Experimental Research on Flow Induced Oscillations in Moonpool Encountered Through Waves

2007 ◽  
Author(s):  
Zhuang Kang ◽  
Xiongliang Yao ◽  
Sadiq Salman
Keyword(s):  
Wave Height ◽  
Experimental Research ◽  
Flow Condition ◽  
Frequency Ratio ◽  
Pressure Sensors ◽  
Breaking Waves ◽  
Green Water ◽  
Wave Condition ◽  
Time Period ◽  
Calm Water

Model experiments in this paper explains the response of the moonpool encountered through waves at different wave heights, time periods and attack angles, which reflect close to real situation at sea for ships equipped with moonpool. EMD method is used to have a meaningful data collected through hydrophone, pressure sensors, acceleration sensor and wave height meter. Results show that fluid natural oscillating frequency remains constant at 0.7 Hz in calm water with forward model speed condition (Fr = 0.26∼1.3), while by increasing the time period, wave height or both; it fluctuates between 0.6 Hz∼0.9 Hz. The fluid inside the moonpool faces internal sloshing, resulting in transverse breaking waves that are added to the vertical motions. Sloshing motion in the moonpool couples with the piston mode due to which results of calm water with forward speed, and combined waves and flow condition are quite different. Square shaped moonpool at different attack angles and circular shaped moonpool are also discussed for fluctuating pressure level (dB) at increasing time period and wave height. Moreover, Oscillation pressure results at only-wave condition and wave and flow condition together are represented by using frequency ratio between ‘oscillation pressure frequency’ and ‘sloshing natural frequency’ with varying ‘KC’ number. KC varies from 4.16 to 5.67 at 1-sec time period having frequency ratio f/fo of 1. Once time period increases to 2-sec, KC becomes around 22.69 at same frequency ratio. Dynamic magnification due to waves and flow combined situation may cause slamming on diving bells or ROV that are launched, green water over the edge of the moonpool which can be dangerous for the crew, or can increase drastically the resistance of the vessel in transit conditions therefore, this experimental research gives very important factors and results for designing moonpool; we believe that this paper has a significant contribution in the permanent literature.

scholarly journals LABORATORY STUDY OF SCALE EFFECTS IN TWO-DIMENSIONAL BEACH PROCESSES

2011 ◽  
Vol 1 (8) ◽  
pp. 14 ◽  
Author(s):  
Yuichi Iwagaki ◽  
Hideaki Noda
Keyword(s):  
Wave Height ◽  
Scale Effects ◽  
Breaking Waves ◽  
Two Dimensional ◽  
Sediment Size ◽  
Beach Processes ◽  
Time Period ◽  
Equilibrium Profile ◽  
Profile Changes ◽  
Constant Slope

In order to disclose the essential relationship between the beach processes and wave characteristics, two dimensional model tests are often performed for beach profile changes due to incident breaking waves normal to the beach. In applying the results of such experiments to the prototype of beaches, the scale effects of waves and sediments on the beach processes with equilibrium beach profiles should necessarily be considered. In this paper, as an approach to solve this problem in two dimensional beach studies, the effects of wave height and sediment size on the shore line movement and equilibrium beach profiles are discussed based on the results of experiments made by the authors and other experiments with smaller and larger scales by some researchers. It has been found that the ratio of wave height to sediment diameter is a very significant factor in this problem. In addition, the changes m a character of breaking waves during the time period of wave action from the beach having an initial constant slope to that with an equilibrium profile are presented.

Oscillations in Moonpool at Static Platform in Waves

2007 ◽  
Author(s):  
Sadiq Salman ◽  
Zhuang Kang ◽  
Xiong-Liang Yao
Keyword(s):  
Wave Height ◽  
Noise Level ◽  
Sound Level ◽  
Actual State ◽  
Offshore Platforms ◽  
Forward Speed ◽  
Structural Elements ◽  
Fluid Medium ◽  
Time Period ◽  
Calm Water

Most of the offshore platforms at sea are static and considered as rigid. This paper presents a series of towing tank experimental research to understand the wave and structure interaction for moonpool installed at static platform. It also gives a comparison of results between static platforms in waves and model moving in calm water with forward speed. Study comprised of circular and square shaped moonpool, while square shaped was further investigated for different attack angles varying from 0–45 degrees with an interval of 15°. Time period of incoming waves was increased from 1 s to 3 s with an interval of 1 s. To have a variety of situations to cater for the actual state at sea, wave height was also increased from 40 mm to 80 mm with an interval of 20 mm. For wave height and time period different combinations are presented to get variety of results. Results are given in terms of ‘dB’ for water oscillation pressure, which governs the water motions inside the moonpool, and for that matter it directly relates resonance in moonpool as the natural frequency of water inside the cavity does not change with a change in the velocity of incoming waves rather it is dependents upon the physical properties of the fluid medium, shape of cavity, size of cavity and the draught of water inside the cavity. With an increase in the time period of incoming waves, sound level ‘dB’ in terms of oscillation pressure frequency generated by the circular moonpool also increases. The same phenomenon is observed once the wave height is increased from 40–80 mm; except for one condition i.e., T = 3 s and λ = 80 mm. This shows that longer and higher waves may not always produce higher noise level for circular moonpools; this is not the case for square shaped moonpool. At increasing attack angles for square shaped moonpool, the acoustic level increases slightly for similar wave conditions. Furthermore, while comparing moving model in calm water with forward speed and static model at in coming waves; it was revealed that, square moonpool at different attack angles in calm water with forward speed condition, produces greater noise level once compared with waves-only condition. This phenomenon is unlike in circle moonpool. The results given in this paper are very important structural elements of the offshore platform during the design process.

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

2020 ◽  
pp. 34-42
Author(s):  
Thibault Chastel ◽  
Kevin Botten ◽  
Nathalie Durand ◽  
Nicole Goutal
Keyword(s):  
Drag Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Empirical Relationship ◽  
Breaking Waves ◽  
Irregular Waves ◽  
Geometrical Parameters ◽  
Flume Experiments ◽  
Seagrass Meadows ◽  
Artificial Vegetation

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.

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.

Distribution of Wave Impact Forces From Breaking and Non-Breaking Waves

2009 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu ◽  
Edward S. Ammeen
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Breaking Waves ◽  
Qualitative Assessment ◽  
Total Force ◽  
Impact Loads ◽  
Wave Impact ◽  
Data Set ◽  
Wave Characteristics ◽  
Wide Range

Impact loads from waves on vessels and coastal structures are highly complex and may involve wave breaking, making these changes difficult to estimate numerically or empirically. Results from previous experiments have shown a wide range of forces and pressures measured from breaking and non-breaking waves, with no clear trend between wave characteristics and the localized forces and pressures that they generate. In 2008, a canonical breaking wave impact data set was obtained at the Naval Surface Warfare Center, Carderock Division, by measuring the distribution of impact pressures of incident non-breaking and breaking waves on one face of a cube. The effects of wave height, wavelength, face orientation, face angle, and submergence depth were investigated. A limited number of runs were made at low forward speeds, ranging from about 0.5 to 2 knots (0.26 to 1.03 m/s). The measurement cube was outfitted with a removable instrumented plate measuring 1 ft2 (0.09 m2), and the wave heights tested ranged from 8–14 inches (20.3 to 35.6 cm). The instrumented plate had 9 slam panels of varying sizes made from polyvinyl chloride (PVC) and 11 pressure gages; this data was collected at 5 kHz to capture the dynamic response of the gages and panels and fully resolve the shapes of the impacts. A Kistler gage was used to measure the total force averaged over the cube face. A bottom mounted acoustic Doppler current profiler (ADCP) was used to obtain measurements of velocity through the water column to provide incoming velocity boundary conditions. A Light Detecting and Ranging (LiDAR) system was also used above the basin to obtain a surface mapping of the free surface over a distance of approximately 15 feet (4.6 m). Additional point measurements of the free surface were made using acoustic distance sensors. Standard and high-speed video cameras were used to capture a qualitative assessment of the impacts. Impact loads on the plate tend to increase with wave height, as well as with plate inclination toward incoming waves. Further trends of the pressures and forces with wave characteristics, cube orientation, draft and face angle are investigated and presented in this paper, and are also compared with previous test results.

scholarly journals Wave transformation around breakwater (case study: tourism harbour, Eastern Bali, Indonesia)

2021 ◽  
Vol 894 (1) ◽  
pp. 012028
Author(s):  
M N Arsyad ◽  
O Setyandito ◽  
L M Kesuma ◽  
H D Armono ◽  
M Anda ◽  
...  
Keyword(s):  
Wave Height ◽  
Wave Transformation ◽  
Wave Condition ◽  
The Past ◽  
Design Wave Height ◽  
Coastal Modeling ◽  
Before And After ◽  
Modeling Software

Abstract An essential aspect in the sustainable design of breakwater is the determination of the design wave condition. It is predicted by utilizing severe wave conditions of the past 10 to 20 years. The tourism harbor at eastern Bali, Indonesia, is located where extreme wave condition occurs. Therefore, this research studies the wave height before and after constructing a breakwater in the harbor area. The wave height was simulated using numerical modeling. The methodology was performed by using the coastal modeling software of the SMS-CGWAVE model. The result shows the highest design wave height value of 3.9 m in the direction from the southeast. The design breakwater can reduce wave height up to 0.9 m or a 75.5% reduction. Further study is needed to simulate the extension of breakwater length to meet the criterion design of wave height in the harbor basin.

scholarly journals Intention, Principle, Outputs and Aims of the Experimental Pavilion Research of Building Envelopes Including Windows for Wooden Buildings

2017 ◽  
Vol 13 (1) ◽  
pp. 42-51 ◽  
Author(s):  
Daniela Štaffenová ◽  
Ján Rybárik ◽  
Miroslav Jakubčík
Keyword(s):  
Experimental Research ◽  
Climatic Conditions ◽  
Point Of View ◽  
Physical Parameters ◽  
Data Sets ◽  
Data Set ◽  
Building Envelopes ◽  
Climate Conditions ◽  
Time Period

AbstractThe aim of experimental research in the area of exterior walls and windows suitable for wooden buildings was to build special pavilion laboratories. These laboratories are ideally isolated from the surrounding environment, airtight and controlled by the constant internal climate. The principle of experimental research is measuring and recording of required physical parameters (e.g. temperature or relative humidity). This is done in layers of experimental fragment sections in the direction from exterior to interior, as well as in critical places by stable interior and real exterior climatic conditions. The outputs are evaluations of experimental structures behaviour during the specified time period, possibly during the whole year by stable interior and real exterior boundary conditions. The main aim of this experimental research is processing of long-term measurements of experimental structures and the subsequent analysis. The next part of the research consists of collecting measurements obtained with assistance of the experimental detached weather station, analysis, evaluation for later setting up of reference data set for the research locality, from the point of view of its comparison to the data sets from Slovak Hydrometeorological Institute (SHMU) and to localities with similar climate conditions. Later on, the data sets could lead to recommendations for design of wooden buildings.

Wave Steepness and Relative Width: Influence on Transmission Coefficient of Horizontal Interlaced, Multilayered, Moored Floating Pipe Breakwater With Five Layers

2011 ◽  
Vol 45 (5) ◽  
pp. 20-27
Author(s):  
Sacchi Rajappa ◽  
Arkal Vittal Hegde ◽  
Subba Rao ◽  
Veena Channegowda
Keyword(s):  
Physical Model ◽  
Transmission Coefficient ◽  
Wave Height ◽  
Incident Wave ◽  
Wave Attenuation ◽  
Transmitted Wave ◽  
Relative Width ◽  
Wave Steepness ◽  
Transmission Characteristics ◽  
Time Period

AbstractThis paper presents the results of a series of physical model scale experiments conducted to determine the transmission characteristics of a horizontal interlaced, multilayered, moored floating pipe breakwater. The studies are conducted on physical breakwater models having five layers of PVC pipes. The wave steepness (Hi/gT2, where Hi is incident wave height, g is acceleration due to gravity, and T is time period) was varied between 0.063 and 0.849, relative width (W/L, where W is width of breakwater and L is the wavelength) was varied between 0.4 and 2.65, and relative spacing (S/D, where S is horizontal centre to centre spacing of pipes and D is the diameter of pipes) was set equal to 2. The transmitted wave height is measured, and the gathered data are analyzed by plotting nondimensional graphs depicting the variation of Kt (transmission coefficient) with Hi/gT2 for values of d/W (d is depth of water) and of Kt with W/L for values of Hi/d. It is observed that Kt decreases as Hi/gT2 increases for the range of d/W between 0.082 and 0.139. It is also observed that Kt decreases with an increase in W/L values for the range of Hi/d from 0.06 to 0.40. The maximum wave attenuation achieved with the present breakwater configuration is 78%.

Weather Window Analysis in Connection With Operation and Maintenance of Ocean Renewable Energy Devices

2016 ◽  
Author(s):  
Tomoki Taniguchi ◽  
Shigesuke Ishida ◽  
Toshifumi Fujiwara ◽  
Shunji Inoue
Keyword(s):  
Renewable Energy ◽  
Wave Height ◽  
Waiting Time ◽  
Wave Condition ◽  
Persistence Probability ◽  
Window Analysis ◽  
Operation And Maintenance ◽  
Japanese Coast ◽  
Ocean Renewable Energy ◽  
Operational Probability

There is an increasing need for utilization of ocean renewable energy (ORE) around Japanese coast because Japan is surrounded by ocean. Because technologies for harnessing ORE have not been mature enough, Japanese government selects some demonstration sites for ORE devices and some demonstration projects are going. As these projects are progressed, the operation and maintenance (O&M) activities will increase and become essential factors for the success of demonstration projects. Hence, weather window analysis is required to quantify the levels of access for ORE devices in the demonstration projects, and commercial projects in the future. In this paper, two new parameters are proposed in order to evaluate accessibility to ORE devices. One is the operational probability, and the other is the forecasted waiting time. The operational probability assesses weather duration with considering variability of wave condition. The forecasted waiting time is an expectation value of waiting time before O&M planners get next chance to arrange the O&M activities. In order to check the effectivity of the proposed 2 parameters, accessibility is evaluated for significant wave height in terms of the 2 proposed parameters, these are • Operational probability • Forecasted waiting time and 3 conventional parameters, these are • Excess probability • Persistence probability • Waiting time between windows The accessibility is evaluated at two locations along the Japanese coast. This study reveals that large differences are caused between persistence probability and operational probability when operational wave height limit occurs intermittently and required window length is long. The forecasted waiting time has the same variation tendency as the waiting time between windows.

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