• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.1-14
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• 1996

Especially in the case of a full form ship, the stability on course can be considered to become severest among 4 items of criteria in Interim Standards for Ship Maneuverability adopted by IMO in 1993. The purpose of this study is to find some ideas for the improvement of stability on course through changes in rudder area with reference to span distance. In this paper, we established the formula on the relation between the experimental constants relevant to rudder normal force and hydrodynamic derivatives of hull-propeller-rudder system. We carried out various kinds of captive model test relevant to rudder normal force etc., and evaluated hydrodynamic derivatives of hull-propeller-rudder system, and analyzed the stability on course with the parameter of changes in rudder area. Furthermore, we also discussed effects of changes in rudder area on maneuvering performance including stability on course, based on computer simulation. As a result, it is clarified that there is a possibility that stability on course may become bad through an increase of rudder area. The reason for the bad stability on course is that the void space between the upper edge of rudder and the lower part of stern overhang decreases. This space change exerts a great influence on straightening coefficient of incoming flow to rudder in maneuvering motion, which has close relation to stability on course.

• The Transactions of the Korea Information Processing Society
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• v.4 no.7
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• pp.1804-1820
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• 1997

In this paper, an efficient call control procedure is presented for next generation wireless ATM networks and its performance is mathematically analyzed using the open queueing network. This procedure is based on a new scheme called as the cell clustering. When we use the cell clustering scheme, at the time that a mobile connection is admitted to the network, a virtual cell is constructed by choosing a group of neighboring base stations to which the call may probabilistically hand over and by assigning to the call a collection of virtual paths between the base stations. Within a microcell/picocell environment, it is seen that the cell clustering can support effectively a very high rate of handovers, provides very high system capacity, and guarantees a high degree of frequency reuse over the same geographical region without requiring the intervention of the network call control processor each time a handover occurs. But since mobiles, once admitted, are free to roam within the virtual cell, overload condition occurs in which the number of calls to be handled by one base station to exceed that cell site's capacity of radio channel. When an overload condition happens, the quality of service is abruptly degraded. We refer to this as the overload state and in order to quantify the degree of degradation we define two metrics, the probability of overload and the normalized average time spent in the overload state. By using the open network queueing model, we derive closed form expressions for the maximum number of calls that can be admitted into the virtual cell such that the two defined metrics are used as the acceptance criteria for call admission control.

• The Journal of the Korea Contents Association
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• v.9 no.4
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• pp.81-94
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• 2009

In ubiquitous environments, the real-time features are necessary to insure the QoS of the intelligent service robots. In this paper, we design and implement a real-time framework for intelligent service robots to support real-time features. The real-time framework to support real-time scheduling services is implemented on the general operating systems. We solve the problem that the scheduler of a general operating system can not support real-time features. This paper also proposes realtime scheduling services to guarantee the QoS of real-time robot applications. We implemented the proposed real-time framework on the Windows operating system and conducted some performance experiments. The experimental results show that the proposed real-time framework can improve thread response times and it has slight performance overhead of $62{\mu}s$.

• The Journal of the Korea Contents Association
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• v.7 no.1
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• pp.73-82
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• 2007

In recent years, embedded systems have been expanding their application domains from traditional applications (such as defense, robots, and artificial satellites) to portable devices which execute more complicated applications such as cellular phones, digital camcoders, PMPs, and MP3 players. So as to manage restricted hardware resources efficiently and to guarantee both temporal and logical correctness, every embedded system use a real-time operating system (RTOS). Only when the RTOS makes kernel services deterministic in time by specifying how long each service call will take to execute, application programers can write predictable applications. Moreover, so as for an RTOS to be deterministic, its scheduling and context switch overhead should also be predictable. In this paper, we present the complete generalized algorithm to determine the highest priority in the ready list with 22r levels of priorities in a constant time without additional memory overhead.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.6
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• pp.1269-1275
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• 2003

This paper addresses several issues on data caching and consistency of cached data in order to process client's queries efficiently in client/server environments. For the purpose, first of all, materialized spatial views are adapted in a client side for data caching, which is called client views. Also, an incremental update scheme using derivation relationships is applied to keep cached data of clients consistent with the rest of server databases. Materialized views support efficient query processing in a client side, however, it is difficult to keep consistent their contents by the update of a server database. In this paper, we devise cost functions on query execution and view maintenance based the cost of spatial operators so as to process client's queries efficiently. When request the client's query, in our query processing scheme, the server determines whether or not materialize it as a view due to evaluation using the related cost functions. Since the scheme supports a hybrid approach based on both view materialization and re-execution, hence, it should improve query execution times in client/server environments.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.1
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• pp.88-100
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• 1990

Since sea state changes engine load instantaneously, the speed governing apparatus is essential for marine engine to maintain constant speed regardless of the load. As governing apparatuses, mechanical, pneumatic, and electric governors have been employed. But, recently, according to the introduction of low speed-ling stroke engines to increase thermal efficiency, the development of governor which has better response characteristics is requisite. In this paper, to design the governor that meets above requirement, author made a performance test for the existing PID control digital governor with the aid of computer simulation, and investigated digital governor applying the optimal control algorithm, then, executed computer simulation by the same way. As the result of simulations, found that the former let engine have large overshoot and long settling time at low speed, on the other hand, the latter made engine have better response. If we design and invent a good observer for delay time element so that the optimal control theory can be applied, better governor will be expected.

• The Journal of the Korea Contents Association
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• v.10 no.1
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• pp.94-102
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• 2010

In recent years, embedded systems such as cellular phones, Portable Multimedia Player, intelligent appliance, automobile engine control are reshaping the way people live, work, and play. Thereby, services application to guarantee various requirements of users become increasingly sophisticated and complicated, such embedded computing platforms use real-time operating systems (RTOSs) with time determinism. These RTOSs must not only provide predictable services but must also be efficient and small in size. Kernel services should also be deterministic by specifying how long each service call will take to execute. Having this information allows the application designers to better plan their real-time application software so as not to miss the deadline of each task. In this paper, we present the complete generalized real-time scheduling algorithm using multi-dimensional methodology to determine the highest priority in the ready list with 2r levels of priorities in a constant time without additional memory overhead.

• The Journal of the Korea Contents Association
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• v.7 no.8
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• pp.31-40
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• 2007

Recently, Embedded systems are different with the past as loading of a simple application program that executed specific functions according to the use and are evolved in the digital convergence integrated multimedia functions and then the complication of the application program is remarkably increased. This application program is combined and evolved with many application program in accordance with the demand of the age. For develope and manage this developing application is necessary standardized interface between developer and manager. POSIX was developed as the standard of the operating system in the standard interface which has the open system structure in computing system, and there is a posix.4 to standard for the system demands the loading of real-time operating system like a digital convergence devices. In this paper, we present the contents of designing and implementing the real-time operating system UbiFOSTM to wrapper for supporting the POSIX.4. Also, Experimental results show that implemented wrapper to application program standardizing POSIX.4 in linux and UbiFOSTM is slight only $3{\sim}9{\mu}s$.

• The Korean Journal of Air & Space Law and Policy
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• v.31 no.1
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• pp.99-144
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• 2016

The summary of the case is as follows: a Korean passenger booked and purchased a business class ticket from Air France that was scheduled to depart from Paris and arrive in Seoul. When the passenger arrived at the check-in counter, he was told that all business class seats were occupied. It was because the flight was overbooked by Air France. The passenger cancelled the Air France flight and took another air carrier. After arriving in Korea, he brought suit against Air France for damages. The purpose of this article is to discuss the governing law when interpreting the contract of international air carriage in accordance with the Korean Private International Act (2001) and to analyze air carrier's civil liability for the bumped passenger in the overbooking case. If the parties have not chosen the applicable law the contract shall be governed by the law of the habitual residence of the consumer in the following situations: prior to the conclusion of the contract, the opposite party of the consumer conducted solicitation of transactions and other occupational or business activities by an advertisement in that country or conducted solicitation of transactions and other occupational or business activities by an advertisement into that country from the areas outside that country and the consumer took all the steps necessary for the conclusion of the contract in that country or in case the opposite party of the consumer received an order of the consumer in that country [Article 27 (1), (2) of the Private International Act]. Since the contract of international carriage falls into the consumer contract, the Supreme Court viewed that the governing law of the contract in this case would be the law of the habitual residence of the consumer (Supreme Court Decision 2013Da8410 decided on Aug. 28, 2014). This interpretation differs from the article 5 (4) of Rome Convention(80/934/EEC) which declares that the consumer contract article shall not apply to neither a contract of carriage nor a contract for the supply of services where the services are to be supplied to the consumer exclusively in a country other than that in which he has his habitual residence. Even though overbooking can be considered as a common industry practice, an air carrier must burden civil liability in case of breach of contract for the involuntary bumped passenger(Seoul Central District Court Decision 2014Na48391 decided on Jan. 29, 2015). In case of involuntary bumping, an air carrier must offer re-routing to passenger's final destination by an alternative flight. If an air carrier fails to effect performance in accordance with the tenor and purport of the obligation, the involuntary bumped passenger may claim damages(Article 390 of the Civil Code).