Hongjun Li, C.K. Hsieh and D.Y. Goswami
A method has been developed for conjugate heat transfer analysis offluid flow inside parallel channels formed by a phase change material (PCM)separated from the fluid by a wall…
Abstract
A method has been developed for conjugate heat transfer analysis of fluid flow inside parallel channels formed by a phase change material (PCM) separated from the fluid by a wall. The phase change in the PCM is two dimensional and a hybrid analysis consisting of an analytical solution in one direction and a finite‐difference method in another direction is used to solve for the temperature in the PCM. The heat transfer fluid (HTF) inlet temperature is given and the heat transfer between the HTF and the PCM is treated as a conjugate problem that requires no iterations to obtain a solution. The numerical results are found to be stable, convergent, and accurate. Application of the method to the solution of heat extraction from a phase‐change energy storage unit is given in detail and the numerical results are shown to be accurate, based on an energy conservation analysis, to within 3%.
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C.K. HSIEH, MEHDI AKBARI and HONGJUN LI
A method has been developed for the solution of inverse heat diffusion problems to find the initial condition, boundary condition, and the source and sink function in the heat…
Abstract
A method has been developed for the solution of inverse heat diffusion problems to find the initial condition, boundary condition, and the source and sink function in the heat diffusion equation. The method has been used in the development of a source‐and‐sink method to find the boundary conditions in inverse Stefan problems. Green's functions have been used in the solution, and the problems are solved by using two approaches: a series solution approach, and a time incremental approach. Both can be used to find the boundary conditions without reliance on the flux information to be supplied at both sides of the interface. The methods are efficient in that they require less equations to be solved for the conditions. The numerical results have shown to be accurate, convergent, and stable. Most of all, the results do not degrade with time as in other time marching schemes reported in the literature. Algorithms can also be easily developed for the solution of the conditions.
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Robert Hamilton, Donald MacKenzie and Hongjun Li
The friction stir welding (FSW) process comprises several highly coupled (and non‐linear) physical phenomena: large plastic deformation, material flow transportation, mechanical…
Abstract
Purpose
The friction stir welding (FSW) process comprises several highly coupled (and non‐linear) physical phenomena: large plastic deformation, material flow transportation, mechanical stirring of the tool, tool‐workpiece surface interaction, dynamic structural evolution, heat generation from friction and plastic deformation. This paper aims to present an advanced finite element (FE) model encapsulating this complex behaviour and various aspects associated with the FE model such as contact modelling, material model and meshing techniques are to be discussed in detail.
Design/methodology/approach
The numerical model is continuum solid mechanics‐based, fully thermo‐mechanically coupled and has successfully simulated the FSW process including plunging, dwelling and welding stages.
Findings
The development of several field variables are quantified by the model: temperature, stress, strain. Material movement is visualized by defining tracer particles at the locations of interest. The numerically computed material flow patterns are in very good agreement with the general findings from experiments.
Originality/value
The model is, to the best of the authors' knowledge, the most advanced simulation of FSW published in the literature.
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A new approach for solving steady incompressible Navier‐Stokes equations is presented in this paper. This method extends the upwind Riemann‐problem‐based techniques to viscous…
Abstract
A new approach for solving steady incompressible Navier‐Stokes equations is presented in this paper. This method extends the upwind Riemann‐problem‐based techniques to viscous flows, which is obtained by applying modified artificial compressibility Navier‐Stokes equations and fully discrete high‐order numerical schemes for systems of advection‐diffusion equations. In this approach, utilizing the local Riemann solutions the steady incompressible viscous flows can be solved in a similar way to that of inviscid hyperbolic conservation laws. Numerical experiments on the driven cavity problem indicate that this approach can give satisfactory solutions.
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Hongjun Shi, Lei Xiong, Xuchen Nie and Qixin Zhu
This paper aims to mainly discuss how to suppress the disturbances accurately and effectively in the wind energy conversion system (WECS) of the direct drive surface mount…
Abstract
Purpose
This paper aims to mainly discuss how to suppress the disturbances accurately and effectively in the wind energy conversion system (WECS) of the direct drive surface mount permanent magnet synchronous generator (SPMSG).
Design/methodology/approach
The disturbances in wind energy conversion system have seriously negative influence on the maximum power tracking performance. Therefore, a model predictive control (MPC) method of model compensation active disturbance rejection control (ADRC) strategy in parallel connection is designed, which optimizes the speed tracking performance compared with the existing control strategy of MPC and ADRC in series connection. Based on the traditional ADRC, a multi parameter model compensation ADRC strategy is added to better estimate the disturbances. At the same time, a torque feedback strategy is added to compensate the disturbances caused by load torque and further optimize the speed loop tracking performance.
Findings
The simulation results show that the designed control method has advantages than the traditional control method in compensating the disturbances and tracking the maximum power more effectively.
Originality/value
The simulation results show that the designed control method is superior to the traditional proportional control method, which can better compensate the internal and external disturbances and track the maximum power more effectively.
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Xiaofeng Quan, Hongjun Xiao, Qiong Ji and Jinkang Zhang
This paper aims to analyse the role of government-led innovative knowledge management platforms in innovation knowledge management, social network effects and innovative resource…
Abstract
Purpose
This paper aims to analyse the role of government-led innovative knowledge management platforms in innovation knowledge management, social network effects and innovative resource clusters in the context of academician workstations in China. Specifically, this paper empirically studies the impact of academician workstations on corporate innovation capabilities and the mechanisms behind this impact.
Design/methodology/approach
This study uses the propensity matching score method and difference-in-differences method to test the relationship between academician workstations and corporate innovation capabilities. Baron and Kenny’s (1986) mediation method is used to test two potential mechanisms.
Findings
Academician workstations significantly improve corporate innovation capabilities because of their contribution to knowledge and innovation management. The facilitation effects are stronger in non-state-owned firms, high-tech firms and firms in industries with low levels of competition. Further, academician workstations enhance corporate innovation capabilities through their funding effect.
Practical implications
This paper encourages policymakers to create a better market environment and stable support policies to facilitate sustainable scientific and technological innovation.
Originality/value
To the best of authors’ knowledge, this study is among the first to empirically analyse the impacts of innovative knowledge management platforms on corporate innovation. It enriches the theoretical perspective of innovation platforms and provides an excellent research perspective for effectively analysing the impacts of innovation platforms. This study also contributes to the literature on the determinants of innovation.
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Lei Xiong, Hongjun Shi and Qixin Zhu
This study aims to construct a novel maximum power tracking control system for the direct drive permanent magnet synchronous generator (PMSG) of the wind energy conversion system…
Abstract
Purpose
This study aims to construct a novel maximum power tracking control system for the direct drive permanent magnet synchronous generator (PMSG) of the wind energy conversion system (WECS) to solve the following problems: how to effectively eliminate the system’s model parameter disturbances and speed up the dynamic performance of the system; and how to eliminate harmonics in WECS under different wind speeds.
Design/methodology/approach
To obtain the maximum output power of PMSG at WECS under different wind speeds, the following issues should be considered: (1) how to effectively eliminate the system’s model parameter disturbances and speed up the dynamic performance of the system; and (2) how to suppress system harmonics. For Problem 1, adding d–q compensation factors to active disturbance rejection control (ADRC) for the current loop realizes the d–q axis decoupling control, which speeds up the dynamic performance of the system. For Problem 2, the resonant controller is introduced into the ADRC for the current loop to suppress harmonic current in WECS under different wind speeds.
Findings
The simulation results demonstrate that the proposed control method is simpler and more reliable than conventional controllers for maximum power tracking.
Originality/value
Compared with traditional controllers, the proposed controller can speed up the dynamic performance of the system and suppress the current harmonic effectively, thus better achieving maximum power tracking.
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Green innovation strategy is not only a new idea to achieve green development but also the inevitable choice for enterprises to upgrade. At present, the research on the driving…
Abstract
Purpose
Green innovation strategy is not only a new idea to achieve green development but also the inevitable choice for enterprises to upgrade. At present, the research on the driving forces of green innovation strategy mainly focus on direct impact of single factor, lacking the overall consideration of internal and external environment. At the same time, research on the contingency effect of top management’s environmental awareness is scarce. This paper aims to explore how external environment pressures (policy pressures and market pressures) and internal environment driving force (innovation resources and innovation capability) make enterprises to choose green innovation strategy with moderating effect of top management’s environmental awareness.
Design/methodology/approach
Based on the sample of 216 enterprises, this paper explores the relationship between policy pressure, market pressure, innovation resources, innovation capability and the green innovation strategy with moderating effect of top management’s environmental awareness from inside and outside driving angle.
Findings
The results of the hierarchical regression model show, first, the driving effect of factors in the external environment. The coercive policy has an inverted U-shaped impact on the green innovation strategy. The incentive policy and the market pressure both have a significant positive impact on the green innovation strategy. Second, the driving effect of factors in the internal environment. The innovation capability has a significant positive impact on the green innovation strategy. The innovation resources have no significant impact on the green innovation strategy. Third, the moderating effect of top management’s environmental awareness. The relationship between the green innovation strategy and the coercive policy is stronger when the top management’s environmental awareness higher. The relationship between the green innovation strategy and the market pressure is stronger when the top management’s environmental awareness higher. The relationship between the green innovation strategy and the innovation resources is stronger when the top management’s environmental awareness higher. Otherwise, the relationship between the green innovation strategy and the innovation capability is weaker when the top management’s environmental awareness higher. And there is no significant change about the relationship between the green innovation strategy and the incentive policy when the top management’s environmental awareness higher.
Originality/value
First, the authors have promoted the integrated research on the drivers of the enterprise’s green innovation strategy. From the perspective of internal and external environment driving forces, this paper analyzes the key factors influencing the decision-making of the green innovation strategy. Second, the study has contributed to the strategic choice theory. This paper studies the driving mechanism of the green innovation strategy from a new perspective of the strategic choice theory.
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We examined the dynamic volatility connectedness and diversification strategies among US real estate investment trusts (REITs) and green finance indices.
Abstract
Purpose
We examined the dynamic volatility connectedness and diversification strategies among US real estate investment trusts (REITs) and green finance indices.
Design/methodology/approach
The DCC-GARCH dynamic connectedness framework and he DCC-GARCH t-copula model were employed in this study.
Findings
Using daily data from 2,206 observations spanning from 2 January 2015 to 31 January 2023 this paper presents the following findings: (1) cross-market spillovers exhibited a high correlation and significant fluctuations, particularly during extreme events; (2) our analysis confirmed that REIT acted as net receivers from other green indices, with the S&P North America Large-MidCap Carbon Efficient Index dominating the in-network volatility spillover; (3) this observation suggests asymmetric spillovers between the two markets and (4) a portfolio analysis was conducted using the DCC-GARCH t-copula framework to estimate hedging ratios and portfolio weights for these indices. When REIT and the Dow Jones US Select ESG REIT Index were simultaneously added to a risk-hedged portfolio, our findings indicated that no risk-hedging effect could be achieved. Moreover, the cost and performance of hedging green assets using REIT were found to be comparable.
Originality/value
We first examined the dynamic volatility connectedness and diversification strategies among US REITs and green finance indices. The outcomes of this study carry practical implications for market participants.
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Aiwu Zhao, Hongjun Guan and Zhenzhen Sun
High-quality development of marine economy is a new concept put forward in response to the current national strategy in China. The purpose of this paper is to thoroughly…
Abstract
Purpose
High-quality development of marine economy is a new concept put forward in response to the current national strategy in China. The purpose of this paper is to thoroughly understand the connotation and significance of high-quality development of marine economy through literature review, and further analyze the prospects for further research.
Design/methodology/approach
The authors first use the information visualization technology of CiteSpace to present a systematic review of the published literature from 2010 to 2019. Then, the authors analyze the researches on high-quality development of marine economy in terms of connotation, evaluation dimension, development path and guarantee mechanism.
Findings
Analysis results show that there is still insufficient understanding of the differences and links between the high-quality development of marine economy and the construction of marine power, intelligent ocean and transparent ocean.
Originality/value
Based on a thorough understanding of the subject, this paper puts forward the direction of further research on evaluation index system, path design scheme and policy system construction for high-quality development of marine economy.