• Ocean Systems Engineering
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• v.7 no.4
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• pp.371-398
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• 2017

Calm water wave resistance plays a very important role in ship hull design. Numerical methods are meaningful for this reason. In this study, two prevailing methods, the Neumann-Kelvin and the Rankine source method, were implemented and compared. The Neumann-Kelvin method assumes linearized free surface boundary condition and only needs to mesh the hull surface. The Rankine source method considers nonlinear free surface boundary condition and meshes both the ship hull surface and free surface. Both methods were implemented and the wave resistance of a Wigley III and three Series 60(Cb=0.6, 0.7, 0.8) hulls were analyzed. The results were compared with experimental results and the merits of both numerical techniques were quantified. Based on the results, it is concluded that the Rankine source method is more accurate in the calculation of the wave-making resistance. Using the Neumann-Kelvin method, it is found to be easier to model the hull and can be used for slender ships to solve problems like wave current coupling calculation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.70-81
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• 2019

An improved three dimensional Rankine source method is developed to solve numerically water wave problems in time domain. The free surface and body surface are both represented by continuous panels rather than a discretization by isolated points. The integral of Rankine source 1/r on free surface panel is calculated analytically instead of numerical approximation. Due to the exact algorithm of Rankine source integral applied on the free surface and body surface, a space increment free surface source distribution method is developed and much smaller amount of source panels are required to cover the fluid domain surface than other numerical approximation methods. The proposed method shows a higher accuracy and efficiency compared to other numerical methods for various water wave problems.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.4
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• pp.363-371
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• 2020

Recently, the technologies to utilize the cold energy of liquefied natural gas (LNG) have attracted significant attention. In this paper, thermodynamic performance analysis of combined cycles consisting of ammonia Rankine cycle (AWR) and organic Rankine cycle (ORC) with LNG Rankine cycle to recover low-grade heat source and the cold energy of LNG. The mathematical models are developed and the effects of the important system parameters such as turbine inlet pressure, ammonia mass fraction, working fluid on the system performance are systematically investigated. The results show that the thermal efficiency of AWR-LNG cycle is higher but the total power production of ORC-LNG cycle is higher.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.1
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• pp.65-72
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• 2012

Rankine cycle using ammonia-water mixture as a working fluid has attracted much attention, since it may be a very useful device to extract power from low-temperature heat source. In this work, the thermodynamic performance of regenerative ammonia-water Rankine cycle is thoroughly investigated based on the second law of thermodynamics and exergy analysis, when the energy source is low-temperature heat source in the form of sensible energy. In analyzing the power cycle, several key system parameters such as ammonia mass concentration in the mixture and turbine inlet pressure are studied to examine their effects on the system performance including exergy destructions or anergies of system components, efficiencies based on the first and second laws of thermodynamics. The results show that as the ammonia concentration increases, exergy exhaust increases but exergy destruction at the heat exchanger increases. The second-law efficiency has an optimum value with respect to the ammonia concentration.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.2
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• pp.148-154
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• 2018

This paper presents a comparative analysis of thermodynamic performance of ammonia-water Rankine cycles with and without regeneration and Kalina cycle for recovery of low-temperature heat source. Special attention is paid to the effect of system parameters such as ammonia mass fraction and turbine inlet pressure on the characteristics of the system. Results show that maximum net power can be obtained in the regenerative Rankine cycle for high turbine inlet pressures. However, Kalina cycle shows better net power and thermal efficiency for low turbine inlet pressures, and the optimum ammonia mass fractions of Kalina cycle are lower than Rankine cycles.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.4
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• pp.225-232
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• 2011

In the present study, a new hull panel generation algorithm, namely panel cutting method, was developed to predict flow phenomena around a ship using the Rankine source potential based panel method, where the iterative method was used to satisfy the nonlinear free surface condition and the trim and sinkage of the ship was taken into account. Numerical computations were performed to investigate the validity of the proposed hull panel generation algorithm for Series 60 ($C_B$=0.60) hull and KRISO container ship (KCS), a container ship designed by Maritime and Ocean Engineering Research Institute (MOERI). The computational results were validated by comparing with the existing experimental data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.3
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• pp.223-230
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• 2011

The power cycle using ammonia-water mixture as a working fluid is a possible way to improve efficiency of the system of low-temperature source. In this work thermodynamic performance of the ammonia-water regenerative Rankine cycle with partial-boiling flow is analyzed for purpose of extracting maximum power from the source. Effects of the system parameters such as mass fraction of ammonia, turbine inlet pressure or ratio of partial-boiling flow on the system are parametrically investigated. Results show that the power output increases with the mass fraction of ammonia but has a maximum value with respect to the turbine inlet pressure, and is able to reach 22 kW per unit mass flow rate of source air at $180^{\circ}C$.

• Bulletin of the Society of Naval Architects of Korea
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• v.19 no.2
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• pp.13-18
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• 1982

The method of Rankine source distribution is emerging as a powerful yet simple alternative for the solution of complicated free surface problems. But it has been uncertain whether the radiation condition could be satisfied exactly by distributing the simple sources on the free surface only. In this paper, it is proved rigorously that the Rankine sources, whose intensities are varying sinusoidally along the axis satisfying the free surface boundary condition, generate the radiation waves both in the infinite and finite-depth flows. A formula is derived to give the upper and lower bounds of the errors in the induced velocity computation that will be introduced by truncating the extent of source distribution on the free surface. Since the truncation is inevitable in the numerical analysis, this formula may be used as a criterion to limit the position of the field points, where velocity computation is made, away from the truncation boundary. A typical analysis shows that the maximum error will be 3.4 percent of the exact induced velocity when the field point is on the free surface two wave lengths away from the truncation boundary.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.12-21
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• 2014

An organic Rankine cycle was analyzed to work at the optimal operating point when the heat source is fluctuated. R245fa was adopted as a working fluid, and an axial-type turbine as expander on the cycle was designed to convert the heat energy to the electricity since the turbo-type expander works at off-design points better than the positive displacement-type expander. A supersonic nozzle was designed to increase the spouting velocity because a higher spouting velocity can produce more output power. They were designed by the method of characteristics for the operating fluid of R245fa. Three different cases, such as various spouting velocities, various inlet total temperatures, and various nozzle numbers, were studied. From these results, an optimal operating cycle can be designed with the organic Rankine cycle when the available heat source as renewable energy is low-grade temperature and fluctuated.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.5
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• pp.597-603
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• 2016

In this paper a comparative thermodynamics analysis is carried out for organic Rankine cycle (ORC) and ammonia-water Rankine cycle (AWRC) utilizing low-grade heat sources. Effects of the working fluid, ammonia concentration, and turbine inlet pressure are systematically investigated on the system performance such as mass flow rate, pressure ratio, turbine-exit volume flow, and net power production as well as the thermal efficiency. Results show that ORC with a proper working fluid shows higher thermal efficiency than AWRC, however, AWRC shows lower mass flow rate of working fluid and lower pressure ratio of expander than ORC.