Stephen Ekwaro-Osire

Life-cycle engineering: Issues, tools and research

Life-cycle engineering (LCE) is a decision-making methodology that considers performance, environmental and cost requirements for the duration of a product. This methodology is becoming a norm for global companies that want to remain competitive. To facilitate and enhance the application of LCE methodology to industrial products, a number of computer tools or utilities that require minimal user input, and hence run automatically in the background of the design process, have been developed. These utilities are intended to provide a feedback on an evolving design without impeding or hampering the design process. There exists a need to continue research on the development of tools that simulate flows in a life-cycle and optimize them. These tools should be based on the client-server model base on the Internet to facilitate the e-Transition.

Experimental Study on an Impact Vibration Absorber

This paper investigates the effects of mass ratio, clearance, and excitation amplitude on system dynamics and impact vibration absorber (IVA) effectiveness. The experimental studies were carried out for both free and forced vibrations. For free vibrations, the effects of system parameters on the rate of decay of vibrations were shown. Constant frequency and frequency sweep experiments were conducted to study the dynamics of the system under forced vibration. Optimum system parameters were extracted, for which the vibration absorption and absorber efficiency is greatest. It was also shown that phase plots and coherence, between the forcing function and the primary system response, offered an insight in the effectiveness of the IVA.

Influence of Tip Relief Modification on the Wear of Spur Gears with Asymmetric Teeth

Recently, spur gears with asymmetric teeth have been considered a way of increasing performance while maintaining the gearbox dimensions. Asymmetric teeth have different pressure angles on drive and coast sides. They provide, among other advantages, a high bending strength and low vibration. In spur gears with asymmetric teeth, wear has been observed to be a major failure mode. In this study, the impact of tip relief modification and pressure angle on the wear of spur gears with asymmetric teeth is numerically investigated. Here, the focus is on sliding wear. A wear model based on Archards equation is employed to predict wear depth. The pressure angle and the tip relief are parameterized. In the analysis, instantaneous contact loads and Hertz pressures are used in wear depth calculations. It is shown that as the amount of the tip relief increases, the wear depth, particularly at the beginning and end of the mesh, decreases. As the number of wear cycles increases, the effect of the tip relief modification on wear depths decreases slightly. It was also shown that with an increase in tip relief, the dynamic load decreases. However, if the amount of tip relief modification increases excessively, the maximum dynamic load also increases. Therefore, an excessive increase in tip relief modification should be avoided, whereby the level of excessive increase depends on the tip relief configuration.

Non-linear least-squares solution to the Moire hole method problem in orthotropic materials, Part I : Residual stresses

The hole method problem relates to two inverse problems of interest: the first, most commonly addressed by practitioners, is to obtain residual stresses; the other, generally neglected, inverse problem can be posed as either a stress separation problem or a material elastic properties identification problem. In both this Paper I and Paper II, we pose and solve this dual hole method problem in an orthotropic plate, using computer generated moiré isothetics, by means of a non-linear least-squares approach. In Paper I we address the residual stress problem. In Paper II we pose the use of moiré isothetics as a means to achieve separation of stresses, but we deal with the determination of the five orthotropic elastic constants, four of which are independent.

Performance of an anisotropic Allman/DKT 3-node thin triangular flat shell element☆

Abstract A simple, explicit formulation of the stiffness matrix for an anisotropic, 3-node, thin triangular flat shell element in global coordinates is presented. An Allman triangle (AT) is used for membrane stiffness. The membrane stiffness matrix is explicitly derived by applying an Allman transformation to a Felippa 6-node linear strain triangle (LST). Bending stiffness is incorporated by the use of a discrete Kirchhoff triangle (DKT) bending element. Stiffness terms resulting from anisotropic membrane-bending coupling are included by integrating, in area coordinates, the membrane and bending strain-displacement matrices. Using the aforementioned approach, the objective of this study is to develop and test the performance of a practical 3-node flat shell element that could be used in plate problems with unsymmetrically stacked composite laminates. The performance of the latter element is tested on plates of varying aspect ratios. The developed 3-node shell element should simplify the programming task and have the potential of reducing the computational time.

High-Level fusion for intelligence applications using Recombinant Cognition Synthesis

Intelligence applications exploit heterogeneous data using High-Level fusion systems to gain information superiority. Whereas Low-Level fusion systems have well established frameworks, High-Level fusion has not yet achieved the same level of maturity. Most High-Level systems implement specialized algorithms that yield useful results, albeit for a very narrow input space, and are characterized by stove-pipe architectures and a fragmented workflow. Recombinant Cognition Synthesis bridges the implementation gap of existing fusion models by defining a comprehensive framework of semantic, temporal, and geospatial enablers comprising the primitives, functions, and models, which through a recombinant workflow, maximize the data exploitation value-chain. This paper presents a methodology and the underlying architectural components necessary to implement a unified High-Level fusion intelligence application, followed by a case study that demonstrates the resulting improvements in knowledge discovery and predictive accuracy.

Non-linear least-squares solution to the moiré hole method problem in orthotropic materials. Part II: Material elastic constants

This is the second of two papers dealing with inverse problems arising from the hole method problem in orthotropic materials. Two inverse problems are of interest in this second paper: one relates to the use of the hole method as a means of separation of stresses; the other deals with using it for orthotropic material elastic constant identification. The problem of separation of stresses is posed and briefly discussed, but the orthotropic material identification problem is addressed, fully showing how to obtain the five orthotropic elastic constants, four of which are independent, when knowing the applied stresses and examining the isothetics or moiré fringes around a through hole in a biaxially loaded thin wood plate.

Uncertainty Considerations in the Dynamic Loading and Failure of Spur Gear Pairs

Gears and gear systems, like any other mechanical system, are subjected to design parameter, and loading uncertainties emanating from inherent randomness, manufacturing, and assembly errors. The traditional deterministic approach to the design of such systems overlooks these uncertainties. This work presents a novel probabilistic multibody dynamic analysis (PMBDA) that enhances the deterministic design practice of gears and gear systems. A contact based, rigid multibody spur gear pair model with random loading, and design parameters has been developed. An advanced mean based on fast probability integration method was implemented to perform a reliability analysis of performance measurements: dynamic factor, root bending stress, and fatigue life of gears. Probabilistic sensitivity analysis of these performance functions to several random variables was also determined. In addition to revealing system reliability or probability of failure, the PMBDA approach also helps designers to consider certain variables critically.

Experimental Investigation of Galling Resistance in OCTG Connections

The results of galling experiments are strongly dependent on the method used and vary from test machine to test machine. However, by a well-developed test method and testing machine, one can obtain reliable and repeatable results. The primary objective of this research is to develop a new test method and machine for evaluating galling resistance in OCTG (oil country tubular goods) connections. Through the application of basic principles of statistical design of experiments, the galling resistance in OCTG threaded connections has been investigated. For estimating the nominal failure stress, two statistical methods, namely, up-and-down and frequency distribution, have been applied and compared. Galling resistance, one of the most important design factors of OCTG connections, has been studied and discussed.

Loading and Design Parameter Uncertainty in the Dynamics and Performance of High-Speed-Parallel-Helical-Stage of a Wind Turbine Gearbox

In operation, wind turbine gearboxes (WTGs) are subjected to variable torsional and nontorsional loads. In addition, the manufacturing and assembly process of these devices results in uncertainty in the design parameters of the system. WTGs are reported to fail in their early life of operation within 3–7 years as opposed to the expected 20 years of operation. Their downtime and maintenance process is the most costly of the failures of any subassembly of wind turbines (WTs). The objective of this work is to perform a probabilistic multibody dynamic analysis (PMBDA) of the high-speed-parallel-helical-stage (HSPHS) of a WTG that considers the uncertainties of generator-side torque-loading and input-shaft speed as well as assembly and design parameter uncertainties. Component reliability (Rc) or probability of failure (Pf) and probabilistic sensitivities of all the input variables toward five performance functions have been measured and conclusions have been drawn. As opposed to the traditional deterministic approach, PMBDA has demonstrated a new aspect of design and installation of WTGs. In addition to revealing Rc or system reliability or underperformance through Pf, the method will also help designers to critically consider certain variables through the probabilistic sensitivity results.