Recent times have seen a great interest on environmental issues and efficient, sustainable systems. This interest has required the employment of advanced composites for a myriad of industrial machines and innovative equipments. Among these applications, Flywheel Energy Storage Systems – FESS – represent a group of machines that are being re-invented through this process. Modeling composite flywheels has proven to be a complex task, which current Finite Element models fail to fulfill in a number of design contexts. This demand to model complex composite geometries and systems induced the proposition of new methods, aiming to capture the various physical effects existing in the problem. In the present contribution, the authors consider that it is viable to model the dynamic behavior of a Flywheel Energy Storage System via an adapted Carrera Unified Formulation, both in terms of accuracy and computational cost, for practical applications. The present work presents and explores a Carrera Unified Formulation model with extended capabilities dedicated to rotordynamics applications. The differences from standard Finite Elements models are presented, evidencing advantages and drawbacks of the proposed methodology over more traditional approaches. A case study is then presented, modeled, and the results are compared with those stemming from established formulations.
In this podcast, Martina Reche Vilanova explains about her research on wind propulsion on commercial ships. Martina is an industrial PhD at DTU and North sails and part of the Maritime Research Alliance PhD network.
The wave loads and the resulting motions of floating wave energy converters are traditionally computed using linear radiation–diffraction methods. Yet for certain cases such as survival conditions, phase control and wave energy converters operating in the resonance region, more complete mathematical models such as computational fluid dynamics are preferred and over the last 5 years, computational fluid dynamics has become more frequently used in the wave energy field. However, rigorous estimation of numerical errors, convergence rates and uncertainties associated with computational fluid dynamics simulations have largely been overlooked in the wave energy sector. In this article, we apply formal verification and validation techniques to computational fluid dynamics simulations of a passively controlled point absorber.
The phase control causes the motion response to be highly nonlinear even for almost linear incident waves. First, we show that the computational fluid dynamics simulations have acceptable agreement to experimental data. We then present a verification and validation study focusing on the solution verification covering spatial and temporal discretization, iterative and domain modelling errors. It is shown that the dominating source of errors is, as expected, the spatial discretization, but temporal and iterative errors cannot be neglected. Using hexahedral cells with low aspect ratio and 30 cells per wave height, we obtain results with less than 5% uncertainty in motion response (except for surge) and restraining forces for the buoy without phase control. The amplified nonlinear response due to phase control caused a large increase in numerical uncertainty, illustrating the difficulty to obtain reliable solutions for highly nonlinear responses, and that much denser meshes are required for such cases.
Improving the power density of solid oxide fuel cell stacks would significantly enhance this technology for transportation. Using a monolithic structure to downsize the stack dimension offers a key to elevate the power density of solid oxide fuel cell stacks. This innovative design is promising but manufacturing is a challenge. The monolith is co-sintered in one firing step, and the gas channels are formed by burning off sacrificial organic materials. Structure distortion or fracture was observed in post-mortem investigations. In this work a multiscale, multiphysics modelling approach is proposed to describe and resolve this challenge in the debinding process occurring in a monolithic stack, i.e. the burning of organics and transportation of gases through the gradually opening microstructure, as well as the pressure build-up in the microstructure due to gas development. Simulation results show that a prominent pressure peak is experienced in the stack when a plasticiser (polyethylene glycol) and a pore-former (polymethyl methacrylate) are decomposed simultaneously. To reduce the high pressures, we investigate two possible strategies: (i) changing the mixture of organic additives; (ii) modifying the debinding temperature profile. Three tapes with different pore-formers are prepared, and the generated pressures during debinding of the three stacks are compared. The corresponding stack shapes after debinding are recorded. Numerical investigations show a good agreement with the post-mortem observations. By changing the composition of organics the distortion or fracturing of the stack can be avoided. Furthermore, to facilitate stack manufacturing, the high pressures can also be reduced by adjusting the heating rates and dwell temperatures of debinding. By using the new temperature profile suggested by the simulation study, the duration of debinding can also be reduced.
Hydrogen is believed as a promising energy carrier that contributes to deep decarbonization, especially for the sectors hard to be directly electrified. A grid-connected wind/hydrogen system is a typical configuration for hydrogen production. For such a system, a critical barrier lies in the poor cost-competitiveness of the produced hydrogen. Researchers have found that flexible operation of a wind/hydrogen system is possible thanks to the excellent dynamic properties of electrolysis. This finding implies the system owner can strategically participate in day-ahead power markets to reduce the hydrogen production cost. However, the uncertainties from imperfect prediction of the fluctuating market price and wind power reduce the effectiveness of the offering strategy in the market. In this paper, we proposed a decision-making framework, which is based on data-driven robust chance constrained programming (DRCCP). This framework also includes multi-layer perception neural network (MLPNN) for wind power and spot electricity price prediction. Such a DRCCP-based decision framework (DDF) is then applied to make the day-ahead decision for a wind/hydrogen system. It can effectively handle the uncertainties, manage the risks and reduce the operation cost. The results show that, for the daily operation in the selected 30 days, offering strategy based on the framework reduces the overall operation cost by 24.36%, compared to the strategy based on imperfect prediction. Besides, we elaborate the parameter selections of the DRCCP to reveal the best parameter combination to obtain better optimization performance. The efficacy of the DRCCP method is also highlighted by the comparison with the chance-constrained programming method.
This study proposes a new application for delay-dependent stability analysis of a shipboard microgrid system. Gain and phase margin values are taken into consideration in delay dependent stability analysis. Since such systems are prone to unwanted frequency oscillations against load disturbances and randomness of renewable resources, a virtual gain and phase margin tester has been incorporated into the system to achieve the desired stabilization specification. In this way, it is considered that the system provides the desired dynamic characteristics (e.g. less oscillation, early damping, etc.) in determining the time delay margin. Firstly, the time delay margin values are obtained and their accuracy in the terms of desired gain and phase margin values are investigated. Then, the accuracy of the time delay margin values obtained by using the real data of renewable energy sources and loads in the shipboard microgrid system is shown in the study. Finally, a real-time hardware-in-the-loop (HIL) simulation based on OPAL-RT is accomplished to affirm the applicability of the suggested method, from a systemic perspective, for the load frequency control problem in the shipboard microgrid.
Existing energy management strategies (EMSs) for hybrid power systems (HPSs) in hydrogen fuel cell vessels (FCVs) are not applicable to scenarios with multiple hydrogen fuel cells (FCs) and lithium batteries (LBs) in parallel, and are difficult to achieve real-time control and optimization for multiple objectives. In this paper, a bi-layer real-time energy management strategy (BLRT-EMS) is proposed. Compared with existing EMSs, the proposed BLRT-EMS implements different control/optimization objectives distributed in the execution layer EMS (EL-EMS) and the decision layer EMS (DL-EMS), which can significantly reduce bus voltage fluctuations, decrease hydrogen consumptions, improve the system efficiency, and have potential for engineering applications. In the first EL-EMS, a decentralized optimal power allocation strategy is proposed, which allows each FC system to allocate the output power ratio according to their generation costs, ensuring consistent performance of multiple FC systems (MFCS) under long-term operating conditions, and thus delaying the degradation rate of FCs. In the second EL-EMS, a distributed cooperative control strategy is proposed to achieve dynamic SoC equalization, proportional output power allocation, and accurate bus voltage restoration among multiple battery storage systems (MBSS) to extend the service life of batteries. In the DL-EMS, an energy coordination optimization strategy between MFCS and MBSS is proposed to achieve hydrogen consumption reduction and system efficiency improvement, thus enhancing the endurance performance of FCV. Finally, test results based on the StarSim experimental platform show that the proposed BLRT-EMS has faster SoC convergence speed, smaller bus voltage deviation, lower hydrogen consumption, higher system efficiency, and lower operation stress than the state-of-the-art methods.
In this paper, the impacts of large-scale OWPPs penetration on the Turkish power system are addressed. The grid compliance analyzes for the large-scale OWPP integration are carried out by using the grid connection criteria defined in the Turkish grid code. PV and QV curves are obtained to assess the effect of OWPP on the static voltage stability limit. Eight scenarios are conducted to analyze the effect of the OWPP on the static and dynamic characteristics of the power grid. To observe the large-scale OWPP impact on the voltage and frequency stability, transient events such as the outage of conventional power plants and three-phase to ground faults are applied. The results of the voltage and frequency stability analysis reveal that the Turkish grid remains stable after the integration of an 1800 MW OWPP. Furthermore, the Turkish system remains stable even in the event of an outage of the international transmission lines to Bulgaria and Greece.
Hydrogen energy is a promising solution for prompting low-carbon port development. This study introduces two hydrogen utilization strategies: hydrogen consumption-driven strategy (HCDS) and hydrogen storage-driven strategy (HSDS). Using data from a real port and a life-cycle assessment approach, a case study is conducted to compare their economic and ecological performances. The results show that HCDS enhances economic benefits, with an annualized cost of 66.1 million CNY, which is 11% lower than HSDS. Additionally, HCDS is sensitive to electricity prices and grid carbon emission factor. In contrast, HSDS offers superior ecological benefits, with an annualized carbon footprint of 31,300 tons of CO₂, which is 12% lower than HCDS, and is mainly sensitive to purchase prices and emission factors of electricity and hydrogen. This study provides critical insights into the trade-offs between economic and ecological performance under different hydrogen utilization strategies, offering practical guidance for implementing hydrogen energy system applications in ports.
Solid-state lithium battery (SSLB) is considered as the most potential energy storage device in the next generation energy system due to its excellent safety performance. However, there are still intimidating safety issues for the SSLB, due to it being still in the development stage. This paper gives an overview of the safety of SSLBs. First, advanced solid-state battery techniques are introduced. Second, the safety issues of SSLBs are discussed. Then, the safety enhancement techniques are provided. Finally, future research opportunities are presented. This paper aims to provide a reference for researchers in the fields of electronic and electrical engineering who want to make some efforts in SSLB safety.