on the Aerodynamics and Ventilation of Vehicle Tunnels, New Brunswick, USA, 13-15 May, BHR Group, 69-80
Nakahori I, Mitani A & Vardy AE (2011) A new ventilation control for inverter driven jet-fans, Proc 14th int symp on Aerodynamics and Ventilation of Tunnels, Dundee, UK, 11-13 May 2011, BHR Group, 431-445
Nakahori I, Sakaguchi T, Mitani A & Vardy AE (2012) Sensor failure detection in road tunnel ventilation, Proc 6th int conf on Tunnel Safety and Ventilation, Graz, Austria, 23-25 April 2012, 179-186
Nakahori I, Sakaguchi T, Kohl B & Vardy AE (2015) Assessment of effects of a zero-flow ventilation strategy for tunnel fires in bidirectional tunnels with longitudinal ventilation, Proc 16th int symp on Aerodynamics, Ventilation and Fire in Tunnels, Seattle, USA, 15-17 Sep 2015, BHR Group, 501-516
Schulte-Werning B, Grgoire R, Malfatti A & Matschke G (Eds) (2002) TRANSAERO - a European initiative on transient aerodynamics for railway system optimisation, Springer-Verlag, Berlin Heidelberg
Tokeida H, Mori E, Yamada S, Vardy AE, Mitani A & Yokota M (2006) Full-scale test for verification to put MPVC into practical use for tunnels with the concentrated exhaust system at portal, Proc 12th int symp on the Aerodynamics and Ventilation of Vehicle Tunnels, Portoroz, Slovenia, 11-13 Jul, BHR Group, 723-733
Vardy AE (1980) Unsteady airflows in rapid transit systems. Proc Inst Mech Engrs, 194(32), 341-356
Vardy AE (1992) Flow measurement in large complex ductwork, Proc int conf on Piping Systems, Manchester UK, BHR Group, Kluwer Academic Pub, 299-310
Vardy AE & Hagenah B (2006) Full-scale flow measurements in a tunnel airshaft, Proc 12th int symp on the Aerodynamics and Ventilation of Vehicle Tunnels, Portoroz, Slovenia, 11-13 Jul, BHR Group, 343-357
Vardy AE & Ichikawa A (2000) Pollution:cost balance in road tunnel ventilation, Proc IMechE, J Power & Energy, 214, Part A, 677-690
Vardy AE, Mori E, Yokota M & Nakahori I (2003) Model-based predictive control of road tunnel portal emissions, ITA World Tunnelling Congress on Reclaiming the Underground Space, Amsterdam, The Netherlands, 12-17 April, International Tunnelling Association, Vol 1, 207-212
