Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

In assembly, error prediction and control according to the error state of the machine parts are the key links to ensuring the accuracy of the entire machine tool. In this study, an assembly error modeling method considering the error of the roller guide and gravity-induced deformation is proposed. First, based on the Hertz contact theory, a nonlinear error propagation model for the roller guide to the moving part is proposed. With this model, the analytical relationship between the straightness error of the guide rail and the errors of the moving part can be established. Then, after the linearization of the guide error model, a machine assembly error model considering the guide error is proposed. This model expresses the linear relationship between the error of the rolling joint surface and the error of the machine tool after the final assembly. Additionally, considering the influence of gravity deformation of structural parts, the gravity deformation is extracted by the finite element analysis method and added to the model by linear superposition. As a result, the model corresponds more with the practical assembly process. Finally, an assembly error prediction method of the precision horizontal machining center is presented, and a case is studied to demonstrate the validity of the proposed model and method.

The present research studies the vibration and bifurcation analysis of a spinning rotor-disk-bearing system to carefully scrutinize the dynamic stability under extrinsic mass unbalance and pulsating axial load. The shaft is flexible and taken into account the geometrical nonlinearities due to large elastic deformation in bending. The rotor is supported by flexible bearings, which are modeled as an equivalent spring-damper system having linear and nonlinear stiffness elements. Equation of motion of the rotating system, which includes flexible shaft, rigid disk, and flexible bearing, is derived using extended Hamilton principle with the assumption of the Euler's beam theory. We studied initially the modal analysis to determine the modal parameters, i.e. natural frequency and mode shapes prior to the investigation of the dynamics of the system. Further, we developed the bifurcation diagram for steady-state solutions and to study the subsequent dynamic stability and verify with the findings solved numerically. The interactive behavior among the nonlinear shaft-bearing, axial load and an unbalance has been analyzed. Numerical simulation tools, i.e. frequency–response characteristics, time history, phase trajectories, and Poincaré map have been used to highlight the presence of nonlinear phenomena and its important role towards evaluating the system dynamics and subsequent stability. This current research showed that flexible bearings stabilize the system as a result of increasing the restoring force. Analyzing the bifurcation diagrams of pulsating axial load, we found that the system exhibits complex phenomena as multiple but stable periodic orbits leading to period doubling. The present system is highly vulnerable to catastrophic failure due to the S–N and Pitchfork bifurcation. The present research enables the notability of axial load and mechanical unbalance on the overall system behavior and stability in real working conditions.

Nonlinear vibration of rotating machinery induced by rolling bearings has gradually become a research issue. In many cases, the rotor discs are not always installed in middle of shaft in actual rotor system, and the influence of disc offset on nonlinear vibration needs to be studied in depth as rotating speed increases. This study deals with the effect mechanism of rotor offset on nonlinear dynamic responses. Nonlinear vibration model of offset rotor is established based on finite element method, and the disc offset position along rotor shaft is concerned. The responses are calculated by Newmark-β integration method, which are also validated by an experimental rig, and the influences of nonlinear parameters of rolling bearings are investigated. The results indicate that disc offset is a crucial factor that can induce more complex nonlinearity coupled with rolling bearing under high-speed conditions.

This paper presents numerical and experimental investigations on the flow and noise characteristics in a forward multi-blade centrifugal fan with step tongue volutes. Numerical simulations are performed by large eddy simulation, and the experiments are conducted to test the effects of the cut-off arrangements on the noise characteristics of the fan. The objective of this work is to explore the effect of the double-stepped tongue and single-stepped tongue on the internal complex flow and the noise generation within the fan. The comparison of the results of numerical calculation demonstrates that the internal complex flow of centrifugal fan can be controlled by the stepped tongue, the flow loss in meridian plane for the double-stepped tongue (HLHL, L stands for low and H for high) model is obviously lower than that of the original model, the Q-criterion value of HLHL model is lower than that of the original model, and the noise of the HLHL model produces an obvious decrease of 1.90 dB compared to that of the reference model. The comparison of the test results further shows that the HLHL model produces a decrease about 1.97 dB compared to that of the reference model, which mainly indicates the double-stepped tongue HLHL model more effectively controls the tonal noise comparing to the single-stepped tongue (HL) model. Meanwhile, the stepped arrangements possess comparable performance characteristics to the reference model. The double-stepped tongue HLHL model makes a positive contribution to the pressure rise of the centrifugal fan.

Sand and gravel blown up by strong wind will cause damage to windows. Following up, it will cause the change in the flow field around a train immediately, which has a significant impact on the aerodynamic performance of the train. Delayed detached-eddy simulation based on the shear stress transport κ-ω turbulence model was used to investigate the aerodynamic characteristics of passenger vehicles under crosswind, and the effect of damaged windows on the train aerodynamic performance and flow field around the train was analyzed and compared. The grid generation and numerical method are verified in the previous studies. Results show that the aerodynamic performance of a passenger vehicle is significantly affected by damaged windows on both sides of the passenger vehicle, both the aerodynamic lateral force and overturning moment of the passenger vehicle were decreased, and this has a small effect on the aerodynamic performance of the downstream passenger vehicle. Fluctuation of the aerodynamic lift, lateral force, and overturning moment of a vehicle with damaged windows on both sides of the vehicle is significantly increased. Damaged windows do not change the existence of the main vortices around vehicles, but the size, location, and strength of the main vortices are obviously changed, especially when windows on both sides of the vehicle are damaged. Therefore, when windows on the windward side of the vehicles are damaged, opening or broking windows on the leeward side of the vehicles will help reduce the risk of vehicles overturning and derailment.

In this paper, the kinematic analysis of a series of variable geometry legged wheels is presented. These mechanisms can transform a circular wheel into a hybrid legged wheel in order to combine the efficiency and ability to traverse difficult terrain of each method of locomotion. The inverse and direct kinematic problems of position and velocity are stated and solved. Then, a singularity analysis of the mechanisms is performed. The geometrical conditions that make the Jacobian matrices of the wheels singular are determined and interpreted. Subsequently, an exploration of the workspace is presented to show kinematic features of the wheels inside their operation region.

In this work the effect of nanoclay, Cloisite 20B inclusion on the mechanical behavior of a woven-type glass fiber reinforced polymer composite was experimentally investigated. Specifically, the study examined the effect of nanoclay with various weight percentages on the tensile, compressive strengths, and modulus of elasticity of glass fiber reinforced polymers in both weft and warp directions. Results showed that depending on the warp and weft directions, the inclusion of nanoclay, Cloisite 20B, significantly improved the mechanical behavior of glass fiber reinforced polymers. A better understanding of nanoclay fillers and their contribution to mechanical behaviors can lead to better design of novel structural composites.

Copper beryllium (CuBe) with good mechanical and high electrical conductivity properties is used in metalworking, electronic devices, automotive systems, and aerospace systems. Having low hardness limits its usage in tribosystems such as internal combustion engine valve train systems. In this study, heat-treated CuBe material was coated with CrN under a micron thickness by cathodic arc physical vapor deposition (arc-PVD) to improve wear resistance not only at unlubricated condition but also at the lubricated condition for tribosystem, especially a material candidate for cam tappets. Therefore, CrN-coated CuBe, CuBe, and AISI52100 steel samples were tested by a tribometer at unlubricated and lubricated sliding conditions. Surface morphological changes and tribochemical formation were investigated by optical microscope, optical profilometer, atomic force microscope, and scanning electron microscope. The results showed that CrN increased the wear resistance of the CuBe significantly, and it can be used as cam tappet material both on unlubricated and boundary lubrication regimes.

Zinc dithiophosphate is the most commonly used antiwear additive in lubricating oil. However, zinc dithiophosphate has a poisoning effect on engine catalysis via phosphorus and zinc content that reduces the efficiency causing hazardous emission increase, therefore, it needs to be replaced with an alternative additive. In this study, the antiwear performance of molybdenum disulfide (MoS₂) is enhanced by zinc sulfate (ZnSO₄) addition and subjected to tribometer tests at different contact pressures to explore the MoS₂ + ZnSO₄friction and antiwear performance against MoS₂and zinc dithiophosphate. Wear rates and surface morphology changes were carried out by an optical microscope, optical profilometer, and atomic force microscope analysis. Furthermore, tribochemical and surface energies of tribofilms were evaluated via scanning electron microscope/energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscope adhesion force mapping analysis. Results showed that ZnSO₄addition to MoS₂ + base oil improves the antiwear performance of the lubricating oil significantly and it presents similar friction characteristics to zinc dithiophosphate.

The choice of a rolling bearing for a particular application relies on performance rating parameters as the static, the dynamic, and the fatigue limit load of bearings. The values of these parameters define the calculated performance of the bearing. Endurance testing of high-quality rolling bearings has been used for the development of rolling bearing performance standards like the ISO 281 and ISO 76 that are commonly used throughout the industry. However, standard test methods for the measurement and validation of load ratings of rolling bearings are not available in the standards. This leads to the undifferentiated use of the “status of the art” standardized performance to the very large variety of rolling bearing types and qualities that are produced today. The current paper revisits the origin, definition, and development of rolling bearing performance parameters. A numerical study for the determination process of bearing load ratings is carried out. The results are compared with standardized values and values quoted by bearing manufacturers. This provides an overview of the load rating practices that are in use. The limitations and possible improvements of the present methodology are discussed.

In this study, the heat transfer characteristics of laminar combined forced convection through a horizontal duct are obtained with the help of the numerical methods. The effect of the geometrical parameters of the cavity and Reynolds number on the heat transfer is investigated. New heat transfer correlation for hydrodynamically fully developed, laminar combined forced convection through a horizontal duct is proposed with an average error of 6.98% and R² of 0.8625. The obtained correlation results are compared with the artificial neural network and adaptive neuro-fuzzy interface system models. Due to the obtained results, good agreement is identified between the numerical results and predicted adaptive neuro-fuzzy interface system results. In conclusion, it is seen that adaptive neuro-fuzzy interface system can predict the Nusselt number distribution with a higher accuracy than the developed correlation and the artificial neural network model. The developed adaptive neuro-fuzzy interface system model predicts the Nusselt number with 1.07% mean average percentage error and 0.9983 R² value. The effect of the different training algorithms and their ability to predict Nusselt number distribution are examined. According to the results, the Bayesian regulation algorithm gives the best approach with a 2.235% error. According to the examination that is performed in this study, the adaptive neuro-fuzzy interface system is a powerful, robust tool that can be used with confidence for predicting the thermal performance.

This paper carried out an experimental study on the critical heat flux during flow boiling of R134a in a vertical helically coiled tube. The length, inner diameter, coil diameter, and pitch of the test tube were 1.85 m, 8 mm, 205 mm, and 25 mm, respectively. Experiments cover the mass flux range of 190–400 kg·m⁻²·s⁻¹, heat flux of 15–55 kW·m⁻², inlet pressure of 0.8–1.1 MPa, and inlet vapor quality of 0.01–0.35. The effects of critical heat flux identification method, mass flux, system pressure, and inlet vapor quality on critical heat flux were presented. The critical heat flux obtained by the wall temperature rise method was larger than that obtained by the wall temperature oscillation method. The deviation of the critical heat flux corresponding to two methods, including wall temperature rises sharply above 10 ℃ and wall temperature drastic oscillation, was about 20% under the present experimental conditions. The critical heat flux increased with mass flux while it decreased with the inlet vapor quality and pressure. The experiment data were compared with four existing empirical correlations. A new correlation is proposed for critical heat flux prediction in vertical helical tubes.

The geometric design, meshing performance, and mechanical behavior of pure rolling helical gear drives are presented. Parametric equations for contact curves on the pinion and gear are determined by coordinate transformation of the active designed pure rolling meshing line for the whole cycle of meshing. Moreover, parametric equations for the tooth surfaces of helical gears with convex-to-convex meshing type are derived according to the motion of generatrices in the transverse section along the calculated contact curves. Then, the basic design parameters are analyzed and formulas for calculation of the geometric size are given. The meshing performance and mechanical behavior, including contact patterns, loaded function of transmission errors, and variation of stresses for two pitch angles of meshing are compared with those of a reference design of micro-geometry modified involute helical gears. Besides, the influence of basic design parameters on tooth contact analysis and stress analysis is studied. The analysis of the results shows that the proposed pure rolling helical gears have the advantage of reducing the relative sliding between tooth surfaces and the possibility of designing pure rolling helical gears with a small number of teeth, though the contact strength of the surfaces is impaired. However, if the appropriate design parameters and Hermite curve parameters for the fillets are properly evaluated as proposed here, the mechanical behavior of the proposed pure rolling helical gear drive, in terms of contact patterns and variation of bending stresses can be superior to that of the micro-geometry modified involute helical gear drives.

Fatigue life analysis of roller bearing is usually performed for bearings under constant rotating speed and invariant loading conditions. For the bearings used in offshore floating direct-drive wind turbines, they often experience oscillating motions with varying loading patterns, for which the standard fatigue life analysis is not valid due to the presence of fluctuating loads. This paper presents the fatigue life analysis of a double-row tapered roller bearing under oscillating external load and speed conditions, which is used to support the main shaft of a large modern direct-drive wind turbine. First, a comprehensive quasi-static model of the double-row tapered roller bearing is developed for determining the internal load distribution of rollers. The contact pressure of rollers is then studied using an iterative scheme based on the elastic contact model. After that, the formulation of basic rating life of the double-row tapered roller bearing with oscillating external load and speed is given to calculate the fatigue life. Numerical simulations are carried out to investigate the effects of the oscillating load and speed, angular misalignment, and internal clearance on the fatigue life of the bearing.