Mitsubishi Heavy Industries Technical Review Vol. 60 No. 1 (March 2023)
1Typhoon Damage Simulation Technology for Improving
Wind Disaster Resilience
SADATO SUGIYAMA*1

HIDEKAZU ISHII*2

REIKO TAKASHIMA*2

SHUNICHI IKESUE*1

RIKUMA SHIJO*3

Natural disasters have been creating catastrophic damage because of climate change
associated with global warming. On the other hand, the social infrastructure constructed in theperiod of rapid economic growth is aging. Therefore, damage risk analysis and new
construction/repair planning for the infrastructure are becoming important. The Research &Innovation Center of Mitsubishi Heavy Industries, Ltd. (MHI) has its own simulation technologies
for various types of disasters such as floods, tsunamis, earthquakes, typhoons, fires andleakage/explosions(1) and has analyzed risks associated with climate change and developed
countermeasure devices intended to improve infrastructure resilience (strength and recoverycapability). In this report, focusing on typhoons, which are disasters familiar to us as they occur
frequently, we introduce the outline of the typhoon damage simulation technology among MHI'ssimulation technologies, simulation examples including the risk analysis for roof uplift damage andstrong wind damage, the development of damage reduction devices and the design wind velocity
maps which visualize typhoon damage risk.

|1. Introduction
In recent years, there have been increasing cases where a typhoon formed in the south ofJapan makes landfall on Japan while maintaining its strength. During typhoon No. 21 in 2018, thepassenger terminal of Kansai International Airport was damaged by flooding due to the storm surge
and it took over two weeks to fully recover from the damage(2). During typhoon No. 15 in 2019,major power outages occurred mainly in Chiba Prefecture due to the collapse of steel towers andelectric poles, etc., and it took about three weeks to restore electric power(3). These disasters arestill fresh in our memory. As seen from these cases, enhancement of resilience (strength andrecovery capability) against typhoon damage is a critical issue.
On the other hand, facilities constructed in the period of rapid economic growth are aging.
Therefore, from the viewpoint of resilience, it is important not just to conduct inspection and repairof defects on an as-needed basis but to make plans for new construction or repair.
As these social needs have grown, it is becoming more important to properly analyze
increasingly catastrophic typhoon damage and thereby to make efficient investments ininfrastructure. In order to analyze typhoon damage with high accuracy, it is necessary to assess thefactors affecting the wind velocity over a wide area of the order of several hundred kilometers to an
extremely narrow area of the order of several tens of meters using (1) the information of a passingtyphoon, (2) the geographical information of the surroundings of the infrastructure and (3) theinformation on the shapes and arrangement of adjacent buildings. In order to satisfy theserequirements, we believe that a numerical simulation that allows effects in a wide area to be applied
to a narrow area is an assessment tool.
In this report, we first explain a risk assessment technology for typhoon damage, in which
three simulation technologies required for assessment of typhoon damage are combined, and its
accuracy, and then introduce examples of risk assessment for typhoon damage and developed*1

Engineering Manager, Fluid Dynamics Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*2

Fluid Dynamics Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

*3Manager, Fluid Dynamics Research Department, Research & Innovation Center, Mitsubishi Heavy Industries, Ltd.

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damage reduction devices, focusing on roof uplift damage and strong wind damage aroundbuildings in a model infrastructure. A visualization example for typhoon damage risk intended toclarify points with any risk in the whole infrastructure is also presented.

|2. What is typhoon damage simulation technology?
2.1

Overview of typhoon damage simulation technology

The typhoon damage simulation technology is a tool for estimating the wind pressure acting
on a building and the wind velocity around the building during the passage of a typhoon. At theinfrastructure planning stage, it can be used for selecting a construction site and planning thearrangement of buildings resistant to typhoon damage. At the infrastructure operation stage, it canbe used for conducting risk analysis for typhoon damage to the building, planning new
construction/repair work and damage reduction devices, developing countermeasure scenarios incase of a typhoon, etc.
Figure 1 shows the flow of the typhoon damage simulation. The typhoon damage
simulation, in which three simulations for different assessment fields are combined, has a feature sothat it can quickly estimate the wind flow around the building in an extremely narrow area (up to0.1 km) based on the information of a typhoon passing in a wide area (up to 1,000 km).
Firstly, (1) by the typhoon simulation, from the information of the typhoon (typhoon central
location, central pressure, radius), the average wind velocity and direction over a flat terrain when
hit by a typhoon are calculated. Next, (2) by the wind conditions simulation, based on the averagewind velocity and direction over a flat terrain and the geographical information of the surroundingsof the construction site, the average wind velocity and direction at the construction site areestimated with geographical effects taken into consideration. Finally, (3) by the wind pressure
simulation, based on the average wind velocity and direction at the construction site and the data on
the building shape and arrangement, the wind pressure acting on the buildings and the windvelocity around the buildings are assessed.
In addition, as for the data which is required for input in the simulation, the databases such as
the Best Track Data by the Japan Meteorological Agency for the typhoon information and theNumerical Map of the Geospatial Information Authority of Japan for the geographical information
can be used. When the shapes and arrangement of buildings to be assessed are input, assessment for
any location and typhoon can be conducted.
As described above, with this simulation technology, the risk of typhoon damage reflecting
the characteristics of a passing typhoon affected by the regional characteristics, surrounding terrain
and buildings can be estimated with high accuracy and it becomes possible to make infrastructure
investments aiming at satisfying both safety and economy.

Figure 1Typhoon damage simulation

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2.2
(1)

Accuracy of each simulation
Typhoon simulation, wind conditions simulation
Figure 2 shows the comparison of the observation result and the simulation result for thewind velocity and direction data at the Nagasaki Local Meteorological Observatory whentyphoon No. 10 was passing in 2020. The average wind velocity over the flat terrain obtainedby the typhoon simulation substantially exceeded the observation result. After the windconditions simulation considering geographical effects was performed, the simulation result
showed good agreement with the observation result and the maximum wind velocity when thetyphoon was passing was reproduced with an error of about 10%. In addition, the geographicaleffects on the wind direction were not so marked as those on the wind velocity, and even only
the typhoon simulation could reproduce the characteristics of the wind direction, whichchanged from the southeast to the southwest when the typhoon was passing.

Figure 2 Validation result of typhoon simulation and wind conditions simulation(2)

Wind pressure simulation
Figure 3 shows the comparison of a past wind tunnel experiment result and thesimulation result for the average wind pressure acting on the building wall surface which is arectangular solid having the ratio of the height, width and depth = 1:0.5:0.5. It is known thatwhen a wind flows from the direction of the corner of a building, the flow separating from thewindward corner of the building entrains on the side face of the building, resulting inoccurrence of conical vortices(4). As shown in Figure 3(a), the wind pressure simulation also
reproduced conical vortices. In addition, as shown in Figure 3(b), a wind pressure distributionin which a strong negative pressure arising from the conical vortices is generated along thecorner of the roof face can be seen in both the wind tunnel experiment and the CFD. The
comparison of the wind pressure distributions in the cross-section B-B’ also showed that thelocal negative pressure obtained by the simulation was reproduced with about 10% error of theexperimental result.

Figure 3 Validation result of wind pressure simulation(5)|3. Typhoon damage simulation examples
3.1

Buildings and typhoon damage to be assessed

In this chapter, with the model infrastructure shown in Figure 4, the risk analysis for
typhoon damage, the planning of typhoon damage reduction devices and the design wind velocity
map by wind direction are described. Since the sea is located in the southwest of the model
infrastructure, there is a risk that typhoon damage may be caused by southwesterly wind. It wasreported that in the target building group 1, the roofs were lifted off by the wind blowing downfrom the windward cylindrical roof and in the target building group 2, the wind passing throughMitsubishi Heavy Industries Technical Review Vol. 60 No. 1 (March 2023)
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between the buildings increased wind velocity and damaged them.

Figure 4

3.2(1)

Arrangement plan of model infrastructure

Typhoon damage assessment examples
Roof uplift damage
Figure 5 shows the result of a roof uplift damage simulation. As shown in the left figure,before taking countermeasures (in the existing conditions), the wind getting over and blowing
down from the cylindrical roof of the building located on the windward side acts directly on thetarget building. In addition, since the target building is open at its southwest face, a positive
pressure (pressing force) acts on the inside wall of the target building and a negative pressure(tensile force) acts on the roof surface, as shown in the right figure. As a result, it was revealed
that the roof was subjected to an upward wind load about twice as large as the self-weight,
which might cause the risk of roof uplift. It is conceivable that against this phenomenon,
countermeasures can be taken such as closing of the southwest semi-open face andreinforcement of the connecting part of the roof and the structure. But around this building,other damage such as toppling of temporary constructions and breakage of exterior materials
also occurred during the typhoon. Therefore, we considered countermeasures that could reduce
typhoon damage over a wide area.
Figure 6 shows the simulation result after taking countermeasures. As shown in the left
figure, when a countermeasure device (vertical panel) was set up on the cylindrical building
top, the wind flow separated at the cylindrical building top and the wind was prevented fromacting directly on the target building. As a result, the roof load was reduced by 84% compared
to before taking countermeasures and we could confirm that it was effective as a roof upliftdamage reduction device.

Figure 5 Roof uplift damage simulation (before countermeasures)

Figure 6(2)Roof uplift damage simulation (after countermeasures)

Strong wind damage
Figure 7 shows the result of a strong wind damage simulation. Since the wind from thesea directly acts on the target buildings, a strong wind occurs in the area where the target
buildings are located in the model infrastructure site. Furthermore, it is considered that the windMitsubishi Heavy Industries Technical Review Vol. 60 No. 1 (March 2023)
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became stronger due to the increased velocity of the flow between the buildings.
Before countermeasure (in the existing conditions), the wind velocity between thebuildings increases by about 15% compared to the upstream wind velocity. After a windbreak
net with a solidity ratio of 50% was set up on the border of the site, the wind velocity becamealmost the same as the upstream wind velocity. It showed that such countermeasure could
reduce the wind velocity by 16% compared to before the countermeasure.

Figure 7

3.3Strong wind damage simulation

Design wind velocity map

In a wind-resistance design, it is necessary to evaluate the integrity of the building byobtaining the design wind velocity for the typhoon that is experienced once on average within acertain recurrence interval. Therefore, in the typhoon simulation, the typhoon parameters weredefined by the probability density function, virtual typhoons were formed over a long period (ofabout 1,000 years) based on random numbers and the design wind velocities were calculated.
Figure 8 shows the design wind velocity maps for different wind directions in a recurrence intervalof 100 years. These maps showed that with the wind direction SE, the design wind velocity became
low because the model infrastructure falls behind the mountain on its southeast side, while with thewind direction SW, the wind blew into the model infrastructure directly from the sea and the design
wind velocity became high. By visualizing the design wind velocity for each wind direction like
this, areas having a high risk of damage and target wind directions can be identified. Therefore, arepair plan, which was conventionally determined based on the years of use of the building or thelike, can be prepared based on an appropriate assessment according to the risk.

Figure 8

Design wind velocity map* The dotted line shows the bordersite of the model infrastructure. Taken fromaerial photographs on Google Map.

|4. Conclusion
Using the typhoon damage simulation, we presented examples of risk analysis for roof upliftdamage and strong wind damage, the development of damage reduction devices and the designMitsubishi Heavy Industries Technical Review Vol. 60 No. 1 (March 2023)
6wind velocity maps that visualize the typhoon damage risk.
It was confirmed that by combining three simulations for different assessment fields andreflecting in each simulation the information about the typhoon, the terrain around theinfrastructure and the shapes and arrangement of adjacent buildings, which are influencing factorsof typhoon damage, we could analyze typhoon risks precisely and develop effective devices for
reducing typhoon damage.
Moving forward, we will make efforts to further improve resilience of infrastructure by
predicting damage and planning evacuation scenarios before a typhoon strikes and developing
technologies that can contribute to the prompt start of restoration work.

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