• Title/Summary/Keyword: Floating Architecture

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A Study on the Feedforward Control Algorithm for Dynamic Positioning System Using Ship Motion Prediction (선체운동 예측을 이용한 Dynamic Positioning System의 피드포워드 제어 알고리즘에 관한 연구)

  • Song, Soon-Seok;Kim, Sang-Hyun;Kim, Hee-Su;Jeon, Ma-Ro
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.22 no.1
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    • pp.129-137
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    • 2016
  • In the present study we verified performance of feed-forward control algorithm using short term prediction of ship motion information by taking advantage of developed numerical simulation model of FPSO motion. Up until now, various studies have been conducted about thrust control and allocation for dynamic positioning systems maintaining positions of ships or marine structures in diverse sea environmental conditions. In the existing studies, however, the dynamic positioning systems consist of only feedback control gains using a motion of vessel derived from environmental loads such as current, wind and wave. This study addresses dynamic positioning systems which have feedforward control gain derived from forecasted value of a motion of vessel occurred by current, wind and wave force. In this study, the future motion of vessel is forecasted via Brown's Exponential Smoothing after calculating the vessel motion via a selected mathematical model, and the control force for maintaining the position and heading angle of a vessel is decided by the feedback controller and the feedforward controller using PID theory and forecasted vessel motion respectively. For the allocation of thrusts, the Lagrange Multiplier Method is exploited. By constructing a simulation code for a dynamic positioning system of FPSO, the performance of feedforward control system which has feedback controller and feedforward controller was assessed. According to the result of this study, in case of using feedforward control system, it shows smaller maximum thrust power than using conventional feedback control system.

A Study on the Structural Reinforcement of the Modified Caisson Floating Dock (개조된 케이슨 플로팅 도크의 구조 보강에 대한 연구)

  • Kim, Hong-Jo;Seo, Kwang-Cheol;Park, Joo-Shin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.27 no.1
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    • pp.172-178
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    • 2021
  • In the ship repair market, interest in maintenance and repair is steadily increasing due to the reinforcement of prevention of environmental pollution caused by ships and the reinforcement of safety standards for ship structures. By reflecting this effect, the number of requests for repairs by foreign shipping companies increases to repair shipbuilders in the Southwest Sea. However, because most of the repair shipbuilders in the southwestern area are small and medium-sized companies, it is difficult to lead to the integrated synergy effect of the repair shipbuilding companies. Moreover, the infrastructure is not integrated; hence, using the infrastructure jointly is a challenge, which acts as an obstacle to the activation of the repair shipbuilding industry. Floating docks are indispensable to operating the repair shipbuilding business; in addition, most of them are operated through renovation/repair after importing aging caisson docks from overseas. However, their service life is more than 30 years; additionally, there is no structure inspection standard. Therefore, it is vulnerable to the safety field. In this study, the finite element analysis program of ANSYS was used to evaluate the structural safety of the modified caisson dock and obtain additional structural reinforcement schemes to solve the derived problems. For the floating docks, there are classification regulations; however, concerning structural strength, the regulations are insufficient, and the applicability is inferior. These insufficient evaluation areas were supplemented through a detailed structural FE-analysis. The reinforcement plan was decided by reinforcing the pontoon deck and reinforcement of the side tank, considering the characteristics of the repair shipyard condition. The final plan was selected to reinforce the side wing tank through the structural analysis of the decision; in addition, the actual structure was fabricated to reflect the reinforcement plan. Our results can be used as reference data for improving the structural strength of similar facilities; we believe that the optimal solution can be found quickly if this method is used during renovation/repair.

A Numerical Study on the Appendage Shape for a Heave Motion Reduction of Floating Cylindrical Structure (원통형 부유체의 heave운동 저감을 위한 부가물 형상에 관한 수치적 연구)

  • Lim, Geun-Nam;Kim, Sang-Hyun;Kim, Dong-Young
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.21 no.4
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    • pp.449-456
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    • 2015
  • In this paper, attaching various damping plates to the cylindrical structure and performing numerical simulations try to study heave RAO and natural period for cylinder. Most of all, we identified heave RAO of the cylinder by simulations of the motion and the wave. And then, we performed numerical simulations by changing the size and shape of heave damping plate attached to the cylinder and reviewed the heave RAO and natural period for each case. The conclusions of this research are as follows. Firstly, the natural period of cylindrical structure is increased by attached to the cylinder with heave damping plate and the heave RAO of cylindrical structure is reduced in the peak period for incident wave by attached to the cylinder with from the size of 1.30D for heave damping plate. Secondly, circular plate has long natural period than Y-type plate in all of these sections. Finally, the motion response spectrum considering the marine environment of Piranema field was identified as the heave motion of cylindrical structure is remarkably reduced with both circular plate and Y-type plate in the peak period for incident wave.

The Garden Drifts seen from Works by Gertrude Jekyll and Piet Oudolf (거투르트 지킬(Gertrude Jekyll)과 피에트 우돌프(Piet Oudolf)의 작품을 통해 본 정원의 드리프트 기법)

  • Park, Eun-Yeong
    • Journal of the Korean Institute of Traditional Landscape Architecture
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    • v.38 no.2
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    • pp.125-131
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    • 2020
  • In this study, the author comparatively analyzed the effects and applicability of drifts, one of planting design methods based on the principle of visual harmony, to look into the definition and characteristics in planing techniques with examples of drifts in gardens designed by Gerturde Jekyll and Piet Oudolf. Sites chosen for the case studies included Jekyll's Upton grey and Hestercomb garden and Oudolf's At Scampston Hall and Trentham Estate Garden. The results showed that Jekyll set layers for vertical and horizontal structures by using plants of different height to make flowers look like floating with their stems unseen and appear in turn over time. Assemble planting of groups was used to conceal rigid, irregular lines so that the plants are recognized as mass with smoother horizontal lines. Clearly visible, repeated drifts creates a sense of unity. Oudolf, in combining grass and perennial plants, used one-to-one correspondence or expansion to express drifts. Grass serves roles as a connecting material inserted when changing space or making transitions of images. Blocks in single species are repeatedly crossed to set scenes, and overlapping and mixing makes them more lively.

Study of seismic performance of super long-span partially earth-anchored cable-stayed bridges

  • Zhang, Xin-Jun;Yu, Cong;Zhao, Jun-Jie
    • Structural Engineering and Mechanics
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    • v.72 no.1
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    • pp.99-111
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    • 2019
  • To investigate the seismic performance of long-span partially earth-anchored cable-stayed bridge, a super long-span partially earth-anchored cable-stayed bridge scheme with main span of 1400m is taken as example, structural response of the bridge under E1 seismic action is investigated numerically by the multimode seismic response spectrum and time-history analysis, seismic behavior and also the effect of structural geometric nonlinearity on the seismic responses of super long-span partially earth-anchored cable-stayed bridges are revealed. The seismic responses are also compared to those of a fully self-anchored cable-stayed bridge with the same main span. The effects of structural parameters including the earth-anchored girder length, the girder width, the girder depth, the tower height to span ratio, the inclination of earth-anchored cables, the installation of auxiliary piers in the side spans and the connection between tower and girder on the seismic responses of partially ground-anchored cable-stayed bridges are investigated, and their reasonable values are also discussed in combination with static performance and structural stability. The results show that the horizontal seismic excitation produces significant seismic responses of the girder and tower, the seismic responses of the towers are greater than those of the girder, and thus the tower becomes the key structural member of seismic design, and more attentions should be paid to seismic design of these sections including the tower bottom, the tower and girder at the junction of tower and girder, the girder at the auxiliary piers in side spans; structural geometric nonlinearity has significant influence on the seismic responses of the bridge, and thus the nonlinear time history analysis is proposed to predict the seismic responses of super long-span partially earth-anchored cable-stayed bridges; as compared to the fully self-anchored cable-stayed bridge with the same main span, several stay cables in the side spans are changed to be earth-anchored, structural stiffness and natural frequency are both increased, the seismic responses of the towers and the longitudinal displacement of the girder are significantly reduced, structural seismic performance is improved, and therefore the partially earth-anchored cable-stayed bridge provides an ideal structural solution for super long-span cable-stayed bridges with kilometer-scale main span; under the case that the ratio of earth-anchored girder length to span is about 0.3, the wider and higher girder is employed, the tower height-to-span ratio is about 0.2, the larger inclination is set for the earth-anchored cables, 1 to 2 auxiliary piers are installed in each of the side spans and the fully floating system is employed, better overall structural performance is achieved for long-span partially earth-anchored cable-stayed bridges.

An Efficient Adaptive Loop Filter Design for HEVC Encoder (HEVC 부호화기를 위한 효율적인 적응적 루프 필터 설계)

  • Shin, Seung-yong;Park, Seung-yong;Ryoo, Kwang-ki
    • Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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    • 2014.10a
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    • pp.295-298
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    • 2014
  • In this paper, an efficient design of HEVC Adaptive Loop Filter(ALF) for filter coefficients estimation is proposed. The ALF performs Cholesky decomposition of $10{\times}10$ matrix iteratively to estimate filter coefficients. The Cholesky decomposition of the ALF consists of root and division operation which is difficult to implement in a hardware design because it needs to many computation rate and processing time due to floating-point unit operation of large values of the Maximum 30bit in a LCU($64{\times}64$). The proposed hardware architecture is implemented by designing a root operation based on Cholesky decomposition by using multiplexer, subtracter and comparator. In addition, The proposed hardware architecture of efficient and low computation rate is implemented by designing a pipeline architecture using characteristic operation steps of Cholesky decomposition. An implemented hardware is designed using Xilinx ISE 14.3 Vertex-6 XC6VCX240T FPGA device and can support a frame rate of 40 4K Ultra HD($4096{\times}2160$) frames per second at maximum operation frequency 150MHz.

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A Fundamental Study of VIV Fatigue Analysis Procedure for Dynamic Power Cables Subjected to Severely Sheared Currents (강한 전단 해류 환경에서 동적 전력케이블의 VIV 피로해석 절차에 관한 기초 연구)

  • Chunsik Shim;Min Suk Kim;Chulmin Kim;Yuho Rho;Jeabok Lee;Kwangsu Chea;Kangho Kim;Daseul Jeong
    • Journal of the Society of Naval Architects of Korea
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    • v.60 no.5
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    • pp.375-387
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    • 2023
  • The subsea power cables are increasingly important for harvesting renewable energies as we develop offshore wind farms located at a long distance from shore. Particularly, the continuous flexural motion of inter-array dynamic power cable of floating offshore wind turbine causes tremendous fatigue damages on the cable. As the subsea power cable consists of the helical structures with various components unlike a mooring line and a steel pipe riser, the fatigue analysis of the cables should be performed using special procedures that consider stick/slip phenomenon. This phenomenon occurs between inner helically wound components when they are tensioned or compressed by environmental loads and the floater motions. In particular, Vortex-induced vibration (VIV) can be generated by currents and have significant impacts on the fatigue life of the cable. In this study, the procedure for VIV fatigue analysis of the dynamic power cable has been established. Additionally, the respective roles of programs employed and required inputs and outputs are explained in detail. Demonstrations of case studies are provided under severely sheared currents to investigate the influences on amplitude variations of dynamic power cables caused by the excitation of high mode numbers. Finally, sensitivity studies have been performed to compare dynamic cable design parameters, specifically, structural damping ratio, higher order harmonics, and lift coefficients tables. In the future, one of the fundamental assumptions to assess the VIV response will be examined in detail, namely a narrow-banded Gaussian process derived from the VIV amplitudes. Although this approach is consistent with current industry standards, the level of consistency and the potential errors between the Gaussian process and the fatigue damage generated from deterministic time-domain results are to be confirmed to verify VIV fatigue analysis procedure for slender marine structures.

A Design of FFT/IFFT Core with R2SDF/R2SDC Hybrid Structure For Terrestrial DMB Modem (지상파 DMB 모뎀용 R2SDF/R2SDC 하이브리드 구조의 FFT/IFFT 코어 설계)

  • Lee Jin-Woo;Shin Kyung-Wook
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.42 no.11
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    • pp.33-40
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    • 2005
  • This paper describes a design of FFT/IFFT Core(FFT256/2k), which is an essential block in terrestrial DMB modem. It has four operation modes including 256/512/1024/2048-point FFT/IFFT in order to support the Eureka-147 transmission modes. The hybrid architecture, which is composed of R2SDF and R2SDC structure, reduces memory by $62\%$ compared to R2SDC structure, and the SQNR performance is improved by TS_CBFP(Two Step Convergent Block Floating Point). Timing simulation results show that it can operate up to 50MHz(a)2.5-V, resulting that a 2048-point FFT/IFFT can be computed in 41-us. The FFT256/2k core designed in Verilog-HDL has about 68,400 gates and 58,130 RAM. The average power consumption estimated using switching activity is about 113-mW, and the total average SQNR of over 50-dB is achieved. The functionality of the core was fully verified by FPGA implementation.

A Study on Safety and Performance Evaluation to Shaver Type Rope Cutter for Ships (선박용 Shaver Type 로프절단장치의 안전성 및 성능평가에 관한 연구)

  • Kang, Sung-Hoon;Ko, Jae-Yong
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.28 no.4
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    • pp.632-638
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    • 2022
  • As Korean coastal activity is high, the incidence of accidents caused by marine waste is extensive. An accident in which marine floating waste ropes and fishing nets are wound around the propeller of a sailing ship is termed "Rope wrapped accident." To prevent such accidents, this study applied the Finite Element Method (F.E.M.) for performance evaluation of the shaver type cutter, commercialized in Korea, through a structural safety review and water tank test. The results demonstrate that all parts constituting the rope cutter were damaged before reaching 0.5s, and the safety factor of each part was found to be at least 2 based on the maximum stress generated compared to the tensile strength. In the basin test, the cutting process of the shaver type rope cutter was reviewed, and the installation angle was set for each case considering that the rope floating in the sea actually enters at various angles. Consequently, as it was successful at cutting in all the cases, it can be concluded that there will be no problem in cutting the rope regardless of the mounted angle of the cutting blade.

Design and Analysis of a Mooring System for an Offshore Platform in the Concept Design Phase (해양플랜트 개념설계 단계에서의 계류계 초기 설계 및 해석)

  • Sungjun Jung;Byeongwon Park;Jaehwan Jung;Seunghoon Oh;Jongchun Park
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.29 no.2
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    • pp.248-253
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    • 2023
  • Most offshore platforms utilize chain mooring systems for position keeping. However, information regarding related design modification processes is scarce in literature. This study focuses on the floating liquefied natural gas (LNG) bunkering terminal (FLBT) as the target of shore platform and analyzes the corresponding initial mooring design and model tests via numerical simulations. Subsequently, based on the modified design conditions, a new mooring system design is proposed. Adjusting the main direction of the mooring line bundle according to the dominant environmental direction is found to significantly reduce the mooring design load. Even turret-moored offshore platforms are exposed to beam sea conditions, leading to high mooring tension due to motions in beam sea conditions. Collinear environmental conditions cannot be considered as design conditions. Mooring design loads occur under complex conditions of wind, waves, and currents in different environmental directions. Therefore, it is essential appropriately assign the roll damping coefficients during mooring analysis because the roll has a significant effect on mooring tension.