Structural configurations and dynamic performances of flexible riser with distributed buoyancy modules based on FEM simulations

Chen Weimin,Guo Shuangxi,Li Yilun,Gai Yuxin,Shen Yijun 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

Flexible risers are usually used as conveying systems to bring ocean resources from sea bed up to onshore. Under ocean environments, risers need to bear complex loads and it is crucial to comprehensively examine riser's configurations and to analyze structural dynamic performances under excitation of bottom vehicle motions, to guarantee structural safe operation and required service lives. In this study, considering a saddle-shaped riser, the influences of some important design parameters, including installation position of buoyancy modules, buoyancy ratio and motion of mining vehicle, on riser's configuration and response are carefully examined. Through our FEM simulations, the spatial distributions of structural tensions and curvatures along of riser length, under different configurations, are compared. Then, the impacts of mining vehicle motion on riser dynamic response are discussed, and structural tolerance performance is assessed. The results show that modules installation position and buoyancy ratio have significant impacts on riser configurations. And, an appropriate riser configuration is obtained through comprehensive analysis on the modules positions and buoyancy ratios. Under this proposed configuration, the structural tension and curvature could moderately change with buoyancy modules and bottom-end conditions, in other words, the proposed saddle-shaped riser has a good tolerance performance to various load excitations.

Temperature effects on riser pressure drop in a circulating fluidized bed

원유섭,정아름,최정후,조성호,류호정,이창근 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.3

Effects of temperature on pressure drop across a riser due to solids holdup in the riser of a circulating fluidized bed (CFB) were investigated at the atmospheric pressure condition. The bed material was a group of sorbent particles and the experimental variables included temperature, gas velocity, and solids flux in the riser. With gas velocity and solids flux held constant, the riser pressure drop decreased as temperature increased. However, temperature effects decreased with increase in gas velocity. The effects of temperature on riser pressure drop were confirmed qualitatively by the same effects on the average ratio of gravity to drag force on a single spherical particle while the particle was accelerated. The pressure drop across the riser increased almost linearly with the ratio of solids flux to gas flux at the given gas velocity. Because gas momentum per unit mass of gas transferred to solids increased, the slope of the linear relationship decreased as temperature increased. This result confirmed the validity of the concept of momentum transfer from gas to particles at high temperature, proposed at ambient temperature in the prior study. The amount of gas momentum per unit mass of gas available to carry over the solid particles was finite; thus as the solids flux increased at the given gas velocity, the gas momentum shared to the unit mass of solids decreased and the mean residence time of solids in the riser, i.e., the pressure drop across the riser increased linearly. The slope of the linear relationship was proportional to the ratio of momentum flux by gravity and buoyancy forces on solids to gas momentum per unit mass of gas by drag force transferred to solids. Correlations were proposed to predict effects of temperature on the pressure drop across the riser and the solids flux in the riser within the range of experimental conditions.

An intelligent recoil controller for riser system based on fuzzy control theory

Liu Xiuquan,Liu Zhaowei,Wang Xianglei,Qiu Na,Zhang Nan,Chang Yuanjiang,Chen Guoming 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1

Riser recoil control is a complicated nonlinear control problem. An intelligent control methodology is proposed to control the complicated riser recoil response based on fuzzy control theory. A dynamic nonlinear model of drilling riser/tensioner coupling system is established for riser recoil analysis. The riser system is divided into several elements and the coupling effect between the riser and discharged mud is considered in the dynamic model. A fuzzy controller for the opening of the recoil control valve is designed for the riser recoil control. A comprehensive analysis method is proposed for riser recoil control simulation. Simulation results show that the designed fuzzy controller can effectively control the riser recoil response. The adaptability of the designed controller is also proved by the simulation results. The application of the designed controller can reduce the risk of accidents during riser recoil process.

A simplified method to predict fatigue damage of offshore riser subjected to vortex-induced vibration by adopting current index concept

Kim, D.K.,Incecik, A.,Choi, H.S.,Wong, E.W.C.,Yu, S.Y.,Park, K.S. Elsevier 2018 Ocean engineering Vol.157 No.-

<P><B>Abstract</B></P> <P>In the present study, an innovative method for estimating fatigue performance of risers under vortex-induced vibration (VIV) is proposed. Generally, fatigue performance is affected by the surrounding environment such as wind, wave, and current. It is well known that current is the most influential load among all for offshore risers. In structural safety aspect, strength and fatigue are the most important factors for riser design. In addition, fatigue design is affinitive to the VIV phenomenon. For the analysis of fatigue performance of riser, SHEAR7 numerical simulation code which is commonly used in offshore industry is applied. In order to identify the relation between current load and fatigue performance of riser, Fatigue damage versus Current index (F-C) diagram has been proposed. F-C diagram may cover change of current profiles and help predict the fatigue damage under VIV. In case of current profile, a total of sixty cases of current scenarios are considered based on six representative sea-states. The obtained results from this study will be a useful guideline to predict the effect of current on the fatigue performance of riser.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An innovative method for the estimation of fatigue performance of offshore riser is proposed. </LI> <LI> Current index (CI) concept is proposed by considering the parameters of current profile. </LI> <LI> F-C (Fatigue damage vs. Current index) diagrams for offshore riser are established. </LI> <LI> The proposed method shows good agreement with existing method. </LI> <LI> The F-C diagrams will be useful in judging the safety level of offshore riser subjected to VIV fatigue by current load. </LI> </UL> </P>

Vortex-induced vibrations and control of marine risers: A review

Hong, Keum-Shik,Shah, Umer Hameed Elsevier 2018 Ocean engineering Vol.152 No.-

<P><B>Abstract</B></P> <P>This paper reviews the dynamics and vibration control techniques for marine riser systems. The riser pipes are modeled as Euler-Bernoulli beams that vibrate under the effects of ocean loads and the movements of the surface vessel, resulting in hybrid ODE-PDE equations. Chronological development of such hybrid models is first discussed, and their approximated ODE models for simulation are examined. Theoretical and experimental techniques for instability and fatigue analyses on the riser systems are also summarized. To increase the fatigue life against ocean currents, passive vibration suppression devices (e.g., strakes and spoilers) were mounted on the surface of the riser. Whereas to tackle the instability problem caused by sea waves, active control techniques utilizing the movements of the vessel were employed. In Conclusions, as future riser technologies, seven research issues are identified.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A review on the dynamics and vortex-induced vibration control methods of marine riser systems. </LI> <LI> The focuses are on mathematical formulations, analyses, and controls (both active and passive methods) of marine risers. </LI> <LI> Identification of future research topics in the area of dynamics and vibration control of marine riser systems. </LI> </UL> </P>

압탕 최소화를 위한 터보차저하우징의 융합 S/W 응용 제조기술 및 실험적 검증

이학철 ( Hak-chul Lee ),서판기 ( Pan-ki Seo ),진철규 ( Chul-kyu Jin ),서형윤 ( Seo-hyung Yoon ),강충길 ( Chung-gil Kang ) 한국주조공학회 2017 한국주조공학회지 Vol.37 No.1

The purpose of this study is to increase the part recovery rate (to more than 70%) during the casting of a ductile cast iron turbo charger housing using a heater around the riser. Before creating a casting mold, various runner and riser systems were designed and analyzed with a casting simulation analysis tool. The design variables were the heater temperature, top insulation, riser location, riser diameter and the riser shape. During the feeding from the riser to the part, the reverse model was better than the forward model. When heating the riser (above 600 ℃), solidification of the riser was delayed and the feeding effect was suitable compared to that without heating. At a higher heating temperature, less solidification shrinkage and porosity were noted inside the part. On the basis of a casting simulation, eight molds were fabricated and casting experiments were conducted. According to the experimental conditions, external and internal defects were analyzed and mechanical properties were tested. The ultimate tensile strength and elongation outcome were correspondingly more than 540MPa and 5% after a heat treatment. In addition, a maximum part recovery rate of 86% was achieved in this study.

Dynamic characteristics and fatigue damage prediction of FRP strengthened marine riser

Islam, A.B.M. Saiful Techno-Press 2018 Ocean systems engineering Vol.8 No.1

Due to the escalation in hydrocarbon consumption, the offshore industry is now looking for advanced technology to be employed for deep sea exploration. Riser system is an integral part of floating structure used for such oil and gas extraction from deep water offering a system of drill twines and production tubing to spread the exploration well towards the ocean bed. Thus, the marine risers need to be precisely employed. The incorporation of the strengthening material, fiber reinforced polymer (FRP) for deep and ultra-deep water riser has drawn extensive curiosity in offshore engineering as it might offer potential weight savings and improved durability. The design for FRP strengthening involves the local design for critical loads along with the global analysis under all possible nonlinearities and imposed loadings such as platform motion, gravity, buoyancy, wave force, hydrostatic pressure, current etc. for computing and evaluating critical situations. Finite element package, ABAQUS/AQUA is the competent tool to analyze the static and dynamic responses under the offshore hydrodynamic loads. The necessities in design and operating conditions are studied. The study includes describing the methodology, procedure of analysis and the local design of composite riser. The responses and fatigue damage characteristics of the risers are explored for the effects of FRP strengthening. A detail assessment on the technical expansion of strengthening riser has been outlined comprising the inquiry on its behavior. The enquiry exemplifies the strengthening of riser as very potential idea and suitable in marine structures to explore oil and gas in deep sea.

Fatigue damage assessment of offshore riser subjected to vortex-induced vibrations by SHEAR7

Lekkala Malakonda Reddy,Latheef Mohamed,Jung Jae Hwan,Kim Young Tae,김도균 대한조선학회 2022 International Journal of Naval Architecture and Oc Vol.14 No.1

Marine risers are a critical component in transporting the produced hydrocarbons from the seabed to the topside facility and vice versa. These risers are subjected to VIV when encountered with ocean currents, leading to the accumulation of fatigue damage, which reduces the risers' service life. Estimation of fatigue damage is an important aspect to assure reliable and operable conditions. SHEAR7 is used in this analysis to estimate the fatigue damage of the Top Tensioned Riser (TTR). SHEAR7 is widely used semiempirical software in the offshore industry to estimate the fatigue damage induced by VIV. Recently, SHEAR7 has been revised to account for the higher harmonic corrections based on experimental and field data. The key pertaining to the revision of adding higher harmonics can contribute 50% higher strain along the length of the riser at some locations (Jhingran and Vandiver, 2007). VIV fatigue damage analysis was conducted using SHEAR7 v4.7b and v4.9b to investigate the effect of the higher harmonics considered in the later version. The TTR model used in this analysis was modelled in OrcaFlex and validated with available references in the literature. TTR with different model scenarios was developed, and comparisons were made between the predicated responses from SHEAR7 v4.b and v4.9b for the riser. It was observed that higher harmonic correction factors have a great impact on the performance of the riser. Finally, sensitivity analyses were carried out to check the effect of individual parameters and higher harmonic correction factors on predicted responses between the two versions of SHEAR7.

여성노인들의 보행 시 보행 턱 높이에 따른 운동학적 분석

황유진(You Jin Hwang),우병훈(Byung Hoon Woo) 한국여성체육학회 2012 한국여성체육학회지 Vol.26 No.1

The purpose of this study was to investigate the kinematical analysis on height of footpath stair riser during gait of old woman. Ten subjects(age: 60.30±0.48yr, height: 157.40±6.42cm, weight: 60.60±6.95kg) were participated in the experiment. The method adopted 3D analysis and 4 cameras for filming to analyze the required displacement of COM, angular displacement of right and left thigh, shank and foot segment using by APAS during go down footpath stair riser. The results were as follows; most displacement of COM, there was no significant. In angular displacement of right thigh segment, the higher stair riser, the bigger displacement in sagittal and coronal plane. In angular displacement of left thigh segment, the higher stair riser, the bigger displacement in sagittal and coronal plane and vise versa for right thigh in sagittal plane. In coronal plane, the lower stair riser, the bigger angular displacement. In angular displacement of right shank segment, the lower stair riser, the bigger displacement in sagittal plane. In angular displacement of right thigh segment, the lower stair riser, the bigger displacement in sagittal plane and for coronal plane is was no significant on height of footpath stair riser.

Sensitivity Study on SCR Design for Spread-Moored FPSO in West Africa

Kwang-Kyu Yoo,Youngseok Joo 한국해양공학회 2017 韓國海洋工學會誌 Vol.31 No.2

It is generally acknowledged that the Steel Catenary Riser (SCR) is the most cost-effective riser type for deep-water offshore fields among various risers, including the SCR, flexible riser, and hybrid riser. However, in West Africa, the SCR type may not be suitable for FPSO systems because the large vertical motion of the floater brings about a considerable riser dynamic response. In this paper, an SCR system is designed for the FPSO in the West African field, where the use of a hybrid riser has been preferred. The proposed SCR configuration fulfills the design criteria of the API, such as the strength check and fatigue life. Moreover, a sensitivity analysis is also carried out to improve the certainty in the SCR design of a deep-water FPSO. The parameters affecting the strength and fatigue performance of the SCR are considered.