scholarly journals Explicit analytical solutions for one-dimensional steady state flow in layered, heterogeneous unsaturated soils under random boundary conditions

2007 ◽  
Vol 43 (9) ◽  
Author(s):  
Zhiming Lu ◽  
Dongxiao Zhang ◽  
Bruce A. Robinson
Keyword(s):  
Steady State ◽  
Boundary Conditions ◽  
Analytical Solutions ◽  
Unsaturated Soils ◽  
Steady State Flow ◽  
Random Boundary ◽  
One Dimensional ◽  
State Flow

Prediction of the steady and non-steady flow performance of a highly loaded mixed flow turbine

1998 ◽  
Vol 212 (3) ◽  
pp. 173-184 ◽  
Author(s):  
M Abidat ◽  
M Hachemi ◽  
M K Hamidou ◽  
N C Baines
Keyword(s):  
Steady State ◽  
Performance Prediction ◽  
Internal Combustion Engines ◽  
Prediction Method ◽  
Combustion Engines ◽  
Steady State Flow ◽  
Mixed Flow ◽  
One Dimensional ◽  
Flow Equations ◽  
State Flow

This paper describes a method for predicting the performance under both turbine inlet steady state and non-steady state flow conditions of a mixed flow turbine used for turbocharged internal combustion engines. The mixed flow turbine steady state performances computed with the steady state performance prediction method are in good agreement with the experimental results obtained in the Imperial College turbocompressor cold air test rig. The unsteady state performance is computed using a one-dimensional model based on the solution of the unsteady one-dimensional flow equations. These equations are solved in the volute by a finite difference method using a four-step explicit Runge—Kutta scheme. The instantaneous volute exit condition is provided by the steady state rotor performance prediction model with the assumption of a quasi-steady state flow in the rotor. The computed instantaneous performances are in reasonable agreement with published experimental data for the same mixed flow turbine. The unsteady flow model is also used to study the effects of the frequency and the amplitude of the pulse on the performances of the mixed flow turbine.

Improved measurement of conductivity on swelling clay soils using a modified disc permeameter method

Soil Research ◽  
2006 ◽  
Vol 44 (7) ◽  
pp. 701 ◽  
Author(s):  
J. L. Foley ◽  
P. E. Tolmie ◽  
D. M. Silburn
Keyword(s):  
Steady State ◽  
Unsaturated Soils ◽  
Strongly Correlated ◽  
Internal Drainage ◽  
Wetting Front ◽  
Steady State Flow ◽  
State Flow ◽  
Modified Method ◽  
Swelling Clays ◽  
Unsaturated Hydraulic Conductivity

Disc permeameters are the preferred method for measuring unsaturated hydraulic conductivity (Kψ) in situ. However, in swelling clays, Kψ measured using 3-D measurement and analysis methods are often several orders of magnitude too high and are of no value for modelling internal drainage. During a series of experiments, the causes of inflated Kψ values were identified and a modified method developed to accurately measure Kψ. On a Black Vertosol, Kψ was strongly correlated with water content and measurement period, with higher flow rates occurring until the soil profile had fully wet up. Near-saturated Kψ measured under permeameters was up to 2 orders of magnitude higher than field-saturated conductivity (KFS) measured in ponded rings. This discrepancy was caused by residual capillarity and unrestricted swelling at the wetting front in unsaturated soils. In addition, lateral flow was common and surface depressions around permeameters filled with water, erroneously contributing to measured infiltration and invalidating assumptions in the 3-D analysis. To prevent this, permeameters were confined within rings to restrict flow to 1D, and measured Kψ (confined) was then compared with Kψ (unconfined) and KFS (ponded rings). Confining flow to 1D reduced Kψ by up to 2 orders of magnitude for a Black Vertosol and by a factor of 3 for a Red Ferrosol. Near-saturated Kψ from confined permeameters agreed well with KFS after similar short measurement durations (e.g. 0.5 h), but Kψ was still overestimated until steady-state flow was established. Therefore, to derive estimates of Kψ that reflect natural flow during internal drainage, we recommend (i) pre-wetting the soil and extending measurement time to attain steady-state flow, and (ii) confining permeameters within rings to restrict flow to 1 dimension. This method was used to compare lucerne ley and annual cropping treatments on 2 Black Vertosols (Bongeen and Waco). Kψ was similar between cropping treatments, suggesting that initial differences in structure and porosity were transient and related to soil moisture content. The Bongeen soil had a significantly lower Kψ (K–1 cm of 0.8 mm/h) than the Waco soil (2.0 mm/h).

Stability of Twin Shallow Tunnels in Unsaturated Soils Considering Vertical Steady State Flow

2019 ◽  
Vol 37 (5) ◽  
pp. 4603-4612
Author(s):  
Zi-han Yang ◽  
Shui-sheng Li ◽  
Dong Yang ◽  
Shuai Zhou ◽  
Quan Zhou
Keyword(s):  
Steady State ◽  
Unsaturated Soils ◽  
Steady State Flow ◽  
State Flow ◽  
Shallow Tunnels ◽  
Twin Shallow Tunnels
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