A new numerical procedure for symmetric eigen value problems

A numerical solution procedure for solving standard symmetric eigen value problems is presented. The solution algorithm is based on a sequence of one dimensional minmax stages and is capable of extracting eigenpairs in either decreasing or increasing orders. Generalized symmetric eigen value problems are transferred to standard form and solved using the same algorithm.     

Experimental Analysis of the Wear,Life and Behavior of PTFE Coated Thrust Washer Bearings Under Non-Axisymmetric Loading

In this work the behavior and life of a PTFE coating on a flat thrust washer bearing is investigated. The thrust washer bearing is located between a helical gear and its carrier, and is subjected to non-axisymmetric loading and wear. The volume of worn material is approximated by measuring the difference in height between the worn and unworn surfaces. It was also found that the surface roughness of tested washers increases with the severity of wear, in most cases. After a finite number of cycles the effective coefficient of friction between the surfaces increases, suggesting that the coating is wearing off and losing effectiveness. The rate at which the coating wears off also varies with load and speed, hence, there is a region of operation that minimizes the wear and friction.     

A Transient Dynamic Analysis of Mechanical Seals Including Asperity Contact and Face Deformation

Face seals are typically designed to be in contact at standstill. However, as speed and pressure build up, the seal faces deform from their factory flat conditions because of viscous and dry friction heating, as well as mechanical and centrifugal effects. It is imperative that such deformations form a converging gap for radial flow to ensure stable operation and to promote favorable dynamic tracking between stator and rotor. A numerical simulation is presented for the transient response of a face seal that is subjected to forcing misalignments while speeds and pressures are ramped up and down. Asperity contact forces and transient face deformation caused by viscous heating are included. A new closed-form solution is obtained for the elastoplastic contact model, which allows seamless transition between contacting and noncontacting modes of operation. The model is then used to calculate face contact forces that occur predominantly during startup and shutdown. The viscous heating model shows that the time-dependent deformation (coning) is hereditary and that it lags behind the instantaneous heat generation. The dynamic analysis provides a numerical solution for the seal motion in axial and angular modes. The eventual build up of hydrostatic pressure and coning during startup generates opening forces and moments that separate the seal faces, resulting in noncontacting operation. The reverse occurs during shutdown; however, because of the thermal time constant a seal may continue to leak even after it returns to standstill. The analysis and simulation results compare very well with a closed-form solution that predicts a critical speed of separation of contacting seals.     

Adaptive on-line parameter identification of a steer-by-wire system

Adaptive compliance control strategy can be a significant advantage for control of steer-by-wire systems. Initially the method is proposed for robotic applications where the main concern is the interaction forces between the robot and its environment. There are several studies about cooperative working of a robot and a human. As long as the steering system is a part of the vehicle where driver interaction is involved, it is reasonable to think that compliance control strategies can be adapted to steer-by-wire systems. Compliance control is a model reference control (MRC) strategy where the measured external force/torque is used as an input to a reference model to calculate its output and where the real system is controlled appropriately to track the reference system output. If a sensor is available to measure the external force/torque, system parameters need not to be estimated. A constant gain feedback controller can be used in such a case. However, if the parameter variations of the system are not within certain bounds, a model reference adaptive controller (MRAC) is needed. In addition to this, examining the change in the dynamics of the system due to the compliance of the driver arms is not possible by direct MRAC, because the driver effect is considered as a disturbance in this strategy. Therefore, in this study, instead of estimating controller parameters using direct MRAC where the main concern is the tracking performance, it is considered to use indirect MRAC in which the system parameters are estimated to observe their variations in the presence of parametric uncertainty and disturbances and to further examine the change in the dynamics of the system due to the compliance of the driver arms forming a closed kinematic structure by constraining the steering wheel. Hence, a steer-by-wire experimental setup including driver interaction and vehicle directional control units has been developed and three well-known adaptive on-line estimation methods, which are output-error method, equation-error method and modified recursive least squares method are evaluated on the driver interaction unit. These three methods are compared in terms of computational complexity, convergence, stability and applicability to real vehicles.     

Influence of autofrettage on fracture toughness

A specimen, called the ring specimen, was developed to determine the fracture toughnessK _tc, under conditions of autofrettage. Tests were carried out on standard arc shaped specimens and ring specimens without autofrettage to obtainK _tc values of a gun barrel steel chosen for study and seen to yield similar results. Tests were also performed on autofrettaged (100 percent overstrain) ring specimens at various crack lengths producing results with a dramatic decrease inK _tc of 60 per cent. From this, it may be inferred that the critical length of a crack in an autofrettaged gun barrel made of this material will be less than anticipated. Although cold work or autofrettage enhances fatigue life by decreasing crack propagation rate, it is seen to decreaseK _tc creating, from this point of view, more dangerous conditions. For a design which must guarantee long life, the accompanying decrease in critical crack size may indeed prove a liability. Of course, this is a result for one particular material with a specific heat treatment and therefore not general; other materials must be tested, as well.

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Résumé On a étudié une éprouvette, dénommée éprouvette en anneau, en vue de déterminer la ténacité à la ruptureK _tc sous des conditions d'auto-frettage. Des essais ont été effectués sur des éprouvettes standards en forme d'arc et sur des éprouvettes en anneau sans auto-frettage en vue d'obtenir les valeurs deK _tc dans le cas d'un acier pour âme de canon choisi pour l'étude. Ces essais ont conduit à des résultats similaires. Des essais ont également été effectués sur des échantillons en anneau auto-frettés à 100% de sur-dilatation correspondant à diverses longueurs de fissure. Les résultats ont montré une diminution deK _tc de l'ordre de 60%. On peut déduire de cette observation que la longueur critique relative à une fissure dans une âme d'un canon auto-fretté réalisé dans ce matériau sera plus faible que prévu. Bien que l'écrouissage où l'auto-frettage améliore l'endurance en fatigue par des croissances de la vitesse de propagation d'une fissure, on constate qu'elle diminue leK _tc, occasionnant de ce point de vue des conditions plus dangereuses. Dans le cas d'une construction qui doit garantir un service de longue durée, la décroissance de la dimension critique d'une fissure peut être pénalisante. Bien entendu, ceci n'est qu'un résultat pour un matériau particulier avec un traitement thermique spécifique, qui dès lors ne peut être généralisé. D'autres matériaux doivent être également testés.

     

Chemical transformation of 3-bromo-2,2-bis(bromomethyl)-propanol under basic conditions

The mechanism of the spontaneous decomposition of 3-bromo-2,2-bis(bromomethyl)propanol (TBNPA) and the kinetics of the reaction of the parent compound and two subsequent products were determined in aqueous solution at temperatures from 30 to 70 degrees C and pH from 7.0 to 9.5. TBNPA is decomposed by a sequence of reactions that form 3,3-bis(bromomethyl)oxetane (BBMO), 3-bromomethyl-3-hydroxymethyloxetane (BMHMO), and 2,6-dioxaspiro[3.3]-heptane (DOH), releasing one bromide ion at each stage. The pseudo-first-order rate constant of the decomposition of TBNPA increases linearlywith the pH. The apparent activation energy of this transformation (98+/-2 KJ/mol) was calculated from the change of the effective second-order rate constant with temperature. The pseudoactivation energies of BBMO and BMHMO were estimated to be 109 and 151 KJ/mol, respectively. Good agreement was found between the rate coefficients derived from changes in the organic molecules concentrations and those determined from the changes in the Br- concentrations. TBNPA is the most abundant semivolatile organic pollutant in the aquitard studied, and together with its byproducts they posess an environmental hazard. TBNPA half-life is estimated to be about 100 years. This implies that high concentrations of TBNPA will persist in the aquifer long after the elimination of all its sources.     

Use of microhardness as a simple means of estimating relative wear resistance of carbide thermal spray coatings: Part 2. wear resistance of cemented carbide coatings

A selection of WC-Co and Cr₃C₂-25%NiCr coatings produced by plasma spray and high velocity oxygen fuel (HVOF) deposition techniques were subjected to various wear tests designed to simulate abrasion, cavitation, sliding, and particle erosion type wear mechanisms. All of the coatings were at least 200 μm thick and were deposited onto stainless steel substrates. In Part 1 of this contribution, the microstructures of the coatings were characterized and their mechanical properties were assessed using microindentation procedures. In this second part of the article, the behavior of the coatings when subjected to the various wear tests is reported and the utility of microhardness testing as an indication of relative wear resistance is discussed. It is shown that correctly performed, appropriate microhardness measurements are a good indication of abrasion resistance and sliding wear resistance, and also correlate well with cavitation resistance in Cr₃C₂-NiCr. The measurements were less useful for predicting erosion resistance for both Cr₃C₂-NiCr and WC-Co, however, and for abrasion resistance when WC-Co was ground against SiC. Here the contribution of micromechanisms involving fracturing and brittle failure is greater than that indicated by the coating microhardness, which is essentially a measurement of resistance to plastic deformation under equilibrium conditions.     

Urban spatial configuration and socio-economic residential differentiation: The case of Tel Aviv

This paper compares the effect of two aspects of a city’s spatial configuration – spatial separation between areas and dissimilarity in spatial integration between areas – on socio-economic residential differentiation in the city of Tel Aviv, Israel. The integration analysis is based on the space syntax methodological–conceptual framework and focuses on Tel Aviv’s core, where the main socio-economic differentiations were identified.     

Almost Passivity and Simple Adaptive Control in Discrete‐Time Systems

Successful implementations of simple direct adaptive control techniques in various domains of application have been presented over the last two decades in the technical literature. The theoretical background concerning basic conditions needed for stability of the controller and the open questions relating the convergence of the adaptive gains have been clarified recently, yet only for the continuous‐time algorithms. Apparently, asymptotic tracking in discrete time systems has been possible only with step input commands and the scope of the so called “almost strictly positive real (ASPR)” condition has also remained not clear. This paper expands the feasibility of discrete simple adaptive control methodology to include any desired input commands and almost all real‐world systems. The proofs of stability are also rigorously revised to solve the ultimate adaptive gain values question that has remained open until now. Finally, a complex algebraic loop that seemed to be inherent in discrete ASPR systems and might prevent the use of passivity properties in discrete systems has also been eliminated.