大家一起学标准之IEC61400-1(20)

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7.6.1.3 Partial safety factor for consequence of failure and component classes

A consequence of failure factor, γn, is introduced to distinguish between:a) component class 1: used for "fail-safe" structural components whose failure does not result in the failure of a major part of a wind turbine, for example replaceable bearings with monitoring;b) component class 2: used for "safe-life" structural components whose failures may lead to the failure of a major part of a wind turbine;c) component class 3: used for "safe-life" mechanical components that link actuators and brakes to main structural components for the purpose of implementing non-redundant wind turbine protection functions. Regarding blocking devices, see 7.4.9.

Partial safety factors for consequences of failure:

·component class 1: γn = 0.9;

·component class 2: γn= 1.0;

·component class 3: γn= 1.2.

The consequences of failure factor shall be included in the test load when performing tests such as, for example, full scale blade testing.

Other values of γn apply for critical deflection an alysis, see 7.6.5.

7.6.1.4 Application of recognized material codes

When determining the structural integrity of elements of a wind turbine, national or international design codes for the relevant material may be employed. Special care shall be taken when partial safety factors from national or international design codes are used together with partial safety factors from this document. It shall be ensured that the resulting safety level is not less than the intended safety level in this document.

Different codes subdivide the partial safety factors for resistance,γM, into several material factors accounting for separate types of uncertainty, for example inherent variability of material strength, extent of production control or production method. If the code gives partial safety factors or uses reduction factors on the characteristic values to account for other uncertainties, these shall also be taken into account.

Individual codes may choose different factorizations of partial safety factors on the load and the material parts of the design verification. The division of factors intended here is the one defined in ISO 2394. If the division of factors in the code of choice deviates from that of ISO 2394, the necessary adjustments in the code of choice shall be taken into account in verifications according to this document.

7.6.2 Ultimate strength an alysis

7.6.2.1 General

The limit state function can be separated into load and resistance functions S and R so that the condition becomes

γn S(Fd)≤Rd {31}

The function S for ultimate strength an alysis is usually defined as the highest value of the structural response, hence S(Fd) = Fd. The equation then becomes

γnγFk ≤Rk/γM {32}

Note that γn is a consequence of failure factor and shall not be treated as a safety factor on materials.

For each wind turbine component assessed and for each load case in Table 2 where ultimate strength a nalysis is appropriate, the limit state condition in Equation (32) shall be verified for the most critical limit state, identified on the basis of having the least margin.

7.6.2.2 Partial safety factors for loads

For DLC 1.1, a characteristic value of load shall be determined by a statistical an alysis of the extreme loading that occurs for normal design situations and shall correspond to one of the following alternatives.

a) The characteristic value is obtained as the largest (or smallest) among the average values of the 10 min extremes determined for each wind speed in the given range, multiplied by 1,35. This method can only be applied for the calculation of the blade root in-plane moment and out-of-plane moment and tip deflection.

b) The characteristic value is obtained as the largest (or smallest) among the 99th percentile (or 1st percentile in the case of minima) values of the 10 min extremes determined for each wind speed in the given range, multiplied by 1,2.

c) The characteristic value is obtained as the value corresponding to a 50 year return period, based on load extrapolation methods, considering the wind speed distribution given in 6.3.2.1 and the normal turbulence model in 6.3.2.3. Guidance about load extrapolation is given in Annex G.

The design load will be then obtained by multiplying the characteristic loads according to any of these alternatives by the partial safety factor for DLC 1.1 defined in Table 3.

For all three alternatives above, data used in the statistical an alysis shall be extracted from time series of turbine simulations of at least 10 minutes in length over the operating range of the turbine for DLC 1.1. A minimum of 15 simulations is required for each wind speed from Vr-2m/s to cut-out, and six simulations are required for each wind speed below Vr-2m/s. When extracting data, the designer shall consider the effect of independence between peaks on the statistical an alysis and minimize dependence when possible. For guidance on dependency checks, see Annex G.

For load cases with specified deterministic wind field events, the characteristic value of the load shall be the worst case computed transient value. If more simulations are performed at a given wind speed, representing the rotor azimuth, the characteristic value for the load case is taken as the average value of the worst case computed transient values at each azimuth. Guidance for the derivation of the contemporaneous load can be found in Annex I. When turbulent inflow is used, the mean value among the worst case computed loads for different 10 min stochastic realizations shall be taken, except for DLC 2.1, 2.2 and 5.1, where the characteristic value of the load shall be the mean value of the largest half of the maximum loads.

Partial safety factors for loads shall be at least the values specified in Table 3.

The approach in 7.6.1.2, where the partial safety factor for loads is applied to the load response, assumes that a proper representation of the dynamic response is of prime concern. Where a proper representation of non-linear material behaviour or geometrical non-linearities (such as, for example, foundations) or both are of primary concern, the design load response Sd shall be obtained from a structural an alysis for the combination of the design loads Fd, where the design load is obtained by multiplication of the characteristic loads Fk by the specified partial load factor γf for favourable and unfavourable loads:

Fd=γfFk {33}

The load responses in the tower at the interface (shear forces and bending moments) factored with γf from Table 3 shall be applied as boundary conditions.

Table 3 – Partial safety factors for loads γf

Use of the partial safety factors for loads for normal and abnormal design situations specified in Table 3 requires that the load calculation model is validated by load measurements. These measurements shall be made on a wind turbine that is similar to the wind turbine design under consideration with respect to aerodynamics, control and dynamic response.

二、精准工程译文（IEC 风电标准术语）

7.6.1.3 失效后果分项安全系数与构件类别

引入失效后果系数\(\boldsymbol{\gamma_\mathrm{n}}\)，用于区分三类构件：a) 1 类构件：故障安全型构件；构件失效不会造成机组主体失效，例如具备监测、可更换轴承；b) 2 类构件：安全寿命型结构构件；构件失效可能引发机组主体失效；c) 3 类构件：安全寿命型机械构件；用于连接执行机构、制动器与主结构，实现无冗余机组保护功能。锁止装置相关要求见 7.4.9。

失效后果分项安全系数取值：

·1 类构件： γn = 0.9;

·2 类构件： γn = 1.0;

·3 类构件： γn = 1.2。

开展全尺寸叶片等试验时，试验荷载中必须计入失效后果系数。临界变形分析采用另行规定的 γn取值，见 7.6.5。

7.6.1.4 公认材料规范的应用

确定机组构件结构完整性时，可采用对应材料的国家或国际设计规范。当外部规范分项安全系数与本标准系数联合使用时需格外谨慎，必须保证最终安全水平不低于本标准规定目标。

不同规范会将抗力分项系数\(\gamma_\mathrm{M}\)进一步拆分为多个材料分项系数，分别考虑材料强度固有离散性、生产管控水平、制造工艺等不确定性。若外部规范采用分项系数或特征值折减系数考虑其他不确定因素，均应一并纳入计算。

各类规范对荷载侧、材料侧分项系数的拆分方式存在差异。本标准系数拆分原则与 ISO 2394 一致；若选用规范的拆分方式与 ISO 2394 不同，按照本标准开展校核时必须进行相应修正。

7.6.2 极限强度分析

7.6.2.1 总则

极限状态函数可拆分为荷载函数S与抗力函数R，极限状态判定条件：

γn S(Fd)≤Rd {31}

极限强度分析中函数S一般取结构响应最大值，即S(Fd) = Fd，公式简化为：

γnγFk ≤Rk/γM {32}

注意：γn为失效后果系数，不得视作材料安全系数。

针对每一个待评估构件，以及表 2 中适用极限强度分析的各个荷载工况，均需按照式 (32) 校核最临界极限状态（裕度最小工况）。

7.6.2.2 荷载分项安全系数

对于 DLC 1.1 工况，应通过正常设计工况极值荷载统计确定荷载特征值，可选用以下三种方法之一：a) 取规定风速区间内各风速 10 分钟极值平均值的最大 / 最小值，再乘以 1.35；该方法仅限用于叶根面内弯矩、面外弯矩以及叶尖挠度计算。b) 取规定风速区间内各风速 10 分钟极值 99% 分位数（最小值采用 1% 分位数）的最大 / 最小值，再乘以 1.2。c) 采用荷载外推方法得到 50 年重现期对应荷载；风速分布依据 6.3.2.1、正常湍流模型依据 6.3.2.3，荷载外推指导见附录 G。

采用上述任意一种方法得到特征荷载后，乘以表 3 规定的 DLC 1.1 荷载分项系数得到设计荷载。

上述三种方法统计所用数据，均取自机组至少 10 分钟时长仿真时程。DLC 1.1 工况下：额定风速减 2 m/s 至切出风速区间，每个风速至少完成 15 次仿真；低于额定风速减 2 m/s 的风速，每个风速至少 6 次仿真。提取数据时需评估峰值之间的相关性影响，尽可能降低数据相关性；相关性校核方法参见附录 G。

对于给定确定性风场事件的工况，荷载特征值取最不利瞬态计算结果；同一风速下开展多组不同风轮方位仿真时，取各方位最不利瞬态结果平均值。同步荷载获取方法参见附录 I。采用湍流入流时，取多组 10 分钟随机仿真最不利荷载的平均值；DLC 2.1、2.2、5.1 除外，这三类工况取全部最大值中较大一半数值的平均值作为荷载特征值。

荷载分项安全系数不得低于表 3 规定数值。

7.6.1.2 中将分项系数施加于荷载响应的思路，适用于重点关注结构动态响应的场景。若分析核心为材料非线性、几何非线性（如基础）或两者共存，则先将特征荷载Fk乘以荷载分项系数 γf得到设计荷载 γd，再通过结构分析求解设计荷载响应Sd：

Fd=γfFk {33}

塔筒界面位置经过表 3γf放大后的荷载响应（剪力、弯矩）应作为边界条件施加。

表 3 荷载分项安全系数γf

采用表 3 正常 / 异常工况荷载分项系数时，荷载计算模型必须通过实测验证；试验机组在气动特性、控制系统、动态响应方面应与目标设计机组相近。

简单总结

本节按照失效后果将构件划分为三类并给出对应的γn系数，同时明确外部材料规范协同使用要求。极限强度校核给出统一判定公式，规定 DLC1.1 等工况荷载特征值三种统计方法、仿真数量要求与各类工况荷载分项安全系数取值规则，并区分线性动态、非线性分析两种不同系数施加路径。

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