Generalized Reliability Analysis of Mechanical Systems with Imperfect Maintenance

Generalized reliability models and failure rate models of mechanical systems are developed in this paper according to the system working mechanism, which take the design parameters as input. The models consider strength degradation and imperfect maintenance. Besides, the models take into account the failure correlation caused by homologous load effect and the maintenance correlation owing to group maintenance. Unlike traditional reliability models, the models do not rely on empirical assumptions when considering failure correlation and maintenance correlation and have clear physical meaning. Moreover, the correctness and effectiveness of the models are verified by Monte Carlo simulations. Finally, the influences of failure correlation and maintenance correlation on generalized reliability, the influences of failure correlation on maintenance correlation, and the influences of maintenance correlation on failure correlation are analyzed via numerical examples. The results show that failure correlation and maintenance correlation have great influences on generalized reliability, and the interaction between the two correlation shows obvious time-varying characteristics.

Anisotropic stress softening of residually stressed solids

Residual stress in purely elastic solids has been extensively studied in the literature. However, to the best of the author’s knowledge, the influence of residual stresses on anisotropic Mullins materials has not been studied. Hence, the aim of this paper is to propose an anisotropic phenomenological model to describe the Mullins phenomena for residually stressed elastomers; taking note that most materials are not purely elastic and some of them exhibit an anisotropic stress-softening phenomenon widely known as the Mullins effect. The anisotropic model is based on the use of direction-dependent damage parameters and a set of anisotropic spectral invariants presented recently in the literature by the author. The spectral invariants have a clear physical meaning that is useful in aiding the design of a rigorous experiment to construct a specific form of constitutive equation. Since boundary value results for residually stressed Mullins material are not found in the literature, the effect of residual stresses on the Mullins phenomena in simple tension, torsion and equibiaxial deformations is discussed in this paper.

Existence of Bounded Solutions to a Modified Version of the Bagley–Torvik Equation

This manuscript reanalyses the Bagley–Torvik equation (BTE). The Riemann–Liouville fractional differential equation (FDE), formulated by R. L. Bagley and P. J. Torvik in 1984, models the vertical motion of a thin plate immersed in a Newtonian fluid, which is held by a spring. From this model, we can derive an FDE for the particular case of lacking the spring. Here, we find conditions for the source term ensuring that the solutions to the equation of the motion are bounded, which has a clear physical meaning.

Interaction of positronium with dissolved oxygen in liquids

The interaction of positronium with molecular oxygen dissolved in liquids is experimentally investigated. A computer software has been developed for fitting the positron annihilation lifetime spectra using parameters with clear physical meaning.

Precise drag prediction of airfoil flows by a new algebraic model

We report the results of accurate prediction of lift ($$C_L$$CL) and drag ($$C_D$$CD) coefficients of two typical airfoil flows (NACA0012 and RAE2822) by a new algebraic turbulence model, in which the eddy viscosity is specified by a stress length (SL) function predicted by structural ensemble dynamics (SED) theory. Unprecedented accuracy of the prediction of $$C_D$$CD with error of a few counts (one count is $$10^{-4}$$10-4) and of $$C_L$$CL with error under 1%-2% are uniformly obtained for varying angles of attack (AoA), indicating an order of magnitude improvement of drag prediction accuracy compared to currently used models (typically around 20 to 30 counts). More interestingly, the SED-SL model is distinguished with fewer parameters of clear physical meaning, which quantify underlying turbulent boundary layer (TBL) with a universal multi-layer structure, and is thus promising to be more easily generalizable to complex TBL. The use of the new model for the calibration of flow condition in experiment and the extraction of flow physics from numerical simulation data of aeronautic flows are discussed.

GENERALIZED MODEL OF CHEMICAL KINETIC OF DETONATION COMBUSTION OF GASEOUS HYDROCARBONS

A two-step generalized model of chemical kinetics of detonation combustion of propylene is presented. The model is consistent with the second law of thermodynamics and Le Chatelier’s principle. Constants of the models have a clear physical meaning. Owing to the simplicity (it includes only one ordinary differential equation) and high accuracy, the model can be used in multi-dimensional numerical calculations of detonation wave parameters and multi-front cellular structure.

О подвижности носителей заряда определенной энергии

The quasi-mobility function of charge carriers with a specified energy for describing their dynamics using the kinetic equation is studied in the important case of two-term isotropic approximation. In the stationary case, the quasi-mobility function is independent of the source function of charge carriers and makes it possible to calculate the integral mobility. The correlation between the quasi-mobility and parameters of the system is analyzed. It is proved that this characteristic does not generally describe the contribution of charge carriers with a specified energy to the integral mobility. In the case of almost elastic scattering, the quasi-mobility, as is known, can have a clear physical meaning; however, in the case of the scattering of charge carriers at acoustic phonons in a solid, this quasi-mobility interpretation is found to be incorrect due to the specific features of the collision integral and the form of the quasi-mobility function.

DNS Study on Vortex and Vorticity in Late Boundary Layer Transition

Vortex and vorticity are two correlated but fundamentally different concepts which have been the central issues in fluid mechanics research. Vorticity has rigorous mathematical definition (curl of velocity), but no clear physical meaning. Vortex has clear physical meaning (rotation) but no rigorous mathematical definition. For a long time, many people treat them as a same thing. However, based on our high-order direct numerical simulation (DNS), we found that first, “vortex” is not “vorticity tube” or “vortex tube” which is widely defined as a bundle of vorticity lines without any vorticity line leak. Actually, vortex is an open area for vorticity line penetration. Second, vortex is not necessarily congregation of vorticity lines, but dispersion in many 3-dimensional cases. Some textbooks say that vortex cannot end inside the flow field but must end on the solid wall (and/or boundaries). Our DNS observation and many other numerical results show almost all vortices are ended inside the flow field. Finally, a more theoretical study shows that neither vortex nor vorticity line can attach to the solid wall and they must be detached from the wall.

Determination of pedestrian displacement velocity for ground exploration programs

In Engineering and Geophysics field exploration, uncertainty for determination of the velocity of ground data acquisition due to extreme topographic conditions has been underestimated in the calculation of the displacement time between stations or sampling points. This lack of reliable models, negatively affects the determination of costs and planning of fieldwork activities. Known models of times and routes of displacement determination such as the “Smaller Cost Routes” are based on the effect of the type of land and the slope. However, these models consider the effect of the slope by means of subjective impedance values which has no a clear physical meaning. Furthermore, the upslope or downslope displacement is not considered to affect the reliability of velocity estimation. In this paper, a model of displacement velocity is proposed taking into account the upslope/downslope factor. The model was determined using real data from a topographical survey along a pipeline of 880 Km extended along terrains with changing climatic and topographic conditions. As a result, the proposed model improves the selection of optimal routes for a reliable time and cost estimation.

Theoretical Estimation of Maximum Ellipsoidal Magnitude of a Low-Viscosity Droplet in a Parallel Gas Stream

ABSTRACTMaximum ellipsoidal magnitude of the droplet is an important basic parameter for calculating drag force, droplets axial-velocity and dispersed-phase pressure gradient in an annular-mist pipe flow. An analytical correlation to predict the maximum ellipsoidal magnitude of a low-viscosity droplet in a parallel gas stream based on energy conservation and volume conservation. Stagnant pressure distribution on droplet surface is revised from Flachsbart's formula. The proposed correlation has clear physical meaning and easy to use. The correlation captures the deformation mechanism with an average absolute percent error of 9.53%. The effect of stagnant pressure distribution on the proposed correlation's accuracy is discussed.