Assessment of Tire Features for Modeling Vehicle Stability in Case of Vertical Road Excitation

Two trends could be observed in the evolution of road transport. First, with the traffic becoming increasingly intensive, the motor road infrastructure is developed; more advanced, greater quality, and more durable materials are used; and pavement laying and repair techniques are improved continuously. The continued growth in the number of vehicles on the road is accompanied by the ongoing improvement of the vehicle design with the view towards greater vehicle controllability as the key traffic safety factor. The change has covered a series of vehicle systems. The tire structure and materials used are subject to continuous improvements in order to provide the maximum possible grip with the road pavement. New solutions in the improvement of the suspension and driving systems are explored. Nonetheless, inevitable controversies have been encountered, primarily, in the efforts to combine riding comfort and vehicle controllability. Practice shows that these systems perform to a satisfactory degree only on good quality roads, as they have been designed specifically for the latter. This could be the cause of the more complicated car control and accidents on the lower-quality roads. Road ruts and local unevenness that impair car stability and traffic safety are not avoided even on the trunk roads. In this work, we investigated the conditions for directional stability, the influence of road and vehicle parameters on the directional stability of the vehicle, and developed recommendations for the road and vehicle control systems to combine to ensure traffic safety. We have developed a refined dynamic model of vehicle stability that evaluates the influence of tire tread and suspensions. The obtained results allow a more accurate assessment of the impact of the road roughness and vehicle suspension and body movements on vehicle stability and the development of recommendations for the safe movement down the road of known characteristics.

Vertical tail sizing of propeller-driven aircraft considering the asymmetric blade effect

An engineering approach is presented to analyse the asymmetric blade thrust effect with the help of analytical and semi-empirical methods. It is shown that the contribution of the asymmetric blade thrust effect in the lateral-directional stability of multi-engine propeller-driven aircraft is significant particularly in critical flight conditions with one engine out of service. Also, in some cases where the engines are rotating in one direction, the asymmetric blade effect has substantial effects on the handling qualities of the aircraft even in normal flight conditions. Overall, due to the significant contribution of this phenomenon in the lateral-directional stability of propeller-driven airplanes, it is important to consider it in the design of the vertical stabilizer and rudder. The resulting analytical method has been used to determine the vertical tail incident angle and desired rudder deflection in accordance with the most critical flight condition for two different cases and validated to ensure the accuracy of the result. In this work, the aerodynamic coefficients as well as the stability and control derivatives have been predicted using analytical and semi-empirical methods validated for light aircraft.

Improving the Directional Behavior of PDC Bits Affected by Stick-Slip: A Statistical Approach

Torsional vibrations are a very common phenomenon affecting drilling operations by limiting efficiency, increasing the risk of downhole equipment failure and generating additional costs, particularly when their most severe form is encountered, the stick-slip. It is less known that torsional vibrations also strongly affect directional drilling operations reducing directional stability and tool face control. In this paper, the highly variable solicitation induced by torsional vibrations is addressed with a statistical approach. This approach, used successfully in Kuwait applications, resulted in an operational savings of 30% of the cost per foot over a panel of more than 15 runs analyzed. Steerability and directional stability is critical on directional wells, especially when using push-the-bit systems with PDC bit due to side force distributed unevenly over one bit revolution. Most of today bit design comparisons are made with an average steerability factor computed over one full revolution of the bit. The method described in this paper is going further in details and looks at the evolution of directional performance indicators within one bit revolution. With the help of a state-of-the-art 3D bit-rock interaction model, which simulates the drilling environment considering the drive system mechanism and both the drill bit and the hole being drilled as a set of 3D meshed surfaces, an accurate picture of the directional stability of the bit design is available. This approach is complemented by a statistical analysis which allows to simulate a multitude of input parameters combinations and to map the directional response of a bit design in a more robust way. Based on the results of the statistical analysis, an optimized design was selected and manufactured for a 12 ¼’-in. rotary steerable system (RSS) directional application known for having torsional vibration limitations. As revealed by the simulation results, this design was expected to exhibit a better directional stability than previous bit design iterations. This optimized design was run on RSS and positive displacement motor (PDM) assemblies and successfully drilled several wells in different fields of Kuwait operations ground. It experienced smooth and stable directional control while reducing the risk for torsional vibrations and resulted in tremendous reduction of the overall cost per foot. PDC bit selection and design process have considerably evolved in the last decade with the use of increasingly accurate simulations models. This paper presents the next step of evolution dedicated to delivering the best adapted solution to any given scenario by examining in greater detail the directional response of a drill bit.