DETERMINATION OF STATIC AND DYNAMIC DIFFUSION COEFFICIENTS OF MOISTURE IN PARTICLEBOARDS

The static and dynamic diffusion coefficients are important coefficients to describe the moisture transfer processes in particleboard. In this paper, the formula of culculating the static and dynamic diffusion coefficients were deduced. At first, the static diffusion coefficients of four kinds of particleboards were determined by using diffusion cup method. The results demonstrated that the static diffusion coefficients parallel to panel surface were 10-20 times as large as that of perpendicular to panel surface for test boards. To determine both dynamic diffusion coefficients and surface emission coefficients of moisture in particleboards in one experimental period, specimens in four different thicknesses of each kind of particleboard were used in the experiment. Then the method of regression was used and the dynamic diffusion coefficients and surface emission coefficients were determined based on the slope and intercept of the regressive line.

Static and Dynamic Indicators in the Analysis of Internal Sources of Companies＇ Investments Financing

The Republic of Serbia is characterized by an unsatisfactory macroeconomic environment. Under the conditions of an evident shortage of liquid assets, the financial capital has moved from real to the financial sector, which led companies to over-indebtedness and shutdown of their own capacities. Therefore, capital investments largely depend on internal financing sources and the ability of companies to internally generate funds for investments. In this regard, an emphasis is placed on the difference in the assessment of the company＇s investment capacity based on internal financing sources, which are measured using static and dynamic indicators in order to prove the necessity of applying dynamic coefficients, which are unfortunately not present in our domestic practice. The paper examines and proves the advantages of the use of the dynamic approach for such analyses using the example of energy sector, which is one of the most important branches in Serbian economy.

"Nonlinear" characteristics of the static earth pressure coefficient in thick alluvium

Exact calculations of the static earth pressure from a thick alluvium require accurate/Co values. These calculations influence the sinking cost and the safety of the freezing method. The static earth pressure coefficient （K0） of thick and deep soil was analyzed using laboratory tests. The results show that the static earth pressure coefficient of thick and deep soils is nonlinear and different from that of superficial soils. The constant of superficial soils is usually invariant and the total stress or incremental stress definitions used in traditional geo-meehanics give the same value. The influence of load increments when calculating for superficial soil is ignored. The difference in values of K0 for thick alluvium defimed by the total stress or the incremental stress methods is over 10%. The effects of the thick alluvium on K0 should be considered during the design of frozen shaft projects. Such things as the frozen shaft thickness and the excavated section height should be chosen to assure the rationality of the design and to avoid potential faults and accidents.

Study on the Test Method of Static Earth Pressure Coefficient of Deep Soils

The static earth pressure coefficient of soils is,approximately,considered to be a constant in the view of clas-sical soil mechanics. This is supported by many research results. The high pressure experimental research and analysis of remolding deep soil described herein indicate that the static earth pressure of thick overburden has a notable non lin-ear characteristic. It also appears larger than that of superficial soils. It is necessary for deep coal mine design and con-struction to consider this particularity of soil pressure so as to avoid engineering accidents and heavy loss of life and property.

Laser Surface Textured PTFE Inhibitation for Stick-Slip Phenomenon Under Boundary Lubrication

When the machine tool is in the start-and stop-stages,the stick-slip phenomenon will be observed and highprecision positioning,machining accuracy and fretting feed will not be guaranteed. The most critical reason is that there is the difference between the dynamic and the static friction coefficients. Textures with different area ratios are fabricated on the surfaces of the upper PTFE-based composite and the friction tests are carried out on a reciprocating tribotester under the boundary lubrication and flat-on-flat contact conditions. The results show that there exists an optimal textured area ratio of 19.6% that can minimize the difference between the dynamic and the static friction coefficients.

Coefficient of consolidation by end of arc method

One of the most important issues in geotechnical engineering is excess pore pressure caused by clay soil loading and consolidation. Regarding uncertainties and complexities, this issue has long been the subject of attention of many researchers. In this work, a one-dimensional consolidation apparatus was equipped in a way that pore water pressure and settlement could be continuously read and recorded during consolidation process under static loading. The end of primary consolidation was obtained using water pressure changes helping to present a new method for determining the end of primary consolidation and consolidation coefficient. This method was then compared with two classical theory methods of lg t and t. Using Terzaghi's theory, the way of pore pressure dissipation for lg t, t and the new method was found and compared with experimental results. It is concluded that the new method has better results.

Investigation of interaction effect between static and rolling friction of corn kernels on repose formation by DEM

The coefficient of static friction(SF),the coefficient of rolling friction(RF)for particles are two key parameters affecting the repose angle formation and flow characteristics.In this paper,the interaction effects of SF and RF on the formation process of corn repose angle was investigated by the discrete element method.Firstly,five shape kinds of corn models(horse tooth,spherical cone,spheroid,oblate,and irregular shape)were established.Secondly,aluminum cylinder and organic glass box were used to conduct the simulation experiments with taking SF and RF as independent factors and seeing the repose angle as dependent value.Based on simulation results the regression equations were established.Simulation results showed the relation between two factors and the rotational kinetic energy is not nonlinear,and SF does not significantly restrict the flow of corn models after increasing the flow direction,and the effect of SF on the contact number between corns and the bottom plate is remarkable,while the effect of RF on the contact number is not remarkable.Finally,the interaction effect of two factors on the repose angle was analyzed by variance analysis and results showed SF and RF all have a significant impact on the repose angle.Moreover,their interaction effect has an impact on the repose angle.

Development and validation of an integrated mechatronic apparatus for measurement of friction coefficients of agricultural products

An integrated mechatronic apparatus was developed based on tilting plate method in order to precisely measure static friction coefficient(SFC)and dynamic friction coefficient(DFC)of agricultural products.The apparatus consisted of two main parts(mechanical and electrical parts).The main element of mechanical part was rotary container.Meanwhile,the electrical part included control,display,goniometer,level controller,rotational power supply,and infrared unit.The apparatus was initially simulated in simulation environment and practically calibrated to achieve high precision measurements.To appraise performance of the apparatus,the SFC and DFC of three grains were measured on five contact surfaces.Experiments were also conducted by means of a typical apparatus operating based on puling force method.Some statistical descriptor parameters such as mean absolute percentage error(MAPE),average of absolute values of measurement errors(AAVME),maximum of absolute values of measurement errors(MAVME),and correlation coefficient were used to compare accuracy of the apparatus with the typical one.The acceptable AAVME(<10%),MAVME(<10%),MAPE(<5%),and correlation coefficient(>0.9)indicated high accuracy,stability,and efficiency of the apparatus for automatic measurements of the SFC and DFC.From practical point of view,the mechatronic apparatus would be a beneficial tool for experimental,educational,demonstrational,and research works.

Effect of Impeller Geometry and Tongue Shape on the Flow Field of Cross Flow Fans

Experiments were conducted to investigate the effect of impeller geometry and tongue shape on the flow field of cross flow fans.Three impellers(Ⅰ，Ⅱ，Ⅲ）having same outer diameter,but different radius ratio and blade angles were employed for the investigation.Each impeller was tested with two tongue shapes.Flow survey was carried out for each impeller and tongue shape at two flow coefficients.and for each flow coefficient at different circumferential positions.The flow is two-dimensional along the blade span except near the shrouds.The total pressure developed by the impellers in each case is found to be maximum at a circumferential position of around 270°.The total and static pressures at the inlet of impellers are more or less same regardless of impeller and tongue geometry,but they vary considerably at exit of the impellers.Impeller Ⅲ with tongue T2 develops higher total pressure and efficiency where as impeller Ⅱ with tongue T2 develops minimum total pressure.Higher diffusion and smaller vortex size are the reasons for better performance of impeller Ⅲwith tongue T2。

FORCES ON A NEAR-WALL CIRCULAR CYLINDER

The pressure distribution around a near-wall smooth circular cylinder incross-flow was mainly investigated. The experiment was conducted at the sub-critical Reynolds numberranging from 2. 24 · 10~4 to 8. 94 · 10~4, at which the regular vortex separation exists on anisolated circular cylinder. The experimental results indicate that the forces on a circular cylindernear a plane wall are different from those on an isolated circular cylinder. Drag and liftcoefficients of a near-wall circular cylinder strongly depend on gap ratio. The increase of gapratio results in the increase of drag coefficient and the declination of lift coefficient, dragcoefficient ranges from 0. 5 to 1. 0, and lift coefficient from 0. 25 to 0 when gap ratio graduallyincreases from 0 to 1. 0, and then the forces tend to be nearly constant with the increase of gapratio. The attraction between a cylinder and a plane wall, i. e. , downward force, occurs when gapratio lies in certain range. The existence of cylinder changes the pressure gradient on the planewall, and the influence extends to the location where x/D 【 - 3.0 and x/D 】 5. 0 .

Determination of the physical and interaction properties of sorghum grains:Application to computational fluid dynamics-discrete element method simulations of the fluid dynamics of a conical spouted bed

Computational simulation is an important tool for design and improvement of industrial units.Computational fluid dynamics(CFD)coupled with the discrete element method(DEM)has been applied to simulate drying equipment that usually involves gas-solid flow.For reliable results of CFD-DEM simulations,the properties related to the interactions of the material within the industrial equipment,such as the restitution or friction coefficients,must be known.In this study,CFD-DEM was applied to simulate the fluid dynamics inside a conical spouted bed operating with sorghum grains.The physical properties of the particulate phase and the particle-particle and particle-wall interaction parameters were determined by the direct measurement approach and applied to CFD-DEM.The interaction parameters were experimentally determined,including the particle-particle interaction parameters ofη=0.46,μ^(S)=0.79,andμ_(R)=0.70,and the particle-wall interaction parameters ofη=0.56,μ_(S)=0.75,andμ_(R)=0.40.The simulated minimum spouting velocity and characteristic curves were compared with the experimental results.There was good agreement between the simulated and experimental results.

Testing development of different surface treatments on pervious concrete

Pervious concrete systems are developing stormwater management technologies which also have wintertime benefits as melting snow may percolate into the system instead of refreezing on the surface. Enhancing the surface microtexture of pervious concrete may also be beneficial in preventing icing or slipping by pedestrians. This research explored different surface treatments on pervious concrete specimens both qualitatively from personal judgements, and quantitatively through static friction measurements with a spring balance with respect to ＂slipperiness＂. The tests were performed on both dry and wet specimens. One aim was to determine whether the spring balance method may be a simple test for comparing surface treatments on pavement samples with little surface area such as laboratory specimens or sidewalk sections. The other purpose was to make a preliminary decision of which surface treatments to use for a sidewalk installation for future studies on wintertime performance. The reliability analysis of the spring balance results showed that there was high operator consistency. In addition, there was a high level of consistency on average results between the quantitative and qualitative methods. This implies that the spring balance test may be an acceptable methodology for comparative analyses with respect to static friction.