Developing a Vehicle Hydroplaning Simulation using Abaqus and CarSim Sankar Mahadevan Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering Saied Taheri, Chair Ronald H. Kennedy Corina Sandu 04-18-2016 Blacksburg, VA Keywords: Abaqus, FEA, Hydroplaning, FSI, CarSim Copyright 2016, Sankar Mahadevan Developing a Vehicle Hydroplaning Simulation using Abaqus and CarSim Sankar Mahadevan Abstract Tires are the most influential component of the vehicle as they constitute the only contact between the vehicle and the road and have to generate and transmit forces necessary for the driver to control the vehicle. Hydroplaning is a phenomenon which occurs when a layer of water builds up between the tires of a vehicle and the road surface which leads to loss of traction that prevents the vehicle from responding to control inputs such as steering, braking or acceleration. It has become an extremely important factor in the automotive and tire industry to study the factors affecting vehicle hydroplaning. Nearly 10-20% of road fatalities are caused by lack of traction on wet surfaces. The tire tread pattern, load, inflation pressure, slip and camber angles influence hydroplaning to a great extent. Finite Element Analysis, although computationally expensive, provides an excellent way to study such Fluid Structure Interactions (FSI) between the tire-water-road surfaces. Abaqus FSI CEL approach has been used to study tire traction with various vehicle configurations. The tire force data obtained from the Finite Element simulations is used to develop a full vehicle hydroplaning model by integrating the relevant outputs with the commercially available vehicle dynamics simulation software, CarSim. Acknowledgement First and foremost, I would like to extend my sincerest gratitude to my graduate advisor, Dr. Saied Taheri, whose dedication towards the research has been an inspiration for me, whose unwavering academic support, collegiality, and mentorship throughout my entire graduate life, has helped me achieve my degree. I also can’t be more thankful to him for spending hours proofreading my thesis, papers and giving me suggestions on improving my writing. CenTiRe at Virginia Tech has been a very integral part of my graduate life and I have loved working with all the professors and students associated with the lab. I would also like to express my deep sense of gratitude to Dr. Ronald Kennedy who has enhanced my understanding on Finite Element Analysis of tires and tire development. I would like to thank him for his unwavering support which has helped me understand several concepts involved in tire FEA. I would also like to thank Dr. Corina Sandu, who have served as my graduate thesis committee member and made significant suggestions in shaping my research work. I would like to express my sincere gratitude to John Lightner, John Lewis and Neel Mani from Bridgestone, who during the course of my summer internship provided me with valuable inputs to develop various tire FEA simulations. Their feedback and support has helped me make vast improvements to my research. I would like to thank my fellow lab members, Yaswanth Siramdasu and Anup Cherukuri, for participating in every discussion related to vehicle dynamics modeling side of the project, and all those who were directly or indirectly involved in the research work. Last but not the least, I want to thank my parents, without whom, I could never have made it. Their consistent support, dedication and compromises have been the source of my strength and determination. iii Contents Acknowledgement ............................................................................................................. iii List of Figures .................................................................................................................... vi List of Tables .................................................................................................................... vii 1. Introduction ................................................................................................................. 1 1.1 Motivation ............................................................................................................ 1 1.2 Research Objectives ............................................................................................. 3 1.3 Thesis Organization.............................................................................................. 3 2 Background and Literature Review ............................................................................. 4 2.1 The Pneumatic Tire .............................................................................................. 4 2.2 Theory of Hydroplaning ....................................................................................... 6 2.3 Empirical Models for Critical Hydroplaning Speed ............................................ 7 2.3.1 Critical Hydroplaning Speed based on Inflation Pressure ............................ 7 2.3.2 Critical Hydroplaning Speed based on Load and Contact Patch .................. 7 2.3.3 Critical Hydroplaning Speed based on Load, Contact Patch, and Water Thickness ..................................................................................................................... 8 2.3.4 Critical Hydroplaning Speed based on Inflation Pressure, Pavement Texture, and Water Thickness ..................................................................................... 8 2.4 Major pavement design factors influencing hydroplaning ................................... 9 2.5 Viscous and dynamic hydroplaning ..................................................................... 9 2.6 Tire-pavement interactions ................................................................................. 10 2.7 Ribbed tire and grooved pavement interaction .................................................. 14 2.8 Modifications to Horne’s equations based on Fwa’s work ................................ 16 2.9 Modified equations for truck tires ...................................................................... 18 2.10 Influence of tire tread geometry on hydroplaning .............................................. 20 2.10.1 Influence of tread pattern ............................................................................ 20 2.10.2 Groove- rib interface study ......................................................................... 22 iv 2.10.3 Influence of tire sipes on hydroplaning ...................................................... 22 2.10.4 Effectiveness of tire groove patterns in reducing the risk of hydroplaning 23 2.10.5 Influence of pattern void on tire performance ............................................ 25 2.11 Wet weather braking performance ..................................................................... 26 2.12 Use of commercial finite element codes for braking simulations ...................... 27 3 Finite Element Tire Modeling ................................................................................... 28 3.1 Finite Element Analysis ..................................................................................... 28 3.2 Implicit vs. Explicit Finite Element Solvers ...................................................... 29 3.3 FSI Simulations for hydroplaning ...................................................................... 30 3.3.1 Eulerian formulation ................................................................................... 30 3.3.2 Lagrangian formulation .............................................................................. 30 3.3.3 Arbitrary Lagrangian-Eulerian formulation ................................................ 31 3.3.4 Coupled Eulerian-Lagrangian formulation ................................................. 31 3.4 Abaqus Tire FEA Procedure .............................................................................. 32 3.4.1 Two dimensional model .............................................................................. 34 3.4.2 Symmetric model generation based on tread pitch ..................................... 34 3.4.3 Three dimensional model ............................................................................ 34 3.4.4 Steady-state transport .................................................................................. 35 3.4.5 Hydroplaning FSI model............................................................................. 37 3.5 Simulation Set up ............................................................................................... 38 3.6 Basis of hydroplaning......................................................................................... 39 3.7 Simulation Validation ........................................................................................ 41 3.8 Braking-Traction Simulations ............................................................................ 44 3.9 Lateral force simulation. .................................................................................... 47 4 CarSim Vehicle Dynamics Simulations .................................................................... 57 4.1 ISO 4138 Constant-Radius Test ......................................................................... 58 4.1.1 Results at 50 km/hr ..................................................................................... 59 4.1.2 Results at 75 km/hr ..................................................................................... 61 4.1.3 Comparison of FEA results with Calspan Test Data .................................. 65 4.2 Double lane change (DLC) at 120 km/hr ........................................................... 67 4.2.1 Comparison of FEA results with Calspan Data - DLC ............................... 70 v 5 Conclusion and future work ...................................................................................... 72 6 References ................................................................................................................. 74 List of Figures Figure 2-1: Construction of a Radial Pneumatic Tire, used under fair use [5] ................... 5 Figure 2-2: Three Zone Concept, used under fair use [7] ................................................... 6 Figure 2-3: Model of a coupled problem of a tire and water film, used under fair use [4] ........................................................................................................................................... 11 Figure 2-4: Comparison of simulation results with the NASA hydroplaning equation, used under fair use [32]..................................................................................................... 17 Figure 2-5: Influence of wheel load, water film thickness on hydroplaning speed, used under fair use [32] ............................................................................................................. 17 Figure 2-6: Influence of inflation pressure and water film thickness on hydroplaning speed, used under fair use [32] ......................................................................................... 18 Figure 2-7: Influence of wheel load, water film thickness on hydroplaning speed of truck tires, used under fair use [32] ............................................................................................ 19 Figure 2-8: Comparison of hydroplaning speed of different tire-tread groove patterns, used under fair use [37]..................................................................................................... 23 Figure 2-9: Influence of groove inclination angle on hydroplaning speed, used under fair use [37].............................................................................................................................. 24 Figure 2-10: Deformation at the leading edge, used under fair use [18] .......................... 25 Figure 2-11: ABS activity on dry (a) and wet pavement surfaces (b), used under fair use [41] .................................................................................................................................... 26 Figure 2-12: ABS activity with reduced inflation pressure of 103.42 kPa (15 psi), used under fair use [41] ............................................................................................................. 27 Figure 2-13: Frictional force versus vehicle speed at braking: (a) wet road (b) dry road , used under fair use [22]..................................................................................................... 28 Figure 3-1: Lagrangian, Eulerian and ALE description, used under fair use [42]............ 31 Figure 3-2: Hydroplaning simulation in Abaqus .............................................................. 33 Figure 3-3: Net Normal load acting on the tire ................................................................. 40 Figure 3-4: Tire footprint results....................................................................................... 41 Figure 3-5 Net Normal Load Acting on the tire at different velocities ............................ 42 Figure 3-6: Traction and Braking simulations .................................................................. 45 Figure 3-7: Change in normal load for traction and braking cases ................................... 46 Figure 3-8: Change in Longitudinal force ........................................................................ 47 Figure 3-9: Calspan test data, used under fair use [49]..................................................... 48 Figure 3-10: Net Normal load at various slip angles- Load 3922 N ................................. 49 vi Figure 3-11: Lateral force acting at different slip angles- Load 3922 N .......................... 50 Figure 3-12: Filtered lateral force data ............................................................................. 51 Figure 3-13: Net Normal load at various slip angles- Load 3200 N ................................. 51 Figure 3-14: Lateral force comparison- Load 3922 N ...................................................... 53 Figure 3-15: Lateral force comparison- Load 3200 N ...................................................... 54 Figure 3-16: Lateral force comparison- Load 5100 N ...................................................... 55 Figure 3-17: Expected Hydroplaning speed on water depth of 3 mm. ............................. 56 Figure 4-1: CarSim lateral force data on Dry surface ....................................................... 57 Figure 4-2: CarSim lateral force data on Wet surface ...................................................... 58 Figure 4-3: Steering wheel angle vs. Lateral acceleration- Speed 50 km/hr .................... 60 Figure 4-4: Steering wheel angle vs. Time- Speed 50 km/hr ........................................... 60 Figure 4-5: Vehicle side slip angle vs. Time – Speed 50 km/hr ....................................... 61 Figure 4-6: Steering wheel angle vs. Lateral Acceleration- Speed 75 km/hr ................... 62 Figure 4-7: Vehicle side slip angle vs. Time – Speed 75 km/hr ....................................... 63 Figure 4-8: Vehicle position at identical times (t=31 s) ................................................... 63 Figure 4-9: Steering wheel angle vs. Lateral acceleration- Wet front tires- Speed 75 km/hr ........................................................................................................................................... 64 Figure 4-10: Vehicle side slip angle vs. Time – Wet front tires- Speed 75 km/hr ........... 65 Figure 4-11: Lateral force based on Calspan test data [53] .............................................. 66 Figure 4-12: Vehicle Side Slip angle based on Calspan Data .......................................... 67 Figure 4-13: DLC on dry surface ...................................................................................... 67 Figure 4-14: DLC on wet surface ..................................................................................... 68 Figure 4-15: Steering wheel angle vs Time- DLC ............................................................ 69 Figure 4-16: Vehicle Path Tracking .................................................................................. 70 Figure 4-17: Steering wheel angle vs Time- DLC- Calspan data ..................................... 71 Figure 4-18: Vehicle Path Tracking- Calspan data ........................................................... 71 List of Tables Table 2-1: Groove dimensions studied, used under fair use [26] ..................................... 11 Table 2-2 : Comparison of grooving measures, used under fair use [28] ......................... 13 Table 2-3: Tire grooving vs pavement grooving effectiveness, used under fair use [3] .. 15 Table 2-4: Factors influencing friction, used under fair use [7] ....................................... 20 Table 3-1: Abaqus Element description ............................................................................ 35 Table 3-2: Model Validation Results ................................................................................ 44 Table 3-3: Lateral force data at a load of 3922 N ............................................................. 52 Table 3-4: Lateral force data at a load of 3200 N ............................................................. 54 Table 3-5: Lateral force data at a load of 5100 N ............................................................. 55 vii 1. Introduction 1.1 Motivation To reduce the product development cycle time and cost, automotive companies rely heavily on computational simulation tools. Before designing a vehicle, most vehicle components are fixed with the exception of tires, suspension, and steering components. These parts can be used to optimize and enhance the vehicle ride and handling performances [1]. This forces the tire developers to utilize complex models to study tire components and properties effecting vehicle characteristics. Hydroplaning is a phenomenon which occurs when a layer of water builds up between the tires of a vehicle and the road surface which leads to loss of traction that prevents the vehicle from responding to control inputs such as steering, braking or accelerating. Hydroplaning occurs when the tire encounters more water than it can expel. As a critical velocity is attained, fluid pressure in front of the wheel forces a wedge of fluid under the leading edge of the tire causing the tire to lift from the road [2]. Statistics from various parts of the world indicate that approximately 20% of all road traffic accidents occur in wet weather conditions. Although there are no detailed statistics on the exact causes of the wet-weather accidents, it is believed that low skid resistance and hydroplaning are major factors leading to the accidents [3]. The frictional force between the tire and the road surface diminishes when the vehicle drives on a road covered by water film. Hydroplaning occurs when the total fluid lift force is greater than or equal to the wheel load. As the velocity increases, dynamic pressure builds up between the tire and the road which tends to lift the tire and increase the chances of hydroplaning [4]. The vehicle velocity must be sufficiently high so that the inertial force developed in the fluid film is comparable to the tire inflation pressure. This effect causes the tire contact patch to buckle thus enabling a large layer of fluid film to support the load. Hydroplaning is a complex phenomenon involving a number of factors such as tire-road interaction, tire deformation, tire pressure, groove patterns, water film depth, etc. It is time consuming and expensive to carry out physical testing using different groove patterns. Hence computational simulations and numerical methods are being used to predict the onset of hydroplaning. Likelihood of hydroplaning increases with • Velocity: in less time the same amount of fluid has to be dissipated 1 • Depth of fluid: more depth increases fluid volume to be dissipated • Viscosity and mass of fluid: results in inertia in the dissipation of the fluid • Tread wear: the grooves are less deep and thus the volume available for fluid storage/transportation is less. • Tire-wideness: narrower tires are less vulnerable to hydroplaning because the vehicle weight is distributed over a smaller footprint, resulting in a greater ability for the tires to push fluid out of the way. Also, the volume of the fluid to be dissipated is smaller for narrower tires Tire manufacturers develop different set of tires for various driving conditions. Typical wet weather tires have a lot more grooves, sipes and void ratio in them as compared to all season or dry weather tires. The use of all season tires on water logged road surfaces can lead to a severe loss of traction because of a drastic reduction of the tire contact patch. This can in turn decrease the force generation capability of tires thus causing a decrease in traction. As tires comprise of extremely non-linear materials, Finite Element Analysis provides excellent means for studying the structural characteristics of tires. Abaqus FEM code has been traditionally used by all major tire manufacturers for in house tire development. Vehicle hydroplaning can lead to serious road accidents and it is necessary to study tire- pavement interactions to devise optimum methods to prevent hydroplaning. Limited efforts have been taken by researchers to study the interactions between road surfaces and treaded tires. Valuable insight could be obtained if vehicle dynamic simulations are developed which take into consideration the tire traction on wet surfaces. Combining a Fluid Structure Interaction hydroplaning simulation with a vehicle dynamics simulation package can be the first step towards understanding the complexities involved in vehicle hydroplaning. This can provide valuable insight to civil engineers, tire manufactures and automotive companies to devise optimum methods to curb vehicle hydroplaning. 2 1.2 Research Objectives The objectives of this research are: 1. Develop a passenger tire FE model and use the Abaqus Fluid Structure Interaction Coupled Eulerian Lagrangian method to study hydroplaning. 2. Develop a hydroplaning tire model by varying: a. Load b. Speed c. Water depth 3. Develop a CarSim full-vehicle hydroplaning simulation model. 4. Evaluate vehicle stability in dry and wet conditions using the CarSim model. 1.3 Thesis Organization The motivation and organization of the thesis are included in Chapter 1. Background and the literature review including tire design, empirical models, FSI simulations and vehicle testing have been discussed in detail in chapter 2. Chapter 3 covers the details of the FSI model used for the thesis. Vehicle dynamics simulations using CarSim have been introduced in Chapter 4. Chapter 5 discusses conclusions and future work. 3