Fast determination of meso-level mechanical parameters of PFC models

To solve the problems of blindness and inefficiency existing in the determination of meso-level mechanical parameters of particle flow code (PFC) models, we firstly designed and numerically carried out orthogonal tests on rock samples to investigate the correlations between macro-and meso-level mechanical parameters of rock-like bonded granular materials. Then based on the artificial intelligent technology, the intelligent prediction systems for nine meso-level mechanical parameters of PFC models were obtained by creating, training and testing the prediction models with the set of data got from the orthogonal tests. Lastly the prediction systems were used to predict the meso-level mechanical parameters of one kind of sandy mudstone, and according to the predicted results the macroscopic properties of the rock were obtained by numerical tests. The maximum relative error between the numerical test results and real rock properties is 3.28% which satisfies the precision requirement in engineering. It shows that this paper provides a fast and accurate method for the determination of meso-level mechanical parameters of PFC models.

Finite Element Analysis and Experiment on Viscous Warm Pressure Bulging of AZ31B Magnesium Alloy

Aiming at overcoming the low plasticity of magnesium alloy at room temperature, we researched viscous warm pressure bulging（VWPB） of AZ31B magnesium alloy based on the excellent thermal stability of viscous medium under the warm forming condition. The potential improvements of plastic deformation ability and forming quality of AZ31B magnesium alloy are expected with the aid of thermal characteristics of viscous medium. During bulging process the velocity field variation and pressure stress field distribution of viscous medium are observed at different temperatures through which the effect of temperature on the mechanical property of viscous medium and AZ31B magnesium alloy are analyzed. The results show that the formability of AZ31B magnesium alloy increases first and then decreases as the temperature increases and it is the best at 200 ℃. On the other hand, the viscous medium which can build non-uniform pressure stress field also exhibits a good flow property at elevated temperature, and it is helpful to improving the formability of AZ31B magnesium alloy.

Investigation on synergistic deposition of wax and hydrates in waxy water-in-oil(W/O) flow systems

Elucidating the synergistic effect of wax and hydrates, involving formation, aggregation and deposition,is imperative to the operation and transportation safety for offshore petroleum fields. To understand the characteristics and mechanism of synergistic deposition of wax and hydrates, flow and deposition experiments of systems with different wax contents(0-2.89 wt%), initial flow rates, pressures and temperatures were conducted in a high pressure visual flow loop. According to the flow rate and pressure drop data as well as the visual window observation, four different types of plugging scenarios of waxhydrate coexisting systems with different flow properties and wall deposition state were summarized,including rapid plugging, transition plugging, gradual plugging type I and gradual plugging type II.Compared with the wax-free system after hydrate formation, even with the addition of anti-agglomerant(AA) with the same concentration, wax-hydrate coexisting systems could not reach stable hydrate slurry flow state, indicating that the existence of wax deteriorated the performance of AA. Aside from the influence of wax crystals on hydrate agglomeration, it was found that wax deposition layer would alter the adhesion and bedding of hydrates, resulting in the variation of flow properties and wall deposition state.For low wax content systems(0.75 wt%) where rapid plugging occurred, the synergistic effect between wax and hydrates promoted the formation of wax-hydrate coupling aggregates, resulting in severe local deposition when the coupling aggregates attained critical deposition size and consequently decreasing flow rate, forming a vicious circle of decreasing transportability. Since bedding of coupling aggregates was hindered by the uniformly coated wax deposition layer on pipe wall, gradual plugging rather than rapid plugging occurred in medium wax content systems(1-1.25 wt%), predominately caused by the gradual increment in viscosity of waxy hydrate slurry. For relatively high wax content systems(2.89 wt%), hydrate formation and plugging did not occur, due to the insulation effect of wax deposition layer. A physical model for the synergistic deposition of wax and hydrates was also presented, which was meaningful to the development of a mathematical model for the prediction of blockage formation and risk analysis.

Preparation of Self-compacting Ultra-high Toughness Cementitious Composite

A self-compacting ultra-high toughness cementitious composite （UHTCC） reinforced by discontinuous short polyvinyl alcohol （PVA） fibers, which exhibits self-compacting performance in the fresh state and strain-hardening and multiple cracking behavior in the hardened state, was developed through controlling flow properties of fresh mortar matrix at constant ingredients concentrations determined by micromechanical design and ensuring uniform fibers dispersion. The superplasticizer was utilized to adjust its flow properties in the fresh state. A series of flow tests, including deformability test, flow rate test, and self-placing test, were conducted to characterize and quantify the fluidity performance of fresh mortar matrix and self-compactability of fresh UHTCC. It is revealed that the utilization of superplasticizer is efficient in producing the fresh mortar matrix with desirable fluidity and the resulting self-compacting UHTCC. In addition, results of four point bending tests on the developed self-compacting UHTCC confirm the insensitivity of mechanical performance of self-compacting UHTCC to the presence of external vibrations as well as the flexural characteristics of deformation hardening and multiple cracking.

Fundamental kinematics laws of interstitial fluid flows on vascular walls

In the previous studies,the phenomenon that the interstitial fluid(ISF)can flow along tunica adventitia of the arteries and veins in both human and animal bodies was reported.On the basis of these studies,this paper aims to:(i)summarize the basic properties of the ISF flows in the walls of arteries and veins,(ii)combine the basic properties with axiomaticism and abstract the axiom for ISF flows,and(iii)propose three fundamental laws of the ISF flow,(i.e.,the existence law,the homotropic law and the reverse law).The three laws provide solid theoretical basement for exploring the kinematic patterns of interstitial fluid flow in the cardiovascular system.

NUMERICAL SIMULATION OF FREE MIXING LAYER WITH CROSS SHEAR

A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whether the cross shear is introduced in theinitial time or in early stage. If cross shear is introduced in the stage that the roll-up ofmixing layer occurs, the turbulent intensities of now will increase and mixture of now willbe enhanced.

THE GENERAL PROPERTIES OF THE SPHERICAL VORTICES（SV）OF n－TH ORDER AND THE CHAOTIC PHENOMENA AND OF THE ORDERED STRUCTURES OF THE SV OF 3RD ORDER

The general properties of the spherical vortices(SV)of n-th order are discussedin this paper Numerical calculations are carried out in the case of n=3.We find outsome interesting phenomena concerning the chaotic regions and ordered islands on the Poincare sections. Interpretations of these phenomena are also given.

A comparison between powder flow property testers

In this work, three different shear testers-the Jenike shear cell tester, the Schulze ring shear tester, and the Brookfield powder flow tester-were compared in terms of the raw shear stress time series, yield loci points, angle of internal friction, cohesion, and unconfined yield strength. The three different powders of dolomitic lime, calcium lactate, and calcium carbonate were used for these comparisons. These three powders were characterized into different flowability classes using the ]enike classification, wherein dolomitic lime falls into the cohesive range, calcium lactate falls into the free-flowing range, and calcium carbonate falls into the very cohesive range. Results showed that the best agreement between the testers was found with moderately cohesive powders such as dolomitic lime. Furthermore, the free-flowing material tends to produce more consistent data between the three testers in terms of shear stresses and yield loci. It should be noted that the pre-shear data of free-flowing powder obtained by the Jenike shear cell must be appropriately interpreted. The largest differences between the testers are found with calcium carbonate, which is a highly compressible powder. The ways in which a high powder compressibility can differently affect the results obtained with the different testers were discussed.

Experimental Study on Engineering Behavior of Solidified Soil for Scour Repair and Protection

A new scour countermeasure using solidified slurry for offshore foundation has been proposed recently.Fluidized solidified slurry is pumped to seabed area around foundation for scour protection or pumped into the developed scour holes for scour repair as the fluidized material solidifies gradually.In the pumping operation and solidification,the engineering behaviors of solidified slurry require to be considered synthetically for the reliable application in scour repair and protection of ocean engineering such as the pumpability related flow value,flow diffusion behavior related rheological property,anti-scour performance related retention rate in solidification and bearing capacity related strength property after solidification.In this study,a series of laboratory tests are conducted to investigate the effects of mix proportion(initial water content and binder content)on the flow value,rheological properties,density,retention rate of solidified slurry and unconfined compressive strength(UCS).The results reveal that the flow value increases with the water content and decreases with the binder amount.All the solidified slurry exhibits Bingham plastic behavior when the shear rate is larger than 5 s^(-1).The Bingham model has been employed to fit the rheology test results,and empirical formulas for obtaining the density,yield stress and viscosity are established,providing scientific support for the numerical assessment of flow and diffusion of solidified slurry.Retention rate of solidified slurry decreases with the water flow velocity and flow value,which means the pumpability of solidified slurry is contrary to anti-scour performance.The unconfined compressive strength after solidification reduces as the water content increases and binder content decreases.A design and application procedure of solidified soil for scour repair and protection is also proposed for engineering reference.

Characterization of powder flow properties from micron to nanoscale using FT4 powder rheometer and PT-X powder tester

The rapid development of nanotechnology has led to a need to further understand the physical char-acteristics of nanoparticles.In this paper,the flow characteristics of micro-nano alumina particles with different particle sizes were characterized.The FT4 powder rheometer and the PT-X powder tester were used to measure the compression,friction,and dynamic properties of powders.Powder compressibility increased significantly as the particle size decreased from 27 μm to 30 nm.Pressure distribution in the silo was measured and predicted by Janssen's theory,with errors mostly less than 10%.The basic flow energy and the specific energy of the three powders were 4983,1734,and 244 mJ,and 6.80,11.70,and 6.70 mJ/g,respectively,indicating that there was no linear relationship between the change in flowability and particle size.The dynamic properties of the powders change from particle-dominated to agglomeration-dominated as the particle size decreases.The conclusion is supported by the results of field emission scanning electron microscopy.

Investigation into the transient flow characteristics of noble gas propellants using the pulsed inductive discharge in electric propulsion

The Pulsed Inductive Thruster(PIT)has the advantages of repeatable startup,no corruption and in-situ propellant feed.To study the flow expansion and circuit characteristics of PITs,the circuit-fluid model is developed,and the high temperature thermodynamic and transport models are combined with the circuit-fluid model to predict the critical plasma parameters.The flow fields of initial mass of 2–8 mg and charge voltages of 10–14 k V are simulated.Comparison of the flow fields of argon and helium propellants suggests that,the flow field structures are similar.Slight differences exist on the magnitude of the density and magnetic field,caused by larger velocity in lighter atom case and difference on the ionization gap between adjacent ionization levels.Analysis of the circuit characteristics by the two-dimensional results indicates that the ratio of coil inductance to circuit inductance affects both the rise rate and phase of the plasma current,the larger the ratio,the greater the rise rate and the better the following characteristic.The calculations show that the magnetic energy obtained within the decoupling distance determines the overall performance the thruster can be obtained;self-induced field maintained by the thermal motion after the main pulse leads to the long attenuation process and difference on the total impulse when the angle of conical pylon is varied under constant coil dimension.

Flow properties of fine powders in powder coating

Three types of nanoparticles and their combinations were blended into a fine powder, which has been used in the powder coating industry. To study their effects on flow properties, the modified powder samples were characterized using a variety of techniques that tested the powder under different powder states ranging from dynamic to static. It was found that all three nanoparticles improved the flow properties of the powder to some degree, though the amounts of the nanoparticles needed were different depending on their physical properties. Secondly, inconsistency among these powder characterization techniques was also found. This is attributed to the different states of the powder samples during a measurement including dynamic, dynamic-static and static states. It was confirmed that characterization techniques which test the flow properties of a powder under all three states are needed to fully describe the flow properties of the powder. Finally, the effects of combinations of nanoparticles were explored, and it was found that combinations of nanoparticles can intensify, weaken or combine the effects of their component nanoparticles. The effects of nanoparticle combinations are not a simple summation of the effects of their comnonent nanoparticles.

Influence of co-solvent hydroxyl group number on properties of water-based conductive carbon pastes

A series of water-based conductive carbon pastes were prepared by wet ball milling, followed by vacuum defoaming using isopropyl alcohol, propylene glycol or glycerin as co-solvents. Screen printing was then used to prepare conductive patterns. To determine the influence of co-solvent hydroxyl group number on the properties of water-based conductive carbon pastes, the rheological properties of the pastes and the surface morphologies and conductivities of the printed patterns were characterized. The results show that paste viscosity increased with the number of hydroxyl groups and the latter also affected thixotropy. In addition, the boiling points and surface tensions of the co-solvents increased consistently with hydroxyl group number, affecting the hydrodynamic flow. The conductive carbon paste created using propylene glycol as a co-solvent was the best for screen printing because of its weak coffee-ring effect and appro- priate rheological properties, resulting in a smooth coating surface and uniform deposition of the fillers. The resistivity of the pattern printed using paste PG, containing the closest packing of conductive carbon black particles, was 0.44 Ω cm.

FLOW PROPERTIES OF COHESIVE NANOPOWDERS

The fundamentals of cohesive powder consolidation and flow behaviour using a reasonable combination of particle and continuum mechanics are explained. By means of the model 搒tiff particles with soft contacts? the influ-ence of elastic-plastic repulsion in particle contacts is demonstrated. With this as the physical basis, the stationary yield locus, instantaneous yield loci and consolidation loci, flow function and compression function are presented. The flow properties of a very cohesive titania nanopowder (dS=200 nm) are shown. These models are used to evaluate shear cell test results as constitutive functions for computer aided apparatus design for reliable powder flow.

Effect of nanocomposite as pour point depressant on the cold flow properties and crystallization behavior of diesel fuel

The high effective nano-hybrid pour point depressant(PPD)has attracted extensive attention for its po-tential application in improving the cold flow properties of diesel fuel.In this paper,the nano-hybrid PPD was prepared by melt-blending method using three different alkyl chain lengths(i.e.,tetradecyl,hexade-cyl,and octodecyl)of n-alkyl methacrylate-maleic anhydride copolymers(R 1 MC-MA,R 1=C_(14),C_(16),C_(18))and SiO_(2)nanoparticles.The effect of those nano-hybrid PPDs on the cold filter plugging point(CFPP)and solidifying point(SP)depressing of diesel fuel were studied.Results indicated that nano-hybrid PPD showed much better performance on diesel fuel.The diesel fuel treated with 0.2 wt%C_(14)MC-MA/SiO_(2)nano-hybrid PPD exhibited the best depression in CFPP and SP by 6℃ and 18℃,respectively,which higher than that of single C 14 MC-MA.Viscosity-temperature curves and polarized optical microscopy were conducted to explore the performance mechanism;and results presented that nano-hybrid PPD of C_(14)MC-MA/SiO_(2)could effectively lower the low-temperature viscosity,and modify the crystallization behavior and crystal morphology of diesel.Therefore,the cold flow properties of diesel were significantly improved.

Aerodynamic and solid flow properties for flaxseeds for pneumatic separation by using air stream

This study aimed to develop simple empirical equations to predict flaxseeds properties.The first part of the present study deals with the physical,aerodynamic and solid flow properties of flaxseeds which are evaluated as a function of change in moisture content from 8.60%to 23.90%dry basis(d.b.),the dimensions of the length,width and thickness varied from 4.14 to 4.32 mm,2.03 to 2.13 mm and 0.88 to 0.93 mm,respectively.As the moisture content increased from 8.60%to 23.90%d.b.,the bulk density,true density and porosity were found to decrease from 46.65 to 44.89 kg/m3;1244 to 1176 kg/m3 and 46.65%to 44.89%,whereas angle of repose and terminal velocity were found to increase from 27.60 to 35.80 and 2.46 to 3.56 m/s,respectively.The static coefficient of friction on various surfaces,namely,plywood,stainless steel,galvanized iron,iron and internal also increased linearly with the increase in moisture content.The results of the experimental investigation may help to optimize some engineering parameters of separation equipment.The second part was carried out on a series of experiments to specify the optimum conditions of separating operation which insure the highest grade of separation efficiency with minimum losses.Pneumatic separation equipment was manufactured and tested under different combinations of the following factors:air stream velocity,feed rate and sample moisture content.The performance of the equipment was evaluated by using the indices separation efficiency and percentage of seed losses.The results of the equipment performances showed that the combinations of air stream velocity,feed rate and sample moisture content affected significantly the separation efficiency and grain losses.Air stream velocity of 2-6 m/s combined with 8.5 kg/h.feed rate and 8.6%moisture content can be considered the most favorable combination values of these variables.They gave the highest grades of separation efficiency and the minimum grain losses.

Improving cold flow properties of palm fatty acid distillate biodiesel through vacuum distillation

Palm fatty acid distillate(PFAD),a by-product of refining process of crude palm oil can be used as a potential feedstock for biodiesel production.However,the application of palm oil-based biodiesel is often hinder by its poor cold flow properties(CFP).Biodiesel fuel with poor CFP may crystallize and result in clogging of fuel lines,filters and injectors that cause engine operability problems.For that,a vacuum distillation method was designed and its feasibility and efficiency in improving the CFP was examined.A total of 13.60wt%of total saturated fatty acid methyl esters were successfully removed from the PFAD biodiesel,resulting in the improvement of the cloud point(CP),cold filter plugging point(CFPP)and pour point(PP)of PFAD biodiesel from 20℃,19℃,and 15℃to 13℃,11℃,and 9℃,respectively.It is remarkable that the improved CFPP satisfied the requirements for grade C summer biodiesel for temperate climates in EN 14212 standard.Additionally,Sarin(U FAME)empirical correlation was evaluated and it was found to have a good prediction of CFP for PFAD biodiesel,with lower than 2℃deviation.

On the nanoparticulate flow

Nanoparticulate flows occur in a wide range of natural and engineering applications hence have received much attention. The purpose of the present paper is to provide a brief review on the research on the nanoparticulate flow in some aspects which consist of the method of moment for solving the particle population balance equation, penetration efficiency, pressure drop and heat transfer in the turbulent nanoparticulate pipe flow, fluctuating-lattice Boltzrnann model for Brownian motion of nanoparticles.

An experimental study of diesel fuel cloud and pour point reduction using different additives

An experimental study was conducted to investigate the effects of four different additives on pour point and cloud point temperatures of a diesel fuel.Sample mixtures were prepared in different volumetric percentages of four different additives(Ethanol,Toluene,n-Heptane and Xylene)and diesel fuel mixture.Pour point and cloud point temperatures of the blends were measured using standard ASTM D2500 and ASTM D97-96a methods,respectively.Introducing the additives to the diesel fuel did not lead to a significant reduction in cloud point temperature of the fuel.In fact,the greatest obtained reduction in cloud point temperature was achieved using 20 vol%or more of Toluene-diesel fuel mixtures.Although cloud points did not change significantly,even the slightest amounts of additives caused a high reduction in the pour point temperature of the fuel.Ethanol was the most effective additive in lowering the pour point temperature of the fuel.A 20%ethanol-fuel mixture caused nearly a 30
reduction in the fuel pour point temperature.Therefore,knowing that none of the additives has a significant effect on cloud point temperature,while the greatest reduction in pour point temperature is achieved using ethanol even in low Vol%s,it can be concluded that the most efficient additive among these four additives to alter cold flow properties of a certain diesel fuel is Ethanol.