Su yapılarında vibrasyon olayı ve Şanlıurfa tünelleri çıkış yapılarının laboratuvarda modellenmesi

Abstract

Bu çalışmanın ilk bölümünde genel anlamda titreşim olayı ele alınmış, titreşimi oluşturan faktörler ve etkileyen büyüklükler, bunların akışkan ortamındaki değişimleri incelenmiş ve bunlara ait genel denklemler gösterilmiştir. İkinci olarak su yapılarında vibrasyon olayı incelenmiştir. Akım ortamında yer alan su yapısında görülebilecek titreşimler sınıflandırılmış, bunların nedenleri yapıya etkileri ve en önemli durum olarak görülen rezonans tehlikesi yaratıp yaratmadıkları, titreşimin yapı için tehlikeli olması durumunda sönümlendirilmesi için alınabilecek önlemlerden söz edilmiş, titreşimlerin laboratuvarda modellenmesi konusu araştırılmıştır. Son kısımda Şanlıurfa tünelleri çıkış yapıları model deneyleri anlatılmış, bu tünellerde işletme koşullarını sağlayan radyal kapaklar ele alınmış ve bu kapaklara ait üç elverişsiz durum için alınan rijit kapak modeline ait sonuçlar örnek olarak verilmiştir. Bu sonuçlar değerlendirilerek, dinamik modelleme ile modelden alınan basınç çalkantılarının frekans analizi yapılarak, hakim frekans değerleri saptanmıştır.

This study is formed by three main parts. Firstly; vibration is examined in general meaning, general vibration equation and the terms of the equation are explained. Change of the equation in the fluid is shown. Second chapter includes vibration phenomena of the hydraulic structures. The dynamic behavior of hydraulic structures are important for the following reasons, 1. Vibration can endanger the costruction and its environment and produce unacceptable noise, 2. Extrapolation of design experiences to large scala structures can be hampered by lack of knowledge of dynamic behavior, 3. Some structures are difficult to modify when vibrations are encountered, 4. When vibrations occur only in the extreme conditions, it is not certain that they will be recognised or detected in time. We can examine the vibration in two ways; 1. Mechanical approach 2. Mathematical approach 1. Mechanical approach: a) Extraneosly induced excitation: It is caused by a pulsation in flow or pressure which is not an intrinsic part of the vibrating system. b) Instability - induced excitation: It is brought about by a flow instability. In most cases, this instability is an intrinsic part of the vibrating system. The flow instability is inseparably connected with the same structures. ix c) Movement - induced excitation: This excitation or body excitation, is due to the exciting forces which arise from the movement of a structure or a body within the vibrating system. 2. Mathematical approach: In order to increasing level of danger the flow induced vibrations can be classified in three categories. a) The passive response to excitation by turbulance, also called forced vibration. This turbulance can be present in the oncoming flow, or it can be induced in the flow by the structure itself. The character of excitation can be either a broad - band spectrum or a narrow-band one. The important characteristic of this class of flow induced vibration is that the force does not depend on structural motion. This vibration is not more than the % 10 of total vibrations. b) Body-controlled excitation, where initially unstable flow phenomena can be amplified by body vibration, or where vibration at the body synchronises the random turbulance excitation acting on different parts. c) Self excitation or negative damping, where the dynamic flow excitation is purely induced by the body vibration itself. At the smaller amplitudes, the excitation force will increase linearly with the vibration movement. If the effect of vibration is periodic, there is a resonance danger. When the frequency of vibration is equal or closer to the body natural frequency, resonance danger can be seen. Under this condition, effect of vibration should be prevented. Some preventation mechanism especially vortex attenuation mechanism is shown in this chapter(Example; vortex generator slotted boundary, asymetric boundary, compliant boundaries). In this chapter, hydraulic gates vibration is examined. Effect of vibration, for the cases self excited, self controlled and forced is shown. Hydraulic gates are used to balance, discharge and water level. We should know dynamic behavior of gates since hydraulic gates in the flow effect flow condition, water level and discharge. Şanliurfa Tunnel system is an important component of the Southeast Anatolian Project (GAP), which will be the largest irrigation project in Turkey. These tunnels are the largest irrigation tunnels of the wo'rld. The system consists of two paralel concretelined tunnels each of which is 7.62 m in diameter and 26.4 km in length. The tunnels will supply water for the irrigation of 476000 ha of land in the Urfa-Harran plain, from reservoir of the Atatürk Dam. ' The tunnels are designed for a total capacity of 328 m3/sn. The outlet structure of each tunnel consists of; two hydraulic radial gates, two x structures for water supply to Şanlıurfa city center, to stilling basin and main transmit channels. A 1:25 scale model of the outlet structure of tunnels is constructed in the laboratory. Model includes only the last 8 m sections parts of the tunnels (300 mm steel pipe), radial gates (plexiglas), stilling basin, entrance of the main irrigation channel and water supply entrance for Şanlıurfa. The aim of the experiments is to determine the vibration behavior of gates, the rating curve of the tunnels and reservoir water level. One set of experiment is performed for the determination of the rating curve of the tunnels. Both tunnels were opened (% 10, % 20, % 80). These situations correspond to the maximum operation conditions for minimum gate openings, maximum discharge and maximum reservoir water level. In this experiment, the hydraulic jump was always submerged for gate openings of % 20 and % 80. Free hydraulic jump is shown only for % 10 gate openings. In model tests, this type of gate can vibrate in the vertical direction as a result of three factors: turbulance (forced vibration), coupling of the hydrodynamic force resulting from the motion of gate with the diplacement (self-excited) and large eddies related to the instability of the seperation zone (self- controlled). The vibration of hydraulic structures can be investigated by three types of model. 1. Rigit Models 2. Oscilator Models 3. Elastic Models In thfs study, tests are performed on a rigit model. Pressure fluctuations were measured by Hottingger P11 inductive and Indevco 8510B-5 piezoresistive pressure transducers installed at two points on the gate model. Both of them were placed on the downstream face of the gate. Pressure signals were transmitted to a MINC DECLAB/23 laboratory computer, after being amplified by a Hottinger KWS 6A.5 amplifier. An A/D converter on the computer sampled at signal at the rate of 150 samples per second and stored on a disk file. A power spectrum of the signal determined using the Fast Fourier Transform. Osilograph is used for long term observation of pressure fluctuations (Figure 1.). XI PIEZURESISTII/E ENDEl/CO B51UB-5 PRESSURE TRANSDUCER INIMIUIVL PRESSURE TRANSDUCERS (IIBM P 11) USCILLUHRAPU (HUM AT-'t IIW-IO CARRIER AMPLITIER (HUM KlılS GA-5) OSCILLUSCUPE (HUM II2V13A) 15 nh. multiplexer MINC/DECLAB-23 A - D Converter T COMPUTER (Digital PDP 11-23) ] c GRAPHIC TERMINAL (Dnn W T 175 with VT 6'»H) DISK, Recorder Graphic Printer * ad modül Clock modul Figure 1. Measurement System Terminal xii During the two tunnels operation experiments, the maximum discharges (150,237,328 m3/sec.) against % 10, % 20, % 80 gate openings were taken. In the model tests, pressure fluctuations were measured by measurement system (Figure 1.) and the result of evaluation of this data, frequency analysis (power spectrum) were done by this analysis, dominant frequencies were defined. For % 10 gate opening free hydraulic jump was shown for the case of 150 nfVsec. discharge passing through the tunnels. The transducer (top one) was not under the water level so pressure fluctuations could not be traced. The bottom one was submerged, pressure fluctuations were shown and therefore frequency analysis could be determined. The other transducer was placed on the outlet axis of the tunnel, this transducer was not necessary for vibration experiment, it was placed to show the need for the electronic manometer. For % 20 and % 80 gate openings all transducers were submerged therefore pressure fluctuations were recorded, their frequency analysis power spectrum is made and dominant frequencies are determined.