On the application of the “Russian Roulette and Splitting” simulation technique for the reliability assessment of mechanical systems

A selective Monte Carlo simulation (MCS) technique, namely, the “Russian Roulette and Splitting” technique, is applied for the assessment of the reliability of structures under stochastic excitations. The basic features of the algorithm are described and discussed. As a numerical example the technique is used for the numerical solution of the first passage problem. The results are compared with available solutions obtained by another variance reduction technique—the “Double & Clump” procedure. Translated from Problemy Prochnosti, No. 3, pp. 131–138, May–June, 1997.     

computer simulation of the processes of mechanical shaping of three-dimensional shells under the conditions of creep. Part 2

On the basis of the moment scheme, we obtain the resolving relations of the method of finite elements in the actual configuration used for the computer simulation of the processes of shaping of spatial shells by using a single finite element across the thickness. The reliability of numerical results is checked by the solution of a test example of shaping of a long narrow rectangular membrane. As an illustration of the possibilities of the developed approach to the analysis of the processes of shaping of thin-walled products with complicated shape, we present the results of numerical simulation of strains in a blank made of D16 alloy in a discrete press tood. Translated from Problemy Prochnosti, No. 5, pp. 69–77, September–October, 1997.     

Reduced-stiffness method in the theory of buckling of stiffened shells

The reduced-stiffness method is used to establish the lower bounds of buckling loads for stringer- or ring-stiffened cylindrical shells. The numerical results obtained by using this method are compared with the experimental data. We also consider the problem of applicability of the reduced-stiffness method in design practice as well as the prospects for its development and generalization. The present work is a continuation of the review [1]. Translated from Problemy Prochnosti, No. 2, pp. 90–104, March–April, 2000.     

On the prediction of the fatigue life of thin-walled structures based on a statistical model

We present experimental results of fatigue tests of AMg6 aluminum alloy model specimens-plates with a single notch, subjected to fully reversed and asymmetric cyclic axial loading. The experimentally determined lives of model specimens are used as the results of the base experiment for predicting the fatigue strength characteristics of large-scale cylindrical shells with circumferential ring-shaped stress raisers loaded by axial forces of a cyclic nature. A numerical study has been performed of the statistical model adopted for predicting the fatigue life of such shells. __________ Translated from Problemy Prochnosti, No. 3, pp. 112–122, May–June, 2006.     

Fabrication and properties of thin-shell monolithic piezoelectric ceramic transducers

Monolithic piezoelectric ceramic transducers with hollow thin shell forms (sphere, cylinder, tube and cone) were successfully fabricated from lead zirconate titanate using slip casting method. Stable and well dispersed water based slurries were prepared under basic conditions with 35–45 vol% solid loading using 0.25–0.50 wt% dispersant. Various characteristic vibration modes, such as length extension, radial expansion, etc., were obtained from the thin shell transducers at 50–200 kHz frequencies. The resonance frequencies of these modes were engineered by changing the shape and dimensions of the shells. Comparison of the numerical calculations and experimental results indicates that slip casting is a viable method to obtain hollow thin shells with reasonable electrical properties.     

Comparison of the results of modeling convective heat transfer in turbulent flows with experimental data

The results of simulation of natural turbulent convection in a square air cavity measuring 0.75 × 0.75 m and having isothermal vertical and highly heat-conducting horizontal walls are compared with the experimental data obtained for this cavity at a Rayleigh number equal to 1.58⋅10⁹. In carrying out numerical investigations, a two-dimensional, low-turbulence, two-parameter k–ε model known as the low-Reynolds-number k–ε turbulence model was used. The results of investigations are presented for the distributions of the velocity and temperature components, as well as local and average values of the Nusselt number. The model was also used in calculating forced turbulent convection in a low-velocity channel with a backward facing step. The results of modeling are compared with experimental data on heat transfer in a turbulent separation flow downstream of the step. In both cases, a satisfactory agreement of the measured values with those predicted by the k–ε turbulence model is obtained.     

Comparative analysis of nonlinear resonances of a mechanical system with unsymmetrical piecewise characteristic of restoring force

We present results of a numerical comparative analysis of superharmonic resonances of the order 2/1-1/5 and subharmonic resonance of the order 1/2 of a mechanical single degree-of-freedom vibrating system with unsymmetrical characteristic of restoring force at different ratios of system rigidities in half-cycles and under the conditions of considerable change in vibration damping level in the system. __________ Translated from Problemy Prochnosti, No. 2, pp. 72–87, March–April, 2007.     

The frequency-pulse method for determining the thermophysical characteristics of solid materials

On the basis of a linear instantaneous heat source, we consider the frequency-pulse method of determining the thermophysical characteristics of solid materials without destruction of their integrity. We present the results for the investigation of the procedural error in the determination of thermophysical coefficients by the method of numerical simulation, as well as the results of experimental investigations. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 2, pp. 336–341, March–April, 1998.     

Microstructure and grindability of as-cast Ti–Sn alloys

In this study, the structure, microhardness, and grindability of a series of binary Ti–Sn alloys with tin contents ranging from 1 to 30 wt% were investigated. Commercially pure titanium (c.p. Ti) was used as a control. The experimental results indicated that all the Ti–Sn alloys showed hcp α structure, and the hardness values of the Ti–Sn alloys increased with greater Sn contents, ranging from 246 HV (Ti–1Sn) to 357 HV (Ti–30Sn). Among these Ti–Sn alloys, the alloy with 30 wt% Sn content showed the highest hardness value. The grindability of each metal was found to be largely dependent on the grinding conditions. The addition of Sn to c.p. Ti did contribute to improving the grindability of c.p. Ti. The Ti–Sn alloys with a higher Sn concentration could be ground more readily. The grinding rate of the Ti–20Sn alloy at 1200 m/min was about 2.8 times higher than that of c.p. Ti. Additionally, the grinding ratios of the Ti–10Sn, Ti–20Sn, and Ti–30Sn alloys at 1200 m/min were about 2.8, 2.7, and 3.4 times that of c.p. Ti, respectively. Our research suggests that the Ti–Sn alloys with Sn contents of 10 wt% and greater developed here are good candidates for machining by the CAD/CAM method.     

Analysis of a single stage production system with heterogeneous machines

The performance of a single stage production system with two heterogeneous machines and two classes of jobs is investigated. The machines have a common buffer with jobs of both classes waiting for service. The arrivals are assumed to follow a Poisson process and the service times to be distributed exponentially. The evaluated production system differs from a classical homogeneous multiple server queueing system with regard to inhomogeneities of the two machines. Time inhomogeneity – the service times of the two machines being unequal – and functional inhomogeneity – one of the machines can handle only one class (A) of jobs – are to be distinguished. In the case of time inhomogeneity the calculation of system performance parameters may be carried out using an explicit formula, whereas for the analysis of functional inhomogeneity a numerical solution has to be derived. The impact of time inhomogeneity is very small and decreases with the system workload. On the contrary, functional inhomogeneity leads to elevated cycle times of up to 40% depending on the degree of inhomogeneity (measured by the fraction of A jobs) and the workload. Therefore, in contrast to the time-inhomogeneous case, single stage production systems with functional inhomogeneity can only be approximated tolerably by a homogeneous multiple server queueing system if the fraction of one-machine jobs is less than 30%. The increased throughput times above 30% are supplied by the diagram developed from the numerical solutions. RID="*" ID="*" While this research was constructed the author was affiliated to Institute of Conveying Technology and Logistics. Correspondence to: C. R. Lippolt     

Modified zonal model for calculating the thermodynamics of the gas in a fire within an atrium

A modified zonal model for calculating the thermodynamics of the gas in a fire has been developed. An equation for determining the flow rates of the gas-mixture and smoke at cross sections of a convective column is proposed. The results of numerical calculations of the parameters of the heat and mass transfer in a fire within an atrium with the use of the modified zonal model as well as zonal and field models are presented and discussed. Specifics of the use of zonal models for estimating the fire hazard in an atrium are considered. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 84–89, March–April, 2007.     

Heat generation and transport in the heart

During contraction of the heart, a large part of the energy in energy metabolism is converted to heat. The article presents the results of measurements of mechanical stresses in the myocardium and blood vessels, temperatures and rate of heat generation. Experimental data correlate well with the numerical solutions of the biothermal problem. Laboratory for Physiology, Institute for Cardiovascular Research, Free University, Amsterdam, the Netherlands. Published in Inzhenerno-Fizicheskii Zhurnal Vol. 69, No. 3, pp. 364–376, May–June, 1996.     

Testing of the \overline {v^2 } - f model of turbulence in calculating the flow and heat transfer in an abruptly expanding duct

This paper presents the results of testing of the model of turbulence with the examples of two-dimensional flow of an incompressible fluid and heat exchange with the walls of an abruptly expanding duct. The calculation data have been compared to the known experimental data, and the data of direct numerical simulation, as well as to results of calculations with the use of two versions of the k-ω model. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 38–44, July–August, 2006.     

Numerical model for nucleation of peritectic alloy during unidirectional solidification

Based on transient nucleation theory, a numerical model has been constructed to describe the nucleation process of a new phase in front of the liquid–solid interface of a prior steady-growth phase in peritectic alloy with the combination of the concentration field calculated by a self-consistent numerical model for cellular/dendritic growth. The results show that the nucleation incubation time of a new phase varies with the solidification rate during unidirectional solidification. During unidirectional solidification of the Zn–4.0 wt.% Cu alloy, the incubation time changes very slightly when the solidification rate increases from 50 to 500 μm/s, but it increases significantly when the solidification rate exceeds 500 μm/s. The calculated results show a reasonable agreement with the experimental ones. This model reveals that nucleation of a new phase is time-dependent and reasonably explains the effect of the solidification velocity on the behaviors of nucleation and growth of ɛ dendrites in the matrix of the η phase in unidirectional solidification of Zn rich Zn–Cu alloys.     

Dielectric properties of SrTiO3 single crystals subjected to high electric fields and later irradiated with X-rays orγ-rays

The dielectric constant (K), loss (tanδ), and hence conductivity (σ) of SrTiO₃ single crystals have been measured in the frequency region 10²–10⁷ Hz and in the temperature range 30°–350° C. Quenching, subjecting the crystals to high electric fields (a.c. or d.c.) and X-ray orγ-ray irradiation, or a combination of these treatments, is found to bring about interesting changes in these properties. An attempt is made to understand the results.     

Transformation toughening in the γ-TiAl–β-Ti–Vsystem: Part II A molecular dynamics study

Molecular dynamics simulations of the evolution of materials in a region surrounding a crack tip were carried out for the case of a crack in a γ-TiAl phase impinging at a right angle onto the interface between a γ-TiAl phase and a metastable Ti–15V (at %) phase. The corresponding linear anisotropic solutions for the singular stress and displacement fields were used to both generate the crack in the original crystal and to prescribe the boundary conditions applied to the computational crystal during the molecular dynamics simulation runs. The atomic interactions were accounted for using appropriated embedded atom method (EAM) type interatomic potentials. The crack-tip behaviour for the two-phase γ–β material was ultimately compared with the one in the corresponding single-phase material, i.e. to the one in pure γ and the one in pure β crystals. The simulation results showed that under the same applied level of external stress, the crack tip became blunt and the crack stopped propagating in the γ-TiAl–β-Ti–15V bicrystal and in the single β-phase crystal while the crack extended by brittle cleavage in the single-phase γ crystal. The blunting process was found to be controlled by the martensitic transformation that took place in the β-phase ahead of the crack tip. Depending on the local stress conditions the crystal structure of martensite was found to be either hexagonal close packed (h.c.p.), body centred orthorhombic (b.c.o.) and/or face centred orthorhombic (f.c.o.). Finally the implications of crack tip martensitic transformation on the toughness of the materials are analysed in quantitative terms using the concept of Eshelby's conservation integral, i.e. the energy release rate. This revised version was published online in November 2006 with corrections to the Cover Date.     

Radiation of the inner surface of a perforated circular cone

We analyze the results of a numerical solution obtained for the problem of finding special features of radiation and the presence of a perforation or channelling effect in anisotropic emission from the inner surface of a circular cone perforated with round holes. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 2, pp. 273–276, March–April, 1998.     

Studies on a.c. properties of Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> perovskites

A.c. measurements were preformed on bulk samples of Ca_1−x Sr _x TiO₃ (CST) perovskites with x = 0, 0.1 and 0.5 as a function of temperature range 300–450 K and frequency range 10³–10⁵ Hz . The experimental results indicate that the a.c. conductivity σ_a.c.(ω), dielectric constant ε′ and dielectric loss ε′′ depend on the temperature and frequency. The a.c. conductivity as a function of frequency is well described by a power law Aω ^S with s the frequency exponent. The obtained values of s > 1 decrease with increasing temperature. The present results are compared to the principal theories that describe the universal dielectric response (UDR) behavior.