Experimental Study on the Stability Performance and Turning Motion of Multi-Connection VAWT

2021 ◽  
Author(s):  
Saika Iwamatsu ◽  
Yasunori Nihei ◽  
Kazuhiro Iijima ◽  
Tomoki Ikoma ◽  
Tomoki Komori
Keyword(s):  
Scaling Law ◽  
Type A ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Water Tank ◽  
Type B ◽  
Floating Bodies ◽  
Stability Performance ◽  
Turning Motion ◽  
The Stability

Abstract In this study, a series of dedicated water tank tests were conducted in wind and waves to investigate the stability performance and turning motion of Floating Offshore Wind Turbine (FOWT) equipped with two vertical axis wind turbines (VAWT). The FOWT targeted in this study is called Multi-connection VAWT, which is a new type of FOWT moored by Single-Point-Mooring (SPM) system. We designed and manufactured two types of semi-submersible floating bodies. One is a type in which VAWTs are mounted in two places of a right-angled isosceles triangle (Type-A) on a single floater, and the other is two independent units equipped with VAWTs on two separate floaters centered on a moored body. This is a type in which two semi-submersible floating bodies are lined up in a straight line (Type-B). The experimental conditions were determined by scaling down to 1/100 using Froude’s scaling law based on a wind thrust load of 320 kN (rated wind speed of 12 m/s) assuming an actual machine. In the free yawing test in waves, Type-A turned downwards, while Type-B was barely affected by the waves. Furthermore, in the free yawing test in wind, both Type-A and Type-B turned leeward and stabilized at a final point where the wind load was balanced.

Feasibility Study of the Floating Axis Wind Turbine: Preliminary Model Experiments

2017 ◽  
Author(s):  
Hiromichi Akimoto ◽  
Kazuhiro Iijima ◽  
Yasuhiro Takata
Keyword(s):  
Wind Turbine ◽  
Feasibility Study ◽  
Vertical Axis ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Water Tank ◽  
Tank Model ◽  
Preliminary Model ◽  
Vertical Axis Turbine ◽  
The Stability

Floating Axis Wind Turbine is a concept of a floating vertical axis offshore wind turbine. In this design, a vertical axis turbine is directly mounted on a rotating spar buoy so that it does not require mechanical bearing supports of the heavy rotor. Multiple roller-generator units are on another small semi-sub float for extracting power from the rotating spar. A water tank model of 1/100 scale 5MW turbine and model power take-off units of about 1/20 scale are used for checking the concept. The results show the stability of the proposed turbine and demonstrates the function of roller-generator units.

scholarly journals Stability Analysis of the Floating Offshore Wind Turbine Support Structure of Cell Spar Type during its Installation

2019 ◽  
Vol 26 (4) ◽  
pp. 109-116
Author(s):  
Paweł Dymarski ◽  
Czesław Dymarski ◽  
Ewelina Ciba
Keyword(s):  
Stability Analysis ◽  
Wind Farms ◽  
Offshore Wind ◽  
Design And Technology ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Support Structure ◽  
Offshore Wind Farms ◽  
University Of Technology ◽  
The Stability

Abstract The article presents the results of selected works related to the wider subject of the research conducted at the Faculty of Ocean Engineering and Ship Technology of the Gdansk University of Technology, which concerns design and technology of construction, towing, and settlement on the seabed, or anchoring, of supporting structures for offshore wind farms. As a result of this research, several designs of this type of objects were developed, including two stationary types: gravitational and Jack-up, which are placed on the seabed, and two floating types: TLP and SPAR, anchored with tendons and anchors in the form of nailed or suction piles. Below presented is the stability analysis of the new floating CELL SPAR type support structure for offshore wind turbines during its installation in waters with a depth of over 65 m.

Weathervane Performance and Stability of Single Point Moored FOWTs Under Wind-Current Coexisting Field

2019 ◽  
Author(s):  
Sharath Srinivasamurthy ◽  
Kazuki Hashimoto ◽  
Kazuhiro Iijima ◽  
Yasunori Nihei
Keyword(s):  
High Speed ◽  
Single Point ◽  
Scaling Law ◽  
Water Tank ◽  
Scaled Model ◽  
Circulating Water ◽  
Osaka Prefecture ◽  
Unstable Oscillation ◽  
The Stability ◽  
Numerical Program

Abstract The objective of this study is to understand the weathervane performance and stability of FOWTs moored to SPM systems under wind and current coexisting field. Two types of FOWT systems, a semi-submersible and a spar (1/200 scale) are designed and manufactured based on Froude’s scaling law. A series of scaled model experiments are conducted and compared during wind-current coexisting field in a circulating water tank at Osaka Prefecture University, Osaka, Japan. Weathervane performance is evaluated under various conditions of wind and current. It is found during experiments that the weathervane performance of the SPM-FOWT systems is acceptable in rated wind and slow current condition. However, in the rated wind and high speed current condition, the weathervane performance is found to be not acceptable and unstable oscillation is observed. A numerical program is also developed to understand the behavior using the maneuvering equations. Further, attempts are made to understand the stability of SPM-FOWT systems based on Eigenvalue analysis.

scholarly journals Volumetric Changes in Morse Taper Connections After Implant Placement in Dense Bone. In-Vitro Study

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2306
Author(s):  
Georgios E. Romanos ◽  
Rafael Arcesio Delgado-Ruiz ◽  
Ana I. Nicolas-Silvente
Keyword(s):  
In Vitro Study ◽  
Type A ◽  
Step Length ◽  
Channel Length ◽  
Type B ◽  
Implant Abutment ◽  
Digital Microscope ◽  
Post Test ◽  
The Stability

The stability of the implant–abutment interface is crucial for the maintenance of the implant index integrity. Several factors are capable of inducing deformation in implant–abutment connection, such as the actual insertion of the implant into the bone. This study aimed to evaluate the deformations produced in the connection after the insertion of the implant. Ten implants with two different implant carriers (Type A: carrier attached to platform and Type B: carrier attached inside the index-connection) were placed in artificial Type II bone, and volumetric changes were evaluated for different connection features with a 3D digital microscope. ANOVA (analysis of variance), Wilcoxon, and Tukey HSD post-test were used for statistical comparisons. Type A implants presented deformation at the platform level (inner slot angles and slot width), but no volumetric changes were observed inside the connection. Type B implants presented deformation in three parameters inside the connection (outer channel length, coronal step width, and coronal step length). Within the limitations of this study, we can conclude that more deformation is expected at the internal connection when the implant carrier engages this area. The engagement area should be as far away as possible from the index connection.

Bidirectional Irrigation System to Treat a Difficult Wound: A Case Series

2020 ◽  
pp. 153473462097455
Author(s):  
Li-Yung Chen ◽  
Jin-De Hou ◽  
Chian-Ze Peng
Keyword(s):  
Healing Rate ◽  
Irrigation System ◽  
Recovery Period ◽  
Case Series ◽  
Type A ◽  
Type B ◽  
Wound Irrigation ◽  
Secondary Infections ◽  
Case Series Study ◽  
The Stability

Aims To date, there is no distinct principle determining whether to use irrigation under negative-pressure wound therapy (NPWT). We developed a new economical device to manage difficult wounds, employing 1 of 2 techniques depending on the wound condition. Methods This case series study was conducted in 12 patients with difficult wound, from 2017 to 2018. Four patients were treated with Type A bidirectional irrigation system (wound irrigation), while 8 patients were treated with Type B bidirectional irrigation system (wound irrigation combined with NPWT). Results In the Type A device group, inflammatory profiles in case I, case IV, and case VIII were not monitored due to the stability of their wound. The mean recovery period was 3.75 weeks (2-8 weeks), with decreases in 100% healing rate. In the Type B device group, we noted an average of 71% reduction in inflammatory profiles. All patients’ infections were resolved or were healing, and 7 patients recovered satisfactorily. The recovery period ranged from 4 to 17 weeks, with a median value of 7 weeks. Conclusion Bidirectional irrigation system decreases secondary infections and complications, and increases the healing rate in patients with difficult wound.

Experimental and Numerical Study of the Influence of Drag Coefficient on Snap Loads in Mooring Lines of a Floating Offshore Wind Turbine

2021 ◽  
Author(s):  
Brendan Guillouzouic ◽  
François Pétrié ◽  
Vincent Lafon ◽  
Fabien Fremont
Keyword(s):  
Numerical Simulations ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Scale Effects ◽  
Numerical Study ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Floating Bodies ◽  
Mooring Lines ◽  
Floating Offshore Wind Turbine

Abstract Mooring is one of the key components of a floating offshore wind turbine since the mooring rupture may lead to the total loss of one or even several turbines in a farm. Even if a large experience in moorings of floating bodies was gained in the oil & gas industry, the renewable energies face new challenges such as reducing the cost as much as possible, reducing the footprint to limit environmental impact or avoid any interference between mooring lines and electrical cables in a farm composed of several tens of turbines. Those constraints may lead to designs suffering snap loads which shall be avoided as far as practicable or addressed with a particular attention, as this quasi-instantaneous stretching of the mooring lines may lead to very high tensions governing the design. This paper presents the results of physical model tests and numerical simulations performed on a typical floating wind turbine concept of semi-submersible type. Both qualitative and quantitative comparisons are performed. The objective is to provide guidelines for FOWT mooring designers regarding the selection of the drag coefficient to consider. A very significant influence of the line’s drag coefficient, on both the probability of occurrence and the magnitude of snap loads, was found. This subject is hereby fully documented on a given case study and general discussions on scale effects, marine growth effects and other parameters are also made. The numerical simulations were performed using the dynamic analysis software ‘OrcaFlex’. The experiments have been carried out by Océanide, in south of France.

scholarly journals Centrifuge Modeling for the Evaluation of the Cyclic Behavior of Offshore Wind Turbine with Tripod Foundation

2021 ◽  
Vol 11 (4) ◽  
pp. 1718
Author(s):  
Yeong-Hoon Jeong ◽  
Seong-Won Lee ◽  
Jae-Hyun Kim
Keyword(s):  
Wind Turbine ◽  
Scaling Law ◽  
Centrifuge Modeling ◽  
Offshore Wind ◽  
Cyclic Behavior ◽  
Soil Conditions ◽  
Offshore Wind Turbine ◽  
Simple Method ◽  
Number Of Cycles

In this study, the cyclic responses of an offshore wind turbine with a tripod foundation installed on an actual site were evaluated in a centrifuge. To understand the behavior of the turbine at the site, the site soil conditions, environmental loads, and real offshore wind turbine structure installed at the actual site were modeled by considering the centrifuge scaling law. From a series of cyclic loading tests, the cyclic responses of the tripod foundation were evaluated in terms of temporary/permanent displacements and cyclic stiffness. Moreover, the long-term behavior of the tripod foundation was predicted from the experimental results. The test results showed that the initial stiffness of the soil–foundation system decreased as the loading amplitude increased and that the stiffness increased with the number of cycles due to soil densification. The findings revealed that the cyclic behaviors of the tripod were more affected by the load amplitude than the number of cycles. In addition, the permanent rotation increased logarithmically with the number of cycles. A simple method to predict the displacement and change in the foundation stiffness of the actual wind turbine is proposed based on the results of the model tests. The results of this study also provide key insights into the long-term cyclic behavior of tripod foundations for offshore wind turbines.

scholarly journals Seismic Fragility Assessment of a Novel Suction Bucket Foundation for Offshore Wind Turbine under Scour Condition

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 499
Author(s):  
Duc-Vu Ngo ◽  
Young-Jin Kim ◽  
Dong-Hyawn Kim
Keyword(s):  
Horizontal Displacement ◽  
Offshore Wind ◽  
Seismic Fragility ◽  
Offshore Wind Turbine ◽  
Environmental Condition ◽  
Offshore Wind Turbines ◽  
Displacement Capacity ◽  
Foundation Model ◽  
The Stability ◽  
External Loads

This study proposed a new suction bucket (SB) foundation model for offshore wind turbines (OWT) suitable for a shallow muddy seabed, using more than three single buckets through kinetic derivation. The performance of new optimal foundation was evaluated by its horizontal displacement capacity and compared with a conventional SB composed of three buckets. Under external loads such as earthquakes, wind, and the combination of the both, the stability of this novel SB foundation was verified. The seismic fragility curve was also evaluated at some scour depths. These results were compared with the response of a tripod suction bucket (TSB) foundation, which was also designed for a shallow muddy seabed. The results indicated that scour significantly changed the dynamic response of this novel SB foundation but it had a better bearing capacity than the TSB foundation, despite its smaller size and weight. The fragility of TSB is always higher than the developed foundation in the same environmental condition. With reasonable volume and size, this novel SB foundation has great potential for future industrialization and commercialization.

Development of a 10-MW Semisubmersible Type Floating Offshore Wind Turbine for the East Sea, Korea

2020 ◽  
Author(s):  
Hyeonjeong Ahn ◽  
Hyunkyoung Shin
Keyword(s):  
Renewable Energy ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Farm ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Mooring Lines ◽  
Floating Offshore Wind Turbines ◽  
Scale Ratio ◽  
The Stability

Abstract The area of renewable energy is expanding rapidly worldwide, with wind turbines being an example. In Korea, many researchers are conducting studies on floating offshore wind turbines (FOWTs) on areas with suitable wind resources. In particular, Ulsan, which is the site selected in this study, started research on the development of a 200-MW floating offshore wind farm. In this study, the references for upscaling are the 5-MW reference wind turbine of the National Renewable Energy Laboratory (NREL), and the OC4-DeepCwind semisubmersible type floating wind turbine. We upscaled the 5-MW wind turbine to a 10-MW FOWT by applying the appropriate scale ratio for each component of the turbine. We upscaled the specifications related to items such as the blades, hub, and nacelle using the power ratio. The mass of the blades was reduced by using carbon fiber-reinforced plastic (CFRP). We upscaled the specifications related to the tower using its deflection ratio, and the tower clearance criterion and the tower campbell diagram were used to confirm that the design is appropriate. We upscaled the specifications related to the platform using the upper structure mass ratio. The GZ curve of the platform was used to confirm the stability, and we used the air gap for safety. Three catenary type mooring lines were also designed. To understand the static response of the initial model of the 10-MW FOWT, a steady-state analysis was performed according to each wind speed. We followed the IEC and DNV standards, and we used NREL FAST in all simulations.

Comparison of Weathervane Performance Between Two Types of FOWT Systems Moored to SPM

2015 ◽  
Author(s):  
Kazuhiro Iijima ◽  
Yuiko Kuroda ◽  
Yasunori Nihei ◽  
Motohiko Murai
Keyword(s):  
Wind Wave ◽  
Single Point ◽  
Equations Of Motion ◽  
Offshore Wind ◽  
Design Parameters ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Turning Motion ◽  
Motion Performance ◽  
The Stability

This paper addresses the weathervane performance of Floating Offshore Wind Turbines (FOWTs) moored to single-point mooring (SPM) systems. A system of equations of motion to describe the motions in horizontal plane around the mooring point in the combined environmental conditions is derived. Wind, wave and current loads are considered. Two types of SPM-FOWT systems proposed by the present authors are considered for comparison. It is found out that the weathervane performance of the SPM-FOWT systems is acceptable in a point that the power generation efficiency does not reduce significantly. The stability is also checked based on the eigenvalue analysis for the linearized equations of motion around the equilibrium point. The stability and the responsivity are discussed in comparison between the two systems. Sensitivity of the stability and responsivity to design parameters such as length between the buoy and the main floater to the turning motion performance is discussed, too.

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