Kıyı yapılarının laboratuvar çalışmaları ve Güzelce yat limanı modelinin incelenmesi

Abstract

Kıyı ve deniz yapılarının, laboratuvarda belli bir ölçekle yapılan modellerinde amaç, projenin minimum maliyetle en iyi performansı göstermesidir. Bu amaçla kurulan modellerde yapılan isler, bu çalışmanın kapsamına alınmıştır. Çalışmanın birinci bölümünde bir limanın en genel tanımı verilerek sınıflandırma yapılmış ve yat limanları (marinalar) hakkında bilgi verilmiştir. Bu bölümde, ayrıca çalışmanın amacı belirtilmiştir. İkinci bölümde, liman model leme çalışmalarında kullanılacak dalga karakteristikleri (dalga yüksekliği, dalga periyodu, v.b.)'nin elde edilmesi için yapılan dalga iklimi çalışmaları anlatılmıştır. Üçüncü bölüm, fiziksel modellere ayrılmış, liman tasarımında fiziksel modellerin yeri ve önemi belirtilmiştir, ölçek seçme kriterleri ile ölçek seçmede kısıtlayıcı faktörlerden sonra, bu çalışmanın yapıldığı iki ve Uç boyutlu model kanal ve havuzları, bu arada da ölçme sistemi tanıtılmıştır. Dördüncü bölümde, açık denizden kıyıya doğru gelen dalgaların dönme, sapma, sığlaşma gibi nedenlerle değişimi ele alınmış, bu konuda yapılmış çalışmalardan söz edilmiştir. Besinci bölüm, kıyı yapılarını etkileyen temel sorunlardan biri olan katı madde hareketine ayrılmıştır. Bu hareketin temel nedenleri etraflıca anlatıldıktan sonra, katı madde süreklilik denklemi ve kıyı boyu katı madde hesabında en çok kullanılan CERC formülü üzerinde bilgiler verilmiştir. Bu bölümün sonunda da kıyı çizgisi değişimlerinin matematik modeli ve sınır koşulları tanıtılmıştır. Çalışmanın altıncı bölümünde ise dalgakıranlar üzerine detaylı bilgi verildikten sonra, dalga etkisi altında meydana gelen hasarlar tanıtılmış ve hasar kriterleri sunulmuştur. Dalgakıranın koruyucu tabakasını oluşturan tasların ağırlığını bulmada kullanılan ve stabilite formülleri olarak adlandırılan formüller ve bu formüllerde stabilite katsayısını etkileyen birincil ve ikincil faktörler anlatılmıştır. Ayrıca dalgakıran tasarımında gözönüne alınması gereken çevresel ve jeolojik faktörler ile risk analizi ve ekonomik çalışmalar hakkında gerekli bilgiler verilmiştir. Yedinci bölümde, yapılan deneyler tanıtılmış ve deney sonuçları verilmiştir. Sekizinci bölümde ise bu sonuçlar değerlendirilmiştir.

The main purpose of a hydraulic model that is set up in a laboratory, is to provide the modelled project, the best performance with a minimum cost. The term "model" is used in hydraulics to describe the simulation of a "prototype", i.e. field size, situation. The hydraulic engineer uses models to predict the effect of a proposed design or scheme; they are tools for producing technically and economically optimal solutions to engineering problems. In other words, a model is a system which will convert a given input (geometry, boundary conditions, force, etc.), into an output (flow rates, levels, pressures, etc.), to be used in civil engineering design and operation. With the development of hydraulics, the scale-model has played an increasing role in the design of hydraulic structures and coastal works in the United States since about 1930. Important model techniques and procedures have been developed, instrumentation has improved, and simulation of more complicated phenomena has become possible through experience and basic research. Engineering experience and the use of analytical methods in the solution of design problems are still important factors in the design of engineering works. For many of the complex problems in coastal engineering, especially those corcerning the effects of wave action, the best approach to the problem of obtaining aspects of design is the use of scale models and the formation of a close alliance between the design engineer and the laboratory engineer. Hydraulic engineering projects include different types of studyas in the other engineering disciplines. These are; (i) Office studies, (ii) Laboratory studies and (iii) Field studies. The aim of this research is to determine the minimum weight of units which are used in the armour layer of a breakwater under the effect of incident waves. In chapter 1, general information about the ports and marinas is given. Chapter 2 includes the Wave Climate Studies which is aimed to determine the characteristics of incident waves, i.e wave height, wave length and wave period. The size of a wave for a particular location will depend on the velocity of the wind, the duration of the wind, the direction of the wind, the greatest distance over which the wind can act, and the depth of the water. xii In determining the wave to be used in the design of a structure at a particular location, only in exceptional cases will the designer be able to rely on a complete set of observations stretching over a sufficiently long period of time. Since World War II considerable work has been done on the forecasting of tide and wave conditions from meteorological, oceanografic, and geographic data. After the war, the advent of offshore structures for oil wells and radar stations kept research work going. The average height of the highest one-third of the waves for a stated interval has been termed the significant height, and it has been found that the highest or maximum wave has a height of about 1.87 times the significant height. In chapter 3, a detailed information about the physical models is given. Physical models provide the engineer and scientist two significant advantages when studying a particular coastal engineering problem. The first is that nature is used to integrate the appropriate equations which govern the phenomena, whether it be wave propagation into harbours or sand transport on a beach. No simplifying assumptions are used and no unknowns are omitted, as often occurs in analytical or numerical modelling. The second advantage is that the size of the model is much smaller than the prototype, permitting the easier acquisition of relevant data. There are, of course, drawbacks, such as the introduction of scale effects, which are due to changes in the relative importance of various forces (such as surface tension) as the model becomes smaller than the prototype. Additionally, the model is generally more simplistic than the prototype, for example, the use of monochromatic (single frequency) waves to study real sea states or, since the advent of spectral wave generators, using "real" sea states, but neglecting wind and other potentially important forces in nature. In coastal engineering, there are two types of model commonly used, fixed bed models (to study, for example, wave propagation and currents) and movable bed models (to study the deposition and transport of sediment). The modeling criteria for each are different. Chapter 4 deals with propagation of water waves. The breaking wave height and breaking wave angle are fundamental quantities required in coastal engineering applications corcerning the longshore current, longshore sediment transport and nearshore environment in general. Information about the local wave heights and wave directions enables a designer to estimate the wave forces and elevations to be expected at a structure or a shoreline. Before breaking, waves behind coastal structures transform under diffraction, refraction and shoaling. It is assumed that the breaking wave height behind an obstacle is proportional to the product of 3 coeffients calculated with linear wave theory: (1) A diffraction coeffient, Kjjj», for waves emanating from the tip of a long breakwater in uniform depth; and (2) & (3) refraction and shoaling coefficents, % and K^, as given, respectively, by Snell's Law xiii for a bottom with straight and parallel contours and by energy conservation. The location of the point of breaking, is determined by the breaking criterion. The following simple breaking criterion is used as a representative one: Hb-$db (1) in which typically (3=0.78. The breaking wave height is known to depend on the bottom slope and incident wave steepness. In Chapter 5, coastal sediment transport is discussed and coastal erosion is explained. Coastal erosion is caused by diverse factors. These include rise in mean sea level, increase in severity of incident waves, change in local magnitude and direction of incident waves, loss of sediment supply from rivers and cliffs, and interruption of the local littoral drift by the structures. If the cause of undesirable erosion in an area cannot be eliminated or corrected, then buildings, roads and other resources will eventually become endangered, and some degree of shore protection must be undertaken. The shore can be protected against erosion through the use of coastal structures, nonstructural procedures, such as beachfill, or a combination of structures and nonstructural methods. In situations where extensive damage may occur because of storm waves and water instrusion, or where nonstructural procedures are not feasible, then seawalls, bulkheads, and coastal dikes are commonly constructed for beach erosion control and for preventing inundation. Numerical models provide a powerfull means for making quantitative estimations of shoreline evolution. In particular, the so-called "one- line" numerical model has been widely applied in recent years. The term "one-line" typically refers to the shoreline; therefore, this model is often called "shore-line" model. The purpose of the shoreline model is to simulate long-term evolution of the shoreline or the beach planform. The governing equation for the shoreline position is obtained from the continuity equation for beach sediment (assumed to be cohesionless sand). A predictive formula for the sand transport rate is necessary to solve the governing equation. Sand transport and the resultant shoreline change depend on the local wind, waves, and currents, beach planform, boundary conditions, and constraints such as the one produced by a seawall. It will be assumed here that the longshore sand transport is produced solely by obliquely incident waves ; other transport mechanisms are possible, such as coastal, tidal, and wind-generated currents. It will be sufficient to use the equation for the shoreline position in its most basic form: xiv where y : shoreline position, m t : time, s D ' : depth of closure, m Q : volume rate of longshore sediment transport, mJ/s x : distance alongshore, m "3, In order to solve Equation 2, three kinds of information are required : (a) the initial location of the shoreline with respect to some coordinate system (Figure 1) in which the x-axis is oriented along the trend of the coast and the y-axis points offshore, (b) an expression for the longshore sand transport rate, Q, and (c) boundary conditions for either y or Q at the two lateral ends of the beach. Of these, the initial position of the shoreline is readily obtained or assumed. ? LATERAL BOUNDARY CONDITION: JETTY LATERAL BOUNDARY CONDITION: NATURAL (FIXED I BEACH- SEAWALL r /.? / 77, > '''>><' /A.- Fig. 1. Definition sketch for coordinate system, shoreline, seawall, and lateral boundary conditions. The longshore transport rate, Q, is usually calculated from the "CERC" formula. 0 - #(H2Cff) b sin2a bs (3) Common lateral boundary conditions are Q=0 at an impermeable barrier such a long jetty or grain, and 3Q/8x=0 on a beach that has a stable shoreline position. The boundary condition on Q can also be expressed as 3y/8t=0. Chapter 6 is about the breakwaters which are a class of port structures. There are several kinds of these structures. xv Rubble mound breakwaters belong to the most popular breakwater type in the world. They deserve this popularity due to their easy construction on most soil conditions, by their progressive damage future instead of a sudden collapse and their relatively easy repairment possibilities. Today, it is possible to find rubble mound breakwater constructions located at a variety of water depths ranging from very shallow water up to 50 meters. They are very expensive in water depth greater than about 6 meters. These structures reduce incident wave reflection and wave breaking over it and viscous losses as water particles interact with the breakwater. Common type cross section is trapezoidal. Construction of rubble-mound breakwaters in relatively deep water and wave-exposed locations necessitates the use of heavy protective armor units, which cannot be obtained economically from a quarry mine. w y a H° Y (4) KA-Ls.-!)* Cota yv where, y3> Vv are the specific weights of armour and water, a is the breakwater slope measured from the horizontal, Kj being empirical stability coefficient and Hp is the zero damage (1% to 5% damage) design wave height. As may be seen equation 4 does not include the effect of wave period in its prediction of armour weight. In chapter 7, laboratory experiments are explained and the results are given. The results of the stability experiments are plotted where the abscissa shows the percentage damage DT, defined by equation 5. DT - total number of displaced armour units total number of armour units used in the test section (5) The results of the experiments realized to predict the water level fluctuation are given with a dimensionless parameter (K), defined by equation 6. K _ Wave height in the harbour basin,^ incident wave height In chapter 8, the evaluations of the experimental studies and the conclusions obtained from these evaluations are presented. These are as follows. For the stability experiments: 1. Incident wave height and period are the main factors that affect the damage on the armour layer of the breakwater. The higher the incident wave and the greater wave period, the greater is the damage on the armour layer of the breakwater. xvi 2. In the economical life of the structure the occurence probability of a wave with a height equal to or greater than the project wave height is calculated according to the risk formula and consequently the damage that will occur on the armour layer of the breakwater can be seen and the dimensions (i.e. the weight) of the stones, which will be used in the armour layer, can be determined. 3. The weight of the stones which will be used in the armour layer must be the same along the breakwater axis in relatively equal water depth. 4. The dimensions of the structures are defined separately whether their locations are in or out of the breaking zone. For the water level fluctuation experiments: l.The water level fluctuations in the harbour basin must be examined on the 3 dimensional laboratory model under the effect of the incident wave from the effective direction for the water level fluctuation. 2. For the conditions when the effective direction (s) can not be examined on the 3 dimensional laboratory model, this effect can be controlled by using the diffraction charts given in [ 2 ]. 3. The appropriate layout of the harbour for the water level fluctuation must be examined on the 3 dimensional laboratory model for both the coastal sediment and sea surface, pollution. 4. Because the waves in the entrance of the harbour are the main causes of the water level fluctuations in the harbour basins, the determination of the angle between the tip of the main breakwater and the effective direction will be the best way to control these fluctuations at the desired level.