Internal Suction Research Articles

Triaxial Apparatus for Applying Liquid Infiltration with Controlled Boundary Conditions and Internal Suction Measurement

This note describes a triaxial apparatus that applies liquid infiltration under automatically controlled boundary conditions while using the new Xeritron sensor to measure suction. Three different infiltration boundary conditions of interest including constant mean stress (CMS), constant volume (CV), and constant stiffness (CS) are applied to examine the influence of boundary conditions on the mechanical and hydraulic behavior of unsaturated clay materials. CMS and CV tests provide limits of infiltration boundary conditions while CS tests represent a flexible spring-type boundary condition. Spatial distribution of gravimetric water content and bulk density are measured to calculate dry density and degree of saturation following testing to determine internal changes to the specimens. The results from initial testing show that the apparatus is providing experimental evidence to evaluate unsaturated flow models and elastic-plastic constitutive models to examine the behavior of swelling clay soils under varying confinement conditions.

Ultimate behavior of reinforced concrete cooling tower: Evaluation and comparison of design guidelines

Taking into account the geometrical and material nonlinearities, an ultimate behavior of reinforced concrete cooling tower shell in hyperbolic configuration is presented. The design wind pressures suggested in the guidelines of the US (ACI) and Germany (VGB), with or without the effect of internal suction, are employed in the analysis to examine the qualitative and quantitative characteristics of each design wind pressure. The geometrical nonlinearity is incorporated by the Green-Lagrange strain tensor. The nonlinear features of concrete, such as the nonlinear stress-strain relation in compression, the tensile cracking with the smeared crack model, an effect of tension stiffening, are taken into account. The biaxial stress state in concrete is represented by an improved work-hardening plasticity model. From the perspective of quality of wind pressures, the two guidelines are determined as highly correlated each other. Through the extensive analysis on the Niederaussem cooling tower in Germany, not only the ultimate load is determined but also the mechanism of failure, distribution of cracks, damage processes, stress redistributions, and mean crack width are examined.

Mechanical properties of the lacunar gas in Egeria densa Planch. shoots

The effects of varying internal and external pressures on the lacunar gas system were examined for the submerged macrophyte Egeria densa Planch. Application of 30 kPa to cut shoots caused gas flow in accordance with the Poiseuille equation, once the meniscus formed by surface tension and hydrostatic pressure was broken. Surface tension averaged 1.85 kPa for the internodal canals and 41.10 kPa for the pores of the nodal diaphragms. According to calculations based on hydrostatic pressure effects, broken shoots will not release gas in water deeper than 2.4 m in the light, and water could infiltrate internodal canals at 2.9 m and nodal pores at 6.8 m. In the dark, when internal suction assists infiltration, the meniscus would break and the internodal canals flood at the surface, and at 4.4 m depth for the diaphragm pores. Yet the nodal diaphragms were remarkably resistant to flooding. Water applied at 50 kPa failed to penetrate them, owing to their high resistance to water flow (130 000 MPa s −1 m −3, cf. 540 MPa s −1 m −3 for the internodal canals) and hydrophobic lining at the pores. Infiltration through broken surfaces is therefore unlikely to cause extensive natural infiltration in Egeria; this probably results from condensation from the surrounding cells. External pressures slightly compressed the lacunae; the lacunar system lost 2.3% of its initial volume at 50 kPa applied pressure. The elastic modulus of the shoots was only 1845 kPa, suggesting that the lacunae are well protected from external pressures by the turgor pressure and wall resistance of the surrounding tissues. The lacunar system did not expand when it was internally pressurised, so lacunar pressurisation does not add buoyancy or mechanical strength in this species.

Experimental study of aerodynamic processes inside the iron of a twisting-drawing frame

Free convective flow of air is the basic gas flow in the iron of a twisting—drawing frame. If special measures are not instituted, this flow separates from the heating surface approximately in the middle of the iron due to the convex shape of the heating surface of the iron. Primary evaporation of oiling agent takes place in the lower part of the iron where the fibre diameter has already decreased significantly. Mixing of oiling agent vapors and air affects the efficiency of operation of the drawing system, Mixing is potentiated near the region of separation of free convective flow due to turbulization of air flow. The method of internal suction in the upper part of the iron prolongs separation of free convective air flow from the surface of the heating element, potentiates mixing of oiling agent vapors, and improves the efficiency of operation of the local exhaust system by approximately one order of magnitude. Preliminary turbulization of the air flow as a result of setting a hydrodynamic brake in the air inlet in the iron improves the efficiency of the local exhaust system by approximately two times, with all other conditions being equal, due to improved mixing of oiling agent vapors and air.