Energy Flow Characteristics Research Articles

Investigation on Energy Flow Characteristics of Fuel Cell System Based on Real Vehicle Tests

For fuel cell hybrid vehicles, the energy distribution mechanism of the fuel cell and power battery should reasonably allocate the power output of the fuel cell and power battery, optimize the efficiency of both and control the power battery SOC to fluctuate within a reasonable range. To test the energy flow and operation characteristics of the powertrain of two hybrid car models on the market, two test vehicles (called vehicle A and vehicle B in this paper) are tested on an AIP 4WD chassis dynamometer under constant power and the China Light-Duty Vehicle Test Cycle-Passenger cycle condition, respectively. The test results show that vehicle A has a smaller power battery SOC variation interval and a lower variable rate than vehicle B. The cumulative power battery output energy of vehicle B is more significant than that of vehicle A. More importantly, the current rare public test reports of fuel cell vehicles make this study very valuable. This paper has important reference significance for the energy flow characteristics and energy management strategy of existing fuel cell hybrid vehicles.

Vibration energy flow transmission in systems with Coulomb friction

This study focusses on the vibration transmission and energy flow characteristics of low dimensional models of dynamical systems with Coulomb friction. The Karnopp friction model and smooth Coulomb friction models are employed to estimate the dry friction force. The steady-state responses of the system are determined by the harmonic balance (HB) approximations with numerical continuations and a time-marching method. The level of vibration transmission and energy dissipation within the system are assessed by the force transmissibility and power flow variables. For a single degree-of-freedom oscillator system, in the low- and high-frequency ranges away from the resonance, it is found that the dry frictional contact can suppress the vibration response and effectively dissipate vibrational energy. For the coupled system, the existence of frictional contact at the interface can lead to a significant growth in the force transmissibility and energy transfer from the force-excited subsystem to the secondary system, especially at the high excitation frequencies. The interfacial frictional contact can also result in a large amount of energy dissipation at the interface. The studies show that vibration transmission and energy dissipation in a dynamic system with contacting subsystems can be tailored by adjusting the properties of the frictional contact. Design strategies can be developed using frictional contacts for vibration suppression by minimizing vibration energy transmission or maximizing energy dissipation.

Energy consumption, flow characteristics and energy-efficient design of cup-shape blade stirred tank reactors: Computational fluid dynamics and artificial neural network investigation

Developing high-efficient and green energy-saving stirred tank reactors is of vital importance in liquid-liquid processing industries. Therefore, this work revealed the energy consumption, flow characteristics, and explored the energy-saving strategies of novel-designed Cup-shape Blade (CB) stirred tank reactors characterized by easy fabrication, low energy consumption and large pumping flow rate. Computational Fluid Dynamics (CFD) and Artificial Neural Network (ANN) were conducted to investigate the influences of geometrical parameters on liquid-liquid power number (NP), flow number (NQ) and flow patterns. The improved method for hyper-parameter specification indicates that the Bayesian regulation training algorithm and the two-hidden-layer scheme possess the best performance. Back Propagation Neural Network (BPNN) presents the best predictive accuracy for NP and NQ, and Learning Vector Quantization (LVQ) network shows the best classification capability of flow patterns. Analyses based on the ANN modeling and the “Local Interpretable Model-agnostic Explanations” method show the joint and complicated effects of geometrical parameters on energy consumption and flow characteristics. Procedures were proposed to ascertain the energy-efficiency blade configuration based on ANN.

Integrated energy system operation optimization with gas linepack and thermal inertia

An optimal scheduling model that can integrate the power, heat and gas networks considering the gas linepack and the thermal inertia of heating system is proposed here. By coupling the characteristics of various energy flows, the flexibility and reliability of system operation can be improved without further investment on the storage equipment. First, the storage capacity of the gas pipeline, the process of thermal system transmission and the heat storage capability at the consumer side are analysed and modelled. The associated gas linepack model, heat system thermal inertia model and primary electricity-gas-heat model are subsequently combined and simplified through incremental linearization to establish an optimal scheduling model that can be applied for the Integrated Energy System (IES) based on the characteristics of thermal inertia and gas linepack. Case studies are conducted to assess the potential of optimizing the two energy flows using the proposed optimal scheduling method and the results indicate that the IES can significantly enhance the system capability to accommodate excessive renewable energy and maintain reliable operation during peak hours.

Investigate aerodynamic performance of wind turbine blades with vortex generators at the transition area

The transition area of the blade had a large relative thickness of airfoil, which was prone to the flow separation. The vortex generators (VGs) could restrain the flow separation. In this paper, the VGs were installed at the transition area of the WindPACT 1.5 MW wind turbine blades. The numerical simulation method was used to investigate the effects of the VGs on the aerodynamic performance of the blade. The high-energy vortexes were generated at the tail by the VG. It could change the energy distribution and flow characteristics of the airflow in the boundary layer. There were influences by the geometric parameters of the VGs. The VGs could change the aerodynamic performance at the transition area of the blade. A satisfactory result was obtained for reasonable geometrical parameters of the VGs. It also could restrain the flow separation of the blade surface and improve the torque.

The many-objective optimal design of renewable energy cogeneration system

To alleviate the issues of climate warming and fossil resources depletion, this paper proposes a wind-photovoltaic-thermal energy storage-electric heater cogeneration system, which adopts the structure of concentrated solar power plant but replaces the expensive collector field and tower with wind and photovoltaic farms and electric heater that converts the excess electricity as thermal energy source. The cogeneration system can effectively regulate the fluctuating wind and photovoltaic output to satisfy electricity load by electric heater based on resistive heating of molten salt, two-tank molten salt thermal energy storage and power block based on steam Rankine cycle, and supply heat load directly from the molten salt heat transfer fluid and heat exchanger. This paper considers minimizing levelized cost of energy, loss of power and heat supply probability, energy reduction rate and lifecycle equivalent CO2 emissions as optimized objectives, and investigates the many-objective (having four or more objectives) capacity optimization problem by Nondominated Sorting Genetic Algorithm-Ⅲ coupled with Principal Component Analysis and Technique for order preference by similarity to ideal solution. Moreover, residual analysis is applied to consider the uncertainty of wind power prediction. The detailed optimization process and performance comparison of many-objective algorithms, the all-year energy flow and seasonal output characteristics analysis of the optimal-compromise solution are presented. Finally, the proposed cogeneration system is compared to the power-only system with the same installed capacity and equivalent load demand, and the comparison results show that the proposed cogeneration system performs better in all evaluation metrics. Therefore, the proposed renewable energy cogeneration system is feasible and cost-effective for practical applications.

A novel approach to CNC machining center processing parameters optimization considering energy-saving and low-cost

NC machining is currently a machining method widely used in mechanical manufacturing systems. Reasonable selection of process parameters can significantly reduce the processing cost and energy consumption. In order to realize the energy-saving and low-cost of CNC machining, the cutting parameters are optimized from the aspects of energy-saving and low-cost, and a process parameter optimization method of CNC machining center that takes into account both energy-saving and low -cost is proposed. The energy flow characteristics of the machining center processing system are analyzed, considering the actual constraints of machine tool performance and tool life in the machining process, a multi-objective optimization model with milling speed, feed per tooth and spindle speed as optimization variables is established, and a weight coefficient is introduced to facilitate the solution to convert it into a single objective optimization model. In order to ensure the accuracy of the model solution, a combinatorial optimization algorithm based on particle swarm optimization and NSGA-II is proposed to solve the model. Finally, take plane milling as an example to verify the feasibility of this method. The experimental results show that the multi-objective optimization model is feasible and effective, and it can effectively help operators to balance the energy consumption and processing cost at the same time, so as to achieve the goal of energy conservation and low-cost. In addition, the combinatorial optimization algorithm is compared with the NSGA-II, the results show that the combinatorial optimization algorithm has better performance in solving speed and optimization accuracy.

Optimal operation of regional integrated energy system considering demand response

Abstract With the deepening of energy market reform, market factors have more and more influence on the operation of energy system. The introduction of demand response mechanism guided by market factors in the optimization of regional integrated energy system (RIES) has become an inevitable trend. Based on the coupling characteristics of heterogeneous energy flow in regional integrated energy system and the response potential of flexible load on the user side, the concept of demand response (DR) in electricity market is extended to cooling and heat in energy system, and an optimal operation planning method of RIES considering demand response is proposed in this paper. In order to solve the problem that the existing evaluation system of energy system is not comprehensive, this paper constructs a regional integrated energy system model considering demand response, which takes the optimal comprehensive evaluation index consisting of economic benefits of both supply side and user side, load peak valley ratio and carbon emission as the objective function. Then, an improved genetic optimization algorithm is used to solve the model, obtaining the optimization results of load demand response and energy networks, which specifically includes the equipment installed capacity, hourly output as well as operation strategy. Finally, an industrial park in Guangzhou is selected for case study. The result shows that user-side demand response reduces the total cost of regional integrated energy system by 5.17% and the peak-to-valley ratio of electric load by 59.9%, which plays a role in cutting peak and filling valley in the energy system.

Simulation of Energy Exchange between Single Prosumer Residential Building and Utility Grid

Modern households usually have independent energy sources such as wind generators, photovoltaic (PV) panels, and similar green energy production equipment. Experts predict that soon, there will be an increasing number of such prosumers who both produce and consume energy. This process alleviates and reduces the load on large national electricity networks and also contributes to overall energy security. In this paper, a simulation model of a household, which employs a wind generator as its independent source of electricity, is developed. It is expected that this approach will be easily replicated for more complex configurations. The other components of the single prosumer microgrid that will be assessed are the non-shiftable electricity consumption equipment, which is used mainly in households and deployed separately for water heater, with a separate battery to meet the needs of these non-shiftable consumers. The 5-min data intervals for the year of simulation have been used. The characteristics of energy flow according to production and consumption schedules and the capacity of storage equipment have been modelled and simulated. Results disclose that wind turbine production size and buffer battery have a crucial impact on the demand cover factor.

Energy flow characteristics of friction-induced nonlinear vibrations in a water-lubricated bearing-shaft coupled system

Based on the energy flow theory of nonlinear dynamical system, the stabilities, bifurcations, possible periodical/chaotic motions of nonlinear water-lubricated bearing-shaft coupled systems are investigated in this paper. It is revealed that the energy flow characteristics around the equlibrium point of system behaving in the three types with different friction-paramters. (a) Energy flow matrix has two negative and one positive energy flow factors, constructing an attractive local zero-energy flow surface, in which free vibrations by initial disturbances show damped modulated oscillations with the system tending its equlibrium state, while forced vibrations by external forces show stable oscillations. (b) Energy flow matrix has one negative and two positive energy flow factors, spaning a divergence local zero-energy flow surface, so that the both free and forced vibrations are divergence oscillations with the system being unstable. (c) Energy flow matrix has a zero-energy flow factor and two opposite factors, which constructes a local zero-energy flow surface dividing the local phase space into stable, unstable and central subspace, and the simulation shows friction self-induced unstable vibrations for both free and forced cases. For a set of friction parameters, the system behaves a periodical oscillation, where the bearing motion tends zero and the shaft motion reaches a stable limit circle in phase space with the instant energy flow tending a constant and the time averaged one tending zero. Numerical simulations have not found any possible chaotic motions of the system. It is discovered that the damping matrices of cases (a), (b) and (c) respectively have positive, negative and zero diagonal elements, resulting in the different dynamic behavour of system, which gives a giderline to design the water-lubricated bearing unit with expected performance by adjusting the friction parameters for applications.Graphic

Operation Optimization of Integrated Energy System under a Renewable Energy Dominated Future Scene Considering Both Independence and Benefit: A Review

An integrated energy system interconnects multiple energies and presents a potential for economics improvement and energy sustainability, which has attracted extensive attention. However, due to the obvious volatility of energy demands, most existing integrated energy systems cannot operate in a totally self-sufficient way but interact with the upper grid frequently. With the increasingly urgent demand for energy saving and emissions reduction, renewable resources have occupied a larger and larger proportion in energy system, and at last they may be dominant in the future. Unlike conventional fossil fuel generation, the renewable resources are less controllable and flexible. To ease the pressure and guarantee the upper grid security, a more independent integrated energy system is required. Driven by that, this paper firstly reviews the optimal strategies considering both independence and benefit from perspectives of individual efforts and union efforts. Firstly, the general optimization process is summarized in terms of energy flows modelling and optimization methods to coordinate supply–demand side and realize benefit maximization. Based on that, handling with uncertainty of high-ratio renewable energy is reviewed from uncertainty modeling methods and multi-stage operation strategy perspectives to make the strategy accurate and reduce the adverse effects on the upper grid. Then, the hybrid timescale characteristics of different energy flows are explored to enhance operation flexibility of integrated energy systems. At last, the coordination among different participants is reviewed to reduce the whole adverse effect as a union. Remarks are conducted in the end of each part and further concluded in the final part. Overall, this study summarizes the research directions in operation optimization of integrated energy systems to cater for a renewable energy dominated scene to inspire the latter research.

A Prediction Method for Acoustic Intensity Vector Field of Elastic Structure in Shallow Water Waveguide

Compared with scalar sound field, vector sound field explained the spatial structure of sound field better since it not only presents the sound energy distribution but also describes the sound energy flow characteristics. Particularly, with more complicated interaction among different wavefronts, the vector sound field characteristics of an elastic structure in a shallow water waveguide are worthy of studying. However, there is no reliable prediction method for the vector sound field of an elastic structure with a high efficiency in a shallow water waveguide. To solve the problem, transfer functions in the waveguide have been modified with some approximations to apply for the vector sound field prediction of elastic structures in shallow water waveguides. The method is based on the combined wave superposition method (CWSM), which has been proved to be efficient for predicting scalar sound field. The rationality of the approximations is validated with simulations. Characteristics of the complex acoustic intensity, especially the vertical components are observed. The results show that, with constructive and destructive interferences in the depth direction, there could be quantities of crests and vortices in the spatial structure of time-dependent complex intensity, which manifest a unique dynamic characteristic of sound energy. With more complicated interactions among the wavefronts, a structure source could not be equivalent to a point source in most instances. The vector sound field characteristics of the two sources could be entirely different, even though the scalar sound field characteristics are similar. Meanwhile, source types, source parameters, ocean environment parameters, and geo parameters may have influence on the vector sound field characteristics, which could be explained with the normal mode theory.

Numerical research on the performance, combustion and energy flow characteristics of gasoline-powered vehicle under WLTC

In order to evaluate and improve the performance of a vehicle equipped with a gasoline engine, an integrated model of the vehicle coupling with a detailed engine model was established to investigate the performance, combustion and energy distribution under the Worldwide Harmonized Light duty Test Cycle (WLTC) of cold start. The results show that 2.3–3.2 kW of brake power is required for the automatic transmission under idling conditions. Brake thermal efficiency mainly ranges from 17.71% to 31.94% apart from the rapid deceleration conditions and exhibits poor fuel economy under low-speed phase. Combustion phase of 50% mass fraction burnt (CA50) is usually delayed in case of knocking combustion under higher speed conditions. Moreover, it is delayed to 65 °CA at the initial stage of cold start for fast light-off of three-way catalyst (TWC), but 10–90% combustion duration (CA10-90) is not very sensitive to the cold start. The heat cumulated in the engine structure is obvious at the initial stage and up to 37.39% but finally occupies 4.93%. The proportion of heat transfer loss to coolant increases after 300 s and finally occupies 22.71%. Exhaust gas loss mainly ranges from 0.91 kW to 28.42 kW and its proportion first decreases and then increases to 26.46%. After 1160 s, it exhibits higher growth rate. Pumping loss varies from 0.1 kW to 2.67 kW and occupies 2.2% in the total energy. Furthermore, the findings in the paper can be applied to evaluate and optimize the energy distribution by changing different technologies or strategies in the future.

Active synthesis of a gyroscopic-nonreciprocal acoustic metamaterial

A class of active nonreciprocal metamaterials is developed to control the flow and distribution of energy along periodic dynamical systems. Such a development constitutes a radical departure from the currently available approaches where the non-reciprocities are generated either by utilizing various physical sources of passive nonlinearities, gyroscopic circulators, spatiotemporal modulation, or active control of nonlinear systems. The proposed active Nonreciprocal Gyroscopic Meta-Material (NGMM) cell consists of a one-dimensional acoustic duct provided with linear dynamic control capabilities that virtually synthesize a gyroscopic control action that generates non-reciprocal characteristics of tunable magnitude and direction. The controller is designed in order to enable the spatial control and redistribution of the wave propagation energy flow along the acoustic duct. During this entire process, the system behaves in a linear fashion. Numerical examples are presented to demonstrate the basic features, non-reciprocal behavior, as well as the energy flow characteristics. The presented concept and controller design of the NGMM can be extended to various critical structures to achieve realistic acoustic diode configurations in a simple and programmable manner.

Analysis of shape memory alloy vibrator using harmonic balance method

Shape memory alloy (SMA) is a very important smart material, which has been widely used in many fields, especially in vibration. Phase transformation can be induced by changing temperature and its stiffness changes accordingly. In this paper, the primary resonance vibration of a one-dimensional SMA oscillator is analyzed using the harmonic balance (HB) method. The amplitude-frequency curves of the SMA oscillator with different temperatures are drawn, and the effect of temperature and frequency on the amplitude is discussed. Then, the energy flow of SMA in the vibration process is researched by the power flow analysis (PFA) approach. The time-averaged input power (TAIP) is calculated using the analytical and numerical method, respectively, and the calculation time is compared. It is found that the difference between the analytical and numerical solutions is not significant in most cases, but the calculation time of analytical solution is only about one-tenth of that of the numerical solution, which is very important in saving computational cost, real-time control and so on. Finally, some other characteristics of energy flow in the SMA oscillator are identified.

Analysis of integration method in multi-heat-source power generation systems based on finite-time thermodynamics

Multi-heat-source power generation system is a promising technology to reduce fossil fuel consumption and save investment costs by integrating several heat sources and sharing power equipment components. Researchers have conducted many case studies based on specific power plants to find the preferred integration scheme. However, there is still no unified theory to guide the integration of different energy sources. To explore a common method to integrate various energy sources, this work developed a general multi-heat-source integrated system model based on finite-time thermodynamics, considering the external and internal irreversibility due to the constraint of finite-time and finite-size. The generalised expressions for optimum integration method are explored and expressed in dimensionless parameters. This study indicated the system with two heat-sources performs differently in four regions due to the variation of endothermic temperatures. The characteristics of energy flow and irreversibility reveal that by adding a second heat-source, the first heat-source energy can be substantially reduced at the cost of system efficiency slightly decreasing. Then four application cases for solar-aided coal-fired power plants are conducted to check its feasibility and potential to provide the performance bound of integrating multi-heat-sources.

Active nonreciprocal metamaterial using an eigen-structure assignment control strategy.

A class of active nonreciprocal metamaterials (ANMMs) is developed to control the flow and distribution of energy along periodic dynamical systems. Such a development constitutes a radical departure from the currently available approaches where the non-reciprocities are generated either by utilizing various sources of passive nonlinearities, gyroscopic circulators, spatiotemporal modulation, or active control of nonlinear systems. The proposed ANMM cell consists of a one-dimensional acoustic duct provided with linear active control capabilities. The controller is designed by simultaneous assignment of both the eigenvalues and eigenvectors, i.e., the entire eigen-structure, of the closed-loop system. Conventionally, the placement of the eigenvalues has been considered to improve the damping and system's response. However, in this study, the emphasis is placed also on tailoring the eigenvectors in order to enable the spatial control and redistribution of the wave propagation energy flow along the acoustic duct in such a manner that it can introduce non-reciprocity as well as control its direction and reversal. During this entire process, the system remains behaving in a linear fashion. Numerical examples are presented to demonstrate the basic features and non-reciprocal behavior, as well as the energy flow characteristics.

Array Antenna Gain Enhancement With the Poynting Streamline Method

Streamlines of the Poynting vector field connect antenna figures of merit with the energy flow characteristics near a receiving antenna. Poynting streamlines properties and absorption aperture of antenna under different load conditions have been studied in this letter. Based on its Poynting streamline characteristics, the short-circuit dipole can be used as a parasitic element to direct the flow of energy, increase the absorption aperture, and enhance the gain of the array. Numerical examples show that this strategy can not only enhance the gain of dipole array, but also improve the gain of circularly polarized antenna array without deteriorating the axial ratio. Poynting streamline-based methods augment commonly used radiation-mode antenna analysis techniques by providing an intuitive and visual way to guide the design of antenna arrays.

MULTISCALE ENVIRONMENTAL MONITORING IN URBAN TOPOCLIMATE

Climate is a complex system subject to much natural and anthropogenic interference. Urban microclimates and topoclimates need effective methodologies to localize coexisting phenomena, including multiscale approaches that demonstrate their relational character. Air temperature, air relative humidity, and wind are microclimatic variables that can be evaluated with respect to their qualitative energy flow characteristics. The technical performance of this monitoring depends on a good estimate of the statistics of the digital signal assessed, which in turn represents greater care in the management and implementation of structural change indicators derived from frequency-domain modeling. Therefore, this study aimed to analyze the power spectra of the air temperature, air relative humidity and wind data series using the traditional Morlet Continuous Wavelet Transform (CWT) and the Cross Wavelet Transform (XWT), with Wavelet Coherence (WC) analysis. The daily, monthly and annual scales were studied, and the results demonstrated significant interrelationships between the variables. The WC values found were validated by the Monte Carlo method, scalograms and spectrograms, representing seasonal and daily cycle frequencies. The urban fractions presented behavior in accordance with the seasonality of tropical climates of the Cerrado, as well as of interference of the urban roughness. The CWT, XWT and WC tools are adequate for urban monitoring and planning analyses, qualitatively reflecting the urban dynamics of microenvironments

Aging effects on the mechanical energy transfer through the lower extremity joints during the swing phase of level walking

Age-related changes of gait performance have been evidenced by the altered kinetic coordination of the lower extremity. However, a systematic approach to explore the gait control in terms of the mechanical energy transfer across multiple segments throughout the gait phases is still not well documented. Ten healthy elderly and ten young adults were asked to walk along a 10-meter walkway at the self-selected and fast walking speeds. The visualized energy flow model of the swing leg was established and the factor analysis was then applied to extract the high-dimensional energy flow characteristics of the swing leg. The results showed that the young adults have similar energy flow characteristics of the swing leg for both fast and self-selected walking speeds, while the elderly showed an opposite energy flow pattern especially at the fast walking speed. The hip power and the knee power were also found to mainly correspond to the swing acceleration and deceleration, respectively. This study demonstrated a valuable tool to explore the change of the gait characteristics in the elderly and could help to facilitate the understanding of the neuromuscular adaptation due to aging.