모델 로켓 연소기에서의 국부 화염묘사함수에 대한 실험적 분석

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2019. 2. 윤영빈.액체 로켓 엔진 개발에 있어 다단 연소 사이클 방식으로의 전환이 이루어지고 있으며, 그 중에서도 전 유량 다단 연소 사이클은 긴 엔진 수명과 보다 높은 신뢰성을 가지고 있기에 차세대 로켓 엔진에 적합하다고 할 수 있다. 이러한 엔진 개발에 있어 연소불안정 현상은 연소 효율 저감과 연소실의 파괴로 이어질 수 있기 때문에 이를 예방하기 위한 연구가 필수적이다. 본 연구의 목적은 로켓 연소와 같이 화염이 길이 방향으로 길 경우에는 공간적인 분석이 중요하다는 것을 인지하고, 기존의 화염전달함수와 화염묘사함수에 대하여 화염의 자발광 이미지를 이용하여 국부적으로 구하여 보는 것이다. 또한 이렇게 구해진 국부 화염전달함수와 화염묘사함수에 대하여 실험적인 접근 방법으로 해석해보려는 시도를 하였다. 그 결과, 화염의 열 방출량 섭동은 화염의 끝 부분으로 갈수록 증가하였고, 이는 국부 화염전달함수와 화염묘사함수의 gain에 영향을 미쳤다. 이는 유동과 화염의 상호작용에 의하여 발생한 현상이라고 밝힐 수 있었다. 또한, 국부 화염묘사함수 계측을 통하여 화염의 끝 부분으로 갈수록 화염의 비선형적 응답특성이 강해지는 것을 알 수 있었고, 국부 화염묘사함수의 gain 특성은 화염의 특성 길이와 연관이 있다는 것을 확인하였다. 이러한 결과들을 바탕으로 로켓 화염과 같이 길이 방향으로 긴 화염의 경우에는 연소불안정을 예측하기 위해 사용되는 화염전달함수 및 화염묘사함수를 국부적으로 구하여 이를 이용하는 것이 화염의 반응을 더 잘 반영할 수 있다고 할 수 있다.In the development of liquid rocket engines, the transition to staged combustion cycle is being made. Among them, full-flow staged combustion cycle (FFSCC) is suitable for next generation of the rocket engines because it has longer engine life and higher reliability. Combustion instability phenomenon, which is considered a main obstacle in development of rocket engines, can lead to reduction of combustion efficiency and destruction of the combustion chamber in severe cases. Therefore, research to prevent such consequence is essential. The purpose of this research is to recognize that spatial analysis is important when the length of the flame is long, such as rocket combustion. So instead of formerly used global flame transfer function (FTF) and flame describing function (FDF), in this study, locally distributed FTF and FDF were measured using OH* chemiluminescence images and attempted to interpret the obtained functions in an experimental approach. As a result, the perturbation of the heat release rate increased towards the flame tip, which affected the gain of local FTF and FDF. This could be explained by the interaction between flow and flame. Moreover, it was found that the nonlinear response of the flame became stronger towards the flame tip through the measurement of local FDF. It was confirmed that the gain tendency of the local FDF was related to the characteristic length of the flame. Based on these results, it can be said that spatially obtained FTF and FDF may better reflect the flame response while used to predict combustion instability, when the flame is long as rocket flame.CONTENTS ABSTRACT i CONTENTS iii LIST OF FIGURES v LIST OF TABLES ix NOMENCLATURE x CHAPTER 1 INTRODUCTION 1 1.1. Full-Flow Staged Combustion Cycle 1 1.2. Combustion Instability 3 1.3. Research Objectives 5 CHAPTER 2 EXPERIMENTAL APPARATUS AND METHOD 6 2.1. Experimental Apparatus and Method 6 2.2. Experimental Conditions 12 CHAPTER 3 RESULTS AND DISCUSSIONS 15 3.1. Global Flame Describing Function 15 3.2. Local Flame Transfer Function 22 3.2.1. Local Heat Release Rate 22 3.2.2. Local Flame Transfer Function Results 24 3.2.3. Effect of Flow Field 29 3.3. Local Flame Describing Function 32 3.3.1. Local Flame Describing Function Results 32 3.3.2. Effect of Flame Length 38 CHAPTER 4 CONCLUSION 41 REFERENCES 42 ABSTRACT IN KOREAN 45Maste

Subdivisional Pathologies in Peripheral Vestibular Disorders

ope

Auricular Reconstruction in Microtia Patients: A Single Institution Experience

Background and Objectives Microtia is a congenital deformity where the pinna and middle ear structures are underdeveloped. Auricular reconstruction in microtia is one of the most difficult surgeries in otolaryngology due to the complex three-dimensional structure of the auricle. This study investigated the post-operative results in total auricular reconstruction performed by otologic surgeons in a single institution. Subjects and Method We analyzed data from 27 microtia patients who underwent auricular reconstruction in our institution from 2011 to 2019. The post-operative results were evaluated in terms of the shape of the auricle, the symmetry of the ear, and the degree of auriculocephalic sulcus stricture. The type and frequency of post-operative complications associated with the reconstruction were also evaluated. Results Of the 24 patients, the shape of the auricle was good in 11 (40.7%), moderate in 11 (40.7%), and poor in 5 (18.6%) patients. The symmetry of the ear size was symmetric in 24 (88.9%) and asymmetric in 3 (11.1%) patients. The degree of auriculocephalic sulcus stricture was good in 11 (40.7%), partial stricture in 12 (44.4%), and severe stricture in 4 (14.8%) patients. Postoperative complications included skin necrosis, suture material exposure, and wound infection with cartilage deformation. Conclusion Total auricular reconstruction is a complex and sophisticated operation utilizing either autologous rib cartilage or artificial implant material. Considering that microtia is often accompanied by ear canal stenosis and hearing impairment, otolaryngologists should be more interested in the field of auricular reconstruction.ope

Surgical outcomes of tympanoplasty using a sterile acellular dermal allograft: a prospective randomised controlled study

Acellular human dermal allografts have been shown to be effective for soft-tissue implantation. We compared treatment outcomes of tympanoplasty using tragal perichondrium and acellular human dermal allograft (MegaDerm®). In a prospective randomised controlled study, 60 patients scheduled to undergo tympanoplasty were randomly assigned to the autologous tragal perichondrium group (n = 33) or acellular human dermal allograft group (n = 27). Postoperative hearing gain, graft success rate at 1 and 6 months and operation times were compared between groups. Graft success rate, defined as the complete closure of tympanic membrane perforation, did not show any significant intergroup difference (75.8% vs 85.2%, p = 0.519). Air conduction thresholds and air-bone gaps showed significant improvements in both groups; from 38.7 ± 15.9 dB to 30.2 ± 15.6 dB (p < 0.001) and from 17.8 ± 7.3 dB to 11.5 ± 7.0 (p = 0.001) in the autologous tragal perichondrium group, and from 30.4 ± 12.2 dB to 24.5 ± 13.0 dB (p = 0.006) and from 14.3 ± 5.1 dB to 7.6 ± 4.6 dB (p < 0.001) in the acellular human dermal allograft group. The amount of hearing gain (p = 0.31) and closure of air-bone gap (p = 0.863) were not meaningfully different between groups. The mean operation time was significantly lower in the acellular human dermal allograft group (35.2 min vs 27.4 min, p = 0.039). In this prospective randomised controlled study, acellular human dermal allograft was shown to be an effective alternative to tragal perichondrium, with similar graft success rates and postoperative hearing results, but with reduced operation times.ope

Molecular architecture underlying fluid absorption by the developing inner ear

Mutations of SLC26A4 are a common cause of hearing loss associated with enlargement of the endolymphatic sac (EES). Slc26a4 expression in the developing mouse endolymphatic sac is required for acquisition of normal inner ear structure and function. Here, we show that the mouse endolymphatic sac absorbs fluid in an SLC26A4-dependent fashion. Fluid absorption was sensitive to ouabain and gadolinium but insensitive to benzamil, bafilomycin and S3226. Single-cell RNA-seq analysis of pre- and postnatal endolymphatic sacs demonstrates two types of differentiated cells. Early ribosome-rich cells (RRCs) have a transcriptomic signature suggesting expression and secretion of extracellular proteins, while mature RRCs express genes implicated in innate immunity. The transcriptomic signature of mitochondria-rich cells (MRCs) indicates that they mediate vectorial ion transport. We propose a molecular mechanism for resorption of NaCl by MRCs during development, and conclude that disruption of this mechanism is the root cause of hearing loss associated with EES.ope

Saccular Pathology Is Most Commonly Found in Patients With General Vestibular Disorders

Objectives: The first purpose of this study was to investigate the difference in the frequency of involvement of the superior vestibular nerve (SVN) and inferior vestibular nerve (IVN) territories in general vestibular disorders, and to identify which IVN territory was more commonly involved in patients with IVN lesions. The second purpose was to investigate the correlation of the degree of each saccular and posterior semicircular canal (PSCC) dysfunction, as represented by the parameters of cervical vestibular evoked myogenic potential (cVEMP) and video head impulse test (vHIT), in patients with pathology of the IVN territory. Methods: In total, 346 patients with dizziness who underwent the caloric test, cVEMP, and vHIT were enrolled. Canal weakness in the caloric test, interaural amplitude difference (IAD) of cVEMP, and vestibulo-ocular reflex gain of the vestibulo-ocular reflex gain of the posterior semicircular canal (p-VOR) in vHIT were analyzed. Results: Among the enrolled patients, 15.6% had total vestibular nerve dysfunction, 14.5% had solely SVN dysfunction, and 29.5% had solely IVN dysfunction. Isolated saccular pathology was most common in patients with IVN pathology, followed by those with total IVN dysfunction and PSCC dysfunction. IAD and p-VOR were statistically well correlated, and the correlation was strongest in patients with both pathologic IAD and pathologic p-VOR (n=23, r=0.944), followed by patients with normal IAD and pathologic p-VOR (n=27, r=0.762) and patients with pathologic IAD and normal p-VOR (n=106, r=0.339). Conclusion: Abnormal results were more common in vestibular tests investigating the IVN than in vestibular tests investigating the SVN in patients with general vestibular disorders. Isolated saccular pathology was more frequent than PSCC or combined pathology in patients with IVN dysfunction. Patients with abnormal p-VOR in vHIT had a higher probability of having both saccular and PSCC pathologies than patients with an abnormal IAD. This study describes the characteristics of vestibular-system subregions and provides guidance for clinically interpreting the combination of cVEMP and vHIT results.ope

A Case of Isolated Congenital Stapedial Suprastructure Fixation

We report a case of conductive hearing loss caused by isolated congenital stapedial suprastructure fixation with normal footplate mobility. A 60-year-old woman visited the clinic for right-sided mixed hearing loss. Exploratory tympanotomy revealed a bony synostosis between the stapedial suprastructure and promontory, while all the ossicles were present and normally shaped. As the bony synostosis was separated, the stapes became mobile. This is the first report in the medical literature of this congenital ear anomaly. This case also illustrates that stapedial fixation can occur in the suprastructure as well as in the footplate; thus, one must be mindful of this when performing exploratory tympanotomy for stapes fixation.ope

Regulation of sodium transport in the inner ear

Na(+) concentrations in endolymph must be controlled to maintain hair cell function since the transduction channels of hair cells are cation-permeable, but not K(+)-selective. Flooding or fluctuations of the hair cell cytosol with Na(+) would be expected to lead to cellular dysfunction, hearing loss and vertigo. This review briefly describes cellular mechanisms known to be responsible for Na(+) homeostasis in each compartment of the inner ear, including the cochlea, saccule, semicircular canals and endolymphatic sac. The influx of Na(+) into endolymph of each of the organs is likely via passive diffusion, but these pathways have not yet been identified or characterized. Na(+) absorption is controlled by gate-keeper channels in the apical (endolymphatic) membrane of the transporting cells. Highly Na(+)-selective epithelial sodium channels (ENaCs) control absorption by Reissner's membrane, saccular extramacular epithelium, semicircular canal duct epithelium and endolymphatic sac. ENaC activity is controlled by a number of signal pathways, but most notably by genomic regulation of channel numbers in the membrane via glucocorticoid signaling. Non-selective cation channels in the apical membrane of outer sulcus epithelial cells and vestibular transitional cells mediate Na(+) and parasensory K(+) absorption. The K(+)-mediated transduction current in hair cells is also accompanied by a Na(+) flux since the transduction channels are non-selective cation channels. Cation absorption by all of these cells is regulated by extracellular ATP via apical non-selective cation channels (P2X receptors). The heterogeneous population of epithelial cells in the endolymphatic sac is thought to have multiple absorptive pathways for Na(+) with regulatory pathways that include glucocorticoids and purinergic agonists.ope

Surgical and Audiologic Comparison Between Sophono and Bone-Anchored Hearing Aids Implantation

OBJECTIVES: Bone-anchored hearing aids (BAHA) occasionally cause soft tissue problems due to abutment. Because Sophono does not have abutment penetrating skin, it is thought that Sophono has no soft tissue problem relating to abutment. On the other hand, transcutaneous device's output is reported to be 10 to 15 dB lower than percutaneous device. Therefore, in this study, Sophono and BAHA were compared to each other from surgical and audiological points of view. METHODS: We retrospectively reviewed the medical records of 9 Sophono patients and 10 BAHA patients. In BAHA cases, single vertical incision without skin thinning technique was done. We compared Sophono to BAHA by operation time, wound healing time, postoperative complications, postoperative hearing gain after switch on, and postoperative air-bone gap. RESULTS: The mean operation time was 60 minutes for Sophono and 25 minutes for BAHA. The wound healing time was 14 days for Sophono and 28 days for BAHA. No major intraoperative complication was observed. Skin problem was not observed in the 2 devices for the follow-up period. Postoperative hearing gain of bilateral aural atresia patients was 39.4 dB for BAHA (n=4) and 25.5 dB for Sophono (n=5). However, the difference was not statistically significant. In all patients included in this study, the difference of air-bone gap between two groups was 16.6 dB at 0.5 kHz and 18.2 dB at 4 kHz. BAHA was statistically significantly better than Sophono. CONCLUSION: Considering the audiologic outcome, BAHA users were thought to have more audiologic benefit than Sophono users. However, Sophono had advantages over BAHA with abutment in cosmetic outcome. Sophono needed no daily skin maintenance and soft tissue complication due to abutment would not happen in Sophono. Therefore, a full explanation about each device is necessary before deciding implantation.ope

A Case of Central Origin Vertigo in Breast Cancer with Brain Metastasis

The incidence of symptomatic brain metastasis among women with breast cancer ranges from 10 to 16%. A metastatic spread of breast cancer to either the brain parenchyma or the leptomeninges is generally a late feature of metastatic progression. The present case of a 55-year-old patient had been considered cured from breast cancer. However, she recently complained of severe dizziness, hearing impairment, and headache. Initially, it was considered to be Meniere’s disease or vestibular migraine, although later dizziness, hearing impairment, and headache were aggravated in spite of medication. Pure tone audiometry showed left-sided sensorineural hearing loss, but her vestibular function was within normal range. She underwent a Gadolinium-enhanced magnetic resonance imaging, and a metastatic brain lesion was noted. With a review of the literature, we present this case of breast cancer with brain metastasis in a 55-year-old woman with vertigo and hearing loss.ope