•Spectral fatigue damage prediction of a tripod offshore wind turbine support structure is conducted.•The power spectral density of the hot spot stress is estimated.•The prediction of fatigue damage ...is evaluated in several spectral fatigue damage models.•The rainflow cycle counting method is assumed to be the “reference” data.•The model that best fits the fatigue damage is identified with the Akaike’s Information Criterion.
This work deals with the evaluation of the spectral fatigue damage prediction of a tripod offshore wind turbine support structure subjected to combined stochastic wave and wind – induced loads. The stochastic loadings are defined using the sea states based on a scatter diagram related to the North Atlantic. Further, the power spectral density of the hot spot stress is estimated accordingly. The prediction of fatigue damage is evaluated in several spectral fatigue damage models including the Rayleigh, Wirsching–Light, Tunna, α0.75, Tovo and Benasciutti, Zhao–Baker, Rice and Dirlik models. Critical hot spot locations, which experience the most fatigue damage, are analysed based on the finite element method and the S–N fatigue damage approach. The time-domain solution based on the rainflow cycle counting method is assumed to be the “real” data and the model that best fits the fatigue damage of the wind turbine support structure is identified with the Akaike’s Information Criterion.
Owing to the different structural configuration of modular steel construction (MSC) joints compared with those in conventional structural frames, the existing loading protocols might not be ...applicable to MSC joints. Suitable loading protocols for MSC joints are therefore required for use in quasi-static cyclic tests, which is the focus of the present study. A representative three-dimensional MSC building was adopted in the numerical simulation programme. Dynamic analyses were carried out using the developed numerical model under a selection of seismic waves, from which the inter-storey displacements were obtained. The rainflow counting method was employed to process the obtained displacement–time histories, and the key parameters for the loading protocol, including the total number of cycles and maximum amplitude etc. were derived accordingly. A quasi-static cyclic loading protocol dedicated to MSC joints was subsequently established. The proposed loading protocol was compared with the existing loading protocols specified in ATC-24 and in FEMA-461 through numerical simulations. The examined loading protocols were applied to two typical MSC joints, and the numerical results indicated that the proposed protocol led to a small increment in the energy consumption, ductility and bearing capacity, in comparison with the two existing loading protocols. The results show that the existing and the proposed loading protocols are all deemed suitable for use in quasi-static cyclic testing of the MSC joints, and the proposed loading protocol with 37 cycles and 0.0158 rad loading peak value could provide a new and alternative loading program for the quasi-static test of MSC joint.
In the present paper, the fatigue lifetime of metallic structural components subjected to variable amplitude loading is evaluated by applying 2 different multiaxial high‐cycle fatigue criteria. Such ...criteria, proposed by some of the present authors, are based on the critical plane approach and aim at reducing a given multiaxial stress state to an equivalent uniaxial stress condition. In particular, the procedure employed by both criteria consists of the following 3 steps: (1) definition of the critical plane; (2) counting of loading cycles; and (3) estimation of fatigue damage. Finally, the previous criteria are validated by comparing the theoretical results with experimental data related to smooth metallic specimens subjected to uniaxial and multiaxial variable amplitude loading.
Highlights
Fatigue lifetime of metallic components subjected to variable amplitude loading is evaluated.
Two multiaxial fatigue criteria based on the critical plane approach are applied.
The amplitude of an equivalent normal stress is used to estimate fatigue damage.
Experimental data related to variable amplitude fatigue tests are examined.
This paper proposes a probability density function model of wind-induced ”rainflow range” in elastic structures for evaluating fatigue damage without time-history response analysis and shows the ...analytical derivation of the model and its validity using time history response analysis. The proposed model is applicable for not only wind-induced narrow-band responses but also broadband responses. The wind-induced fatigue of elastic structures has been studied based on narrow-band vibration following Rayleigh distribution. However, the number of buildings with vibration-damping system or seismic isolation structures which have large damping increased, and a method for evaluating ”rainflow range” of wide-band vibration is needed.
As fruitful clean energy, offshore wind turbine power develops rapidly at the coastal area of China that contributes to enabling carbon neutralization. However, the cyclic change of climatic ...conditions inevitably leads to fatigue issue of wind turbine. This paper makes a survey on the climate condition at Jintang island, Zhoushan islands, China within one year to perform fatigue analysis of in-service composite wind turbine blades. First, the wind velocity rose diagram measured at Jintang island is obtained by investigation, which is used to calculate the wind pressure under some wind velocity and the corresponding direction and frequency, by combining with the modified blade element momentum (BEM) theory. Second, finite element analysis (FEA) of the full-scale composite blade under different wind velocity is performed, where it is almost the first time to introduce the damage model of composites to predict progressive failure properties and stress distributions of composite skin for fatigue analysis. Finally, the fatigue life for blade with three kinds of composite materials for skin is evaluated comparatively by combining with the rainflow counting method, the S–N fatigue curve and the cumulative damage principle. Numerical results show that the fatigue life of blades with three kinds of materials for skin falls within 19–22 years, consistent with the design value of blade in China.
Floating marine structures are exposed to various environmental loads. When the response of structures caused by these loads can be expressed as a multi-modal spectrum in the frequency domain. To ...estimate the fatigue damage by these loads, various fatigue damage models have been suggested by many previous researches. The offshore riser system, for example, that is a typical marine structure shows a quarter-modal response. However, existing fatigue damage models are suitable for spectrum with tri-modal in maximum. Consequently, it is necessary to develop a new fatigue damage model that can accurately calculate fatigue damage of quarter-modal spectrum. In this research, the Benasciutti and Tovo model was adopted for developing a new fatigue damage model. And 900 quarter-modal spectra are used to derive a new weighting factor in the Benasciutti and Tovo model by investigating the relationship between the linear weighting factor and the bandwidth parameters. Finally, a new linear weighting factor is derived using the least square method. The suitability of the new fatigue damage model with the derived weighting factor is evaluated by frequency domain and time domain results and their comparison with existing model’s results.
Aimed at fracture of transmission shaft about some kind of transport for bulk dry-mixed mortar,this paper designed a set of testing equipment which can test torque,run out,revolving speed. This ...testing equipment provides with analyzed data on fault diagnosis and maintenance of this kind of brand new car. This set of testing equipment was also applied to the fault diagnosis of concrete pump truck and mix concrete truck. The place where the fracture of transmission taken place is very complex and it is very difficult to do the stress measurement of the hot spot of fracture taken place. This paper converted the measure data of torque into the stress of the hot spot of fatigue by using the FEA. Calculating the fatigue life of shaft by combining the structural S-N curve and the modified Miner’s rule were carried out. This method can provide a way of calculating fatigue life of shaft of engineering machine.
Thin-walled connection structures are commonly used in the hot-end components of aerospace vehicles. Large deflection nonlinear responses and fatigue failure occur due to their discontinuous mass ...distribution and prominent cross-sectional changes under the action of complex thermal, aerodynamic, and noise loads. A thermoacoustic fatigue test was carried out to obtain the acoustic and vibration responses and fatigue life changes of the connection structure under heat flow conditions in engineering applications. The high-temperature acoustic fatigue test system of aviation thin-walled structures was used, taking the high-temperature alloy thin-walled plate-load-bearing frame bolted connection structure as the research object. As a result, the vibration response and fatigue life under different thermoacoustic loads were obtained. The contact finite element method was used to simulate the connection pre-tightening force, and the coupled finite element/boundary element method was used to calculate the acoustic and vibration response of the heat flow conditions. The changing rules of the frequency response peak value at the critical point of the thin-walled connection structure under the effects of different temperature fields, fluid fields, and sound fields were obtained through the processing and analysis of the calculation results. Considering the structural vibration fatigue damage mechanism, this study employed an improved rainflow counting method to compute the rainflow circulation matrix (RFM) and rainflow damage matrix (RFD) of the vibration stress time history at critical points within the structure framework. Said method was combined with Miner’s linear cumulative damage theory to estimate the fatigue life under various thermal-fluid-acoustic coupled loads. A comprehensive analysis validates the accuracy of the established numerical simulation calculation model in identifying critical connection points within structures subjected to pre-tightening forces. This model effectively characterizes thermal, aerodynamic, and acoustic loads on high-temperature alloy thin-walled-load-bearing frame bolted connection structures. It delineates the relationship between vibration response and fatigue life while assessing the impact of three distinct load parameters.
AbstractCentral heating is the main heating method in cities in northern China in winter, and it is also an important part of urban utilities. The safety of the heating pipe network operation is an ...important livelihood issue. Temperature fatigue damage of the central heating pipeline has a severe impact on the safe operation of the system, and reasonable estimation of the number of fatigue cycles during the service life of the pipeline is an essential link in the pipeline design of a district heating (DH) system. The temperature data of five typical secondary networks of heat exchanger stations in Jiancao District of Taiyuan City in four heating seasons were collected. The frequency of temperature change during operation was counted, and the maximum total temperature difference cycle number of pipelines was estimated. In this paper, the regression analysis method is adopted to fit the design equation of the number of temperature cycles of water supply and return pipelines in 30 years of service life, which provides a way of thinking for predicting the number of temperature difference fatigue cycles of pipelines in the design stage. In the calculation of the number of maximum total temperature difference cycles, the different values of temperature difference defining parameter b and reference temperature difference ΔTref are analyzed. The results show that the selection of temperature difference defining parameter b can effectively distinguish the effect of large and small temperature difference on the number of fatigue cycles of pipelines; at the same time, the cyclic temperature difference is normalized within a specific range of design temperature difference, which overcomes the problem of simplifying the guidance of the operation parameters of the central heating system and makes the predicted maximum total temperature difference cycle have universal guiding significance in a specific heating area.
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