• Journal of Mechanical Science and Technology
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• 제19권9호
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• pp.1821-1832
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• 2005

This study realizes the conceptual method to predict combustion instability in actual full-scale combustion chamber of rocket engines by experimental tests with model (sub-scale) chamber. The model chamber was designed based on the methodologies proposed in the previous work regarding geometrical dimensions and operating conditions, and hot-fire test procedures were followed to obtain stability boundaries. From the experimental tests, two instability regions are presented by the parameters of combustion-chamber pressure and mixture (oxidizer/fuel) ratio, which are customary for combustor designers. It is found that instability characteristics in the chamber with the adopted jet injectors can be explained by the correlation between the characteristic burning or mixing time and the characteristic acoustic time: In each instability region, dynamic behaviors of flames are investigated to verify the hydrodynamically-derived characteristic lengths of the jet injectors. Large-amplitude pressure oscillation observed in upper instability region is found to be generated by lifted-off flames.

• 대한기계학회논문집B
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• 제25권6호
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• pp.829-836
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• 2001

A dependable boundary reconstruction technique is proposed. The finite element method is used for the analysis of the direct heat conduction problem to realize the deformable grid system. An appropriate strategy for grid update is suggested. A complete sensitivity analysis is performed to obtain the derivatives required for restoration of the optimal boundary. With the result of the sensitivity analysis, the unknown boundary is sought using the sequential quadratic programming. The method is applied to reconstruction of boundaries with sinusoidal, step, and cavity form. The overall performance of the proposed method is examined by comparison between the estimated the exact boundaries.

• 대한기계학회논문집A
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• 제30권6호
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• pp.705-712
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• 2006

A finite element method based on the penalized subdomain-interface framework is proposed for fully-coupled, nonlinear thermomechanical analyses with thermal contact anuor radiation boundaries. In the variational formulation, a well-known penalty functional scheme is adopted for connecting subdomains and interfaces that satisfy various continuity requirements. As a logical consequence, the whole domain can be arbitrarily divided into independently-modeled subdomains without considering the conformity of meshes along their interfaces. Since the nonlinearities due to the contact and radiation boundaries can be localized within a few subdomains, the computational efficiency of the present method is greatly increased with appropriate solution algorithms. By solving some numerical problems, these advantageous features are confirmed carefully.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2007년도 한국음성과학회 공동학술대회 발표논문집
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• pp.114-118
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• 2007

The current study investigates the degree to which various prosodic cues at the boundaries of a prosodic phrase in Korean (Accentual Phrase) contributed to word segmentation. Since most phonological words in Korean are produced as one AP, it was hypothesized that the detection of acoustic cues at AP boundaries would facilitate word segmentation. The prosodic characteristics of Korean APs include initial strengthening at the beginning of the phrase and pitch rise and final lengthening at the end. A perception experiment revealed that the cues that conform to the above-mentioned prosodic characteristics of Korean facilitated listeners' word segmentation. Results also showed that duration and amplitude cues were more helpful in segmentation than pitch. Further, the results showed that a pitch cue that did not conform to the Korean AP interfered with segmentation.

• 한국음향학회:학술대회논문집
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• 한국음향학회 1998년도 제15회 음성통신 및 신호처리 워크샵(KSCSP 98 15권1호)
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• pp.87-92
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• 1998

In general, the synthesis unit database was constructed by recording isolated word. In that case, each boundary of word has typical prosodic pattern like a falling intonation or preboundary lengthening. To get natural synthetic speech using these kinds of database, we must artificially distort original speech. However, that artificial process rather resulted in unnatural, unintelligible synthetic speech due to the excessive prosodic modification on speech signal. To overcome these problems, we gathered thousands of sentences for synthesis database. To make a phone level synthesis unit, we trained speech recognizer with the recorded speech, and then segmented phone boundaries automatically. In addition, we used laryngo graph for the epoch detection. From the automatically generated synthesis database, we chose the best phone and directly concatenated it without any prosody processing. To select the best phone among multiple phone candidates, we used prosodic information such as break strength of word boundaries, phonetic contexts, cepstrum, pitch, energy, and phone duration. From the pilot test, we obtained some positive results.

• 한국해양공학회지
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• 제24권2호
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• pp.53-56
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• 2010

Oil spills and red tide can be very damaging to the environment and fishery farming. These catastrophic accidents must be detected as quickly as possible. In this paper, we report the results of applying the wavelet transform to SAR or marine radar images for the detection of the boundaries of an oil spill or red tide. The application of the wavelet transform to these phenomena looks quite promising in detecting the boundaries of oil spills and red tide areas.

• 한국항해항만학회지
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• 제30권2호
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• pp.145-150
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• 2006

Recently we have seen a noticeable trend in ports to establish port clusters. Despite this trend, little research has actually been undertaken to fully define and analyse port clusters. A couple of exceptions have descriptively defined port clusters but the boundaries of port clusters are not apparent. Therefore, the aim of this paper is to define port clusters in terms of set theory and in particular look at them in terms of their distinct characteristics and system boundaries. The main concern of this paper is that there is a need to distinguish, from a system and a competition perspective, between port clusters, ports, maritime clusters and port ranges. This paper proposes a conceptual model relevant to the relationship among port clusters related assemblages and that has been applied to the north western europe region This model suggests six levels of competition that will help port authorities and government to develop appropriate policies and strategies for port operation and port industry.

• 물과 미래
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• 제20권3호
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• pp.219-228
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• 1987

만내 및 입구부에 대한 흐름해석으로 천수방정식이 이용되었으며, 개방경계의 위치를 변화시키며 해석하였다. 만입구로부터의 거리를 변화시키며 설정된 반도형태의 개방경계에 대한 수치해석결과 적절한 개방경계의 위치는 만입구의 폭을 2B라 했을 때 이에 대한 관계로 표현할 수 있고 3B 이상인 경우에서 해는 안정한 상태로 되어 최적의 개방경계위치는 3B가 적절할 것으로 판단되었다. 천수방정식에 대한 수치기법으로는 전형적인 Galerkin 방법에 의한 유한요소법이 적용되었다.

• 말소리와 음성과학
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• 제2권1호
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• pp.87-95
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• 2010

In this paper, we address issues associated with mixed-lingual text-to-speech based on context-dependent HMMs, where there are multiple sets of HMMs corresponding to each individual language. In particular, we propose smoothing techniques of synthesis parameters at the boundaries between different languages to obtain more natural quality of speech. In other words, mel-frequency cepstral coefficients (MFCCs) at the language boundaries are smoothed by applying several linear and nonlinear approximation techniques. It is shown from an informal listening test that synthesized speech smoothed by a modified version of linear least square approximation (MLLSA) and a quadratic interpolation (QI) method is preferred than that without using any smoothing technique.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.386-386
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• 2000

Cell mapping is a powerful computational technique for analyzing the global behavior of nonlinear dynamic systems. It simplifies the task of analyzing a continuous phase space by partitioning it into a finite number of disjoint cells and approximating system trajectories as cell transitions. A cell map for the system is then constructed based on the allowable control actions. Next search algorithms are employed to identify the optimal or near-optimal sequence(s) of control actions required to drive the system from each cell to the target cell by an "unravelling algorithm." Errors resulting from the cell center-point approximation could be reduced and eliminated by fuzzifying the bonders of cells. The dynamic system control method based on the cell mapping has been demonstrated for a motor control problem.l problem.