Turbine Parts Research Articles

DEVELOPMENT OF NEW DESIGNS OF HORIZONTAL BULB HYDROTURBINES

The key aspects and methods of increasing the energy and operational efficiency of hydraulic turbine equipment at hydroelectric power plants areconsidered. A detailed analysis of directions for improving the main indicators characterizing the advantages of horizontal-type bladed hydraulicturbines has been carried out. Particular attention is paid to direct-flow rotary-blade hydraulic turbines with a horizontal axis of rotation for thehydraulic unit. These hydraulic turbines offer significant advantages over those using a spiral casing for water supply, including high throughput and awide range of operating pressures and flow rates. The focus of the article is on the advantages of direct-flow bulb hydraulic turbines and their potentialuse at high pressures. However, existing direct-flow hydraulic units operate at low heads of up to 25 m. Therefore, there is a need to develop newdesigns for these turbines to operate efficiently at higher heads up to 280 m, expanding the reliable operation zone. The paper examines new designsolutions for which Ukrainian patents have been received, aiming at the effective use of horizontal bulb hydraulic units. The text highlights theproblems of increasing the energy and operational performance of hydraulic turbine equipment at hydroelectric power plants, presenting importanttasks for researchers to optimize structures and improve efficiency. Recommendations for carrying out numerical modeling in CFD (ComputationalFluid Dynamics) programs are proposed to provide a detailed understanding of hydrodynamic processes in the flow parts of hydraulic turbines. Thepurpose of numerical modeling is to evaluate the efficiency and productivity of new hydroturbines in different operating modes. This includesanalyzing the pressure distribution, flow rate and other characteristics inside the turbine. The obtained data will allow to identify potential "weak"points and optimize the blading and other structural elements for maximum efficiency. This integrated research approach, including both experimentaland multiple methods, will contribute to the development of efficient and reliable hydroturbines in line with modern requirements for sustainableenergy development.

Effect of Single Crystal Growth and Solidification Grain Boundaries on Weld Solidification Cracking Behavior of CMSX-4 Superalloy

Single-crystal superalloys have been popularly employed in high-temperature parts of gas turbines, such as blades. However, the welds of such alloys are highly susceptible to solidification cracking, which limits their applicability to high-temperature turbine blades. In this study, the effects of characteristics of weld solidification on solidification cracking susceptibilities (solidification brittle temperature range, BTR) were fundamentally investigated for the CMSX-4 single-crystal superalloy. We applied a transverse-Varestraint test procedure for both the linear and oscillated arc welds by changing the weld solidification characteristics, such as the degree of single crystal growth and formation of solidification grain boundaries. The BTR for the CMSX-4 alloy is 336 K for linear welding condition, whereas the values are 434 K and 342 K for 0.6 and 1.5 Hz oscillated welds. Interestingly, the BTR continuously increases with the weld oscillation frequency. By contrast, almost no changes in the weld mushy-zone temperature range are theoretically calculated for each welding condition via the diffusion-controlled Scheil model. The mechanism underlying the increase in BTR under oscillation welding is clarified based on the relationship between the achievement ratio of the weld single crystal growth and fraction of high-angle (>15<sup>o</sup>) solidification boundaries, which affect severe dendrite coalescence undercooling. The lower fraction of the high-angle weld solidification grain boundaries attributed to the superior achievement ratio of weld single crystal growth, which reduces the dendrite coalescence undercooling and BTR. Consequently, it enhances the solidification crack propagation resistance.

The use of natural heat of dry hot rocks of the earth with a gas coolant

The energy options for utilizing the deep heat of the Earth using n-pentane as a working fluid for generating electricity in the organic Rankine cycle are analyzed. The relationships between the initial and final parameters of the cycle are determined. The ratio of the average diameters of turbine stages to the working blades height along the flow part is estimated. A satisfactory profile of the flow part of an axial single-flow multistage jet turbine with subsonic flow rates of the working gas has been obtained.

Research on the design and application of wind turbine mechanical parts based on parametric modeling

Abstract Based on ANSYS finite element analysis software, a parametric modeling interface for wind turbine blades and pitch bearings is developed using parametric design language. The parametric modeling interface is used to quickly establish a simplified finite element model of the blade and pitch bearing so as to optimize the design of the blade structure, calculate the maximum tensile stress of the bearing and bolt connection, and analyze the relationship between the working stress of the bearing and bolt and the bolt preload. The analysis and calculation results guide the safety and reliability of wind turbine parts design. After analysis, the optimization of blade structure is mainly in the region of leaf root enhancement, the number of layers laid in the cross-section of No. 1-3 has no major modification, the bi-directional cloth in the cross-section of No. 3-6 is increased by 55 layers, 5 layers reduce the cross-section of No. 7-8, and the cross-section of No. 16-23, 1 layer of the bi-directional cloth is increased in order to improve the strength of the tip of the blade and the resistance to bending capacity. The preload force applied to the pitch bearing during the actual installation process is generally 50% to 70% of the yield limit of the bolt material. The pitch bearings have the best load-carrying capacity under ultimate loads, with the ditch curvature radius coefficient and clearance generally around 0.530 and −0.12mm.

Damage Detection and Localization at the Jacket Support of an Offshore Wind Turbine Using Transformer Models

Early detection of damage in the support structure (submerged part) of an offshore wind turbine is crucial as it can help to prevent emergency shutdowns and extend the lifespan of the turbine. To this end, a promising proof-of-concept is stated, based on a transformer network, for the detection and localization of damage at the jacket-type support of an offshore wind turbine. To the best of the authors’ knowledge, this is the first time transformer-based models have been used for offshore wind turbine structural health monitoring. The proposed strategy employs a transformer-based framework for learning multivariate time series representation. The framework is based on the transformer architecture, which is a neural network architecture that has been shown to be highly effective for natural language processing tasks. A down-scaled laboratory model of an offshore wind turbine that simulates the different regions of operation of the wind turbine is employed to develop and validate the proposed methodology. The vibration signals collected from 8 accelerometers are used to analyze the dynamic behavior of the structure. The results obtained show a significant improvement compared to other approaches previously proposed in the literature. In particular, the stated methodology achieves an accuracy of 99.96% with an average training time of only 6.13 minutes due to the high parallelizability of the transformer network. In fact, as it is computationally highly efficient, it has the potential to be a useful tool for implementation in real-time monitoring systems.

Numerical Study on the Flow and Heat Transfer Characteristics in Mortise and Tenon Gap under Rotating Conditions

Mortise and tenon are very important parts of gas turbine dealing operation safety. Additionally, the temperature distribution of the turbine blade and disk is affected by the heat transfer characteristics in its gap. Then, the S-shaped mortise and tenon gap were numerically studied under rotating conditions, and the flow and heat transfer characteristics were analyzed. First, the heat transfer coefficient (HTC) of the mortise and tenon surfaces was measured with thermochromic liquid crystal. Then, the numerical method was verified using the test results, and the grid independence analysis was conducted. Finally, the flow and heat transfer characteristics of the gap under static and rotating conditions were numerically studied, five different Reynolds numbers (Re = 15,000, 20,000, 25,000, 30,000, 35,000) and five gap widths (d = 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm) were conducted and analyzed in detail. The results show that, under the rotating condition, the pressure distribution in the gap is different from that of the static condition; the pressure increases along the radial direction due to the action of centrifugal force and reaches its maximum value at the corner of the “S” shaped structure. With the increase in Re, the heat transfer intensity of the gap increases gradually. Additionally, the heat transfer intensity of the gap increases with an increase in its width.

Exergy analysis of thermodynamic performance of a gas turbine unit

BACKGROUND: Gas turbine units are the most widespread type of power plants used in almost all industries. Such a wide distribution in combination with a high level of energy characteristics, high specific power and flexibility determine the relevance of research in the field of assessing their operating parameters.
 AIM: Determining the exergy characteristics (exergy efficiency and exergy dissipation factor) of a gas turbine plant and evaluation the efficiency of energy use in a gas turbine plant, as well as analysis of the influence of ambient temperature on the selected parameters.
 METHODS: The paper presents the results of an exergy analysis of the gas turbine plant as part of the Jandar Thermal Power Plant, Syria. To evaluate the described parameters, the method of exergy analysis of the thermodynamic characteristics of a gas turbine plant based on the first and second laws of thermodynamics in conjunction with the laws of conservation of mass and energy was used. An important feature of the study, which also emphasizes its novelty, is taking into account the chemical exergy of combustion gases during the exergy analysis.
 RESULTS: Based on the results of the study, it was found that the maximum exergy efficiency was 92.8% and was typical for a turbine as part of a gas turbine, while the highest exergy dissipation was observed in the process of fuel combustion in the combustion chamber and was equal to 80% (117.3 MW). The lowest exergy values corresponded to the compressor — 6.0% (9 MW). For the gas turbine unit as a whole, the total exergy dissipation was 147.3 MW and the exergy efficiency was 53.3%. In this case, the main sources of irreversibility in the gas turbine unit are the combustion chamber and combustion gases.
 CONCLUSION: Exergy analysis is a convenient method for evaluating the thermodynamic perfection of gas turbine units. As a further line of the study, it is necessary to evaluate the effects of various conditions, such as air humidity or compressor pressure ratio, on the exergy characteristics of the gas turbine fuller.

Simulation of energy losses in an inflow turbine with partial blading of the runner

Studying the coefficients of kinetic energy losses of the nozzle diaphragm and the runner in an inflow turbine with partial blading of the runner is carried out. It is noted that inflow low-consumption turbines are reliable and productive devices designed to drive various units. Due to their compact size, they are especially in demand in various branches of mechanical engineering. However, in order to increase efficiency and reduce production costs, it is necessary to constantly improve the technology of manufacturing turbine stages. Some inflow turbines are partial, which leads to additional energy losses. Partial stages in which there are no losses from ventilation, namely, turbines with partial flapping of the runner are considered. To simulate such turbines, the ANSYS CFX software package is used in the work. By using ANSYS Design Modeler to create a geometric model and determine boundary conditions, as well as selecting the appropriate grid, the dependences of the loss coefficients in the nozzle and the runner are obtained. The study has shown that the degree of partiality and the Mach number of the turbine stage have a significant impact on the losses coefficients in the exact part of the nozzle and the runner. To account for these dependencies in the modeling process, empirical dependencies, which are an integral part of the design process of inflow turbines, are obtained. The use of the obtained empirical dependences makes it possible to more accurately predict the characteristics and performance of turbines of this type, as well as to supplement the existing mathematical model of the flow in the flow part of a low-consumption inflow turbine with partial blading of the runner.

Effect of Aging Parameters on Inconel 718 Fabricated by Laser Directed Energy Deposition

Inconel 718 is a nickel-based superalloy of high interest in high temperature applications such as turbine parts. To be used in such applications, heat treatments are commonly applied to dissolute Laves phase and to achieve γ′′ phase. However, conventional heat treatment methods for wrought Inconel 718 may not be suitable for Inconel 718 fabricated by laser directed energy deposition (LDED) due to its unique microstructure formed during the rapid solidification process. There has been a lack of investigation in heat treatments for Inconel 718 fabricated by this process, specifically around the impact of aging parameters on this alloy. In this study, the effects of aging parameters were studied by performing seven different heat treatments, including solutionising and aging treatments. Our results indicate that for LDED Inconel 718, a high temperature solution treatment of 1100 ℃ for 1 h followed by single aging at 650 ℃ for 20 h achieved a tensile strength and elongation of 1247 MPa and 23%, respectively. Further, results indicated that even with a shorter aging time of 10 h, γ′′ phase was found to be of comparable size to the standard double aged treatment.

Persistent Voltage Control of a Wind Turbine-Driven Isolated Multiphase Induction Machine

The growing concern about the energy crisis and environmental protection has caused a growing interest in wind power generation systems. Researchers and engineers urgently need to create new multiphase induction machines for the production of wind energy, since they are essential parts of wind turbines. This study offers control and stability analysis of a multiphase induction machine based on the entropy stability requirements for its linearized model. The generated model was used to assess the on-load properties of the multiphase induction machine and calculate its steady-state parameters under each operating circumstance. According to the analysis, the eigenvalues depend on the machine parameters, with the excitation capacitance and speed variation being the most important. Stabilization of the multiphase induction machine is the main focus of the singular values, which vary according to its variables. The simulated results include an examination of a multiphase induction machine steady state for voltage build-up at various types of load.

COMPARATIVE ANALYSIS OF SOFTWARE SYSTEMS FOR HYDRAULIC TURBINE FLOW SIMULATION

A comprehensive review of modern software complexes used for calculating spatial flow in hydraulic turbine flow parts was conducted. The widely used software system, Ansys, was analyzed. An overview of Ansys was provided, including its history, popularity within the CFD community, key features, and capabilities for analyzing the flow parts of hydraulic turbines. The preprocessing tools, solver parameters, post-processing functions, and visualization capabilities of Ansys were described. The advantages and limitations of using Ansys for calculating spatial flow in hydraulic turbine flow parts were analyzed. The open-source CFD software complex, OpenFOAM, was discussed. The main functions and capabilities of the OpenFOAM program were described. Information about solver libraries, meshing capabilities, advantages, and limitations for analyzing hydraulic turbines was presented, along with insights into the support from the scientific community and resources available to OpenFOAM users. SolidWorks FlowSimulation, which integrates with SolidWorks software, was examined. The unique features of SolidWorks FlowSimulation for analyzing spatial flow in hydraulic turbines were highlighted. The possibilities of CAD integration and the advantages of accurate geometric models were discussed. The capabilities of parametric analysis were explored, and the advantages and limitations of using SolidWorks FlowSimulation for calculating spatial flow in hydraulic turbine flow parts were analyzed. A comparison of the three software complexes was conducted based on their capabilities, ease of use, accuracy, computational resources required, and cost. An assessment of the advantages and disadvantages of each program was provided, along with recommendations for choosing the most suitable program based on specific use cases, objectives, and user requirements. This article serves as a valuable resource for engineers, designers, and researchers seeking insights into the available software systems for analyzing hydraulic turbine flow parts. It enables them to make informed decisions in selecting the most suitable software system based on their specific requirements, ultimately contributing to the optimization of hydraulic turbine performance and efficiency.

Инновационные технологии повышения производительности и качества механической обработки полимерных композиционных материалов

An urgent problem for improving the efficiency and machining operation quality for new polymer composite materials (PCM) based on carbon fiber in the operation of rocket and space equipment and aircraft engineering parts is solved in the article. One of the breakthroughs of the Russian domestic engineering is the introduction of wing elements of the new MS-21 civil airliner, the production of noise suppression bodies, compressor blades and other parts of gas turbine engines made of carbon fiber, requiring high-quality and productive machining. Machining operation of these products involves difficulties caused by the requirements of the design documentation to ensure the necessary degree of roughness, soundness of the machined surface and high strength of the finish-machined component. This article presents the results of a study of the application of high-performance technology of sequential blade-abrasive processing of carbon fiber-based PCM products. This article presents the results of a study of the application of high-performance technology of sequential blade-abrasive operation of carbon fiber-based PCM products. The rational geometry of the blade cutting tool for primary machining of the PCM is determined. An adequate empirical mathematical model of cutting modes influence on the surface layer roughness in the milling operation has been developed, as well as rational processing modes have been determined.
 The results of experimental studies of the abrasion of PCM with rigid grinding wheels made of white electrocorundum, green silicon carbide and elborum are presented. The dependences of the surface layer roughness on the grinding modes are given. According to the research results and the developed mathematical model, the rational characteristics of grinding wheels and processing modes are determined. For the first time, the issues of the influence of machining defects on the strength of PCM are viewed. Comparative tensile and tear strength tests of samples made by traditional edge cutting machining and sequential edge-cutting-abrasive operation are presented. The increase in tensile and tear strength of PCM parts manufactured according to the technology of sequential edge-cutting-abrasive operation by 20.30% compared to traditional edge-cutting operation has been proved.

π-FBG Fiber Optic Acoustic Emission Sensor for the Crack Detection of Wind Turbine Blades.

Wind power is growing rapidly as a green and clean energy source. As the core part of a wind turbine, the blades are subjected to enormous stress in harsh environments over a long period of time and are therefore extremely susceptible to damage, while at the same time, they are costly, so it is important to monitor their damage in a timely manner. This paper is based on the detection of blade damage using acoustic emission signals, which can detect early minor damage and internal damage to the blades. Instead of conventional piezoelectric sensors, we use fiber optic gratings as sensing units, which have the advantage of small size and corrosion resistance. Furthermore, the sensitivity of the system is doubled by replacing the conventional FBG (fiber Bragg grating) with a π-phase-shifted FBG. For the noise problem existing in the system, this paper combines the traditional WPD (wavelet packet decomposition) denoising method with EMD (empirical mode decomposition) to achieve a better noise reduction effect. Finally, small wind turbine blades are used in the experiment and their acoustic emission signals with different damage are collected for feature analysis, which sets the stage for the subsequent detection of different damage degrees and types.

Advanced Pitch Angle Control Based on Genetic Algorithm and Particle Swarm Optimisation on FAST Turbine Systems

In this paper, the increase in the quality of the rotor speed of wind turbines and the decrease in mechanical loads on the turbines are investigated. Adjusting the angle of the blade to the nominal wind speed, the rotor speed of the wind turbine is maintained at its nominal value. Using control methods (such as proportional integral (PI), genetic algorithms (GAs), and particle swarm optimisation (PSO)), different results can be recovered. In addition, individual control of the blade tilt angle allows us to reduce the mechanical loads on the turbine with the control methods. The wind turbine was modelled in Matlab/Simulink. The simulation results show that individual control of the blade tilt angle ensures the quality of the rotor speed of the wind turbine and reduces the balanced periodic loads on the wind turbine. In the first part, we study the wind turbine in a global way, as well as the method used to calculate them. Then, we discuss the FAST system, which was used to model the wind turbine, as well as the design of individual pitch angle control. As a result, it is possible to reduce the fatigue of the mechanical wind turbine parts. According to the study, the mechanical load for all three blades was reduced by an average of 44 % compared to the PI and PSO methods and by 1 % compared to the PI and GA methods. The control of the pitch angle in wind energy systems is performed with different control methods. The study analysis of the mechanical loads found that they are largely balanced. Winds that blow perpendicular to the turbine blades on the x-axis provide these loads.

Influence of the spatial variation of upstream velocity on a vertical-axis tidal turbine performance

Assessment of the upstream flow available to the tidal energy converters (TEC) is key to evaluate its performance. Simultaneously, TEC technology has been innovating on its concepts and designs to expand the potential sites to harvest energy generated by tidal currents and rivers. The Gkinetic CEFA 12 is an easy-to-deploy device suitable to operate on estuary environments. The design consists of two 1.2 m vertical axis turbines attached to the sides of a buoyant platform, which uses a bluff body to accelerate the incoming flow to the rotors. The device was deployed on a single point mooring enabling passive flow alignment. As part of the Vertical axis tidal turbines in Strangford lough project (VATTS), the upstream flow has been measured using acoustic doppler profilers (ADP) mounted on the TEC during its operation in Strangford lough. Recommendations of IEC-200 were followed when mounting the ADPs relative to Gkinetic. However, the continuous repositioning of the TEC according to the prevailing tidal regime affects the ADPs heading. The implications of the spatial variation of the rotor’s upstream velocity on the resource assessment and device performance are not clear since this situation is not typical.To investigate the spatial variation of the upstream velocity two ADCP deployment locations were made. A seabed (upward facing) ADCP as per the current standards and a device mounted (downward facing) ADCP upstream of the rotor plane. Evaluation of the influence of the following three factors were made: i) the ADPs direction repositioning according to prevailing tidal regime, ii) the proximity of the sensors to the sea-surface, and iii) the proximity of the sensors to the TEC.These three factors will be evaluated using ADP datasets collected at Strangford narrows during the VATTS project. The datasets were obtained at approximately the same location of the TEC operation. They enable the study of the following scenarios 1) incoming flow to the rotors during operation, 2) incoming flow on undisturbed conditions (no turbine operation), and 3) a harmonic analysis prediction of the undisturbed incoming flow, which solely captures the tidal-driven flow.The investigation of these three scenarios will provide a better understanding on the rotor’s upstream flow spatial variation, and the influence of the device’s proximity and near sea surface conditions on the mean flow. These findings would benefit developers of alternative TEC designs that operate near the sea-surface.

THE STUDY OF LAMINAR AND TURBULENT FLOW IN TURBINE TYPE OF FLOW METERS

The paper studies the operation of a turbine-type flow meter under various operating modes. In the industry, flow measuring devices are widely used on oil and gas platforms and terminals. In the processes of production, processing and transportation of oil and gas, which is a strategic raw material, strict state control of its consumption is carried out precisely by means of consumption measurement. A performance study has been carried out for turbine - type gas flow meters under laminar and turbulent gas flow conditions .. One of the main factors that cause damage to the mechanical parts of turbine and rotor type gas flow meters during operation was the study of flow changes. The proposed method to prevent flow changes was considered. The principle of work of the proposed scheme is based on the connection of a flow regulator before the flow meter being tested to the same gas line. In this case, the transition of the flow from the laminar regime to the turbulent regime is prevented, as well as the rotating mechanical parts are protected from sudden rotation and damage. In ideal rotation, it is assumed that the flow through the turbine meter is uniform, incompressible, and steady, and the turbine blade rotates without friction. Under these conditions, the speed of rotation of the impeller is determined by the pitch of the turbine impeller. Keywords: turbine-type flow meter, ideal rotation, turbulent flow, laminar flow, Reynolds number.

Вплив температурного перепаду на ступінь підвищення тиску у вентиляторному контурі турбовентиляторної приставки ГТД

The subject of this study is the working process in a turbofan attachment of a gas turbine engine. The object of study is the fan part of the impeller of a turbofan attachment. The aim of this study was to evaluate the effect of temperature difference in a two-tier impeller on the degree of pressure increase in the fan part of a two-tier impeller of a turbofan attachment of a three-circuit engine. To achieve this goal, the following tasks were solved: to simulate the flow in a turbofan attachment; to calculate the dependence of the degree of pressure increase in the fan part of the impeller of the turbofan attachment on the Mach number for the operating mode at altitudes of 0 km, 9 km and 11 km; to evaluate the temperature difference in the two-tier impeller of the turbofan attachment. The study was carried out by the method of numerical experiment. Results: The dependence of the degree of pressure increase of the fan circuit of the turbofan attachment on the Mach number at the inlet is obtained, taking into account the effect of hot gases of the turbine circuit of the turbofan attachment. It is shown that the flow of hot gases affects the degree of pressure increase in the fan circuit. The presence of the turbine part of the two-tier impeller leads to a slight deterioration in the characteristics of the fan part. The degree of pressure increase is reduced by 0.2 ... 4.8 %. The greatest influence is manifested in the operating mode H = 11 km. Visualization of the flow velocity field in the fan part of the turbofan unit showed that during the operation of the turbine circuit, the nature of the leakage in the fan part changes by approximately 50% of the blade height. An increase in temperature contributes to the intensification of the energy of the boundary layer around the lower part of the blade of the fan circuit, which has a positive effect on the reduction of zero velocity zones during the flow. Scientific novelty and practical significance: new data were obtained on the effect of temperature difference in a two-tier impeller on the degree of pressure increase in the fan part of a two-tier impeller of a turbofan attachment of a three-circuit engine. The results obtained can be used to optimize the turbofan attachment of a gas turbine engine.

Characteristics and performance of suspension plasma sprayed thermal barrier coatings on additively manufactured superalloy substrates

The complex-shaped hot-section parts of new-generation turbine engines demand unique design solutions. Additive Manufacturing (AM) is an emergent production method that can produce metallic parts with complex geometries and minimal material wastage. In this work, the characteristics and performance behavior of Thermal Barrier Coatings (TBCs) deposited on forged and AM-built HAYNES®282® superalloy substrates were studied and compared. The bond coats were produced by High-Velocity Air-Fuel (HVAF) spraying using NiCoCrAlY powder feedstock and TBC top-coats by Suspension Plasma Spraying (SPS) using water- and ethanol-based suspensions of Yttria-Stabilized Zirconia (YSZ). The microstructural features, adhesion, Thermal Cycling Fatigue (TCF) lifetime, and thermal shock lifetimes of the TBCs were comprehensively investigated. The results showed that the deposition of bond coats reduced the roughness and asperities of the AM-built substrates. Depending on the type of suspension used and the spray parameters employed, the TBCs exhibited vertically cracked and columnar microstructures. However, no significant differences in TCF and thermal shock lifetimes of TBCs on AM and forged substrates were observed. It is demonstrated that TBC systems can be produced on AM-built metallic substrates, and the resulting TBCs can have similar microstructures and properties as TBCs deposited on conventional substrates.

Acoustic Simulation of Hydraulic Turbine Top Bolt Fatigue Crack Detection Based on DG-FEM

The top bolt is one of the important parts of turbine, and its health condition affects the stable operation of the pumping and storage unit. In this paper, the DG-FEM method was used to simulate ultrasonic waves to detect bolt crack defects. In the experiment, the ultrasonic propagation of single thread side and double thread side was simulated respectively under the condition of center excitation and bias excitation, and the feasibility of ultrasonic detection of bolt crack was explored. In addition, the reflection wave shapes of the two days under different excites of the center and the offset were compared, and the conclusion was drawn that the offset excites were more sensitive to the detection of bolt cracks than the center excites, and the reflected wave peaks were higher, which was conducive to improving the success rate of defect detection. It is prepared for the practical application of engineering and has certain reference value.

Life extension of AC-DC converters for hydrogen electrolysers operating as part of offshore wind turbines

Energy resources based on green hydrogen are nowadays beginning to enjoy wide adoption and draw considerable interest. There are different types of hydrogen production, but it is green hydrogen that is becoming an attractive energy development capable of replacing blue and grey hydrogen as well as fossil fuels, Thereby the carbon footprint will be reduced for a number of industrial processes. Proton exchange membrane electrolyzers used for the production of environmentally friendly hydrogen have one key shortcoming, which is the short service life of the equipment. This paper presents a comparative study of the commonly applied PLL control of AC-DC converters. To improve the control of the proton exchange membrane of the electrolyzer, a vector control arrangement is adopted, which allows, by relying on cascade control loops, maintaining different DC link voltage levels and thereby extending the DC link input voltage variation range.