Data-driven farm-wide fatigue estimation on jacket foundation OWTs for multiple SHM setups

The sustained development over the past decades of the offshore wind industry has seen older wind farms beginning to reach their design lifetime. This has led to a greater interest in wind turbine fatigue, the remaining useful lifetime and lifetime extensions. In an attempt to quantify the progression of fatigue life for offshore wind turbines, also referred to as a fatigue assessment, structural health monitoring (SHM) appears as a valuable contribution. Accurate information from a SHM system, can enable informed decisions regarding lifetime extensions. Unfortunately direct measurement of fatigue loads typically revolves around the use of strain gauges and the installation of strain gauges on all turbines of a given farm is generally not considered economically feasible. However, when we consider that great amounts of data, such as Supervisory Control And Data Acquisition (SCADA) and accelerometer data (of cheaper installation than strain gauges), is already being captured, this data might be used to circumvent the lack of direct measurements. It is then highly relevant to know what is the minimal sensor instrumentation required for a proper fatigue assessment. In order to determine this minimal instrumentation, a data-driven methodology is developed for real-world jacket-foundation Offshore Wind Turbines (OWT). Firstly, high-frequent 1s SCADA data is used to train an Artificial Neural Network (ANN) that seeks to estimate the quasi-static thrust load, and able to accurately estimate the thrust load with a Mean Absolute Error (MAE) below 2 %. The thrust load is then, along with 1s SCADA and acceleration data, processed into 10-minute metrics and undergoes a comparative analysis of feature selection algorithms with the goal of performing the most efficient dimensionality reduction possible. The features selected by each method are compared and related to the sensors. The variables chosen by the best-performing feature selection algorithm then serve as the input for a second ANN which estimates the tower fore-aft (FA) bending moment Damage Equivalent Loads (DEL), a valuable metric closely related to fatigue. This approach can then be understood as a two-tier model: the first tier concerns itself with engineering and processing 10 minute features, which will serve as an input for the second tier. It is this two-tier methodology that is used to assess the performance of 8 realistic instrumentation setups (ranging from 10 minute SCADA to 1s SCADA, thrust load and dedicated tower SHM accelerometers). Amongst other findings, it was seen that accelerations are essential for the model's generalization. The best performing instrumentation setup is looked in greater depth, with validation results of the tower FA DEL ANN model show an accuracy of around 1 % (MAE) for the training turbine and below 3 % for other turbines, with a slight underprediction of fatigue rates. Finally, the ANN DEL estimation model – based on a intermediate instrumentation setup (1s SCADA, thrust load, low quality accelerations) – is employed in a farm-wide setting, and the probable causes for outlier behaviour investigated.

Mechanical Behavior of Ultrahigh-Performance Concrete Tunnel Lining Segments

Ultrahigh-performance concrete (UHPC) is a novel material demonstrating superior mechanical, durability and sustainability performance. However, its implementation in massive structures is hampered by its high initial cost and the lack of stakeholders’ confidence, especially in developing countries. Therefore, the present study explores, for the first time, a novel application of UHPC, incorporating hybrid steel fibers in precast tunnel lining segments. Reduced scale curved tunnel lining segments were cast using UHPC incorporating hybrid 8 mm and 16 mm steel fibers at dosages of 1%, 2% and 3% by mixture volume. Flexural and thrust load tests were conducted to investigate the mechanical behavior of UHPC tunnel lining segments thus produced. It was observed that the flow of UHPC mixtures decreased due to steel fibers addition, yet steel fibers increased the mechanical and durability properties. Flexural tests on lining segments showed that both the strain hardening (multiple cracking) and strain softening (post-peak behavior) phases were enhanced due to hybrid addition of steel fibers in comparison with the control segments without fibers. Specimens incorporating 3% of hybrid steel fibers achieved 57% increase in ultimate load carrying capacity and exhibited multiple cracking patterns compared to that of identical UHPC segments with 1% fibers. Moreover, segments without fibers incurred excessive cracking and spalling of concrete at the base under the thrust load test. However, more stable behavior was observed for segments incorporating steel fibers under the thrust load, indicating its capability to resist typical thrust loads during tunnel lining field installation. This study highlights the potential use of UHPC with hybrid steel fibers for improved structural behavior. Moreover, the use of UHPC allows producing structural members with reduced cross-sectional dimensions, leading to reduced overall structural weight and increased clear space.

Analysis of Weakening Law and Stability of Sliding Zone Soil in Thrust-Load-Induced Accumulation Landslides Triggered by Rainfall Infiltration

This study investigated the weakening model, law of mechanics parameters, and stability of the sliding zone soil associated with thrust-load-induced accumulation landslides triggered by rainfall infiltration. The spatial and morphological characteristics and rule of the sapping process were analyzed, considering the constitutive equation of the sliding zone soil, in order to establish a state curve equation for the weakening coefficient of sliding zone soil based on the “S”-shaped curve. Moreover, a formula for calculating slope stability with this failure mode was derived and applied to calculate the stability of a deformation body in Danbo reservoir, China. The results show that the sliding zone in this type of landslide exhibits steep upward and slow downward trends, and affected by rainfall infiltration, its failure develops gradually from the trailing edge to the front edge. In the constitutive equation, the weakening of soil mechanical parameters is manifested as the weakening of shear stiffness, while the “S”-shaped curve of the weakening coefficient reflects the spatial characteristics of the weakening process. The main factors affecting the accuracy of the slope stability calculation are the values of model parameters and assessment of the development characteristics and weakening stage of the sliding zone.

Effect of Leakage Flow Path Wear on Axial Thrust in Downhole Electrical Submersible Pump Unit

Subsea production fluid is quite often characterized by the presence of frac sand, which causes wear within the pump, and alters the performance envelop. One of the design parameters critically affecting reliability is the thrust load generated by an impeller. The change in thrust load due to the erosion of the pump stages is not completely understood, and no relationship exists to foresee these reactive forces due to the complexity involved in predicting the flow characteristics. The purpose of this study is to understand the change in axial thrust due to commonly encountered wear mechanisms across the pump section especially wear across stage clearance seals. Based on in-house erosion testing of a mixed flow pump, three mesh models were built with each representing the pump condition at three different time intervals, namely, 0 h, 52 h, and 117 h of the total test time. The pump numerical models were validated using performance data collected from experimental testing. Axial thrust was found to increase with an increase in wear rate across stage seals. Since the increased clearance causes head degradation as well as an increase in thrust, the relationship of this head degradation is correlated with a change in thrust to further expand the affinity laws.

Performance of asmetric structures reviewed with based plastic design performance (case study of application on building in Pekan Baru)

Performance-Based Plastic Design (PBPD) is a structural analysis that can be used to review structural performance. This method is increasingly popular to be used in the earthquake-prone area. This method is based on energy method that can be applied to steel or concrete structures. Meanwhile, Indonesia has already SNI 1726:2102 to be used as a guide in designing the thrust load to review the level of structural performance. Both of these things need to be used as a reference in areas that were initially considered safe from the earthquake but based on the development of earthquake micro zonation maps, it is very possible to become potential areas that also become earthquake regions. For this reason, the case of the structure that was built in the Pekanbaru area was taken. From the analyses of structural behavior, the structure that applied PBPD has greater displacement than the structures that apply the thrust load of SNI 1726: 2012. The percentage of displacement that occurred was 8-37 %. Based on performance analysis, the structures according to PBPD shows a better level of performance to the application of SNI 1726: 2012 thrust load.

Towards Visualisation of Capacity, Bearing Thrust Load and Reaction Variation With Aerofoil Skew in a Gas Turbine

The requirements in the design of aerofoils for gas turbines are not limited to only meeting the aerothermal performance. A typical scenario for a turbine is to understand the impact of aerofoil skew on capacity, reaction and bearing thrust load. A means to achieve the target capacity could be by skewing the aerofoil. This, however, changes the stage reaction which in turn impacts the bearing thrust load. In the case of a multi stage turbine, the work split between the stages impacts the ratio of pressure drops and hence the contribution of the individual aerofoil rows to the overall capacity and bearing thrust load variation. This paper deals with a generic approach to visualise the variation of capacity and bearing thrust load with aerofoil skew for a stage of interest along with the Constraints that could be potentially imposed on the stage. This methodology provides a useful mapping between parameters which are directly under the aerodynamicist’s control (i.e. aerofoil skew) to module- and system-level behaviours (i.e. capacity, bearing thrust load). It thereby allows informed choices to be made throughout the design process which deliver the turbine aerodynamic performance targets whilst respecting wider system-level constraints. Suitable optimisation within this design space will yield a design that is fundamentally robust to small deviations in skew angle. Additionally, qualitative variation of the gas path static pressure and reaction based on aerofoil skews are explained pictorially to facilitate the understanding.

Experimental Investigation of the Dynamic Loads in a Ball Bearing Turbocharger

The objectives of this investigation were to design and develop an experimental turbocharger test rig (TTR) to measure the shaft whirl of the rotating assembly and the axial and frictional loads experienced by the bearings. The TTR contains a ball bearing turbocharger (TC) that was instrumented and operated under various test conditions up to 55,000 rpm. In order to measure the thrust loads on the compressor and turbine sides, customized sensors were integrated into the TC housing. The anti-rotation (AR) pin that normally prevents the bearing cartridge from rotating was replaced with a custom-made load cell adapter system. This sensor was used to measure the frictional losses in the bearing cartridge without altering the operation of the TC. Proximity sensors (probes) were also installed in the compressor housing to monitor shaft whirl. Axial load results indicated that the compressor side bears most of the thrust load. As the backpressure or the speed of the TC was increased, the thrust load also increased. Frictional measurements from the AR pin sensor demonstrated low power losses in the ball bearing cartridge. For certain shaft speed ranges, the data from the sensors illustrated periodic trends in response to the subsynchronous whirl of the shaft.