Reduction In Frictional Resistance Research Articles

Friction behaviors and flow resistances of rock-ice avalanches

Rock-ice avalanches have high mobility and enormous destructive potential. However, the friction behaviors and flow resistance during the transition of flow regimes of the rock-ice avalanche remains an unsolved problem. Based on a series of measurements of normal, shear stress and pore water pressure at the rotating drum in a temperature-controllable laboratory, we quantify the influence of the ice content, particle size, drum velocity, and meltwater on the friction behaviors. The findings reveal that ice acts as a low-friction particle, leading to a significant reduction in frictional resistance of both particle-particle and particle-base. Furthermore, meltwater lubricates the particles and provides buoyancy, which also increases the mobility of the rock-ice avalanche. In addition, the augmentation of flow resistance is attributed to the increased particle size and drum velocity, thereby intensifying shear motion. In order to propose an unify theoretical model to calculate the flow resistance of rock-ice avalanche in various flow regimes. A heuristic model that relies on the extended dynamics theory is modified and can be well described the flow resistance of the tests involved in this paper. This study in the friction behaviors and flow resistance depending on the internal/external factors may be considered in hazard assessments of rock-ice avalanches in cold high-mountain regions.

Surface-tension change of graphene-based water nanofluid and its effects on heat-transfer process

Nanofluids with high thermal conductivities are gaining attention for heat-exchange applications, particularly in boiling processes. Nanofluid heat-transfer efficiency is significantly influenced by the surface tension (ST) and wettability patterns of the nanofluid. This study investigated graphene-based water nanofluids prepared from three different viscoelastic polymer solutions. The effects of the dispersant, graphene concentration, and temperature on the ST were investigated, and the wetting behavior of nanofluids on stainless steel and polypropylene random surfaces was determined. The results indicated that the ST of the nanofluids exhibited a negative correlation with the dispersant concentration and temperature. Additionally, the inclusion of graphene reduced the ST in xanthan-gum systems but increased it in sodium carboxymethyl cellulose and polyethylene-oxide systems. Overall, the nanofluids exhibited a lower ST than water. The decrease in the nanofluid ST is ascribed to the development of a rigid network resulting from the co-adsorption of graphene nanoparticles and the dispersant at the gas–liquid interface. Furthermore, graphene has been demonstrated to enhance the wettability of the base fluids of various materials. A decrease in ST led to increased frictional resistance; however, this was counteracted by an increase in the contact angle, resulting in an overall reduction in frictional resistance. Moreover, reducing the ST can improve the fluid boiling heat transfer. Therefore, these nanofluids exhibited the dual effect of reduced flow resistance and enhanced heat-transfer efficiency. This study offers valuable insights into the behavior of nanofluids and their potential applications in areas such as energy storage and spacecraft thermal management.

Sand-Carrying Law and Influencing Factors in Complex Fractures of Nano-Clean Fracturing Fluid

Nano-clean fracturing fluids have broad application potential in coalbed methane reservoir fracturing owing to their high stability, good temperature resistance, low filtration loss, and strong frictional resistance reduction. However, the sand-carrying regularity of nano-clean fracturing fluids in coalbed methane reservoirs is unclear, especially for complex fractures with variable directions. This study established a sand transport model that considers proppant collision, wall friction blocking, fracture fluid filtration loss, and the fracture branching angle to study the sand-carrying law of nano-clean fracturing fluids and its influencing factors in complex fractures. The degrees of influence on equilibrium height and placement rate from high to low were the proppant particle size, proppant density, fracturing fluid properties, sand ratio, and pumping discharge volume, and the correlation degrees obtained by grey correlation analysis are 0.862, 0.861, 0.855, 0.854, and 0.832, respectively. As the complexity of the fractures deepens and the resistance increases, the flow rate of the fracturing fluid is reduced, making it difficult for the proppant to enter the branching joints. The sand-carrying performance of a nano-clean fracturing fluid is better than that of a common clear-water fracturing fluid. The fluid-structure coupling model of a nano-clean fracturing fluid can accurately characterize the sand-carrying law of nano-clean fracturing fluids, providing a research basis for optimizing high efficiency sand-carrying fracturing fluid parameters in coalbed methane reservoir fracturing construction.

Study on the drag reduction performance of high-temperature exhaust pipe by spray cooling

The drag of the exhaust pipe greatly influences the engine power performance of an engineering vehicle. The engine power performance would decrease significantly when the exhaust drag is large. The drag reduction effect achieved by the existing drag reduction is relatively weak; thus, based on spray cooling, drag reduction technology is introduced to solve this problem. The present study aims to determine the influence of spray parameters on drag reduction using an electric heating test bench and to clarify why spray significantly reduces drag using numerical simulations based on Discrete Phase Modeling (DPM). The obtained results prove that increasing the flow value in the test spray flow range of 12–24 ml/s can significantly improve the drag reduction performance. When the spray inclination increases from 45° to 90°, the drag reduction remains, in the beginning, unchanged and then decreases. Under the synergistic effect of the frictional resistance reduction and the dynamic pressure reduction, the resistance downstream of the spray location is significantly reduced. Compared with the existing drag reduction, the spray drag reduction has obtained the ultimate drag reduction effect, and the drag reduction rate is as high as 90 %. To conclude, this research will help promote the application of spray drag reduction to engineering vehicles.

Study on the Influence of Excavation Unloading on Pile Depth in Sandy Soil

With the development of urban construction, uplift pile has been widely used in underground structure bearing buoyancy. The pile is buried deep underground, and the foundation pit is excavated on the pile foundation, the stress redistribution of the soil after the foundation pit excavation will reduce the lateral stress of the pile at the bottom of the pit, resulting in the reduction of friction resistance, but this effect is limited to a certain depth at the bottom of the foundation pit. Referring to the unloading influence depth corresponding to the vertical unloading coefficient in the spring back calculation of foundation pit and introducing the unloading influence depth corresponding to the horizontal unloading coefficient, it is deduced that the relationship between the horizontal unloading coefficient and the vertical unloading coefficient is based on the friction angle. Based on the bearing capacity control and numerical simulation, it is determined that the corresponding depth when the horizontal unloading coefficient is 0.95 is the unloading influence depth. The depth to width ratio of excavation has a great influence on unloading influence depth, and the internal friction angle of soil has little influence on unloading influence depth, while the influences of pile diameter and pile-soil friction coefficient can be ignored. The formula of unloading influence depth is derived in this paper. Comparing the unloading influence depth of sand and soft soil, the unloading influence depth of sand is greater than that of soft soil.

Numerical investigations of micro bubble drag reduction effect for container ships

In the course of the most recent decades reduction of ship resistance and saving fuel consumption to accomplish higher speed with reduction of pollutants has been the significant subject for researchers. Micro bubble drag reduction technique is one of the most interesting thoughts in this field owing to its great advantages, such as considerable potential drag reduction, easy operations, environmental friendliness and low costs. In this study a 3-D numerical investigation into frictional drag reduction by air micro bubbles is applied on KRISO container ship model. The objective is to understand the mechanism of resistance reduction through micro bubbles injection under model ship at different Froude numbers, injection rate and of course volume fractions. The numerical simulations are performed using a commercial CFD code solving Reynolds averaged Navier–Stokes (RANS) equations. A large number of simulations has been performed to investigate the effect of injection of micro bubble under ship model hull to estimate the local coefficient of friction values along ship hull model. The results show that at all of the examined Froude’s numbers, frictional resistance reduction attained at different rates and a maximum drag reduction of 27.6% was obtained at 0.282 Froude number with 4.8% air volume fraction.

The Efficiency of UV Picosecond Laser Processing in the Shaping of Surface Structures on Elastomers.

Elastomers are used as construction materials in numerous industries, and in particular the biomedical industry, mechatronics, electronics, the automotive industry, and chemical devices. The paper presents the results of tests involving the effects of microprocessing of elastomeric materials using a UV laser emitting picosecond pulses. In particular, it presents an analysis of the influence of the parameters of processing on its efficiency. The paper provides a recommendation of the most advantageous processing parameters for materials such as polyurethane and silicone (MVQ). The authors see prospects for the use of the developed technology in the techniques of sealing and microfluidisation. The final part of the paper presents examples of surface structures generated on elements made of artificial materials and the results of tests involving reduction of friction resistance of sealing rings in a pneumatic actuator.

Study on the effect of laser-assisted machining on tool wear based on molecular dynamics simulation

During the nanometric cutting of single crystal silicon, the wear of the diamond tool is rapid. Despite laser-assisted machining (LAM) has been used to mitigate tool wear, the specific mechanism is not clear. In this paper, molecular dynamics simulations have been successfully used to explain the effect of LAM on tool wear. The long-range carbon bond order potential (LCBOP) is used to describe the interaction of atoms in the diamond tool. The simulation results show that it has the ability to accurately simulate the graphitization of diamond. LAM enhances ductile response of silicon and reduces the cutting force. But only at the appropriate laser power, LAM will inhibit the formation of silicon carbide and mitigate tool wear. The effect of laser power on the tool rake face and clearance face is different. When the laser power is about 50 eV/ps, the wear of tool clearance face is significantly suppressed, which is attributed to the reduction of frictional resistance. When the laser power is about 150 eV/ps, the reduction in cutting forces and silicon carbide results in smaller tool wear of the rake face. At other laser powers, a large increase in chip temperature may promote tool wear to some extent. Therefore, proper laser power is necessary during LAM.

EFFECT OF THE PLASTIC STRAIN AND DRAWING QUALITY ON THE FRICTIONAL RESISTANCE OF STEEL SHEETS

The aim of the research presented in this article is to investigate the frictional resistance of steel sheets with different drawing quality. Friction tests have been carried out using the bending under tension (BUT) test which simulates the contact conditions at the rounded edges of the punch and die in sheet metal forming operations. The effect of sheet deformation and temper state on the value of the coefficient of friction has been studied. It was found that increasing the value of elongation of the sheet is associated with an increase in the value of the COF for both friction conditions analysed. The intensity of work hardening, by changing the mechanical properties of the sheet, is a factor that changes contact conditions. The lubricant which is typically used in plastic working provided a reduction of frictional resistance by approximately 3.6-14%, depending on the degree of sheet deformation.

旋回流式マイクロバブル発生器の性能向上（テーパ型渦流室出口形状による微細化効果）

Recently, the micro bubble with bubble diameter of less than 50μm is paid to attention. As for this micro bubble, various characteristics that bubble with diameter of several mm doesn’t have are possessed. For instance, water purification, oil separating, growth promotion of creature, and reduction of frictional resistance are reported. The swirl type method, the pressurizing dissolution method, and the perforated plate method, etc. are proposed as the method for generation of micro bubble. The swirl type method can comparatively generate the micro bubble even by low-pressure power in simple structure. In this present study, the effect of shape of swirl chamber on bubble diameter was examined by using the three kinds of shape of swirl type micro bubble generators, which were cylindrical type, taper type, and improved taper type. As a result, it was found to be able to reduce the bubble diameter in the order of improved taper type, taper type, and cylindrical type. And it was clarified that radial outflow type generator could make bubble diameter small compared with axial outflow type generator, and the optimum nozzle shape was the nozzle with inlet angle of 45 degrees, outlet angle of 60 degrees, and nozzle diameter of 3mm. Moreover, it was found that the average bubble diameter of 30μm was obtained under pressure condition of 0.22MPaG in the above-mentioned nozzle shape.

マイクロバブルを利用した液滴の微粒化（気泡径とボイド率が液滴径に及ぼす影響）

The atomization technology of liquid is applied to a lot of fields like internal combustion engine, agriculture, chemistry, food, and medical supply, etc. now, and the important technology for solving the problems of environmental problems and energy conservation. In recent years, a micro bubble with diameter of tens of μm or less is paid to attention. As for this micro bubble, various characteristics that bubble with diameter of several mm doesn't have are possessed and, for instance, water purification, oil separating, growth promotion of creature, and reduction of frictional resistance are reported. In this study, it was examined whether making a further water drop minute was possible by mixing micro bubbles into water using a whirl type injection valve. Moreover, the influences of micro bubble diameter and void fraction on water drop diameter were examined. As a result, in low-pressure of atomizing pressure Ps=0.2MPaG, the maximum 32% effect of atomization was able to be achieved by mixing micro bubbles into water. Moreover, it was clarified that the effects of atomization were almost the same in 0.1% or more of void fraction.

Influence of boron nitride nano additives in cutting fluid for improving surface roughness with MRR

Surface quality is the essential requirement of industrial sector which depends on the certain machining parameters such as surface roughness, material removal rate and indirectly on frictional resistance and heat transfer characteristics during machining. Selection of cutting fluids enables the reduction of frictional resistance and heat generation between tool and work. At present, quality and machining characteristics of cutting fluids attain better focus to improve the surface finish using blends and additives, obviously nano additives are assumed to be a possible solution in betterment of machining outcome. Present work discusses the preparation of nano cutting fluids using boron nitride, characteristics and influence on machining parameters such as material removal rate, tool life particularly surface quality in surface grinding operation. The output results revealed that addition of boron nitride particles is providing greater surface finish when compared to the conventional cutting fluids.

Comparative Evaluation of Frictional Resistance of Silver-Coated Stainless Steel Wires with Uncoated Stainless Steel Wires: An In vitro Study.

Background:Silver is known for its antimicrobial activity. Silver coating effectively reduces Lactobacillus acidophilus and Streptococcus mutans count, thus reducing chances of dental plaque and caries. This silver coating may have effect on frictional property of orthodontic wires.Aim:The aim of this study is to evaluate and compare frictional resistance of silver-coated and uncoated stainless steel (SS) wires.Methods:Forty SS wires were divided into four groups of 10 each: Group 1 – 0.017 × 0.025 inch SS wires (silver coated), Group 2 – 0.017 × 0.025 inch SS wires (control), Group 3 – 0.019 × 0.025 inch SS wires (silver coated), and Group 4 – 0.019 × 0.025 inch SS wires (control). Surface modification of wires was carried out by the thermal vacuum evaporation method with silver (10 nm size) using vacuum-coating unit model. The frictional resistances of all forty wires were checked on forty 0.022 × 0.028 inch slot central incisor brackets (SS wires and brackets from American Orthodontics, St Paul, USA) mounted on metal plates using universal testing machine.Results:There was no significant difference found in frictional resistance between silver-coated and uncoated 0.017 × 0.025 inch SS wires group (P = 0.854). Statistically significant reduction in frictional resistance was observed in 0.019 × 0.025 inch coated SS wires in comparison to uncoated wires (P = 0.032).Conclusion:Overall silver coating either did not affect the frictional resistance (0.017 × 0.025 inch SS wires) or reduced it (0.019 × 0.025 inch coated SS wires) compared to uncoated wires. Findings suggest that the use of silver-coated SS wires in routine orthodontic practice can be implemented after further in vivo human clinical trials.

상사축척법에 기반한 저마찰 선박 방오도료의 실선 마찰저항 저감성능 추정

상사축척법에 기반한 저마찰 선박 방오도료의 실선 마찰저항 저감성능 추정

Resistance reduction on trimaran ship model by biopolymer of eel slime

Resistance reduction in ship becomes an important issue to be investigated. Energy consumption and its efficiency are related toward drag reduction. Drag reduction in fluid flow can be obtained by providing polymer additives, coating, surfactants, fiber and special roughness on the surface hull. Fish skin surface coated with biopolymers viscous fluid (slime) is one method in frictional resistance reduction. The aim of this is to understanding the effect of drag reduction using eel slime biopolymer in unsymmetrical trimaran ship model. The Investigation was conducted using towing tank test with variation of velocity. The dimension of trimaran model are L = 2 m, B = 0.20 m and T = 0.065 m. The ship model resistance was precisely measured by a load cell transducer. The comparison of resistance on trimaran ship model coated and uncoated by eel slime are shown on the graph as a function of the total drag coefficient and Froude number. It is discovered the trimaran ship model by eel slime has higher drag reduction compared to trimaran with no eel slime at similar displacement. The result shows the drag reduction about 11 % at Fr 0.35.

Air Lubrication Influence on Frictional Resistance Reduction of Multi-Purpose Amphibious Vehicle

The presentarticle focuses on the hydrodynamic resistance reduction of Multipurpose Amphibious Vehicles (MAV) usingthe air lubrication layer effect. The use of air cushions to support marine vehicles, heavy floating structures and in other operation is well known. The main problem in Multi-purpose Amphibious Vehicles (MAV) is the amount of power needed in order to overcome the hydrodynamic resistance acting on the hull which is included the frictional and pressure resistances. Therefore, more power is needed to move the MAV forward. In this respect, more fuel will be required to operate the amphibious vehicles. This problem could be effectively reduced by the introduction of the air cushion concept. With the air being drawn from top of craft to the cavity below the hull will produce some cushioning effect and also help to reduce skin friction drag. In this paper, air cushion effect will be studied in rigid surface cavity instead of using flexible skirts. This would avoid the problem of high maintenance due to replacement of damaged skirts. Finally, the MAV will be supported using air cavity and bubbles generated by an air pump (compressor and air pressure vessel) to pushes the hull of multi-purpose amphibious vehicle up and reduce the frictional resistance due to draft and wetted surface reduction and layer of air between hull surface and water. This research would be done via CFD (ANSYS-CFX 14.0) and analyzed the hydrodynamic resistance.

Experimental investigation of frictional resistance reduction with air layer on the hull bottom of a ship

In an effort to cope with recent high oil price and global warming, developments of air lubricated ships have been pursued to reduce greenhouse gas emissions and to save fuel costs by reducing the frictional resistance. In this study, reduction in the frictional resistance by air lubrication with air layers generated on the lower surface of a flat plate was investigated experimentally in the large water tunnel of SSMB. The generated air layers were observed, and changes in the local frictional drag were measured at various flow rates of injected air. The results indicated that air lubrication with air layers might be useful in reducing the frictional resistance at specific conditions of air injection. Accordingly, resistance and self-propulsion tests for a 66K DWT bulk carrier were carried out in the towing tank of SSMB to estimate the expected net power savings.

低摩擦型船底防汚塗料の実船評価 - 船底防汚塗料の低摩擦化への挑戦

低摩擦型船底防汚塗料の実船評価 - 船底防汚塗料の低摩擦化への挑戦

Assessment of phosphorus retention in irrigation laterals

Irrigation laterals transport irrigation return flow, including water, sediment, and dissolved nutrients, such as phosphorus (P), back to surface water bodies. Phosphorus transformations during transport can affect both P bioavailability and the best management practices selected to minimize P inputs to waters of the United States. The objective of this study was to determine P retention in three irrigation laterals. Soluble reactive P (SRP) concentrations in lateral waters were increased from 0.08 to 0.25 mg L⁻¹ (0.08 to 0.25 ppm) by constantly injecting a phosphate (PO₄) solution for 2.5 hours. Bromide (Br) was used as a conservative tracer to determine dilution effects. Water was sampled at 10-minute intervals, beginning 30 minutes prior to injection and 120 minutes following injection, at one upstream location and various downstream locations to approximately 1,550 m (~1 mi) from injection sites. When at steady state, SRP concentrations only decreased by 5% over the lengths studied, equating to P uptake lengths of over 18 km (11.2 mi), which was one to two orders of magnitude greater than natural streams; the linear SRP uptake rate was 0.011 mg L⁻¹ km⁻¹ (0.018 ppm mi⁻¹). Longer P uptake lengths and lower uptake rates in irrigation laterals, as compared to natural streams, may be due to the elevated sediment equilibrium P concentration, greater water velocities, and removal of vegetation causing a reduction in frictional resistance. Reducing water velocities should optimize irrigation lateral conditions to reduce uptake length and maximize P uptake.

The peeling behaviour of a graphene sheet on a nano-scale corrugated surface

The peeling process and average peeling force of a graphene (GE) sheet on a corrugated surface are investigated using molecular dynamics simulation. It is found that the peeling behaviour varies with the substrate surface roughness and the peeling angle. Three kinds of typically peeling behaviours include (a) GE sheet directly passing the valley of the substrate roughness; (b) bouncing off from the substrate; and (c) continuously peeling off similarly to that on a flat substrate. As a result, the average peeling force is strongly dependent of the peeling behaviours. Furthermore, some interesting phenomena are caught, such as partial detaching and partial sliding of GE sheet in the valley of the substrate roughness, which are mainly due to the effects of pre-tension in GE sheet and the reduction of friction resistance. The results in this paper should be useful for the design of nano-film/substrate systems.