Development of Combined Load Spectra for Offshore Structures Subjected to Wind, Wave, and Ice Loading

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider the effects of ice loading and its stochastic nature on the fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.

Investigation on fatigue damage equivalence probability for the structure with similar fatigue hazardous detail parts

Fatigue damage of a whole structure with multiple similar fatigue hazardous detail parts is unclear. This paper focuses on the concept of quantified fatigue damage for the structure with similar fatigue hazardous detail parts by using the probability method and fatigue failure probability of the severe load spectrum. The probability criterion and calculation method of equivalent damage with different load spectra were proposed. The fatigue life probability distribution of the severe load spectrum was analyzed, and the acceleration ratio was defined by the similar details number of fatigue cracking in combination with the fatigue failure probability characteristics of the severe load spectrum. The results show that there is good agreement between the similar details number range of fatigue cracking in two load spectra, which means they are considered to be equivalent. The ratio of the sum of two similar details number ranges is used as acceleration ratio to evaluate the severe load spectrum. The application of this study in the statistical sense of engineering structure fatigue failure is more convincing.

Development of Combined Load Spectra for Offshore Structures Subjected to Wind, Wave, and Ice Loading

Fixed offshore wind turbines continue to be developed for high latitude areas where not only wind and wave loads need to be considered, but also moving sea ice. Current rules and regulations for the design of fixed offshore structures in ice-covered waters do not adequately consider effects of ice loading and its stochastic nature on fatigue life of the structure. Ice crushing on such structures results in ice-induced vibrations, which can be represented by loading the structure using a variable-amplitude loading (VAL) sequence. Typical offshore load spectra are developed for wave and wind loading. Thus, a combined VAL spectrum is developed for wind, wave, and ice action. To this goal, numerical models are used to simulate the dynamic ice-, wind-, and wave-structure interaction. The stress time-history at an exemplarily selected critical point in an offshore wind energy monopile support structure is extracted from the model and translated into a VAL sequence, which can then be used as a loading sequence for the fatigue assessment or fatigue testing of welded joints of offshore wind turbine support structures. This study presents the approach to determine combined load spectra and standardized time series for wind, wave, and ice action.

A load spectra design method for multi-stress accelerated testing

Accelerated testing (AT) is an effective testing method for evaluating the reliability of highly reliable products. In many applications, such products are often subject to multiple stresses in actual working environments. Then, how to design the load spectra for multi-stress AT becomes a critical issue. In this paper, a new load spectra design method is proposed to overcome this challenge. Considering the properties of multiple stresses, a novel multi-stress loading matrix (MSLM) is modified to fully describe the load spectra in actual working environments and to generate the corresponding load spectra for AT. For illustration purposes, an inverse Gaussian (IG) process incorporating life-stress relationships is adopted to model product degradation under multiple stresses. A case study on a type of hydraulic piston pump is provided to demonstrate the use of the proposed method in guiding the load spectra design for multi-stress AT.

Investigation of Fatigue Crack Growth in Full-Scale Railway Axles Subjected to Service Load Spectra: Experiments and Predictive Models

In this paper, a series of experimental investigations was performed on full-scale railway axles to analyze the fatigue crack growth behavior of EA4T steel under load spectrum derived from real operating conditions. The experimental results were compared to life predictions carried out adopting two models: (i) the conventional Nasgro equation and (ii) the cyclic R-curve concept implemented in the Modified Nasgro equation for describing the crack growth behavior of an arbitrary crack length. The results show that the life predictions performed by means of the Modified Nasgro equation coincide well with the experimental results with an underestimation of the residual lifetime less than 32%, while the traditional Nasgro equation leads to significant overestimation (≈120%) of the residual lifetime for load spectra close to the in service scenario.

Analysis and Determination of Axle Load Spectra and Traffic Input for Pavement Design

This study examines the vehicle class distribution, hourly distribution factors, weekly distribution factors, monthly distribution factors, axle load spectra for each vehicle class, and each axle of each vehicle class for the WIM station installed on the N-55 highway to aid analysis and design of new Mechanistic-Empirical Pavement Design Guide. The maximum, minimum and permissible load limit for the different vehicle class, average gross vehicle weight (GWV) and permissible load limits also being incorporated. The directional distribution for north bound and south bound traffic were observed to be almost 50% for both directions, except for 5 axle trucks which was 74% for north bound and 26% for south bound. The truck class most prevalent on the highway were identified to be 3-axle tandem truck (47.50%) and also it was observed that 94.1% of this vehicle class carried load above permissible limits. Keywords: Traffic characteristics, Load distribution factor, Axle Load Spectra.

Verification of the Axle Load Spectra Databases Using Stationary and Portable Weight-in-Motion Devices in Overload Corridors of East Texas

Axle Load Spectra (ALS) data collected from the Portable Weight-in-Motion (P-WIM) devices, provides the primary Mechanistic-Empirical (ME) traffic data input for optimal and accurate pavement design and analysis. Reliable readings from the P-WIM devices are the key factors that contribute to the accuracy of the analysis results. Therefore, this study was aimed to accurately assess the reliability and quality of the traffic data directly derived from the field data collection efforts. To accomplish this objective, the authors initially deployed P-WIM devices to US281 highway as a representative site in Texas overload corridors to collect the traffic data. The results were synthesized to compile the site-specific axle load spectra database, comprising of traffic information on the axle weights, vehicle classifications, and axle configurations. Subsequently, to assess the reliability of the collected data, P-WIM achieved traffic data were contrasted with those captured by the stationary WIM located at the vicinity of the evaluated site, using the available databases. Comparative analysis results indicated that traffic characterizations using the two WIM systems led to comparable outcomes, validating the accuracy and reliability of the P-WIM data measurements in the field. Additionally, as a practical means to investigate the quality of the recorded data, the longevity of the P-WIM piezo-sensors in several sites with different traffic patterns was investigated. Hence, the deterioration of the calibration factors over the operational life of the installed piezo-electric sensors in the field was analyzed. The post-processed results revealed that the piezo-electric sensors sustained substantial damage after nearly 37 days of operation in the field. Consequently, proper quantification of the ALS should include cross-validation assessments, as well as continuous evaluations of the calibration factors throughout the P-WIM data collection process to achieve good-quality, accurate, and reliable traffic data.

Landing gear ground manoeuvre statistics from automatic dependent surveillance-broadcast transponder data

ABSTRACT Landing gear are exposed to cyclic loads from the ground manoeuvres that aircraft perform in-service. Variability is observed in the loading magnitude associated with ground manoeuvres, along with the per-flight variability in ground manoeuvre occurrence and sequencing. Whilst loading magnitude variability has been widely characterised, significant assumptions are required regarding manoeuvre occurrence and sequencing when constructing landing gear load spectra for fatigue design. These assumptions are required due to the limited availability of data concerning ground manoeuvre occurrence and sequencing relating to aircraft in-service and require validation to facilitate the design of more efficient components. ‘Big-Data’ approaches, employing Automatic Dependent Surveillance-Broadcast (ADS-B) transponder data, enable aircraft ground tracks to be identified. This paper presents a methodology to characterise the variability in ground manoeuvre occurrence and sequencing using ADS-B data sourced from Flightradar24® for a wide-body aircraft fleet. Using statistics generated for the fleet, it was identified that significant variability exists in the occurrence and sequencing of turning and braking manoeuvres. The statistics also validate existing assumptions, including that the proportional share of left and right turning manoeuvres is equal. Finally, this paper discusses the utility of ADS-B datasets for constructing landing gear load spectra and monitoring of landing gear in-service.