From Soft Mooring System to Active Positioning in Laboratory Experiments

2020 ◽  
Author(s):  
Thomas Sauder ◽  
Galin Tahchiev
Keyword(s):  
Laboratory Experiments ◽  
Low Frequency ◽  
Positioning System ◽  
Mooring System ◽  
Passive System ◽  
Active System ◽  
Floating Structures ◽  
Main Components

Abstract This paper presents an active positioning system aimed at replacing the classical “passive” soft horizontal mooring system used in seakeeping tests of floating structures. We discuss the limitations of the passive approach, present the main components of the active system, and demonstrate its ability to reproduce results obtained with the passive system. We then show how the active system allow controlling the low-frequency damping applied to the floater. We conclude on the possibilities offered by this apparatus.

Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation

2016 ◽  
Author(s):  
Shaowu Ou ◽  
Shixiao Fu ◽  
Wei Wei ◽  
Tao Peng ◽  
Xuefeng Wang
Keyword(s):  
Numerical Study ◽  
Low Frequency ◽  
Optimal Operation ◽  
Hydrodynamic Interactions ◽  
Irregular Waves ◽  
Mooring System ◽  
Time Varying ◽  
Body System ◽  
The Time Domain ◽  
Two Bodies

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.

Low Frequency Noise Annoyance Assessment by Low Frequency Noise Rating (LFNR) Curves

1983 ◽  
Vol 2 (1) ◽  
pp. 20-28 ◽  
Author(s):  
N. Broner ◽  
H.G. Leventhall
Keyword(s):  
Laboratory Experiments ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Noise Annoyance

Over recent years, it has become apparent that low frequency noise annoyance is more widespread than originally believed. Annoyance has occurred where the emitted noise is unbalanced towards the low frequencies even though the dB(A) level has been low. Following laboratory experiments carried out as part of an investigation into low frequency annoyance, combined with field annoyance data, the Low Frequency Noise Rating (LFNR) curves are proposed for the assessment of low frequency noise annoyance complaints.

scholarly journals The active dynamic vibration damper in non-stationary operation of a vibroactive unit

2021 ◽  
pp. 13-17
Author(s):  
D. V. Sitnikov ◽  
◽  
A. A. Burian ◽  
Keyword(s):  
Vibration Isolation ◽  
Low Frequency ◽  
Resonance Region ◽  
Frequency Region ◽  
Vibration Damper ◽  
Passive System ◽  
Isolation System ◽  
Vibration Isolation System ◽  
Dynamic Vibration ◽  
Impulse Characteristics

The paper considers a vibration isolation system, in which a force is applied to the moving mass of the active dynamic vibration damper by an actuator in proportion to the measured value of the base response. The amplitude-frequency and impulse characteristics are plotted depending on the parameters of the system, assuming the actuator without distortion generates the force proportional to the base response. It is shown that the considered vibration isolation system is quite effective in the low-frequency region, including in the resonance region of the passive system, both in stationary and nonstationary modes of vibroactive forces

Severe Accident Analysis for BWR With Containment Outer Pool

2012 ◽  
Author(s):  
Koki Yoshimura ◽  
Kohei Hisamochi
Keyword(s):  
Cooling System ◽  
Water Injection ◽  
Heat Removal ◽  
Severe Accident ◽  
Gas Temperature ◽  
Passive System ◽  
Active Components ◽  
Active System ◽  
Station Blackout ◽  
Materials Used

Newly designed plants, e.g., next-generation light water reactor or ESBWR, employ a passive containment cooling system and have an enhanced safety with RHRs (Residual Heat Removal system) including active components. Passive containment cooling systems have the advantage of a simple mechanism, while materials used for the systems are too large to employ these systems to existing plants. Combination of passive system and active system is considered to decrease amount of material for existing plants. In this study, alternatives of applying containment outer pool as a passive system have been developed for existing BWRs, and effects of outer pool on BDBA (Beyond Design Basis Accident) have been evaluated. For the evaluation of containment outer pool, it is assumed that there would be no on-site power at the loss of off-site power event, so called “SBO (Station BlackOut)”. Then, the core of this plant would be uncovered, heated up, and damaged. Finally, the reactor pressure vessel would be breached. Containment gas temperature reached the containment failure temperature criteria without water injection. With water injection, containment pressure reached the failure pressure criteria. With this situation, using outer pool is one of the candidates to mitigate the accident. Several case studies for the outer pool have been carried out considering several parts of containment surface area, which are PCV (Pressure Containment vessel) head, W/W (Wet Well), and PCV shell. As a result of these studies, the characteristics of each containment outer pool strategies have become clear. Cooling PCV head can protect it from over-temperature, although its effect is limited and W/W venting can not be delayed. Cooling suppression pool has an effect of pressure suppressing effect when RPV is intact. Cooling PCV shell has both effect of decreasing gas temperature and suppressing pressure.

Research on the Optimization of the Offset and the Power Consumption for a DP Assisted Mooring System

2013 ◽  
Author(s):  
Hongchao Wang ◽  
Lei Wang ◽  
Hanlin Liu
Keyword(s):  
Power Consumption ◽  
The Other ◽  
Engineering Practice ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Mooring System ◽  
Mooring Lines ◽  
Positioning Accuracy ◽  
Dynamic Positioning System ◽  
Two Measures

DP assisted mooring system is a new positioning system including mooring system and dynamic positioning system. In this paper, two measures are proposed to reduce the offset and the power consumption of a generic semi-submersible platform which is equipped with a DP assisted mooring system during operation. One is to tighten the windward mooring lines and slacken the leeward mooring lines, the other is to reduce or cancel the forbidden angles of the thrusters adjacent to the failed thrusters. Given that the two measures can both reduce the offset and the power consumption of the semi-submersible unit, it is suggested to combine the two measures together to obtain better positioning accuracy. This paper is helpful to engineering practice.

Zero-Energy Active Suspension System for Automobiles With Adaptive Sky-Hook Damping

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Kalpesh Singal ◽  
Rajesh Rajamani
Keyword(s):  
Active Suspension ◽  
Suspension System ◽  
Energy Management System ◽  
Zero Energy ◽  
Passive System ◽  
Active System ◽  
Active Suspensions ◽  
Resonant Frequencies ◽  
Active Systems ◽  
Automotive Suspension

Previous research has shown that a semiactive automotive suspension system can provide significant benefits compared to a passive suspension but cannot quite match the performance of a fully active system. The advantage of the semiactive system over an active system is that it consumes almost zero energy by utilizing a variable damper whose damping coefficient is changed in real time, while a fully active suspension consumes significant power for its operation. This paper explores a new zero-energy active suspension system that combines the advantages of semiactive and active suspensions by providing the performance of the active system at zero energy cost. Unlike a semiactive system in which the energy is always dissipated, the proposed system harvests and recycles energy to achieve active operation. An electrical motor-generator is used as the zero-energy actuator and a controller and energy management system are developed. An energy adaptive sky-hook gain is proposed to prevent the system from running out of energy, thereby eliminating the need to switch between passive and active systems. The results show that the system performs at least as well as a passive system for all frequencies, and is equivalent to an active system for a broad range of frequencies including both resonant frequencies.

Influence of Nonlinear Mooring Stiffness on Hydrodynamic Performance of Floating Bodies

2009 ◽  
Author(s):  
Huilong Ren ◽  
Jian Zhang ◽  
Guoqing Feng ◽  
Hui Li ◽  
Chenfeng Li
Keyword(s):  
Equilibrium Position ◽  
Equations Of Motion ◽  
Offshore Structures ◽  
Hydrodynamic Performance ◽  
Coupled Analysis ◽  
Mooring System ◽  
Main Function ◽  
Ocean Engineering ◽  
Mooring Lines ◽  
Floating Structures

Coupled dynamic analysis between floating marine structures and flexible members such as mooring lines and risers, is a challenging work in the ocean engineering field. Coupled analysis on mooring-buoy interactions has been paid more and more concern for recent years. For floating offshore structures at sea, the motions driven by environmental loads are inevitable. The movement of mooring lines occurs due to the excitation on the top by floating structures. Meanwhile the lines restrict the buoy’s motion by forces acting on the fareleads. Positioning is the main function of mooring system, its orientation effects can’t be ignored for floating structures such as semi-submersible, FPS, and TLP, especially when the buoy’s equilibrium position shifting to another place. Similar as hydrostatic restoring forces, mooring force related with the buoy’s displacement can be transformed into mooring stiffness and can be added in the differential equations of motion, which is calculated at its equilibrium point. For linear hydrodynamic analysis in frequency domain, any physical quantity should be linear or be linearized, however mooring stiffness is nonlinear in essence, so the tangent or differential stiffness is used. Steel chains are widely used in catenary mooring system. An explicit formulation of catenary mooring stiffness is derived in this article, which consists of coupled relations between horizontal and vertical mooring forces. The effects of changing stiffness due to the shift of equilibrium position on the buoy’s hydrodynamic performance are investigated.

FEASIBILITY STUDIES FOR THE IMPLEMENTATION OF NUCLEAR MAGNETIC RESONANCE IN A 25T HYBRID MAGNET

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3405-3405
Author(s):  
P. J. M. VAN BENTUM ◽  
J. C. MAAN ◽  
J. W. M. VAN OS ◽  
A. P. M. KENTGENS
Keyword(s):  
Magnetic Resonance ◽  
Power Supply ◽  
Reference Signal ◽  
Low Frequency ◽  
Feasibility Studies ◽  
Feedback System ◽  
Hybrid Magnet ◽  
Simultaneous Acquisition ◽  
Field Fluctuations ◽  
Main Components

As an exploratory study for NMR experiments in the future 20 MW Nijmegen high field magnet laboratory, the possibilities of field stabilization and field gradient compensation in a 25 T hybrid magnet in the present installation were evaluated. High frequency field fluctuations from the power supply can be compensated to better than 10-3 ppm in the 10 Hz-10 kHz range using a computer controlled feedback system. Field mapping by 2H magnetic resonance using a homebuilt device not only showed that there are substantial axial but also strong radial field gradients. It can be shown that for any cylindrical multicoil Bitter magnet the main components of these gradients can be compensated with simple ferromagnetic inserts. In this way we achieved a linewidth under 5 ppm in 1 mm3 without further shimming or optimization. The low frequency drift of the field due to instabilities of the present power supply and the effects of temperature fluctuations of the coil are determined by simultaneous acquisition of an in-situ deuterium reference signal together with the signal of interest. This allows for a full compensation of the field fluctuations by deconvolution techniques. We will report preliminary NMR results on solid27 Al samples in fields up to 25 T.

The Application of FPSO in Oil and Gas Exploitation

2012 ◽  
Vol 256-259 ◽  
pp. 1952-1955
Author(s):  
Ting Guo ◽  
Hong De Qin
Keyword(s):  
Oil And Gas ◽  
Single Point ◽  
Mooring System ◽  
Hydrodynamic Analysis ◽  
Comprehensive Review ◽  
Floating Structures ◽  
The World

The far-flung ocean has abundant resource and the exploitation area of ocean oil and gas is developing from offshore to deepwater and ultra-deepwater following the increase demand for oil and gas resource. Therefore, one of the floating structures for deepwater exploitation is FPSO. The yaw of FPSO is more important problem to solve. This paper use Hydrostar to compute the RAOs, 1st-order and 2nd-order force of FPSO. A comprehensive review is introduced about the research on FPSO hydrodynamic in the world, including the coupling hydrodynamic analysis of deepwater FPSO with the mooring system. The results indicate that the FPSO’s 1st-order force and moment is a little large, however, the RAOs and 2nd-order force and moment are good. The FPSO with single point mooring system can control the displacement of FPSO effectively.

scholarly journals Experimental and numerical studies of an eastward jet over topography

2001 ◽  
Vol 438 ◽  
pp. 129-157 ◽  
Author(s):  
YUDONG TIAN ◽  
ERIC R. WEEKS ◽  
KAYO IDE ◽  
J. S. URBACH ◽  
CHARLES N. BAROUD ◽  
...  
Keyword(s):  
Parameter Space ◽  
Laboratory Experiments ◽  
Multiple Equilibria ◽  
Low Frequency ◽  
Zonal Flow ◽  
Azimuthal Velocity ◽  
Flow Patterns ◽  
Initial State ◽  
Similar Frequency ◽  
Zonal Flows

Motivated by the phenomena of blocked and zonal flows in Earth's atmosphere, we conducted laboratory experiments and numerical simulations to study the dynamics of an eastward jet flowing over wavenumber-two topography. The laboratory experiments studied the dynamical behaviour of the flow in a barotropic rotating annulus as a function of the experimental Rossby and Ekman numbers. Two distinct flow patterns, resembling blocked and zonal flows in the atmosphere, were observed to persist for long time intervals.Earlier model studies had suggested that the atmosphere's normally upstream- propagating Rossby waves can resonantly lock to the underlying topography, and that this topographic resonance separates zonal from blocked flows. In the annulus, the zonal flows did indeed have super-resonant mean zonal velocities, while the blocked flows appear subresonant. Low-frequency variability, periodic or irregular, was present in the measured time series of azimuthal velocity in the blocked regime, with dominant periodicities in the range of 6–25 annulus rotations. Oscillations have also been detected in zonal states, with smaller amplitude and similar frequency. In addition, over a large region of parameter space the two flow states exhibited spontaneous, intermittent transitions from the one to the other.We numerically simulated the laboratory flow geometry in a quasi-geostrophic barotropic model over a similar range of parameters. Both flow regimes, blocked and zonal, were reproduced in the simulations, with similar spatial and temporal characteristics, including the low-frequency oscillations associated with the blocked flow. The blocked and zonal flow patterns are present over wide ranges of forcing, topographic height, and bottom friction. For a significant portion of parameter space, both model flows are stable. Depending on the initial state, either the blocked or the zonal flow is obtained and persists indefinitely, showing the existence of multiple equilibria.

Sign in / Sign up

Export Citation Format

Share Document