Browsing by Author "Wimalsiri, WK"

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item: Thesis-Full-text
An Inviscid model for predicting unsteady forces in doubly connected domains
Gunarathna, MACK; Wimalsiri, WK; Dassanayake, VPC
Inviscid analytical-numerical model for predicting unsteady forces on two aerofoil configurations is developed and validated with the past literature. First the unsteady inviscid, incompressible and irrotational, except the logarithmic singularities at vortex points, flow field around the doubly connected domain is evaluated using a conformal mapping method. A discrete vortex shedding mechanism is incorporated to model the free shear layers of the real fluid flow. The complex potential associated with uniform flow and the vortex motion is obtained using elliptic functions and the modified Green’s function respectively. The strengths of the vortices are evaluated using Kutta condition which keeps the regularity of the flow field. Circulation development around the aerofoils is quantified by utilizing Kelvin’s circulation theorem. The unsteady forces are obtained using the unsteady version of the Blasius equation. Both trapezoidal rule and finite difference method are incorporated to solve the unsteady Blasius equation. The developed inviscid model is applied to various aerofoil configurations to predict the unsteady forces on the aerofoils. The results obtained were validated to the past relevant literature. Results showed a good agreement with the past literature.
item: Conference-Full-text
Knowledge based software for loading and stability of ships
(2000) Wimalsiri, WK
Loading and Stability calculations of ships became a more and more complicated and time consuming process as the ship sizes and design complexity increased. Accurate and efficient methods of evaluating and analysing stability of ships for a given loading condition became very important as the safety become equally comparable with efficiency of operation. These requirements lead to introduction of dedicated computer systems onboard ships for loading and stability monitoring in the past. At present Ports-State Control requires details of loading and stability of the ship as it arrives to a particular port. With the development of the personal computer and windows environment, it is now possible to demonstrate actual loading and stability not only on onboard computer, but also at the shore based offices of the shipping agencies that do cargo planning. Any loading condition can be studied together with required stability prior to actual loading taking place. Alterations of loading can he suggested to optimize any loading condition. Although there are specialized producers of such software to the global shipping industries, this paper presents development of such software for a local ship owner.
item: Conference-Full-text
Refrigeration system for Sri Lankan fishing boats
(1999) Wimalsiri, WK; Weerakoon, DAW; Weerasinghe, NMC; Fernando, MJP
The fisheries sector in Sri Lanka has been expanding during past decade with growing local demand and export of fish. In order to cope with the demand, the size of fishing boat used for multi-day, deep-sea fishing has now increased up to 60 ft. There are more than 1700 such boats working around Sri Lanka and building of such boats progress continuously. Most of these designs are based on the extension of small multi-day boats but no attention is paid to the technical feasibility of increasing boat capacity by scaling up the dimension to make the boat bigger. Although there are important factors and views to be discussed with regard to altering a design, such factors are beyond the scope of this research. In view of the operation of these boats at least 2-3 weeks are needed to complete one voyage of fishing. However, the concept of fish preservation still remains conventional by using the ice cold fish hold that was used for small multi day boats. This method offish preservation would have been economical for small boats that carry about 2-5 tonne of fish but as the boat size increases, preservation by ice may have following disadvantages. a. Full capacity offish hold cannot be used for storing fish b. High fuel consumption at departure condition to carry considerable amount of ice. c. Impossible to maintain an acceptable temperature inside the fish-hold. d. Duration of fishing and amount of the catch is limited depending on available ice. e. Operating cost of the vessel increases and the quality of fish becomes poor due to the all above factors. Although there are refrigeration systems available in the foreign market, the cost and compatibility of such systems to local requirement are questionable. A system that satisfies required refrigeration capacity for a 40 ft boat costs about 1.5 million rupees. Intention of this research is to investigate the economical feasibility of designing and construction of suitable refrigeration system to overcome the above problem.