RESEARCH GROUPS

Hull Optimization Group
Computational Wave-Making Analysis and Hull Form Optimization for Minimum Resistance. Local hull-shape optimization procedure is based on potential flow solvers for bow form and boundary layer integral technique as well as a data base for the aft form.

Bow form optimization is carried out by assuming the total resistance to be the sum of frictional resistance (ITTC-1957) and wave resistance, which is based on thin-ship theory. Tent functions are used to approximate the hull geometry. Thus, the approximated total resistance is reduced to a quadratic programming (QP) problem with linear inequality design constraints. This QP problem is then solved by Wolfe’s algorithm. The bow form improvement process is commenced with an initial ship geometry. The resultant optimal forms are then numerically tested with regards to their wave-making characteristics by a more sophisticated potential flow solver.

The flow solver used in wave-making analyses was developed at ITU by using the Dawson’s algorithm in Hess and Smith’s panel method. This code has been tested numerous times in the past and found capable of giving sensitive results for wave-making characteristics. In a recent EUCLID project (RTP 10.14), ITU’s flow solver proved itself to be the best for moderate Froude numbers among the 4 partners.

The optimization code and potential flow code are the components of the whole optimization process. This process has been used more then 20 times in the last decade and has been able to attain at least 4 % gain in total resistance and more than 10 % gains in some cases due to bow modifications. A detailed explanation of the above mentioned processes could also be found in the following research papers:

[1] Gören, Ö., Helvacioğlu, Ş. and Insel, M., “Bow Form Optimization of Displacement Ships by Mathematical Programming”, Ship Technology Research, Vol.44, No.2, 1997.

[2] Danisman, D.B., Gören, Ö., Insel, M. and Atlar, M., “An Optimization Study for the Bow Form of High-Speed Displacement Catamarans”, Marine Technology, Vol. 38, No. 2, 2001.

Manoeuver Group
Manoeuvering Performance Assessment
The manoeuvrability is one of the main considerations in any ship design study. The İTÜ manoeuvering simulation software is based on relaible and well-proven procedures developed, originally by Vladimir Ankudinov, who has many years of experience in numerical ship manoeuvring prediction. The crucial part of the software is the prediction of hydrodynamic coefficients. Due to the strong influence of viscous effects these coefficients are difficult to estimate using pure theoretical methods. The prediction of hydrodyanmic coefficents is based on the regression of a wide range of experimental and full-scale data. These data were obtained from, basically, the US Army Corps of Engineers, MARAD, main experimental tanks such as SSPA and the open literature.

The program can be used for two basic purposes

· Evaluation of basic ship manoeuvring characteristics over the range of loading and environmental conditions (fast time simulation)

· Validation or verification of passage plans through specified channels under a range of environmental conditions (real time simulation)

In the fast time simulation mode, the equations are integrated as fast as possible by the computer and the rudder/propulsion system commands are controlled by some predetermined logic. This mode is used to simulate standard definitive manoeuvres including turns, zigzags, and spirals. This mode can also be used for simulation of manoeuvres controlled by an autopilot.

In the real time mode the program integrates equations at a rate, which corresponds to real time, and a visual scene through the computer screen is provided. The visual scene is updated as the ship motion model computes a new ship’s position and heading resulting from manual control input based on the pilot’s commands (rudder, engine throttle, and tug commands), ship hydrodynamics, and external forces. The external force capability of the simulator includes effects of wind, waves, currents, banks, shallow water, ship/ship interaction, and tugboats. In addition to the visual scene, the user is provided with navigation information such as speed and heading of the vessel, wind speed and direction, magnitude and direction of current, etc.

Seakeeping Perfermance Assessment
The comprehensive consideration of seakeeping performance in the early stages of ship design has been a subject of a wide-ranging research programme at İstanbul Technical University. The result of these studies has been the development of alternative analysis procedures, which allow seakeeping to become a routine part of monohull form design.

The assessment of seakeeping performance depends on three factors, environmental conditions, ship responses and seakeeping criteria. These factors are combined to form a seakeeping performance database, which contains the details of seakeeping characteristics of a given design. The major difficulty in evaluating the seakeeping performance of a ship arises from the stochastic nature of the sea environment. Since the sea conditions and the motions of the ship in waves prevailing at any instant of time cannot be determined exactly, they have to be approximated in a probabilistic manner. Therefore, a stochastic rather than deterministic approach is required to take into account correctly the complexities of the sea environment.

The prediction of ship responses in a given sea state is performed in two stages. The first stage is the computation of response amplitude operators (RAOs) in regular waves of unit amplitude. A two-dimensional strip theory based computer program is used for the calculations. Both the theory and the program have been validated with a large number of experimental and full-scale trial results for high-speed warship forms.

The environmental conditions are specified by sea state numbers, which are defined as a function of significant wave height, and some related parameters might be included such as fetch and wind speed. When the operational area is not specified a standard ITTC one parameter spectrum is recommended. However, the significant wave height parameter may not be sufficient to represent littoral waters and a second parameter, generally the modal wave period, should also be specified.

The RAOs or statistical responses in given sea states may not be sufficient to assess the seakeeping performance of a given design. A realistic assessment should be based on the mission capability of the designs in specified operational areas. In order to assess the effect of seakeeping performance on the mission capability of the vessel the mission requirements need to be translated into seakeeping performance requirements. For example, operation of an ASW helicopter in sea state 5 may be limited with a significant roll angle of 8 degrees.

The responses are specified as significant single amplitudes and assumed to be independent of each other and of equal importance. Exceedance of one or more of these criteria at a given speed and heading combination is assumed to preclude operation at those conditions

A realistic way of comparing the seakeeping performance of alternative designs is thought to be the operability indices derived from speed polar plots for each sea state. In order to calculate operability indices, seakeeping responses need to be predicted for each sea state, operational area, ship speed and wave heading. Typical speed polar plots for two alternative designs in sea state 5 are shown in Figure 3, where the concentric circles represent ship speeds and the radial lines represent ship headings relative to the waves. The contour lines are plots of speed-heading combinations at which one of the seakeeping criteria is exceeded, i.e. the ship cannot operate beyond this limit without exceeding the relevant criterion. An envelope defined by the shaded area represents the combinations of speed and heading at which the ship cannot operate without exceeding any of the criteria. These plots can be developed for each operational area and sea state considered and operability indices, defined as the ratio of the clear area to the total area can be calculated.

Structures and Vibration Group
The Structures and Vibration Group undertakes the calculations necessary for the structural design of a new ship or the evaluation of an existing ship. This group uses a large computer programs inventory, developed at various universities abroad as well as those developed in the ITU Naval Architecture and Ocean Engineering Faculty. Furthermore, industry standard programs licensed to ITU are used where necessary. The capabilities of the Structures and Vibration Group are summarised below.

1- Scantlings and Structural Properties of Cross-sections
· Weight optimisation and scantlings of structural members,
· Cross-section properties (the distributions along the ship of static moment, moment of inertia, effective shear area, polar moment of inertia etc.),
· The distribution along the ship of the design bending moment and the permissible stress according to specified rules.

These calculations are carried out using the ITUgemSTATIK program suite.

2- Conventional Longitudinal Strength Analysis
The conventional longitudinal strength analysis incorporates the shear force and bending moment distributions along the hull, as well as the deck and keel stresses, the elastic deformation of the hull beam.

· Longitudinal strength under calm water, wave crest and wave trough conditions,
· Progressive longitudinal strength calculations for loading and unloading, preparation of the loading manual,
· Progressive longitudinal strength calculations for floating procedures of a grounded vessel,
· Longitudinal strength calculations in accordance with a specified classification society or a naval standard (e.g. BV 1040).

These calculations are carried out using the ITUgemMUK program suite.

3- Global and Local Vibration Characteristics
· Vertical, horizontal and torsional resonant frequencies of the hull,
· The resonant frequencies of grillage systems, panels and bulkheads.

These calculations are carried out using a database of a large number of merchant and naval ships with semi-empiric methods.

4- Dynamic Strenght Calculations
In this section, the behaviour of a ship in extreme sea states is analised usin a 2-D hydroelastic theory developed in England and later in ITU.

· The representation of the irregular waves by a given sea state and a locality using appropriate wave energy spectra,
· The calculation of the continuous wave excitation and the transient wave impact forces (slamming pressures and forces),
· The time series of the dynamic shear force and bending moment values at all required sections along the hull,
· The time series of rigid and elastic ship motions such as heaving, pitching and vertical deformation,
· The statistical analysis of the time series and the determination of the “survivalibility condition” with respect to ship speed and sea state.

The intermediate results, such as the natural mode shapes and natural frequencies of the hull, vertical velocities and accelerations, slamming pressure histories are used for vibration and seakeeping analyses if required.

These calculations are carried out using the ITUDINSIM computer program suite.

5- Detailed Structural Design with Finite Element Method
The local and global design of the ship structures are carried out by ANSYS 5.5 FEM program, using 2-D or 3-D models as required.

· Stress – strain calculations,
· Vibration analysis,
· Buckling controls.

6- 3-D Hydroelastic Analysis
The 2-D dynamic strength calculations summarised in paragraph 4 are extended to 3-D methods developed in ITU. In this approach, 3-D fine element representation of the structure is used instead of the 2-D beam model. The fluid forces and actions are calculated by a 3-D potential theory method. The results and their utilisation are as explained in paragraph 4.

The 3-D hydroelastic analysis is carried out using the ITUgemHEA computer program suite.

Marine Engineering Group

Reliability, availability and maintainability (RAM) analysis of machinery systems

Machinery room vibration analysis
· machinery foundation
· shafting system
· air and exhaust ducts

Piping system design
· optimal pipe routing
· vibration analysis
· economic design

Heating, Ventilation and Air-Conditioning system design
· Velocity and temperature disributions of air within the engine room
· Air intake and exhaust system design

Refrigeration system design
· Determination of storage conditions
· Thermal insulation
· Temperature and velocity distributions of air in refrigerated spaces

Fire safety analysis

Fire, noise and thermal insulation