Effect Of Hydrodynamic Pressure Research Articles

Attenuation behavior of pavement concrete under rolling load and hydrodynamic pressure coupling

In addition to rolling vehicle load, the damage of hydrodynamic pressure to pavement concrete cannot be ignored. To investigate the attenuation behavior of pavement concrete under the coupling effect of rolling load and hydrodynamic pressure, an indoor-accelerated loading test was conducted. The decay rules of strength, dynamic elastic modulus, and impermeability were studied, and the correlation between pore structure and macro-properties was analyzed. The results show that hydrodynamic pressure has significant additional degradation effect on strength and dynamic elastic modulus at the later stage of loading (more than 100 thousand times). The chloride permeability coefficient increases in parabolic shape under rolling load, whereas it amplifies exponentially under the coupling of load and hydrodynamic pressure. The pore structure of pavement concrete presents a “coarsening - refining” trend under the coupling effect. The attenuation of flexural strength and dynamic elastic modulus has great correlation with the total aperture area, mean pore diameter, and area median aperture, and the chloride diffusion coefficient is greatly affected by porosity and total aperture area.

Influences on the Seismic Response of a Gravity Dam with Different Foundation and Reservoir Modeling Assumptions

The seismic design and dynamic analysis of high concrete gravity dams is a challenge due to the dams’ high levels of designed seismic intensity, dam height, and water pressure. In this study, the rigid, massless, and viscoelastic artificial boundary foundation models were established to consider the effect of dam–foundation dynamic interaction on the dynamic responses of the dam. Three reservoir water simulation methods, namely, the Westergaard added mass method, and incompressible and compressible potential fluid methods, were used to account for the effect of hydrodynamic pressure on the dynamic characteristics and seismic responses of the dam. The ranges of the truncation boundary of the foundation and reservoir in numerical analysis were further investigated. The research results showed that the viscoelastic artificial boundary foundation was more efficient than the massless foundation in the simulation of the radiation damping effect of the far-field foundation. It was found that a foundation size of 3 times the dam height was the most reasonable range of the truncation boundary of the foundation. The dynamic interaction of the reservoir foundation had a significant influence on the dam stress.

Elucidation of material removal mechanism in float polishing

Float polishing (FP) is a non-contact polishing method in which a thin layer of fluid is maintained between the workpiece and precision lap by hydrodynamic pressure effect. While it is known to consistently produce atomically flat surfaces with little or no sub-surface damage, the characteristics of polishing fluid flow and material removal have not been studied in-depth. In this research, the underlying mechanism in FP is investigated by means of computational fluid dynamics (CFD) and molecular dynamics (MD) simulation. It is revealed that a fluid gap few microns in height is generated by the wedge effect of slurry. The near wall flow condition is further investigated by direct observation and tracing of cavitation bubbles. Abrasive particle trajectory tracing is carried out with a well calibrated CFD model, and suggests that single abrasive particles move almost parallel to the workpiece surface at a relative speed of around 0.5 mm/s. Next, single abrasive particle interactions with the surface of a Ni crystal are simulated by MD to predict the required conditions in terms of kinetic energy for effective smoothing of the surface. Finally, it is concluded that the material removal mechanism in FP is dependent on a minimum size of nano-abrasive agglomerates of several 100 nm, and the existence of two types of smoothing phenomena: atomic removal and atomic transfer.

Tribological performance of hydrophobic and micro/nano triangle textured rake face of cutting tools

In the process of metal cutting, the friction between the tool and the workpiece wears the tool seriously and degrades the surface quality of the workpiece.In order to reduce the friction coefficient, we micro/nano-textured the tool rake face triangularly with femtosecond laser and fluoridizedit with fluorosilane. We evaluated the tribological performance of the tool rake face through friction and wear experiments as well as cutting experiments, in which textures with different wetting characteristics, depths and pattern arrangements are studied. Our experiment results and theory-based analysis show that the tribological performance and machining quality of the tool are improved due to the unidirectional convergent texture and hydrophobicity of the cutting tool. When the monopulse energy was 2.5 μJ and the scanning depth was 7 μm, the micro/nano textured and fluoridized tool has the best anti-adhesion, anti-friction and wear resistance performance, the hydrodynamic pressure effect is obvious. The tribological performance of cutting tools are also increased by the bearing capacity of film between friction pairs.

Study on the effect of hydrodynamic pressure on the tribological performance of textured bioimplants

Surface texturing is an effective technology in improving the tribological performance of artificial joints. However, the mechanism behind it is still a controversial topic, especially when talking about the functionality of hydrodynamic pressure. In this paper, Finite Difference Method was used to solve the steady-state Reynolds equation. It was found that, under the given conditions, hydrodynamic pressure only played a minor role in the tribological performance of textured bioimplants. A further theoretical study indicated that this phenomenon was attributed to the working environments of artificial joints: low viscosity lubricant and low sliding speed. A comparison study between tribo-systems with various working conditions also showed that hydrodynamic pressure played a more important role in the systems either under fast speed or lubricated by high-viscosity solution. Finally, a pin-on-disk frictional study was carried out with different sliding velocities and it was confirmed that hydrodynamic pressure has little effect on the tribological performance of textured bioimplants.

The impact of the electrical behavior of oil-brine-rock interfaces on the ionic transport rate in a thin film, hydrodynamic pressure, and low salinity waterflooding effect

Wettability alteration is the principal low-salinity-effect (LSE) in many oil-brine-rock (OBR) systems. Our recent experimental results have demonstrated that wettability alteration by low salinity is slow. It is expected that the electrical behavior of oil/brine and rock/brine interfaces and the water film geometry control both the transient hydrodynamic pressure, and the time-scale of ionic transport in the film, thus the kinetics and degree of wettability alteration. In this paper, the electro-diffusion process induced by the imposed ionic strength gradient is simulated by solving Poisson-Nernst-Planck equations in a water film bound between two charged surfaces, using a finite element-based computational fluid dynamics method. Both the non-equilibrium electric-double-layer (EDL) pressure and the time-scale of diffusion under different plausible electrical boundary conditions (BCs) are determined. The numerical results show that electro-diffusion in the thin film is non-Fickian, strongly dependent on the electrical BCs, and significantly (10–20 times) slower than Fickian diffusion. Among various BCs, those which lead to the strengthening of the electrostatic force, or electric field (such as constant charge BC), are the most favorable in terms of observing LSE. Moreover, it is found that the contribution of the osmotic pressure in the vicinity of the pore (bulk) fluid is negligible and that Maxwell stress is the dominant source of EDL force build-up. This force can then trigger wettability alteration. Furthermore, while both film length and thickness influence the electrical interaction of interfaces, the film thickness affects mainly the EDL force rather than the rate of ionic transport. On the contrary, the film length has a significant effect on the time-scale of diffusion. The effect of the ionic strength gradient on the time-scale of diffusion and LSE is relatively minor. This study provides novel insights into the role of the electrical behavior of OBR interfaces and film phenomena in the rate of ionic transport and establishment of low salinity in the film. Thin film modeling is a means to develop predictive capability for LSWF, screen OBR candidates, and to determine favorable conditions to observe LSE. Moreover, the slow kinetics of LSE necessitates accounting for the time-effect in the experimental evaluation of LSWF.

An Investigation into the Texture Transfer in the Process of Lubricated Skin Pass Rolling

Abstract This article investigates the surface texture transfer mechanisms in lubricated skin pass rolling of metal strips with three-dimensional rough surfaces of both regular patterns and random surface asperity distributions. Two important steps have been completed. The first is the successful establishment of an efficient numerical method for predicting the 3D texture transfer. It was identified that the new method can be used reliably with the key complex factors coupled in skin pass rolling, such as the effects of lubricant and surface roughness. The second is the exploration of the texture transfer mechanisms with the aid of this new method. In addition, the effects of hydrodynamic pressure on the texture transfer efficiency were comprehensively investigated by a dynamic explicit finite element analysis. It was found that lubrication plays a critical role in determining the surface texture transfer. The texture transfer ratio decreases with increasing the lubricant viscosity. A larger pressure coefficient brings about a lower texture transfer ratio, but a larger reduction ratio leads to a greater texture transfer.

Mechanical properties of CFRP-strengthened prestressed concrete cylinder pipe based on multi-field coupling

Broken prestressing wires in prestressed concrete cylinder pipe (PCCP) can cause incident of pipe burst. A method was proposed to repair damaged PCCP with broken wires by externally bonding carbon fiber reinforced polymer (CFRP). A finite element model was established and calibrated against the data from a prototype-scale laboratory test. Upon calibration, a three-dimensional numerical model was built to simulate the response of PCCP pipeline with five segments. Multi-field coupling was accomplished by Mesh-based parallel Code Coupling Interface (MpCCI) to incorporate the soil–pipe interaction and the effect of hydrodynamic pressure for PCCP. The effect of externally bonded CFRP to repair PCCP with broken wires was systematically analyzed. Results show that at a certain number of broken wires, the use of CFRP for pipe repair can significantly reduce the strains for each pipe component and increase the resilience of PCCP. The improved PCCP performance was assessed on the basis of crack visibility in the concrete core, and the deformation of the steel cylinder. The CFRP strain was much less than its ultimate strain, when cracks in the concrete core became visible and the steel cylinder yielded, suggesting that failure of PCCP could be ahead of CFRP.

Evaluation of the Hydrodynamic Pressure Effect of Cylindrical Liquid Storage Tank on The Granular Soil Behavior Under Seismic Excitation

Many liquid storage tanks around the world have been affected by earthquakes, and the seismic analysis of such tanks is much more complicated due to the Fluid-Structure Interaction. Besides, when the soil properties are taken into the consideration, the analysis with the Fluid-Soil-Structure Interaction becomes very complicated. In this paper, a series of shaking table tests are conducted on a model of the cylindrical water tank rested on dry granular soil and the equivalent load is considered to study the effect of hydrodynamic pressure generated in the storage water tank on the soil behavior. An experimental investigation of (1:100) scale model has been carried out on a shake table that was manufactured with specific mechanical parts and flexible laminar shear box. The preparation of the test included three cases in different relative densities (medium, dense, medium-dense). Three earthquake histories (Kobe, El-Centro and Ali Al-Gharbi) were implemented to study a wide range of the acceleration. The results showed that the acceleration at the bottom-depth of the soil column is slightly higher than at the mid-depth, while at the top portion of the soil column, the acceleration comparatively becomes less than that at the mid-depth. The settlement due to hydrodynamic pressure in the storage base tank is significantly reduced compared with results of nonhydrodynamic pressure in all cases of the acceleration history. In addition, the lateral stress at the surface gives higher than the stress at a depth equal to the diameter of the base tank.

Effect of Hydrodynamic Pressure on Saturated Sand Supporting Liquid Storage Tank During the Earthquake

This paper aims to illuminate the influence of hydrodynamic pressure generated in a water storage tank on the behavior of saturated sand that its support. Experimental tests were performed on two cylindrical water tank models using a fabricated shaking table which consists of a flexible laminar shear box. The first model is a water storage tank partially full of water, and the second one is a tank model with an equivalent load of water pressure to simulate the water storage tank without hydrodynamic pressure. Three earthquake histories (Kobe, El-Centro, and Ali Al Gharbi) were implemented on models to study a varied range of acceleration. It was found that the settlement and lateral displacement directions in the water storage tank were significantly increased compared to the equivalent load resulted in the second model in all cases of the acceleration histories. Also, it was monitored the pore water pressure during the testing period, and it was noticed that the excess pore pressures were affected by the hydrodynamic pressure and increased compared to the results recorded at the condition of no hydrodynamic pressure.

Electrohydrodynamic droplet formation in a T-junction microfluidic device

Abstract

Investigations of chloride ions permeability of pavement concrete under coupled effect of fatigue loading and hydrodynamic pressure

ABSTRACT To investigate the combined effects of fatigue loading and hydrodynamic pressure on the chloride penetration and damage process of pavement concrete, a series of chloride penetrations tests, mercury intrusion porosimetry (MIP) tests and scanning electron microscopy (SEM) tests were carried out on specimens after experienced different conditions. Three exposure conditions (i.e. (i): fatigue loading, (ii): fatigue loading and hydrodynamic pressure, (iii): fatigue loading, hydrodynamic pressure and salt–freezing-thawing) were set, and two stress levels (0.5 and 0.7 f) and two pressure values (0.25 and 0.5 MPa) were applied to the specimens. The variation of pore and crack structures of the concrete under different conditions and loading stages was characterised. The results showed that the stress level had a prominent influence on the chloride ion diffusion coefficient (DRCM) when the number of loading cycles ranged from 30 to 60 thousand times, while hydrodynamic pressure promoted the accumulation of damage and presented a distinct effect on DRCM at the latter loading stage. The total capillary pore volume, threshold pore diameter and fractal dimension showed a close positive correlation with DRCM, suggesting that the diffusivity change of concrete accord well with microstructure evolution during the loading process.

Simulation and Experimental Investigation on Friction Reduction by Partial Laser Surface Texturing on Piston Ring

Numerical models for barrel-shaped rings with four textures were established using MATLAB and the corresponding specimens were fabricated by laser surface texturing. The performance was compared both theoretically and experimentally in order to investigate the effects of geometrical characteristics. The results of the theoretical analysis indicated that a microdimple texture on both sides of the ring surface was a suitable option to improve the lubricating property due to the “collective’’ effect, thus reducing friction of the piston ring. This result was confirmed experimentally. The microdimple texture at the crowning of the ring face weakened the hydrodynamic pressure effect and increased friction, as demonstrated by both theoretical and experimental results.

Seismic behavior analysis of wind turbine tower affected by hydrodynamic pressure based on a simplified calculation model

Abstract The interaction between water and structure will inevitably lead to the hydrodynamic pressure, which could change the dynamic behavior of the wind turbine tower under earthquake action. Based on the Morison hydrodynamic theory, a simplified calculation method of hydrodynamic pressure was proposed, and the effects of different water depths and hydrodynamic pressure on the seismic behavior of the wind turbine tower is investigated. The main results include: wind turbine tower in deep water is sensitive to water, and the deformation and energy dissipation capacity of the wind turbine tower are decreased affected by the hydrodynamic pressure; the influence of hydrodynamic pressure on the acceleration and displacement is related to the high frequency components of the seismic wave, and the effect of hydrodynamic pressure on the internal force, displacement, and acceleration increases with the increasing of the water depths under different earthquakes. Finally, a shaking table test is carried out, and the experimental results are in good agreement with the calculated results using our proposed method.

Semi-active Control of Continuous Girder Bridges Considering the Coupling Effect of Earthquake and Hydrodynamic Pressure

Semi-active Control of Continuous Girder Bridges Considering the Coupling Effect of Earthquake and Hydrodynamic Pressure

Lateral Vibration of Offshore Piles Considering Pile-Water Interaction

The dynamic response of an offshore pile in saturated soil subjected to lateral harmonic loading is theoretically investigated by considering the dynamic pile-water interaction. The governing equation of water is solved based on the separation of variable method, and the analytical expression of the hydrodynamic force applied on the pile is then obtained. Based on the continuous conditions at the pile-soil interface and pile-water interface, the analytical solution of the dynamic impedance of the offshore pile is derived by using transfer matrix method. To verify this solution, the dynamic impedance obtained for a cylinder in water is compared with that of a partially embedded pile. Based on this solution, the effect of hydrodynamic pressure and other parameters on the dynamic response of offshore piles is investigated. The results show that the analytical model ignoring the hydrodynamic force applied on the pile misestimates the impedance of the pile in the high frequency range.

Seismic water-structure interaction analysis using a modified SBFEM and FEM coupling in a frequency domain

The seismic responses of offshore structures and dams can be affected by the water-structure interaction. The structures are commonly modelled by finite element method (FEM). If the infinite water layer is also modelled by FEM, then the computational costs are high. In this paper, an accurate and efficient substructure method is presented in a frequency domain for a 2D water-structure interaction analysis, in which the modified scaled boundary finite element method (SBFEM) is applied at a general shaped water-structure interface to replace the compressible water layer. Several numerical examples, including offshore structures and a typical-geometry gravity dam, are provided to demonstrate the computational efficiency and accuracy of the proposed substructure method. The effects of hydrodynamic pressure, water compressibility and structure geometry on the seismic responses of offshore structures are analysed based on the proposed method.

Modelling Transitions in Regimes of Lubrication for Rough Surface Contact

Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubrication regime with increasing sliding velocity. Through correlation with pin-on-disk frictional measurements, the slope of the limiting shear stress-pressure relation γ and the pressure coefficient of boundary shear strength m for the studied engine lubricants are determined. Thus, the proposed approach presents an effective and robust semi-empirical framework to determine shear properties of fully-formulated engine lubricants. These parameters are essential for application in mathematical tools to predict more accurately the frictional performance of lubrication systems operating across a wide range of lubrication regimes.

Experimental Investigation on Rotordynamic Characteristics and Rotor System Stability of a Novel Negative Dislocated Seal

Air-induced force generated in seals is one key factor on the stability of the rotor system. In this paper, a novel negative dislocated seal (NDS) was developed in respect of dislocated bearing theory, to reduce hydrodynamic pressure effect and air-induced force and improve rotor stability as well. A test rig was built to test rotordynamic characteristics and rotor stability of the NDS. The rotordynamic characteristics of seals were investigated based on the unbalanced synchronous excitation method, and seal-rotor system stability was evaluated by the identification method with an electromagnetic bearing exciter. The effects of both rotating speed and inlet/outlet pressure ratio on the rotordynamic characteristics and rotor stability of both NDS and conventional cylindrical labyrinth seal were experimentally investigated. The results show that with the increasing rotating speed, inlet/outlet pressure ratio is promising to reduce the direct stiffness coefficients of seals and the logarithmic decrement rate of seal-rotor system and enhance both cross stiffness and damping coefficient as well. Besides, the developed NDS effectively reduces cross-stiffness coefficients and increases direct damping coefficients and the logarithmic decrement rate of the seal-rotor system, relative to the conventional cylindrical seal. The proposed seal can effectively improve seal stability of turbomachinery.

Unstable crack growth in hydraulic fracturing: The combined effects of pressure and shear stress for a power-law fluid

The underlying mechanisms of hydraulic fracturing remain elusive, and the optimization of the related processes for rocks of low permeability is challenging. There exists local crack closure induced by shear stress, which is one of the crack instabilities for a straight crack. In this study, we develop a full-stress model, which includes the combined effects of hydrodynamic pressure and shear stress on the crack surfaces. The hydrodynamic pressure is a driving force, while the shear stress is a resistance force. A novel criterion for crack propagation is derived based on the asymptotic solution of shear stress. The asymptotic solution, which is derived using perturbation analysis in the toughness-dominant regime, reveals the existence of the crack-closure phenomenon and shear-stress-dominant regime. The necessary condition for the crack closure is obtained according to numerical calculations. An energy analysis is conducted to discuss the difference between the shear-stress-dominant and the viscosity-dominant regimes. The existence of the crack closure is shown to be independent of two assumptions, lubrication theory and no-fluid-lag zone. The results presented in this study are useful for the simulation and design of hydraulic fracturing.