Su yapılarında hidrodinamik etkiler ve Şanlıurfa tünelleri çıkış yapıları örneği

Abstract

Bu çalışmanın temelini, Şanlıurfa tünelleri çıkış kontrol yapılarının değişik isletme koşullarında, performans lar in m incelenmesi oluşturmaktadır. Akım alanında bulunan bir su yapısına, hidrostakik yükten başka, akımın doğurduğu türbülans, his, basınç çalkantısı ve çevrilerden dolayı oluşan dinamik yüklerde etkir. Bu yükler değişken karekterde olduklarından yapının titreşimine neden olurlar. Yapı stabilitesi açısından önemli olan, dinamik yüklerin, yapıya etkisi çalışma konusunu oluşturmaktadır. Bu çalışmanın ilk bölümünde titreşilsin teorik olarak tanımlaması yapılmıştır. Akısı alanında bulunan bir su yapısına etkiyen dinamik yüklerin yapıya etkisi, bu etkilerin yok edilse metodları anlatılmıştır. Müteakip bölümde vibrasyon olayının modellemesi üserinde durulmuştur. Şanlıurfa Tünelleri modelinin temelini olşturan Froude modeli anlatılmıştır. Daha sonra titreşimin incelenmesinde bilgisayar kullanımı anlatılmıştır. Deney sonuçlarının analla edilmesinde ve gerekli sonuçların alınmasında kullanılan sistem tanıtılmış t ir. Çalışmanın son bölümünde i.T.ö. inşaat Fakültesi Hidrolik Labora tu varında, İ/25 ölçekli olarak Froude benzeşim modeline göre inşa edilmiş olan Şanlıurfa Tünelleri modeli üserinde deneyler yapılmıştır. Tek tünel işletmesinde muhtelif noktalara basınç dönüştürücüler vasıtasıyla, yapıya etkiyen dinamik basınçların karekterleri belirlenmiştir. Su yapısı tabanındaki basınç dönüştürücülerden okunan değerlerde, birkaç noktada negatif basınca rastlanılmıştır. Basınç çalkantı değerlerinin ortalaması, her ne kadar negatif delefde olmasa bile, kısa aralıklarla görülen negatif basınç değerleri, yapı tabanında kavitasyona sebep olabilecgi için. incelenmesi büyük önem taşımaktadır. Bu deneylere ait istatistik analisler ve frekans spektrumları, çalışmanın sonunda verilmiştir. Dinamik kuvvetlerden dolayı, titreşime maruz kalacak olan su yapısının, performansının sallanması yönünde, alınması gereken önlemler, çalışma sonunda anlatılmıştır.

This study primarily aim at investigating the attitute of the outlet structures of Sanliurfa Tunnels against the dynamic loads under various current conditions. Dynamics loads, consisting of current- created turbulance, speed current agitation and cycles, we have effects on a water structure existing within the current field. These currents are in terms of water structures performance. What is targeted is the investigation of the effects of these currents on the structure. In the first part of the study; the vibration subject is discussed in a general sense. The free vibration and the general vibration equation under any F(t) external force are explained. Furthermore, the vibration of the object within the current is explained. The dynamic loads are important in terms of the structures stability. The reasons of the Investigation of the dynamic forces are provided below. 1-Vibrations may give rise to collaps of the water, structure where greate speeds and agitations are observed. 2-Vibration may give rise to noise in the water structure. 3-Vibration, if occured in the border conditions, may not be estimated previously. 4- I t is very hard to repair the vibration problem to be occured after the construction of water structure. 5-Dynamic effects must be calculated during the project making phase of the important water structures. We may classify the vibrations as follows; 1. Mechanical Classification: 1.1. Vibration occurud as the result of the current and the loads taken place in the beginning. 1.2. Vibration occured due to unstabillty created as the result of the position of an object within the fluid. 1.3. Vibrations occured when the movement of an object within the fluid connected to current. X 2. Mathematical Classification 2.1. Forced Vibrations It is the vibrations of a water structure within the current field deu to turbulance effect. The aralitute of the vibration is small. Since the forces of the vibrations are periodical, they pose no haaard in the water structure. 2.2. Self Excited Vibration This kind of vibration are important in teras of water structure"" s stability. Since the forces of current are not periodical, they help increase the vibration, âs a result of this, attenuation will be negative. In order that such a vibration say occur, the deplacement in the water structure must fora so» hydrodynamic forces which will increase the movement in the same direction. -. 2.3. Self Controlled Vibrations When the vibrations of the instable periodical current, which are arround the water structure. Graudally increase, this kind of vibration will occur. And if the vibration frequancy of the current is equivalent or near to the natural frequency of te structure, then the resonance event will occur The following precautions aus be taken in. order to prevent the resonance occurance in the structures. 1- The dynamic forces must be taken into consideration when determining the dimensions of the structure. 2- The rigity of the structure must be increased to the economical extent. 3- In order to prevent the occui'ance of self excited vibration, where the current is connected with and separated frost the structure 4- The current environment must be designed in such a way that no negative pressure will occur. 5- In order to end up hasard of self-controlled vibration, the periodical nature of the current arrond the structure roust be abolished. 8- The vibrations to be occured as a result of the interaction betwen vortexes must be broken. In the third part the aodelling of the vibration is discussed. The basic principles on the modelling of the vibration of the vibration are provided. And the necassary formulas are given. The Froude model, used often for the Xi modelling of the free-surface currents, IS also discussed. The basic principles used for the formation of Froude model are explined. There are three seperate »odels used for the modelling of water structures. 1 " Ri j it Models : In this type of models, the water structure is made steady in every respect. No vibration is alloved. 2. Oscillator Modele: In this type of models, the structure is freed form the direction where the vibration is to be investigated. The structure is fixed to somewhere with a spring in this direction. 3. Elastic Models: In this models, the rigidity, mass and elasticity characteristics of the structure are made analogous. They are not Buch used in practice. In the fourth part, the determination of dynamic forces effecting the water structure and the calculation of this forces, not calculated by analytical ways, by computer-assistance are explained. The hydrodynamie magnititutea havin accident.''. 1 variable chareters are calculated by.aeams of transducer developed in recent years. These transducrs tranduce the meehenioa.l »agnititutes In the current field to electricity signals. The mechanical magtitubed transduced to electricity signal are sent, after strenghened with the assphibilicafcor, to digital system. RAP Is the greatest development project of Turkey since its founding. Besides it is also one of the most important development projects of the world. GAP Is an Integrated project which consist of dams, hydroelectric station and irrigation plants contemplated to be constructed on the Euphrates and Tigris Rivers. The Sanliurfa Tunnels consist of two tunnels having a length of 28400 m and having an internal diameter of 7.82 m The distance betwen the axles of the tunnels are 40 m. The slope of tunnels is 0.0008439. The tunnels were designed in such a way that a flow of maximum 328 m^/see may pass. Each tunnel has a radial gate. There is a energy-breaker pool which breaks the energy of the water coming f roa the radial gates. There are two water-taking mouths which meet the water requirement of Sanliurfa by the year 2020. The outlet structure model of Sanliurfa Tunnels have been costructed in the Hydrolic Laboratory of Construction Faculty of i.T.fJ as having a mesuring unit (scale) of 1/25. This model Xii - 1 -.-V^V >,.»??-' -~rt, ??,..^-1 :-? hj ? {;? ~^T, ?k Figure 1 Şanlıurfa Tunnels Plan and laboratuar y Model consist of the last 200 m section of the tunnels. The connecting parts Sring water and river-mouth cofferdams, the radial gates and also energy-breaker pool. The outlet structures have been manufactured from plexiglass metarial in order that the current »sab be investigated easily. In the model trials; some pressure transducers have been installed at 10 critical points on model. The dynamic pressure and pressure agitatations have been measured with these transducer. In this trails, some measurement have been made at rate of 10%, 20%, 60% of the gates in one tunnel facility. The signals received from the pressure transducer are sthrengened with the amplhibilicator and sent thereafter to the laboratory computer of MIN-DECLÂG/23 type.After having evaluated in the computer, the necessary statical results and frequency spectrums have been received from a printer of DEC VT 125 Type. A floww of maximum 76.92 m^/sec, is passing trough the. tunnel when the gate is open at the rate of 10%. There occured a free spatter in the gate mouth. Negative pressure have been observed in the points no (3), (4) and (8). Since the negative pressure may give rise to cavitation in the structure base, the necassery precautions must be taken. When the gates is open at the rate of 20%, a flow maximum 122.46 m3/sec, is passing trough the tunnel. This gates openness is taken as an example since the same is suitable opening for appearence of extreme values. Negative pressure has been observed on point no (7) and (8). When the gates is open at the rate of 60%, a flow of maximum 192.50 a3/sec, is passing trough tunnel. There is no any particular spatter in the gate mouth. When this gate is opened there is no any negative situation in terms ofstructure stability.