Search results

This study aims to deal with the performance of symmetric/asymmetric slot entry hybrid journal bearing system considering the effect of three dimensional irregularities in the analysis.

The asperity profile of three-dimensional irregularities has been modeled in both circumferential and axial directions. To compute the bearing performance characteristics parameter, finite element formulation of governing Reynolds equation has been derived using Galerkin’s technique.

Based on the numerically simulated results, it has been observed that the three-dimensional irregularities enhance the value of minimum fluid film thickness (h̄_min), lubricant flow (Q̄) and fluid film damping coefficients (C̄₁₁,C̄₂₂) approximately by order of magnitude of 24-26, 43-51 and 18-66 per cent, respectively, for the case of asymmetric slot entry configuration. Whereas, the values of fluid film stiffness coefficients (S̄₁₁,S̄₂₂) and threshold speed (ω̄_th) reduces approximately by order of 1-6 and 0-3 per cent, respectively, for the case of symmetric slot entry configuration.

The present paper describes that the influence of three-dimensional irregularities on bearing surface on the performance of slot entry hybrid journal bearing is original in literature gaps. The numerically simulated results presented in this study are expected to be quite useful to the bearing designers.

Realistic composite vehicles with 2, 3, 5 and 9 axles, consisting of a truck with one or two trailers, are addressed in this paper by computational models for vehicle–bridge interaction analysis.

The vehicle–bridge interaction (VBI) models are formed by sets of 2-D rigid blocks interconnected by mass, damping and stiffness elements to simulate their suspension system. The passage of the vehicles is performed at different speeds. Several rolling surface profiles are admitted, considering the maintenance grade of the pavement. The spectral density functions are generated from an experimental database to form the longitudinal surface irregularity profiles. A computational code written in Phyton based on the finite element method was developed considering the Euler–Bernoulli beam model.

Several models of composite heavy vehicles are presented as manufactured and currently travel on major roads. Dynamic amplification factors are presented for each type of composite vehicle.

The VBI models for compound heavy vehicles are 2-D.

This work contributes to improving the safety and lifetime of the bridges, as well as the stability and comfort of the vehicles when passing over a bridge.

The structural response of the bridge is affected by the type and size of the compound vehicles, their speed and the conservative grade of the pavement. Moreover, one axle produces vibrations that can be superposed by the vibrations of the other axles. This effect can generate not usual dynamic responses.

The Brush Surface Analyzer is designed for rapidly analyzing and directly recording the irregularities of finished surfaces of metals, glass, paper, plated and painted surfaces and the like. It consists of three principal units: an analyzing head, a calibrating amplifier and a direct inking oscillograph. These three units give an instantaneous and permanent record of a finished surface, the irregularities of which may be magnified as desired up to 100,000 times.

The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses.

Flow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration.

The spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism.

The spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics.

The spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.

DURING the past eight or ten years the speeds of most types of aeroplanes have been practically doubled. Part of this impressive advance has resulted from the use of increased power, but most of it has come from the reduction of aerodynamic drag. The largest and most obvious “built‐in head winds” such as exposed engine cylinders, landing gear struts and wires were first eliminated and attention was then directed to successively smaller factors. The stage has now been reached where it is necessary to consider the effects on drag of such items as rivets, sheet‐metal joints and other irregularities on the surfaces exposed to air flow.

This study aims to investigate the impact of surface waviness on the static performance parameters of hydrodynamic journal bearings operating with lubricants containing copper oxide (CuO) and cerium oxide (CeO₂) nanoparticles.

The static performance parameters of bearings with surface waviness and the addition of nanoparticles in lubricants were calculated using the nondimensional form of Reynolds equation and finite element method. Static performance parameters are calculated at different waviness numbers in the circumferential, axial and both directions at various wave amplitudes with variable viscosities of lubricants with nanoparticles using the viscosity equation forming a relationship between the relative viscosity, temperature and weight fraction of nanoparticles in lubricant developed from the experimental results.

The computed results indicate that the impact of waviness on the bearing surface enhances the load capacity, reduces friction coefficient, and is more effective in the circumferential direction than in the axial direction or in both directions. The addition of CuO and CeO₂ to the lubricant enhanced its viscosity which further improved the steady-state parameters of the wave bearing.

This study is based on a numerical technique, which has significant limitations, and the simulated results must be tested experimentally.

The current findings will be beneficial for designers to improve the performance of hydrodynamic journal bearings.

The calculated results demonstrate that the combined effect of the surface waviness on bearings and the addition of nanoparticles to lubricants can greatly increase the performance of hydrodynamic journal bearings.

The issue of evaluating the dynamic characteristics of a bridge due to the presence of rapidly moving vehicles has considerable importance. This study aims to conduct a comprehensive study on the variables that influence the dynamic behavior of a thin-walled box-girder bridge exposed to high-speed train loads using regression analysis.

The high-speed train is mathematically represented by a system with 38 degrees of freedom (DOF), while the sub-track system uses China’s Railway Track System slab track. The numerical modeling of the bridge is accomplished using computationally efficient finite elements that represent thin-walled box-beams. The rail’s imperfections are also accounted for, and they are represented using a power spectral density function. The dynamic response of the bridge is calculated using the Newmark-beta technique, considering several DOFs and stress resultants.

A thorough parametric analysis of the factors affecting the dynamic response of the bridge is conducted and a regression model has been proposed. The regression equation yields an excellent fit for shear force, distortional moment and distortional bimoment, with an R² value near 1. It has also been observed that the range of the coefficient R² in case of bending moment, torsion, torsional bimoment and vertical deflection typically falls between 0.82 and 0.9. R² value near to 1 indicates that it is quite accurate in forecasting the dynamic influence of high-speed trains on the bridge’s response.

The originality of this research lies in pioneering the regression modeling of dynamic responses in thin-walled box-girder bridges and uniquely modeling high-speed trains with 38 DOF, which has not been previously explored in existing studies.

This investigation is devoted to analyze the electroosmotic flow characteristics in a sinusoidal micropipe through a porous medium. This study aims to investigate the impact of surface waviness on Darcy–Brinkman flow in the presence of electroosmotic force, achieved through the unification of perturbation techniques.

Analytical approximate solutions for the governing flow equations are obtained through the utilization of a perturbation method.

The analytical study reveals that the periodic roughness on the surface of the micropipe generates periodic disturbances not only in the potential fields but also in the velocity profiles. An increase in the relative waviness of the pipe leads to the generation of corresponding waviness within the boundary layers of the flow. Surface waviness reduces the average velocity by increasing frictional resistance, while higher Darcy numbers and electroosmotic parameters lead to higher velocities by reducing flow resistance and enhancing electrokinetic forces, respectively. In addition, the presence of waviness introduces higher flow resistivity, contributing to an overall increase in the friction factor. Higher permeability in porous media induces boundary-layer reverse flows, resulting in elevated flow resistivity.

The current findings offer valuable insights for researchers in biomedical engineering and related fields. The author’s discoveries have the potential to drive advancements in microfluidic systems, benefiting various domains. These include optimizing drug delivery in biomedical devices, improving blood filtration applications and enhancing the efficiency of fluid transport in porous media for engineering applications.

To develop an analysis methodology to evaluate the dynamic behaviour and fatigue assessment of highway bridges due to vehicle passage on irregular pavement surfaces. The approach considers the non-deterministic nature of the parameters of the vehicle-bridge system using Monte Carlo simulations.

In the proposed approach, 11 vehicle-bridge system parameters are modelled as random variables with predefined probability distributions. The dynamic analysis considers the vehicle-structure-pavement interaction, in which road surface roughness is defined based on the use of the power spectral density function, as an expression of the road surface random irregularities. Based on the results of the dynamic analysis, a fatigue assessment is performed. To demonstrate the applicability of the methodology, a case study of a 40-m-span steel-concrete composite highway bridge was selected, considering two levels of pavement quality.

The results reveal that vehicle speed, sprung masses, bridge mass and rear axle and tire stiffness are the parameters that most influence vertical displacement, bending stress and fatigue life. Numerical simulations showed that the pavement deterioration reduced fatigue life by up to 98.6%, increasing the failure probability.

The dynamic behaviour and fatigue of a highway bridge are evaluated by means of vehicle-structure interaction analyses, in which the randomness of 11 parameters of the vehicle-bridge system is simulated. This includes dynamic parameters of the suspension and tires, whose variability is rarely considered due to the difficulty in obtaining sample data.

The purpose of this paper is to investigate and contribute to a better understanding of cutting process characteristics using the proposed RBD Palm Olein-based organic mixed coolant.

In this research, refined, bleached and deodorized (RBD) Palm Olein is selected as the base oil for organic coolant and mixed coolant (base oil mixed with chemicals) to compare with the cutting performance of industrial water-soluble chemical (inorganic) coolant. Using coated carbide tool, JIS SS400 Mild Steel was tested in milling process. At fixed spindle speed, the relations between feed rate and depth of cut (DOC) on cutting temperature and surface roughness were investigated. Also, the dynamic viscosity, specific heat capacity and pH level for each coolant are taken into consideration.

As predicted, cutting fluid with lower viscosity removes more heat. The cutting temperature increased with increasing feed rate and DOC. However, surface roughness increased with increasing feed rate but decreased with increasing DOC. From the data gathered, the proposed RBD Palm Olein-based organic mixed coolant showed better heat removal properties than organic coolant and it produced a far better machined surface than inorganic coolant.

Overall, the proposed organic mixed coolant has shown great potential to be a good cutting fluid when balance between cooling properties and lubricity, and consistent quality of cutting fluids are sought to produce environmental friendly quality workpiece.