Dov Ingman

Pore ensemble statistics in application to lubrication under reciprocating motion

The concept of pore ensemble is applied to piston ring lubrication. The solution of the two-dimensional Reynolds equation is given for reciprocating motion of a compression piston ring with circular micropores of rectangular profile on its sliding surface. Minimal film thickness between ring and cylinder is considered for identical and diverse pore ensembles. It was shown that the pores provide hydrodynamic load support, sufficient to keep the ring and cylinder apart even in cases of a linear ring profile and ring surface parallelism to the cylinder wall, through the whole piston stroke including the dead points. Calculations for a id pore cluster with diverse pore radius and depth (each with not less than 20 percent variance) show that fluctuation of the resulting film thickness is reduced up to 0.5 percent variance, while the thickness values of ensembles of diverse pores differ by more than 1. 5 times from that found for an identical pore population. There is apparently no need for perfect identity of the pores during production, but pore ensemble statistics must be taken into consideration in proper lubrication calculations. In general, the pore ensemble is an essential aspect in exact determination of the load support and better insight is provided into the tribological behavior of pore-covered surfaces. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Maximum entropy signal reconstruction with neural networks

The implementation of the maximum entropy reconstruction algorithms by means of neural networks is discussed. It is shown that the solutions of the maximum entropy problem correspond to the steady states of the appropriate Hopfield net. The choice of network parameters is discussed, and existence of the maximum entropy solution is proved.

Adaptive Control Limits for Bivariate Process Monitoring

Biparameter description of sample averages and standard deviations is proposed as an alternative to standard charting methods as the optimal method of process control. The proposed control chart with adaptive limits indicates the process state and..

Effect of pore ensemble statistics on load support of mechanical seals with pore-covered faces

A mathematical model was developed for predicting the performance of laser-textured seals with pores. A solution of the two-dimensional steady-state Reynolds equation was given for rectangular and exponential pores, as well as expressions for the hydrodynamic pressure distribution over the control cell and for the cell load support. The difference between the two pore shapes can be reduced from a factor of multiple times to 30 percent at most-if the pore volume is kept constant. It was also shown that the total hydrodynamically induced load-carrying capacity can be obtained with accuracy, even if the pore radius of the seal surface is assumed to vary over a wide interval about its mean value, as it does in reality. Diameters in an ensemble of over 4 . 10 4 pores were run at random for 500 seal faces. It was established for the first time that load support of an ensemble exceeds by 22 percent the one determined for N identical pores. The model for the entire pore population as an ensemble with size variation is more realistic, and substantiates the possibilities and advisability of pore size diversity, hitherto considered undesirable in the pore production process. In general, the pore ensemble is an essential aspect in exact determination of the load support and better insight into the tribologic behavior of pore-covered surfaces.

Local minimum escape using thermodynamic properties of neural networks

Abstract The article presents a new thermodynamic model of continuous-time neural networks. The model is based on the thermodynamic fluctuations theory. The differential equations describing the behavior of the network in time are derived and analyzed. The analysis shows that the dynamics of the network is characterized by the time behavior of the Helmholtz free energy of the system. The possibility to control this behavior by the time-dependent temperature schedule is also discussed. The emphasis of the article is on the local energy minima escape in optimization problems. Two simulations of the Traveling Salesman Problem (TSP) have been used to demonstrate the discussed approach.

A percolation model for lifetime variability in polymeric materials under creep conditions

The authors propose a microlevel theory of damage accumulation in polymeric materials. On the basis of experimental data on submicro- and microcracks, they relate the time-dependent strength distribution in polymeric materials under applied load to the distribution of the largest cluster size in a site percolation lattice well below the percolation threshold ρc. The empty sites fraction ρ in the percolation lattice is suggested to increase with a constant rate, evaluated using the model of a trigger-type molecular reaction described in the literature. Duxbury’s initial study of the largest cluster size distribution is extended by Monte Carlo simulations. While the latter distribution is confirmed to be double exponential, the characteristic largest cluster size (the distribution mode) is found to increase exponentially with ρ within the range ρ0<ρ≪ρc, ρ0 being a constant, although for small ρ<ρ0 the conventional logarithmic dependence is preferable. For the considered two-dimensional square lattice ρ0 is ...

Sequential Test for Arbitrary Ratio of Mean Times Between Failures

This paper describes a planning methodology and tools for a truncated SPRT (sequential probability ratio test) for checking the means ratio of the times between failures (assumed to be exponentially distributed) of two items. The problem is considered for the situation in which the ratio may differ from unity, whereby the results are applicable for any specified ratio, or wherever multiple copies of each item are tested simultaneously (group test). The authors present a methodology for optimal test choice and dependences for determining the acceptance/rejection boundaries of such a test with given characteristics. Planning and implementation of a group test are illustrated in an example, including substantiation of the choice of the number of new-item copies.

Correlation between gas molecular weight, heating value and sonic speed under variable compositions of natural gas

Abstract A simulation study of likely uncertainties in molecular weight and heating value of the gas mixture as predicted from measured or calculated sonic speed. The sonic speed, molecular weight and heating value of natural gas were studied as a function of random fluctuation of the gas fractions. A method of sonic speed prediction was developed and used for over 50,000 computer-simulated variants of component concentrations in four- and five-component mixtures. Comparison of the obtained and the reference data on binary (methane–ethane) and multicomponent (Gulf Coast) gas mixtures under standard pressure and moderate temperatures indicates predictability of sonic speed on the basis of the binary virial coefficients, sonic speeds and heat capacities of the pure components. The results for two natural gas mixtures — with and without nonflammable components — are reported. Bivariate distribution and covariance elliptic zone plots are presented for three pairs of dependences of practical interest: molecular weight–sonic speed, heating value–sonic speed and heating value–molecular weight. The correlation coefficients, covariance, and regression equations are given for each pair of variance and mixture.

Dynamic character of failure state in damage accumulation processes

This paper reports on an exact analytical solution of a reliability evolution equation obtained for steady-state loading conditions. This solution is used as a Greens function for more complicated loading. The importance of the dynamic aspects of failure conditions is revealed. The observable effects of an abrupt decrease in component reliability with a stepwise stress increase and the effects of apparent ceasing of deterioration with a stepwise stress reduction are explained. It is shown that deviations from the life fraction rule result from the combined dynamics of damage accumulation and failure processes rather than from requirements of nonlinearity of damage mechanisms with time.

Sequential testing for two exponential distributions at arbitrary risks

Purpose – This paper aims to propose a methodology for planning of a truncated sequential probability ratio test (SPRT) in which two systems with exponentially distributed times between failures (TBFs) are compared. The study is concerned with tests with arbitrary probabilities of I‐ and II‐type errors.Design/methodology/approach – The study methodology, based on the proposed optimality criteria for these tests, permitted comparison of different modes of truncation and obviated the drawbacks of discreteness and multidimensionality of their characteristics.Findings – The solution permits planning of a heavily‐truncated test with an average sample number exceeding its counterpart for the optimal (non‐truncated) test by at most a specified percentage. Relationships are outlined for optimal selection of the truncated test boundaries. So are optimality estimation criteria for the constructed test. The superiority of the SPRTs, truncated by the proposed methodology, over their counterparts, processed according ...