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Parametric active contour model is an efficient approach for image segmentation. However, the high cost of evolution computation has restricted their potential applications to contour segmentation with long perimeter. Extensive algorithm debugging and analysis indicate that the inverse matrix calculation and the matrix multiplication are the two major reasons. In this paper, a novel simple and efficient algorithm for evolution computation is proposed. Motivated by the relationship between the eigenvalues and the entries in the circular Toeplitz matrix, each entry expression of inverse matrix is firstly derived through mathematical deduction, and then, the matrix multiplication is simplified into a more efficient convolution operation. Experimental results show that the proposed algorithm can significantly improve the computational speed by one to two orders of magnitude and is even more efficient for contour extraction with large perimeter. [ABSTRACT FROM AUTHOR]

Boundary conditions play a crucial role from theoretical and experimental perspectives in comprehending the dynamics of wave propagation in elastic solids. Stress free boundary conditions, are achieved by setting the surface tractions to zero, while for rigid surface boundary conditions displacements, are equated to zero. Despite utility of these two types of boundary conditions, it is crucial to acknowledge that these conditions are the extreme idealizations, and real-world scenarios often fall somewhere between the extremes of stress free and rigid surface boundary conditions. In the current investigation, the elastically restrained boundary conditions (ERBC) are proposed to examine the propagation of plane waves at the surface of semi-infinite elastic media. The elastically restrained boundary conditions act as an intermediate link between traction-free and rigid surface conditions. In the study, a microstructural couple stress half-space is considered to comprehend the propagation of surface waves. The impacts of boundary conditions are depicted through three parameters called as normal stiffness , shear stiffness , and rotational stiffness . The characteristic length scale parameter (l) within the couple stress model represents the influence of microstructural effects. Dispersion relations have been derived analytically and the classical cases of stress-free (Rayleigh type wave), rigid surface boundary conditions are obtained as the special cases. Mathematical results have been illustrated graphically. [ABSTRACT FROM AUTHOR]

The aim of this study was to carry out the investigation and analysis of two-stage magnetic precession gear dynamics and the determination of the resonance frequencies, which can be a cause of the powertrain system failures. Graphical interpretation of the two-stage precession gear is presented, and two equations of the dynamics of the movable elements of the presented gearbox were determined. On the basis of these equations, the stiffness coefficients and resonance frequencies of the presented gearbox were mathematically derived. The next step was to develop a numerical model of the magnetic precession gear dynamics in the environment of MATLAB Simulink. The elaborated model allowed us to analyze the influence of varying the input speed and the load torque on the operation of the magnetic precession gear. The performed analyses of the dynamics of the magnetic precession gear showed the occurrence of a resonance phenomenon under the influence of load torque ripples with a frequency close to the natural frequency of the studied system. [ABSTRACT FROM AUTHOR]

This research paper explores potential enhancements to the CRASH algorithm by proposing a hypothesis that relates deformation to applied stress instead of force. By incorporating stress instead of force, the calculation can account for the contact area, leading to a more precise estimation of impact velocity, particularly in side impacts. An initial evaluation of this energy absorption calculation formula is presented, focusing on side impacts in vehicle "2022 Hyundai Ion." Two side impact reports for the vehicle from the National Highway Traffic Safety Administration (NHTSA) database were utilized. One report involved the vehicle tilted at a 45-degree angle against a fixed pole with a 254 mm diameter, while the other examined the vehicle colliding with a moving deformable barrier (MDB) at various speeds. Additionally, a Monte Carlo simulation was conducted to validate the model's applicability. The verification process involved estimating stiffness coefficients from the first report and employing them to calculate energy absorption during the crash against the moving deformable barrier. The analysis demonstrates promising improvements in accurately calculating deformation energy absorbed during impacts. • The CRASH algorithm was reviewed and developed into computer-usable functions. • Adaptation of the general formula by substituting force with stress than developing an equation that is suitable for implementation in a computer program. • Application of the two algorithms twice: first, to find the stiffness coefficients (A, B) and (A′, B′) of the first crash test; then, to use these coefficients to estimate the impact speed of a side collision of a second crash test, with results compared. • Monte Carlo simulation applied to predict and visualize the effects of input variability on both formulas. [ABSTRACT FROM AUTHOR]

The need to improve on analysis and design of structural members for overall weight, material and financial economy is indispensable. This paper presents the results of post-buckling analysis of an axially loaded prismatic column. The theory of elasticity was employed to formulate the total potential energy functional for a prismatic column in the post buckling regime. The derived functional was minimized with respect to deflection function to obtain the governing equation of equilibrium. The governing equation was then solved to obtain the deflection equation. Again, the functional was minimized with respect to the coefficient of the obtained deflection function to obtain the formula for calculating the post-buckling load of the prismatic column. A numerical example was given to demonstrate the applicability of the present formulation. The prismatic column was analyzed within the post buckling regime to determine the stiffness coefficients. It was shown that as the deflection-thickness (Δ/t) ratio increased, the combined buckling stress increased geometrically. It was found that the critical buckling load obtained from the present method and those obtained from literature showed consistency. It was also found that at the buckled state of the prismatic column, the yield strength of the column material has not been attained and deflection is very small. This gives room for the column to take on more loads before it fails either by excessive deflection or by stress exceeding the material strength. [ABSTRACT FROM AUTHOR]

The Bayesian inference with prior knowledge has been proposed recently to solve the inverse problem in resonant ultrasound spectroscopy. It allows inferring the elastic properties of high damping materials, such as cortical bone with less dependence on the initial guessed values. In this method, the estimation of the stiffness coefficients is expressed as a probabilistic solution to the inverse problem, which can be achieved by sampling or optimization methods. However, the detailed performance comparison of these two strategies applied to high damping materials has not been fully studied. In this work, the full stiffness tensor of 52 transversely isotropic cortical bone specimens was obtained using Markov chain Monte Carlo (MCMC) sampling and particle swarm optimization (PSO), respectively. Results showed that the local probability distributions of stiffness coefficients estimated by the two methods are consistent. Compared with MCMC, the average calculation speed of PSO is ten times faster [614 s ± 59 s (MCMC) versus 53 s ± 22 s (PSO)]. The mean standard error between theoretical and experimental resonant frequencies was slightly smaller for PSO compared with MCMC. In conclusion, PSO, a global optimization strategy, is suitable to solve the inverse problem for high damping materials. [ABSTRACT FROM AUTHOR]

The need to improve on analysis and design of structural members for overall weight, material and financial economy is indispensable. This paper presents the results of post-buckling analysis of an axially loaded prismatic column. The theory of elasticity was employed to formulate the total potential energy functional for a prismatic column in the post buckling regime. The derived functional was minimized with respect to deflection function to obtain the governing equation of equilibrium. The governing equation was then solved to obtain the deflection equation. Again, the functional was minimized with respect to the coefficient of the obtained deflection function to obtain the formula for calculating the post-buckling load of the prismatic column. A numerical example was given to demonstrate the applicability of the present formulation. The prismatic column was analyzed within the post buckling regime to determine the stiffness coefficients. It was shown that as the deflection-thickness (Δ/t) ratio increased, the combined buckling stress increased geometrically. It was found that the critical buckling load obtained from the present method and those obtained from literature showed consistency. It was also found that at the buckled state of the prismatic column, the yield strength of the column material has not been attained and deflection is very small. This gives room for the column to take on more loads before it fails either by excessive deflection or by stress exceeding the material strength. [ABSTRACT FROM AUTHOR]

The stiffness coefficients of two linear and two angular elements for the generic harmonic field model are derived from the stiffness coefficients of two linear elements for the central force field model. Recalculation is carried out through frequencies of three-node element assembled from these elements. Numerical modeling of uniform stretching of silicene samples was performed. Longitudinal and two transverse elastic modules are found to be dependent on linear dimensions.

In this study, the mechanical model of the circumferentially distributed rods and the nonlinear contact stiffness matrix which characterizes the contact effect between the disks are established. The contact stiffness matrix is composed of seven stiffness coefficients that characterize the lateral stiffness, shear stiffness, bending stiffness, and torsional stiffness of the contact interface. Then the influence of pre-tightening load, rod diameter, contact surface roughness, deformation phase and uneven pre-tightening load on stiffness coefficients is analyzed. Finally, combined with the experimentally verified nonlinear oil film force model based on short bearing theory, the dynamic model of the rod-fastening rotor-bearing system is established. By means of spectrum cascades and Campbell diagrams, the influence of the pre-tightening load, rod diameter, contact surface roughness and uneven pre-tightening load on the nonlinear dynamic characteristics of the rod-fastening rotor-bearing system is numerically analyzed. The results show that increasing the pre-tightening load can increase the contact stiffness, and make the dynamic characteristics of the rod-fastening rotor bearing system closer to that of the complete rotor bearing system. The increase in the diameters of rods significantly delay the partial separation of the contact surfaces. The smooth contact surface provides higher contact stiffness, but it is not conducive to maintaining the full contact state of the contact surfaces. The stiffness coefficients fluctuate with the deformation of the rotor, and the process is significantly affected by uneven pre-tightening load. Moreover, a self-excited vibration frequency f l accompanied by a combination frequency f b = 3 f l appears when the uneven pre-tightening load is caused by individual faulty rod. The number of rods, rod diameter, and contact surface roughness have similar effects on the dynamic characteristics of rod-fastening rotor bearing systems, which lead to fluent whirl and fluent whip appear in advance, reducing the stability of the system. [ABSTRACT FROM AUTHOR]

The paper deals with methods of equivalence of boundary conditions in finite element models that are based on finite element model updating technique. The proposed methods are based on the determination of the stiffness parameters in the section plate or region, where the boundary condition or the removed part of the model is replaced by the bushing connector. Two methods for determining its elastic properties are described. In the first case, the stiffness coefficients are determined by a series of static finite element analyses that are used to obtain the response of the removed part to the six basic types of loads. The second method is a combination of experimental and numerical approaches. The natural frequencies obtained by the measurement are used in finite element (FE) optimization, in which the response of the model is tuned by changing the stiffness coefficients of the bushing. Both methods provide a good estimate of the stiffness at the region where the model is replaced by an equivalent boundary condition. This increases the accuracy of the numerical model and also saves computational time and capacity due to element reduction. [ABSTRACT FROM AUTHOR]

The present paper introduces a theoretical study carried out to investigate the effect of shaft lateral misalignment on the dynamic characteristics of labyrinth seals under stationary conditions. The flow inside the seal is considered to be laminar, incompressible and three-dimensional. It is required to obtain the direct and cross-coupled stiffness and damping coefficients of the seal. Determination of the dynamic coefficients of the seal is obtained using the method of small disturbances. The governing equations of motion are derived for small motion of the shaft center in two orthogonal coordinates and the equations governing the variations of the flow variables are obtained for different shaft eccentricity ratios. By integration in axial and circumferential directions, the aerodynamic forces, direct and cross-coupled stiffness and damping coefficients are determined. In the absence of shaft rotation, the effects of aspect ratio and eccentricity ratio on the dynamic characteristics are examined for different seal geometries. The results show that when the leakage rate or the aspect ratio increases the dynamic coefficients increase. These effects become more pronounced as the misalignment of the shaft is increased. [ABSTRACT FROM AUTHOR]

A numerical three-dimensional computational fluid dynamics-fluid structure interaction (CFD-FSI) model including lining deformation and cavitation is developed to evaluate the effect of perturbation amplitudes on stiffness coefficients of hydrodynamic water-lubricated plain journal bearings. Three types of bearing with rubber, polymer and steel lining materials are compared in terms of stiffness coefficients, load-carrying capacity and journal center equilibrium position under different eccentricity (ɛ) conditions. The simulation results indicate that perturbation amplitudes have great influence on the four stiffness coefficients of water film of hard lining bearings at large ɛ. However, when ɛ ≤ 0.5 and the perturbation varies within 2.9% of the bearing radial clearance, the effect is less than 10% regardless the lining materials. For the rubber lining bearing, the effect of perturbation amplitudes on the stiffness coefficients is negligible due to the rubber deformation, even at ɛ = 1.9 and the perturbation amplitudes up to 7% of the radial clearance. Lining deformation also affects the attitude angle of the journal and the stiffness of water film. The calculation results demonstrate that the lining deformation and journal perturbation amplitudes are two important factors which cannot be ignored in the calculation of bearing stiffness in case of the journal at large eccentricity ratios. [ABSTRACT FROM AUTHOR]

Abstract Background The mechanical parameters of the Ilizarov fixator are influenced by many factors related to its spatial configuration. The aim of this study was to experimentally evaluate the impact of the type of implant and the number of distraction rods on the uniformity of loading of distraction rods and stiffness coefficients of the Ilizarov fixator. Methods The tests were carried out on a physical model. The model was mounted in a universal loading station MTS 858 Mini Bionix. Forces in distraction rods are measured with the use of strain gauge force transducers. Displacements of bone fragments were measured by means of digital image correction. Findings In the case of a fixator with 3 distraction rods, configuration of implants has no statistically significant effect on the forces occurring in distraction rods. In the case of a fixator with 4 distraction rods, there are statistically significant differences in the forces in distraction rods. The highest transverse stiffness coefficients occurs in the system with 4 distraction rods and the configuration of 1K1S implants, while the smallest transverse stiffness coefficients occurs in the fixator with 4 distraction rods and the configuration of 0K1S implants. Interpretation Based on the results of experiments on the physical model, we observed an asymmetry in the distribution of forces transmitted through distraction rods. The configuration with 3 distraction rods provides more uniform distribution of forces in distraction rods and reduces the impact of the implant configuration on transverse stiffness coefficients. The use of a configurations with 4 rods may be advantageous when we want to obtain greater transverse stiffness coefficients of a system consisting of the fixator and fragments of the lengthened bone. Highlights • We observed an asymmetry in the distribution of forces transmitted through distraction rods. • The configuration with three distraction rods provides more uniform distribution of forces in distraction rods. • The most uniform distribution of forces transmitted through distraction rods is ensured by the 1K1S configurations. • The use of a configurations with 4 rods may be advantageous when we want to obtain greater transverse stiffness coefficients. [ABSTRACT FROM AUTHOR]

The paper deals with methods of equivalence of boundary conditions in finite element models that are based on finite element model updating technique. The proposed methods are based on the determination of the stiffness parameters in the section plate or region, where the boundary condition or the removed part of the model is replaced by the bushing connector. Two methods for determining its elastic properties are described. In the first case, the stiffness coefficients are determined by a series of static finite element analyses that are used to obtain the response of the removed part to the six basic types of loads. The second method is a combination of experimental and numerical approaches. The natural frequencies obtained by the measurement are used in finite element (FE) optimization, in which the response of the model is tuned by changing the stiffness coefficients of the bushing. Both methods provide a good estimate of the stiffness at the region where the model is replaced by an equivalent boundary condition. This increases the accuracy of the numerical model and also saves computational time and capacity due to element reduction.

Purpose.The success of the traffic on the railways of Ukraine depends on the number and the operational fleet of electric locomotives. Today, the locomotive depot exploit physically and morally outdated locomotives that have low reliability. Modernization of electric locomotives is not economically justified. The aim of this study is to improve the safety of the traction rolling stock by the frequency analysis of dynamical systems, which allows conducting the calculation of the natural (of resonant) frequencies of the design and related forms of vibrations.Methodology.The study was conducted by methods of analytical mechanics and mathematical modeling of operating loads of freight locomotive when driving at different speeds on the straight and curved track sections. The theoretical value of the work is the technique of choice of constructive schemes and rational parameters of perspective electric locomotive taking into account the electric inertia ratios and stiffness coefficients of Lagrange second-order equations.Findings. The problems of theoretical research and the development of a mathematical model of the spatial electric vibrations are solved. The theoretical studies of the effect of inertia ratios and stiffness coefficients on the dynamic values and the parameter values of electric locomotive undercarriages are presented.Originality.The set of developed regulations and obtained results is a practical solution to selecting rational parameters of bogies of the freight mainline locomotive for railways of Ukraine. A concept of choice of constructive scheme and rational parameters of perspective locomotive is formulated. It is developed the method of calculation of spatial electric locomotive oscillations to determine its dynamic performance. The software complex for processing the data of experimental studies of dynamic parameters of electric locomotive and comparing the results of the theoretical calculations with the data of full-scale tests is implemented.Practicalvalue.The theoretical study allows objectively assessing the impact of the partial frequency of electric locomotive elements on both the rational parameters of its underframe, and the performance and physiological condition of the locomotive crew. Thus, the practical value of the whole complex of theoretical research was to develop an algorithm and program, choosing rational parameters and design scheme of electric locomotive running gear. Using a software package for the study of spatial fluctuations of electric locomotive made it possible to evaluate the dynamic performance of the electric locomotive underframe with sufficient accuracy for practical problems.

An analytical approach using the three-dimensional displacement of a soil is investigated to provide analytical solutions of the horizontal response of a circular pile subjected to lateral loads in nonhomogeneous soil. The rocking stiffness coefficient of the pile shaft in homogeneous soil is derived from the analytical solution taking into account the three-dimensional displacement represented in terms of scalar potentials in the elastic three-dimensional analysis. The lateral stiffness coefficient of the pile shaft in nonhomogeneous soil is derived from the rocking stiffness coefficient taking into account the rocking rotation of a rigid pile shaft. The relationship between horizontal displacement, rotation, moment, and shear force of a pile subjected to horizontal loads in nonhomogeneous soil is obtainable in the form of the recurrence equation. The formulation of the lateral displacement and rotation of the pile base subjected to lateral loads in nonhomogeneous soils is presented by taking into account Mindlin's equation and the equivalent thickness for soil layers in the equivalent elastic method. There is little difference between lateral, rocking, and couple stiffness coefficients each obtained from both the two-dimensional and three-dimensional methods except for the case of Poisson's ratio near 0.5. The comparison of results calculated by the current method for a pile subjected to lateral loads in homogeneous and nonhomogeneous soils has shown good agreement with those obtained from analytical and numerical methods. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, by defining a novel analytical derivation method for a composite beam, using the suitable assumptions, the stiffness coefficients and torsional rigidity (shear modulus) for single-cell and multicell thin walled layer wise composite sections of a beam are calculated. The results are presented in the form of Maple and FORTRAN codes in order to calculate these parameters in a timely manner. These parameters are used for the preliminary structural analysis of the beam. The nonlinear Euler Bernoulli beam assumptions are used to derive the stress-strain and strain-curvature relations. Next, by using the potential energy and elastic curvature relation for elastic beams, the stiffness parameter is calculated. Then, the equivalent torsional rigidity is introduced for single and multi-cell thin walled layer wise composite sections, using the stiffness parameter. To verify the validity of the computations, the results are compared with the numerical results obtained from a finite element analysis. The results show that applying this method for the calculation of the torsional rigidity of single and multi-cell thin-walled composite sections is a viable method and is very useful in obtaining a suitable, initial analytical approximation in the preliminary design of engineering structures, particularly in that of composite structures utilized in aerial industries. [ABSTRACT FROM AUTHOR]

The problem of plates supported on an elastic medium, characterized by several stiffness coefficients corresponding to both linear displacements and rotations, is analysed. This model can be adopted for flexible plates supported on piles. Some particular cases, based on the results presented in [1], [2], are discussed and developed. A case study is performed and the main conclusions from design point of view are drawn.

Ultrasonic guided wave methods are widely used to determine the stiffness coefficients of anisotropic composites. When faced with the challenge of multiple stiffness coefficients, the sensitivity of ultrasonic waves to each stiffness coefficient should be analyzed to ensure the reliability of the identified results. In this paper, a novel method is developed to directly relate the wave velocities to the decoupled stiffness coefficients, allowing for efficient sensitivity analysis and providing good explanations for the sensitivity behaviors using the wave structure properties. Numerical sensitivity analysis is performed for various propagation directions, mode types and frequencies. Experiments are carried out based on the sensitivity results to reconstruct the material properties by inversion of suitable wave velocities measured using a non-contact laser ultrasonic system. [ABSTRACT FROM AUTHOR]

This work describes a new top-down design method for the stiffness of precision machine tools that considers the entire machine stiffness to guarantee the stiffness requirements in the initial design stage. A stiffness modelling method and a stiffness matching design method are presented to achieve the top-down design of the stiffness. A new stiffness characterisation using the stiffness coefficients for characterising the stiffness of the structural parts and the functional units is proposed. The deformation model of the entire machine is established based on multi-body system theory, and the equations of the stiffness coefficients for the deformations of the components are established based on the simultaneous equations of the static equilibrium equations, the deformation compatibility equations and the physical equations. The three-direction (3D) stiffness model is obtained by substituting the equations into the deformation model that reflects the stiffness characteristics of the machine tool. Thus, the reliability of the stiffness model is verified by experiments. Next, the stiffness matching design is performed to confirm the reasonable stiffness values of the parts based on the stiffness model. The finite element method (FEM) is used to validate the proposed method. The contribution rate of the stiffness of the parts to the stiffness of the entire machine is analysed. [ABSTRACT FROM AUTHOR]

Child cortical bone tissue is rarely studied because of the difficulty of obtaining samples. Yet the preparation and ultrasonic characterization of the small samples available, while challenging, is one of the most promising ways of obtaining information on the mechanical behavior of non-pathological children׳s bone. We investigated children׳s cortical bone obtained from chirurgical waste. 22 fibula or femur samples from 21 children (1–18 years old, mean age: 9.7±5.8 years old) were compared to 16 fibula samples from 16 elderly patients (50–95 years old, mean age: 76.2±13.5 years old). Stiffness coefficients were evaluated via an ultrasonic method and anisotropy ratios were calculated as the ratio of C 33 /C 11 , C 33 /C 22 and C 11 /C 22 . Stiffness coefficients were highly correlated with age in children ( R >0.56, p <0.01). No significant difference was found between C 11 and C 22 for either adult or child bone ( p >0.5), nor between C 44 and C 55 ( p >0.5). We observe a transverse isotropy with C 33 >C 22 =C 11 >C 44 C 55 >C 66 . For both groups, we found no correlation between age and anisotropy ratios. This study offers the first complete analysis of stiffness coefficients in the three orthogonal bone axes in children, giving some indication of how bone anisotropy is related to age. Future perspectives include studying the effect of the structure and composition of bone on its mechanical behavior. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to provide an efficient method for determining the stiffness coefficients of hydrodynamic plain journal bearings lubricated by water. In addition to the different physical properties of water and oil, the cavitation effect of water is taken into account. The relationships between the stiffness coefficients and the load for bearings with different relative clearances, different length-to-diameter ratios and different rotational speeds are obtained. Bearings with different diameters are also studied to determine how load carrying capacity and stiffness coefficients change with diameter. Finally, a method is provided for determining the stiffness coefficients of such bearings. [ABSTRACT FROM AUTHOR]

A new type o f multileaf oil lubricated foil bearing with flexible supported back spring structure was proposed to satisfy the requirement o f high rotating velocity for turbo pump, where the rotor was submerged in the hydraulic oil. The numerical analysis was carried out in this paper. Based on the structure o f oil foil bearing, the film thickness model was established without foil deformation. By employing Castigliano's theorem, the total flexibility matrix including the elastic back spring and cantilevered curved beam was calculated, and then compared with commercial finite element software to verify the accuracy of the proposed model. The obtained flexibility matrix was brought into the static and dynamic oil lubricated Reynolds equation. The Reynolds boundary condition was considered to simulate the oil film rupture effect. The deformation equation for the structure and the Reynolds equation were solved coupled by the successive over relaxation method. The static and dynamic characteristics o f the oil lubricated multileaf foil bearing with supported back spring were acquired. The effect o f the foil thickness on the load capacity was discussed. The variation of the dynamic coefficients with bearing load was acquired. By employing Routh-Hurwitz method, the stability of the bearing was analyzed. The results indicated that the load capacity o f the foil bearing with back supported spring was bigger than that of the foil bearing without back supported spring. The stability characteristics of the foil bearing with back supported structure was better than traditional rigid self-acting bearing, particular for the high rotating speed case. [ABSTRACT FROM AUTHOR]

As described in Part I (Zhang et al" "Performance Analysis o f Oil Lubricated Foil Bearing With Flexible Supported Back Spring Structure-Part I: Model Development and Numerical Investigation", ASME J. Eng. Gas Turbines Power, 136(11), p. 112501), a new type of multileaf oil lubricated foil bearing with flexible supported back spring structure was proposed and the characteristics were obtained by theoretical analysis and numerical simulation. Until now, nearly no paper about the modeling method and experimental verification for this type foil bearing published. So it is necessary to study the performance of this kind bearing by experiments. The experimental rig for the static and dynamic characteristics of the bearing was installed and the experiments were carried out. The stiffness of the back supported spring was measured. By employing the dynamic coefficients identification algorithm for oil foil bearing, the data acquisition delay was compensated. The load capacity, stiffness coefficients and damping coefficients were obtained. The load capacity resulting from the experiment was coincided with the theoretical simulation well. The stiffness and damping coefficients from the experiments had the similar tendency with those from the theoretical analysis. The stiffness coefficients obtained from experiments were coincided well with the numerical simulation results, and the difference of damping coefficients was a little bigger. [ABSTRACT FROM AUTHOR]

This paper presents a case study in which a high speed gas lift centrifugal compressor experienced significant vibration problems associated with start-up and operation. The two-stage 8-impeller unit was used to compressor natural gas associated with oil production. During operation the unit experienced significant levels of vibration that made its continued operation impossible. A rotor-dynamic analysis of the compressor unit confirmed the presence of significant unbalance mass, a direct result of liquid within the process gas (‘liquid carry over’). Results of the rotor dynamic analysis was validated with field data. In addition, the paper shows the difference in rotor vibration synchronous response for varying molecular gas weights, particularly at critical speed. [ABSTRACT FROM AUTHOR]

Objective:The objective of this study was a thorough reconsideration, within the framework of Newtonian mechanics and work–energy relationships, of the empirically interpreted relationships employed within the CRASH3 damage analysis algorithm in regards to linearity between barrier equivalent velocity (BEV) or peak collision force magnitude and residual damage depth. Methods:The CRASH3 damage analysis algorithm was considered, first in terms of the cases of collisions that produced no residual damage, in order to properly explain the damage onset speed and crush resistance terms. Under the modeling constraints of the collision partners representing a closed system and the a priori assumption of linearity between BEV or peak collision force magnitude and residual damage depth, the equations for the sole realistic model were derived. Results:Evaluation of the work–energy relationships for collisions at or below the elastic limit revealed that the BEV or peak collision force magnitude relationships are bifurcated based upon the residual damage depth. Rather than being additive terms from the linear curve fits employed in the CRASH3 damage analysis algorithm, the Campbellb0and CRASH3ALterms represent the maximum values that can be ascribed to the BEV or peak collision force magnitude, respectively, for collisions that produce zero residual damage. Collisions resulting in the production of non-zero residual damage depth already account for the surpassing of the elastic limit during closure and therefore the secondary addition of the elastic limit terms represents a double accounting of the same. This evaluation shows that the current energy absorbed formulation utilized in the CRASH3 damage analysis algorithm extraneously includes terms associated with theAandGstiffness coefficients. This sole realistic model, however, is limited, secondary to reducing the coefficient of restitution to a constant value for all cases in which the residual damage depth is nonzero. Conclusion:Linearity between BEV or peak collision force magnitude and residual damage depth may be applicable for particular ranges of residual damage depth for any given region of any given vehicle. Within the modeling construct employed by the CRASH3 damage algorithm, the case of uniform and ubiquitous linearity cannot be supported. Considerations regarding the inclusion of internal work recovered and restitution for modeling the separation phase change in velocity magnitude should account for not only the effects present during the evaluation of a vehicle-to-vehicle collision of interest but also to the approach taken for modeling the force–deflection response for each collision partner. Supplemental materials are available for this article. Go to the publisher's online edition ofTraffic Injury Preventionto view the supplemental file. [ABSTRACT FROM PUBLISHER]

The traditional bearing applied in the turbo-pump for the hydraulic servo system is rolling element bearing. To satisfy the demand of the high rotating speed for turbo-pump, the oil lubricated foil bearing can be employed in the rotor system. For the working liquid of the servo system is oil and the rotor for the turbo pump is submerged in the hydraulic oil, the bearing has to operate in an oil-rich environment, where the air bearing cannot be employed. The theoretical analysis and numerical simulation are carried out in this study to investigate the static and dynamic characteristics of multi-leaf oil lubricated foil bearing. For the structure form of the multi-leaf foil bearing with five symmetrical arrangements, the foil deformation equation and the Reynolds equation are solved coupled by successive over relaxation method, where the Reynolds boundary condition is employed. Then the load capacity, lift-off speed and static equilibrium position are acquired. By deriving the dynamic deformation equation of the foil, the dynamic stiffness coefficients and damping coefficients are obtained based on the perturbation method. The effect of the rotating speed and perturbation frequency on dynamic characteristics is analyzed. It indicates that the load capacity of the multi-leaf foil bearing is smaller than that of the fixed geometry oil bearing without foil deformation, whereas the stability of the bearing is increased. [ABSTRACT FROM PUBLISHER]

An active hydromagnetic journal bearing is designed and presented in this study, which is a new and innovative type of hybrid journal bearing. The proposed new mechatronic smart device has a common bearing shell that contains the two parts of the bearing, which is an attempt to combine the advantages of both types of bearings to overcome their drawbacks and give rise to new possibilities for instability control, increased load-carrying capacity, diagnostics of the rotor system, etc. The active hydromagnetic journal bearing should operate as either a hydrodynamic, active magnetic or hybrid journal bearing, depending on the needs of the rotating machinery. The hydrodynamic lubrication is developed in the inner bearing surface, and the electromagnets of the magnetic bearing are placed outside its outer surface. The active hydromagnetic journal bearing is designed with the appropriate clearance, so that both the hydrodynamic and magnetic bearings can operate. The suitable operational regions for the active hydromagnetic journal bearing are calculated and presented as a combination of the optimum ratio between the air gap and the clearance. Additionally, a simulation code using the two-dimensional finite element method (ANSYS) is developed to simulate the performance of the magnetic component of the active hydromagnetic journal bearing, and the ANSYS software is used to obtain a solution for the hydrodynamic pressure field. The dynamic characteristics of the hybrid journal bearing in terms of the stiffness and damping coefficients versus the Sommerfeld number are calculated and presented. In the hybrid bearing operation, the corresponding stiffness and damping coefficients are used to simulate the hydromagnetic bearing dynamic behaviour. Each hybrid coefficient consists of two parts; the hydrodynamic and the magnetic part. When the operation is purely hydrodynamic, the magnetic parts of the dynamic coefficients are zero and vice versa, whereas both parts are present in the hybrid operation mode. [ABSTRACT FROM PUBLISHER]

The acoustic properties of crystalline double lead molybdate, which are promising for acoustooptics, have been investigated. All elasticity coefficients of PbMoO crystal, the phase velocities of acoustic waves, and the angles between the vectors of phase and group velocities of this material have been determined. The acoustic parameters of the crystal have been calculated based on experimental data from the Schaefer-Bergmann diagrams. The phase velocity of acoustic waves along some directions has also been determined by the standard (in acoustics) echo-pulse method. [ABSTRACT FROM AUTHOR]

Considering the transient squeezing motion, the magneto-hydrodynamic (MHD) steady and dynamic characteristics of one-dimensional slider bearings lubricated with an electrically conducting fluid in the consideration of a transverse magnetic field are numerically investigated. Using the MHD motion equations and, the continuity equation, we have derived a MHD dynamic Reynolds-type equation, which is applicable to slider bearings taking into account the squeezing effect ∂h/∂t, in which the general film-shape function is described by h = h(x, t). A closed-formsolution for the pressure of an inclined-plane slider is obtained and applied to predict theMHDdynamic stiffness and damping characteristics of bearings. According to the results obtained, the application of externally applied magnetic fields signifies an apparent increase in the MHD steady film pressure. Comparing with the classical non-conducting-lubricant case, the applied magnetic-field effects characterized by the Hartmann number provide significant improvement in the MHD steady load-carrying capacity, the MHD dynamic stiffness coefficient, and the MHD dynamic damping coefficient. The improvement of dynamic characteristics of MHD bearings is more pronounced with large Hartmann numbers and small minimum film thicknesses. For guiding the use of the present study, a design example is illustrated. Further results shown in the tables are provided for engineering application. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is to propose a simplified approach to the evaluation of the critical buckling load of multi-story frames with semi-rigid connections. To that effect, analytical expressions and corresponding graphs accounting for the boundary conditions of the column under investigation are proposed for the calculation of the effective buckling length coefficient for different levels of frame sway ability. In addition, a complete set of rotational stiffness coefficients is derived, which is then used for the replacement of members converging at the bottom and top ends of the column in question by equivalent springs. All possible rotational and translational boundary conditions at the far end of these members, featuring semi-rigid connection at their near end as well as the eventual presence of axial force, are considered. Examples of sway, non-sway and partially-sway frames with semi-rigid connections are presented, where the proposed approach is found to be in excellent agreement with the finite element results, while the application of codes such as Eurocode 3 and LRFD leads to significant inaccuracies. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to propose improved expressions for the effective buckling length coefficient of columns in multi-story sway frames. To that effect, a complete set of rotational stiffness coefficients are derived, which are then used for the replacement of members converging at the bottom and top ends of the column in question by equivalent springs. All possible rotational and translational boundary conditions at the far end of these members, as well as the eventual presence of axial force, are considered. An analytical expression and a corresponding graph similar to those used by Eurocode 3 are then proposed for the calculation of the effective buckling length coefficient. Examples of three-story sway frames are presented, where the proposed approach is found to be in excellent agreement with finite element results, while applications of Eurocode 3 and LRFD lead to significant inaccuracies. [Copyright &y& Elsevier]

The sensitivity of laminated cylindrical shell to imperfection is considered, via the initial post-buckling analysis, on the bases of Sanders’ theory. A general code is developed and used in studying the effect of the stretching–bending coupling (B) and the flexural (D) stiffness matrices on the buckling and the post-buckling behavior of the shell, thereby improving its behavior. [Copyright &y& Elsevier]

The results of calculating the stress-strain state of composite beams, based on a nonclassical iterative model, in relation to their physicomechanical, geometrical, and kinematic parameters are presented. The convergence of the iterative process and the influence of the initial conditions on deformations are analyzed and the theoretical and experimental components of the stress-strain state are compared. [ABSTRACT FROM AUTHOR]

Ultrasonic waves are generated through a composite material by means of a noncontact technique. It uses a Nd:Yag LASER for the generation and an interferometric probe for the detection of acoustic waveforms. From a suitable set of experimental data, an inversion scheme is used for the recovering of four stiffness coefficients. They characterize the elasticity in a principal plane of symmetry of the material which exhibits an orthorhombic symmetry. The measurements are performed at various temperatures, elevated by steps up to 300°C for two specimen. The sensitivity of the method appears convenient to measure the temperature induced stiffness changes. The anisotropic degradation of the material properties are then pointed out. [ABSTRACT FROM AUTHOR]