Study on the pipe friction resistance in long-distance rock pipe jacking engineering

Previous studies on pipe friction resistance are mainly concentrated in the soil layer,whereas the study on that in the rock stratum is limited.To estimate the pipe friction resistance in the rock stratum,the calculation models of pipe friction resistance and their applica-tion conditions were compared first.Then the friction resistance calculation model for pipe jacking in the rock stratum was established and simplified.Lastly,the measured(FM)and the computed(FN)pipe friction resistance was compared to validate the simplified friction resistance calculation model.The following conclusions can be drawn:(1)The existing calculation methods of pipe friction resistance can be well verified in the soil layer but cannot be applied in the rock stratum.(2)Sediment,pipe–rock friction coefficient and mud buoyancy are the main factors affecting the pipe friction resistance in long-distance rock pipe jacking engineering.(3)The simplified calculation model established by Deng et al.can estimate the pipe friction resistance in different rock strata at different jacking stages with satisfac-tory outcomes.Further research on the pipe-rock friction coefficient in different rock strata with different pipe–rock contact conditions merits further investigation to better predict the pipe friction resistance in the rock stratum.The research results have certain practica-bility and can provide a reference for similar projects.

Laboratory and field evaluation of asphalt pavement surface friction resistance

Pavement surface friction is a significant factor for driving safety and plays a critical role in reducing wet- pavement crashes. However, the current asphalt mixture design procedure does not directly consider friction as a requirement. The objective of this study was to develop a surface friction prediction model that can be used during a wearing course mixture design. To achieve the objective, an experimental study was conducted on the frictional characteristics of typical wearing course mixtures in Louisiana. Twelve wearing course mixtures including dense-graded and open-graded mixes with different combinations of aggregate sources were evaluated in laboratory using an accelerated polishing and testing procedure considering both micro- and macro texture properties. In addition, the surface frictional properties of asphalt mixtures were measured on twenty-two selected asphalt pavement sections using different in situ devices including Dynamic Friction Tester （DFT）, Circular Texture Meter （CTM）, and Lock-Wheel Skid Trailer （LWST）. The results have led to develop a procedure for predicting pavement end-of-life skid resistance based on the aggregate blend polish stone value, gradation parameters, and traffic, which is suited in checking whether the selected aggregates in a wearing course mix design would meet field friction requirements under a certain design traffic polishing.

静水中高速双体船气动、水动力学效应的数值和实验研究

In this paper,the effect of water and air fluids on the behavior of a planing catamaran in calm water was studied separately in calm water by using experimental and numerical methods.Experiments were conducted in a towing tank over the Froude number range of 0.49–2.9 with two degrees of freedom.The model vessel displacement of 5.3 kg was implemented in experimental tests.Craft behavior was evaluated at the displacements of 5.3,4.6,and 4 kg by using the numerical method.The numerical simulation results for the hull’s resistance force were validated with similar experimental data.The fluid volume model was applied to simulate two-phase flow.The SST k-ωturbulence model was used to investigate the effect of turbulence on the catamaran.The results showed that in the planing mode,the contribution of air to pressure resistance increased by 55%,40%,and 60%at the mentioned displacements,whereas the contribution of air to friction resistance was less than 15%on average.The contribution of the air to the total lift force at the abovementioned displacements exceeded 70%,60%,and 50%in the planing mode but was less than 10%in the displacement mode.At the displacements of 5.3 and 4 kg,the area under the effect of maximum pressure moved around the center of gravity and caused porpoising longitudinal instability at the Froude numbers of 2.9 and 2.4,respectively.However,at the displacement of 4.6 kg,this effect did not occur,and the vessel maintained its stability.

Properties of a High Hydrolysis Stable Nitrogenous Benzo-heterocyclic Borates

A benzotriazole-containing derivative was synthesized via the Mannich reaction.The structure was characterized by NMR spectroscopy.By utilizing computational chemistry and molecular simulation,the calculation and mapping of atomic charge and frontier molecular orbitals with complex structure of the borate were carried out.The acid number of BTBE(nitrogen-containing heterocyclic borate)was determined by the standard test method for acid number and the open observation method.The results showed that BTBE had a low initial acid number,because the acid number was changed only after 72 hours of hydrolysis,and it was negative after the hydrolysis reached 120 hours.The extreme-pressure friction resistance of BTBE and other four base oils was also determined.For 5 kinds of base oils,the friction experiment was carried out under a load of 30 kgf,and the BTBE showed a lowest wear scar diameter(0.365 mm)along with a highest maximum non-seizure load.The results showed that the EP friction resistance of BTBE was stronger than that of other four base oils under the same test conditions.The results of hydrolysis performance showed that the synthesized nitrogencontaining heterocyclic borate had a high resistance to hydrolysis,while demonstrating broad application prospects.

Two-dimensional Dynamics Simulation of Two-phase Debris Flow

To investigate the movement mechanism of debris flow, a two-dimensional, two-phase, depthintegrated model is introduced. The model uses Mohr-Coulomb plasticity for the solid rheology, and the fluid stress is modeled as a Newtonian fluid. The interaction between solid and liquid phases, which plays a major role in debris flow movement, is assumed to consist of drag and buoyancy forces. The applicability of drag force formulas is discussed. Considering the complex interaction between debris flow and the bed surface, a combined friction boundary condition is imposed on the bottom, and this is also discussed. To solve the complex model equations, a numerical method with second-order accuracy based on the finite volume method is proposed. Several numerical experiments are performed to verify the feasibilities of model and numerical schemes. Numerical results demonstrate that different solid volume fractions substantially affect debris flow movement.

Properties of copper/graphite/carbon nanotubes composite reinforced by carbon nanotubes

Electroless Cu plating was used for flake G powder and CNTs, Cu-G-CNTs （copper/graphite/carbon nanotubes） composites were manufactured by means of powder metallurgical method. The influences of CNTs on the mechanical properties, conductivity properties, friction, and wear performance of the composite were examined. The results indicate that adding a small amount of CNTs can improve comprehensive property of the composites, especially mechanical property. However, excessive CNT, which is easily winding reunion and grain boundary seg- regation, results in performances degradation.

具有阶梯状海底的表面穿透柔性多孔屏障结构斜波捕获

This study presents a simple numerical method that can be used to evaluate the hydrodynamic performances of antifouling paints.Steady Reynolds-averaged Navier-Stokes equations were solved through a finite volume technique,whereas roughness was modeled with experimentally determined roughness functions.First,the methodology was validated with previous experimental studies with a flat plate.Second,flow around the Kriso Container Ship was examined.Lastly,full-scale results were predicted using Granville’s similarity law.Results indicated that roughness has a similar effect on the viscous pressure resistance and frictional resistance around a Reynolds number of 10^7.Moreover,the increase in frictional resistance due to roughness was calculated to be approximately 3%-5%at the ship scale depending on the paint.

Influence of Non-smooth Surface on Tribological Properties of Glass Fiber-epoxy Resin Composite Sliding against Stainless Steel under Natural Seawater Lubrication

With the development of bionics, the bionic non-smooth surfaces are introduced to the field of tribology. Although non-smooth surface has been studied widely, the studies of non-smooth surface under the natural seawater lubrication are still very fewer, especially experimental research. The influences of smooth and non-smooth surface on the frictional properties of the glass fiber-epoxy resin composite（GF/EPR） coupled with stainless steel 316 L are investigated under natural seawater lubrication in this paper. The tested non-smooth surfaces include the surfaces with semi-spherical pits, the conical pits, the cone-cylinder combined pits, the cylindrical pits and through holes. The friction and wear tests are performed using a ring-on-disc test rig under 60 N load and 1000 r/min rotational speed. The tests results show that GF/EPR with bionic non-smooth surface has quite lower friction coefficient and better wear resistance than GF/EPR with smooth surface without pits. The average friction coefficient of GF/EPR with semi-spherical pits is 0.088, which shows the largest reduction is approximately 63.18% of GF/EPR with smooth surface. In addition, the wear debris on the worn surfaces of GF/EPR are observed by a confocal scanning laser microscope. It is shown that the primary wear mechanism is the abrasive wear. The research results provide some design parameters for non-smooth surface, and the experiment results can serve as a beneficial supplement to non-smooth surface study.

High-precision Thickness Setting Models for Titanium Alloy Plate Cold Rolling without Tension

Due to its highly favorable physical and chemical properties,titanium and titanium alloy are widely used in a variety of industries.Because of the low output of a single batch,plate cold rolling without tension is the most common rolling production method for titanium alloy.This method is lack of on-line thickness closed-loop control,with carefully thickness setting models for precision.A set of high-precision thickness setting models are proposed to suit the production method.Because of frequent variations in rolling specification,a model structural for the combination of analytical models and statistical models is adopted to replace the traditional self-learning method.The deformation resistance and friction factor,the primary factors which affect model precision,are considered as the objectives of statistical modeling.Firstly,the coefficient fitting of deformation resistance analytical model based on over-determined equations set is adopted.Additionally,a support vector machine（SVM）is applied to the modeling of the deformation resistance and friction factor.The setting models are applied to a 1450 plate-coiling mill for titanium alloy plate rolling,and then thickness precision is found consistently to be within 3%,exceeding the precision of traditional setting models with a self-learning method based on a large number of stable rolling data.Excellent application performance is obtained.The proposed research provides a set of high-precision thickness setting models which are well adapted to the characteristics of titanium alloy plate cold rolling without tension.

DYNAMIC EFFECTIVE SHEAR STRENGTH OF SATURATED SAND

The dynamic effective shear strength of saturated sand under cyclic loading is discussed in this paper.The discussion includes the transient time depen- dency behaviors based on the analysis of the results obtained in conventional cyclic triaxial tests and cyclic torsional shear triaxial tests.It has been found that the dy- namic effective shear strength is composed of effective frictional resistance and viscous resistance,which are characterized by the strain rate dependent feature of strength magnitude,the coupling of consolidation stress with cyclic stress and the dependency of time needed to make the soil strength sufficiently mobilized,and can also be ex- pressed by the extended Mohr-Coulomb's law.The two strength parameters of the dynamic effective internal frictional angle φd and the dynamic viscosity coefficient η are determined.The former is unvaried for different number of cyclic loading,dy- namic stress form and consolidation stress ratio.And the later is unvaried for the different dynamic shear strain rate γt developed during the sand liquefaction,but increases with the increase of initial density of sand.The generalization of dynamic effective stress strength criterion in the 3-dimensional effective stress space is studied in detail for the purpose of its practical use.

Effects of inner sleeves on the inner frictional resistance of open-ended piles driven into sand

In open-ended piles, inner friction is developed between inner pile shaf and the inner soil. Inner frictional resistance depends largely on the degree of soil plugging, which is influenced by many factors including pile diameter, relative density and end conditions of piles. In this paper, effects of inner sleeves on inner frictional resistance are discussed. The experiments were conducted on a medium-dense sandy ground using laboratory-scale piles. It was observed that the piles penetrated under partially-plugged or unplugged state. The results suggest that inner fiictional resistance, Qin increases with sleeve height, l linearly and requires 2D （D is pile outer diameter） of l to produce a large as 50% of Qt by Qin （Qt is total resistance）. The results also indicate that bearing capacity increases with wall thickness at the pile tip, which can be attributed to the increase in annular area. The results also indicate that soil plug height is independent of sleeve height. The results also reveal that the penetration of straight piles is closer to unplugged state than the sleeved piles. The results of incremental filling ratio and plug length ratio also indicate that the degree of soil plugging is affected by the sleeve height.

Degradation Behaviour Analysis of SMA Aggregate and Skeleton

Based on laboratory tests and field materials evaluation, the inner frictional resistance of SMA skeleton was investigated and then the degradation behaviour of SMA skeleton was characterized for recycling purpose. Inner frictional resistance test was designed to investigate the skeleton characteristics of SMA aggregate mixture. The experimental results indicate that SMA skeleton has much stronger inner frictional resistance than AC skeleton, and coarse aggregates provide main contributions to the inner frictional resistance of SMA skeleton. Crushing test and superpave gyratory compactor （SGC） test were designed to reveal the degradation behaviour of SMA skeleton. To verify the laboratory characterization, field materials were also evaluated. The results indicate that the degradation of SMA skeleton is not random but has fixed internal trend, especially the 4.75mm aggregate plays a key role in the graded aggregates. Based on the testing results, it can be concluded that long-term repeated loading can cause degradation of SMA skeleton. However, the gradation does not keep deteriorating under repeated loading. When the inner frictional resistance is small enough, outside pressure will cause flow deformation of skeleton instead of degradation. Thus, well-designed SMA aggregate mixture is valuable for recycling after long-term in service. And it is important to restore the skeleton, especially the coarse aggregate part.

表面粗糙度对水面舰船粘性阻力分量影响的数值研究

Recently,computational fluid dynamics(CFD)approaches have been effectively used by researchers to calculate the resistance characteristics of ships that have rough outer surfaces.These approaches are mainly based on modifying wall functions using experimentally pre-determined roughness functions.Although several recent studies have shown that CFD can be an effective tool to calculate resistance components of ships for different roughness conditions,most of these studies were performed using the same ship geometry(KRISO Container Ship).Thus,the effect of ship geometry on the resistance characteristics of rough hull surfaces is worth investigating.In this study,viscous resistance components of four different ships are calculated for different roughness conditions.First,flat plate simulations are performed using a previous experimental study for comparison purposes.Then,the viscous resistance components of three-dimensional hulls are calculated.All simulations are performed using two different turbulence models to investigate the effect of the turbulence model on the results.An examination of the distributions of the local skin friction coefficients of the DTMB 5415 and Series 60 showed that the plumpness of the bow form has a significant effect on the increase in frictional resistance with increasing roughness.Another significant finding of the study is that viscous pressure resistance is directly affected by the surface roughness.For all geometries,viscous pressure resistances showed a significant increase for highly rough surfaces.

THEORETICAL ANALYSIS OF TURBULENT FRICTIONAL RESISTANCE INSIDE DUCTS OF ARBITRARY ANGULAR CROSS SECTIONS

It is recognized that for turbulent flow inside a duct of angular cross section,devi- ation will take place if the hydraulic diameter is taken as the equivalent diameter to calculate the mean friction coefficient of the duct wall.It still remains a question to determine the extent of the deviation as no common formula is available and only a few cross sections have been tested. This paper presents an approach which takes the angle area of the angular cross section as an ad- dition to the angle-less cross section,analyses and calculates the size of laminar flow area of the angle area,quantifies the amount of deviation of using hydraulic diameter as the equivalent di- ameter and finally obtains the formula for calculating the turbulent friction coefficients of the ducts of arbitrary angular cross sections.The formula derived is universally applicable to cross sections with arbitrary number of angles and arbitrary forms of angles,i.e.,arbitrary angular cross sections.Experience shows it is easy to use and the result obtained has a good agreement with physical mechanism and test measurements.

THE FRICTIONAL RESISTANCE CHARACTERISTICS OF GAS LIQUID TWO PHASE FLOW IN HELICAL COILED TUBES

This paper deal with the frictional resistance characteristics of gas liquid two phase flow in vertical upward helical coiled tubes under the system pressure 0.1 0.6MPa. By means of dimension analysis and π theorem, the correlation formulas were obtained for calculating the frictional resistance coefficients of gas liquid two phase flow in helical coiled tubes. The calculated results agree well with the experimental results.

Surface Properties of Cement Paste Evaluated by Scanning Probe Microscopy

The microscopic physical properties of Hardened Cement Paste (HCP) surfaces were evaluated by using Scanning Probe Microscopy (SPM). The cement pastes were cured under a hydrostatic pressure of 400 MPa and the contacting surfaces with a slide glass during the curing were studied. Scanning Electron Microscope (SEM) observation at a magnification of 7000 revealed smooth surfaces with no holes. The surface roughness calculated from the SPM measurement was 4 nm. The surface potential and the frictional force measured by SPM were uniform throughout the measured area 24 h after the curing. However, spots of low surface potential and stains of low frictional force and low viscoelasticity were observed one month after curing. This change was attributed to the carbonation of hydrates.

Investigations of Water Flow Behaviors Induced by Local Temperature Variations through a Single Rough Fracture for the Enhanced Geothermal Systems

In recent years,Enhanced Geothermal System(EGS)technologies have been applied to the geothermal resources production in the Hot Dry Rock(HDR).The core of EGS technologies is to adopt hydraulic fracturing in the reservoir to create a connected network of discrete fractures with the consideration of water as a working fluid for hydraulic fracturing and heat production.This paper investigates the characteristics of water flow behaviors through a single rough fracture under different temperature and pressure conditions.A single fracture model with rough fracture surfaces is constructed and then characterized,and influences of the anisotropic factor on the average tortuosity and frictional resistance coefficient of water flow through a single fracture with rough surfaces have been compared and analyzed.With consideration of other impacting factors(temperature,pressure,fracture roughness),the impact of mass flow rate has also been presented.Numerical simulation results present that changes of average tortuosity for water flow through a single rough facture are mainly affected by temperature.It can be observed that higher temperature leads to larger average tortuosity but the frictional resistance coefficient shows an opposite trend.As for pressure conditions,it is found that effects of pressure on average tortuosity and frictional resistance coefficient is very small,which can be neglected under high pressure conditions.Furthermore,the average tortuosity shows a progressively linear relationship with the mass flow rate.On the contrary,the frictional resistance coefficient has a negative relationship with the mass flow rate.It is revealed that when the mass flow rate reaches a critical point,the influences of temperature on the frictional resistance coefficient will be negligible.Comparisons of single rough fractures with different anisotropic factors show that values of average tortuosity and frictional resistance coefficient have positive relationships with the increase of anisotropic factors.

Numerical investigation of frictional drag reduction with an air layer concept on the hull of a ship

A novel air bubble lubrication method using the winged air induction pipe (WAIP) device is used to reduce the frictional drag of the hull of the ship and hence increase the efficiency of the propulsion system. This bubble lubrication technique utilizes the negative pressure region above the upper surface of the hydrofoil as the ship moves forward to drive air to the skin of the hull. In the present study, the reduction rate of the drag by applying the WAIP device is numerically investigated with the open source toolbox OpenFOAM. The generated air layer and the bubbles are observed. The numerical results indicate that the reduction rate of the drag closely depends on the depth of the submergence of the hydrofoil, the angle of attack of the hydrofoil, and the pressure in the air inlet. It is also proportional to the air flow rate. The underlying physics of the fluid dynamics is explored.

Multifaceted Bioinspiration for Improving the Shaft Resistance of Deep Foundations

This paper describes the bioinspiration process to derive design concepts for new deep foundation systems that have greater axial capacity per unit volume of pile material compared to conventional deep foundations.The study led to bioinspired ideas that provide greater load capacity by increasing the pile shaft resistance.The bioinspiration approach used problem-solving strategies to define the problem and transfer strategies from biology to geotechnical engineering.The bioinspiration considered the load transfer mechanism of hydroskeletons and the anchorage of the earthworm,razor clam,kelp,and lateral roots of plants.The biostrategies that were transferred to the engineering domain included a flexible but incompressible core,passive behaviour against external loading,a longitudinally split shell that allows expansion for anchorage,and lateral root-type or setae-type anchoring elements.The concepts of three bioinspired deep foundation systems were proposed and described.The advantage of this approach was illustrated with two examples of the new laterally expansive pile in drained sand under axial compression.The finite element analysis of these examples showed that the new laterally expansive pile can provide considerably greater load capacity compared to a conventional cylindrical pile due to the increased lateral confining pressure developed along the expanded pile core.

Solid state crack repair by friction stir processing in 304L stainless steel

Friction stir processing （FSP） was investigated as a method of repairing cracks in 12 mm thick 304L stainless steel plate. Healing feasibility was demonstrated by processing a tapered crack using a PCBN/W- Re tool with a 25 mm diameter shoulder and a pin length of 6.4 mm. The experiment showed that it was possible to heal a crack that begins narrow and then progressively grows up to a width of 2 mm. Bead on plate experiments were used to find the best parameters for creating a consolidated stir zone with the least amount of hardness difference compared to the base metal. Grain refinement in some specimens resulted in much higher stir zone hardness, compared to base metal, A plot of grain size versus microhardness showed a very strong inverse correlation between grain size and hardness, as expected from the Hall- Perch relationship. Corrosion testing was carried out in order to evaluate the effect of FSP on potential sensitization of the stir zone. After 1000 h of intermittent immersion in 3.5% saline solution at room temperature it was found that no corrosion products formed on the base material controls or on any of the friction stir processed specimens.