Internal Boundary Conditions Research Articles

Entropy and exergy analysis of coupled radiative heat transfer and heat conduction: A new thermodynamics approach

This study presents a new approach for evaluating the thermodynamic efficiency of a coupled radiative and conductive heat transfer process with an internal heat source. In this approach, the exergy balance equation is derived, and the exergy augmentation rate due to the internal heat source is found to be the sum of the exergy of the system output to the environment surroundings, the exergy stored in the system, and the exergy consumption rate due to the irreversibility of heat transfer in the system. The exergetic efficiency of the coupled heat transfer process is then obtained according to the radiative exergy balance equation. Based on the above theoretical derivation, we carry out a thermodynamic analysis of an example including five coupled heat conduction-radiation transfer systems with a uniform internal heat source and different boundary conditions. The variations in the numerical results are discussed according to the exergy balance principle, and the behaviours of the exergy components over time under transient conditions are analysed. Our numerical results show that increasing the area of the adiabatic boundary and reducing the heat loss of the system should be considered when designing heat-transfer systems (as the exergetic efficiency increases from 0.515 to 0.617). The larger the area of the adiabatic boundary of the system, the stronger the effect of increasing this area on the overall optimisation. When a system has two adiabatic boundaries, a symmetrical arrangement of the adiabatic boundaries is suggested, although this is much less effective than increasing the number of adiabatic boundaries.

Comparison of internal boundary conditions for optical diffusion calculations considering reflection and refraction

A method to treat the internal boundary condition in an optical diffusion calculation is proposed and is compared with the conventional methods. One of the existing internal boundary conditions is Haskel's method, which uses the effective reflection coefficient for partial currents. However, Haskel's method ignores incoming partial currents from the adjacent mesh in its derivation. As a result, the accuracy at the internal boundary is lower. This paper proposes a method to improve the accuracy by iteratively updating the effective reflection coefficient for partial current. The proposed method was applied to the benchmark calculations on a one-dimensional slab geometry and its accuracy was confirmed by comparing it with the reference solution obtained by the Monte Carlo code MCML, along with the previously proposed Haskel's method and Aronson's method. As a result, it was confirmed that the proposed method is more accurate than Haskel's method at the internal boundary and gives the same result as Aronson's method. The convergence of the effective reflection coefficient using iterative calculations in the proposed method was good.

Temperature behavior of cable-stayed bridges. Part I — Global 3D temperature distribution by integrating heat-transfer analysis and field monitoring data

Varying temperatures significantly affect long-span cable-stayed bridges. However, quantitative studies on their temperature behaviors are limited. Existing studies focus on 2D or 3D models of bridge segments only, exclude cables from heat-transfer analysis, and utilize inaccurate environmental conditions. For the first time, this study comprehensively and accurately investigates the global 3D temperature distribution of long-span cable-stayed bridges by integrating the heat-transfer analysis and field monitoring data. A navigation channel bridge of the Hong Kong‒Zhuhai‒Macao Bridge is used as the testbed. A global 3D refined finite element model of the entire bridge is established. The external thermal boundary conditions of the outer surfaces of the structure are carefully determined based on the real-time ambient temperature, wind, and solar radiation, which are tailored for each surface to reflect the influence of the geometric configuration. The internal thermal boundary conditions of the inner surfaces of the box girder and tower are dependent on the measured ambient temperature, considering the vertical temperature difference of the girder and the uniform temperature inside the tower. Then, the numerical heat-transfer analysis and field monitoring data are integrated to calculate the detailed temperature distribution of the entire bridge in different seasons. Results show that ambient temperature, wind, and solar radiation significantly affect the temperature distribution. For the girder, the vertical temperature difference is significant throughout the year, and the transverse temperature difference is nonnegligible in winter and summer, while the longitudinal temperature difference is trivial. The internal temperature of the tower remains stable owing to the insulation of the concrete. The temperatures of the cables vary from each other, which may cause stress redistribution within the structure. The calculated temperatures are in good agreement with their measured counterparts. The temperature results will be used to calculate the thermal-induced responses in the companion paper in a unified manner.

Wave equation with viscoelastic acoustic boundary conditions and supercritical source term

This paper is concerning with the study of Hadamard well-posedness for a wave equation with nonlinear internal damping and acoustic boundary conditions for non-locally reacting boundary. On the boundary we consider the action of viscoelastic and frictional damping and also a supercritical source term. To prove the existence of solution we use semigroup theory. We also study the asymptotic behavior of the functional energy associated to the problem.

Shock Equations and Jump Conditions for the 2D Adjoint Euler Equations

This paper considers the formulation of the adjoint problem in two dimensions when there are shocks in the flow solution. For typical cost functions, the adjoint variables are continuous at shocks, wherein they have to obey an internal boundary condition, but their derivatives may be discontinuous. The derivation of the adjoint shock equations is reviewed and detailed predictions for the behavior of the gradients of the adjoint variables at shocks are obtained as jump conditions for the normal adjoint gradients in terms of the tangent gradients. Several numerical computations on a very fine mesh are used to illustrate the behavior of numerical adjoint solutions at shocks.

The spark plug’s thermal state simulation

BACKGROUND: Spark plugs are among the most important components of the ignition system of an internal combustion engine (ICE). The spark-over produced by the ignition system should have sufficient energy for combustion initiation at any engine operation mode in all the service conditions. Start properties, reliability, power, fuel efficiency and exhaust toxicity of an ICE essentially depend on excellence of design and manufacturing quality of a spark plug. On the other hand, functional properties of spark plugs depend on concordance to ICE with main dimensions, design, heat properties and value of a spark gap. AIMS: Use of the methods of the spark plugs temperature field simulation in order to reduce the amount of experimental studies and to reduce the number of specimen options subjected to laboratory and on-road engine tests.
 METHODS: The simulation model of the temperature field of a spark plug of an internal combustion engine (ICE) was developed in this study.
 RESULTS: The representation of temperature distribution in the insulators thermal cone and other ceramic elements of a spark plug was obtained. The dependence of thermal conductivity and specific thermal capacity of corundum ceramics on temperature was derived. The dependencies of thermal conductivity coefficient of the plugs ceramic insulator are presented. The analysis of thermophysical properties of the substances made of various materials was carried out. The equations of the temperature field of all parts of a spark plug (a contact head, glass sealant, an insulator, a central electrode, a spark plugs body, a heat-sinking washer, a sealing ring, a cylinder head) were developed. The schematic representation of the spark plug geometry, used in the temperature field calculation, was obtained. The requirements for boundary conditions for calculation of the temperature field of a spark plug were determined. The calculation scheme of the spark plug is presented. The condition of heat exchange at the boundary between the selected part of a cylinder head and the cooling system of an internal combustion engine was considered. The study of heat transfer between the structural elements of a spark plug and the air inside the ICE compartment was carried out. The dependencies describing the heat exchange between the structural elements of a spark plug being in thermal contact with each other were determined and the internal boundary conditions were established.
 CONCLUSIONS: The presented methods and algorithms of spark plugs thermal state simulation helped to perform the calculation of dependencies of thermal conductivity and specific thermal capacity of the insulators ceramics as well as the thermal conductivity coefficient of the plugs ceramic elements on temperature.

The Impact of Board Governance on Firm Risk among China’s A-Share Market-Listed Companies from 2010 to 2019

This paper selects firm downside risk and firm upside risk as proxy variables of enterprise risk, and the proportion of independent directors as a proxy variable of board governance. Using the panel data of Chinese listed companies from 2010 to 2019, a multiple linear regression model is established to empirically study the impact of supervisory function and advisory function of board governance on the downside risk and the upside risk, to test whether the two functions of the board of directors play a role in the enterprise risk management (ERM). The internal mechanism and boundary conditions of board governance that affect firm risk are also explored in this paper. It is found that the sample enterprises pay more attention to the board‘s supervisory function. At the same time, they reduce the firm’s overall risk by reducing the downside risk and the upside risk while performing this function. We also identify that boards are more likely to use meetings to communicate and strategize to prevent upside risks than to identify and control downside risks. Finally, boards are negatively affected by CEO duality in performing their oversight functions.

Research on the Impact of Green Innovation Network Embeddedness on Corporate Environmental Responsibility

In the process of China's economic transformation, enterprises urgently need to use green innovation networks to realize corporate sustainability. Based on resource-based theory, this study explores the internal mechanism and boundary conditions of green innovation network embeddedness that affect corporate environmental responsibility. This paper conducts an empirical study based on panel data of listed companies engaged in green innovation in China from 2010 to 2020. Drawing on network embeddedness theory and resource-based theory, we found that relational and structural embeddedness influenced green reputation, which affected corporate environmental responsibility. We also identified the importance of ethical leadership and examined its role in moderating the effect of green innovation network embeddedness. A further investigation revealed that the impact of network embeddedness on corporate environmental responsibility was particularly pronounced in the samples of enterprises with high-level political ties, loose financing restrictions, and nonstate ownership. Our findings highlight the advantages of embedded green innovation networks and offer theoretical references and recommendations for enterprises considering network participation. Enterprises should attach great importance to the network embedding strategy of green innovation for corporate environmental responsibility and actively integrate the concept of green development into network relationship embedding and network structure embedding. Moreover, the relevant government department should provide necessary environment incentive policies according to the enterprise's development needs, especially for the enterprises with low-level political ties, high financing restrictions, and state ownership.

A new riemann solver for modelling bridges in flood flows - Development and experimental validation

Flows in rivers can be strongly affected by obstacles to flow or artificial structures such as bridges, weirs and dams. This is especially true during floods, where significant backwater effects or diversion of flow out of bank can result. However, within contemporary industry practice, linear features such as bridges are often modelled using coarse approximations, empirically based methods or are omitted entirely. Presented within this paper is a novel Riemann solver which is capable of modelling the influence of such features within hydrodynamic flood models using finite volume schemes to solve the shallow water equations. The solution procedure represents structures at the interface between neighbouring cells and uses a combination of internal boundary conditions and a different form of the conservation laws in the adjacent cells to resolve numerical fluxes across the interface. Since the procedure only applies to the cells adjacent to the interface at which a structure is being modelled, the method is therefore potentially compatible with existing hydrodynamic models. Comparisons with validation data collected from a state of the art research flume demonstrate that the solver is suitable for modelling a range of flow conditions and structure configurations such as bridges and gates.

Development of Smoothed Particle Hydrodynamics based water hammer model for water distribution systems

ABSTRACTSmoothed Particle Hydrodynamics (SPH) method is used to solve water hammer equations for pipeline systems due to its potential advantages of easily capturing column separation and slug impact. Currently, the SPH-based water hammer model has been only developed to simulate single pipe flow with simple boundary conditions. It is still a challenge to apply the SPH-based water hammer model to practical water distribution systems (WDSs). To address this issue, this study develops a complete SPH-based Water Hammer model for Water Distribution System (SPH-WHWDS). Within the proposed method, the complex internal and external boundary condition treatment models of the multi-pipe joint junction and different hydraulic components are developed. Buffer and mirror particles are designed for boundary treatment coupling with the method of characteristics (MOC). Two benchmark test cases, including an unsteady pipe flow experiment and a complex WDS, are used to validate the proposed model, with the data from the experimental test in the literature and the simulation results by the classical MOC. The results show the proposed SPH-WHWDS model is capable to simulate transient flows with accurate and robust results for pipeline systems, which may provide further insights and an alternative tool to study water hammer phenomena in complex WDSs.

Prediction identification method of time-varying internal heat source based on inverse heat transfer problem

Purpose This paper aims to discuss the inverse problems that arise in various practical heat transfer processes. The purpose of this paper is to provide an identification method for predicting the internal boundary conditions for thermal analysis of mechanical structure. A few examples of heat transfer systems are given to illustrate the applicability of the method and the challenges that must be addressed in solving the inverse problem. Design/methodology/approach In this paper, the thermal network method and the finite difference method are used to model the two-dimensional heat conduction inverse problem of the tube structure, and the heat balance equation is arranged into an explicit form for heat load prediction. To solve the matrix ill-conditioned problem in the process of solving the inverse problem, a Tikhonov regularization parameter selection method based on the inverse computation-contrast-adjustment-approach was proposed. Findings The applicability of the proposed method is illustrated by numerical examples for different dynamically varying heat source functions. It is proved that the method can predict dynamic heat source with different complexity. Practical implications The modeling calculation method described in this paper can be used to predict the boundary conditions for the inner wall of the heat transfer tube, where the temperature sensor cannot be placed. Originality/value This paper presents a general method for the direct prediction of heat sources or boundary conditions in mechanical structure. It can directly obtain the time-varying heat flux load and thtemperature field of the machine structure.

The virtuous circle between green product innovation and performance: The role of financial constraint and corporate brand

Although the nexus between green product innovation (GPI) and firm performance has been studied, the impact of GPI on firm performance remains little understood and findings have been mixed. These mixed results of prior studies are attributable to failures to incorporate the intervening mechanism in studying the nexus between GPI and firm performance and to examine the impact of closely interlinked pertinent internal boundary conditions. This study attempts to overcome these shortcomings and contributes to the relevant literature in three significant ways. First, the findings indicate that GPI impacts a firm’s financial constraint, which affects its current and anticipated performance. Second, the relationship between GPI and financial constraint is moderated by a firm’s corporate brand equity. Third, GPI is both a predictor and a consequence of financial performance, indicating that the relationship between the two constitutes a virtuous circle. The results are robust to alternative measures of the performance variable and the alternative model estimation method.

Structural Characterization of a Toppling Rock Slab From Array‐Based Ambient Vibration Measurements and Numerical Modal Analysis

AbstractAccurate assessments of the internal structure and boundary conditions of unstable rock slopes are imperative for evaluating landslide hazard scenarios. However, instability characterization at depth remains challenging and is often limited by costly or invasive subsurface investigations. Here, we develop a new approach coupling array‐based ambient vibration modal analysis and numerical modeling to improve structural characterization of rock slope instabilities at depth. We used ambient noise cross‐correlation on 4 hr of seismic data recorded by an array of 30 nodal geophones at a 500‐m‐long toppling rock slab in Utah, USA to identify modal frequencies between 0.8 and 3.5 Hz and derive modal displacements. We show that transverse and longitudinal bending modes span the length of the instability, indicating an interconnected slab. Statistical comparison of field results with outputs from >1,000 finite element models with varying boundary conditions showed that the instability depth varies between 40–70 and 10–20 m in the middle and lateral regions, respectively. Our approach yields new information on the structural conditions of rock cliff and column instabilities at depth, which is not easily obtained by other means but is imperative for change detection monitoring and improved hazard assessments.

Thermal mass impact on energy consumption for buildings in hot climates: A novel finite element modelling study comparing building constructions for arid climates in Saudi Arabia

Contradictory conclusions have been reported on whether thermal mass reduces or increases energy demand in hot and cold climates. A novel approach to measuring the impact of thermal mass on the building’s energy consumption is presented. The method aims to better represent reality and applies two different control conditions simultaneously in a numerical model: the first condition, which has been used in past studies, adjusts the internal boundary condition based on the time duration of heating/cooling activation (simulating an occupancy pattern) and the second, which has not been used in past studies, adjusts the internal boundary condition based on both the time duration and the internal temperature (simulating an occupancy pattern and the thermostatic control system). When investigating the impact of thermal mass on the internal temperature in a scenario where no heat is transferred into the building, the high thermal mass outperforms the low thermal mass, showing a time-shifting effect, long time lag, and small decrement factor. However, when modelled using the method presented in this paper, high thermal mass results in greater energy consumption during summer and winter periods in Saudi Arabia. During transition seasons where temperature swings occur on either side of the indoor set-point temperatures, thermal mass reduces thermal transmission. The impact of thermal mass is also investigated for several climatic conditions in Saudi Arabia. Simulation results show that an internally exposed thermal massive wall section results in greater energy consumption when compared to a similar building with isolated thermal mass (i.e. insulated internally). This is due to the fact that even though the internal temperature inside the building is being cooled/warmed up to the set-point, the thermal mass continues to transfer heat that is absorbed by the building’s fabric from/to the interior, placing a greater demand on the cooling/heating system. Over the course of a year, however, the impact of thermal mass is negligible when compared to other factors, such as the insulative properties of the building’s fabric.

Efficient Long-Term Simulation of the Heat Equation with Application in Geothermal Energy Storage

Long-term evolutions of parabolic partial differential equations, such as the heat equation, are the subject of interest in many applications. There are several numerical solvers marking the state-of-the-art in diverse scientific fields that may be used with benefit for the numerical simulation of such long-term scenarios. We show how to adapt some of the currently most efficient numerical approaches for solving the fundamental problem of long-term linear heat evolution with internal and external boundary conditions as well as source terms. Such long-term simulations are required for the optimal dimensioning of geothermal energy storages and their profitability assessment, for which we provide a comprehensive analytical and numerical model. Implicit methods are usually considered the best choice for resolving long-term simulations of linear parabolic problems; however, in practice the efficiency of such schemes in terms of the combination of computational load and obtained accuracy may be a delicate issue, as it depends very much on the properties of the underlying model. For example, one of the challenges in long-term simulation may arise by the presence of time-dependent boundary conditions, as in our application. In order to provide both a computationally efficient and accurate enough simulation, we give a thorough discussion of the various numerical solvers along with many technical details and own adaptations. By our investigation, we focus on two largely competitive approaches for our application, namely the fast explicit diffusion method originating in image processing and an adaptation of the Krylov subspace model order reduction method. We validate our numerical findings via several experiments using synthetic and real-world data. We show that we can obtain fast and accurate long-term simulations of typical geothermal energy storage facilities. We conjecture that our techniques can be highly useful for tackling long-term heat evolution in many applications.

Internal absorbing boundary conditions for closed-aperture wavefield decomposition in solid media with unknown interiors.

We present a method to create an internal numerical absorbing boundary within elastic solid media whose properties are largely unknown and use it to create the first wavefield separation method that retrieves all orders of outgoing elastic wavefield constituents for real data recorded on a closed free surface. The recorded data are injected into a numerical finite-difference (FD) simulation along a closed, transparent surface, and the new internal numerical absorbing boundary condition achieves high attenuation of the ingoing waves radiated from the injection surface. This internal wave absorption enables the data injection to radiate all outgoing waves for experimental domains that include arbitrary unknown scatterers in the interior. The injection-absorption-based separation scheme is validated using three-dimensional (3D) synthetic modeling and a real data experiment acquired using a 3D laser Doppler vibrometer on a granite rock. The wavefield separation method forms a key component of an elastic immersive wave experimentation laboratory, and the ability to numerically absorb ingoing scattered energy in an uncharacterized medium while still radiating the true outgoing energy is intriguing and may lead to other development and applications in the future.

The Impact of Policy Orientation on Green Innovative Performance: The Role of Green Innovative Capacity and Absorptive Capacity

Green innovation has been recognized as a key factor for balancing environmental sustainability and financial growth. Although the literature has examined the impacts of policy orientation on green innovation, there are still outstanding issues to be addressed. On the one hand, existing studies have focused on the direct impact of environmental regulation or institutional pressure on green innovation, but fail to account for the issue of intermediate mechanisms between policy orientation and green innovations. On the other hand, there are inconsistent findings in the current empirical evidence on the impact of environmental policies on green innovation. Therefore, this study tries to address these research gaps by clarifying the internal mechanisms and boundary conditions between policy orientation and green innovation. Based on Porter’s hypothesis and absorptive capacity perspective, this study explores the mediation effect of green innovative capability and the moderation effect of absorptive capacity in the relationship between policy orientation and green innovative capacity. To test the research model, we collected data from 359 Chinese green manufacturing companies. Our findings suggest that whether policy orientation has a significant positive effect on a firm’s green innovation performance depends on the firm’s absorptive capacity. In addition, green innovative capacity mediated the effect of policy orientation on green innovation performance. Furthermore, absorptive capacity strengthens this mediation effect. Therefore, we identified the mediating role of green innovative capacity and the moderating role of absorptive capacity between policy orientation and green innovation performance. Our findings theoretically enrich the literature on Porter’s hypothesis and absorptive capacity perspectives and provide a reference for green innovation practices.

Influence of Boundary Conditions and Internal Fluid Types on Dynamic Characteristics of a Deepwater Riser

Deepwater Steel Catenary Riser (DSCR) is the key structure of oil and gas production system in the ocean. To design an optimized DSCR system, the dynamic characteristics of the DSCR are analyzed by setting some different boundary condi-tions and internal fluid types. The main vibration mode of the DSCR is found orthogonal to both mass and stiffness according to the normalization condition of the main mode, and then the regular mode function and the jth order principal stiffness Kpj are obtained. Under different initial conditions, the transverse responses of DSCR represented by regular coordinates under arbitrary excitation are obtained. Then, a dynamic model in-duced by both axial load and transverse load is reconstructed for comparative study, and the axial load is found to have a great effect on the transverse dynamic characteristics. The effects of internal fluid and boundary conditions on the natural frequency of DSCR are also found at last.

Theoretical analysis of local indentation by the wedge indenter for pressurised pipeline

ABSTRACT External impact is one of the potential hazards for in-service subsea pipelines. The stress concentration by external impact can create a dent that affects the pipeline's ultimate bearing capacity. In this paper, a theoretical model based on the string-on-plastic foundation is established to model the local indentation of pressurised pipelines by a wedge indenter. The effects of internal pressure and boundary conditions on the denting process are investigated. With this model, the relationship between the indenting force and the dented depth is obtained under a set of two boundary conditions. The accuracy of the new analytical models is validated by comparing them with the specification and numerical simulation model. It is believed that the new analytical models will provide theoretical guidance for maintaining the reliability and integrity of in-service pressurised pipelines.

Socially Responsible human resource management and employees' turnover intention: the effect of psychological contract violation and moral identity

AbstractThis study explores the impact of socially responsible human resource management (SR-HRM) on the turnover intention by exploring the effects of psychological contract violation (PCV) and moral identity. Using a sample of 284 employees in China, we found that PCV mediated the negative relationship between SR-HRM and turnover intention. Moral identity moderated the direct effect of PCV on turnover intention as well as the indirect effect of SR-HRM on turnover intention via PCV, such that both the direct and indirect effects were stronger for employees with a low level of moral identity compared to those with the high level of moral identity. Findings from this study provide a greater understanding of the internal mechanisms and boundary conditions of SR-HRM that affect turnover intentions. Study findings also provide guidance to organizations seeking to reduce employee turnover.