Pitfalls for Accurate Steady-State Port Flow Simulations

Steady-state port flow simulations were carried out with a commercial three dimensional (3D) Computational Fluid Dynamics (CFD) code using Cartesian mesh with cut cells to study the prediction accuracy. The accuracy is assessed by comparing predicted and measured mass-flow rate and swirl and tumble torques at various valve lifts using different boundary condition setup and mesh topology relative to port orientation. The measured data is taken from standard steady-state flow bench tests of a production intake port. The predicted mass-flow rates agree to within 1% with the measured data between the intermediate and high valve lifts. At low valve lifts, slight over prediction in mass-flow rate can be observed. The predicted swirl and tumble torques are within 25% of the flow bench measurements. Several meshing parameters were examined in this study. These include: inlet plenum shape and outlet plenum/extension size, embedded sphere with varying minimum mesh size, finer meshes on port and valve surface, orientation of valve and port centerline relative to the mesh lines. For all model orientations examined, only the mesh topology with the valve axis aligned closely with the mesh lines can capture the mass-flow rate drop for very high valve lifts due to flow separation. This study further demonstrated that it is possible to perform 3D CFD flow analyses to adequately simulate steady-state flow bench tests.

Mechanism for the Reduction of Lateral Friction Capabilities of a Delaminated Tire

Tire delamination is a significant vehicle dynamics safety problem contributing to the loss of control of passenger vehicles, often resulting in accidents and injuries. This paper examines vehicle handling characteristics after a complete outer tread belt separation on 2-steel belt and 3-steel belt tires. The test vehicle used to examine this phenomenon was a Ford 15-passenger van. The test procedure was the SAE J266 circle test, and the measure of effectiveness was taken to be the lateral acceleration at which the vehicle transitioned to an oversteer characteristic. For a typical tread separation on a 2-steel belted tire, the tire loses one of its steel belts and thus much of its structural rigidity. Vehicle testing using a 3-steel belted tire, in which only the outermost single belt was removed, and the remaining two belts were oriented along opposite diagonals, showed that the vehicle remained in an understeer condition at higher lateral accelerations than with the 2-steel belted tire, indicating that the retention of greater structural rigidity to the impaired tire resulted in it maintaining much of its cornering stiffness. Until now, it has been assumed that the reduction in cornering stiffness of a delaminated tire was predominately due to the low coefficient of friction of the exposed steel belt after delamination. The testing described in this paper suggests that a significant influence on the remaining cornering stiffness of the tire after tread separation is the overall remaining structural rigidity of the tire. From this testing, it is theorized that the rigidity of the delaminated tire is at least as important as the reduced coefficient of friction for the purposes of maintaining vehicle understeer behavior after a delamination.

Preserving Passenger Comfort Through RWI Analysis

The air conditioning systems designed for passenger rail cars typically exchange heat with the outside air environment; when the trains operate within tunnels, the effectiveness of the air conditioning systems may diminish if the tunnel is too warm. Therefore, one of the traditional activation modes associated with rail tunnel ventilation systems is summertime cooling — for the purpose of maintaining onboard passenger comfort. However, summertime cooling modes can be problematic from the standpoints of fan operating pressure (i.e. an opposing air pressure is created whenever trains approach ventilation shafts), energy consumption and emergency preparedness (i.e. fans operating in the wrong direction when a fire is detected). In this paper, the thermal comfort of rail transportation passengers was studied in detail using the Relative Warmth Index (RWI) analyses to determine if the combination of: warm outdoor weather, the tunnel heat-sink effect, the rail coach design air temperature and typical commuting scenarios necessitated running the tunnel fans in a summertime cooling mode to preserve passenger comfort. If the summertime cooling mode could be eliminated, or even minimized, the tunnel ventilation usage/operating costs would be reduced, the fans would have a longer service life and the system would have greater overall availability for emergency events.

Design and Analysis of a Series Hybrid Electric Vehicle for Indian Conditions

Electric and hybrid vehicles are emerging rapidly in the automotive market as alternatives to the traditional Internal Combustion Engine (ICE) driven vehicles to meet stringent emission standards, environmental and energy concerns. Recently, Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) have been introduced in many countries including India. One configuration of a HEV is the Series Hybrid Electric Vehicle (SHEV). The design and analysis of the drive system of a SHEV under Indian conditions is the focus of this paper. In conventional vehicles, the ICE is the power source that drives the vehicle. The energy from the ICE is distributed to the wheels through the transmission, which is then used to generate the traction force at the tyre-road interface. In a HEV, both the engine and the electric motor provide the energy to drive the vehicle. In a SHEV, the energy generated by the electric motor is transmitted through the transmission to meet the torque demand at the wheels. Based on the driver’s acceleration demand and the state of charge of the battery, the controller manages the ICE, the generator and the battery to supply the required energy to the motor. The motor finally develops the required drive torque to generate the traction force at the wheels to meet the vehicle drive performance requirements like gradeability, acceleration and maximum speed. The objective of this paper is to discuss the design of the drive system of a SHEV. This involves the calculation of the power specifications of the electric motor based on the vehicle drive performance requirements. The equations for performing these calculations are presented. The procedure is then demonstrated by considering a typical Indian commercial vehicle along with its typical vehicle parameter values. A simulation study has also been performed by considering the Indian drive cycle to demonstrate the energy savings obtained by the use of a SHEV.

Numerical Investigation on Impact Energy Absorption of Single-Walled Carbon Nanotube Reinforced Composites

With the exceptional mechanical properties, carbon nanotubes (CNTs) are considered to be attractive candidate reinforcements for composite materials and to have potential applications in improving the energy absorption capability of matrix material. However, it is still difficult to reveal the micro-mechanisms of the impact energy absorption of CNT-reinforced composites by experiments, hence, the numerical investigation is helpful. In this paper, a unit cell of single-walled CNTs (SWCNTs) embedded in metal matrix is modeled by nano-scale finite element method. Under impact loads, the failure modes of a single SWCNT and the SWCNT in matrix are predicted, respectively, and several possible energy absorption mechanisms are explained and compared. The investigation shows that, the metal matrix restraints the radial expansion of the SWCNT and therefore improves its crush buckling resistance, and makes it absorb more energy before collapse. The specific energy absorption of SWCNTs-reinforce composites increases with the increasing volume fraction of SWCNTs in both matrixes, and ascends more quickly in magnesium alloy than in aluminum alloy matrix.

Time-Efficient Method for Test-Based Optimization of Technical Systems Using Physical Models

Technical systems must be continuously improved so that they can remain competitive on the market. Also, the time-to-market is an important factor for the success of a product. To achieve this goal, new methods and processes are needed. Especially the testing and calibration are important phases in the development process. This paper introduces a method, which helps to reduce the time effort while increasing the quality of the calibration process. The basic idea is to use measured test data to parameterize a physical (or mostly physical) model structure to create adequate models for the optimization. The main advantage of the method is the reduction of test effort because the number of variations of the design parameter is one, or extremely decreased (depending on the system). Another advantage is that the uncertainty and the limit of the model can be quantified more accurately compared to common approaches based on non-physical model structures. These normally use artificial neuronal networks (ANN) or polynomial approaches for the test-based optimization. This contribution illustrates the method by using the example of the calibration process of a double clutch gearbox (DCT) regarding energy efficiency and drivability on a roller test bench. First step is the test planning and test execution. In this step the method calculates the optimal execution order of the measuring points. In this example 81% timesaving can be achieved compared to the equivalent on the test track. The second step is the automated generation of the simulation model. In this step the unknown parameters of the model structure are calculated. The contribution shows different approaches for the identification of non-linear systems. In the last step the model is used to perform the optimization of the design parameters.

Modeling of Vehicle Magnetic Footprint in 3-D Space for Type Detection

This paper presents a modified multiple 3-D dipole model to capture the complex magnetic footprints created by different vehicles on the road. In this study, laboratory bench tests were carried out to record the magnetic behavior of single dipole magnets and road tests were then conducted to record the complex magnetic behavior of vehicles. A preliminary 2-D modified dipole model similar to literature was developed and then expanded to a high fidelity 3-D multiple dipole model. An exhaustive parametric study was conducted to identify relevant design parameters for model matching. The 2-D model helped corroborate the results of laboratory bench tests using magnets and showed that the magnetic sensor was capable of identifying different sized magnets based on their magnetic footprints. Similar conclusions were made when applying the 3-D multiple dipole model to the experimental road tests. Different analytical functions were developed to help distinguish vehicle types based on their magnetic footprint. The analytical and experimental study conducted showed that vehicle magnetic footprint could be captured by mathematical models and that the magnetic sensor could be used to identify vehicle types.

Examination of the Ability of Conceptual Airbag Systems to Affect Restrained Occupant Kinematics and Associated Neck Loads During Rollover Impact Conditions

Rollover occupant protection systems consist of many design elements such as various seat belt types, airbags, active and passive seats, and deployable systems in rollover impacts. In this study conceptual airbag systems intended to modify occupant kinematics were examined. The potential effects of these systems on occupant neck loads were evaluated. Finite element models of an LTV type vehicle and a 50th percentile dummy were utilized to evaluate the effects of alternative designs on neck loads under example rollover conditions. CAE representations of deployable airbag system types were created. Results of the study are summarized below.

Assessment of the Dynamic Behavior of a Single Person ATV in Presence of a Passenger: Outcome on the Rider and Passenger Crash Impact Kinematics Using Computational Model

An ATV (All-terrain vehicle) is a gasoline powered, fast moving off road vehicle often used for farming and industrial activities as well as recreational activities. The popularity of this type of vehicle has increased over the last decade with more than 10 million in use today. Most ATVs are designed for only single rider even though the seat of the ATV may appear big enough to carry a passenger. The presence of an additional person on a single person ATV greatly affects its dynamic handling characteristics. This change increases the risk of a crash and subsequent injuries to both riders. ATV crashes involving climbing and descending on steep hills are common. Lateral rollover crashes are often the result of riding an ATV at a high speed on uneven terrain. The presence of passenger on a single person ATV during these conditions changes the rider impact kinematics and resulting injury outcome, as the ATV behaves differently in the presence of an additional person. The computational model of a single person, adult-sized ATV, as developed previously for the study of child injury prevention, was used for this study. The multi-body computational model of this ATV was developed using biodynamic code MADYMO. This computational model was validated against the laboratory test for its dynamic and suspension characteristics. The tilt table test and the drop test were employed to compare the computational model result. This computer model was used to simulate the crash mechanism involving climbing and descending steep hills with two people on the ATV. This model was also used to simulate the lateral rollover of ATV with two people. The rider and the additional passenger on this single rider ATV were modeled using a 50th percentile male and a 5th percentile female. The two rider simulation was compared with single rider simulation for similar terrain and ATV speed to gain insight about the influence of this additional passenger weight on the crash kinematics of the ATV and the rider. These simulations will also be used in the future to generate more visually dramatic videos for educational intervention for ATV safety programs and other injury prevention activities.

Adaptive Vehicle Stability Control With Optimal Tire Force Allocation

Vehicle stability control systems have been receiving increasing attention, especially over the past decade, owing to the advances in on-board electronics that enables successful implementation of complex algorithms. Another major reason for their increasing popularity lies in their effectiveness. Considering the studies that expose supporting results for reducing crash risk or fatality, organizations such as E.U. and NHTSA are taking steps to mandate the use of such safety systems on vehicles. The current technology has advanced in many aspects, and undoubtedly has improved vehicle stability as mentioned above; however there are still many areas of potential improvements. Especially being able to utilize information about tire-vehicle states (tire forces, tire-slip angle, and tire-road friction) would be significant due to the key role tires play in providing directional stability and control. This paper presents an adaptive vehicle stability controller that makes use of tire force and slip-angle information from an online tire monitoring system. Solving the optimality problem for the tire force allocation ensures that the control system does not push the tires into the saturation region where neither the driver nor the controller commands are implemented properly. The proposed control algorithm is implemented using MATLAB/CarSim® software packages. The performance of the system is evaluated under an evasive double lane change maneuver on high and low friction surfaces. The results indicate that the system can successfully stabilize the vehicle as well as adapting to the changes in surface conditions.