A parametric study on fatigue of a top-tensioned riser subjected to vortex-induced vibrations

Kim, Do Kyun,Wong, Eileen Wee Chin,Lekkala, Mala Konda Reddy Techno-Press 2019 Structural monitoring and maintenance Vol.6 No.4

This study aims to provide useful information on the fatigue assessment of a top-tensioned riser (TTR) subjected to vortex-induced vibration (VIV) by performing parametric study. The effects of principal design parameters, i.e., riser diameter, wall thickness, water depth (related to riser length), top tension, current velocity, and shear rate (or shear profile of current) are investigated. To prepare the base model of TTR for parametric studies, three (3) riser modelling techniques in the OrcaFlex were investigated and validated against a reference model by Knardahl (2012). The selected riser model was used to perform parametric studies to investigate the effects of design parameters on the VIV fatigue damage of TTR. From the obtained comparison results of VIV analysis, it was demonstrated that a model with a single line model ending at the lower flex joint (LFJ) and pinned connection with finite rotation stiffness to simulate the LFJ properties at the bottom end of the line model produced acceptable prediction. Moreover, it was suitable for VIV analysis purposes. Findings from parametric studies showed that VIV fatigue damage increased with increasing current velocity, riser outer diameter and water depth, and decreased with increasing shear rate and top tension of riser. With regard to the effects of wall thickness, it was not significant to VIV fatigue damage of TTR. The detailed outcomes were documented with parametric study results.

General considerations for sample size estimation in animal study

Ko Mun Jung,임지연 대한마취통증의학회 2021 Korean Journal of Anesthesiology Vol.74 No.1

The aim of this paper is to introduce basic concepts and methods for calculating sample size in animal studies. At the planning stage of clinical studies, the determination of the sample size is a very important process to show the validity, accuracy, and reliability of the study. However, not all studies require a sample size to be calculated. Before conducting the study, it is essential to determine whether the study objectives suggest a pilot and exploratory study, as well as the purpose of testing the hypothesis of interest. Since most animal experiments are pilot and exploratory studies, it would be more appropriate to review other considerations for conducting an experiment while maintaining scientific and qualitative levels rather than sample size estimation. Sample size is calculated in various situations in animal studies. Therefore, it can be estimated according to the situations and objectives through the methods of precision analysis, power analysis, and so on. In some cases, nonparametric methods can be employed if the assumptions of normality is not met or a small sample is available for the study.

Parametric studies on punching shear behavior of RC flat slabs without shear reinforcement

Galal Elsamak,Sabry Fayed 사단법인 한국계산역학회 2020 Computers and Concrete, An International Journal Vol.25 No.4

This paper proposed a numerical investigation based on finite elements analysis (FEA) in order to study the punching shear behavior of reinforced concrete (RC) flat slabs using ABAQUS and SAP2000 programs. Firstly, the concrete and the steel reinforcements were modeled by hexahedral 3D solid and linear elements respectively, and the nonlinearity of the used materials was considered. In order to validate this model, experimental results considered in literature were compared with the proposed FE model. After validation, a parametric study was performed. The parameters include the slab thickness, the flexure reinforcement ratios and the axial membrane loads. Then, to reduce the time of FEA, a simplified modelling using 3D layered shell element and shear hinge concept was also induced. The effect of the footings settlement was studied using the proposed simplified nonlinear model as a case study. Results of numerical models showed that increase of the slab thickness by 185.7% enhanced the ultimate load by 439.1%, accompanied with a brittle punching failure. The punching failure occurred in one of the tested specimens when the tensile reinforcement ratio increased more than 0.65% and the punching capacity improved with increasing the horizontal flexural reinforcement; it decreased by 30% with the settlement of the outer footings.

A Parametric Study of Confinement Evaluation of Spent Fuel Dry Storage Systems for Accident Condition

Siwan Noh,Ki-Seog Seo,Sang Soon Cho 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

In order to construct and operate the dry storage systems, it is essential to confirm the safety of the systems through safety analysis. If the dry storage cask is damaged due to an accident, a large amount of radioactive material may be leaked to the outside and cause radiation exposure to surrounding workers and nearby public, so the effect thereof should be evaluated. Many input parameter are required in the confinement evaluation for accident condition, and in this study, the change in the confinement evaluation result according to the change of major input parameter is to be studied. In this study, we selected fractions of radioactive materials available for release from spent fuel, cooling time, and distance to exclusive area boundary as the major input parameter. In general, the release fraction suggested by NUREG-1536 has been used, but NUREG-2224 provides the fraction for high burn-up spent fuel in fire and impact accident conditions, unlike NUREG-1536 which provide a single value. In the case of the distance to exclusive area boundary, 100 to 800 m was considered, and in the case of the cooling time, 10 to 50 years was considered in this study. In order to compare the dose change by the parameter, we set up the hypothetical storage system. A storage cask of the system contain 21 PWR spent fuel assemblies with an initial enrichment of 4.5wt%, burnup of 45,000 MWD/MTU. During the accident condition, it is assumed that the cask is leaked at 1.0×10?7cm3·sec?1. Since the main dose criterion for accident conditions is 50 mSv of effective dose, effective doses are calculated in this study. In an accident condition, transuranic particulate contribute most of the doses, so the doses are determined according to the fraction for the particulate. Therefore, it was confirmed that the dose was almost the same as the fraction for the accident conditions in NUREG-1536 and the fraction for the impact accident conditions in NUREG-2224 is 3×10?5, but the dose was also 100 times higher as the fraction for the fire accident conditions in NUREG-2224 is 3×10?3. In the case of the cooling time, it was confirmed that the dose change according to the cooling time was not significant because the dose contribution of transuranic elements having very long half-life was very large. In the case of the distance, it was confirmed that the dose decreased exponentially as the atmospheric dispersion factor decreased exponentially with the distance.

센터필러-루프레일 결합부의 강성에 영향을 미치는 인자 연구

이상범,임홍재,이종선 한국공작기계학회 2004 한국생산제조학회지 Vol.13 No.1

The global stiffnesses and vibration characteristics of vehicle structures are mainly influenced by the local stifnesses of the joint structures consisted of complicated thin-walled panels. In this paper, the parametric study for the stiffnesses of the center pillar-roof rail joint of vehicle structure is performed through the hear static analysis. The analysis result shows that the reinforcement panel much affects the joint stiffness of out-plane direction (ie., z-direction). And also, the flange radius and width of the joint structure much affect the joint stiffness of out-plane direction. The study shows that vehicle joint stiffnesses can be effectively determined in designing vehicle structure through the parametric study.

A Parametric Study of the Functioning of an Axisymmetric Explosive Separation Device

Guangyu Wang,Quan Wen,Xiaopeng Wang,Yushi Wang 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.6

At present, the design and optimization of the linear explosive separation device mainly depends on experiment, which is not only costly but also low efficient. The introduction of finite element analysis prior to experiment may reduce the cost to design a linear explosive separation device. Herein, arbitrary Lagrangian–Eulerian (ALE) numerical method is utilized to investigate the functioning of an axisymmetric explosive separation device. Firstly, several ALE models are validated via explosive separation experiments and photonic Doppler velocimetry (PDV) measurements, and found to have reasonable accuracy. Then, a series of ALE models are developed to study the transient separation process of an axisymmetric explosive separation device. Multiple factors which may influence the process are identified through parametric study. Especially, it is found that the linear density of the explosive core in the detonating cord and the bottom radius of the v-notch on the separation plate are critical for the accumulation of effective plastic strain at the v-notch. In addition, the material of the protection plate and the angle of the v-notch have a certain influence on the effective plastic strain at the v-notch. The material strength of the protection plate almost has little influence on the effective plastic strain at the v-notch. The study may facilitate the optimal design of the axisymmetric explosive separation device.

Stress Analysis of Tractor Front-End Loader against Impact Load Using Flexible Multi-Body Dynamic Simulation

Chang-Seop Shin(신창섭),Beom-Soo Kim(김범수),Hyun-Woo Han(한현우),Woo-Jin Chung(정우진),Seung-Je Cho(조승제),Young-Jun Park(박영준) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.3

This study was conducted to analyze the stresses by impact loads on front-end loaders attached to tractors using flexible multi-body dynamics. The model was designed and validated by comparing previous experimental data with the simulation data obtained in this study. Nine sets of conditions were designed using three weights (500, 300, and 100 kg) loaded inside a bucket and three heights (1700, 1350, and 1000 mm) of the bucket from ground level. A parametric study was carried out at five locations for two types of parts of a front-end loader. All the safety factors for the five locations under all conditions were calculated and were greater than 1. Thus, the designs of the front-end loaders were structurally safe. Based on this study, front-end loaders attached to tractors can be designed effectively in terms of cost and safety.

Aerodynamic Analysis and Parametric Study of the Blended-Wing-Body-Type Business Jet

최현민,Jinsoo Cho 한국항공우주학회 2019 International Journal of Aeronautical and Space Sc Vol.20 No.2

The market demand on business jets is growing fast. The Blended-Wing-Body (BWB) configuration is adapted to design high-efficient green business jet. Conceptual study of the BWB-type transonic business jet is carried out. The BWB-type business jet expected to provide a better cabin space and aerodynamic performance to compare with the conventional business jet. An aerodynamic analysis of the BWB-type transonic business jet is performed to understand the flow field around the aircraft at a high subsonic flight speed. The commercial CFD (Computational Fluid Dynamics) code, ANSYS Fluent, is used for aerodynamic analysis. A parametric study is carried out to analyze the relation between the design parameters and aerodynamic characteristics. The commercial PIDO (Process Integration and Design Optimization) tool, PIAnO, is used to perform a parametric study. As a result of parametric study, the sensitivity of the design parameters is analyzed and a proportion of aerodynamic influence of each design parameter is presented. One of the sample design configurations for detailed aerodynamic analysis is selected. As a result of the aerodynamic analysis, aerodynamic coefficients and pressure coefficient distribution around the BWB-type business jet are presented. Increase of AOA and Mach number produces stronger shock and drag coefficient is increased due to wave drag.

센서 부재 환경에서 건물 시스템 단위 이상 진단 모델의 성능 향상 방안

김륜희(Ryunhee Kim),윤성민(Sungmin Yoon),김용식(Yong-Shik Kim) 대한설비공학회 2021 대한설비공학회 학술발표대회논문집 Vol.2021 No.6

Virtual sensors are widely used to overcome the limited sensing environment in building systems in these days. However, developed virtual sensors can involve uncertainty of systems and it could affect the performance of virtual sensors. In this paper, the method for improving the performance of virtual sensor using parametric study on assistance virtual sensor is proposed. Suggested method is experimentally applied to the fault detection model. Several calibration constant are selected through the parametric study and used for the assistance virtual sensor to calibrate its uncertainty. The result shows that using the calibration constant could significantly improve the performance of the fault detection model.

Stress Optimization of plastic IC package in reflow soldering process

김근우(Geun Woo Kim),이강용(Kang Yong Lee),이택성(Taek Sung Lee),김옥환(Ok Whan Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8

In order to reduce stress in the plastic small outline J-lead(SOJ) package and prevent the interface delamination under the infrared(IR) soldering process, parameterization, parametric study and optimization are used. The design variables of dimensions and material properties are determined among all the possible variables from the parametric study. Their optimized values are determined by applying the constraint optimization to the parameterized IC package.