Experimental and Numerical Study of Air Vessel in Quasi-Two-Dimensional Transient Flow Analysis

An air vessel is a simple and effective device for protecting a pipeline system from abnormal pressure events. In order to design and select a suitable air vessel, analysis of the pipeline system is necessary. A quasi-2D approach can overcome some of the limitations of the conventional one-dimensional transient flow analysis method. However, only a few hydraulic components can be implemented in the quasi-2D approach. In this study, we propose a methodology for applying an air vessel in the quasi-2D model. An experimental study is performed for validating the proposed model. Although an identical approach involving an accumulator model is used to model the air vessel as in the 1D model, the quasi-2D model shows improved performance for the experimental system.

Rapid Drawdown in Homogeneous Earth Dam Considering Transient Flow and Suction

The present work intends to demonstrate the advantages of considering transient flow regime in the stability analysis of the upstream slope for the rapid drawdown situation of a homogeneous earth dam. Upstream slope stability evaluations were carried out, considering pore pressure and suction from transient flow analysis while simulating rapid drawdown of the reservoir. The evaluations comprised different geometries of the upstream slope (from 1V:1.1H to 1V:2.5H) and heights varying from 10 m to 50 m, as well as several low permeability materials (SM, SM-SC, SC, ML, ML-CL, CL, MH and CH). In addition, equations relating the safety factor to such slopes or dam height were adjusted to the analysis data, in order to define the minimum slope for a certain dam height or the maximum height for a given upstream slope. The results have shown that, considering the transient flow condition, including suction, within the slope stability analysis of the rapid drawdown situation, increases the safety factor in relation to the simplified analysis that is usually adopted. This also results in much steeper slopes (for a safety factor of 1.1) than the ones recommended by the U.S. Bureau of Reclamation (USBR), suggesting the importance of performing transient flow analysis for rapid drawdown situations and considering its results instability analysis.

Modelling the Unsteady Flow of Water into a Partly Saturated Soil

Flows in unsaturated medium are frequent in the field of civil engineering and more particularly in geotechnics. The study undertaken here tries to solve the unsaturated transient flow equation in porous media using the finite element method. Numerical solution of a finite element discretization is used along with an implicit integration scheme of the time stepping. A functional one that makes it possible to find the distribution of the hydraulic load has been proposed and a calculation program has been developed. The results obtained by this program called TFAP (Transient Flow Analysis Program) are compared to other previous work in the subject. The authors show the importance of this study through two real examples. Liakopoulos conducted several experiments on the water drainage through a vertical column filled with Del Monte sand. One of these experiments was chosen to perform a simulation by the model. The results of the calculation are compared with the experimental data as well.

Transient Pressure and Rate Decline Analysis for Horizontal Well in Stress-Sensitive Composite Reservoir

The existence of stress sensitivity effect made the percolation mechanism of low-permeability reservoirs significantly complex. Further, numerous reservoirs have composite stratum properties in actual development procedure. This paper based on the concept of permeability stress sensitivity presents an unsteady flow model for horizontal well taking both stress sensitivity and composite reservoir into account. Analytic solutions for the transient pressure and the rate decline behaviors are obtained by comprehensive utilization of regular perturbation method, Laplace transformation, orthogonal transformation, and Stehfest numerical inversion. The example analysis verifies that the proposed model is reliable and practical. Likewise, there is a discussion of the influence of permeability modulus and other relevant parameters on the transient pressure and the rate decline for horizontal well in stress-sensitive composite reservoir. The work of this paper improved the previous researches and provided a more accurate basis for transient flow analysis and formation evaluation of this typical reservoir.

Pump-stoppage-induced water hammer in a long-distance pipe: a case from the Yellow River in China

Pump stoppage can instantaneously increase the pressure within a pipeline, which is an extreme condition and poses a severe threat to the safety of long-distance water transmission projects. Reducing positive and negative pressures is essential to reducing this risk, improving operational efficiency, and avoiding system component fatigue. This study investigated the performance of a combination of dimensionless pump parameters and pipeline pressure in providing detailed information for designing protective equipment to mitigate water hammer effects, which are generated by sudden pump stoppage. The conditions of the method of characteristics were satisfied by conducting an overall transient flow analysis to estimate the potential of the increased pressure relevant to all types of operating schemes. Extreme pressure waves, produced by pump failure or rapid valve closure, can be prevented using efficient protective designs. The findings of this study can be instructive to alleviating the potential damage engendered by water hammer.