Experimental investigation of vortex- and wake-induced vibration of tandem cylinders

This paper presents the experimental investigation of wake-induced vibration (WIV) and vortex-induced vibration (VIV) acting on two circular cylinders. In particular, a riser installed in a offshore field may experience flow interferences between adjacent risers. Accordingly, scaled models were arranged in a tandem configuration in order to observe the flow interference between the cylinders. While an upstream cylinder is fixed or allowed to have one degree of freedom(1-DOF) motion, a downstream cylinder is allowed to have two degree of freedom(2-DOF) motion. An experimental test is carried out in a circulating water channel with cylinders which are connected by linear springs in two horizontal directions. A three-dimensional displacement meter and a load cell were used to measure cylinder's motion and hydrodynamic force of a cylinder, respectively. In order to implement single and dual resonance condition, natural frequency ratio of in-line to cross-flow directions, f*=fnx/fny, was set as 1.0 and 1.9. To validate an experimental result, it is compared with that of previous study in terms of cylinder's motion response amplitude and oscillation frequency. From the experiment, we have identified that there are relative effects between VIV and WIV with respect to selected parameters. Influence of WIV are also quantitatively observed with in-line motion power spectral density and cross-flow motion time history.1. Introduction 1.1 Background 1 1.2 Literature review 3 1.3 Objectives and Scopes 6 2. Experimental set-up 2.1 Circulating Water Channel 7 2.2 Experimental equipment 8 2.3 Rigid circular cylinder models 10 2.4 Fixed and two degree of freedom 12 2.5 One and two degree of freedom 14 3. Test matrix for experiment 3.1 Parameters set-up 15 3.2 Cases for model experiment 18 4. Amplitudes and frequencies of cylinder's motion 4.1 Single cylinder with 1-DOF and 2-DOF motions 20 4.2 Downstream cylinder of WIV 24 4.2.1 Fixed upstream cylinder & 2-DOF downstream cylinder 24 4.2.2 1-DOF upstream cylinder & 2-DOF downstream cylinder 32 5. An effect of WIV excitation mechanism 5.1 Time history and Power spectral density 37 5.2 Trajectories of motion 42 5.3 Flow interference between tandem cylinders 45 5.4 Force coefficients with Wake shielding effect 47 6. Conclusions References 50Maste

The Association Between Second-Line Oral Antihyperglycemic Medication on Types of Dementia in Type 2 Diabetes: A Nationwide Real-World Longitudinal Study

Background: There are few reports that evaluated the association between various types of dementia and dual oral therapy with antihyperglycemic medication. Objective: The goal of this study was to investigate the association between treatment of dual antihyperglycemic medication and dementia subclass in type 2 diabetes mellitus using the Korean National Health Insurance System. Methods: This study included 701,193 individuals with diabetes prescribed dual oral therapy between 2009 and 2012 from the Korean National Health Insurance Service Database, which were tracked until 2017. All-cause, Alzheimer's (AD) and vascular dementia (VaD) were investigated by dual oral therapy. Adjustments were made for age, sex, income, diabetes duration, hypertension, dyslipidemia, smoking, drinking, exercise, body mass index, glucose level, and estimated glomerular filtration rate. Results: Dual therapy with metformin (Met) + dipeptidyl peptidase-4 inhibitor (DPP-4i), Met + thiazolidinedione (TZD), and sulfonylurea (SU) + thiazolidinediones (TZD) were significantly associated with all-cause dementia (HR = 0.904, 0.804, and 0.962, respectively) and VaD (HR = 0.865, 0.725, and 0.911, respectively), compared with Met + SU. Met + DPP-4i and Met + TZD were associated with significantly lower risk of AD (HR = 0.922 and 0.812), compared with Met + SU. Dual therapy with TZD was associated with a significantly lower risk of all-cause dementia, AD, and VaD than nonusers of TZD (HR = 0.918, 0.925 and 0.859, respectively). Conclusion: Adding TZD or DPP-4i instead of SU as second-line anti-diabetic treatment may be considered for delaying or preventing dementia. Also, TZD users relative to TZD non-users on dual oral therapy were significantly associated with lower risk of various types of dementia

A fundamental study on surface fatigue crack under pseudo-random loading

학위논문(석사) - 한국과학기술원 : 자동화및설계공학과, 1996.8, [ iv, 48 p. ]한국과학기술원 : 자동화및설계공학과

Active transport of potassium ion through the sulfonated poly(styrene-Co-divinylbenzene) membrane

학위논문(석사) - 한국과학기술원 : 화학공학과, 1986.2, [ iii, 51 p. ]한국과학기술원 : 화학공학과

Context Adaptive Personalized Psychological State Sampling Method and Apparatus for Wearable Devices

웨어러블 기기를 위한 상황 적응형 개인화 심리상태 표집 방법 및 장치가 제시된다. 본 발명에서 제안하는 웨어러블 기기를 위한 상황 적응형 개인화 심리상태 표집 장치는 모바일 및 웨어러블 기기를 활용하여 센서 데이터를 수집하는 센서 데이터 수집부, 수집된 센서 데이터를 활용하여 사용자의 신체활동을 추론하는 신체활동 분류부, 추론된 신체활동 별로 추출된 센서 데이터 특징 값을 활용하여 데이터를 군집화하는 센서 데이터 비지도학습부, 센서 데이터 비지도학습부를 통해 분류된 데이터에 기초하여 해당 센서 데이터로 현재의 심리상태를 추론하는 계층화 심리상태 분류부, 추론된 현재의 심리상태, 수집된 레이블 정보, 센서 데이터, 사용자 부담도 중 적어도 하나 이상에 기초하여 사용자에게 자가정보수집을 요청할지 여부를 결정하는 정보수집 요청 판단부 및 정보수집 요청 판단부에서 사용자에게 자가보고 정보를 수집하기로 결정할 경우 사용자로부터 자가보고 정보를 입력 받는 정보수집 인터페이스를 포함한다