2)

SHIP STRUCTURAL STRENGTH

2.1)

EXPRESSION OF SHIP LONGITUDINAL STRENGTH

Structural strength can be explained as the protection of integrity, without structural deformation, under preloaded loading conditions against all internal and external forces. But there is no form can be protected against all the forces without distorting its shape. For example, when a soft metal pipe is pulled from both ends by machines, the length will increase after a while and we will examine it from the center line its thickness get thinner or if we press the sides upwards after a certain period of time, its middle will fall down. There are a lot of examples like this and this. (Ref )There are two important points in this resistance against the forces.1.The portion that reaches to the elastic deformation and corresponds to the flow point.2.The extent of the flow limit that also specified as the stress.The structural strength of a ship in engineering terminology is determined by two important conditions I have mentioned. In order to be safe against specified loading conditions and against all forces and loads that may be externally influenced, the self-tension of the build must remain under yield stress. This ratio is limited to about 6% or even less.The ship is a complex building with a lot of structural details. Based on the static assumption of longitudinal strength (structural strength) of the ship in the loading condition, the calculation of the cross-sectional shear force and bending moment distributions of the loads acting on the ship in the direction of the acceptance of the structural integrity as a beam and the preparation of the section in such a way as to be based on the case where the stress is less than the yield limit, all of the examinations for determining the problems to be caused due to the deterioration which may be happening possibility on the sectional surfaces can be determined as the strength of the ship. (ref den431e)Nonetheless, the possible analysis problems can be solved by making some changes in weight distribution or the mid ship sectional strength module. (ref erkek tez)Generally, the analysis are done while the movement of the ship is very slow in the case of calm water and very long period fluctuations.Therefore, the dynamic loads that can occur due to their level that can be neglected. In this direction, loads can be assumed as static assumptions while longitudinal strength is considered.(yukardaki ref)

2.2

) THE LOADS EFFECTING ON SHIP

Loads affecting the ship’s structure can be examined in 2 main roads depending on the load source and frequency.2.2.1) Loads Depending On The Load Source

The two

most important classifications that affect the structural form of the ship and

depend on freight sources are as follows.

2.2.1.1)

Structural Weight

Structural weights mentioned here can be described as steel

vessel weight of the ship, main and auxiliary machines, outfitting weights,

cargo loads and ballasts.(yukardaki ref)

2.2.1.2)

Structural Buoyancy

Hydrostatic calculations after the determination of the ship

form and a continuously available qualification as determined by Bon Jean

Curves and structural weight.(yukardaki ref)

There are

still two more load types which are depending on the situation.

2.2.1.3) Point Loads

These loads are the loads

that can occur during a landing from the ship, or when sitting on the ground on

land, but they need to be inspected when necessary. (yukardaki ref)

2.2.1.4) Thermal Loads

Separately, the cooling that

exists in vessels working on cold glacier cuts, or arthritis or antarctica,

causes extra strain. Practically,

these loads do not have much maintenance unless they constitute an extra case

They do not need to be taken into much attention.(yukardaki ref)

2.2.2)

Loads Depending On The Frequency

The classification of the loads on the ship

according to their frequencies can be examined separately as follows.

2.2.2.1)

Static Loads

They are loads that are dependent on ship’s weight in long-term changes such as loading or unloading at ports, fuel consumption during cruising and consumption in water tanks. The sudden change in these loads can already be offset by ballast intake.Also including force in the load category depends on buoyancy distribution on calm sea water. (ref erkek tez ile tezinin 11 ve k?z?n 8)

2.2.2.2)

Low Frequency (Semi-Static) Loads

Short term loads that changes in varying between a few minutes to seconds .According to the amount of vibration, their created frequency that can be counted as low as possible. The loads that affects to the ship structure on wavy sea conditions. The wave caused by the wave impact brings the additional mass and damping factor from the opposite reaction of the sea to the ship movements. Assuming that the amount of change is slow, and doing calculations by ignoring variables related to velocity and acceleration can cause a very large error that can not to be ignored. However, in order to obtain accurate calculations and results, the motions must not be ignored and dynamic load factors should be included in the analysis. (ref erkek tez ile tezinin 11 ve k?z?n 8)

2.2.2.3)

High Frequency Loads

They are loads that are

connected to vibrations, which are usually caused by the main machine and

auxiliary machinery.They been come up with the transmission and vibrational

interaction of the vibration acting on the ship with the main and auxilary

machines and theirs steel bedded bearings which they are assembled. It occurs

in one part due to the vibration that is transmitted to the ship’s body from

the propeller and shaft area.They are partial loads.If the time interval is

shorter than the low frequency, or if the available loads are small, they can

cause high fluctuations, causing high shifts by increasing the amount of high

frequency vibration. (ref erkek tez ile tezinin 11 ve k?z?n 8)

2.2.2.4)

Impact Loads

The waves of breaking caused by ship’s head – stern hitting movements or wavy sea slamming is overly challenging loads that can result in collisions in any segment of the craft.. Since the repetition periods are quite short, from 0,0005 seconds to 0,005 seconds, they can take place locally on the natural crane of the ship structure and causes the remaining vibrations to flow. (ref erkek tez ile tezinin 11 ve k?z?n 8)

2.3)

THE OPPOSITE REACTIONS OF THE SHIP DUE TO THE ACTING FORCES

The responses of ships to the forces they are subjected to are examined in three main groups.

2.3.1)

First Group Reactions

They are the contrasts that the ship shows against the forces

under the influence as a whole. They are adverse reactions that occur when they are exposed

to static and semi – static forces. Ship integrity is examined and the shear

strength and bending moment strengths of the sections are examined. Two methods

are followed during this analysis. First, the structure is considered as a

beam, and static assumption analysis and calculations are made in this

acceptance direction. However, it should not be overlooked that the ship form

must be in a delicate structure when this is accepted. Secondly, finite element method is used in

order to make more accurate calculations and obtain more accurate analysis

results in building forms that are not in more delicate structure.(k?z

8)

2.3.2)

Second Group Reactions

The ship is divided into zones and is the only form of

reaction that is shown against the forces that are influential in the area of

??the selected zone.

For example, it can be specified

as the reactions that a side-by-side block structure or a cargo hold indicates.

It may come from the high

frequency forces or from the distributed states of the regional forces. (k?z

ve k?z 8)

When such interaction reactions are analyzed, beam stress

analysis is carried out by making the structure studied in the regional case

well protected and becoming a simpler system. (k?z ve k?z 8)

Beam strength calculations can also be done with 2 methods.As

the hypothetical static approach can be examined as a two-dimensional plane,

inspections of the same region can be made by inspecting the model with finite

element method. Therefore, it is more appropriate to make analysis in this way

in the design phase as more accurate results can be obtained.

(k?z ve k?z 8)

2.3.3)

Third Group Reactions

It is the response that can be customized by the minimally zoning of the forces acting on the ship and by the reaction state of a single structural element. The most qualifying example is the outer cover presses between the two mattresses, that is, the strength of the local plate strength. These kinds of reactions are generally concerned with structural fracture, fatigue and loss of strength. (k?z ve k?z 8)

Figure 2.1: Classification of Response Groups Against Loads Exposed by Vessels

2.4)

THE LONGITUDINAL STRENGTH ANAYSIS BASED ON THE QUASI – STATIC ASSUMPTION OF THE

LOADING CONDITIONS

When structural analysis of the static assumption is made, the ship is regarded as a beam, and static conditions are kept. These analyzes are examined in 3 cases. These are defining as calm water, wave crest and wave trough conditions. The most challenging condition in the wave crest and trough is that the length of the ship and wave are the same size.For this reason, analyzes are made considering this condition. In the case of the wave’s hill, the peak of the wave height is kept in the mastori.In the wave pit, there are 2 peak points and these two wave height lines should be kept between the aft and fore peak verticals. Once these alignments are made correctly, the analysis is carried out in a fully loaded condition and the unloaded condition in which ony the ballast is taken.(Ryok)

3)

THE WEIGHT CALCULATIONS

The weight distribution of the calculations is examined as two main headings. These first main headings are the weight of the “Lightship”, the weight of the steel boat, the weight of the top deck body area, we call “superstructure”, the weights of the main machine and the auxiliary machines and the weights equipments.The second one is the type of weight, which is referred to as “deadweight” and in which the remaining ballast weights, cargo loads, personnel weights, food weights, fuel quantities, capacities of fresh water tanks, and lubrication oil weights are specified. These two main categories specify the total weight of the ship, and in which ship length the weight distribution is determined by empirical weight calculation and distribution forms. It is determined how the weight distribution is formed between the lengths of the ships in the direction of the ship determined in the direction of this table.(ref erkek ve ders)

The assuming of the weight P, which is a specific weight in uniformly linearly spread loads, unit length of the vessel in the longitudinal dimension of the area dL, C1 be the distance from the unit length of the center of gravity to the half of the center of gravity.In this situation, it is the case that the weight is converted from the trapezoid to a straight linearly spreading load. This cycle is indicated by the formulas below. (ref erkek)3.1)LIGHTSHIP WEIGHT

The lightship weight of

the ship is examined in 4 main ways. P hull steel hull, P ss superstructure, P

eq outfitting and P m is referred as

main engine and auxilaries weights. (ref erkek)

The parts of the empty vessel weight in each

individual piece are distributed according to the size of the boat they are on

and together form pieces the lightship weight distribution can be made.

.3.1.1)

Steel Hull Weight

The weight of the steel vessel is not a weight which is followed and distributed in a uniform direction from the beginning to the end.Depending on some empirical formulas, the weight of the steel craft is calculated. The weight obtained after these empirical formulas is obtained by dividing the distribution into 3 separate groups by a system called trapezium method. However, this distribution is carried out in the direction of the ship’s length by following the intervals very often and distributed smoothly.(ref ders) In order to determine the weight of the steel hull, it has to be characterized by the entire ship form structure, especially during the preliminary design process. Because it is one of the most important detail elements that should be obtained during longitudinal strength analysis in the preliminary stages. (ref ders)

Empirically from the above formulas, the steel vessel weight is graphically distributed with a variance depending on the block coefficient (Cb). In there, Ws is the whole weight of the steel hull, L ship length, B ship beam, H the height of the ship or its depth, ws the amount of weight distribution per meter of the length of the ship. l1 the extended length from board to board, l2 not extented length of superstructure from board to board.(ref ders)Other than these empirical formulations, more detailed and more precise steel vessel weight calculations are available. (ref erkek)

K hull,ss is a

coefficient and the determination of

this value with usign of the formula down below. ? displacement tonnage.

In there L ship length,

E material elasticity modulus and this module for the steel boats expressed as 2.06

10^5 N/mm^2.

The consideration of

the parameters as Lc parallel body length of the ship, dL one unit of the ship

length, X hull the distance travelled along the ship. (ref erkek)

3.1.2)

Main Engine Weights

The main machine weight is one of uniformly spread loads which alignment, usually on the stern side. Some empirical formulas can be used to determine the weight distribution of the engine that will work with respect to the ship dependent variables. (ref ders)

On the formula, P the engine power reffered as kW, N the rpm value depend machine work period, and lm is engine’s length. If the power value of the main machine is not determined before calculations, working service velocity Vo, ? ship displacement tonnage and Lpp the length between perpendiculars as acceptable terms for the calculation of the P engine power.The calculation formula expressed down below. If the N value is still an unknown value, the availabilities at low speed diesel engines N=110, for the middle speed diesel engines N=450 and for the high speed diesel engines N=850 can be made in the forms. (ref erkek)

A more detailed study can be obtained with secondary calculations.

The refferatations can be

made as Ler is the main engine compartment’s length, Neff the power of the main engine that uses maximum

efficiency, A m and B m weight distribution coefficients and Xer the distance of the main machine room’s weight

centroid. (ref erkek)

3.1.3)

Auxiliary Machine Weights

The empirical calculations

of this weight based on the amin engine performance properties and its power. In

that case the gathered weight’s distribution along the engine room length can be

made with uniform spreading. P is the power of the main engine in terms of KW,

la engine room length , Wa auxilary machines overall weights and wa in the unit

length of auxiliaries weight distribution.(ref ders)

3.1.4)

Superstructure Weight

The weight of the upper building is taken in

such a way that it can include the freeboard deck, aligned in a tiny section of

the stern and head, the weight determinations are made by empirical formulas

and the weight distribution is finalized. (ref erkek)

With

the help of the above empirical formulas, weights are calculated and their

distributions are made according to the determined alignments.