1 Introduction

Wind energy is one of the most reliable energy alternatives for countries that have sufficiently large wind sources.Given the presence of steady and strong winds, as well as a location beyond viewing range from the coastline, offshore wind farms have become highly attractive energy crisis solutions. Floating wind turbine systems are being considered as the key concept that makes offshore wind farms feasible from an economic viewpoint and viable as an energy resource (Berteaux, 1991). This study presents the design process of a floating offshore wind turbine buoy (similar to that shown in Fig.1).

One of the immediate challenges that applies to all support structure designs is the ability to predict loads and resulting dynamic responses of the coupled wind turbine and platform system to combined stochastic wave and wind loading (Flocard and Finnigan, 2010). In the offshore environment, additional load sources pose new and difficult challenges for wind turbine analysts. Fig.2 illustrates the range of different loading sources and additional degrees of freedom needed to model floating platforms (Muliawan et al., 2013; Turmelle and Chad, 2009).The present study will focus on buoy angle changes due to wind loads on the turbine and buoy dynamics in response to wave excitation (Jonkman et al., 2009; Utsunomiya et al., 1996). Onshore wind turbines are often placed on vast wind farms, thereby taking up large amounts of usable land. Wind flow is disrupted by large cities and land formations, thereby resulting in a turbulent wind flow. New wind farms also often face opposition from nearby residents because they interrupt the natural views of the surrounding land (Müller et al., 2014).

Fig.1 Statoil hydro model.

Wind turbines affect fishing and tourism when they are installed close to the shore. Thus, wind turbines should be installed a good distance from the coast. Installing wind turbines far from the coast is a costly endeavor, especially because the turbine body should be installed on the sea floor. However, wind energy on the open sea increases the farther one moves away from the shore. The cost, tourism,fishing, and wind potential are considered in designing new-generation buoys that can balance on the ocean surface far from the shore. Two types of buoy designs have been studied. This project aimed to design a buoy to support a 10 kW wind turbine and its tower. The buoy must be capable of surviving hurricane conditions, including 9 m waves and 50 cm s−1 currents. It will be moored in 52 m of water at an existing test site. In the upcoming years, a full-scale prototype may be constructed and deployed at the University of New Hampshire’s (UNH) Center of Ocean Renewable Energy (CORE) testing site at the Isles of Shoals off the coast of Portsmouth, NH, as shown in Fig.3. Before a prototype can be manufactured, the buoy must be modeled and tested in the UNH wave/tow tank.

第二次施测获得有效被试300名，平均年龄为33.17岁，SD=8.27岁，Range=17～68岁，其中男性133名，女性167名，用于BA量表的验证性因素分析。其中有子女的172名被试被用于PDCA量表的验证性因素分析，被试平均年龄为37.35岁，SD=6.97岁，Range=25～68岁，男性78名，女性94名。

Fig.2 Offshore turbine loading sources.

Fig.3 Map of UNH campus and test sites.

2 Design

The goal of this project was to design a buoy to support a 10 kW turbine. Several criteria must be accounted for during the design process. The buoy must withstand 9 m high waves and hurricane winds that may exceed 70 km h−1. The buoy inclination angle during steady storm winds must not exceed 5˚. Once the design criteria of buoy vertical (heave) and angular (pitch) motion were minimized over the range of wave frequencies expected at the CORE site set, the design process began with buoy type selection.The two major buoy designs are the spar-type design and the wave follower design. The left side of Fig.4 shows a spar buoy with a catenary mooring system, and the right side shows a barge or wave follower buoy (Azcona et al.,2014).

The selected buoy type for our design was a spar buoy with catenary drag embedded mooring. The advantage of the spar design over the wave follower buoy is the drastically smaller waterplane area, which is the cross-sectional area of the buoy at the waterline. As the waterplane area decreases, so does the expected excitation of the buoy.With this knowledge, two spar buoys were designed to compare different aspects of geometry and their relationship to wave excitation and wind force (Martin et al.,2012).

Fig.4 Floating turbine concepts (Ravi and Krishna, 2012).

2.1 Two Spar Buoy Designs

5.3.4 Wave response theory

1.4 统计学分析 本研究采用SPSS 19.0统计软件进行统计，计量资料用表示，采用t检验；计数资料用例(%)表示，组间比较采用χ2检验，P<0.05差异具有统计学意义。

Design 1 consists of a hub, tower, spar, free pipe, and ballast (Fig.5). Its dimensions are given in Table 1. The spar-type buoy is 19 m above the waterline in draft (from the water line to the top of the tower) and has circular sections with a diameter of 4 m at the upper part, 1 m at the middle part, and 2.5 m at the lower part. The lower part is made of concrete and filled with ballast concrete,while the upper part and the tower are made of steel.

Turmelle found that a typical chain for this full-scale application is a 90-foot portion of a 1 in steel stud link chain (Turmelle and Chad, 2009). The full-scale specification was Froude-scaled using the 1/21.31 employed in this study. This chain portion was scaled to 50.7 in. A chain with the appropriate length-to-weight ratio could not be found. Thus, small lead sheet squares were attached to the chain until the desired weight was reached.The full-scale line used in this application was a 525.7 in long and 2 in thick Spectra ™ line. The line used in the model had no elastic properties. Thus, the line was cut in half and connected by a 20 in rubber section to simulate the full-scale elasticity. A 25-pound lead weight was used to model the full-scale plow embedment anchor. The weight was sufficiently heavy, thereby allowing it to remain stationary during dynamic wave testing. A picture of the modeled mooring system is shown in Fig.9.

Design 2 consists of a hub, tower, shaft, spar, free pipe,and ballast (Fig.6). Its dimensions are given in Table 2.The overall height is 33.5 m. The spar-type buoy is 14.4 m above the waterline in draft (from the water line to the top of the tower (Fig.6)) and has circular sections with a diameter of 2 m at the upper part, 3 m at the middle part,and 4 m at the lower part. Unlike the spar in the first design, the spar in this design is under the water level. The lower part is made of concrete and filled with ballast concrete, while the upper part and the tower are made of steel.

Fig.5 Design 1 with labeled components.

Fig.6 Design 2 with labeled components.

Table 1 Dimensions of Design 1

No. Name Height (m) Outer diameter (m) Inner diameter (m) Mass (kg) VCG (m)1 Spar Cap-1 0.01 4 – 939.6 23.040 2 Spar 6 4 2.9746 7375.3 20.035 3 Spar Cap-2 0.01 4 – 939.6 17.030 4 Spar Gusset 1.635 1.5 0.0127 978.0 16.53 5 Free Pipe 12 1 0.9746 3339.6 11.025 6 Hole – 0.49 – – –7 Ballast Gusset 1.635 0.75 0.0127 489.0 5.570 8 Ballast Cap-1 0.01 2.5 – 498.4 5.019 9 Ballast 5 2.5 – 60935.6 2.513 10 Ballast cap-2 0.01 2.5 – 489.4 0.006

Table 2 Dimensions of Design 2

No. Name Height (m) Outer diameter (m) Inner diameter (m) Mass (kg) VCG (m)1 Upper Spar Cap 0.0127 2 – 313.2 21.557 2 Upper Spar 10 2 1.9746 6224.2 16.551 3 Upper Spar Gusset 1.25 0.5 0.0127 (thickness) 124.6 11.967 4 Lower Spar Cap-1 0.0127 3 – 704.7 11.544 5 Lower Spar 5 3 2.9746 4678.1 9.038 6 Lower Spar Cap-2 0.0127 3 – 704.7 6.532 7 Lower Spar Gusset 1.25 1 0.0127 (thickness) 249.23 6.109 8 Free Flooding Pipe 5 1 0.9746 1391.5 4.025 9 Hole – 0.444 – – –10 Ballast Gusset 1.25 1.5 0.0127 (thickness) 373.9 1.942 11 Ballast Cap-1 0.0127 4 – 1252.8 1.519 12 Ballast 1.5 4 – 44839.4 0.763 13 Ballast Cap-2 0.0127 4 – 1252.8 0.0064

2.2 Hydrostatic Calculations

Both buoys were cylindrical in shape; therefore, most calculations were based on formulas for circular areas and moments of inertia. Each spar was designed as a steel pipe with 0.5 in thick walls. At either end of the open pipe,0.5 in caps would be welded to make the pipe air tight. A series of calculations was completed for each component of the buoy (Roddier et al., 2010). With a selected height,exterior diameter, and thickness of each component, the interior and exterior cross-sectional area was calculated.Interior and exterior volumes were then calculated by multiplying the height by the calculated areas. Two volumes were subtracted, thereby obtaining the material volume for each section as follows:

Mass was then calculated by multiplying the density of steel by the material volume for each component. The only exception was the concrete section of the ballast,which was multiplied by the density of concrete instead of steel Eq. (2). Thus,

where ρ is the material density, and ΔV is the component material volume. The vertical center of gravity was found for each component and was used to find the center of mass (COM) and the center of buoyancy (COB) for the entire design (Luan et al., 2014). The vertical center of gravity for each component is denoted by VCGc (Eqs. (3),(4) and (5)),

(1)政府方面。农村健康教育是不容忽视的,是中国健康教育最基本的特色,是符合中国国情的,积极发挥政府职能,探索将健康教育纳入公共卫生、医疗保险统筹报销范围;完善相关制度,增强农村留守老人关爱工作。

为了验证H1和H2，我们使用经过处理的90956个项目数据，进行主成分分析，试图从存储库数据中直接得出影响项目的因素，并通过回归拟合处理分析验证主成分的软件工程实践意义.由于Github社区通常用Star数作为衡量项目流行度的度量元，而流行度从某种程度上代表了用户参与项目的程度，因此，先不包含star进行主成分分析，总方差解释结果如表2所示.

The vertical mass moment is thus

while the vertical volume moment is

The sum of the vertical mass moments and the vertical COM was then divided by the total mass of the buoy to find its COM. The sum of the vertical volume moments was divided by the total submerged volume to find the COB (Eqs. (6) and (7)). Thus,

The next calculation was the buoyancy force caused by complete submergence of the buoy. This force was calculated using Eq. (8)

临床上，胃癌属于是一种具有高发病率的恶性肿瘤类疾病，在消化道肿瘤中占据首位，特别是在近几年当中，随着生活环境与生活习惯的转变，人们罹患胃癌的风险显著增加[1] 。而早期的正确诊治则是提高胃癌患者生存质量以及改善预后的关键，所以，临床医师有必要为早期胃癌患者寻找一种可行性更高的诊治手段。目前，放射检查在我国临床上有着非常广泛的应用，具有操作简便以及诊断结果可靠等特点，此研究，笔者将着重分析早期胃癌应用放射临床诊断方法的效果，总结如下。

The weight force in Newton was calculated using Eq.(9)

运动控制系统一般在三年级下学期或四年级上学期开设，此时学生的专业基础课和专业课已基本学完，然而在各门课程的知识理解和灵活运用上，相当一部分学生还有待提高，这就给学生学习该课程带来困难。随着课程进度的深入，一些学生会感觉跟不上课程的节奏，出现掉队的现象，教师不得不在运动控制系统课程的课堂上重新复习以上专业基础课程中的相关知识，在授课学时受限的情况下影响课程教学进度，很多与课程内容相关的前沿知识和扩展知识无法进行补充。课程内容经典但略显陈旧，没能完全调动起学生的内在主动性和学习积极性。因此需要对理论教学进行改革，课程群的概念应运而生。通过四届学生的教学实践，取得较好的效果，学生和教师反映也不错。

The difference between this buoyancy and weight force is considered the weight required to fully submerge the buoy or reserve buoyancy Eq. (10)

The test tank of the Ocean Engineering Department was used for the construction of the experimental setup and the construction of the tests. I am very grateful to University of New Hampshire for their support.

一要进一步加大民族政策法律法规宣传教育。将党和政府的民族政策和法律法规培训纳入公务员入职培训和窗口服务行业专业知识培训，特别是要对行政执法部门、公共管理部门以及各区县中青年干部加强党的民族政策和法律法规、工作方式方法等专业培训，让其了解和掌握民族知识和民族政策，提高其对做好城市少数民族流动人口服务工作重要性的认识，提高其做好少数民族流动人口服务的能力和水平，拓宽为少数民族外来人口服务的渠道。

To calculate the tipping caused by wind force, the metacentric height must be found. This value is the sum of the distance between the COB and COM and the area moment of inertia, Ι, over the submerged volume. Thus,metacentric height is

The area moment of inertia for the waterplane area was calculated by

where Do is the outer diameter of the spar at the waterline.Upsetting moments due to turbine drag forces of 3 and 10 kN are provided in Tables 3 and 4 for each design. Upsetting moment is the force acting on the turbine blades times the height of the turbine hub relative to mooring collection so that

ΣH will change as the mooring location changes. When the mooring is attached at the bottom of the ballast, ΣH will be the total height of the entire structure and referred to as the worst case (Fig.7). If the mooring is attached at the waterline, then ΣH will be equal to the tower height plus the freeboard. The tipping angle (Fig.7) can then be found by Eq. (15), and results are given in Tables 3 and 4.The restoring moment induced by the vertical component of the mooring is neglected. In all cases, the tipping angle is less than the design criteria of 5˚ (Karimirad and Michailides, 2015).

BIM技术的应用实现了对整个施工过程的空间、时间和资源的动态统一管理，提高了施工生产效率，降低了能耗，有效促进了绿色施工。施工场地基坑平面布置如图2所示。

Table 3 Design-1 tipping angles due to steady storm force winds on turbine

Design #1 Worse case Midpoint Waterline Worse case Midpoint Waterline Force (N) 3000 3000 3000 10000 10000 10000 Upsetting Moment (kN) 124633 93116 55500 415444 310386 185000 GM (m) 11.54 11.54 11.54 11.54 11.54 11.54 Theta (degrees) 0.823 0.615 0.316 2.743 2.049 1.22

Table 4 Design-2 tipping angles due to steady storm force winds on turbine

Design #2 Worse case Midpoint Waterline Worse case Midpoint Waterline Force (N) 3000 3000 3000 10000 10000 10000 Upsetting Moment (kN) 97580 76873 56166 340635 268351 196068 GM (m) 6.17 6.17 6.17 6.17 6.17 6.17 Theta (degrees) 1.404 1.1 0.808 4.910 3.86 2.82

Fig.7 Angle of inclination (Soulard et al., 2009).

3 Physical Models (Froude Scaling)

Once the full-scale designs were completed, the models were designed for testing. Using the actual ocean depth of 52 m and the UNH tow tank depth of 2.44 m to establish the scale ratio, Froude scaling was applied to scale down the full-scale design so the model could be tested in the UNH wave/tow tank. Matching Froude numbers at full and model scale requires Eq. (16)

where Fr is the Froude number, U is the characteristic velocity, and d is the characteristic length. The test site and the tank are at depths of 52 and 2.44 m, respectively.Thus, (dfs/dm) was 21.31. With this ratio, the model weight and height of each component of the buoy could be calculated (Fig.8). The total height of Design 1 was 76.7 in with a total weight of 17.5 lbs, and the total height of Design 2 was 62.93 in with a total weight of 14.97 lbs.Finally, Moment = Force * Distance that equation is used(Mahmuddin, 2013).

Fig.8 Design-1 and Design-2 Froude-Scaled Physical Models.

4 Mooring Model

2.1.2 Design 2

Fig.9 Mooring System Model.

5 Dynamic Testing and Analysis

5.1 Experimental Approach

Free-release and wave response testing were performed on each scale model in the UNH wave/tow tank to determine specific characteristics and behaviors of each design.In both cases, buoy position and angle were determined optically using the Optical Positioning Instrumentation and Evaluation System (OPIE) system described in the next section. Free-release testing was conducted by displacing each model from its equilibrium state and observing the time response motion due to the displacement.For heave testing, the model was displaced vertically and released from rest. For pitch testing, the model was rotated slightly and released from rest. The model then oscillated about the equilibrium position; vertical motion was applied for heave testing, and angular motion was used for pitch testing. Plotting these oscillations can obtain the damped natural period and frequencies for each model. Parameters such as total mass and damping ratios can also be inferred by applying a theoretical model for heave motion. For wave testing, the model was held using a single-leg catenary mooring and subjected to a series of single frequency waves. Time series for heave (vertical)motion and pitch (angular) motion were recorded. The response amplitudes is then was normalized by dividing by wave amplitude to find response amplitude operators(RAOs) as a function of frequency. With the use of parameter values from the heave free-release tests, a theoretical model for heave RAO was applied to each buoy model.

5.2 Optical Positioning Instrumentation and Evaluation Software

Motion data from the model were acquired using the OPIE. It is an external, non-invasive measuring system that uses a black-and-white digital camera to follow up to two designated black dots fixed on the buoy on the basis of the contrast between light and dark pixels. This camera was placed perpendicular to the buoy during testing. The digital camera captures frames of the test at 30 Hz and transmits the images to the computer. The OPIE software,which is written in MATLAB, tracks the position of the dark pixels through time. From the dot position, the velocity and acceleration in both vertical and horizontal directions were calculated. If two dots are placed along the axis of the buoy, then pitch angle (angle from the vertical), angular velocity, and angular acceleration can be calculated as well (Murray and Rastegar, 2009).

在确定建筑场地后，应研究气候特征。根据建筑的功能要求，通过合理的外部环境设计，改善气候环境，营造良好的建筑节能环境。同时，可以通过增加建筑物周围的树木和植被的布置来有效地净化空气、屏蔽风沙、遮蔽阳光、减少噪声；同时可以在建筑物附近创造一个人工湖，用来收集雨水和平衡周边环境的湿度。

5.3 Free-Release

5.3.1 Free-release theory

Free-release testing was conducted by displacing each model from its equilibrium position, releasing from rest,and observing the time response motion. For heave testing, the model was displaced vertically and released from rest. For pitch testing, the model was rotated slightly and released from rest (Takagi et al., 2002). The model then oscillated about the equilibrium position; vertical motion was applied for heave testing, and angular motion was applied for pitch testing. Plotting these oscillations can obtain the damped natural period. For example, the time interval between successive upward zero crossings could be used. To infer other parameters, a theoretical model for heave is useful. For the case of no waves and linear direction, Eq. (17) can be used

where mt is the total mass =m+ma, ma= added mass, x is the vertical displacement, b is the linear damping constant,and S is the cross section area. This equation may take the standard damped harmonic oscillator form

using where ω0 is the undamped natural frequency, and ζ is the damping ratio. If the buoy is released from rest at height A, then the solution for vertical displacement is

思维警示：用原子守恒法解题时，脱水缩合所脱去的水中H和O的个数很容易被忽略，即H、O守恒的方程式很容易出错。

where=tan−1and Td is the damped natural period. Applying the solution at two times Td apart and forming the ratio obtains

The theory may be used to measure the time series by obtaining Td and Rmeasured directly from the measurements and using Eq. (20) andto calculate ω0 and ζ. Once these (ω0 and ζ) are known, total mass mt and damping parameter b may be found using the above definitions.

A: Area (m2)

A set of at least four free-release tests were performed for each model to find an average response. Tests were conducted in the UNH wave/tow tank with the buoy in the window on the side of the tank to allow OPIE’s camera to capture the movement. The OPIE capture sequence was started a few moments before displacement to obtain the initial position at equilibrium. To displace the models for heave testing, they were pushed vertically into the water less than 2 in and released. Pitch testing was performed by displacing the models by an angle less than 15˚,and then they were released.

5.3.3 Free-release results

As previously stated in the criteria, the design should survive hurricane force winds (Bhattacharya and Bhattacharjee, 2010). The maximum acceptable tipping angle for the design was set at 5˚. To find the force that would be acting on the turbine blades, a calculation was performed to scale up the forces applied in a previous study.In the experiment by Turmelle (2009), the steady horizontal force that acted on the model was 29.4 N. Froude scaling was used to find the force that acted on the fullscale model by multiplying the 29.4 N force by the scale factor cubed. This force was then multiplied by the ratio of the blade diameters squared. The resultant 2865 N force would act on the 10 kW turbine blades. To account for a worst-case scenario and incorporate a safety factor greater than 3, a force of 10 kN was used in tipping angle calculations.

Data collected from OPIE during free-release testing was imported into MATLAB® in the form of arrays. For the heave test data, the vertical movement of the buoys was plotted against time; for the pitch test data, the angular displacement of the buoys was plotted versus time. Typical data for heave tests on each model are shown in Fig.10,and pitch time series are shown in Fig.11. Damped natural periods obtained directly from the time series are provided by Froude scaling (Eq. (16)). Natural periods for Design 2 are more than twice as long as those for Design 1.

Fig.10 Average Heave Free-Release Test Data from each Model (Design 1 and 2).

Fig.11 Average Pitch Free-Release Test Data from each Model (Design 1 and 2).

2.1.1 Design 1

RAOs were used to investigate the cage’s heave (vertical translation), and pitch (rotation about a horizontal axis parallel to the wave crest) (Jonkman et al., 2009). RAOs,which are in effect transfer functions, are defined as the ratio of the cage response amplitude to the wave forcing amplitude or

where ar is the amplitude of the response, and af is the amplitude of the forcing. The investigated RAOs that were used to determine the cage response (Eq. (21)).

Wave amplitude, rather than wave slope, was used to define the pitch RAO. Wave slope played a small role in forcing pitch motion because of the small waterplane area.Thus, wave amplitude was used instead. The amplitudes of heave and pitch were obtained directly from the experimental data. Detrending the data sets and averaging the respective values resolved the individual mean amplitudes for each experiments. Additional insight into wave response was obtained by applying a theoretical model of buoy heave motion. Neglecting mooring loads and assuming linear damping, the equation of motion in the vertical direction may be written as

通过对2001～2017年发表在管理学国际主流期刊(USDallas 24种期刊和Financial Times Top 50)和组织行为学权威期刊上的56篇实证研究论文进行分析，可以发现，大多数研究聚焦于个人特质和工作特征如何调节工作重塑诱因对重塑行为的影响，并验证工作重塑对主客观结果的影响。

where η=(H/2)cosωt, H is the wave height, ω is the wave frequency=2π/T, T is the wave period, d is the wave damping coefficient, k=2π/L, L is the wave length, and m′is the added mass. The steady state solution has a normalized amplitude. Thus, the heave RAO is given by

This solution was evaluated for both designs assuming damping coefficients are equal, b=d, and added mass are equal ma= m′. Damping and added mass values were evaluated from the results of the free-release experiments.Wave number k was evaluated by solving the dispersion relation Eq. (24),

where h is the water depth. Results at model scale are given in Table 5, while plots are compared with measured RAOs in the next section.

Table 5 Calculations of RAO Heave for Design 1 and Design 2 at model scale

RAO Design #2 0.5 12.56 16.08 2E−08 5E−06 T(s)W(rad s−1)k Wave number RAO Design #1 0.8 7.85 6.282 0.0018 0.004 1.1 5.709 3.322 2.1916 0.025 1.5 4.187 1.787 1.532 0.038 2 3.14 1.005 1.457 0.303 2.6 2.415 0.595 1.245 2.456 3 2.093 0.447 1.123 1.864 4 1.57 0.251 1.065 1.203

5.3.5 Wave response experimental procedures

To keep the buoy models within OPIE’s viewframe during wave testing, a mooring line was attached to the model. Only a single mooring line was needed because the waves act on the buoy in only one direction within the tank, and that is the only force that needs to be opposed to keep the buoys in place (Fowler et al., 2013). A series of 16 tests was performed with a range of regular waves to capture the characteristics of the full-scale site. Wave generation was started a few moments before data collection to ensure that each buoy reached a steady state before the capture sequence began.

5.3.6 Wave response results

进入21世纪，随着国家大力发展经济，尤其是国家创新驱动发展战略的强力推进，知识产权转移转化也取得了明显成效，初步形成了多渠道、多方式共同推动科技成果转化的局面。但是科技成果转化是一项系统工程，需要综合施策，尤其是针对国防知识产权转移转化的法律法规、机构建设管理、利益分配、评估评价和激励机制等方面还有很多问题，具体表现在以下几个方面。

Regular wave tests were studied through the use of theoretical and physical models; a total of 16 regular wave regimes were investigated (Huijs et al., 2014). These two designs were processed and calculated in a way that enabled comparisons between theoretical and experimental data by normalizing different wave heights. Results are shown in Figs.12 and 13, and in Table 6.

Differences are found between the experimental and theoretical results in Fig.14, which may be due to a number of reasons. One of the most important reasons is that the selected section is a hollow section while the model is being constructed. Hollow sections are thought to be unable to adequately represent the structure property when transmitting the applied vibration.

外婆说：“拜托，今天有考试呀！”我一听赶紧一骨碌爬起来，但脑袋还是晕晕的，坐在床上发呆。这时爸爸也走过来了，说：“今天考试，快复习呀。”我赶紧换好衣服，跟着爸爸来到了阳台。爸爸把书拿出来，给我好好复习了一遍，我想应该没问题了。走在路上我也在背要考的内容。

Fig.12 RAOs heave test data for models.

Fig.13 RAOs pitch test data for models.

6 Conclusion

In this paper, the motion of spar-type buoys is examined experimentally by using a 1/21.31 scale model of the prototype, and the motions are compared with the calculated results. Good agreement was found between the experiments and verified results of the RAOs. Physical model testing found that Design 1 has a considerably fast time response to disturbances, damping out around 16 s during free-release testing, whereas Design 2 damps out well beyond 25 s. Although Design 1 may seem to be the better option, because of Design 2’s slower response, it responds better to wave excitation. However, Design 1 may oscillate more than Design 2 in hurricane conditions.

These buoys were implemented and compared with wave tank measurements of the spar displacement at a reference elevation of 2.44 m above the mean water level.Eight tests are completed for each model in both different periods and wave heights to investigate the buoy’s dynamic response in an ocean environment. The buoy is a wave follower with respect to vertical motion for large,long-period waves occur during storms. The heave response at higher frequencies is associated with small, fairweather waves. A comparison between the theoretical and experimental model testing results shows that with the exception of the heave RAO, the pitch RAO plots are similar for both designs. Results are shown in Figs.12–15,and in Table 6. Fair-weather seas typically have waves with periods in the 2–5 s range. Storm seas have large waves with periods in the 6–12 s range. The RAO plots of both models show that Design 1 has a considerably higher RAO close to fair-weather waves for heave motion, Design 2 seems to have much smaller heave motion in fairweather waves, and both models seem approximately the same in storm conditions. This finding makes Design 2 seem like the better choice. In the pitch RAO results, Design 1 has a smaller RAO in fair- weather conditions. Table 7 shows the calculated inertia and center of gravity values for both designs; center of gravity values areandfor Designs 1 and 2, respectively, and inertia values are Ixx=117011.72 cm4, Iyy=19124.86 cm4 and Izz=7029.06 cm4 for design 1, and Ixx=101583.30 cm4,Iyy=12586.95 cm4 and Izz=8163.38 cm4 for design 2. Therefore, if the second design is lower than the center of gravity according to the first design, then the system can achieve balance faster.

Fig.14 Comparison between experimental and theoretically heave results for Design-1.

Fig.15 Comparison between experimental and theoretically heave results for Design-2.

Table 6 Calculated and measured RAOs for heave and pitch on buoy models

Wave height H (cm)Period T (s)Measured RAO for Design #1 Freq.W (rad s-1) Heave Pitch Heave Heave Pitch Heave Calculated RAO for Design #1 Measured RAO for Design #2 Calculated RAO for Design #2 5 0.8 7.85 0.242 0.889 2E-08 0.259 0.653 5E-06 5 1 6.28 0.845 1.097 0.0018 0.273 1.243 0.004 8 1.3 4.83 3.71 1.140 2.1916 0.431 0.967 0.025 10 1.5 4.19 1.687 1.989 1.532 0.502 1.510 0.038 10 1.8 3.49 1.524 2.111 1.457 0.570 2.500 0.303 10 2 3.14 1.490 2.056 1.245 0.649 2.077 2.456 10 2.3 2.73 0.960 1.126 1.123 0.794 1.655 1.864 10 2.5 2.51 1.016 0.583 1.097 2.344 0.779 1.36 10 4 1.57 1.004 0.387 1.065 1.011 0.538 1.203

Table 7 Calculated dimensions compared to measured dimensions for Design 1 and 2

Scale ratio=21.31 Calculated Measured Calculated Measured Design 1 Design 2 Total height (m) 1.948 1.981 1.585 1.666 Total weight (kg) 7.94 7.98 6.79 6.89 C.O.M location from bottom (m) 0.274 0.277 0.190 0.193 C.O.B location from bottom (m) 0.815 0.824 0.481 0.482 Freeboard measured from top (m) 0.095 0.10 0.334 0.332 Ixx (cm4) 117011.72 101583.3 Iyy (cm4) 19124.86 12586.95519 Izz (cm4) 7029.06 8163.383742 CoG (m)X=Z= 0,Y=0.622X=Z= 0,Y=0.500

The full-scale buoy is scheduled to be constructed and deployed within the next year. All internal components,such as electronics and the turbine generator, need to be designed. While deployed at the site, the buoy will collect wind data and determine the amount of power that can be generated from the wind.

Acknowledgements

With the reserve buoyancy force, the freeboard may be calculated using Eq. (11)

Nomenclature

5.3.2 Free-release experimental procedures

V: Volume (m3)

L: Wave length (m)

H: Wave height (m)

m: Mass (kg)

VCGc: Vertical center of gravity

VCGm: Vertical volume moment

COM: Center of mass

COB: Center of buoyancy

T: Wave period (s)

F: Force (N)

ρ: Density (kg m−3)

I: Area moment of inertia (m4)

M: Moment (Nm)

θrad: Tipping angle (˚)

D0:Diameter (m)

ω: Wav

e fr

equency (s−1)

k: Wave number

g: Acceleration of gravity (m s−2)

d: Wave damping coefficient

References

Azcona, J., Bouchotrouch, F., Gonz alez, M., Garciandía, J.,Munduate, X., Kelberlau, F., and Nygaard, T. A., 2014. Aerodynamic thrust modelling in wave tank tests of offshore floating wind turbines using a ducted fan. Journal of Physics,Conference Series 524: 012-089.

Berteaux, H. O., 1991. Coastal and Oceanic Buoy Engineering.the University of Michigan, Massachusetts, 285pp.

Bhattacharya, P., and Bhattacharjee, R., 2010. A study on Weibull distribution for estimating the parameters. Journal of Applied Quantitative Methods, 5: 234-241.

Flocard, F., and Finnigan, T. D., 2010. Laboratory experiments on the power capture of pitching vertical cylinders in waves.Ocean Engineering, 37: 989-997.

Fowler, M. J., Kimball, R. W., Thomas, D. A., and Goupee, A. J.,2013. Design and testing of scale model wind turbines for use in wind/wave basin model tests of floating offshore wind turbines. Proceedings of the ASME 32nd International Conference on Ocean, Offshore and Arctic Engineering. Nantes,France, Paper No. OMAE2013-10122.

Huijs, F., Ridder, E. J., and Savenije, F., 2014. Comparison offloating wind turbine. In: Proceedings of the ASME 33rd International Conference on Ocean, Offshore and Arctic Engineering. San Francisco, California, USA, 1-10.

Jonkman, J., Butterfield, S., Musial, W., and Scott, G., 2009.Definition of a 5-MW reference wind turbine for offshore system development. Technical Report, NREL/TP-500-38060,National Renewable Energy Laboratory.

Karimirad, M., and Michailides, C., 2015. V-shaped semisubmersible offshore wind turbine: An alternative concept for offshore wind technology. Renewable Energy, 83: 126-143.

Luan, C., Gao, Z., and Moan, T., 2014. Conceptual designs of a 5-MW and a 10-MW semisubmersible wind turbine with emphasis on the design procedure. Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. San Francisco, California, USA, Paper no.OMAE2014-24215.

Mahmuddin, F., 2013. A study on wind energy density with Weibull distribution. Journal of Ocean Technology Research,20:147-154.

Martin, H. R., Kimball, R. W., Viselli, A. M., and Goupee, A. J.,2012. Methodology for wind/wave basin testing of floating offshore wind turbies. Proceedings of the ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. Rio de Janeiro, Brazil, Paper No. OMAE2012- 83627.

Muliawan, M. J., Karimirad, M., and Moan, T., 2013. Dynamic response and power performance of a combined spar-type floating wind turbine and coaxial floating wave energy converter. Renewable Energy, 50: 47-57.

Müller, K., Sandner, F., Bredmose, H., Azcona, J., Manjock, A.,and Pereira, R., 2014. Improve tank test procedures for scaled floating offshore wind turbines. The International Wind Engineering Conference, Support Structures & Electrical Systems. Hannover, Germany, 1-12.

Murray, R., and Rastegar, J., 2009. Novel two-stage piezoelectric-based ocean wave energy harvesters for moored or unmoored buoys. Active and Passive Smart Structures and Integrated Systems, 7288: 1117-1129.

Ravi, T. T., and Krishna, C. T., 2012. Computation of natural frequencies of multi degree of freedom system. International Journal of Engineering Research and Technology (IJERT), 10:2278-2281.

Roddier, D., Cermelli, C., Aubault, A., and Weinstein, A., 2010.WindFloat: A floating foundation for offshore wind turbines,Journal of Renewable and Sustainable Energy, 2: 83-94.

Soulard, T., Babarit, A., Borgarino, B., Wyns, M., and Harismendy, M., 2009. C-HYP: A combined wave and wind energy platform with balanced contributions. Proceedings of the ASME 28th International Conference on Ocean, Offshore and Arctic Engineering OMAE2009. Honolulu, Hawaii, USA, 40-52.

Takagi, K., Yamamoto, K., Kondo, M., Funaki, T., and Kawazaki,Z., 2002. Conceptual design of a very large mobile structure for the renewable energy plant. In: Proceedings of the Asia Pacific Workshop on Marine Hydrodynamics, 82: 239-244.

Turmelle, C. A., 2009. Development of a 20-ton capacity open ocean aquaculture feed buoy. Master Thesis. University of New Hampshire.

Utsunomiya, T., Matsukuma, H., Sato, T., and Yago, K., 1996.Experimental validation for motion of a spar-type floating offshore wind turbine using 1/22.5 scale model. Draft report Washington Department of Fish and Wildlife. American Society of Mechanical Engineers, New York, No. OMAE2009-79695.