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Abstract Reliability analysis of a large-scale system under random dynamic loads can be a very time-consuming task since it requires repeated studies of the system. In many engineering problems, for example, wave loads on an offshore platform, the excitation loads are defined using a power spectral density (PSD) function. For a given PSD function, one needs to generate many time histories to make sure the excitation load is modeled accurately. Global and local approximation methods are available to predict the system response efficiently. Each way has their advantages and shortcomings. The combined approximations (CA) method is an efficient method, which combines the advantages of local and global approximations. This work demonstrates two methodologies that utilize CA to reduce the cost of crude or separable Monte Carlo simulation (MCS) of linear dynamic systems when the excitation loads are defined using PSD functions.

Recent fluctuation in oil prices has generated interest in fuel-efficient vehicles, especially their aerodynamic profile. The literature indicates that turbulent wakes that form at the rear end of the vehicle contribute to vehicle drag in a major way. Minor studies have addressed the effects of rear-end wall angle to the drag force through effecting the wake behind the vehicle; however, this study assesses the reduction of drag using angular side walls. A previous simulation of external airflow over Ahmed's body was investigated, utilizing the k-ω SST models. Different angles of side walls were analyzed, and a maximum 36.85% reduction in drag coefficient was achieved using an angular rear side wall. The turbulent model was validated and the effectiveness of angular rear side walls thus proven. The study then simulated the flow for a road vehicle model to investigate the real world effect of angular rear side walls.

Road vibrations cause fatigue failures in vehicle components and systems. Therefore, reliable and accurate damage and life assessment is crucial to the durability and reliability performances of vehicles, especially at early design stages. However, durability and reliability assessment is difficult not only because of the unknown underlying damage mechanisms, such as crack initiation and crack growth, but also due to the large uncertainties introduced by many factors during operation. How to effectively and accurately assess the damage status and quantitatively measure the uncertainties in a damage evolution process is an important but still unsolved task in engineering probabilistic analysis. In this paper, a new procedure is developed to assess the durability and reliability performance, and characterize the uncertainties of damage evolution of components under constant amplitude loadings.

This paper describes the development and testing of a Dynamic Vibration Absorber to reduce frame beaming vibration in a highway tractor. Frame beaming occurs when the first vertical bending mode of the frame is excited by road or wheel-end inputs. It is primarily a problem for driver comfort. Up until now, few options were available to resolve this problem. The paper will review the phenomenon, design factors affecting a vehicle's sensitivity to frame beaming, and the principles of Dynamic Vibration Absorbers (AKA Tuned Mass Dampers). Finally, the paper will describe simulation and testing that led to the development of an effective vibration absorber as a field fix.

A novel speed and position dependent Lane Keeping Assistance (LKA) control strategy for heavy vehicles is proposed. This LKA system can be implemented with any torque overlay system capable of accepting external position or torque commands. The proposed algorithm tackles the problem of lane keeping in two ways from a heavy vehicle's perspective. First, it stabilizes the vehicle's lateral position by bringing it to the center of the lane and giving it the correct heading to stay there. This is done using a speed and position dependent control strategy that becomes less aggressive as the vehicle's speed increases and as it gets closer to the center of the lane. Such speed and position dependency is especially critical in heavy vehicles where unnecessary aggressive control can lead to oscillations about the lane's centerline when cruising at high speeds.

Terrestrial winds play an important role in affecting the aerodynamics of road vehicles. Of increasing importance is the effect of the unsteady turbulence structure of these winds and their influence on the process of optimizing aerodynamic performance to reduce fuel consumption. In an effort to predict better the aerodynamic performance of heavy-duty vehicles and various drag reduction technologies, a study was undertaken to measure the turbulent wind characteristics experienced by heavy-duty vehicles on the road. To measure the winds experienced on the road, a sport utility vehicle (SUV) was outfitted with an array of four fast-response pressure probes that could be arranged in vertical or horizontal rake configurations that provided measurements up to 4.0 m from the ground and spanning a width of 2.4 m. To characterize the influence of the proximity of the vehicle on the pressure signals of the probes, the SUV and its measurements system was calibrated in a large wind tunnel.

In tire development, the dynamic tire-road contact forces are an important indicator to assess structure-borne interior cabin noise. This type of noise is the dominant source in the frequency range from 50-450 Hz, especially when rolling with constant angular velocity on a rough road. The spatial force distribution is difficult or sometimes even impossible to simulate or measure in practice. So, the use of an inverse technique is proposed. This technique uses response measurements in combination with a digital twin simulation model to obtain the input forces in an inverse way. The responses and model properties are expressed in the time domain, since it is specifically aimed to trace back the impact locations from road surface texture indents on the tire. In order to do so, the transient responses of the travelling waves as a result of these impacts is used. The framework expresses responses as a convolution product of the unknown loads and impulse response measurements.

Driving cycles are typically used for estimation of vehicle fuel/energy consumption and CO2 emissions. In most of applications only the vehicle velocity vs. time profile is considered as a driving cycle, while a road slope is typically omitted. Since the road slope significantly impacts the fuel consumption, it should be included into realistic driving cycles for hilly roads. As a part of wider research of multidimensional driving cycle synthesis, this paper focuses on analysis of a broad city bus driving cycle dataset recorded in the city of Dubrovnik. The analysis is aimed at revealing the impact of road slope on velocity and acceleration distributions, and clustering the recorded data into several groups reflecting various driving and traffic congestion characteristics. Finally, the Markov chain method is employed to synthesize 3D driving cycles for the selected data clusters, where the Markov chain states include vehicle velocity, vehicle acceleration, and road slope.

Lift axle is essentially provided in commercial vehicles to increase the vehicle’s load-carrying capacity. The axle is lowered in the case of a high payload and the load is evenly distributed among the wheels both on fixed axles and the lift axle. This ability to lift the axle implies better maneuverability in turns, better fuel consumption, and less wear and tear on the tires and brake shoes. Also, it will reduce the damage to the road surfaces. This lowering and lifting of the lift axle are controlled by a series of valves together called the Lift Axle Control System (LACS). This LACS must consider the vehicle load condition, the ignition state, and gear state to decide if the axle must be lifted or lowered. This paper deals with the modeling and simulation of the LACS system at the vehicle level and optimize the design for the respective desired design solution.

Despite numerous research efforts, there is no reliable and widely accepted tool for the prediction of erosion prone material surfaces due to collapse of cavitation bubbles. In the present paper an Erosion Aggressiveness Index (EAI) is proposed, based on the pressure loads which develop on the material surface and the material yield stress. EAI depends on parameters of the liquid quality and includes the fourth power of the maximum bubble radius and the bubble size number density distribution. Both the newly proposed EAI and the Cavitation Aggressiveness Index (CAI), which has been previously proposed by the authors based on the total derivative of pressure at locations of bubble collapse (DP/Dt>0, Dα/Dt<0), are computed for a cavitating flow orifice, for which experimental and numerical results on material erosion have been published. The predicted surface area prone to cavitation damage, as shown by the CAI and EAI indexes, is correlated with the experiments.

In vehicle dynamics modelling, the road profile is generally treated in one of two ways; either the gradient is a property that changes over a length scale far greater than that of the vehicle's wheelbase, or as a very detailed road surface model for determining the behaviour of vehicle suspensions. Occasionally, for modelling the behaviour of off-road vehicles, step-climbing manoeuvres are modelled. We propose an extension of these step-climbing models to a general, continuously varying road gradient model for cases where the distance over which the large gradient change occurs are of similar length-scale as the vehicle wheelbase. The motivation behind this work comes from a road gradient and vehicle mass estimation problem where it was noticed that very sudden gradient changes have a significant impact on the powertrain, but in a way that is not proportional to the attitude change of the vehicle.

The research on the characteristics of vehicle movement is the premise to guarantee the smooth operation of electric vehicles, and it’s also the basis for developing the vehicle ability in depth. Therefore, it’s essential to study on the vehicle movement characteristics. And steering on ramp is a typical working condition for tracked vehicle. Firstly, the kinematics and dynamics of tracked vehicle during the steering process on ramp are analyzed in detail aiming at the problem that it’s complex and difficult to describe the process of steering, and the dynamics model of tracked vehicle is established in the condition of the offset of instantaneous steering center and the sliding of the track and other factors. Second, the relationships between driving force, steering radius and slop are obtained by simulation, and the variation rules of these parameters are analyzed. Finally, the model of steering on ramp is verified using electric tracked vehicle.

Due to the variability of real traffic conditions for vehicle testing, real-world vehicle performance estimation using simulation method become vital. Especially for heavy duty vehicles (e.g. 40 t trucks), which are used for international freight transport, real-world tests are difficult, complex and expensive. Vehicle simulations use mathematical methods or commercial software, which take given driving cycles as inputs. However, the road situations in real driving are different from the driving cycles, whose speed profiles are obtained under specific conditions. In this paper, a real-world vehicle performance estimation method using simulation was proposed, also it took traffic and real road situations into consideration, which made it possible to investigate the performance of vehicles operating on any roads and traffic conditions. The proposed approach is applicable to all kind of road vehicles, e.g. trucks, buses, etc. In the method, the real-road network includes road elevation.

Fuel consumption has been a core consideration since the beginning of the transportation era. These are reasons related to our environment, and to economics. In the competitive truck industry fuel consumption is an important sales argument, since customers on an average drive their trucks for distances of 150 000 km per year, which means that fuel becomes a large part of the lifetime cost for a vehicle. Existing braking system design in commercial vehicles are basically air assisted, which utilizes the compressed air from reservoir, which is being replenished based on requirement by a positive displacement compressor, generally driven directly by vehicle power pack. In this paper, an effort has been made to partially use the energy stored in the springs (induced due to road undulations) for compressed air generation through a single acting positive displacement pump.

Vehicles on the road operate in the turbulent flow field resulting from the combined effects of the natural wind and the wakes of other vehicles. While substantial data exists on the properties of the natural wind, much less information is available for the wake properties of road vehicles. The wake information available for road vehicle shapes is mainly restricted to the near wake region, but to understand the vehicle operating environment it is the wake downstream of this region which is of interest. To determine the range of this area of interest requires some knowledge of the decay of the wake properties. From wind tunnel studies using small simple bluff bodies in free stream and in ground proximity the principle wake properties, velocity deficit and peak turbulence intensity have been measured. The maximum velocity deficit is shown to approximately decay with x-2/3, where x is the distance downstream, while turbulence intensity decays at a slightly slower rate.

Durability and reliability performance is one of the most important concerns of a recently developed Thermal Regeneration Unit for Exhaust (T.R.U.E-Clean®) for exhaust emission control. Like other ground vehicle systems, the T.R.U.E-Clean® system experiences cyclic loadings due to road vibrations leading to fatigue failure over time. Creep and oxidation cause damage at high temperature conditions which further shortens the life of the system and makes fatigue life assessment even more complex. Great efforts have been made to develop the ability to accurately and quickly assess the durability/reliability of the system in the early development stage. However, reliable and validated simplified engineering methods with rigorous mathematical and physical bases are still urgently needed to accurately manage the margin of safety and decrease the cost, whereas iterative testing is expensive and time consuming.

Technological developments in road vehicles over the last two decades have received considerable attention towards pushing the safe performance limits to their ultimate levels. Towards this goal, Active Front Steering (AFS) and Direct Yaw-moment Control (DYC) systems have been widely investigated. AFS systems introduce corrective steering angles to conventional system in order to realize target handling response for a given speed and steering input. It is thus expected that such an action under severe maneuvers may cause one tire to reach saturation while the other tire may be capable of developing more force. This study, therefore, proposes an Active Independent Front Steering (AIFS) system capable of controlling a wheel independently. At low speeds, the proposed AIFS system will modify the steer angle with speeds while maintaining pro-ackerman geometry similar to an AFS system. In doing so, it will realize a target response defined as one provided by a neutral steer system.

Fatigue, creep, oxidation, or their combinations have long been recognized as the principal failure mechanisms in many high-temperature applications such as exhaust manifolds and thermal regeneration units used in commercial vehicle aftertreatment systems. Depending on the specific materials, loading, and temperature levels, the role of each damage mechanism may change significantly, ranging from independent development to competing and combined creep-fatigue, fatigue-oxidation, creep-fatigue-oxidation. Several multiple failure mechanisms based material damage models have been developed, and products to resist these failure mechanisms have been designed and produced. However, one of the key challenges posed to design engineers is to find a way to accelerate the durability and reliability tests of auto exhaust in component and system levels and to validate the product design within development cycle to satisfy customer and market's requirements.

After initial trials on Homogeneous Charge Compression Ignition (HCCI) engine design and tests pursuing feedback control to avoid misfire and knocking over wide transient operation ranges, Engineers at the US Environmental Protection Agency's (EPA) National Vehicle Fuel and Emissions Laboratory identified the crucial engine state variable, MRPR (Maximum Rate of Pressure Rise) and successfully controlled a 1.9L HCCI engine in pure HCCI mode [1]. This engine was used to power a hybrid Ford F-150 truck which successfully ran FTP75 tests in 2004. In subsequent research, efforts have been focused on practical issues such as improving transient rate, system simplification for controllability and packaging, application of production grade in-cylinder pressure sensors, cold start, idling and calibration for ambient conditions as well as oxidation catalyst applications for better turbine efficiency and HC and CO emissions control.

In this paper, a method for directional control of articulated heavy vehicles is proposed. The tractor yaw rate, the tractor lateral velocity and the articulation angle are selected as the control variables. The desired values of these states are defined in such way to improve the maneuverability and the stability of the articulated vehicle. A linear quadratic regulator controller is designed based on the linear model of the articulated vehicle to make the control variables follow the desired responses. Furthermore, a nonlinear 14 Degrees of freedom (DoF) model is developed to evaluate the proposed control method. The significant effect of the proposed method on improving the directional behavior of the articulated vehicle is proved through the simulations of the high speed lane change maneuver on a slippery road.