Friction Coefficient Resistance Research Articles

Numerical analysis of flowing characteristics of turbulent flow in rectangular channels in ocean environment

Because of the periodic effects of ocean waves, there are great discrepancies between the operational characteristics of nuclear power systems in ocean environment and that of land-based nuclear power systems. In some special operational status, like natural circulation, the additional forces due to ocean environment may impose so great disturbance on the coolant flow that theatres the safety operation of the systems. In the present paper, the turbulent flow in rectangular channels in ocean environments is investigated theoretically with CFD code FLUENT. The effects of several parameters on turbulent flow are analyzed. The effects of rolling motion includes two parts, the first part is the additional force parallel to flowing direction, which can affect on the pressure drop of the flow and change the flowing velocity, and the other part is the additional force perpendicular to flowing direction. In ocean environments, the flowing characteristics of turbulent flow are dominated by the additional force parallel to flowing direction. The effect of additional force perpendicular to flowing direction is very limited. In rolling and heaving motions, if the flowing velocity is the same, the flowing characteristics of turbulent flow are nearly the same, too. The bigger the Reynolds number is, the more serious the oscillation of turbulent kinetic energy and frictional resistance coefficient is, and the more the oscillation of turbulent flow is. The relationship between average frictional resistance coefficient and velocity oscillating amplitude is quadratic. And the oscillating amplitude of frictional resistance coefficient is in direct ratio with velocity oscillating amplitude.

Physical and mechanical properties of tomato fruits as related to robot’s harvesting

In order to better design, fabricate and control tomato harvesting robot, selected physical properties such as height, diameter, sphericity, surface area, volume, total mass, mass of pericarp and gelatinous matter, bulk density, density of pericarp and gelatinous matter, porosity, projected area, shape factor, and radius of curvature of two cultivar tomato fruits with different locule numbers were mainly investigated by image analysis and water displacement method. Mechanical properties such as friction and rolling resistance coefficients, and rupture energy, rupture force, compressibility, and loading slope of tomato fruits at two loading positions were determined by pull and loading test. Results showed the locule number had a significant effect ( P < 0.05) on certain physical and mechanical parameters, such as height, diameter, surface area, rupture force, compressibility, and friction coefficient. The loading position also showed a significant effect ( P < 0.05) on certain mechanical parameters, such as compressibility. The obtained properties are closely related to robot’s harvesting.

Sliding friction and wear behaviors of surface-coated natural serpentine mineral powders as lubricant additive

This work aims to investigate the friction and wear properties of surface-coated natural serpentine powders (SP) suspended in diesel engine oil using an Optimal SRV oscillating friction and wear tester. The worn surface was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Results indicated that the additives can improve the wear resistance and decrease friction coefficient of carbon steel friction couples. The 0.5wt% content of serpentine powders is found most efficient in reducing friction and wear at the load of 50N. The SEM and XPS analysis results demonstrate that a tribofilm forms on the worn surface, which is responsible for the decrease in friction and wear, mainly with iron oxides, silicon oxides, graphite and organic compounds.

Effect of rolling on the flowing and heat transfer characteristic of turbulent flow in sub-channels

The flowing and heat transfer of turbulent flow in typical 4 rod bundles in rolling motion is investigated with LES and URANS. As the rolling period decreases, the average wall shear stress increases, and the frictional resistance increases. The wall shear stress solved by LES is not good enough, while that of URANS is consistent with experiments. The variation of frictional resistance coefficient, Nusselt number and Reynolds stress with rolling amplitude is very weak. In rolling motion, the biggest frictional resistance coefficient is not located in a constant time.

A fine surface roughness electroless Ni–P–PTFE composite modified stamper for light guide plate application

Electroless Ni–P–PTFE composite coating technology takes advantage of the beneficial properties from both Ni–P alloy and PTFE, such as good wear resistance, good anti-adhesion, dry lubrication, low coefficient of friction and good corrosion resistance. It has been applied in many mold industries. However, the Ni–P–PTFE composite coating suffers from bad surface roughness, when the PTFE particles incorporate into a Ni–P matrix. This severely hampers the technology to be applied to optical grade applications. In this paper, we propose a trick to generate a fine surface roughness (FSR) electroless Ni–P–PTFE composite to modify a nickel stamper. Using this new method, the nickel stamper can be covered by a Ni–P–PTFE functional layer and can keep the original surface property at the same time, namely the optical properties. We have chosen 4.5 inch (97 mm × 59 mm × 0.6 mm) light guide plates (LGPs) to demonstrate the effectiveness of the procedure. For the sake of comparison, the LGPs were produced by injection molding with three kinds of stampers including an original SUS430 master, an electroless Ni–P–PTFE composite coated nickel stamper and an FSR electroless Ni–P–PTFE composite modified stamper. We measured and discussed the optical performances at both the element level and system level, namely complete back light units.

CFD Analysis of Turbulent Flow in Typical Rod Bundles in Rolling Motion

The influence mechanism of rolling motion on the flowing and heat transfer characteristics of turbulent flow in typical four rod bundles is investigated with FLUENT code. The flowing and heat transfer characteristics of turbulent flow in rod bundles can be affected by rolling motion. But the flowing similarity of turbulent flow in adiabatic and non-adiabatic can not be affected. If the rolling amplitude is big or if the rolling period is small, the radial additional force can make the parameter profiles and the turbulent flowing and heat transfer change greatly. And the frictional resistance coefficient and heat transfer coefficient can not be solved by the correlations in steady state. In rolling motion, as the pitch to diameter ratio decrease, especially if it is less than 1.1, the flowing and heat transfer of turbulent flow in rolling motion change significantly.

Theoretical models of turbulent flow in rolling motion

The flowing and heat transfer characteristics of turbulent flow in tubes and rectangular channels in rolling motion are investigated theoretically. The flowing and heat transfer models of turbulent flow in rolling motion are established. The correlations of frictional resistance coefficient and Nusselt number are derived. The results are also validated with experiments. The effects of several parameters on frictional resistance coefficient and Nusselt number are investigated. The oscillating amplitude of Nusselt number is in direct ratio with Prandtl number and rolling frequency approximately. The more the flowing velocity is, the less the effect of rolling motion on the flow is. The variation of initial phase difference between Nusselt number and rolling motion with rolling frequency is very limited.

Improvement of High Temperature Wear Resistance of AISI 316 ASS through NiCrBSiCFe Plasma Spray Coating

In this work, the microstructural description, mechanical properties and dry sliding wear features of NiCrBSiCFe plasma sprayed on AISI 316 austenitic stainless steel (ASS) substrate were examined. Defect-free metallurgically bonded coatings were obtained. Wear tests were carried out at 2 m/s sliding velocity under the load of 20N for 2000 m sliding distance at various conditions like room temperature (35°C), 150°C, 250°C and 350°C using a EN-8 medium carbon steel pin as a counterface material. The properties namely coating density, micro hardness, coefficient of friction (CoF) and wear resistance of the coating were studied. NiCrBSiCFe plasma spray coated steel substrate showed superior wear resistance properties than the uncoated steel substrate in all the temperatures. The sliding wear resistance was improved up to 4.5 times than that of the uncoated material. In wear test carried out at 350oC, the coated substrates showed relatively lesser wear than in other temperatures due to the oxide formation, which acted as a protective layer. In addition, the shallow ploughing mode of wear reduced the severity of material removal at 350°C. Using scanning electron microscope (SEM) pictures, the wear properties of the coated steel substrate were evaluated in terms of plastic deformation, material transfer and abrasion.

Model-and Full-Scale URANS Simulations of Athena Resistance, Powering, Seakeeping, and 5415 Maneuvering

This study demonstrates the versatility of a two-point, multilayer wall function in computing model-and full-scale ship flows with wall roughness and pressure gradient effects. The wall-function model is validated for smooth flat-plate flows at Reynolds numbers up to 109, and it is applied to the Athena R/V for resistance, propulsion, and seakeeping calculations and to fully appended DTMB 5415 for a maneuvering simulation. Resistance predictions for Athena bare hull with skeg at the model scale compare well with the near-wall turbulence model results and experimental fluid dynamics (EFD) data. For full-scale simulations, frictional resistance coefficient predictions using smooth wall are in good agreement with the International Towing Tank Conference (ITTC) line. Rough-wall simulations show higher frictional and total resistance coefficients, where the former is found to be in good agreement with the ITTC correlation allowance. Self-propelled simulations for the fully appended Athena performed at full scale using rough-wall conditions compare well with full-scale data extrapolated from model-scale measurements using the ITTC ship-model correlation line including a correlation allowance. Full-scale computations are performed for the towed fully appended Athena free to sink and trim and the boundary layer and wake profiles are compared with full-scale EFD data. Rough-wall results are found to be in better agree-ment with the EFD data than the smooth-wall results. Seakeeping calculations are performed for the demonstration purpose at both model-and full-scale. Maneuvering calculation shows slightly more efficient rudder action, lower heading angle overshoots, and lower roll damping for full-scale than shown by the model scale.

Wear behavior of plasma and HVOF sprayed WC-12Co + 6% ETFE coatings on AA2024-T6 aluminum alloy

In this study, WC-12Co + 6% ethylene trifluoroethylene (ETFE) coatings were formed on the surface of an AA2024-T6 aluminum alloy using both plasma spray and high velocity oxygen fuel (HVOF) processes. The characterization of the coatings was made by microscopic examinations, thickness, porosity, contact angle and hardness measurements and X-ray diffraction (XRD) analysis. The coefficient of friction and wear resistance of coatings were obtained using a reciprocating wear tester by rubbing a 10 mm diameter Al 2O 3 ball on the coatings in dry and acid environments. It was observed that the WC-12Co + 6% ETFE coating sprayed using HVOF method exhibited higher hardness and contact angle, better tribological performance and higher amount of retained WC when compared to the plasma sprayed WC-12Co + 6% ETFE coating. The wear resistance of the HVOF sprayed WC-12Co + 6% ETFE coating tested in acid environment was almost one and a half times bigger than that of dry sliding condition, but the plasma sprayed WC-12Co + 6% ETFE coating tested in acid environment showed a lower wear resistance when compared to the result of the experiment performed on dry sliding condition.

Fracturing control method for deep volcanic rock gas reservoirs in Daqing exploration area

Abstract Pores, cavities and fractures are well-developed in deep volcanic reservoirs. The simultaneous break and extension of multi-fractures in treatment caused early stage sand-block, low fracturing success ratios, small treatment scales, and bad stimulation results. Based on the geologic characteristics of the deep volcanic rocks, this paper establishes a fracturing break and extension model of volcanic rocks, introducing with time-relevant leaking factor, peak factor and modulus factor. The model is used to better describe the process of initiation and extension of major fractures and micro-fractures. On this basis, the evaluating method for the “three highs” of pump off pressure gradient, near well friction resistance and leakoff coefficient is studied, and through field practices, integrated processing measures are formed: use rubber plugging to deal with near-well high friction resistances, use silts to seal natural fractures, adjust prepad fluid ratios, and inject multi-section silt slugs. The success ratio of volcanic rock gas reservoir fracturing is raised to 90.0% from the past 36.0%.

Corrosion and tribological behaviors of chromium oxide coatings prepared by the glow-discharge plasma technique

In order to improve the corrosion and tribological properties of steel, chromium oxide coatings were prepared by a new combined process, namely, chromizing and plasma oxidizing treatments using double glow plasma technology under various oxygen flow rates. The composition and microstructure of the coatings were analyzed respectively by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results indicated that the oxygen flow rates had a great effect on the surface structure of the prepared Cr 2O 3 coatings, and dense and smooth Cr 2O 3 coatings were prepared at the oxygen flow rate of 10 sccm. The Cr 2O 3 coatings exhibited the better corrosion resistance which was in good agreement with the results obtained by the microstructure studied. Further mechanical properties test showed that the Cr 2O 3 coatings with high hardness and elastic modulus adhered well to the steel substrates and displayed excellent wear resistance and low coefficient of friction under dry sliding wear test conditions. The wear mechanism was mostly dominated by the “soft abrasion”.

Nanotribological Characteristics of Cu6Sn5, Cu3Sn, and Ni3Sn4 Intermetallic Compounds

Nanotribological characteristics, including the coefficient of friction, wear coefficient, and wear resistance, of Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 intermetallic compounds developed by the annealing of Sn-Cu or Sn-Ni diffusion couples were investigated in this work. The scratch test conditions combined a constant normal load of 10 mN, 20 mN, or 30 mN and a scratch rate of 0.1 μm/s, 1 μm/s, or 10 μm/s. Experimental results indicated that, as the normal load increases, the pile-up grows taller and the scratch deepens, leading to a greater coefficient of friction and wear coefficient, and reduced wear resistance. Moreover, the scratch rate does not have a significant effect on the nanotribological characteristics except for those of Cu 6 Sn 5 and Cu 3 Sn under a normal load of 10 mN. Though the hardness of Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 is similar, Ni 3 Sn 4 appears to be more prone to wear damage.

Numerical study on scale effect of form factor

The scale effect of form factor is investigated via a numerical approach in this paper, where the turbulent ship flow is computed by solving the steady and incompressible Reynolds-averaged Navier–Stokes and continuity equations. A wall function approach is employed to bridge the near-wall and outer turbulent flow region. The numerical scheme based on a finite-volume formulation is applied to discretize the coupled governing equation. For the sake of numerical stability, accuracy and economy, an identical grid is employed to compute ship flow at different Reynolds number, where the grid is optimized for the medium Reynolds number of the investigated range. Four surface ships and two sub-bodies with notably different geometrical characteristics are chosen as the investigated cases, where double-model flow without appendages is computed. The calculated total resistance coefficient shows a decreasing tendency against Reynolds number among all studied hulls. Similar to the calculated total resistance coefficient, the calculated friction resistance coefficient decreases with the Reynolds number and varies relatively little for a given Reynolds number among different hulls. The viscous pressure resistance coefficient is less insensitive to the Reynolds number but apparently depends on hull form. Compared with the form factor calculation based on empirical friction lines, the flat-plate friction prediction based on CFD approach clearly gives smaller Re-dependent form factor, which should more realistically reflect the scale effect of form factor. The form factor exhibits a near linear and increasing dependence on Reynolds number. The numerical results show that the dependence of r P on Reynolds number mainly governs the scale effect of form factor.

Abrasion of abutment screw coated with TiN

STATEMENT OF PROBLEMScrew loosening has been a common complication and still reported frequently.PURPOSEThe purpose of this study was to evaluate abrasion of the implant fixture and TiN coated abutment screw after repeated delivery and removal with universal measuring microscope.MATERIAL AND METHODSImplant systems used for this study were Osstem and 3i. Seven pairs of implant fixtures, abutments and abutment screws for each system were selected and all the fixtures were perpendicularly mounted in liquid unsaturated polyesther with dental surveyor. After 20 times of repeated closing and opening test, the evaluation for the change of inner surface of implant and TiN-coated abutment screw, and weight loss were measured. Mann-Whitney test with SPSS statistical software for Window was applied to analyze the measurement of weight loss.RESULTSTiN-coated abutment screws of Osstem and 3i showed lesser loss of weight than non-coated those of Osstem and 3i (P < .05, Mann-Whitney test).CONCLUSIONConclusively, TiN coating of abutment screw showed better resistance to abrasion than titanium abutment screw. It was concluded that TiN coating of abutment screw would reduce the loss of preload with good abrasion resistance and low coefficient of friction, and help to maintain screw joint stability.

Poly(vinyl alcohol)–acrylamide hydrogels as load-bearing cartilage substitute

Poly(vinyl alcohol) (PVA) has been advanced as a biomaterial for the fabrication of medical devices to be used as synthetic articular cartilage because of its viscoelastic nature, high water content, and biocompatibility. Key material requirements for such devices are high creep resistance to prevent mechanical instability in the joint and high water content to maintain a lubricious surface to minimize wear and damage of the cartilage counterface during articulation. The creep resistance of PVA hydrogels can be increased by high temperature annealing; however this process also collapses the pores, reducing the water content and consequently reducing the lubricity of the hydrogel surface [Bodugoz-Senturk H, Choi J, Oral E, Kung JH, Macias CE, Braithwaite G, et al. The effect of polyethylene glycol on the stability of pores in polyvinyl alcohol hydrogels during annealing. Biomaterials 2008;29(2):141–9.]. We hypothesized that polymerizing acrylamide (AAm) in the pores of the PVA hydrogel would minimize the loss of lubricity during annealing by preventing the collapse of the pores and loss of water content. Increasing AAm content increased porosity and equilibrium water content and decreased the coefficient of friction, tear strength, crystallinity, and creep resistance in annealed PVA hydrogels.

Ultra Starvation Studied in the Spiral Orbit Tribometer

Spiral orbit tribometry has been used to study the coefficient of friction and electrical contact resistance of two vacuum lubricants in both the flooded system and the regime in which only a few nanoliters (μ g) of the lubricant are present, and the latter regime is designated here as ultrastarved. The experiment was supported by the extension to the ultrastarved regime of the recent analysis by Cann and coworkers of contact film thickness as a function of the lubricant volume in the heavily starved regime. The coefficients of friction in the ultrastarved regime were found to be the same as for the flooded system. The contact resistance was found to be zero at the beginning of the tests in the ultrastarved regime. The analysis by Cann and coworkers predicts the absence of a mobile liquid film at the contact in the ultrastarved regime. It is speculated that this persistence of lubrication into the ultrastarved regime is due to the retention of adherent lubricant molecules on the contacting surfaces and the sliding of these molecules over each other. An incomplete coverage of these molecules permits zero contact resistance at the start of the test. The results indicate that ball bearings can operate normally in the ultrastarved regime until the lubricant is consumed by tribochemical reaction.

Development and performance analysis of novel cast copper–SiC–Gr hybrid composites

Copper based composites having hard reinforcements like alumina, silicon carbide and cerium oxide possess higher strength, better wear resistance and higher coefficient of friction when compared to copper. However, they pose machining issues such as higher tool wear and rough surface finish. Conversely, copper composites with soft dispersoids such as graphite and molybdenum disulphide exhibit lower coefficient of friction and better machinability characteristics. Hence an attempt is made to develop a new class of copper based composite material by dispersing both hard and soft reinforcement in appropriate proportions to ensure optimum tribological characteristics. The present investigation deals with the development of copper–SiC–Gr hybrid composites by liquid metallurgy route. Metallographic study, microhardness, tensile strength, friction and wear tests have been conducted. The results show that the hybrid composites possess higher hardness, higher tensile strength, better wear resistance and lower coefficient of friction when compared to pure copper.

The numerical friction line

This paper presents a study on the numerical calculation of the friction resistance coefficient of an infinitely thin plate as a function of the Reynolds number. Seven eddy-viscosity models have been selected: the one-equation turbulence models of Menter and Spalart–Allmaras; the k-ω two-equation model proposed by Wilcox and its TNT, BSL and SST variants and the $$ k \text{-}\!\sqrt k L $$ two-equation model. The flow has been computed at 14 Reynolds numbers in sets of seven geometrically similar Cartesian grids to allow a reliable estimation of the numerical uncertainty. The effect of the computational domain size has been reduced to negligible levels (below the numerical uncertainty). And the same holds for the iterative and round-off errors. In the finest grids of each set, the numerical uncertainty of the friction resistance coefficient is always below 1%. Special attention has further been given to the solution behaviour in the laminar-to-turbulent transition region. Curve fits have been applied to the data obtained at the 14 Reynolds numbers and the numerical friction lines are compared with four proposals from the open literature: the 1957 ITTC line, the Schoenherr line and the lines suggested by Grigson and Katsui et al. The differences between the numerical friction lines obtained with the seven turbulence models are smaller than the differences between the four lines proposed in the open literature.

On the numerical accuracy of the prediction of resistance coefficients in ship stern flow calculations

This article presents a study on the accuracy of the numerical determination of the friction and pressure resistance coefficients of ship hulls. The investigation was carried out for the KVLCC2 tanker at model- and full-scale Reynolds numbers. Gravity waves were neglected, i.e., we adopted the so-called double-model flow. Single-block grids with H–O topology were adopted for all the calculations. Three eddy viscosity models were employed: the one-equation eddy viscosity and the two-equation \( k \text{-}\!\sqrt k L \) models proposed by Menter and the TNT version of the two-equation k-ω model. Verification exercises were performed in sets of nearly geometrically similar grids with different densities in the streamwise, normal, and girthwise directions. The friction and pressure resistance coefficients were calculated for different levels of the iterative error and for computational domains of different size. The results show that on the level of grid refinement used, it is possible to calculate the viscous resistance coefficients in H–O grids that do not match the ship contour with a numerical uncertainty of less than 1%. The differences between the predictions of different turbulence models were larger than the numerical uncertainty; however, these differences tended to decrease with increases in the Reynolds number. The pressure resistance was remarkably sensitive to domain size and far-field boundary conditions. Either a large domain or the application of a viscous–inviscid interaction procedure is needed for reliable results.