수직 와후류 시스템의 소산 특성에 대한 연구

학위논문(박사)--서울대학교 대학원 :공과대학 기계항공공학부,2020. 2. 이관중.The wake vortices of an aircraft descend by self-induction that enables a pilot to identify wake locations. A pilot taking off an aircraft can avoid a wake vortex encounter by performing early rotation and flying at or above the climb path of the preceding aircraft. Such an operation results in a situation, in which two wake vortices are present in the air simultaneously in close proximity. Also, there is a possibility of interactions among vortices where runways are parallel so that a pair of vortices from an aircraft moves to another runway due to crosswind. If the interaction between wake vortex pairs induces a rapid dissipation, it may be possible to adjust the take-off separation time and, therefore, in-crease the airport capacity. In this study, the transport and decay characteristic processes involving interactions between the wake vortex pairs formed by the preceding and following aircraft have been analyzed. The decay processes were ana-lyzed by selecting suitable initial conditions that took into account the high altitude of the following aircraft and the descent of the preceding wake vortices. The high altitude of the following aircraft was included as initial conditions, and atmospheric turbulence conditions were applied to large eddy simulations to account for the vortex core instability and non-linear transport and decay. The obtained results were analyzed to identify the decay characteristic processes that induce the rapid dissipation of the wake vortices and their conditions. The numerical simulation results were analyzed to identify the decay processes that induce the rapid dissipation of wake vortices such as merging into a single counter-rotating pair, rapid dissipation, and formation of a vortex ring with or without a deformation of the lower vortex pair. The third process could be effectively used to adjust the take-off separation time for increasing the capacity at airports.항공기의 와후류는 자기 유도에 의해 하강하는 특징을 가지기 때문에 그 위치를 식별할 수 있다 . 이륙하는 조종사는 선행 항공기의 이륙 지점 앞에서 이륙하고 선행 항공기의 등반 경로 위로 비행하면 와후류 를 피할 수 있다 . 이러한 회피 비행은 두 개의 와후류 가 동시에 근접하여 대기 중에 존재하는 상황 이 발생할 수 있으며 두 쌍 사이의 거리가 충분히 가까운 경우 상호작용이 발생할 것이다 또한 선행 항공기 에서 발생한 와후류 가 인접 활주로로 이동할 경우 에도 와후류 간의 상호작용이 발생할 수 있다. 본 연구는 선행 항공기와 후행 공기에 의해 생성된 서로 다른 wake vortex pair 간의 상호 작용으로 인해 발생하는 이동 및 소산 특성 프로세스를 수치해석으로 분석하였다. 후행 항공기의 높은 고도는 초기 조건으로 고려되었으며, 와후류 의 불안정성과 비선형 수송 및 붕괴를 설명하기 위해 대기 난류 조건이 수치해석 에 적용되었다 . 해석 결과를 분석하여 단일 와후류 쌍으 로의 합병 , 빠른 소산 , vortex ring 의 형성 이후 하부 vortex pair 를 변형하거나 변형없이 각각 소산하는 프로세스를 확인하였다.Chapter 1. Introduction 1 1.1 Airport capacity and wake vortex 1 1.2 Previous study about wake vortex 7 1.3 Outline of Dissertation 13 Chapter 2. Numerical simulations 14 2.1 Large eddy simulation and computational domain 16 2.1.1 Reynolds averaging 18 2.1.2 Favre (mass) averaging 19 2.1.3 Favre- and Reynolds-Averaged Navier-Stokes Equations 20 2.1.4 Spatial filtering 22 2.1.5 Filtered governing equations 23 2.1.6 Subgrid-scale modeling 25 2.1.7 Numerical scheme 27 2.1.8 Computational grid 32 2.2 Background turbulence field 33 2.2.1 Stochastic Noise Generation and Radiation (SNGR) 34 2.2.2 Artificial External Forcing 35 2.3 Wake vortex initialization 39 2.4 Core line identification and calculations of wake vortex parameters 40 2.5 Validation of numerical methods 43 Chapter 3. Time delay wake vortex interaction 48 3.1 Single Pair of Vortices 51 3.2 Interaction Between Two Pairs of Vortices 55 3.2.1 Light medium wake vortices interaction 55 3.2.2 Medium medium wake vortices interaction 59 3.2.1 Medium heavy wake vortices interaction 62 3.3 Summary of the time delay interaction 64 Chapter 4. Vertical Four Vortex System 66 4.1 Definition of a vertical four-vortex system 66 4.2 V4VS numerical simulation cases 68 4.3 Overall temporal evolutions of V4VS 69 4.3.1 Effect of the vertical distance at a large circulation ratio 71 4.3.2 Effect of the vertical distance at the same circulation 73 4.3.3 Effect of the vertical distance at a small circulation ratio 75 4.4 Criteria for switching between different decay processes 77 4.4.1 Non-linear interactions of the co-rotating pair 79 4.4.2 Two decay processes occurring at a high vertical distance 81 4.4.3 Linking of the upper vortex pair 84 4.5 Four decay processes of V4VS 86 4.5.1 Merging the 1st V4VS characteristic decay process 88 4.5.2 Wrapping the 2nd V4VS characteristic decay process 91 4.5.3 Ring deformation the 3rd V4VS characteristic decay process 94 4.5.4 Parallel ring dissipation the 4th V4VS characteristic decay process 97 4.6 Dissipation effects of various V4VS decay processes 100 4.7 V4VS efficiency assessment for increasing airport efficiency 102 Chapter 5. Conclusion 104 References . 107 Appendix A. deterministic wake vortex model (DVM) [17] 113 Appendix B. Vortex parameters raw data for vertical four vortex interaction cases 115 B.1 Hv05Rg10 116 B.2 Hv10Rg10 117 B.3 Hv15Rg10 118 B.4 Hv20Rg10 119 B.5 Hv25Rg10 120 B.6 Hv30Rg10 121 B.7 Hv05Rg15 122 B.8 Hv10Rg15 123 B.9 Hv15Rg15 124 B.10 Hv20Rg15 125 B.11 Hv25Rg15 126 B.12 Hv30Rg15 127 B.13 Hv05Rg07 128 B.14 Hv10Rg07 129 B.15 Hv15Rg07 130 B.16 Hv20Rg07 131 B.17 Hv25Rg07 132 B.18 Hv30Rg07 133 B.19 Single wake vortex pair at Γ0=530m2/s 134 B.20 Single wake vortex pair at Γ0=360m2/s 135 국문초록 136Docto

Usefulness of transparent mask for communication in emergency room

Background: It is important to communicate accurately in the emergency department. Due to COVID-19 pandemic, a mask is mandatory to protect medical staffs and patients from infectious diseases, and the mask is known to disturb speech intelligibility. The objective of this study is to find out if a transparent mask can affect communication. Methods : We conducted a randomized pre- and post-test trial with 40 participants in a real emergency room environment. The reader puts on a mask and read aloud sentences which are frequently used between medical staffs and patients or among medical staffs. The type of mask was randomly assigned to the reader which was transparent or non-transparent. Frequently used 5 sentences between medical staffs and patients and 5 sentences among medical staffs from prepared 100 sentences were randomly selected and recited. Participants were told to write down the sentences they heard. Each sentence written down was graded 0 or 1. After writing down 10 sentences, reader puts on another type of mask and the same experiment was done. The order of transparent/non-transparent mask was randomly allocated to each participant. Results : In frequently used sentences between medical staffs and patient, average score with a transparent mask was 4.88, and with a non-transparent mask was 4.50(p=0.001). In frequently used sentences among medical staffs, average score with a transparent was 4.77, and with a non-transparent mask was 4.05(p<0.001). Conclusions: This study showed the transparent mask improves speech intelligibility when communicating in an emergency room.ope

External validation of STONE score and modified STONE score

Objective: The STONE score and modified STONE score are useful clinical prediction rules for ureteral calculi. This study performed an external validation of the STONE score and modified STONE score. The purpose of this study was to minimize the economic cost and radiation exposure of computed tomography. Method: The electronic medical records of patients complaining of flank pain from January 2016 to December 2017 at a single emergency department were reviewed retrospectively. The patients were classified into three groups according to the STONE score and modified STONE score. The prevalence of urethral calculi and other important alternative diagnoses were calculated in each group. Results: Out of 561 patients, 266 patients were enrolled in this study, and 222 patients (83.5%) had a ureteral calculus. The same 266 patients were compared using the two clinical decision rule, STONE score, and the modified STONE score. The patients were classified into three groups. The prevalence of ureteral stones in the STONE score was 18.8% in the low-score group, 81.7% in the moderate-score group, and 91.1% in the high-score group. The prevalence of the modified STONE score was 20.0% in the low-score group, 54.1% in the moderate-score group, and 93.0% in the highscore group. The area under the curve of the modified STONE score was 0.779 higher than the area under the STONE score curve 0.73. Conclusion: The modified STONE score has superior diagnostic specificity to the STONE score.ope

The effect of paramedic’s emergency patient simulation training - course using standardized communication tools and simulation

Background : Since primary emergency treatment should be performed appropriately and promptly, efficient and accurate communication between paramedics and medical staff is paramount to a successful primary emergency treatment and patient handover. The problem of the training program in Korea is that it concentrates more on in-class lectures, often delivered by non-medical specialists, who may lack in practical experience and without proper communication training. To solve this problem, we have devised a simulation based training that focuses on event debriefings and two-way communication. Methods : 62 paramedics from 3 stations enrolled in the study. 4 different courses with different emergency situations were created and each course was taken twice resulting in a total of 8 classes. All courses were based on actual cases. The curriculum consisted of subject lectures with guidelines, skill practice courses, and simulation courses based on hands-on method. In simulation courses, paramedics use standardized check list to communicate with medical specialists. All curriculums except subject lectures include debriefing, which allows free talking with educators comprised of medical specialists. In order to measure the educational impact, all students performed self-assessment through a structured questionnaire before and after the training. Results : Regardless different situations and paramedics’ education level, their performance and communication skills have improved after simulation training course. Paramedics mentioned learning skills in simulation course through communication with medical staffs as the biggest advantage. Conclusion : Receiving the simulation training with standardized communication tools is effective at enhancing the communication between the paramedics and medical staff.ope

Empathy and Quality of Life in Korean Emergency Physicians

Purpose: Empathy in medical practice is related to medical communication and clinical competence. In previous stud ies, low quality of life and other factors play an integral role in low empathy among physicians. We evaluated the rela tionships between empathy, quality of life, and other factors among Korean emergency physicians. Methods: The survey was conducted using email to emer gency physicians. The respondents completed a question naire including demographic information, the Jefferson Scale of Empathy, and the Brief version of the World Health Organization Quality of Life assessment instrument. Correlation analyses were performed, along with sub-analy ses according to gender. Results: A total of 180 questionnaires were analyzed. The median value of the empathy scale was 89.0, and quality of life 64.8. Empathy was positively correlated with quality of life, age, and work experience as a specialist in total sam ples and males. Only work experience as a specialist showed correlation with empathy in females. Quality of life showed no association with age, work experience, and work load. However, quality of life showed negative correla tion with age and work experience in female physicians. Conclusion: The more experienced specialist emergency physicians are, and the better quality of life they have, the higher level of empathy scale they have. Therefore, good quality of life could lead to good empathy, and vice versa. Good quality of life and good empathy could lead to the bet ter outcome in emergency care. However, because the female physicians show different patterns of empathy and quality of life, further study is neededope

Consent for withholding life-sustaining treatment in cancer patients: a retrospective comparative analysis before and after the enforcement of the Life Extension Medical Decision law

Background: The Life Extension Medical Decision law enacted on February 4, 2018 in South Korea was the first to consider the suspension of futile life-sustaining treatment, and its enactment caused a big controversy in Korean society. However, no study has evaluated whether the actual implementation of life-sustaining treatment has decreased after the enforcement of this law. This study aimed to compare the provision of patient consent before and after the enforcement of this law among cancer patients who visited a tertiary university hospital's emergency room to understand the effects of this law on the clinical care of cancer patients. Methods: This retrospective single cohort study included advanced cancer patients aged over 19 years who visited the emergency room of a tertiary university hospital. The two study periods were as follows: from February 2017 to January 2018 (before) and from May 2018 to April 2019 (after). The primary outcome was the length of hospital stay. The consent rates to perform cardiopulmonary resuscitation (CPR), intubation, continuous renal replacement therapy (CRRT), and intensive care unit (ICU) admission were the secondary outcomes. Results: The length of hospital stay decreased after the law was enforced from 4 to 2 days (p = 0.001). The rates of direct transfers to secondary hospitals and nursing hospitals increased from 8.2 to 21.2% (p = 0.001) and from 1.0 to 9.7%, respectively (p < 0.001). The consent rate for admission to the ICU decreased from 6.7 to 2.3% (p = 0.032). For CPR and CRRT, the consent rates decreased from 1.0 to 0.0% and from 13.9 to 8.8%, respectively, but the differences were not significant (p = 0.226 and p = 0.109, respectively). Conclusion: After the enforcement of the Life Extension Medical Decision law, the length of stay in the tertiary university hospital decreased in patients who established their life-sustaining treatment plans in the emergency room. Moreover, the rate of consent for ICU admission decreased.ope

The Poisoning Information Database Covers a Large Proportion of Real Poisoning Cases in Korea.

The poisoning information database (PIDB) provides clinical toxicological information on commonly encountered toxic substances in Korea. The aim of this study was to estimate the coverage rate of the PIDB by comparing the database with the distribution of toxic substances that real poisoning patients presented to 20 emergency departments. Development of the PIDB started in 2007, and the number of toxic substances increased annually from 50 to 470 substances in 2014. We retrospectively reviewed the medical records of patients with toxic exposure who visited 20 emergency departments in Korea from January to December 2013. Identified toxic substances were classified as prescription drug, agricultural chemical, household product, animal or plant, herbal drug, or other. We calculated the coverage rate of the PIDB for both the number of poisoning cases and the kinds of toxic substances. A total of 10,887 cases of intoxication among 8,145 patients was collected. The 470 substances registered in the PIDB covered 89.3% of 8,891 identified cases related to poisoning, while the same substances only covered 45.3% of the 671 kinds of identified toxic substances. According to category, 211 prescription drugs, 58 agricultural chemicals, 28 household products, and 32 animals or plants were not covered by the PIDB. This study suggested that the PIDB covered a large proportion of real poisoning cases in Korea. However, the database should be continuously extended to provide information for even rare toxic substances.ope

High-Performance and Low-Complexity Decoding of High-Weight LDPC Codes

Low-density parity-check (LDPC) 부호의 복호에는 성능이 좋은 합곱 알고리즘(sum-product algorithm; SPA)과 하드웨어가 간단한 비트 반전(bit-flipping; BF) 알고리즘이 많이 쓰이고 있다. 본 논문은 이들 두 가지 방법의 장점을 가지는 저복잡도 고성능 복호 알고리즘을 제안한다. 본 제안된 유연 비트 반전(soft bit-flipping) 알고리즘은 비트와 체크 노드 사이에 전달되는 메시지를 계산하는 데 단순한 비교와 덧셈 연산만을 필요로 하며 연산량이 적다는 장점이 있다. 또한 연산이 완료된 메시지의 활용률을 높이고 비균등 양자화(non-uniform quantization)를 채용하여 1000 내외의 부호 길이에서 SPA 에 0.4dB 근접하는 신호대 잡음비(signal-to-noise ratio)를 달성하였다. 본 논문에서 제안된 알고리즘을 이용하면, 행 무게(row weight)와 열 무게(column weight)가 높아서 종래의 SPA로 구현하기 어려웠던 부호를 비교적 좋은 오율 성능을 유지하면서 실용적으로 구현할 수 있다. ; A high-performance low-complexity decoding algorithm for LDPC codes is proposed in this paper, which has the advantages of both bit-flipping (BF) algorithm and sum-product algorithm (SPA). The proposed soft bit-flipping algorithm requires only simple comparison and addition operations for computing the messages between bit and check nodes, and the amount of those operations is also small. By increasing the utilization ratio of the computed messages and by adopting nonuniform quantization, the signal-to-noise ratio (SNR) gap to the SPA is reduced to 0.4dB at the frame error rate of 10-4 with only 5-bit assignment for quantization. LDPC codes with high column or row weights, which are not suitable for the SPA decoding due to the complexity, can be practically implemented without much worsening the error performance.본 연구는 교육과학기술부의 BK21 사업, 그리고 하이닉스 반도체 주식회사의 지원으로 수행되었습니다

Equipment for Difficult Airways in 67 Korean Academic Emergency Departments

Purpose: In Korea, there has been no research about the devices that are used for dealing with difficult airways in emergency departments (ED). This study reports the results of the first research of this kind, assessing the equipment in Korean EDs that is used to manage patients with difficult airways. Methods: We surveyed 92 EDs via the Internet from October 2007 to March 2008. All respondents were asked if they have the following categories of devices in their EDs; alternative intubation devices, alternative rescue ventilation devices, and surgical airway devices. Alternative intubation devices were defined as devices that do not use a direct laryngoscope for tracheal tube insertion. Alternative rescue ventilation devices were defined as ventilation devices that do not use a face mask. Surgical airway devices were defined as devices that use a surgical technique for the placement of endotracheal tube. Results: We obtained data from 67 of the 92 (72.8%) EDs we contacted. Of those, 32 (47.8%) EDs have at least one alternative intubation device, 52 (77.6%) EDs have at least one alternative rescue ventilation device, and 59 (88.1%) EDs have at least one surgical airway device. A total of 30 (44.8%) EDs have equipment in all 3 categories, but 4 (6.0%) EDs do not have any equipment for dealing with difficult airways. The most common alternative intubation device was a flexible fiberscope (29.9%). Conclusion: The possession of devices to deal with difficult airways varies across EDs. It seems that not all Korean EDs have enough devices for difficult airwaysope

Survey of the Management Systems and Decision-making Process of Emergency Medicine and Psychiatry for Patients Attempting Suicide

Purpose: Most patients attempting suicide present to the emergency department (ED). Active post-event intervention is helpful in preventing additional self harm. However, the current management system and decision-making processes of individual doctors are highly variable. This survey aimed to describe the ED management system and to compare the decisions of doctors in emergency medicine and psychiatry for patients for attempting suicide. Methods: Questionnaires were sent by e-mail to directors of both ED and psychiatry departments in all Korean teaching hospitals. The questionnaires surveyed the current management system for suicidal patients in the ED, the medical director`s opinion about the management of suicidal patients, and decisions about disposition of the three clinical scenarios. Results: Sixty-four out of 180 surveys(36%) were returned. The average number of suicidal patients visiting the ED was 13.6 per month and the number referred to a psychiatrist was 11.3 per month. Half of EDs(15/30) had established criteria for patient disposition, but only 7% of ED and 82% of psychiatry departments had practice guidelines for doctors. Only 4% of ED performed any active post-event intervention other than psychiatry out-patient visits. Decisions of emergency physicians and psychiatrists about referring a patient to the psychiatrist in the three clinical scenarios were in part statistically different. Conclusion: This study suggests that appropriate facilities and standard guidelines for suicidal patients are needed. Each hospital should develop a common management protocol with collaboration between emergency medicine and psychiatry departments.ope