Studies on droplet-turbulence interactions

The present study focuses on numerical modeling for droplet dispersion by turbulence and turbulence modulation by droplets. To account for the dense spray effects, modulation models, a droplet collision model, and the Reitz’s wave instability breakup model are incorporated into a state-of-the-art multiphase all-speed transient flow solution procedure. A parcel probability density function(PDF) approach is implemented to improve the efficiency in droplet dispersion calculations. The numerical results indicate that the present parcel PDF model has the capability to realistically represent turbulent dispersion in dilute and dense sprays with improved efficiency over the delta function stochastic separated flow(SSF) model. Comparative performance of the existing turbulence modulation models are discussed in detail.     

Dynamics of rotor rub in annular clearance with experimental evaluation

Rubbing phenomena in rotor dynamics are investigated by theoretical and experimental approaches. Generating conditions of forward whirling, backward rolling, backward slipping, and partial rubbing are established for system parameters and rotor speeds. Possible whirling motions of the rotor in annular clearance are calculated for full annular rub under the conditions of positive normal force and geometric constraints. The theoretical calculations show that greater clearance results in greater runout and normal force, and the whirling responses are characterized by which natural frequency of the rotor or the stator is greater than the other. Receptances of the rotor and stator are used to explain the possibility of slipping for backward slipping and forward whirling, respectively. Effect of rotor eccentricity is also considered to find the maximum rotor speed for backward slipping during increasing rotor speed and the occurrence of forward whirl. Experiments are performed for two cases. The experimental results show good agreements with the theoretical predictions.     

Identification of cubic stiffness nonlinearity by linearity-conserved NARMAX modeling

A modeling technique to estimate a NARMAX model is developed to identify nonlinearities which are contained in linear-based nonlinear systems. Considering great contributions by linear parts of the NARMAX model on describing nonlinearities, a linear model, which is estimated from small amplitude input and the corresponding output is taken as the linear part of the NARMAX model. Hence, the capabilities of the model to predict nonlinear behaviors for any input within stable region are fairly improved, and multiplicity problem in selecting a nonlinear regression model is also resolved. As an illustration, one degree of freedom system with cubic stiffness is identified in terms of NARMAX modeling technique using the procedure proposed in this work and conventional one, respectively. By extraction higher order FRFs from the NARMAX models, dominant nonlinearities of the system are predicted, and the results by the two methods are compared with analytic one, which shows the priority of the modeling technique proposed.     

Experiments on the turbulent shear flow in a turn-around duct(I)—The mean flow characteristics

The Complex turbulent water flow in a strongly curved turn-around duct has been studied. The turn-around duct had an aspect ratio of 10∶1 and the ratio of the channel height to the mean radius was 1.0. Extensive measurements throughout the curved duct including wall static pressures and mean velocities were made using Laser Doppler Velocimeter for a Reynolds number of 210,000 based on the height of the channel and the average velocity. Analytical calculations of the potential flow were made using Green’s function and the Rayleigh-Ritz method. Based on the turbulence mechanism and stability consideration, a simplified physical model for the outer layer near the start, of the turn along the inner convex wall was hypothesized. This physical model leads to a system of non-linear equations represented in orthogonal curvilinear coordinates. These equations were solved numerically using an iteration method. Comparison of the measured data with the calculated values reveals that the present flow shows the characteristics of an inertial dominated, developing curved flow. The outer layer in a quasi-laminar flow was governed by inviscid-rotational motion. The numerical solution for this region was verified by comparing the calculated and measured flow results. Near the turn exit along the inner wall, a large flow reversal was observed. Spanwise measurements showed that the present turn-around duct flow was approximately two-dimensional. The local mean velocity profiles in the turn for different flow rates were similar when normalized by the average velocity.     

An analytical and experimental study of impulsive stress of square plates at an impact loading point by the 3-dimensional dynamic theory of elasticity

In this paper, a new method is proposed to analyze impulsive stresses at an impact loading point, which cannot be solved by the classical plate theory. Particularly, impulsive stresses at an impact loading point under any impact conditions (regardless of mass of impactor, velocity of impactor, stiffness of plate, etc.), can be obtained by the three-dimensional dynamic theory of elasticity and potential theory of displacement. In addition, by using the Hertzian contact theory, impact loading can be analyzed to account for the local deformation, and this load is applied to the impulsive stress analysis by approximating the impact loading to an analyzable function. In the numerical analysis, the Fourier transform (FFT) algorithm and the numerical inverse Laplace transformation are utilized. Using a new equation, it was possible to analyze impulsive stresses at an impact loading point, and good agreement between the experimental and theoretical results was established.     

A filtration model of microporous membrane filters in liquids

A theoretical study on particulate retention by microporous membrane filters during liquid filtration has been investigated. A model to predict particle retention using a multi-layer concept for filter retention by sieving and using flow resistance for cake filtration was developed to predict particle retention as a function of particle diameter and particle loading. Filter efficiency for the 0.45 μm rated membranes predicted 99.95% for the particle diameter of 0.453 μm. Filter efficiency by sieving model decreased with increased particle loading on the filter. After substantial particle loading, filter efficiency was found to increase with increased particle loading due to the combined effect of sieving and cake filtration. Theoretical particle retention modeling showed good agreement with experimental results.     

Interpretation of emission image of an axisymmetric diffusion flame into 2-dimensional temperature data using a simplified computed tomography

Photographic images of axisymmetric diffusion flames were interpreted using the computed tomographic techinque. The two dimensional images of an axisymmetric diffusion flame were measured by a commercial CCD array camera and a frame grabber. The image data were then used to reconstruct the original three dimensional spatially resolved distributions of emission intensities by using the computed tomographic technique. The reconstructed volumetric emission intensities were then converted into optical temperatures of soot particles by assuming that the system response parameters were constant. The constants were determined from the calibration tests with a blackbody cavity, and with thermocouple measurements. The reconstructed temperatures, which were considered as the temperatures of soot particles, showed reasonable resemblance to the expected temperature distribution. The characteristics of the optical system, such as F number and pixel distance (magnification of image), with respect to the accuracy of reconstructed data were discussed.     

Natural frequencies of shear deformable rhombic plates with clamped and simply supported edges

The natural vibrations of thick and thin rhombic plates with clamped and simply supported edges are analyzed, using assemblages of nine-node Lagrangian isoparametric quadrilateral C⁰ continuous finite elements based on a higher-order shear deformable thick plate theory. Here, additional nodal displacement degrees of freedom are derived by retaining higher-order powers of the thickness coordinate in the in-plane displacement fields, which in turn allows for the proper representation of the transverse shear strains of thick plates. Essential rotary inertia terms are derived and included in the present analysis. Nondimensional frequencies are calculated for thick and thin rhombic plates having various combinations of clamped and simply supported edge conditions, and skew angles. The efficacy of using higher-order shear deformable plate finite elements for predicting the in-plane vibration modes of rhombic plates is found to increase as the span-to-thickness ratio decreases and the skew angle increases. The present work shows that higher-order shear deformable finite elements essentially eliminate the transverse shear over-correction of thick rhombic plate frequencies that is produced when finite elements based on the widely used first-order Reissner-Mindlin plate theory are utilized.     

Influence of viscosity modifiers on the rheological properties of synthetic oils

The study of the effect that the molecular weight and concentration of the polymer gelling additive PMMA (polymethylmethacrylate) introduced into the synthetic base oil PAO6 has on viscosity. The empirical dependence of the viscosity of the thickened oil on the content of additives has been established and the coefficients of the thickening efficiency of additive have been determined. An experimental study of the viscosity of synthetic oils on the shear rate has been carried out at different contents of viscosity modifier PMMA with different molecular weights in a base of PAO6. The ranges of velocities have been determined at which the oil exhibits properties of non-Newtonian fluid. It has been shown that, with an increase in the molecular weight of PMMA of additive at the same concentration in its base, the non-Newtonian behavior of oil begins to emerge at lower shear rates. It has been found that the use of an acoustic arsenal of the operational control of the viscosity of lubricating oils based both on the piezoelectric and the magnetoelastic interaction is promising for the operational control of the viscosity of lubricating oils.     

Use of Au Nanoparticle-Filled PTFE Films to Produce Low-Friction and Low-Wear Surface Coatings

Polytetrafluoroethylene (PTFE) possesses exceptional lubricating properties; however, its uses are limited due to its high susceptibility to wear. In an effort to overcome this shortcoming, a great deal of focus is placed on creating PTFE composites that exploit the strengths of PTFE and also reduce or eliminate its weaknesses. This investigation explores the use of Au nanoparticle-filled PTFE films to produce low-friction and low-wear surface coatings. PTFE + Au nanoparticle composite films were produced by dip coating stainless steel substrates into a mixture of colloidal PTFE and Au nanoparticles. Tribological tests showed that the composite film has a wear life that is twice that of pure PTFE and possesses an average coefficient of friction that is up to 50 % lower. PTFE suffers delamination as a result of poor adhesion of the film to the substrate and tearing resulting from a dominant adhesive wear mode. PTFE + Au, on the other hand, shows no sign of delamination or adhesive wear. This change in wear mode caused by the addition of Au nanoparticles significantly increases the wear resistance and durability of PTFE.     

Morphology of Surface Integrity as Effect of Cold Forging of Aluminum Alloy

Aluminum and its alloys represent a common raw material for components released through a cold machining routine (i.e., forging, cold heading, and rolling processes). They offer easy manufacturing and high plastic strength, together with light weight, long life span, and easy recycling and are heavily used in the transport industry (P. M. G. P. Moreira, et al. (1 Moreira, P. M. G. P., de Jesus, A. M. P., Ribeiro, A. S., and de Castro, P. M. S. T. (2008), “Fatigue Crack Growth in Friction Stir Welds of 6082-T6 and 6061-T6 Aluminium Alloys: A Comparison,” Theoretical and Applied Fracture Mechanics, 50, pp 81–91.[Crossref], [Web of Science ®] , [Google Scholar]), Theoretical and Applied Fracture Mechanics, 50, pp 81–91, 2008; H. Yoshimura and K. Tanaka (2 Yoshimura, H., and Tanaka, K. (2000), “Precision Forging of Aluminum and Steel,” Journal of Materials Processing Technology, 98, pp 196–204.[Crossref], [Web of Science ®] , [Google Scholar]), Journal of Materials Processing Technology, 98, pp 196–204, 2000). However, during processing, the sample–tool interfaces can generate sticking mechanisms that result in an increase in friction values and high wear rates, leading to irreversible damage to the workpiece surface. The surface morphology provides characteristics that allow detection of the damage amplitude. The hard contact between asperities causes nucleation and the formation of adhesive wear. The normal load and lubrication conditions may further affect the quantity of wear elements (A. Hase and H. Mishina (3 Hase, A., and Mishina, H. (2009), “Wear Elements Generated in the Elementary Process of Wear,” Tribology International, 42, pp 1684–1690.[Crossref], [Web of Science ®] , [Google Scholar]), Tribology International, 42, pp 1684–1690, 2009). Optical nondestructive observations permit the detection of the quantity of wear elements as per material transfer from one side (specimen surface) to the other side (contactor surface).

This article presents the mechanisms of the adhesive layer and material transfer that are directly proportional to the new roughness stature. A robust finite element method analysis was embedded to establish a relationship between time, plastic deformation, friction coefficients, and surface defects.     

Mechanical and Tribological Properties of Ekonol Blends as Frictional Materials of Ultrasonic Motors

While high friction coefficients and good wear resistance are antagonistic properties of most materials, these properties are expected to promote excellent torque-speed characteristics and extend the life span of ultrasonic motors. Blending is an accepted technique for modifying tribological applications. p-Hydroxybenzoic acid polymer (Ekonol) blends with different compositions, and proportions were prepared through mechanical blending. Poly(tetrafluoroethylene) (PTFE), poly(etheretherketone), and poly(phylenesulfide) (PPS) were selected as dispersed phases. The mechanical properties of the blends were investigated, and their tribological performance was tested using a block-on-ring wear meter. The worn surfaces of Ekonol blends were observed using a scanning electron microscope to elucidate the relevant wear mechanisms. Results showed that the dispersed phases have distinct effects on the impact strength and hardness, as well as friction coefficient and wear rate, of the blends. Curves of hardness and friction coefficient versus the dispersed phase content showed apparent similarities, which indicates that hardness influences the friction of polymer blends in contact with carbon steel. Worn tracks on the surfaces of different polymer materials showed that the dominant wear mechanism transforms from fatigue and abrasion into adhesion with the addition of a dispersed phase; delamination was observed in the transfer films, especially those formed by the Ekonol/PTFE and Ekonol/PPS blends.     

Leonardo da Vinci’s Friction Experiments: An Old Story Acknowledged and Repeated

Leonardo da Vinci (1452–1519) is universally regarded as a brilliant polymath, designer, astronomer, artist, philosopher, and a visionary engineer of the Renaissance era. Interestingly, due to the delayed discovery of several caches of his notebook pages (as late as the 1960s), his immense contribution to the field of tribology has only recently surfaced. From these salvaged documents, da Vinci’s three notable observations that preceded the development of the laws of friction were uncovered: (1) Friction is independent of apparent contact area, (2) the resistance of friction is directly proportional to applied load, and (3) friction has a consistent value of µ = 0.25. In this work, we have attempted to construct a nearly faithful recreation of Leonardo da Vinci’s apparatus for measuring friction based on his notebook illustrations and investigate the conditions under which Leonardo da Vinci’s experiments produced his findings. Our experiments, performed roughly 500 years later, reproduced Leonardo da Vinci’s findings of friction coefficients with wood of µ = 0.25, but only under conditions of roughly cut and brusquely squared samples of dry wood that were handled and sullied by hand in a fashion typical of wood working but inconsistent with the modern laboratory practice. Thus, our interpretation of Leonardo da Vinci’s findings is that these first tribological studies were actually performed on roughly cut and unpolished samples that had been handled extensively prior to and during testing; Such a procedure of sample preparation is entirely reasonable for the time period and suggests an active, dusty, and dynamic laboratory environment.     

Comment on “Multiple cycle economic lot and delivery-scheduling problem in a two-echelon supply chain”

This paper revisits the work-in process inventory formulation presented by Torabi and Jenabi which appeared in Int J Adv Manuf Technol (43:785–798, 2009, doi: 10.1007/s00170-008-1752-6).     

The Role of Functional End Groups of Perfluoropolyether (Z-dol and Z-03) Lubricants in Augmenting the Tribology of SU-8 Composites

In an earlier work, we demonstrated the development of SU-8 composites using perfluoropolyether (PFPE) as lubricant filler which reduced friction coefficient by ~7 times and enhanced wear life of SU-8 by more than four orders of magnitude. In this work, we have investigated the role of chemical bonding between SU-8 and PFPE molecules using two types of PFPE lubricants (i.e., Fomblin^® Z-dol and Z-03) in improving the tribological properties of the composite. Z-dol has polar (–OH) end groups whereas Z-03 has non-polar (CF₃) end groups. SU-8 with Z-dol (SU-8 + Z-dol) films yielded ~8 times greater wear life than SU-8 with Z-03 (SU-8 + Z-03) films and more by four orders of magnitude than pure SU-8. The nature of the films was analyzed in detail by chemical and physical characterization techniques like X-ray photoelectron spectroscopy, water contact angle and thermo-gravimetric analysis. The results validated the role of polar end functional group of Z-dol in covalent binding with SU-8 upon UV plasma treatment that resulted in improved tribological properties.     

An experimental study on crack healing of various glassy polymers

The validity of a simple tube model proposed by the senior author for crack healing recovery of various polymeric materials such as PMMA(Polymethyl-methacrylate) and Homalite-100(A Polyester) has been tested. The experimental results of recovery in terms of healing fracture toughness were compared with the theoretically predicted trends of recovered fracture toughness. The agreements between these results were found to be reasonable within the limitation of experimental method. After healing the PMMA CT (compact tension) specimens with various solvents having different solubility parameters(δ), the healing recovery (R) was measured by both the method of maximum load and the method of caustics. The relationship between R and solubility differences (Δδ) between a solven and a glass polymer was found to be R∝(Δδ)?1/4.     

Study on rock reaction force depending on PDC cutter placement

The article focuses on the problem of polycrystalline diamond cutter (PDC) cutters' overlapping influence on rock reaction force. This study proposed a static force balance model, based on the model of Wojtanowicz and Kuru (1993 Wojtanowicz, A.K.; Kuru, E. (1993) Mathematical modeling of PDC bit drilling process based on a single-cutter mechanics. Journal of Energy Resources Technology-Transactions of the ASME, 115(4): 247–256.[Crossref], [Web of Science ®] , [Google Scholar]). The innovation of this model is considering two types of friction forces, acting on the contact frontal surface and the lateral surface of a PDC cutter, respectively. Additionally, the proposed model assumes a rock reaction force direction not orthogonal to the contact surface of a cutter but parallel to the crack propagation direction and similar to the rock heterogeneity direction.

Numerical study was provided for a new and a worn PDC cutter to define a rock reaction force depending on options of adjacent cutters' placement (cutters' shape, cutter sizes, bake rake angle, side rake angle, etc.). Two main tendencies were observed: increasing of lateral plot of a cutter decreases rock reaction force, and deviation between directions of cutting force and crack propagation is an extremely significant factor and affects rock reaction force magnitude.     

Numerical Study of the Sensitivity of Tilting-Pad Journal Bearing Performance Characteristics to Manufacturing Tolerances: Dynamic Analysis

In engineering practice, the predictions of bearing steady state and the dynamic characteristics are based on the bearing nominal dimensions. However, as the authors showed in a previous study (Fillon, et al. (1) Fillon, M., Dmochowski, W. and Dadouche, A. 2007. Sensitivity of Tilting Pad Journal Bearing Performance Characteristics to Manufacturing Tolerances. Trib. Transactions, 50: 387–400. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), manufacturing tolerances related to the bearing geometry (e.g., bearing clearances or angular pivot position) can significantly affect the steady-state characteristics such as the operating temperature, the minimum film thickness, and the power loss. This paper investigates changes to the bearing dynamic properties due to variations of the design parameters within the manufacturing tolerances. The dynamic properties of the tilting-pad journal bearings are represented by eight linear coefficients of stiffness and damping.

The study presents results obtained for realistic variations of bearing clearance, preload, pivot offset, as well as the pad angular extension. As an example, five-pad tilting-pad journal bearings with a diameter of 76.2 mm (3 in.) and three different L/d ratios have been used.     

Numerical Aspects of Cone Beam Contour Reconstruction

We describe a method for directly calculating the contours of a function from cone beam data. The algorithm is based on a new inversion formula for the gradient of a function presented in Louis (Inverse Probl 32(11):115005, 2016. http://stacks.iop.org/0266-5611/32/i=11/a=115005). The Radon transform of the gradient is found by using a Grangeat type of formula, reducing the inversion problem to the inversion of the Radon transform. In that way the influence of the scanning curve, vital for all exact inversion formulas for complete data, is avoided Numerical results are presented for the circular scanning geometry which neither fulfills the Tuy–Kirillov condition nor the much weaker condition given by the author in Louis (Inverse Probl 32(11):115005, 2016. http://stacks.iop.org/0266-5611/32/i=11/a=115005).     

Unified synthesis of Watt-I six-link mechanisms using evolutionary optimization

A Watt-I mechanism can operate in eight different combinations of assembly modes and output link. In this paper, a novel approach is presented for carrying out unified optimum synthesis of various combination types of Watt-I mechanism, irrespective of whether identical or different ranges of variables are specified for different combination types. By carrying out unified synthesis the less suited combination types can be identified, leading to their elimination from the synthesis process. This results in a saving of the overall computational time. The presented approach can be implemented with most of the evolutionary optimization methods. In this paper, the Differential Evolution algorithm is chosen as the optimization method. Unified optimization results are presented for two problems. The proposed approach is general and can be used, with suitable modifications, to carry out unified optimum design of alternate mechanical systems which can perform a given task.