Liquid Friction Research Articles

Simulation Analysis of Nonlinear Friction of Rod String in Sucker Rod Pumping System

The nonlinear friction of rod string is an important foundation of dynamic simulation and efficiency optimization in sucker rod pumping system (SRPS). As we know, there are geometrical nonlinearity and contact nonlinearity of rod string in special oil well. Considering the earlier practical problems, a novel computational method of nonlinear friction of rod string is given. First, the simulation model of nonlinear friction is built. In the detail, the nonlinear friction of sucker rod string is made up of four parts: the viscous damping friction of rod surface, the viscous damping friction of rod coupling, liquid friction of centralizer, and the nonlinear Coulomb friction between rod and tube. Second, considering the rheology property of multiphase fluid in annular space, a simulation method of fluid pressure is proposed with software ansys. Based on earlier models, a numerical simulation model of nonlinear friction of rod string is built with visualbasic 6.0. Comparing experiment results with simulated results, good agreement is found, which shows the simulation model is feasible. The characteristics of fluid pressure and pressure gradient are analyzed. The instantaneous friction of rod string is simulated, and the sensitive factors of rod friction are analyzed. The novel simulation method solves the problem of environmental load calculation of large deformation rod. The analysis results have an important significance to guidance of optimization and design of SRPS.

Solid–Liquid Triboelectrification Control and Antistatic Materials Design Based on Interface Wettability Control

AbstractSolid–liquid contact triboelectrification has been a hot and important topic due to its severe electrostatic hazards in the petroleum industry and its positive potential application in energy harvesting. Here, the influence of surface structure, composition, and interfacial wettability on the solid–liquid triboelectrification basing on the friction of polypropylene (PP) films and deionized water is systematically studied. PP films with different nanowire structures are prepared by a hot pressing method with varied anodic aluminum oxide as templates. The PP films are surface functionalized with three different functional groups by a surface self‐assembly technology. The results show that compared with the surface structure, the solid–liquid triboelectrification is more sensitive to the surface components. While from the macroscopic view the interfacial wettability plays a dominant role in its electrical output, with the failure of the hydrophobic surface of the PP film, the triboelectrical output continues to deteriorate. Moreover, the increase or decrease of solid–liquid triboelectrification can be achieved by controlling the structure or composition. This study demonstrates the possibility of adjusting the solid–liquid contact electrification in a controllable manner and provides a basis for the utilization or the prevention of solid–liquid friction charges.

Estimation of probability Density Functions for model input parameters using inverse uncertainty quantification with bias terms

The documentation of most nuclear thermal-hydraulics codes does not provide sufficient information on uncertainty of physical models (e.g. interfacial heat transfer coefficients). These models were derived based on experimental data and implemented as empirical correlations in the computational code. The uncertainty quantification for the relevant output quantity (e.g. Peak Cladding Temperature) requires estimation of the Probability Density Functions (PDFs) of the code inputs, such as physical models. In this paper, we investigate the effect of boundary conditions (outlet pressure, inlet liquid temperature, and inlet flow rate) on the uncertainty of two physical models (the interfacial friction coefficient and the wall to liquid friction coefficient). The boundary conditions effect was accounted for by adding a bias term to the mathematical framework of two existing methods for Inverse Uncertainty Quantification (IUQ): the Maximum Likelihood Estimation (MLE) method and the Maximum A Posterior (MAP) method. The two methods were demonstrated using the BFBT benchmark, experimental data was compared to code predictions of the RSTART thermal-hydraulics code for two different cases: without and with bias term. The results show an evident improvement in code prediction when the bias term is used. Finally, a validation set of experimental data was used to investigate the possibility of data overfitting, and the proposed methodology showed absence of overfitting when bias terms are used.

Effect of mesh refinement on the estimation of model input parameters using Inverse Uncertainty Quantification

Proper quantification of the uncertainties in the input parameters of a thermal-hydraulics code (e.g. physical models) is an essential part of the forward Uncertainty Quantification (UQ) problem. Such quantification can be systematically achieved by solving the Inverse Uncertainty Quantification (IUQ) problem using data from code predictions and experimental measurements. The IUQ problem is highly dependent on several factors such as geometry and discretization. In this paper, we study the effect of mesh refinement on the statistical parameters of three uncertain physical models (interfacial friction coefficient, wall to liquid friction coefficient and critical heat flux). A mathematical framework based on MLE and MAP algorithms is implemented to perform IUQ for the physical models of the thermal-hydraulics code RSTART based on experimental data from the OECD/NEA BWR Full-size Fine-mesh Bundle Test (BFBT) benchmark. Sensitivity analysis required for the IUQ problem was achieved by implementing discrete adjoint methods in the thermal-hydraulics code. The statistical parameters of the three physical models were obtained by implementing the MLE and MAP methods using code predictions that correspond to three different mesh sizes. Results from MLE and MAP showed a noticeable effect of mesh refinement on the estimates of the mean and a negligible effect on the estimates of the variance of the physical models. The compensation of error due to mesh refinement was studied by running the code with perturbation values calculated using the three different mesh sizes. It was shown that the results based on the most refined mesh led to best agreement between experimental data and code prediction.

Influence of additives on the friction and wear reduction of oil-based drilling fluid

In comparison to conventional vertical hole drilling, extended reach drilling wells with long horizontal section require higher driving torque due to the increased drag on the drill string, drill column, casing and other equipment. This has led to higher friction and wear on the drilling equipment. Friction and wear preventive properties of oil-based drilling fluid is therefore important to keep oil extraction economical and sustainable. The addition of small concentrations of hydrocarbon additives to drilling fluid has shown significant positive effects on these properties. In this study, improvements in friction and wear properties of drilling fluid with the use of friction reduction additives was analyzed using a four-ball experimental configuration. Experiments resulted in wear in boundary and mixed lubrication regimes due to significant metal-metal interaction. The results showed that liquid friction reduction additives with long hydrocarbon tails and high metal affinity polar heads achieved better performance than additives that contained molybdenum dialkyldithiocarbamate. Energy dispersive spectroscopy results indicated lower levels of salts and corrosive chemicals on the surface of the wear scars for the best preforming additives.

Tendencies in the field of application of metal-powder materials for repair and maintenance of railway equipment

Logistics strategy in railway transport provides for a comprehensive solution of four tasks: technical, technological, economic and management. At the same time the technical task is one of the most important, because it ensures reliability of the equipment, an uninterrupted delivery of goods, a reduction of the idle time of locomotives and wagons, which in turn depends on the quality of the repair and the parts used. In the article the main tendencies in field of application of modern metal-ceramic materials for production, repair and operation of railway transport equipment are considered, modern directions in powder technologies and applied materials are shown, as well as possibilities of increasing reliability and safety of used powder parts. The basic properties and advantages of parts from powder materials are estimated. The possibilities of using powder details in various units of rolling stock are shown, as more reliable, safe and economically profitable. Among them: metal-powder slide bearings based on iron-copper, the main advantage of which is the presence of residual porosity, which contributes to the formation of a stable oil film in the bearing; bushings of valves of diesel motors, gears of oil and water pumps possessing high wear resistance; friction discs and brake pads designed to work in brakes and friction clutches in conditions of dry and liquid friction.

German Bond Yields and Debt Supply: Is There a 'Bund Premium'?

Are Bunds special? This paper estimates the 'Bund premium' as the difference in convenience yields between other sovereign safe assets and German government bonds adjusted for sovereign credit risk, liquidity and swap market frictions. A higher premium suggests less substitutability of sovereign bonds. We document a rise in the 'Bund premium' in the post-crisis period. We show that there is a negative relationship of the premium with the relative supply of German sovereign bonds, which is more pronounced for higher maturities and when risk aversion proxied by bond market volatility is high. Going forward, we expect German government debt supply to remain scarce, with important implications for the ECB's monetary policy strategy.

Hydrogen Bonding as a Clustering Agent in Protic Ionic Liquids: Like-Charge vs Opposite-Charge Dimer Formation.

The local structure of a series of homologous protic ionic liquids (PILs) is investigated using ab initio computations and ab initio-based molecular dynamics. The purpose of this work is to show that in PILs the network of hydrogen bonds may promote like-charge clustering between anionic species. We correlate the theoretical evidence of this possibility with viscosity experimental data. The homologous series of liquids is obtained by coupling choline with amino acid anions and varying the side chain. We find that the frictional properties of the liquids are clearly connected to the ability of the side chain to establish additional hydrogen bonds (other than the trivial cation–anion interaction). We also show that the large variation of bulk properties along the series of compounds can be explained by assuming that one of the sources of friction in the bulk liquid is the like-charge interaction between anions.

Effect of Mini/Micro/Nanostructures on Filmwise Condensation of Low-Surface-Tension Fluids

Micro/nanostructured surfaces have been widely explored to enhance condensation heat transfer over the past decades. When there is no flooding, micro/nanostructures can enable dropwise condensation by reducing solid-droplet adhesion. However, micro/nanostructures have mixed effects on filmwise condensation because the structures can simultaneously thin the condensate film and increase the fluid–solid friction. Although oil infusion of structured surfaces has recently been shown to render filmwise condensation dropwise in many cases, challenges remain in the case of extremely low-surface-tension fluids. This work aims to provide a unified experimental platform and study the impact of mini/micro/nanostructures on condensation heat transfer of low-surface-tension fluids in a customized environmental chamber. We first investigate the effect of microstructures, hydrophobic coating, as well as oil infusion on the filmwise condensation of a low-surface-tension fluid, e.g., refrigerant, on microporous aluminum surfaces. And we show that for low-surface-tension condensates, microstructures, hydrophobic coating, or oil infusion do not play a considerable role in enhancing or deteriorating heat transfer. Next, we study how the addition of nanostructures affects the condensation performance of the refrigerant on copper mini-fin structures. It is found that nanostructures slightly deteriorate the condensation performance due to the dominance of solid–liquid friction, although the performance of these mini-fins with nanostructured surfaces is still better than that of the mini-pin-fins. These results provide guidelines of designing mini/micro/nanoscale surface structures for enhanced condensation applications.

Automatic Control System of an Oil Pressure Regulator for Hydraulic Press Assembly of Interference Fits

В статье рассматривается система автоматического управления регулятором давления масла на основе пропорционального регулятора, а также ее функциональная схема, составленная в соответствии с исходными данными об используемом технологическом оборудовании в исследуемом регуляторе давления и алгоритм управления данным регулятором. Приведены результаты тестовых испытаний регулятора давления с предлагаемым алгоритмом управления с целью определения оптимальных границ зоны нечувствительности (область, в которой изменения регулируемого давления не вызывают действия регулятора) исходя из стабильности работы системы с минимальной статической ошибкой. Предложенная система управления позволяет регулятору давления обеспечивать поддержание величины давления масла в требуемом диапазоне. Процесс автоматизированной гидропрессовой сборки гарантированно осуществляется в режиме жидкостного трения, реализуя достоинства технологии, а именно, сохранность сопрягаемых поверхностей и прочность соединения.

Cohesion‐Induced Stabilization in Stick‐Slip Dynamics of Weakly Wet, Sheared Granular Fault Gouge

AbstractWe use three‐dimensional discrete element calculations to study stick‐slip dynamics in a weakly wet granular layer designed to simulate fault gouge. The granular gouge is constituted by 8,000 spherical particles with a polydisperse size distribution. At very low liquid content, liquids impose cohesive and viscous forces on particles. Our simulations show that by increasing the liquid content, friction increases and granular layer shows higher recurrence time between slip events. We also observe that slip events exhibit larger friction drop and layer compaction in wet system compared to dry. We demonstrate that a small volume of liquid induces cohesive forces between wet particles that are responsible for an increase in coordination number leading to a more stable arrangement of particles. This stabilization is evidenced with 2 orders of magnitude lower particle kinetic energy in wet system during stick phase. Similar to previous experimental studies, we observe enhanced frictional strength for wet granular layers. In experiments, the physicochemical processes are believed to be the main reason for such behavior; we show, however, that at low confining stresses, the hydromechanical effects of induced cohesion are sufficient for observed behavior. Our simulations illuminate the role of particle interactions and demonstrate the conditions under which induced cohesion plays a significant role in fault zone processes, including slip initiation, weakening, and failure.

SIMULATION OF SLAG SKULL FORMATION ON THE WALL OF CCM MOLD

The processes of formation of the skull and liquid film between the mold and surface of the billet effect on quality indicators and stability of the continuous casting of steel. A number of theoretical studies devoted to the forecast of skull thickness and the film of liquid slag are known. However, these studies do not take into account the mutual influence of formation processes of skull and film, as well as formation of shell thickness of the billet. In this connection, the paper presents a mathematical model of interrelated thermal processes developed by the authors in the system of layers “copper wall of crystallizer – skull – film of liquid slag – crust of ingot”. The model makes it possible to predict the dynamics of formation of the thickness of the ingot crust, slag skull and the layer of liquid slag along the height of the mold and the length of liquid friction portion in it, depending on casting speed, temperature of casting steel and melting of the slag, thickness of the slab and working layer of the copper wall. The adequacy of the model to the object is determined by such parameters, as surface temperature of the billet, thickness of the crust, specific heat flux in the mold and temperature of the working wall. An example of application of the developed model is shown, in which the effect of casting speed on length of the liquid friction portion in the mold is investigated. It was found that at speeds of 0.8; 1.0 and 1.2 m/min the slag layer is retained for 0.331; 0.415 and 0.498 m from the meniscus of the metal, respectively. At the same time, the thickness of the skull reaches a maximum value of 0.77 mm. Further formation of the preform occurs in the absence of lubrication in the mold. The possibility of using the developed model by technologists for selecting the chemical composition of casting powder, which provides the required length of the liquid slag section, is indicated by the designers when choosing the mold profile, taking into account the thickness of the skull, and, also for educational purposes.

The Origins of the International Monetary System: A Revisionist History

This paper situates the early history of the Bank of England in the 17th century environment where the circulation of specie-based coin caused it to wear down, prompting debasement by monetary authorities (Lane and Mueller 1985). Thus, the 19th Gold Standard was only possible because of prior institutional changes that made a fixed specie standard practicable: these changes included the 1696 recoinage that committed Britain to a fixed specie standard, the 1694 founding of the Bank of England that reduced the need for coin by substituting Bank notes as high powered money, and the reformation of the payments system that reduced the need for coin in local markets. In order to understand the value of introducing a bank-based money supply into a coin-based economy, this paper uses a liquidity frictions model to frame the discussion and to explore the important role played by the Bank of England in the British monetary system from the Bank’s earliest decades.

60NiTi: A Review of Recent Research Findings, Potential for Structural and Mechanical Applications, and Areas of Continued Investigations

Recent advances in the manufacture and processing of high purity NiTinol 60 (60 wt% Ni–40 wt% Ti) has spurred a renewed interest in the use of this alloy for structural and mechanical component applications. NiTinol 60 (60NiTi) exhibits excellent corrosion resistance, can be hardened to high levels, has a low elastic modulus and extensive elastic range that imparts high mechanical contact load resilience. It is dimensionally stable, has good bio-compatibility, can be machined into precision components and is non-magnetic. This unique set of characteristics make the intermetallic 60NiTi suitable for a wide variety of applications in the marine, medical, aerospace and food processing industries. This article surveys and reviews a broad range of historic and recent publications on 60NiTi to highlight what is known and areas that require further study. In particular, recent results indicate a dichotomy in friction and wear behavior. Under good lubrication (liquid or solid) both friction and wear are low but in dry un-lubricated sliding, wear exceeds that of other materials such as steel that have comparable hardness. This unexpected behavior is proposed as an important topic for future investigations before any of widespread adoption in engineering applications.

Mixture of distribution hypothesis: Analyzing daily liquidity frictions and information flows

The mixture of distribution hypothesis (MDH) model offers an appealing explanation for the positive relation between trading volume and volatility of returns. In this specification, the information flow constitutes the only mixing variable responsible for all changes. However, this single static latent mixing variable cannot account for the observed short-run dynamics of volume and volatility. In this paper, we propose a dynamic extension of the MDH that specifies the impact of information arrival on market characteristics in the context of liquidity frictions. We distinguish between short-term and long-term liquidity frictions. Our results highlight the economic value and statistical accuracy of our specification. First, based on some goodness of fit tests, we show that our dynamic two-latent factor model outperforms all competing specifications. Second, the information flow latent variable can be used to propose a new momentum strategy. We show that this signal improves once we allow for a second signal – the liquidity frictions latent variable – as the momentum strategies based on our model present better performance than those based on competing models.

РОЗРАХУНОК КОМБІНОВАНИХ ГІДРОСТАТИЧНИХ ПІДШИПНИКІВ ЗДВОЄНОГО ТИПУ ПРИ СТАЦІОНАРНОМУ ЗОВНІШНЬОМУ НАВАНТАЖЕННІ

The relevance of the application of combined hydrostatic bearings of the twin type in various units and power plants is shown, the loads in which reach ten tons. The most complicated modes of operation of rotor supports associated with starting and stopping are described. The current method for improving the liquid friction regime at nuclear power plants, associated with the use of auxiliary containers with a working fluid, which are set at a certain height, provides the working fluid to the bearings by gravity and thus improves the friction regime. The design of a combined bearing is proposed that improves the operation of turbines in the start-up and shutdown modes and allows for the abandonment of additional containers with working fluid, and also increases the reliability and durability of turbine operation. It is the objective of this work, which consists in calculating characteristics of a combined hydrostatic bearing tandem type, providing reliable operation of the turbine in all possible modes of its operation. Shows a structural scheme of the combined hydrostatic bearing tandem type and the principle of its operation is described in case of overloads, failure of hydraulic fluid supply system as well as to start and stop modes, these modes are included in the operation of hydrostatic bearings instead of bearings. Theoretical dependences have been developed that allow determining the main characteristics of a combined hydrostatic bearing of a dual type with a stationary external load. It is shown that the basis for determining the characteristics of the bearing is the function of the distribution of pressure along the working surface of the bearing, by means of which the bearing capacity of the bearing, the flow rate of the working fluid and the loss of power for friction are determined. A mathematical model is presented, brought to a kind adapted for numerical realization. The most rational numerical methods for implementing mathematical dependencies are applied. A generalization of the mathematical model to the case of non-laminar flow of a working fluid is carried out using the turbulence coefficients proposed by V. N. Konstantinesku. The analysis of the results of calculation of combined hydrostatic bearings of a twin type in a wide range of external loads and bearing diameters is given

Dynamic analysis of the mechanical seals of the rotor of the labyrinth screw pump

A mathematical model of the work of the mechanical seal with smooth rings made from cast tungsten carbide in the condition of liquid friction is drawn up. A special feature of this model is the allowance for the thermal expansion of a liquid in the gap between the rings; this effect acting in the conjunction with the frictional forces creates additional pressure and lift which in its turn depends on the width of the gap and the speed of sliding. The developed model displays the processes of separation, transportation and heat removal in the compaction elements and also the resistance to axial movement of the ring arising in the gap caused by the pumping effect and the friction in the flowing liquid; the inertia of this fluid is taken into account by the mass reduction method. The linearization of the model is performed and the dynamic characteristics of the transient processes and the forced oscillations of the device are obtained. The conditions imposed on the parameters of the mechanical seal are formulated to provide a regime of the liquid friction, which minimizes the wear.

The impact of liquidity crises on cash flow sensitivities

Abstract We examine the relationship between liquidity crises and frictions in raising funds, and find that both the gap between the cash flow sensitivities of financially healthy and weak firms and the cash flow sensitivities of healthy and weak firms themselves are positively correlated with the severity of liquidity crises. Using a multi-equation model of cash flow sensitivities, we find that moderate liquidity crises mostly affect firms’ financing activities. The recent financial crisis was especially severe for financially weak firms and curtailed both their investment and financing decisions. Financially healthy firms were able to protect their investments by maintaining financial flexibility.

Methods for Research of Joints with Composite Materials

В данной научной статье проведен анализ различных методов неразрушающего контроля для обоснования их применения в качестве инструмента исследования прочности клеевых соединений с композиционными материалами. Приведены прочностные свойства соединений с натягом, в зону сопряжения которых введены компаунды, с плохо изученными адгезионными свойствами, проведены серии контрольных экспериментов на основе неразрушающих и разрушающих методов, дана оценка напряженному состоянию сопряжения и прилегающих к ней слоев. Необходимые свойства клеевого соединения зависят от множества факторов, одним из которых является взаимодействие с особыми участками склеиваемых поверхностей; другой - среднее значение контактного давления, которое требуется для максимального прилегания поверхностей. Независимо от конструктивных параметров (соединение с зазором или соединение с натягом) способ сборки обеспечивает гарантированное заполнение пространства между сопрягаемыми деталями композиционным материалом, подаваемым в зону сопряжения различными способами. Для обеспечения дальнейшего применения соединений необходимо установить взаимосвязь прочности, определенной экспериментально, и показаний приборов при неразрушающем методе контроля. Такой подход позволит расширить область применения как клеевых соединений, так и соединений с прослойкой из наноструктурированного компаунда. Сборка соединений может осуществляться при относительном смещении собираемых деталей в условиях жидкостного трения, обеспеченного материалом клеевого компаунда. Проведен выбор наиболее оптимального, с точки зрения практики, метода контроля клеевых соединений с натягом с композиционной прослойкой. Показано преимущество метода введения сегнетоэлектрических добавок в клеевой слой для оценки прочностных характеристик клеевых соединений при использовании акустоэлектромагнитного метода.

Modeling of inertial multi-phase flows through high permeability porous media: Friction closure laws

During a severe accident in a nuclear reactor, the core may be fragmented in a debris bed made of millimetric particles. The main safety procedure consists in injecting water into the core leading to a steam-water flow through a hot porous medium. To assess the coolability of debris bed, there is a need for an accurate two-phase flow model including closure laws for the pressure drop. In this article, a new model for calculating pressure losses in two-phase, incompressible, Newtonian fluid flows through homogeneous porous media is proposed. It has been obtained following recent developments in theoretical averaging of momentum equations in porous media. The pressure drops in the momentum equations are determined by eight terms corresponding to the viscous and inertial friction in liquid and gas phases, and interfacial friction between the phases. Analytical correlations with the void fraction have been formulated for each term using an original experimental database containing measurements of pressure drops, average velocities and void fractions from the IRSN CALIDE experiment. The new model has then been validated against the experimental data for various liquid and gas Reynolds numbers up to several hundreds. Finally, it has been compared to the models, usually used in the “severe accident” codes, which are based on a generalization of the Ergun law for multi-phase flows. The results show that the new model gives a better prediction both for the pressure drop and for the void fraction.