Effect of Initial Stresses on the Response of FRP Plates under Low Velocity Transverse Impact
S.M.R. Khalili, R.K. Mittal

Dynamic Characteristics of Marine Hubless Screw Propellers
V. Amminikutty, V. Anantha Subramanian, G.Dhinesh

Improvement of the Michell Method based on Sigmoidal transformation for Solving Waves
D. Rostamy, M. Rostamy, S. Khalehoghli

Optimising Funnel Height to Avoid Smoke Ingress Problem in Naval Ships
R.Vijayakumar, S.N. Singh, V. Seshadri, P.R. Kulkarni

Studies in a Low Speed Wind Tunnel and Validation of CFD Predictions
H.N. Das, P. Jayakumar, A. Saiju

Methanol Induction in Marine Diesel Engines: A Technique to Reduce Exhaust Emissions
B.V. Appa Rao, N. Haribabu, K.Ram Babu

Discovery and Restoration of Documentary Film “India’s Struggle for National Shipping”
Amrit Gangar

BACK COVER – Vol 4, No. 2, July 2008

Effect of Initial Stresses on the Response of FRP Plates under Low Velocity Transverse Impact
S.M.R. Khalili, R.K. Mittal

ABSTRACT
The effect of initial stresses on the impact response of large fiber-reinforced plastic plates is considered in this paper. The plates can be in the form of a unidirectional lamina or a symmetric laminate and the impact is due to a moving projectile striking the plate transversely. The initial stress state may be due to pre-existing service loads, environmental factors or residual stresses which have been generally ignored in the literature. These stresses may be uni-axial or bi-axial, and tensile or compressive. The contact phenomenon between the impactor and the plate is described in terms of Sveklo's contact theory due to the anisotropic nature of the plate. The impact response parameters considered are: contact force, contact time and the deflection of the plate at the centre of the contact patch. The effects of both the uni-axial and bi-axial initial stresses on the impact response are obtained analytically for various ply-sequences of the plate.
It is shown that the ply-sequence has an appreciable effect on the impact response. In the presence of the tensile pre-stress, the contact force is marginally higher and contact time lesser. Also, the deflection of the plate at the centre of the contact patch is less.

Keywords: Fiber-reinforced composites, laminates, impact, initial stresses, dynamic contact

Dynamic Characteristics of Marine Hubless Screw Propellers
V. Amminikutty, V. Anantha Subramanian, G.Dhinesh

ABSTRACT
Marine screw propellers are the main means of ship propulsion. Propeller design aims at achieving high propulsive efficiency at low levels of vibration and noise, usually with minimum cavitation. Improvements in propulsion have been proposed to enhance performance and many concepts have been implemented with varying degrees of success. Computational fluid dynamics (CFD) has emerged as a potential versatile tool in recent years and has promising applications. This work investigates the application of CFD to the analysis of openwater test on screw propellers. The hubless propeller is a new concept and a propeller has been designed with a rational pitch and chord distribution based on performance considerations, by adapting it from conventional screw propeller blade geometry for a given application. The analysis brings out thrust characteristics as well as dynamic aspects of flow in relation with the geometry of the hubless propeller configuration. The performance characteristics of the hubless propeller are brought out in terms of improved thrust delivery and torque absorption, though there is no significant improvement of efficiency at low advance coefficients. The limited quantified data suggest that the hubless propeller may be considered for higher thrust requirements in constrained space conditions.

Keywords: Propellers, CFD, hubless propeller.

Improvement of the Michell Method based on Sigmoidal transformation for Solving Waves
D. Rostamy, M. Rostamy, S. Khalehoghli

ABSTRACT
Shallow-water ship-waves, known as wash waves, are important in marine engineering. These waves can affect coastal structures and change near-shore morphology. They can also cause damage to the ship itself in finite depth channels. There are different theoretical methods to consider these waves. In this paper shallow-water ship-waves are simulated numerically by sigmoidal transformations and Michell's thin-ship. The new method is an improvement of the theory used in ‘Michlet’ software. By introduction of a sigmoidal transformation, the application of the trapezoidal rule to the transformed integral gives a higher rate of convergence. In this study the flow is considered incompressible and irrotational. However for the accuracy of simulation the effect of eddy viscosity is then considered. The numerical results were compared with other models and experimental results for a series 60 hull form. It showed that development of Michell's thin-ship theory could simulate this kind of waves with greater accuracy and reliability.

Keywords: Numerical analysis, ship waves, shallow water, sigmoidal integration.

Optimising Funnel Height to Avoid Smoke Ingress Problem in Naval Ships
R.Vijayakumar, S.N. Singh, V. Seshadri, P.R. Kulkarni

ABSTRACT
Funnels are designed and fitted on board naval ships to discharge the exhaust gases in a way that the exhaust gases stay clear of the ship and do not interfere with the sensitive fittings on the superstructure. Ideally the funnel height should be high enough to extend beyond the thickness of turbulent boundary layer of the superstructure. However, modern warship design practice favors a tall mast to house sensors and electronics adjacent to short funnels, which leads to the problem of smoke nuisance on board naval vessels. The traditional use of empirical formula in designing the funnel height at very early stages of design also fails to eliminate the problem of smoke nuisance in the modern warship. This paper presents CFD and experimental simulation of exhaust emission on a representative top side of a generic frigate. The emphasis of the study is to provide guiding polar plots for the designer to choose the appropriate funnel height for naval ships during initial stages of design. CFD simulation has been carried out for different funnel height to mast height ratios (from 0.35 to 1) along with Gas Turbine (GT) intakes for wind directions (yaw angles) between -30O to 30O, for three velocity ratios (0.5, 1 and 1.5). The results have been presented in the form of polar plots. The CFD simulation has identified smoke downwash in the wake of the bluff bodies of superstructure with respect to various funnel heights and the conditions which lead to ingress of exhaust smoke into GT intake. The experimental studies of flow over the model superstructure with exhaust flow from the funnel and simulation of GT intakes were conducted in a wind tunnel for initial validation/comparison with CFD studies.

Keywords: Smoke ingress, Superstructure, Funnel design, CFD, ship aerodynamics

Studies in a Low Speed Wind Tunnel and Validation of CFD Predictions
H.N. Das, P. Jayakumar, A. Saiju

ABSTRACT
CFD was employed to predict the behaviour of different configurations of instruments within a low speed wind tunnel at NSTL during its set up. Computational studies were made to estimate the optimum position of a wake traverse gear inside the test section of the wind tunnel. The aim was to position the instrument in such a way to cause minimum disturbance to the flow. CFD was also used to design a wake rake to measure the velocity profile inside the wind tunnel. Present paper describes the execution of these two tasks using CFD.
The segregated solver of Fluent 6.2 was used for the entire computation. The Reynolds Time Averaged Navier-Stokes (RANS) Equations were framed for each control volume in the discretised form using finite volume method. The STANDARD scheme was employed for pressure and SIMPLE (Strongly Implicit Pressure Link Equations) procedure for calculation of pressure field from the continuity equation. Standard k-e model was used with standard wall functions.
The CFD analysis successfully estimated the dimensions / configurations of the wake traverse gear and the wake rake. Some of the computational results could be validated satisfactorily against the measurements taken from the wind tunnel itself. This paper demonstrates the utility of CFD even for setting up of an experimental facility.

Keywords: RANS, CFD, Wind Tunnel, Wake Traverse Gear, Finite Volume Method

Methanol Induction in Marine Diesel Engines: A Technique to Reduce Exhaust Emissions
B.V. Appa Rao, N. Haribabu, K.Ram Babu

ABSTRACT
Advent of bio-diesel for marine power generation applications offers a possibility to reduce exhaust pollution. However, bio-diesels cause an increase in Nitric Oxide (NO) emission, which is also responsible for surface ozone depletion. One of the techniques to reduce NO emission is the induction of methanol at the suction end of diesel engine running on bio-diesel. A set of experiments was carried out on a single cylinder direct injection diesel engine, loaded with an eddy current dynamometer to examine the effect of variation of methanol injection rate on the emissions of the engine. The engine is operated in dual fuel mode, with Pongamia methyl ester being injected and heated methanol vapour is added to the incoming air, the flow rate being defined by the throttle opening of the carburettor. The emissions were analysed for various throttle openings and it was found that a flow rate of 16.2 mg/sec was found to give maximum reduction in the engine emission in terms of CO2, CO, hydrocarbons and NO. The effect of methanol flow rate on engine vibration 2 was also examined.

Keywords: Dual fuel, direct injection diesel, bio-diesel, methanol injection, Pongamia methyl ester, carburettion, vibration.

Discovery and Restoration of Documentary Film “India’s Struggle for National Shipping”
Amrit Gangar

ABSTRACT
In 1990, while setting up a database for the Films Division's archive of over 8,000 documentary films, newsreels, featurettes, short films and animation films, the author came across several films related to shipping industry in India. There was one film titled “India's Struggle for National Shipping” which seemed to have been lost. The film was an important national document. Produced in 1946 for the Scindia Steam Navigation Co. Limited., the film “India's Struggle for National Shipping” was set in the pre-independence era, depicting the events and milestones of a colonized India's struggle for independent statehood, in the form of a struggle for National Shipping, and the struggle for setting up modern India's shipbuilding industry. The talented German filmmaker, Paul Zils, who stayed in India for a little over a decade and half, had directed the film. The author was instrumental in discovering this historic national document, rescuing it from eventual 'death' and restoring it in the nation's film archives, thus saving it for our progeny. The author narrates a first person account of the story of this rescue and restoration.

Keywords: National Heritage, Film Archive, Maritime History