Turbulence Measurements from Compliant Moorings. Part I: Motion Characterization

2017 ◽  
Vol 34 (6) ◽  
pp. 1235-1247 ◽  
Author(s):  
Samuel Harding ◽  
Levi Kilcher ◽  
Jim Thomson
Keyword(s):  
Vertical Direction ◽  
Vertical Motion ◽  
Inertial Subrange ◽  
Motion Sensors ◽  
Similar Frequency ◽  
Dynamic Motion ◽  
Flow Speeds ◽  
Motion Characterization ◽  
Motion Characteristics ◽  
Vessel Motion

AbstractHigh-fidelity measurements of turbulence in the ocean have long been challenging to collect, in particular in the middle of the water column. In response, a measurement technique has been developed to deploy an acoustic Doppler velocimeter (ADV) to midwater locations on a compliant mooring. A variety of instrumentation platforms have been deployed as part of this work with a range of dynamic motion characteristics. The platforms discussed herein include the streamlined StableMoor buoy (SMB), the Tidal Turbulence Mooring (TTM) system based on a conventional 0.9-m spherical buoy, and a 100-lb sounding weight suspended from the stern of a research vessel. The ADV head motion is computed from inertial motion sensors integrated into an ADV, and the spectra of these signals are investigated to quantify the motion of each platform. The SMB with a single ADV head mounted on the nose provided the most stable platform for the measurement of tidal turbulence in the inertial subrange for flow speeds exceeding 1.0 m s−1. The modification of the SMB with a transverse wing configuration for multiple ADVs showed a similar frequency response to the nose configuration in the horizontal plane but with large contamination in the vertical direction as a result of platform roll. While the ADV motion on the TTM was significant in the horizontal directions, the vertical motion of this configuration was the most stable of all configurations tested. The sounding weight measurements showed the greatest motion at the ADV head but are likely to be influenced by both prop-wash and vessel motion.

A State of Art FPSO With Dry Tree System

2009 ◽  
Author(s):  
Chunqun Ji
Keyword(s):  
Environmental Conditions ◽  
Vertical Direction ◽  
Vertical Motion ◽  
Wide Range ◽  
Floating System ◽  
Motion Characteristics ◽  
Heave Motion ◽  
State Of Art

This paper provides a state of art dry tree floating system by using a moored column-buoy connected to a ship shaped vessel. The Buoy Moored Floating Production Storage and Offloading system (BMFPSO) uses a column-buoy instead of the turret in a conventional FPSO design. Similar to the turret, the column-buoy allows the vessel to weather vane about the column-buoy. In addition, the vessel can move in vertical direction relative to the column-buoy. Thus vertical motion of the column-buoy is de-coupled from the FPSO hull motion. The buoy will have relatively small heave motion allowing the use of proven top tensioned riser technology. The motion characteristics of the system make it operable in a wide range of environmental conditions.

The Heave Response of a Central Spar Fish Cage

2002 ◽  
Author(s):  
David W. Fredriksson ◽  
M. Robinson Swift ◽  
James D. Irish ◽  
Barbaros Celikkol
Keyword(s):  
Structural Integrity ◽  
Damping Ratio ◽  
Vertical Direction ◽  
Field Tests ◽  
Vertical Motion ◽  
Nonlinear Damping ◽  
Test Results ◽  
Natural Period ◽  
Reynolds Number Effects ◽  
Motion Characteristics

As the aquaculture industry considers moving into the open ocean, understanding the dynamic response of fish containment structures becomes critical. Identification of possible resonant conditions and motion characteristics is necessary for system structural integrity and maximizing fish survivability. In this study, heave (vertical motion) free release tests of a central spar fish cage were conducted using a combination of physical and finite element models and field observations. These tests were performed to investigate the added mass, damping ratio and natural period of the system in the vertical direction. The test results were analyzed considering both linear and nonlinear damping. The comparison of these tests show that (1) the damped natural period of this fish cage is longer than 20 seconds, (2) the numerical model underestimates the damping and the cage oscillates longer and at a higher frequency than observed with the field tests and (3) the physical model is nearly critically damped near equilibrium due to Reynolds number effects at the model scale.

The Heave Response of a Central Spar Fish Cage

2003 ◽  
Vol 125 (4) ◽  
pp. 242-248 ◽  
Author(s):  
David W. Fredriksson ◽  
James D. Irish ◽  
M. Robinson Swift ◽  
Barbaros Celikkol
Keyword(s):  
Structural Integrity ◽  
Vertical Direction ◽  
Field Tests ◽  
Vertical Motion ◽  
Nonlinear Damping ◽  
Test Results ◽  
Natural Period ◽  
Aquaculture Industry ◽  
Reynolds Number Effects ◽  
Motion Characteristics

As the aquaculture industry considers moving into the open ocean, understanding the dynamic response of fish containment structures becomes critical. Identification of possible resonant conditions and motion characteristics is necessary for system structural integrity and maximizing fish survivability. In this study, heave (vertical motion) free release tests of a central spar fish cage were conducted using a combination of physical and finite-element (FE) models and field observations. These tests were performed to investigate the added mass, damping and natural period characteristics of the system in the vertical direction. The test results were analyzed considering both linear and nonlinear damping. The comparison of these tests show that: the damped natural period of this fish cage is longer than 20 seconds; the numerical model underestimates the damping and the cage oscillates longer and at a higher frequency than observed with the field tests; and the physical model is nearly critically damped near equilibrium due to Reynolds number effects at the model scale.

Motion Characteristics of Composite-Type Sea Cage under Pure Wave

2012 ◽  
Vol 490-495 ◽  
pp. 3405-3409
Author(s):  
Chun Liu Li ◽  
Yun Peng Zhao
Keyword(s):  
Experimental Data ◽  
Wave Height ◽  
Vertical Motion ◽  
Data Acquisition System ◽  
Horizontal Motion ◽  
Wave Condition ◽  
Composite Type ◽  
Motion Range ◽  
Motion Characteristics ◽  
Sea Cage

To study motion range changes with wave condition and motion relationship between cages, physical model experiments were carried out. The authors designed 2 models of composite-type sea cages. Experimental data obtained by the CCD data acquisition system. The experiment results showed that 1.in the same period, horizontal motion range,vertical motion range and inclination changes of float collar increase with wave height; 2.In the same wave height, horizontal motion range of the float collar increases with period; 3.The laws between vertical motion and period are not obvious 4.The laws between inclination changes and period are not obvious 5.Motion range of the first cage along the direction of waves is less than other cages.

Combination Resonance of a Magnet Over a High-TC Superconductor Excited Vertically

2001 ◽  
Author(s):  
Toshihiko Sugiura ◽  
Masayuki Kondo
Keyword(s):  
Magnetic Force ◽  
Vertical Direction ◽  
Vertical Motion ◽  
Mirror Image ◽  
Image Method ◽  
Combination Resonance ◽  
Nonlinear Functions ◽  
High Tc ◽  
High Tc Superconductor ◽  
Oscillation Modes

Abstract This research deals with nonlinear dynamics of a permanent magnet freely levitated above a high-Tc superconductor (HTSC) excited in the vertical direction. Magnetic force and torque can be evaluated analytically by the advanced mirror image method as nonlinear functions of both displacement and roll angle of the magnet. Equations of 3 d.o.f. motion show that the magnet has two oscillation modes due to linear coupling of the horizontal and roll motions. The both modes can be excited by nonlinear coupling with vertical motion when the superconductor is exited vertically in the neighborhood of the sum of the natural frequency of each mode. Frequency response of this combination resonance was numerically simulated. This resonance was also observed in experiments.

An Investigation into the Motion Behaviour of a Wind Farm Mothership

2015 ◽  
Author(s):  
Blanca Peña ◽  
Erik P. ter Brake ◽  
Kyriakos Moschonas
Keyword(s):  
Numerical Simulations ◽  
Wind Farm ◽  
Wind Farms ◽  
Weather Conditions ◽  
Offshore Wind ◽  
Financial Benefit ◽  
Offshore Wind Farms ◽  
Motion Characteristics ◽  
Vessel Motion ◽  
Motion Behavior

A number of UK Round Three offshore wind farms are located relatively far from the coast making crew transfer to the sites time consuming, more prone to interruption by weather conditions and increasingly costly. In order to optimize the functionality of a permanent accommodation vessel, Houlder has developed a dedicated Accommodation and Maintenance Wind Farm vessel based on an oil & gas work-over vessel that has been successfully deployed for many years. The Accommodation and Maintenance (A&M) Wind Farm vessel is designed to provide an infield base for Marine Wind Farm operation. The A&M vessel is designed for high operability when it comes to crew access and performance of maintenance and repair of wind turbine components in its workshops. Also general comfort on board is of high regard. As such, the seakeeping behavior of the unit is of great importance. In this publication, the seakeeping behavior is presented on the basis of numerical simulations using 3D diffraction software. The first design iteration is driven by achieving high maneuverability and good motion characteristics for operational up-time and personnel comfort on board the vessel. Model test data of the original work-over vessel has been used to validate and calibrate the numerical simulations. On this basis, parametric studies can be performed to fine-tune a potential new hull form. In turn, this could reduce the number of required physical model tests providing a potential financial benefit and optimized delivery schedule. The vessel motion behavior was tested against the acceptability criteria and crew comfort guidelines of motion behavior for a North Sea environment.

Effect of different connection modes of electromagnets on the performance of levitation control

2018 ◽  
Vol 232 (8) ◽  
pp. 2111-2125 ◽  
Author(s):  
Zhang Min ◽  
Gao Chang ◽  
MA Weihua
Keyword(s):  
Vertical Direction ◽  
Vertical Motion ◽  
Vertical Displacement ◽  
Control Mode ◽  
Adjustment Process ◽  
Dynamic Adjustment ◽  
Series Connection ◽  
Relative Safety ◽  
The Mean ◽  
Mean Current

In medium- and low-speed maglev vehicles, each levitation module contains four electromagnetic coils. In order to find a better coil control mode, the difference between the series connection in the control mode of the first and third coils (M1,3) and the series connection in the control mode of the first and second coils (M1,2) was analysed in this paper. By applying a malposition excitation of +2 mm in the vertical direction of the track for comparing the dynamic adjustment processes of the levitation module (including the vertical motion and rotation) in the two control modes, according to the current fluctuation in the coils in the above processes, the extreme position parameters and the mean current values during the adjustment were obtained. The adjustment process was analysed based on the instantaneous levitation force and the torque of the plate at the extreme positions in different control modes; the performance of the levitation module in the adjustment process and during the fluctuation of the coil current was analysed. The results indicate that for the dangerous ends at the two extreme positions in the selected working condition, the vertical displacement in M1,3 reduces by 11.11 and 48.98%, respectively, compared with that in M1,2. In the whole adjustment process, the mean current of the front and rear controllers in M1,3 reduces by 0.25 and 0.36 A, respectively. Therefore, it has been concluded that with regard to the relative safety and coil heating during vibration of the levitation module, M1,3 performs better than M1,2.

Loess Slope Stability Analysis under the Action of Seismic Forces

2014 ◽  
Vol 501-504 ◽  
pp. 1623-1627
Author(s):  
Da Wei Lv ◽  
Fei Wang ◽  
Guan Jun Xu
Keyword(s):  
Stability Analysis ◽  
Slope Stability ◽  
Comparative Study ◽  
Random Quantity ◽  
Mean Square ◽  
Dynamic Motion ◽  
Sine Curve ◽  
Loess Slope ◽  
Motion Characteristics ◽  
Seismic Forces

Considering that during the earthquake, the maximum peak of acceleration changing in the process is a random quantity, which cant be regarded as a sign of dynamic motion characteristics. Therefore, in this paper, the root mean square acceleration is employed to calculate the corresponding seismic forces. Then according to the sine curve, seismic forces are loaded on the different layers of slope of loess slope. Giving a comparative study on the safety of the loess slope under the force of the earthquake provides reference for the design of loess slope against earthquake.

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