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Building occupancy is an important basic factor in building energy simulation but it is hard to represent due to its temporal and spatial stochastic nature. This paper presents a novel approach for building occupancy simulation based on the Markov chain. In this study, occupancy is handled as the straightforward result of occupant movement processes which occur among the spaces inside and outside a building. By using the Markov chain method to simulate this stochastic movement process, the model can generate the location for each occupant and the zone-level occupancy for the whole building. There is no explicit or implicit constraint to the number of occupants and the number of zones in the model while maintaining a simple and clear set of input parameters. From the case study of an office building, it can be seen that the model can produce realistic occupancy variations in the office building for a typical workday with key statistical properties of occupancy such as the time of morning arrival and night departure, lunch time, periods of intermediate walking-around, etc. Due to simplicity, accuracy and unrestraint, this model is sufficient and practical to simulate occupancy for building energy simulations and stochastic analysis of building heating, ventilation, and air conditioning (HVAC) systems.

Building occupancy is an important basic factor in building energy simulation but it is hard to represent due to its temporal and spatial stochastic nature. This paper presents a novel approach for building occupancy simulation based on the Markov chain. In this study, occupancy is handled as the straightforward result of occupant movement processes which occur among the spaces inside and outside a building. By using the Markov chain method to simulate this stochastic movement process, the model can generate the location for each occupant and the zone-level occupancy for the whole building. There is no explicit or implicit constraint to the number of occupants and the number of zones in the model while maintaining a simple and clear set of input parameters. From the case study of an office building, it can be seen that the model can produce realistic occupancy variations in the office building for a typical workday with key statistical properties of occupancy such as the time of morning arrival and night departure, lunch time, periods of intermediate walking-around, etc. Due to simplicity, accuracy and unrestraint, this model is sufficient and practical to simulate occupancy for building energy simulations and stochastic analysis of building heating, ventilation, and air conditioning (HVAC) systems.

Extended from the electrochemo-mechanical single particle model, an electrochemo-mechanical impedance model for porous electrode in LIB, which consider the effect of the contact stress, is proposed in this work. A modified coefficient ζ which links the mechanical properties of the electrode and particle material is introduced to describe the effect of contact stress. Firstly, we find that the contact stress can weaken the stress-induced semicircle in the low frequency range through analyzing the Faradaic part of the impedance. Secondly, considering the contact stress is determined by the mechanical bonding between electrode layer and the current collector, we introduce a pseudo-elastic boundary condition to analyze the bonding effect. For rigid substrate, namely the in-plane deformation is totally restricted, the effect of the contact stress is strong. For free substrate, namely the in-plane deformation is not restricted, the contact stress is not induced thus its effect on impedance disappears. Lastly, we discuss the interaction effect of stress and the ionic transport in the electrolyte and find that the interaction is strong for silicon-based material, which indicates the stress effect needs to be considered when interpreting the impedance data in this case.

Extended from the electrochemo-mechanical single particle model, an electrochemo-mechanical impedance model for porous electrode in LIB, which consider the effect of the contact stress, is proposed in this work. A modified coefficient ζ which links the mechanical properties of the electrode and particle material is introduced to describe the effect of contact stress. Firstly, we find that the contact stress can weaken the stress-induced semicircle in the low frequency range through analyzing the Faradaic part of the impedance. Secondly, considering the contact stress is determined by the mechanical bonding between electrode layer and the current collector, we introduce a pseudo-elastic boundary condition to analyze the bonding effect. For rigid substrate, namely the in-plane deformation is totally restricted, the effect of the contact stress is strong. For free substrate, namely the in-plane deformation is not restricted, the contact stress is not induced thus its effect on impedance disappears. Lastly, we discuss the interaction effect of stress and the ionic transport in the electrolyte and find that the interaction is strong for silicon-based material, which indicates the stress effect needs to be considered when interpreting the impedance data in this case.

Abstract Thousands of spherical fuel elements are transported pneumatically in pipelines in a pebble bed reactor every day. The motion of the fuel element has a strong influence on the efficiency and reliability of the reactor. The motion is determined by the force condition of the fuel element which is determined by the characteristics of the flow field in turn. Thus, it is of great significance to analyze the characteristics of the flow field and the force conditions of the fuel element. In this paper, we carry out simulations of the flow field with a structured mesh based on CFD (computational fluid dynamics). We analyze the effect of the motion and position of the fuel element on the flow field. Then we accomplish the force analysis of the fuel element in the flow, and acquire the fitting formulae of the force and torque on the fuel element. The experiment was performed on the experimental platform. The experimental results are in agreement with the theoretical analysis and verify its accuracy. This research may provide an important rationale for the dynamic and kinematic analysis of the fuel element pneumatic transportation as well as the basis for the stable operation of the reactor.

Abstract Thousands of spherical fuel elements are transported pneumatically in pipelines in a pebble bed reactor every day. The motion of the fuel element has a strong influence on the efficiency and reliability of the reactor. The motion is determined by the force condition of the fuel element which is determined by the characteristics of the flow field in turn. Thus, it is of great significance to analyze the characteristics of the flow field and the force conditions of the fuel element. In this paper, we carry out simulations of the flow field with a structured mesh based on CFD (computational fluid dynamics). We analyze the effect of the motion and position of the fuel element on the flow field. Then we accomplish the force analysis of the fuel element in the flow, and acquire the fitting formulae of the force and torque on the fuel element. The experiment was performed on the experimental platform. The experimental results are in agreement with the theoretical analysis and verify its accuracy. This research may provide an important rationale for the dynamic and kinematic analysis of the fuel element pneumatic transportation as well as the basis for the stable operation of the reactor.

Indoor humidity directly impacts the health of indoor populations. In arid and semi-arid cities, the buildings indoor humidity is typically higher than outdoors, and the presence of water vapor results from water dissipation inside the buildings. Few studies have explored indoor humidity features and vapor distribution or evaluated water dissipation inside buildings. This study examined temperature and relative humidity (RH) changes in typical residential and office buildings. The results indicate a relatively stable temperature with vary range of ±1°C and a fluctuation RH trend which is similarly to that of water use. We proposed the concept of building water dissipation to describe the transformation of liquid water into gaseous water during water consumption and to develop a building water dissipation model that involves two main parameters: indoor population and total floor area. The simulated values were verified by measuring water consumption and water drainage, and the resulting simulation errors were lower for residential than for office buildings. The results indicate that bathroom vapor accounts for 70% of water dissipation in residential buildings. We conclude that indoor humidity was largely a result of water dissipation indoors, and building water dissipation should be considered in urban hydrological cycles.