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Kang, Hooi-Siang,Kim, Moo-Hyun,Bhat Aramanadka, Shankar S.,Kang, Heon-Yong,Lee, Kee-Quen Techno-Press 2017 Ocean systems engineering Vol.7 No.3
Excessive dynamic-tension variations on the top-tensioned risers (TTRs) deteriorate the structural integrity and cause potential safety hazards. This phenomenon has become more remarkable in the development of deep-water fields with harsher environmental loads. The conventional prediction method of tension variations in hydro-pneumatic tensioner (HPT) has the disadvantage to underestimate the magnitude of cyclic loads. The actual excessive dynamic tension variations are larger when considering the viscous frictional fluid effects. In this paper, a suppression method of tension variations in HPT is modeled by incorporating the magneto-rheological (MR) damper and linear-force actuator. The mathematical models of the combined HPT and MR damper are developed and a force-control scheme is introduced to compensate the excessive tension variations on the riser tensioner ring. Numerical simulations and analyses are conducted to evaluate the suppression of tension variations in HPT under both regular- and irregular-wave conditions for a drilling riser of a tensioned-leg platform (TLP). The results show that significant reduction of tension variations can be achieved by introducing the proposed system. This research has provided a theoretical foundation for the HPT tension control and related structural protection.
Kang, Hooi-Siang,Kim, Moo-Hyun,Aramanadka, Shankar S. Bhat Techno-Press 2017 Ocean systems engineering Vol.7 No.1
In real sea environments, excessive dynamic axial tension variations can be exerted on the top-tensioned risers (TTRs) and lead to structural integrity issues. The traditional riser-tension-variation analysis, however, by using parametric formulation is only conditionally valid under certain strict limits and potentially underestimates the total magnitudes of tension variations. This phenomenon is especially important for the long stroke tensioner in dry-tree semisubmersible with larger global heave motion and longer stroke. In this paper, the hydro-pneumatic tensioner (HPT) is modeled in detailed component-level which includes a set of hydraulic and pneumatic components. The viscous fluid frictional effect in the HPT is considered. The main objectives are (i) to develop a detailed tension variation model of the HPT; (ii) to identify the deviations between the conventional parametric formulation and component-level formulation; (iii) to numerically analyze the tension variation of long stroke tensioner in a dry-tree semisubmersible (DTS). The results demonstrate the necessity of component-level formulation for long stroke tensioner in the development of DTS.
Effects of the Liquid Surface Tension on the Ejected Droplet Volume in a Pneumatic Printing System
이상민(Sangmin Lee),최인호(In Ho Choi),김준원(Joonwon Kim) Korean Society for Precision Engineering 2018 한국정밀공학회지 Vol.35 No.6
This paper presents results for effects of the liquid surface tension on the ejected droplet volume using a pneumatic printing system. The low surface tension of the solution causes the liquid wetting around the nozzle, and then the wetted nozzle also inhibits stable formation of droplets. First, we confirmed the maximum inlet pressure (i.e., balanced with capillary force on the outlet channel) corresponding to varied surface tensions of the solutions, prepared by controlling the concentration of a surfactant. The ejected droplet volumes with the surfactant concentrations was varied within approximately 7% at each maximum inlet pressure, and the volume variation decreased to a fifth as compared with a high surface tension liquid.
Design of Automatic Tension Control Device for a Vibrating Wire Sensor
Keun-Ho Rew,Seok-Jo Go,Jang-Sik Park,Ki-Ho Yu,Seung-Hoon Lee 제어로봇시스템학회 2012 제어로봇시스템학회 국제학술대회 논문집 Vol.2012 No.10
The vibrating wire sensor is the structural health monitoring sensor which uses the vibration signal induced from the tension difference of a sensor attached to a structure. Vibrating wire sensors have produced by tuning the tension manually through measuring the frequency of the vibrating wire then fixed by pressing both ends of wire. Therefore, the accuracy of the product was determined by manual skill and this was the weak point to be enhanced. In particular, percentage defect was 75% mainly during the pressing process, which requires the expert. In this study, we developed the tuning device to adjust tension automatically with enhancing the precision and productivity of vibrating wire sensors. After tuning the tension, the fixing wire end is pressed pneumatically, the performance was monitored. Precision evaluation test confirmed that the nonlinearity of sensors is reduced from 0.398 to 0.056%.
Zainuddin, Zaid,Kim, Moo-Hyun,Kang, Heon-Yong,Bhat, Shankar Techno-Press 2018 Ocean systems engineering Vol.8 No.2
In case of conventional shallow-draft semisubmersibles, unacceptably large riser stroke was the restricting factor for dry-tree-riser-semisubmersible development. Many attempts to address this issue have focused on using larger draft and size with extra heave-damping plates, which results in a huge cost increase. The objective of this paper is to investigate an alternative solution by improving riser systems through the implementation of a magneto-rheological damper (MR Damper) so that it can be used with moderate-size/draft semisubmersibles. In this regard, MR-damper riser systems and connections are numerically modeled so that they can couple with hull-mooring time-domain simulations. The simulation results show that the moderate-size semisubmersible with MR damper system can be used with conventional dry-tree pneumatic tensioners by effectively reducing stroke-distance even in the most severe (1000-yr) storm environments. Furthermore, the damping level of the MR damper can be controlled to best fit target cases by changing input electric currents. The reduction in stroke allows smaller topside deck spacing, which in turn leads to smaller deck and hull. As the penalty of reducing riser stroke by MR damper, the force on the MR-damper can significantly be increased, which requires applying optimal electric currents.
진동현 센서 제작 공정 자동화를 위한 자동 장력 조절 및 접합 장치의 개발
고석조(Seok-Jo Go),박장식(Jang-Sik Park),유기호(Ki-Ho Yu),김성원(Seong-Won Kim),이승훈(Seung-Hoon Lee) 한국산업융합학회 2014 한국산업융합학회 논문집 Vol.17 No.2
Constructing structures is the basic process requiring establishment of grounds. However, cracks due to sinking and distorting ground influence directly on the safety of structural health. Vibrating wire sensor measures the crack of structure by detecting the differences of wire tensions in analogue manner. In the previous production process, the tension is adjusted manually measuring the frequency of vibrating wire. Therefore, the accuracy of a sensor was depends on the skill level of labor. In this study, the automatic tension control and fixing devise is developed to enhance both accuracy and productivity. To evaluate the performance of the vibrating wire sensor, the nonlinearity of sensor is measured. The automatic tension control and fixing devise enhances the nonlinearity of the sensor from 0.398 to 0.056%. Therefore, the accuracy of the newly proposed method is successful.