Hydraulic Transients Research Articles

Response spectrum analysis of piping systems with elastic-plastic gap supports

A new seismic support device and its application in piping systems is described. The device, E-BAR (patented), can be cost effectively used for snubber replacement programs, mitigation of hydraulic transients, pipe whip and as a thermal stop. The device has pre-set gaps to allow free thermal movement. During a seismic or other dynamic load event, if the pipe movement exceeds the gap dimension, the device acts as an elastic or elastic-plastic restraint. The device also has a unique design feature for not exceeding the restraint force beyond a specified limit design value. To analyze piping systems with gap supports having elastic-plastic characteristics, modal analysis procedures for both response spectrum and time history methods are developed. The comparison of responses obtained from the procedures with nonlinear time history analysis and test results available in the literature shows excellent correlation. A pilot program conducted for snubber replacement with E-BARs demonstrates that the limit force feature of E-BAR makes them very attractive for snubber replacement. This is because a particular E-BAR with a specified limit design force can be selected, such that, the E-BAR replacing the snubber does not require any modifications be made to the existing support steel and hardware.

SOME CONSIDERATIONS ON UNSTEADY FLOWS IN UNDERGROUND CHANNELS

Hydraulic transients in the underground channel system such as the underground flood way and the sewer network are investigated experimentally and numerically. The typical features of unsteady flows induced by the inflow discharge into the underground channel are clarified by the fundamental hydraulic experiments. It is also shown that the hydraulic transients with the propagation of an interface between the open channel flow and the pressurized pipe flow can be reproduced by using the numerical model. Numerical model is extended to predict the hydraulic transients with the interaction between the overland surface flow and the underground channel flow, considering the inflow and outflow discharge through manholes.

Modelling the Damage Induced by Pressure Transients in Elasto-Plastic Pipes

This paper is concerned with the analysis of pressure transients in damageable elasto-plastic piping systems. The fluid dynamics and pipewall deformation are modelled by the classical water hammer theory, whereas pipewall mechanical behavior is described by an internal variable constitutive theory. The constitutive model coupling plasticity and damage used herein gives rise to a nonlinear hyperbolic problem in which the wavespeeds are altered by damage evolution. The problem is numerically approximated by means of a technique based on an additive decomposition together with the Glimm's method and a special Euler-type time integration scheme. Examples concerning the structural integrity analysis of a reservoir-pipe-valve installation, where hydraulic transients are generated by valve slam, are presented to illustrate the applicability of both theory and numerical method.

地表流と地下水路流の相互作用を考慮した非定常流解析法

地表流と地下水路流の相互作用を考慮した非定常流解析法

Use of variable orifice “duckbill” valves for hydraulic and dilution optimization of multiport diffusers

The use of variable orifice “duckbill” valves hydraulically optimizes marine effluent diffusers by generating higher jet velocity at low flows, reduced headloss at peak flow, and a more uniform port discharge distribution. Recent laboratory experiments showed that near field mixing and dilution were substantially improved with duckbill valves, and the purging of salt water from an outfall occurs at much lower flow than the theoretical flow required to purge a conventional outfall. An inherent characteristic of the duckbill valve is that it is a check valve that prevents the ingress of salt water, sediment, and marine organisms into the outfall during periods of low flow and hydraulic transients. This paper presents the hydraulic advantages of variable orifice duckbills verses fixed orifices with emphasis on enhancements in initial dilution and minimization of headloss at peak flow. The process of salt water purging will also be presented along with a brief discussion on failure mechanisms of conventional diffusers.

Simulation of hydraulic power plant transients using neural networks

In this work the efficiency of the artificial neural network technology for evaluating the turbine speed and drain synchronous valve during the turn-off transient phase of an actual hydraulic power plant has been evaluated. These results have been achieved avoiding a detailed time consuming analysis of the power plant. Several net architectures have been set up and verified with regard to their response to this strongly non-linear problem.

Optimal Design for Automatic Control of On-Demand Canal Systems

A methodology is developed for the design of an automatic gate controller for an on-demand canal system. The design is based on the EL-FLO plus RESET control concept developed previously by the U.S. Bureau of Reclamation. Two additional design parameters are included in this study to ensure a smooth upstream gate operation. The basic design parameters are optimized to achieve a stable flow condition in the entire canal system where multiple gates are operated to supply water to meet unexpected turnout demands along the canal. Due to the complexity involved in canal hydraulics, the optimization model is highly nonlinear. Decomposition allied with successive approximations is used for solution. The proposed design methodology, when applied to a section of the Caraibas Project in northeastern Brazil, showed that the proposed methodology is successful in minimizing hydraulic transients in a multipool canal system. A sensitivity analysis of the optimal design is conducted with respect to maximum demand level and the two new design parameters.

LESOTHO HIGHLANDS WATER PROJECT - DESIGN OF THE 'MUELA HYDROPOWER STATION.

Keywords MOTT MACDONALD, LAHMEYER MACDONALD WATER, PROJECTS, HYDROPOWER, STATIONS, PRODUCTION, HYDROELECTRICITY, POWER STATIONS, UNDERGROUND, DAMS, RESERVOIRS, REGULATING, COUNTRIES, DEVELOPING, CONSULTANTS, CONSORTIA, HYDRAULIC, TRANSIENTS, CLAYS, LAYERS, ABUTMENTS, TRANSFER, TUNNELS, PLANT, GEOLOGY, BASALT, UPSTREAM, SURGES, SHAFTS, SITES, ARCHES, FINITE ELEMENTS, ANALYSIS, PROGRAMS, DRAINAGE, GROUTING, CONTRACTS MUELA, HIGHLANDS LESOTHO, SOUTH AFRICA, AFRICA... Show All

Hydraulic Analysis of Undular Bore in Open Channels with Circular Cross Section

Rapidly varied unsteady flow in open channels with the circular cross section is investigated to predict the hydraulic transients in the underground floodways, which have been constructed to mitigate the flood disaster in the metropolitan area for the last decade. The momentum equation for open channel flows with the circular cross section including the effect of the vertical acceleration is derived in this study. The basic equations are applied to the laboratory test on the undular bore, and are verified through the comparison of the calculated results to the experimental ones.

Air Influence on Similarity of Hydraulic Transients and Vibrations

The effects of wave speed variation due to air content on the validity of similarity laws for model studies of hydraulic transients and hydraulic vibrations were investigated. Studies show that hydraulic similarities between geometrically similar model and prototype are reduced substantially for cases involving two- or three-phase flow. For flow with intensive cavitation, analysis shows that there is no hydraulic similarity between model and prototype. For pump discharge pipeline and turbine draft tube where two phase flow of air-water mixture occurs, analysis shows that the natural frequency and the response characteristics of the fluid system are a strong function of the local wave speed variation within the fluid system. This local wave speed variation is a function of the local transient air content and transient pressure.

A perturbation solution to the transient pipe flow problem

The analysis of hydraulic transients in pipes is traditionally carried out numerically. An approximate analytical solution of the nonlinear problem of unsteady flow in pipes is presented herein. The continuity and momentum equations are combined to give a nonlinear second-order hyperbolic partial differential equation whose approximate solution is derived using a perturbation technique called the delta expansion. It is shown that the zeroth-order perturbation solution gives ample accuracy for practical application. Useful series expansions for small values of the waterhammer parameter k are also obtained which compare extremely well with the results of the method of characteristics especially at small times. The explicit and simple form of the solution is suitable for further mathematical analysis and manipulation such as determining the maximal values and their time of occurrence. They are especially useful in determining the minimum time of closure possible while keeping the transient pressure in the pi...

Numerical Simulation of Hydraulic Transients in Hydropower Plant Using Safety Membranes

A new mechanical device consisting of a set of safety membranes has been used in several small hydropower stations in China in lieu of a surge tank. Safety membranes are controlled weak points mounted on the penstock near the powerhouse. Whenever pressure on the membranes rises to the preset value, one or more membranes rupture, protecting the penstock and the unit effectively. The device is simple, reliable, and beneficial. This paper proposes a mathematical model for analyzing hydraulic transients of a hydropower plant where a set of safety membranes is mounted to replace an expensive surge tank. The prevailing method is employed in order to solve the momentum and continuity equations describing transient flow in closed conduits. An optimization procedure is developed to guarantee the convergence of the interative process for calculating pressure rises due to water hammer when Kaplan turbines are installed. Using this model, transients of generator load rejections are calculated in Linzhengqu hydropower...

Pressure wave behaviour and leak detection in pipelines

In the present work on-line computational techniques have been developed and used in the analysis of hydraulic transients caused by leakage, in order to detect and locate pipeline ruptures. Pressure transients were obtained in two PVC pipelines 3 4 ″ diameter by using four pressure transducers connected to a PC computer equipped with A/D and D/A converters. The pipelines were 433 m and 1,248 m long. Leaks were simulated at different positions along the pipelines. Experiments were carried out for different liquid flow rates corresponding to Reynolds number in the range from 2,000 to 13,000. Leak percentage were in the range from 5% to 50% of the nominal liquid flow. A computer program to be run on-line was developed to simulate the leak, to read and filter the pressure transducers data, to display the pressure transient plots and to obtain leak location information. The detection system showed good performance in the detection of small leaks. Leaks as small as 5 % of the nominal liquid flow rate are readily detected. Leak locations were computed from pulse time delay between the various pressure transducers. The computed leak positions approached the actual values with precision. The developed software shows to be a very useful tool to the automatic supervision of pipelines as instantaneous leaks are readily detected and located.

Evaluation of Filter Media for Upgrading Existing Filter Performance

A pilot-scale study to select new media was conducted to upgrade the filters at the Rossdale Water Treatment Plant in Edmonton, Alberta, Canada in order to meet a new more stringent regulation which existing filters would have difficulty achieving. Performance of crushed quartz mono-media, anthracite/rounded sand dual-media, and the existing filter sand was assessed in terms of the new regulations and in-plant objectives by in-depth investigation of factors such as filtration rate, filter run length, resistance to hydraulic transients, polymer addition and filter ripening sequence. Half-normal plots of factorial designed experiments were used to study significant effects on filter performance. In terms of turbidity removal at the filtration rates used, crushed quartz performed the best overall. This may be related to the angular nature of the material. However, this physical characteristic may change due to abrasion during backwash, resulting in poorer performance. To assess this, abrasion resistance tests such as friability, changes in particle size distribution and acid solubility were performed. Scanning electron microscopy was used to explore the characteristics such as surface cracks, pores, particle accumulation on the media surface. Results indicated that the crushed quartz is quite resistant to abrasion and should retain its angularity.

Hydraulic transients cause low‐pressure problems

Mysterious short‐term pressure drops at the top of Cat Mountain prompted an investigation that revealed hydraulic transients as the culprit.Most engineers are familiar with hydraulic transients that cause problems with excessive pressure in water distribution systems. However, transients can also cause short‐lived low‐pressure problems. This article describes the analysis conducted by the Austin (Texas) Water and Wastewater Utility that identified transients as the source of low pressures in a portion of the city. Pressures recorded during controlled conditions provided the key in identifying pump and valve operation as the source of the problem.

Discussion of “ Influence of Liquid Length Variation in Hydraulic Transients ” by E. Cabrera, J. Abreu, R. Perez, and A. Vela (December, 1992, Vol. 118, No. 12)

Discussion of “ <i>Influence of Liquid Length Variation in Hydraulic Transients</i> ” by E. Cabrera, J. Abreu, R. Perez, and A. Vela (December, 1992, Vol. 118, No. 12)

Closure to “ Influence of Liquid Length Variation in Hydraulic Transients ” by E. Cabrera, J. Abreu, R. Perez, and A. Vela (December, 1992, Vol. 118, No. 12)

Closure to “ <i>Influence of Liquid Length Variation in Hydraulic Transients</i> ” by E. Cabrera, J. Abreu, R. Perez, and A. Vela (December, 1992, Vol. 118, No. 12)

Hydraulic Effects on a Large Piping System During Strong Earthquakes

Liquid in a large piping system could become a resonance column under axial excitations. A 1000-m long closed-boundaries pipeline with pressure wave propagation velocity of 1000 m/s would have the fundamental liquid resonance frequency of 0.5 Hz. Then, some hydraulic transients might occur during strong earthquakes. If dynamic pressure amplitude exceeds the value of system stationary pressure, then vaporizing at negative pressure, and after that, cavity or liquid column separation and reconnection can be produced. One of the effects of these behaviors would be equivalent damping of dynamic response, and the other an impact force on pipe structural system. The latter effect is considered as one of potential damage factors of a large liquid piping system. In this paper, an analytical method of earthquake-induced hydraulic transients of piping system is applied to a real underground large piping system subjected to a strong earthquake motion which has occurred in Japan. The results of the analysis have shown that the occurrence of earthquake-induced negative pressure in liquid column is possible. Further, the analysis has explained the difference between two long straight pipelines buried in the same route, one failed by axial cracking and the other had no damages.

Energy interpretation of hydraulic transients in power plant with surge tank

The energy concept sheds light upon the hydraulic system that comprises the throttled surge tank, the tunnel and the penstock. The mathematical manipulation of the governing differential equations of water hammer yields an energy (power) equation in point form. By integration with respect to pipe distance, this relation is extended first to an individual pipe, then to the surge-tank system with branching connection. The system energy (power) equation states the relationship between the total (internal plus kinetic) energy, the convective energy, the work done on the system and the energy dissipation. A case study identifies the conversion between the internal and kinetic energy, and quantifies the behaviour and magnitudes of related energy components of the system.

ANALYSIS OF TRANSIENT PRESSURES IN TWO-COMPONENT TWO-PHASE FLOW

In this paper, the problem of hydraulic transients resulting from valve closure in a branched pipe carrying a two-component, two-phase flow is theoretically investigated. The governing equations were derived on the basis of one dimensional flow. The method of characteristics was used for solving the resulting differential equations. The evaluation of time interval was made in such a way to be suitable for use in a branched pipe system having branches of different lengths. The analysis of many investigated cases reveals that the maximum pressure rise increases with the increase of the delivery pipeline diameter and with the decrease of valve closure time and void fraction. Moreover the study shows that in all investigated cases, the lowest value of maximum pressure rise occurs when the piping lengths ratio C branched dead end pipe to upstream pipe lengths ) approaches unity.