High Hydraulic Pressure Research Articles

Experimental Study on the Influence of Freezing Pressure on the Uniaxial Mechanical Properties of Ice

In this study, a test technique that enables continuous control of the sample stress state from freezing to testing is proposed to investigate the influence of freezing pressure on the mechanical properties of ice under uniaxial compression. In this method, the water is frozen into the standard cylindrical ice specimen under high hydraulic pressure in a triaxial pressure chamber, and then, the temperature field and stress field of the ice specimens are adjusted to the initial state of the test; finally, an in situ mechanical test is conducted in the triaxial chamber. The uniaxial compression test of ice specimens with temperature of −20°C and freezing pressure of 0.5–30 MPa is performed in the strain rate range of 5 × 10−5−1.5 × 10−6 s−1. The results show that, as the freezing pressure increases, the ductile-to-brittle transition zone of the ice specimen during failure moves to the low strain rate range, and the failure mode of the specimen changes from shear failure to splitting failure. Further, the brittleness index of the ice specimen first increases, then decreases, and then again increases with the increase in freezing pressure. The brittleness index reaches the maximum (minimum) when the freezing pressure is 30 MPa (20 MPa). The peak stress of the ice specimen also increases first, then decreases, and then increases with the increase in freezing pressure. The maximum value is also at the freezing pressure of 30 MPa, but the minimum value is obtained at the freezing pressure of 0.5 MPa. The failure strain of the ice specimen first decreases and then increases with the increase in freezing pressure, and the maximum (minimum) value is achieved at the freezing pressure of 0.5 MPa (10 MPa). When the ice specimen exhibits brittle failure, the relationships between the residual stress and the freezing pressure and between the peak stress and freezing pressure are the same, but when the ice specimen exhibits ductile failure, there is no obvious relationship between the residual stress and the freezing pressure.

MECHANICAL PROPERTIES OF SANDSTONE SUBJECTED TO COUPLING OF TEMPERATURE–SEEPAGE–STRESS

ABSTRACT: The deformation and fracture of rock mass in deep rock mass engineering are affected by the coupling of temperature, seepage, and stress. A test and a calculation model for sandstone under thermal–hydrological–mechanical (THM) coupling were proposed to reveal the mechanical properties of sandstone. The law of coupling for mechanical indicators of sandstone was established by laboratory tests and numerical simulations. The permeability, peak strength, peak strain, residual strength, elastic modulus, plastic deformation area, and stress–strain cloud diagram were analyzed by the steady state seepage method and THM coupling principle, and the accuracy of the model was verified. Results demonstrate that: (1) As the temperature rises and the peak deformation increases, the sample slowly drops to the residual strength level after the peak stress. (2) The main factor that affects peak strength is confining pressure. In the temperature range of 25 °C–50 °C, the maximum peak strength and peak deformation are increased by heating, and the increases in confining pressure and temperature reduce the reduction coefficient of the residual strength. Moreover, the elastic modulus increases with the increase in confining pressure, but it shows a downward trend when the temperature increases. (3) The plastic deformation zone and stress–strain cloud diagram indicated that when the temperature and osmotic pressure increase, the specimen enters the plastic zone earlier, the effective plastic zone increases, the stress increases, and the deformation is intensified. The proposed method provides a certain reference for the permeability and stability evaluation of rock mass under the conditions of “three-high” (high confining pressure, high hydraulic pressure, and high stress) engineering. Keywords: temperature–seepage–stress coupling, sandstone, mechanical properties

Ultra-strong polymeric hollow fiber membranes for saline dewatering and desalination

Osmotically assisted reverse osmosis (OARO) has become an emerging membrane technology to tackle the limitations of a reverse osmosis (RO) process for water desalination. A strong membrane that can withstand a high hydraulic pressure is crucial for the OARO process. Here, we develop ultra-strong polymeric thin film composite (TFC) hollow fiber membranes with exceptionally high hydraulic burst pressures of up to 110 bar, while maintaining high pure water permeance of around 3 litre/(m2 h bar) and a NaCl rejection of about 98%. The ultra-strong TFC hollow fiber membranes are achieved mainly by tuning the concentration of the host polymer in spinning dopes and engineering the fiber dimension and morphology. The optimal TFC membranes display promising water permeance under the OR and OARO operation modes. This work may shed new light on the fabrication of ultra-strong TFC hollow fiber membranes for water treatments and desalination.

Interaction between Hydraulic Fracture and Pre-Existing Fracture under Pulse Hydraulic Fracturing

Summary Pulse hydraulic fracturing technology can greatly improve the effect of fracture propagation in rock and form complex fracture networks in reservoirs. The interaction mechanism between hydraulic fractures and pre-existing fractures under pulse hydraulic pressure is unclear. The induced laws of pre-existing fractures on the propagation direction of hydraulic fractures under different pulse frequencies and pulse hydraulic pressures are revealed in this work. We have carried out traditional hydraulic fracturing (THF) tests and pulse hydraulic fracturing tests with rock-like specimens. We compared the interaction between hydraulic fractures and pre-existing fractures in the two hydraulic fracturing tests. Acoustic emission (AE) characteristics of the interaction between hydraulic fractures and pre-existing fractures during pulse hydraulic fracturing are analyzed. The results show that pre-existing fractures in the rock-like specimen can induce the direction of propagation of hydraulic fractures. The influence of pre-existing fracture tips on hydraulic fracture propagation is greater with low pulse frequencies than with traditional hydraulic pressures and high pulse frequencies. When the pulse frequency is 1 Hz, hydraulic fractures are easily induced by pre-existing fracture tips. With increasing pulse frequency, the hydraulic fracture propagation direction gradually moves away from the pre-existing fracture tips and extends perpendicularly to the direction of the minimum principal stress. Under pulse hydraulic loading, more hydraulic fractures are generated around the wellbore than under THF and extend to the pre-existing fracture, and more hydraulic fractures around the wellbore are created with low-frequency pulse loading than with high-frequency pulse loading. Compared with traditional hydraulic pressures, hydraulic fracture propagation with low pulse frequencies (1 and 3 Hz) is more complex than hydraulic fracture propagation with traditional hydraulic pressures and high pulse frequencies (5 Hz). Under high pulse hydraulic pressure and pulse frequency, hydraulic fractures easily extend along the direction perpendicular to the direction of the minimum principal stress like propagation under traditional hydraulic pressure. The study of the interaction mechanism between hydraulic fractures and natural fractures under pulsating hydraulic pressure can provide a method for the formation of fracture network systems in large-scale fracturing and may improve the fracturing efficiency.

A study of influence of hydraulic pressure on micro-hydromechanical deep drawing considering size effects and surface roughness

Micro-hydromechanical deep drawing (MHDD) is a promising micro-manufacturing technology to fabricate micro-metallic products in batch scale. Size effects significantly affect MHDD regarding both material properties and friction. Hydraulic pressure on the blank and its development differ from that in conventional hydromechanical deep drawing. Combined influence of fluid pressure, surface roughness and material inhomogeneity of the blank was investigated in this study via MHDD experiments and advanced FE simulation considering strong fluid-solid interaction (FSI) and size effects. The MHDD experiments under different hydraulic pressures were conducted using the annealed foil followed by the advanced FE simulation. The foil can be successfully drawn into micro-cups, however, wrinkles occurred under high hydraulic pressures. Wrinkle height and number are affected by hydraulic pressure and size effects. Average hydraulic pressure on the blank is lower than the inlet pressure, and pressure development on the blank depends on location and is complex, due to transition of sealing between the blank and die. The maximum drawing force increases, while the contact forces and pressures on the blank holder and die decrease with an increase of hydraulic pressure. Optimal hydraulic pressure for MHDD should be determined with consideration of size effects and MHDD tool geometry.

Experimental study on the long-term stability of shale rock wellbore under high hydraulic pressure

Hydraulic pressure is one of the important factors influencing the stability of well rock. In this paper, the sleeve typed shale rock specimens were used to laboratory simulate the long-term stability of shale rock wellbore under hydro-mechanical coupled condition. Based on the analysis of triaxial tests data, the strength characteristic of the saturated shale specimens was first studied. The results show that the strength presents an exponential decreasing trend with increasing hydraulic pressure; 5 MPa hydraulic pressure resulted in the axial compressive strength declined by around 12.20% and about 17.78% fell under the hydraulic pressure of 10 MPa. The creep behavior of the shale was also analyzed in detail. It was found that 60% of the triaxial compression strength can easily lead to rupture of specimen under hydraulic pressure of 5 MPa, while more than 73% of the triaxial compression strength is needed under the same confining pressure without hydraulic pressure. The hydraulic pressure as well as its action time obviously affects the wellbore failure characteristics, which may lead to the damage area appearing pulverized, seriously reducing its mechanical properties. A new viscoelastic-plastic creep damage model was proposed to describe the creep behavior of shale rock, and it was found that the creep model can be used to predict the long-term stability of the wellbore.

Design and Numerical Simulation-Based Optimization of a Novel Flat-Face Coupling System for Hydraulic Power Equipment

Coupling systems play a vital role in hydraulic power transmission equipment. In recent years, flat-face coupling systems have been extensively studied due to their environment friendly features. The difficulty of the connection process of hydraulic equipment increases with the increase in their working pressure. To improve the convenience of making high-pressure connections, a novel flat-face coupling system is proposed in this article. In the proposed design, which is based on the conventional flat-face coupling system, the resistance caused by high hydraulic fluid pressure during coupling is drastically reduced by the addition of an instantaneous pressure relief module. In this study, the theoretical model of the system kinetics is established to illustrate the operational mechanism of the novel design, and a series of computational fluid dynamics numerical investigations based on the novel dynamic mesh technology and Ansys Mosaic meshing technology are implemented to verify the rationality of the proposed design. Additionally, an optimal design of the novel flat-face coupling system is proposed to reduce the energy loss during hydraulic power transmission.

Simulation of subway tunnel construction process based on fi-nite element analysis

Simulation of subway tunnel construction process based on fi-nite element analysis

Application of constitutive model in simulation analysis of tunnel construction

Application of constitutive model in simulation analysis of tunnel construction

Molecular “wiring” of plasma amine oxidase: Green and enzyme friendly approaches

The study describes two approaches to enhance oxidoreductases. Both target molecular “wiring” of enzymes using green processes. The concepts were tested on plasma amine oxidase (PAO). In the first procedure PAO was transiently exposed to an ionic liquid (IL) in the presence of redox molecules, which resulted in partial unfolding. During subsequent dialysis, the enzyme refolded entrapping redox units and affording shorter distances for electron tunneling, hence a molecular “wire” to PAO's prosthetic groups. The other procedure described herein was totally reagentless, using high hydraulic pressure (HHP) to partially denature PAO (in the presence of redox molecules) followed by dialysis and refolding. The two approaches to enzyme “wiring” are discussed comparatively from the point of view of the parameters used during the procedure, residual enzyme activity, nature of the modifier, interaction between PAO and the redox molecules, and stability over time. The most active modified PAO (PAO-ME) from each series was tested in a biosensor for amine detection, toward applications in the food industry and clinical laboratory. Our approaches used “green” reagents (IL) and were made enzyme-friendly as well by the choice of “wires”.

Evaluation of the effectiveness and strength characteristics of Scotchkote® 2400 pipe coating

The article is concerned with the current problem of restoring the required performance of water pipelines of public water supply systems. The effectiveness of using trenchless pipe rehabilitation technologies is noted. The article analyzes the results of the experiments for determining the strength characteristics of Scotchkote® 2400 protective corrosion resistant coating of pipes that were carried out in the laboratory of the Water Supply and Sanitation Department of the Moscow State University of Civil Engineering with Instron 3345 electromechanical tensile testing machine. The effectiveness of Scotchkote® 2400 protective coating relative to restoring and improving the strength and hydraulic characteristics of worn water pipelines was shown. The author comes to the conclusion that Scotchkote®2400 protective coating is a substantial alternative to cement-sand and other internal coatings, since in many respects it surpasses them owing to the ability of colmatage sealing of large diameter holes; high wear resistance; smooth surface; ability to endure high hydraulic pressures. The coating does not overlap service connections and slightly reduces the diameter of the restored pipelines. Based on the studies, comparative characteristics of Scotchkote® 2400 protective coating spraying technology with the basic methods of trenchless pipeline reconstruction are presented. Mathematical processing of the results of experimental studies of the physicomechanical characteristics of Scotchkote® 2400 coating is given. As a result of the studies, the calculated values of the protective coating thicknesses for partially worn and completely worn out pipelines are obtained and recommended.

Strength characteristics and effectiveness of Scotchkote® 2400 liner used for rehabilitation of utility potable water transport pipelines

The article considers the problem of potable water transport pipelines rehabilitation. The article analyzes the results of the experiments for determining the strength characteristics of Scotchkote® 2400 protective corrosion resistant coating of pipes, that were carried out in the laboratory of the Water Supply and Sanitation Department of the Moscow State University of Civil Engineering with Instron 3345 electromechanical tensile testing machine. The effectiveness of Scotchkote® 2400 liner relative to restoring and improving the strength and hydraulic characteristics of worn water pipelines. The author comes to the conclusion that Scotchkote® 2400 liner is a substantial alternative to cement-sand and other internal coatings, since in many respects it surpasses them owing to the ability of colmatage sealing of large diameter holes; high wear resistance; smooth surface; ability to endure high hydraulic pressures. The coating does not overlap service connections and only slightly reduces the diameter of the restored pipelines. Based on the conducted research the characteristics of Scotchkote® 2400 liner spraying technology are presented compared to the basic methods of trenchless pipeline reconstruction. Mathematical processing of the results of experimental studies of the physical and mechanical characteristics of Scotchkote® 2400 liner is given. As a result of the studies, the calculated values of the protective coating thicknesses for partially worn and worn out pipelines have been obtained and recommended.

Modeling technical, economic and environmental parameters of a forwarder in a Eucalyptus forest

ABSTRACT The introduction of the forwarder for wood extraction has provided significant improvements in forest harvesting operations. However, these machines have a high energy demand due to the high engine speed and hydraulic system pressure. Such circumstances increase the operational cost and the emission of polluting gases. Therefore, the objective of this research was to quantify technical, economic, and environmental forwarder parameters as a function of hydraulic pump pressure and engine speed. The research was carried out in the northeastern part of Brazil. The machine operations were analyzed in forest stands with average individual volumes of 0.10 and 0.29 m3 trees−1. During the experiment, the machine was configured to operate with pump pressures of 240, 235, and 230 bar and engine speeds of 1550, 1475, and 1400 rpm, totaling 9 combinations. The technical analysis included the study of times and movements, productivity, and fuel consumption per cubic meter. Regarding the economic parameters, the production costs of the machine were determined. Environmental impact was measured by determining the amount of carbon dioxide and methane emitted. The results were analyzed by regression analysis. For the volume of 0.10 m3 tree−1, the combination of pump pressure of 230 bar and engine speed of 1400 rpm showed the best results. For the volume of 0.29 m3 tree−1, the combination of pump flow of 240 bar and engine speed of 1550 rpm provided the best results.

Experimental study of similar simulation of locked-in stress in rock based on simplified mechanical model

In the environment of deep earth, the “locked-in” stress is widely distributed and considered to be the main cause of rock engineering disaster. But when the rock sample is brought back to the laboratory from deep rock mass of high stress, temperature, and hydraulic pressure, the locked-in stress is dissipated over time. In this paper, similar materials are used to simulate the locked-in stress in the rock. Assuming that “locked-in” stresses in the rock are randomly distributed in the form of spherical inclusions, a simplified geometric model is proposed. By making the “locked-in” stress in rock equivalent to the thermal stress caused by the uncoordinated deformation of inclusion in the rock-like material, the elastic theory formula which expresses the relationship among temperature increment, mechanical parameters of rock-like materials, mechanical parameters of inclusions, and equivalent locked-in stress is deduced. According to the thermodynamic properties of various materials, nitrile rubber is selected as inclusion material. On the basis of the relationship among the temperature increment, the mechanical parameters of the rock-like material and that of the mechanical parameters of the inclusions, and the equivalent “locked-in” stress, an appropriate rock-like material is selected as the matrix material. The “locked-in” stress produced by the inclusions in different ambient temperatures was tested by self-designed method. By comparing and revising, the empirical equation to quantify the locked-in stress is obtained.

Diffusion-layer-free air cathode based on ionic conductive hydrogel for microbial fuel cells

High hydraulic pressure in air-cathode microbial fuel cells (MFCs) can lead to severe cathodic water leakage and power reduction, thereby hindering the practical applications of MFCs. In this study, an alternative air cathode without a diffusion layer was developed using a cross-linked hydrogel, oxidized konjac glucomannan/2-hydroxypropytrimethyl ammonium chloride chitosan (OKH), for ion bridging. The cathode was placed horizontally to avoid hydraulic pressure on its surface. Ion transportation was sustained with a minimal OKH hydrogel loading of 10 mg/cm2. A maximum power density of 1.0 ± 0.04 W/m2 was achieved, which was only slightly lower than the 1.28 ± 0.02 W/m2 of common air cathodes. Moreover, the cost of the OKH hydrogel is only $0.12/m2, which can reduce ~85% of the cathode cost without using the advanced polyvinylidene fluoride diffusion layer. Therefore, the development of this new diffusion-layer-free air cathode using conductive ionic hydrogel provides a low-cost strategy for stable MFC operation, thereby demonstrating great potential for practical applications of MFC technology.

Process parameters selection in manufacturing of sharp conical parts based on Taguchi design of experiments

Among the sheet metal forming processes, hydrodynamics deep drawing and hydromechanical deep drawing process are two main types of the deep drawing process that can fabricate complicated parts. In the hydroforming process, the blank is formed to the desired shape by applying a considerably high hydraulic pressure. In this article, the selection of the process parameters will be investigated during the manufacturing of a pure copper sharp conical part by finite element analysis and experimental tests. Two finite element models are developed for hydrodynamics deep drawing and hydromechanical deep drawing processes. After verification of the FE model by experimental results, the effect of process parameters includes the applied pressure, friction coefficient, die radius and blank holder force on thinning of the blank are investigated. The thinning ratio of blank is calculated in different zones of the conical part under different working conditions determined according to the Taguchi design of experiment methods. Signal to noise ratio analysis has been carried out and the influence of process parameters on the thinning ratio is determined at different zones of the conical part. The results show that the friction coefficient has an important role in the thinning of the conical nose while at the lateral surface of the cone, the die radius is the most effective parameter on the thinning ratio. The results show that by implementing statistical tools (Taguchi method and signal to noise ratio analysis), it is possible to select the proper process parameters conditions and fabricate defect-free parts. In addition, a non-linear regression equation is developed for prediction of thinning ratio in the hydrodynamics deep drawing and hydromechanical deep drawing processes.

Mathematical methods to unloading creep constitutive model of rock mass under high stress and hydraulic pressure

The main purpose of this paper is to study the unloading mechanical characteristics of rock mass unloading under high stress and high water pressure. An unloading creep test of deep sandstone was conducted under different initial stresses and hydraulic pressures by using the TFD-2000 rock triaxial rheological test system. Based on the experimental results, we can explore unloading creep properties and time-dependent deformation characteristics of rock mass. Deformation characteristics of rock masses during the attenuation and stable creep stages under different stresses and hydraulic pressure conditions were analyzed, and the variation laws of creep parameters in different creep stages were studied and fitted by a mathematical model. The applicability of the fitting results was discussed. A nonlinear unloading creep constitutive model and mathematicalmethods of rock mass under high stress and high hydraulic pressure was proposed based on element model theory. Parameters of this nonlinear creep constitutive model were recognized. Results demonstrated that the nonlinear deformation characteristics run through the entire creep stage. During the attenuation and stable creep stages, elastic deformation parameters generally present exponential functional variations with the increase in time and hydraulic pressure. In the accelerating creep stage, viscous deformation parameters also present an exponential functional variation. The test curve fits with the model curve obtained by the optimal numerical analysis software 1stOpt, which verifies the accuracy and applicability of the model. This study can provide theoretical references for accurate prediction of time-dependent deformation of deep rocks under high stresses and high hydraulic pressures.

Enhanced water management via the optimization of cathode microporous layer using 3D graphene frameworks for direct methanol fuel cell

Water management is one of the key roles in determining the output performance of a passive direct methanol fuel cell (DMFC). By decreasing the size of hydrophobic pores inside the cathode microporous layer (MPL), a high hydraulic pressure can be built up inside the cathode catalyst layer, which enhances the water recovery from cathode to anode and thus improves the cathode mass transfer. To achieve this, three-dimensional graphene frameworks are adopted to construct cathode MPL for the first time, whose intrinsic pore structure and characteristics contribute to an enhanced water management. Experimental results show that the performance and stability of the as-prepared DMFC are significantly improved. To illustrate the mechanism of the improvement, the in-situ measurements of polarization and methanol crossover are conducted, which reveals a greatly lowered water transport coefficient, along with a reduced in-situ methanol crossover rate. Since the role of polytetrafluoroethylene (PTFE) is weakened in the novel design of MPL, a further optimization via reducing PTFE content is realized, leading to a total increase of 43% of the output performance. The significant elevation of both the performance and stability of DMFC can expand its potential as a green energy source in practical applications.

Failure of circular shaft subjected to hydraulic uplift: Field and numerical investigation

A working shaft for pipe-jacking is going to be excavated into a sand stratum with high hydraulic pressure in Guangzhou, China. A newly assembled pre-stressed retaining system has been proposed to support the shaft for its efficiency, safety and sustainability. Full-scale field tests and numerical analysis were conducted to analyze the base failure of the circular shaft with confined water. The failure process of the shaft was observed on site. The construction process of step-by-step excavation of shaft and layer-by-layer assembly of pre-stressed structure was simulated in detail. Simulation results agree well with the phenomenon on site. The base failure modes present that tensile damage generates at the center of the base due to non-uniform uplift and shear failure occurs along the soil-structure interface. The effects of shaft size and confined water head were also discussed. As a result, a critical ratio of diameter to shaft depth is put forward to assess the size effect of circular shaft. A conclusion that the soil strength should be partially considered in anti-inrushing safety factor calculation is drawn by analysis and comparison of various calculation methods. This research provides a reference for the base stability evaluation of similar shaft subjected to hydraulic uplift.

In situ self-assembled biosupramolecular porphyrin nanofibers for enhancing photodynamic therapy in tumors.

Due to the complicated environment and high tissue hydraulic pressure in tumors that easily pumps the nanomedicines back to the systemic circulation, the concentration of released photosensitizers (PSs) retained in a tumor by a traditional nano-delivery system is very low, causing an unsatisfactory photodynamic therapy (PDT) effect. Therefore, we prepared a pH/H2O2-responsive nano-system (ZnP-OC-M) through modified porphyrin PS units with a long-unsaturated oleoyl chloride chain, and by the further introduction of hydrophilic hydroxyl groups and MnO2 through a cis-addition reaction between the unsaturated double bonds of oleoyl chloride and dilute KMnO4 solution. Making use of the sensitivity of MnO2 to the H2O2 in the acid environment of tumor cells, ZnP-OC-M selectively realized responsive disintegration and O2 generation. More importantly, the rich amphiphilic PS units were shedded simultaneously and spontaneously completed the self-assembly into nanofibers in situ by helical stacking, which displayed a 1.85-fold higher retention effect of PSs in vivo compared with free PS groups and showed a great tumor inhibition effect in enhancing PDT. This nanosystem effectively solves the problem of the low retention abilities leading to a poor PS concentration in a tumor, prolonging the treatment time window efficiently after only a single administration and achieving the purpose of PDT enhancement.