Dynamic Energy Conversion Research Articles

Coupled dynamic response and energy conversion characteristics of 10 MW floating vertical axis wind turbine with different configurations

Vertical axis wind turbines (VAWTs) are superior because they have compact structure, good wind adaptability and strong scalability. The coupling dynamic response mechanisms between different configurations of wind turbines and floating platforms are different. Based on the CFD method, dynamic fluid body interaction (DFBI), overlapping grid and dynamic grid techniques are used for numerical simulations. The force characteristics and self-starting features of H-type and Φ-type VAWTs are compared. The aerodynamic performance and motion response of the floating VAWT (FVAWT) are studied under different tip-speed ratios (TSR) and aspect ratios (η). The results show that the power coefficient (Cp) of H-type and Φ-type FVAWTs reaches the peak when TSR = 6 and TSR = 7, respectively. The optimal η for both is 1.2. The H-type FVAWT improves the Cp by 34.3% compared to Φ-type FVAWT. H-type FVAWT has a large thrust and excellent stability. The Φ-type FVAWT requires less initial thrust, and the self-starting performance is 12% superior to H-type FVAWT. With the increase of TSR and η, the heave motion of both FVAWTs is almost unaffected, but the pitch motion sensitivity is stronger. The heave amplitude of H-type FVAWT is 282% larger than Φ-type FVAWT, which has a gain effect on energy conversion. The Φ-type FVAWT has better safety. The strengthened structure of Φ-type VAWT has a noticeable impact on velocity and vortex distribution. In addition, the aerodynamic and hydrodynamic performance of the FVAWT is improved.

Improvement of dynamic response and energy conversion ratio of a global type solenoid for high-speed valve by using an innovative magnet ring

The transient behavior and energy transmission of a global type solenoid for high-speed valve (HSV) depend upon the magnetic force acting on the sphere. Rapid responses are challenging to achieve because of the limited power supply energy, which makes it hard to optimize the magnetic force through its own structural characteristics for HSV. Aiming to obtain higher magnetic force without increasing the input electric power, an innovative magnet radial ring is presented and a relative evaluation of magnetic forces exerted on a global type solenoid for HSVs is conducted. A hollow-plunger-type magnet radial ring is engineered as a novel magnet ring form. The magnetic forces and transient action time of the conventional HSV and innovative HSV are evaluated by means of finite element method (FEM) analysis and demonstrated by verification of the experimental data. The assessment of the magnetic forces involves every solenoid with a diverse magnet ring shape with the variation of height and thickness. The suggested novel magnet ring successfully increases the magnetic force applied to the sphere by changing the internal magnetic connection structure and increasing the mechanical energy conversion ratio, according to a methodical comparison of the two HSVs' transient performances. Meanwhile the innovative magnet ring can reduce the strength of iron loss occurred in the magnetic field of HSV to realize the reduction of useless power loss. At the magnetization position at the attraction, the magnetic force is 17.35 N, while the magnetic ring increases the magnetic force to 28.84 N. Also, the maximum rising speed of the magnetic force is improved from 14945 N/ms to 38904 N/ms, and the transient action time is reduced from 3.74 ms to 1.30 ms. For the mechanical energy and iron loss energy in energy conversion occurred in solenoid, the mechanical energy ratio increases from 16.2 % (conventional valve) to 27.8 % (innovative valve) with height 26 mm and thickness 3.5 mm, while the iron loss energy ratio decreases from 40.7 % (conventional valve) to 31.8 % (innovative valve) synchronously.

Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

Dynamic behavior modeling and energy conversion characteristic analysis of a thermoacoustic-piezoelectric generator with the consideration of thermal and viscous losses

The amalgamation of thermoacoustic and piezoelectric principles represents a promising approach to bolster energy harvesting capabilities, offering a viable solution to address the increasingly pressing environmental concerns and energy shortages. This research introduces a thermoacoustic piezoelectric generator, serving as a versatile platform for the efficient interplay of thermal, acoustical, mechanical, and electrical energies. The proposed system comprises distinct components, including a hot buffer, stack, resonators, and piezoelectric transducer. At the left end of the system, a generalized impedance boundary condition is employed. Theoretical models, rooted in the wave equation and thermoacoustic theory, are meticulously developed. These models leverage the smoothed-Fourier series and the Galerkin method, presenting a generalized eigenvalue problem encompassing oscillation frequency and the corresponding coefficients of acoustic pressure. These models are rigorously validated through comparisons with existing literature. Building upon the established model, this study thoroughly investigates the influence of various geometrical and electrical parameters, such as tube length, stack position, external load, and the impact of the general impedance boundary condition, on dynamic behaviors. These dynamic behaviors encompass the onset frequency, and the distributions of acoustic pressure, volume velocity, acoustic impedance, as well as energy conversion characteristics, including captured energy and energy capture efficiency. The theoretical model and analytical framework developed in this study hold significant utility in the design and optimization of thermoacoustic piezoelectric generators. They are poised to advance the field of energy harvesting technology, fostering substantial growth across a multitude of industrial applications.

Investigation of temperature-dependent dynamic hysteresis loop and thermal energy conversion for Sn doped Ba0.95Sr0.05Ti0.95Zr0.05O3 ceramics

Investigation of temperature-dependent dynamic hysteresis loop and thermal energy conversion for Sn doped Ba0.95Sr0.05Ti0.95Zr0.05O3 ceramics

Study on water entry characteristics of the projectile colliding with the floating ice based on fluid-structure interaction method: Dynamic response and energy conversion

This study investigates the water entry process of the collision between the ocean detector and the floating ice in polar environments, which is crucial for detecting polar ocean energy. The study utilizes the fluid-structure interaction (FSI) method to analyze the dynamic characteristics of the projectile colliding with the floating ice and the energy change between objects. The effect of the size, structure, and distribution of the floating ice on the water entry process is also taken into account. Experiments have verified the accuracy of the FSI method. The presence of floating ice alters the cavity evolution and subsequently affects the water entry state of the projectile. The width of the floating ice also has a noticeable effect on the cavity evolution during collision water entry. Smaller floating ice sizes result in lower kinetic energy loss after the projectile collides with the floating ice. As the mass of the floating ice increases, the elastic strain energy generated by the projectile when it first collides with the floating ice increases. After the collision separation, the elastic strain energy generated by the second collision is also greater. Additionally, stress concentration occurs during the collision, and the hydrodynamic force on the object is influenced by the evolution of the cavity. When the projectile collides with the edges of the floating ice on both sides, a unique spherical splash crown is formed. This collision mode results in a lower loss of kinetic energy and elastic strain energy compared to colliding with single floating ice.

Effects of Layering Angle and Prestress on Dynamic Load Energy Conversion and Damage Mechanism of Sandstone

Previously conducted studies have established the conversion relationship between incident energy, reflected energy, transmitted energy and absorbed energy of rocks under dynamic load. In this paper, the combined dynamic and static loading tests of sandstone under different prestress and different bedding angles are carried out to explore the law of the influence of prestress and bedding angles on energy evolution and damage evolution. The purpose is to provide some reference for deep mining, rock engineering design and geological hazard assessment. The energy conversion and damage characteristics of sandstone in the whole process of deformation are studied, and the internal energy conversion mechanism of sandstone under dynamic load is proposed. It is found that the increase in prestress will lead to the increase in the initial energy value of sandstone and further affect the shape of the energy evolution curve. In addition, the relationship between strain and energy transformation is established, and it is found that the energy transformation in different stages is different. At the same time, the relationship between prestress and damage characteristics and bedding angle and damage characteristics is established, and it is found that bedding angle and prestress significantly affect the damage characteristics.

Annual performance and dynamic characteristics of a hybrid wind-wave floating energy system at a localized site in the North Sea

A hybrid system consisting of a spar-type wind turbine and an annular wave energy converter (WEC) is prospective in joint offshore wind-wave energy exploitation. Its coupled dynamic and power features in vast operating sea states are a valuable reference for design but are poorly understood. This study aims to fill the gap. By combining the wind module of OpenFAST and an in-house code, a numerical tool that can tackle the full aero-servo-hydro-mooring couplings in the hybrid system is developed. Dynamic features, mooring tensions, and energy conversion performance of a Hywind-annular WEC hybrid system are analyzed in a wide range of operating conditions with varying speeds of steady winds and periods of regular waves, emphasizing the effect of the annular WEC on the dynamic and power performance of the Hywind. Results show that the annular WEC improves the wind power generation below the rated wind speed and the stability of the Hywind by reducing its pitch displacement. But it also increases the motion amplitude in the heave direction. The annular WEC has a neglectable influence on the maximum mooring tensions. An evaluation of the annual wind-wave power based on hindcast sea states shows that wave power can effectively supplement wind power.

Modeling and Detection of Dynamic Position Sensor Offset Error in PMSM Drives

Rotor position information obtained through a position sensor is crucial for proper field-oriented control (FOC) of permanent magnet synchronous machine-based high dynamic energy conversion applications. In applications such as transportation and industrial, PMSM energy conversion systems are subjected to harsh environmental conditions such as vibration, shock, and thermal shock causing mechanical interfaces holding position sensors to fail, introducing errors to the position measurement. A dynamic position sensor offset error (DPSOE), being such a failure mode has the potential to degrade system torque output or more adversely, reverse machine torque output that may cause catastrophic outcomes. This paper evaluates different DPSOE scenarios, presents an approach to model the failure mode for analysis and proposes two novel, and robust DPSOE detection methods for PMSM drive systems. The proposed detection methods are analytically proven and supported by simulation and experimental results under multiple operating conditions proving robustness.

A new assessment mechanism of primary frequency regulation capability for a supercritical thermal power plant in deep peaking

AbstractWith the rapid development of renewable energy, the primary frequency control (PFC) is becoming more critical and significant to ensure the stability of the electrical power system. As the main role of PFC, the thermal power unit tends to in a wide operation interval, and the changes in PFC characteristics along with working conditions are inevitable. By decomposing and quantifying the dynamic energy conversion process, this paper proposes a novel mechanism to evaluate the PFC capability for the supercritical thermal power plants that covered 30%–100% of the rated load. In the mechanism, a refined steam turbine model is established to reflect the short‐term dynamic response of PFC by combining it with the coupling characteristics of the main steam valve and main steam pressure in the later phase. Meanwhile, as a new prior assessment index, the equivalent electricity has been put forward to quantify the PFC capability for the power plant. In a case study of a 600 MW supercritical power plant, the capacities of PFC under 30%–50% of the rated load are quantified for the first time. Comparison results between theoretical calculation and real PFC test show that the proposed PFC capability assessment mechanism has acceptable accuracy of 96.1%, which could be effective to assess the frequency response reserve and stability margin in the grid.

Numerical analysis of a solar driven thermoelectric generator brick with phase change materials: Performance evaluation and parametric investigations

Thermoelectric generator (TEG) integrated with phase change material (PCM) has attracted increasingly wide attentions in the past few years, such as PCM applied on the hot side to stabilize the temperature fluctuations or applied on the cold side to strengthen the heat dissipation. However, the dynamic characteristics and energy conversion potential of TEG with PCM on both sides have not been systematically investigated, especially in low-carbon buildings. In the present work, a three-dimensional model of an innovative solar thermoelectric generator brick with double phase change materials (STEGB-DPCM) applied on the hot and cold sides simultaneously has been conducted, aiming to identify the energy conservation potential of the proposed system. This study is carried out with variable solar radiations, convective heat transfer coefficients and PCM thicknesses to illustrate the mechanism of different parameters on the STEGB-PCM from multiple indicators, including temperature difference, output power, energy and exergy efficiencies, and heat flux. Furthermore, the performance of STEGB-DPCM has been compared with solar thermoelectric generator brick with PCM on the hot side or cold side (STEGB-HPCM or STEGB-CPCM) and solar thermoelectric generator brick without PCM (STEGB). The results show that the output power of STEGB-DPCM can be enhanced by 138.5% for solar radiation of 600–1000 W/m2. Meanwhile, the energy and exergy efficiencies of STEGB-DPCM are positive in proportion to the convective heat transfer coefficient with the energy efficiency of 0.113% and exergy efficiency of 0.122% at 3600 s for h = 15 W/(m2 K). Although the output power of STEGB-DPCM decreases with the PCM thickness, the heat flux and the brick temperature can be effectively reduced by 92.1 W/m2 and 18.49 K, indicating a diminished demand for indoor cooling implement. This study will provide a worthwhile design assistance for building envelope system on improving thermal technology performance and indoor thermal environment.

Thermodynamic-Dynamic coupling of a Stirling engine for space exploration

As the new space era advances, there is an increasing demand for long-term missions beyond Earth’s orbit, such as on Mars and the Moon. The level of complexity of these missions is higher than conventional missions in terms of duration, particularly the energy demand required. To become viable, power generation systems must have a high power density, that is, high power associated with low mass. From this perspective, dynamic nuclear power generation systems coupled with electric propulsion are considered the most promising systems for deep-space exploration and colonization missions. Thus, to provide valuable information for the development of a dynamic energy conversion system for space, this study carried out thermodynamic modeling of a nuclear-powered Stirling cycle coupled with a dynamic engine model for space purposes. By means of numerical modeling, the constructive parameters of the Stirling engine, such as regenerator efficiency, compression ratio, heat exchanger thermal conductance, engine frequency, piston stroke, and area, are varied to understand the impact of these parameters on the final system performance. The results show that the regenerator efficiency can provide significant gains in the engine efficiency. However, a very high regenerator efficiency reduces the power of the cycle. The engine compression ratio tends to increase the engine efficiency, but a compression ratio above six provides marginal gains for cycle efficiency. From the results obtained, the best parameters yielded a system with a power output of 260.5 kW and a power density of 35.38 kg∙kW-1. This study can serve as a theoretical guideline for the future design of nuclear-powered Stirling engines for space applications, providing insight into the constructive parameters that influence the overall performance of the system.

Future Changes of Atmospheric Energy Cycle in CMIP5 Climate Models

AbstractFuture changes in the atmospheric energy cycle were estimated by using 12 climate models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and mass‐weighted isentropic zonal‐mean framework. In this framework, the zonal‐mean available potential energy (AZ) is converted to the zonal‐mean kinetic energy (KZ) through mean‐meridional direct circulations, and KZ is converted to the wave energy (W), the sum of eddy available potential energy and eddy kinetic energy, through wave‐mean flow interactions. The comparison between the late 21st century in a high emission scenario and the late 20th century in the historical scenario indicates a significant increase in AZ and KZ in winter in the Northern Hemisphere (NH) and the Southern Hemisphere (SH). The wave energy significantly decreases in the NH winter but slightly increases in the SH winter. In the NH winter, the stationary wave energy significantly decreases, and the transient wave energy shifts poleward. Global warming reduces the baroclinic instability wave activity, which suppresses the upward Eliassen‐Palm flux and wave‐induced extratropical direct circulation. It decreases the dynamic energy conversion rates C(AZ, KZ) and C(KZ, W). On the other hand, the diabatic wave energy generation rate (QE) is projected to increase, particularly in the SH. The future W change is consistent with the change in the sum of C(KZ, W) and QE. Changes in both the dynamical energy conversion associated with wave‐mean flow interactions and the generation of eddy available potential energy associated with diabatic heating processes are necessary to explain the wave energy change.

A Review on Switched Reluctance Generators in Wind Power Applications: Fundamentals, Control and Future Trends

With the ever growing environmental concerns, renewable energy sources emerge as a promise of clean and abundant energy, enabling long-term sustainable development. In this context, wind power gained significant interest due to its relative low cost and availability. Switched reluctance generators (SRGs) are suitable candidates for wind energy conversion systems, as they present a simple structure, robustness, a wide range of speed and are capable of operating in harsh environments. The machine, however, poses challenges such as high torque ripple, acoustic noise production and highly nonlinear behavior. Nonetheless, with the use of adequate control strategies, high dynamic performance SRG-based wind energy conversion systems can be achieved. As a result, this article presents a state of the art review of SRGs in wind power applications. First, the fundamentals of the SRG are presented. Next, two categories of firing angle control are reviewed: optimization and closed-loop control. Then, voltage and power control strategies are discussed, being divided in model-independent and model-based approaches. After that, a review on grid-tied SRG-based wind energy conversion systems is carried out. The most common filter topologies as well as the employed control strategies are detailed. Lastly, an outline of the discussed topics is presented and future trends as well as suggestions for future investigation are listed.

Improving the energy efficiency of electric drives for auxiliary units of traction rolling stock

The review of technical solutions and schematic characteristics of auxiliary drives for traction vehicles has shown that the most rational variant is an electric drive with an induction machine. Given the operating modes of the auxiliary drives and the share of their power consumption in the total locomotive power, the task of using scalar control systems for induction machines becomes relevant. Based on a mathematical model describing the dynamic energy conversion processes in the T-shape substitution circuit of an induction motor, taking into account stator steel losses and current displacement effects in the rotor winding and saturation along the main magnetic path, possibilities for reducing stator current have been investigated. In order to improve the energy efficiency of electric drives two variants of control system have been proposed. One based on search method of self-tuning to the stator current minimum and the other - on maintaining the power factor of induction motor at the level that ensures equality of active and reactive components of stator current. The hardware and software requirements for implementing control systems have been analysed. Modelling using Matlab has shown that both control systems work - power loss reduction can be as low as 50% and as high as 60% in certain modes.

A novel in situ synthesis of nitrogen-doped graphene with excellent electrocatalytic performance for oxygen reduction reaction

The heteroatom doped carbon-based materials have a promising application in fuel cell electrocatalysis. However, current metal-free catalyst always suffers drawbacks of slow dynamic rate and limited energy conversion efficiency. Here, nitrogen-doped graphene (N-G) with layered structure has been successfully in situ synthesized via magnesium reduction of graphitic carbon nitride (g-C3N4) at 800 °C. Due to its excellent structure and properties including high BET surface area (437 m2 g−1), plenty of graphitized nitrogen and pyridine nitrogen on the surface, and remarkable conductivity, the obtained 10N-G-800 demonstrates a prominent catalytic efficiency in electrocatalytic oxygen reduction reaction (ORR) via mainly four-electron pathway. In addition, an obviously better long-term catalytic stability and methanol tolerance than commercial platinum-carbon counterparts are also determined for our 10N-G-800 catalyst. The 10N-G-800 exhibits high power density (203 mW cm−2), long-term durability and high rate capacity as the air electrode catalyst of Zn-air battery. This article provides a novel and efficient approach for the design of metal-free ORR catalyst.

Polarization analysis of a micro direct methanol fuel cell stack based on Debye-Hückel ionic atmosphere theory

In this paper, a micro direct methanol fuel cell (μDMFC) stack model is developed in order to analyze the polarization characteristics. The model employed the Debye-Hückel ionic atmosphere theory to describe the charge conductions and electrochemical kinetics during the polarization coupling. The simulated current-power profiles of the model are verified experimentally. Compared with the μDMFC stack model based on conventional polarization theory, the error of the proposed μDMFC stack model reduces by about 8% at average. For every 10 mol · m−3 increase in cathodic oxygen concentration, the increase in polarization coupling efficiency alone can improve the output power by about 2% on average. The increase of operating temperature from 293 K to 333 K weakens the coupling forces within the μDMFC stack. The analyzing results of dynamic operation show that the polarization coupling causes a voltage peak during unloading. High loading current and unloading speed raise the voltage peak. The energy loss caused by methanol crossover decreases during dynamic operating process. The dynamic energy conversion efficiency of the μDMFC stack is relatively high. The proposed μDMFC stack model solves the polarization coupling problem and makes it possible to analyze the polarization coupling between μDMFC stack and modern microelectronic portable systems.

Failure Behavior of Double-Layer-Domes Subjected to Impact

The dynamic failure behavior of double-layer-domes subjected to impact is studied numerically through the nonlinear finite element software LS-DYNA. The parameters considered in this work include the mass, velocity, and size of impactor, impact direction, roof weigh, geometric imperfection, rise-to-span ratio, and depth of dome. The dynamic time-history response and energy conversion of the structure are utilized to distinguish between the failure mechanism types. For the cases studied, it is found that failure of the structures falls into one of the three categories: (1) local shear failure, (2) partial progressive failure, and (3) full progressive failure. Non-failure case dominates the dome response when the kinetic energy of the impactor is small enough, and the structure can convert most of the kinetic energy into the strain energy, thereby absorbing the impact. Local shear failure occurs in a double-layer-dome when an impactor with very high kinetic energy strikes the dome. For an impactor striking with a mass of 5 to 300[Formula: see text]ton and a velocity of 50 to 120[Formula: see text]m/s, the double-layer-dome studied will suffer from partial progressive failure. Varying mass and velocity of the impactor in the range of 1 to 300[Formula: see text]ton and 200 to 400[Formula: see text]m/s, respectively, results in a tendency of the dome to exhibit local shear failure. Although impact direction does not cause a change in the failure mechanism type, there is a reduction in the severity of failure of the system as the impact angle increases. Roof weight has no dominant effect on the failure mechanism of the double-layer-dome. A small initial member imperfection with amplitude 0.001[Formula: see text] does not change the progressive failure type. A large member imperfection of 0.01[Formula: see text] triggers member buckling and leads to local shear failure of the dome. Except for some loading cases, the change in the rise to span ratio and depth of the dome does not seriously affect the failure mode.

Dynamic energy conversion and management strategy for an integrated electricity and natural gas system with renewable energy: Deep reinforcement learning approach

With the application of advanced information technology for the integration of electricity and natural gas systems, formulating an excellent energy conversion and management strategy has become an effective method to achieve established goals. Differing from previous works, this paper proposes a peak load shifting model to smooth the net load curve of an integrated electricity and natural gas system by coordinating the operations of the power-to-gas unit and generators. Moreover, the study aims to achieve multi-objective optimization while considering the economy of the system. A dynamic energy conversion and management strategy is proposed, which coordinates both the economic cost target and the peak load shifting target by adjusting an economic coefficient. To illustrate the complex energy conversion process, deep reinforcement learning is used to formulate the dynamic energy conversion and management problem as a discrete Markov decision process, and a deep deterministic policy gradient is adopted to solve the decision-making problem. By using the deep reinforcement learning method, the system operator can adaptively determine the conversion ratio of wind power, power-to-gas and gas turbine operations, and generator output through an online process, where the flexibility of wind power generation, wholesale gas price, and the uncertainties of energy demand are considered. Simulation results show that the proposed algorithm can increase the profit of the system operator, reduce wind power curtailment, and smooth the net load curves effectively in real time.

Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy.

Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.