Vehicles, pedestrians and flood risk

157 Pages·2016·27.03 MB·English

Vehicles, pedestrians and flood risk: a focus on the incipient
motion due to the mean flow

Dissertation
submitted to and approved by the

Department of Architecture, Civil Engineering and Environmental Sciences
University of Braunschweig – Institute of Technology
and the
Department of Civil and Environmental Engineering
University of Florence

in candidacy for the degree of a
Doktor-Ingenieur (Dr.-Ing.) /
In Civil and Environmental Engineering

by
Chiara Arrighi
born 09/03/1986
in Fiesole (FI), Italy

Submitted on 1st March 2016
Oral examination on 9th May 2016
Professorial advisors Prof. Fabio Castelli
Prof. Hocine Oumeraci

2016
i
UNIVERSITYOFFLORENCE
Abstract
FacultyofEngineering
DepartmentofCivilandEnvironmentalEngineering
DoctorofPhilosophy
Vehicles,pedestriansandfloodrisk: afocusonincipientmotionduetothemeanflow
byChiara ARRIGHI
Floodsareoverflowingofwaterontoland,whichisnormallydryandareoneofthecostliest
natural hazards. According to global scale reports, in the last decade floods affected the largest
numberofpeoplewithrespecttootherhazardssuchasearthquakesordroughts.Besidethedam-
agestostructuresandinfrastructures, floodsalsocausemanyfatalitiesandinjuries. Ithasbeen
demonstrated that the majority of fatalities occurs as a consequence of inappropriate high-risk
behaviours like driving and walking in floodwaters. In fact, vehicles can lose stability also for
very low water depths and may turn into deadly traps. For flood risk managers, people safety
istheprimaryobjective, butalthoughvehiclesaresocrucial, verylittleisknownaboutthecrit-
ical conditions in which the onset of motion occurs. Besides, the existing instability criteria for
pedestriansunderwaterflowsufferfromthelargescatterofexperimentalpairsofcriticalwater
depthandvelocity. Asamatteroffact,theinstabilityconditionsofbothvehiclesandpedestrians
are affected not only by flood parameters (i.e. water depth and velocity), but also by geometric
andphysicalpropertiesof theobject. The mainaimofthisPhDresearch projectistobetterun-
derstandtheinstabilitymechanismsforpedestriansandvehicles,whichareresponsibleformost
of the casualties in order to introduce new hazard criteria capable of accounting for both flood
andobjectcharacteristics.Forthispurpose,acomprehensiveanalysisofthecurrentknowledgeis
firstlypresented. Secondly,theforcesactingonapartlyimmersedvehicleandhumansubjectare
examinedandtwodimensionlessmobilityparametersareintroduced. Theexistingexperimental
data on vehicles and people instability are used to identify a dimensionless critical threshold of
incipient motion. Thirdly, a 3D numerical model in the OpenFOAM framework is adopted to
clarify the role of hydrodynamic forces and determine relevant dimensionless parameters and
scaling numbers involved in the instability mechanisms, considering the mean flow properties.
Then, the results of the numerical simulations for a selected vehicle, which reproduce a set of
existingexperiments,areanalysedanddiscussed. Finally,twocasestudiesarepresentedinorder
todemonstratetheapplicabilityofthemobilityparameterstothefieldscaleandtheadvantages
of hazard maps implemented with the proposed method. The results show that the scatter of
existingexperimentaldatacanbeovercomeusingadimensionlessapproach,whichaccountsfor
bothfloodsandobjectsproperties. Sincethecriticalthresholdsaredimensionless,theinstability
conditionsforpeopleandvehiclescanbeeasilycomparedinordertodevelopbehaviouralrules,
managementstrategiesandsupportpeopleeducation.Thenumericalmodelhintstheimportance
offlowregimesforthehydrodynamiceffectsandclarifiesthecontributionofdragandliftforces.
Theapplicationofthemobilityparameterstoinundationmapsdemonstratestheapplicabilityof
themethodtothefieldscale. Thequalitativecomparisonbetweenthereconstructedinundation
mapsandthegeoreferencedpicturestakenafterthe2014floodeventinGenoashowsaverygood
accordance,thusthemethodappearspromisingandprovidesanimprovedbasisforfloodhazard
andriskmapping.

iii
Acknowledgements
The present PhD research has been conducted thanks to a PhD scholarship given by
theUniversityofFlorence(Italy)whichisgreatlyacknowledged. Iwouldliketoexpress
myspecialgratitudetoProf. Dr. IngHocineOumeraciandProf. Dr. IngFabioCastellifor
allowingmetoconductthePhDstudyundertheirsupervisionintheLeichtweiss-Institut
Hydraulic Engineering and Water Resources (LWI), Braunschweig, Germany and in the
Department of Civil and Environmental Engineering, Florence (Italy) and for encourag-
ing my research with their valuable suggestions. The support from Prof. Dr. Ing. Fed-
ericoDomenichini(UniversityofFlorence)andProf. Dr. Ing. AbdellatifOuhasine(UTC,
Compiègne) during the PhD research is acknowledged. A special thanks to Dr. Simone
Gabellani (CIMA Research Foundation, Italy) and to Ing. Patrick Chassé (CEREMA,
France) for providing the inundation model datasets. The laboratory Lasis at the Uni-
versity of Florence is acknowledged for having provided the 3D numerical geometry of
thesimulatedcarmodel. IwouldalsoliketothankmycolleagueJuanCarlosAlcèrreca-
Huertaforhisfriendship,guidanceandassistanceduringmystayinBraunschweig.

v
Contents
Abstract i
Acknowledgements iii
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Expectedresultsandimpacts . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Currentstateofknowledgeandmodelling 5
2.1 Floodriskinurbanareas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Impactsoffloods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 FloodriskdefinitionandEuropeanlegislation . . . . . . . . . . . . 6
2.1.3 Hazardmodelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.4 Damageassessment . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1.5 Riskassessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.6 Peoplefatalities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Experimentaldataonvehiclesandpeople . . . . . . . . . . . . . . . . . . . 14
2.2.1 Experimentsonincipientmotionofsmallscalevehiclemodels . . 14
2.2.2 Experimentsonpeopleinstabilityinfloodflows . . . . . . . . . . . 19
2.3 Numericalmodelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.1 Effectsofanobstacleinafluidflow . . . . . . . . . . . . . . . . . . 23
2.3.2 CFDnumericalmodelling . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.3 CFDcodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4 Summaryandimplicationsfortheresearch . . . . . . . . . . . . . . . . . . 27
2.5 Specificationofobjectivesandmethodology . . . . . . . . . . . . . . . . . 27
2.5.1 Specificationofobjectives . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5.2 Specificationofmethodology . . . . . . . . . . . . . . . . . . . . . . 28
3 Incipientmotionofparkedcarsandpedestriansunderwaterflow 33
3.1 Incipientmotionofparkedcars . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.1.1 Mobilityparameterofparkedcars . . . . . . . . . . . . . . . . . . . 33
3.1.2 Application of the mobility parameter to available experimental
data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.1.3 Effectoffloworientationonthemobilityparameter . . . . . . . . . 38
3.1.4 Sensitivityanalysisofθ touncertaintiesinH andU . . . . . . . . 42
V
3.2 Incipientmotionofpedestriansstandinginfloodwaters . . . . . . . . . . . 43
3.2.1 Mobilityparameterofpedestrians . . . . . . . . . . . . . . . . . . . 43
3.2.2 Applicationofthemobilityparametertoexistingexperimentaldata 47
3.3 Comparisonbetweenmobilityparametersforvehiclesandpeople . . . . 48
3.4 Summaryofkeyresultsandimplications . . . . . . . . . . . . . . . . . . . 49
vi
4 Numericalmodelset-upinOpenFOAM 53
4.1 TheOpenFOAMframework . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.2 GoverningequationsoftheCFDmodel . . . . . . . . . . . . . . . . . . . . 55
4.3 Numericalmodelsetup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.1 StructureofasimulationinOpenFOAM . . . . . . . . . . . . . . . 56
4.3.2 Solver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.3.3 Meshgeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.3.4 Relaxationzones,boundaryandinitialconditions . . . . . . . . . . 61
4.3.5 Controlofthesimulationandforcescalculation . . . . . . . . . . . 61
4.4 Sensitivityanalysistotheappliedmeshsizeandturbulencemodel . . . . 62
4.4.1 Sensitivityoftheresultstothemeshsize . . . . . . . . . . . . . . . 62
4.4.2 Sensitivityoftheresultstotheturbulencemodel . . . . . . . . . . . 64
4.5 Testprogrammefortheparameterstudy . . . . . . . . . . . . . . . . . . . 65
4.5.1 TestprogrammefortheFordFocus . . . . . . . . . . . . . . . . . . 65
4.5.2 Testprogrammeforhumansubjects . . . . . . . . . . . . . . . . . . 65
4.6 ApplicabilityandlimitationsoftheCFDsimulations . . . . . . . . . . . . 69
4.7 Summaryofthechapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 Numericalresultsanddataanalysis 73
5.1 NumericalresultsofthesimulationsoftheFordFocuscar . . . . . . . . . 73
5.1.1 FlowaroundtheFordFocus. . . . . . . . . . . . . . . . . . . . . . . 73
5.1.2 ForcesandforcecoefficientsforscaleandprototypeFordFocusfor
anglesofflowincidenceβ = 0◦ andβ = 180◦ . . . . . . . . . . . . . 75
5.1.3 Comparisonofnumericalresultswithexperiments . . . . . . . . . 82
5.1.4 Discussionoftheassumptions"rigidbodyandconstantfrictionco-
efficient" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.1.5 Effectoftheangleofflowincidence . . . . . . . . . . . . . . . . . . 85
5.1.6 Forcesandforcescoefficientsfordifferentanglesofflowincidence 86
5.1.7 SummaryofthenumericalresultsoftheFordFocus . . . . . . . . . 89
5.2 Numericalresultsofthesimulationsofpedestrians . . . . . . . . . . . . . 92
5.2.1 Flowcharacteristicsaroundanuprightstandinghumanbody . . . 92
5.2.2 Forcesandforcecoefficients . . . . . . . . . . . . . . . . . . . . . . . 93
5.2.3 Identificationofmotionmechanisms . . . . . . . . . . . . . . . . . . 97
5.2.4 Comparisonwithexperimentaldataanddiscussion . . . . . . . . . 99
5.2.5 Summary and discussion of the results of the numerical simula-
tionsofpeople . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
5.3 Summaryofthechapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6 Applicationtotwocasestudies 105
6.1 Definitionofhazardcriteria . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
6.1.1 Hazardcriteriaforvehicles . . . . . . . . . . . . . . . . . . . . . . . 105
6.1.2 Hazardcriteriaforpedestrians . . . . . . . . . . . . . . . . . . . . . 106
6.2 TheTELEMAC-MASCARETsuite . . . . . . . . . . . . . . . . . . . . . . . 107
6.3 ThecasestudyofAjaccioinCorsica(France) . . . . . . . . . . . . . . . . . 108
6.3.1 Casestudydescription . . . . . . . . . . . . . . . . . . . . . . . . . . 108
6.3.2 Inundationcharacteristicsandhazardmapsforvehiclesandpedes-
trians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
6.4 ThecasestudyofGenova(Italy) . . . . . . . . . . . . . . . . . . . . . . . . 113
6.4.1 Casestudydescription . . . . . . . . . . . . . . . . . . . . . . . . . . 113
6.4.2 Inundationcharacteristicsandhazardmapsforvehiclesandpedes-
trians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
vii
6.4.3 Comparison of proposed hazard criteria with photos of the flood
event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7 Summary,conclusionsandoutlook 123
7.1 Generalsummary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
7.2 Mobilityparametersandnumericalmodelling . . . . . . . . . . . . . . . . 123
7.3 Limitationsoftheresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.4 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

ix
List of Figures
1.1 AnepisodeofflashfloodinAthens(leftpanel,source: www.timesofmalta.com)
andtheaftermathofthe2011floodinGenova(rightpanel,source: www.adnkronos.com). 1
2.1 Humanimpactsbydisastertypeinthedecade2002-2012(EM-DAT,2012) 6
2.2 Hazard,vulnerabilityandexposure(fromMerzetal.,2004). . . . . . . . . 7
2.3 Standard flow chart for flood risk assessment based on flood depth maps
andsocio-economicdata(fromArrighietal.,2013). . . . . . . . . . . . . . 8
2.4 The2013flashfloodinAthens(source: http://www.timesofmalta.com). . 14
2.5 The aftermath of Genoa 2011 flood event (source: http://www.italia45-
45.it/alluvioni). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.6 Experiments on fully (a) and partially (b) submerged Mitsubishi Pajero
(1:18)(fromXiaetal.,2011). . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.7 Criticalthresholdvaluesofhydraulicinstabilityforvehicles(Teoetal. 2012) 19
2.8 Experiments on human instability: water depth 1.07 m and velocity 1.0
m/s(fromKarvonenetal.,2000) . . . . . . . . . . . . . . . . . . . . . . . . 21
2.9 Humanmodel(scale1:5.54)testedbyXiaetal. 2014 . . . . . . . . . . . . . 22
2.10 Proposedhazardregimesforpeople(fromRussoetal.,2013) . . . . . . . . 22
2.11 Summaryofthetopicsdescribedinthereviewofthecurrentknowledge. 30
2.12 MethodologyoftheresearchandstructureofthePhDthesis. . . . . . . . . 31
3.1 Forcesactingonaparkedvehicleunderwaterflow. . . . . . . . . . . . . . 33
3.2 Definitionofgeometricparametersofthevehicleandwaterflowparameters. 34
3.3 Mobilityparameterθ versusFroudenumberFr ofundisturbedflowus-
V
ingtheexperimentaldataofXiaetal. (2011)andShuetal. (2011). . . . . . 36
3.4 Experimental data by Shu et al. 2011 (left panel) and by Xia et al. 2011
(rightpanel)scaledtoprototypevalues. . . . . . . . . . . . . . . . . . . . . 37
3.5 Mobilityparameterθ versusFroudenumberFr ofthevehicleusingthe
V v
experimentaldataofXiaetal. (2011)andShuetal. (2011). . . . . . . . . . 38
3.6 Plan view of the surfaces affected by drag force according to the angle of
flowincidence.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.7 Geometricschemeforavehiclewithangleofflowincidenceβ.. . . . . . . 39
3.8 Mobility parameter accounting for the angle of flow incidence (experi-
mentswith90◦ anglerepresentedwithdiamonds,Xiaetal.,2013) . . . . . 41
3.9 Effectofadditionofasmallrandomnoisetothepairs(H,V)onthemobil-
ityparameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.10 Effectofadditionofalargerandomnoisetothepairs(H,V)onthemobility
parameter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.11 Mobilising and resisting forces on a human body in floodwater (a) lateral
view,frontalview(b). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.12 Mobilityparameterθ versusFroudenumberFrfortheexperimentsfrom
P
publishedselectedstudies. . . . . . . . . . . . . . . . . . . . . . . . . . . . 47