The effect of water hammer on pressure increases in pipelines protected by an air vessel

U tlačnim cjevovodima može, pri nestacionarnom režimu rada, doći do pojave vodnog udara. Uobičajeno je da se takovi cjevovodi štite zračnim kotlom pri čemu se kod uključivanja i isključivanja crpki formiraju oscilacije vodnih masa. U ovom radu opisan je doprinos elastičnih sila na prirast tlaka u cjevovodima štićenim zračnim kotlom. Kao primjer je prikazan tlačni cjevovod od crpilišta Ravnik do vodospreme Veliko Brdo na kojem su provedena mjerenja oscilacija tlaka prilikom ispada crpki iz pogona uspoređena s izračunatim vrijednostima. Primijećeno je da, iako zračni kotao formira oscilacije vodnih masa, postoje i varijacije tlaka koje su posljedica vodnog udara. Istraživanje ističe vezu između pretvaranja kinetičke energije u značajnu i naglu promjenu tlaka (pojava nazvana vodni udar), ovisno o promjeni brzine u vremenu.In the pipelines of water supply systems, the water hammer phenomenon often arises during rapid unsteady developments. Pipelines are mostly protected using an air vessel, which is designed by means of equations for oscillations of water mass. In this study, an analysis is made of the impact of pressure increases caused by water hammer on pressure variations in pipelines protected by an air vessel. The analysed unsteady (transient) developments occurred in a pressure system between the Ravnik pumping station and the Veliko Brdo reservoir, and thereby the measured pressure values were compared with values calculated with a numerical model. It was observed that although the air vessel converts kinetic energy into oscillations of water mass, part of the energy is transformed into elastic deformations of pipelines and into water compression. This study assesses the relationship of the conversion of kinetic energy into significant changes in pressure (phenomenon called water hammer), depending on the extent of the velocity change in time

Diffusion through Pulverized Stone Compared to Other Mineral Barrier Materials

Construction of a waste disposal site requires an effective barrier that separates waste from a sub-base and minimizes the migration of contaminants from the site to an aquifer. Barrier layers most often used are natural clayey deposits or compacted clay liners and PEHD geomembranes. However, some regions, the Croatian karst for example, are mostly short of clay. For this reason, the use of pulverized stone, the by-product in the building-stone industry – as a potential liner material was investigated. Considering diffusion is an important mechanism of contaminant transport through barriers, this paper describes the method and apparatus for determining the diffusion coefficient of pulverized stone. Measured diffusion values were related to sample compaction and compared with the physical properties of clay, geosynthetic clay liners and PEHD geomembranes. Other physical properties of pulverized stone such as the filtration coefficient, density and particle size distribution are also presented. Finally, the suitability of pulverized stone for barrier construction is discussed based on the results obtained

Folk Architecture of the Surrounding of Zagreb

At the investigation of the Croatian Ethnological Society, the Ethnographic Museum organized an ethnological research of the metropolitan area of Zagreb. Started in 1969, the research was planned as a long-term action which should encompass larger village settlements north and south of Zagreb. In the recent past, this area witnessed an intensive construction of modern family houses, while the old-style wooden architecture is disappearing. Up to the present the research has been completed in the villages of Resnik and Ščitarjevo to the south of Zagreb, and Čučerje, Markuševac, Šestine and Mikulići north of the city. As a member of the team of researchers, I worked on the theme: Folk architecture and interior decoration. Two types of villages exist in this area: dispersed villages with hamlets in the north, conditioned by hilly land configuration, and street-type villages in the southern plains, where narrow side of the house is always oriented to the street. While types of villages differ in this relatively small area, the house itself shows many common characteristics. In the past, it was always a frame house with a straw roof, its size and interior layout depending on the material status of the family. Very few of such houses as well as other farm buildings, are preserved. Some elements of the old-style building technique, like open-hearth kitchens, are nowhere to be seen any more. Built ceramic stoves in rooms are also rare. Other items of the house inventory and furniture are to be found only as residue. The structure of these villages has been changed by the proximity and influences of the city, as well as by the changes in the village life and economics. The construction of modern roads and houses also contributes to the change in the original outlook of the villages (which date back to the 12th century), and to their gradual incorporation into the urban whole

The effect of water hammer on pressure increases in pipelines protected by an air vessel

U tlačnim cjevovodima može, pri nestacionarnom režimu rada, doći do pojave vodnog udara. Uobičajeno je da se takovi cjevovodi štite zračnim kotlom pri čemu se kod uključivanja i isključivanja crpki formiraju oscilacije vodnih masa. U ovom radu opisan je doprinos elastičnih sila na prirast tlaka u cjevovodima štićenim zračnim kotlom. Kao primjer je prikazan tlačni cjevovod od crpilišta Ravnik do vodospreme Veliko Brdo na kojem su provedena mjerenja oscilacija tlaka prilikom ispada crpki iz pogona uspoređena s izračunatim vrijednostima. Primijećeno je da, iako zračni kotao formira oscilacije vodnih masa, postoje i varijacije tlaka koje su posljedica vodnog udara. Istraživanje ističe vezu između pretvaranja kinetičke energije u značajnu i naglu promjenu tlaka (pojava nazvana vodni udar), ovisno o promjeni brzine u vremenu.In the pipelines of water supply systems, the water hammer phenomenon often arises during rapid unsteady developments. Pipelines are mostly protected using an air vessel, which is designed by means of equations for oscillations of water mass. In this study, an analysis is made of the impact of pressure increases caused by water hammer on pressure variations in pipelines protected by an air vessel. The analysed unsteady (transient) developments occurred in a pressure system between the Ravnik pumping station and the Veliko Brdo reservoir, and thereby the measured pressure values were compared with values calculated with a numerical model. It was observed that although the air vessel converts kinetic energy into oscillations of water mass, part of the energy is transformed into elastic deformations of pipelines and into water compression. This study assesses the relationship of the conversion of kinetic energy into significant changes in pressure (phenomenon called water hammer), depending on the extent of the velocity change in time

Water hammer in irrigation systems

U sustavima navodnjavanja se često koriste samohodni sektorski raspršivači (tifoni) i samohodni automatizirani uređaji za linijsko ili kružno navodnjavanje na kojima uslijed naglog zatvaranja zasuna na ulazu u uređaj može doći do pojave neželjenog predtlaka. Sustav se štiti od neželjenog predtlaka postupnim zatvaranjem zasuna. U radu je na primjeru hidrauličkog proračuna nestacionarnih stanja na sustavu navodnjavanja Blata – Cerna definirana zaštita sustava od prevelikih i premalih tlakova te utjecaj istodobnog zatvaranja zasuna na rubnim dijelovima mreže.Self-propelled sectorial rain guns (typhones) and self-propelled automated devices for linear or circular irrigation are often used in irrigation systems. However, unwanted overpressure can occur due to sudden closure of valves at the entrance segment of these devices. The system is protected against such overpressure by gradual closure of valves. The protection of the system against excessive and insufficient pressures, and the impact of simultaneous closure of valves at peripheral parts of the network, are defined in the paper based on an example of hydraulic calculation of unsteady flows at the Blata - Cerna Irrigation System

Hydraulic properties of U-shaped stormwater overflows

Opisuju se hidrauličke karakteristike kišnog preljeva U oblika, alternativnog rješenja kojim se omogućuje smanjenje ukupne duljine preljevne građevine. Prikazani su rezultati hidrauličkih ispitivanja koja su provedena zbog toga što su nedostajali podaci o svojstvima preljeva toga oblika. Ispitivanje na fizikalnom modelu poslužilo je i za optimizaciju preljeva koja je provedena u dva koraka. Opisane su i odgovarajuće numeričke analize radi usporedbe s rezultatima na modelu.Authors describe hydraulic properties of the U-shaped stormwater overflows, which constitute an alternative solution for reducing an overall length of traditional stormwater overflow facilities. Results of hydraulic tests conducted to obtain additional data about properties of such overflows are presented. Physical model tests were also conducted to optimise overflow facilities using a two-step process. Appropriate numerical analyses are also given to enable comparison with scale model results

Comparison of results obtained by physical and numerical in-plane flow models

Prikazana je usporedba rezultata proračuna i mjerenja polja brzine strujanja na dionici umirivanja toka i ulijevanja u more za projektno rješenje HE Ombla u područje izvorišne špilje i jezerca. U istraživanjima su uspoređeni rezultati brzina dobiveni mjerenjem na fizikalnom modelu i proračunom ravninskih modela. Rabljena su dva numerička modela temeljeni na metodama konačnih diferencija i volumena. Numerički rezultati uspoređeni su s rezultatima mjerenja na fizikalnom modelu.The comparison of calculated and measured field flow velocities at the flow steadying and sea discharge section, for the zone of the source cave and lake, is presented in the scope of design solution development for the Ombla hydropower plant. Velocity results obtained by physical model measurements and in-plane model analyses are compared. Two numerical models, based on the finite difference and volume methods, are used. Numerical results are compared with results obtained by physical model measurements

Near-bottom pollution transport modelling

Opisano je modeliranje pronosa pridneno ispuštenog onečišćenja pri stacionarnom tečenju u kanalu jednolikog pravokutnog presjeka s primjenom dvodimenzionalnih i trodimenzionalnih modela. Osim usporedbe rezultata ravninskog i prostornog numeričkog modeliranja raspodjele koncentracije pridneno ispuštenog onečišćenja u kanalu idealiziranih geometrijskih obilježja, dana je i usporedba reprezentativne veličine tzv. brzine miješanja s rezultatima dobivenim fizikalnim modeliranjem.The near-bottom transport of pollution, discharged during stationary flow into a channel of uniform rectangular cross section, is modelled by means of two-dimensional and three-dimensional models. Comparison between in-plane and three-dimensional numerical modelling results, defining distribution of near-bottom pollution in a channel of idealized geometrical properties, is provided. A comparison between the representative value of the so called mixing velocity, and the results obtained by physical modelling, is also presented