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|Title:||Sempatik Kıyı Koruma Yapısı Olarak Kazıklı Dalgakıranların Düzenli Ve Düzensiz Dalgalar Altındaki Performanslarının Ve Üzerine Gelen Yüklerin İncelenmesi|
|Authors:||Kapdaşlı, M. Sedat|
Hidrolik ve Su Kaynakları Mühendisliği
Hydraulics and Water Resources Engineering
Kıyı koruma yapıları
Shore protection structures
|Publisher:||Fen Bilimleri Enstitüsü|
Institute of Science and Technology
|Abstract:||Kıyı koruma yapısı olarak dalgakıranların tarih içerisindeki gelişimi incelendiğinde oldukça eski bir mazisi olduğu görülmektedir. Taş duvar olarak Alexandria' da (Mısır) milattan önce 2000 yıllarında inşa edilen dalgakıran en eski yapı olarak bilinmektedir. Ancak tabakalı dökmetaş dalgakıran olarak en eski yapı halen mevcut olan İtalya' nın Civitavecchia şehrinde milattan sonra 53 ile 117 yılları arasında Romalı İmparator Trajanus tarafından yapılmış yapıdır. Cherbourg, Plymouth ve Dover 'de bulunan dalgakıranlar ise geleneksel dalgakıranların öncülerindendir. Özellikle son yıllara kadar bu geleneksel yapılar yalnızca insanoğlunun denizlerden mümkün olduğunca yararlanması ve onun zarar verici etkilerinden de korunması amacı ile tasarlanmışladır. Ancak geçen zaman içinde insanların kıyı bölgelerine bakış açısı değişmiş ve beklentileri de farklılaşmıştır. Yapıldığı koşullarda belli amaçlara hizmet etmesi gereken yapıların daha sonraları pek çok fiziksel ve ekolojik çevresel etkileri olduğu görülmüştür. İnsanoğlu bir taraftan yeraltı kaynakları, beslenme, ulaşım ve dinlenme gibi etkenlerden dolayı denizlere ve kıyı bölgelerine giderek daha bağımlı hale gelirken, bilinçlenmesinden dolayı da çevresel kaygıları içinde taşımaya ve dolayısı ile ekonomik gelişimine sırtını dönmeden sağlıklı temiz bir çevre oluşturmanın yollarını aramaya başlamıştır. Başlangıçta iki farklı uçta gibi görünen bu fikirleri aynı potada eriten Sürdürülebilir Kalkınma fikri ortaya atılmış ve üzerinde yoğun bir şekilde çalışılmaya başlanmıştır. Bu fikirle birlikte artık tüm kıyı mühendisliği tasarımlarında çevresel ve ekolojik parametreler de projelere yön vermeye başlamıştır. Sürdürülebilir kalkınma fikri ile yapılan yapı tasarımlan literatürde "doğa ile inşaat" veya "sempatik kıyı koruma yapılan" şeklinde tanımlanmaktadırlar. Bu tür yapıların boyutları klasik yapılara göre çok daha küçük ve çevresel etkileri ise oldukça azdır. Bu çalışmanın hareket noktası olan kazıklı yapılar ise, bilindiği gibi çevresel etkileri en az olan yapı türlerindendir. Tasarlanmış şekli ile gelen dalgaları kırılmaya zorlayarak kara tarafına geçen dalga enerjisi miktarını azaltan çok şuralı kazıklı bir dalgakıran, düzenli ve düzensiz dalgalar altında kırılan ve kırılmayan dalga durumları için denenmiş, yapının hidrodinamik performansı ve üzerine gelen yükler belirlenmeye çalışılmıştır. Kırılan dalga durumunda ortaya çıkan kısa süreli şok dalga basınçları çalışmanın kapsamı dışında tutulmuştur. Elde edilen deneysel verilerin bir kısmı özel koşullar için tanımlanan teorik ifadeler için kıyaslanmıştır. Sonuçlar ileriki çalışmalar için oldukça ümit vericidir.|
Coastal areas have always played an important role in the life of mankind. By the increasing growth of trade, tourism and rapid travel, mankind has realised the value of these areas. So he wanted to use the coastal resources for his benefits, (life support, economical gain, recreation etc.). Tourism or industry induced high mobility have led to the need for structural defences against the catastrophic effects of the sea. Breakwaters, seawalls, groins, wave absorbing block mounds and artificial reefs are few examples of these coastal structures. Coastal protection has a long history. Breakwaters constructed in ancient times were presumably simple mounds made from stones. However, as early as 2000 B.C. a stone masonry breakwater was constructed in Alexandria, (Egypt). Another old rubble mound breakwater located in Civitavecchia, Italy, which was constructed by the Roman Emperor Trajanus (A.D. 53-117) and is thought to have started in the latter half of the 18th century, corresponding to the industrial revolution. The breakwaters built in Cherbourg, Plymouth and Dover are considered to be the pioneers of the modern day breakwaters. On the other hand aforementioned human activities and coastal constructions have caused an increasing pressure over the decades for coastal zone and coastal resources even they are not infinite. Also designers have planned the coastal construction projects from one-dimensional point of view, namely, taking measures against the severe attacks of the high storm waves. He did not take into account the nature itself in the planning, design and construction stages. However, today we know that shore protection is interference into the natural system around the borderline between land and water. By good luck mankind have realised the delicate balances existing between the prevailing physical conditions and often rich ecosystems of coastal regions. Every engineering activity, if not properly planned, designed and executed, presents a threat for disturbing the existing states of dynamic equilibrium in coastal ecology and for causing irreversible, undesirable changes in this highly valuable environment. The traditional coastal engineering profession has been developed over the goals of enhancement and protection of the economical interest of mankind in coastal regions. XXX So he have built conventional hard stability coastal structures like rubble mound breakwaters which have high cost, extreme environmental and ecological impact. Recently, researchers and engineers talk about the best way forward would seem to be "to work with rather than against the natural system", (Carter, 1988). This is a new understanding that is required for a sustainable development of the coastal zone, which some call it "building with nature" and some call it "nature-friendly", (Kapdaşlı, 1992). In the light of this new philosophy coastal engineers must minimise and remedy the environmental impacts of coastal regions on physical characteristics and ecological properties. Also, he has to find appropriate solutions to coastal problems named as "environmentally acceptable" or "environmentally friendly". According to this new philosophy a new package of coastal protection structures should be introduced which will have less environmental effect, may have low-cost in many cases, small structural members, fragile structures (not robust) and better for landscape as the coasts look the most natural. From our point view, an engineer should prefer structures on piles instead of impermeable walls or rubble mound structures since they do not totally intercept not only water and sediment movement, but also that offish and other wildlife. As a combination of the given results, a new wave barrier which have been supported on piles is introduced in this thesis for friendly shore protection by means of hydraulic experiments and two analytical models both for wave transmission and forces acting on the piled breakwater, (Fig. 1). However, the theoretical models are restricted to one row option as a result of the sophisticated and turbulent flow media. The object of this thesis is to define the hydrodynamic performance of this multi-row piled breakwater (wave barrier) under regular and random waves by means of transmission coefficient Cx = Ht/Hi, reflection coefficient Cr = Hr/Hi and energy loss coefficient Cl = Hl/Hi, where Hi is the incident, Hr is the reflected and Hl is the energy loss wave height, respectively. Also spectral values of these coefficients corresponding to random waves are defined. Acting wave forces under regular and random waves are analysed via pressure transducers. Total force acting on the structure has been calculated by integration technic. Figure 1. Proposed Piled Breakwater For Friendly Shore Protection. xxxi The model experiments referred to above were conducted in a 2-D wave flume with a flap type and pc based piston wave generator, which can generate both regular and random waves in the Hydraulics Laboratory of Istanbul Technical University. The wave flume is 24.0 m long, 1 m wide, 1 m high, (Fig.2). Piston PI R P3 Barier P4 Hume Bed Beach Figure 2. General lay-out of the wave flume The sine waves generated digitally by digital simulation technique and random waves generated by mathematical spectrum model which is Pierson-Moskowitz for this study valid for fully arisen sea conditions, was sent to the wave maker paddle via the D/A converter card (PCL-812PG) which converts the digital signal into a continuous analog signal at a specified rate. The tests were carried out for wave period ranging from approximately 0.84 sec to 1.66 sec and wave height ranging from 4.00 cm to 15.00 cm. The incident wave heights obtained from the above methods are compared with the actual incident wave height, which was measured without the reflecting structure for regular waves. Desired wave heights and periods have been reproduced easily via the computer controlled wave generation system which can control piston displacement and velocity for each signal (double-check system). The wave maker flap was brought back to its vertical position by sending the zero signal for a few seconds at the beginning of the each test. At the end of flume opposite the wave generator, a sand beach with one on eight slope and another gravel one behind the generator have been built in order to dissipate the wave energy and to prevent re-reflection. Three vertical and horizontal slab elements made of Plexiglas are used, occupying the full width of the flume, 15 mm thick and supported from the base by two thick steel rods for each row and screwed to the full height. C clamps and steel construction have been used for support rigidity of the model set. The elevations of the tip of the plates were changed. Seven hundred and forty-four experimental series have been conducted for twelve different configurations. The water surface time histories were recorded using parallel wire resistance probes. They were calibrated in the flume by moving them up and down. The first wave probe (PI) from the structure was fixed at 1.95 m and the second (P2) 1.30 m and the third (P3) 0.65 m, as shown in Fig. 1. In order to measure the transmitted wave height another XXXll wave probe (P4) was fixed 3.00 m from the structure on the leeward side. Wave probes were in conjunction with a wave probe monitor (HRLM Wallingford, CLE C30) which amplifies the analogue signals from the wave probes and sends to the pc for data acquisition via the analogue-digital converter card (PCL-812PG). This card converts the analogue signals into digital values. A pc based data acquisition and processing system have been used in the 2D experiments in order to make simultaneous data collection which is very important to evaluate the real time agitation pattern in the landward of the structures (Fig 2). All software were coded in Borland C++. The pressure time series were recorded using two HBM PI 1 pressure transducers. They were calibrated in the wave flume by increasing and decreasing the water column on them and reading the voltage values for known static pressure values. Only the maximum horizontal orbital velocities have been measured by a micro muline. All the data processing procedure is the same as for the water surface time series. Analogue Signal TH Wave Monitor ( Amplifier ) Pressure Monitor ( Amplifier ) PCL-812PG A/D Card PC Computer PC Screen Storage HDD,Floppy Printer Figure 3. Data Acquisition & Processing System In each test, the data were collected from four wave probes with 0.02 sec time interval for a time duration of 30 second for regular waves and 60 second for random waves, were stored in the computer for post processing. The wave and pressure amplitudes were determined using zero up crossing method. XXXlll Numerical procedure of Goda and Suzuki (1976) for random waves and Mansard and Funke (1980) for regular waves have been used for separating incident and reflected wave trains. After analysing the experimental data, it is found that offered piled breakwater is more effective in damping steep waves than flat waves. This corresponds to waves with high wave height and relatively small wave period like storm waves. That means after construction we will have a structure with increasing effectiveness parallel to increasing storm wave condition. On the other hand in relatively calm sea conditions, it allows the waves to pass, which have small amplitude and required for the circulation in the landward side of the structure from the ecological point of view. Another important result is about the point that differs this structure from other piled breakwaters. This structure includes the incoming waves to break and the waves can overtop which is not valid for the previous structures. With this feature, it is not objected to high breaking impact wave forces. Also it is found that once breaking occurs, the actual reflection becomes smaller than expected and considerable energy is lost through turbulence resulting in the reduction of the wave energy. Minimum transmission is not achieved when reflection is maximum but when energy loss is at its peak. This indicates a greater proportion of wave energy is dissipated by turbulence due to breaking, rather than being reflected seaward.
|Description:||Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1998|
Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 1998
|Appears in Collections:||Hidrolik ve Su Kaynakları Mühendisliği Lisansüstü Programı - Doktora|
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