Two-node Model Research Articles

State estimation of resistive domestic hot water heaters in arbitrary operation modes for demand side management

Utilizing domestic hot water heaters (DHWH) for demand side management (DSM) requires physical models of DHWH dynamic behavior. An ideal dynamic DHWH model is simple as well as accurate. However, system identification and state estimation, which are necessary for real-life implementation, are usually not considered. This work reviews standard thermal models, such as the single-node model, the multi-node model, a two-mass composite model and a two-node hybrid model with thermocline tracking. A prediction error method (PEM), applicable to all four models, is developed. 16 weeks of user and switching data from a DSM field test are used to operate a laboratory DHWH realistically. The temperature distribution within the heater, as well as electrical power input, water volume flow, inlet and outlet water temperature, temperature of the surroundings, and thermal well temperature are recorded. System identification and state estimation routines are developed based on the data available for a retrofitted system. Using cross-validation on the available user and operation scenarios from the lab, the approaches are compared with respect to average and outlet temperature estimation errors, model robustness and computational costs. The results show that a single-node model, which incorporates information on stratification during heating intervals in assuming a linear temperature distribution in the lower part of the tank, performs nearly as well in predicting the average temperature (mean average percentage error of 6%) as the 50 times more computationally expensive multi-layer model (mean average percentage error of 4%) and better than all other single-layer model based approaches considered.

Contribution of wetted clothing to body energy exchange and heat stress

Quantifying the impact of clothing thermal and evaporation resistance is essential to providing representative boundary conditions for physiological modeling. In many models, sweat is assumed to drip off the skin surface to the environment and is not captured in clothing. In high metabolic rate and high temperature and humidity conditions the sweat produced by the body has the potential to saturate semipermeable clothing ensembles, changing the assumptions of the model. Workers, athletes and soldiers commonly wear encapsulating versions of such clothing to protect against environmental hazards. A saturated clothing model is proposed based on the ASHRAE two-node model using a saturated spot element in parallel with the existing method to account for sweat absorbed in the clothing. The work uses fundamental heat and mass transfer principles, modifying the existing formula using clothing measurements and basic assumptions. The effectiveness of the model is demonstrated by comparing the predictions of the original and proposed models, to the results of 21 soldiers exercising. The soldiers wore combat pants and shirt, helmet, gloves, shoes, socks, and underwear, and walked in a thermal chamber for 2 h at 42.2 °C dry bulb temperature, 54.4 °C wet bulb temperature, 20% relative humidity, and airspeed of 2 m/s. Core temperature, seven skin temperatures, heart rate, and total sweat loss were measured. The original model provides an average core temperature difference compared with the human subject results of 1.31 °C (SD = 0.557 °C) while the modified model improves the final prediction of core temperature to within an average of 0.15 °C (SD = 0.383 °C). The new model shows an improvement in the prediction of human core temperature under the tested conditions where dripping sweat will saturate clothing. The format can be used in multi-segmented thermal models and can continue to be developed and improved as more information on wetted clothing properties become available.

Calculation and analysis of water activation products source term in AP1000

During AP1000 operation, the water itself in the primary loop and the impurities in the water will be activated by neutrons. The activation products 16N, 17N, 3H and 14C are considerable radiation hazard in AP1000. In this paper, two analysis models (homogeneous model and two-node model) are developed to calculate the radioactivity of activation products in the primary coolant of AP1000. The calculated density of each radionuclide at chosen region is introduced into ARShield code and then converted to dose rate using point kernel integration method. In addition, for 3H, inventory produced under mechanical shim operating mode is calculated by the ladder model proposed in this article and the influence of 7Li abundance is analyzed. The results lead to the following conclusions: (1) coolant flow has obvious impact on the radioactivity of nuclides 16N, 17N and 3H and the results from the two-node model considering coolant flow are more conservative; (2) purification has obvious impact on the radioactivity of long-lived nuclides 3H and 14C, while has almost no impact on the radioactivity of short-lived nuclides 16N and 17N; (3) the major contributors of dose rate are 16N and 17N and the total dose rate of the primary loop is 4.056E-01 mSv/h after one year's operation; (4) under mechanical shim operating mode of AP1000, the quantity of 3H produced by soluble boron is approximately 21.12% higher than that under chemical shim operating mode; (5) the contribution of lithium to 3H production decreases linearly with increasing 7Li abundance in LiOH in the water.

System dynamics of human body thermal regulation in outdoor environments

Thermal comfort of people in outdoor urban spaces is a growing concern in cities due to climate change and urbanization. In outdoor settings the climate and behavior of people are more dynamic than in indoor situations, therefore a steady state of the thermoregulatory system is rarely reached. Understanding the dynamics of outdoor thermal comfort requires accurate predictive models. In this paper we extend a classical two-node model of human body thermal regulation. We give a detailed description and interpretation of all the components and parameter values and test the dynamics of the model against experimental data. We propose a modification of the skin blood flow model which, while keeping realistic values and responsiveness, improves skin temperature prediction nearly fourfold. We further analyze the sensitivity of the model with respect to climatic and personal parameters. This analysis reveals the relative importance of, for instance, air temperature, wind speed and clothing, in thermoregulatory processes of the human body in various climatic settings. We conclude, that our model realistically reproduces the dynamics of aggregate measures of human body thermal regulation. Validated for cool, warm and hot environments, the model is shown to be accurate in terms of its dynamics and it is conceptually and computationally far more efficient than any existing multi-node and multi-part model.

Activation analysis of coolant in a water-cooled loop of China fusion engineering test reactor

In the design scheme of China Fusion Engineering Test Reactor (CFETR), water will be adopted as the coolant in some cooling loops. The water itself and the impurities in it will be activated by neutrons, and the activation products 16N, 17N, 3H and 14C are important to the occupational radiation exposure (ORE) during operation and maintenance. In this paper, two analysis models (homogeneous model and two-node model) are developed to calculate the radioactivity of activation products in the water-cooled loop. Then, the impact of water chemistry parameters (pH and 7Li abundance) on tritium production is analyzed. At last, the dose rate of one typical blanket water-cooled loop is calculated using the point kernel code ARShield. The results show that: (1) the radioactivity of short-lived nuclides 16N and 17N is obviously affected by coolant flow and the results from the two-node model considering coolant flow are more conservative; (2) the radioactivity of long-lived nuclides 3H and 14C is obviously affected by purification; (3) 16N and 17N are the main contributors to radioactivity, whose radioactivity are several orders of magnitude higher than that of 3H and 14C; (4) tritium is susceptible to water chemistry environment, and at pH of 7.1 tritium radioactivity is about two orders of magnitude higher than that at pH of 5.7; (5) at pH of 7.1, the contribution of lithium to tritium production increases linearly with increase of 7Li abundance in LiOH in the water.

Analysis and test for thermal performance of High Altitude Super Pressure Balloons during ascending process

A two-node model for thermal characteristics and a dynamic model of High Altitude Super Pressure Balloon (HASPB) during ascending process are established. The thermal performance of HASPB during ascending process is analyzed. Several simulations are conducted under the same conditions with the real flight test. Results show that supercool phenomenon occurs during ascending caused by free expansion of gas, and the value is about 10-15 K. Once the balloon reaches the design height and becomes over-pressured, the temperature of balloon rises rapidly, and this adjustment process lasts for about 10 minutes. The real flight test to 20000 m validates the reliability of the two-node model.

Performance and Cost Considerations for Providing Geo-Elasticity in Database Clouds

Online applications that serve global workload have become a norm and those applications are experiencing not only temporal but also spatial workload variations. In addition, more applications are hosting their backend tiers separately for benefits such as ease of management. To provision for such applications, traditional elasticity approaches that only consider temporal workload dynamics and assume well-provisioned backends are insufficient. Instead, in this article, we propose a new type of provisioning mechanisms—geo-elasticity, by utilizing distributed clouds with different locations. Centered on this idea, we build a system called DBScale that tracks geographic variations in the workload to dynamically provision database replicas at different cloud locations across the globe. Our geo-elastic provisioning approach comprises a regression-based model that infers database query workload from spatially distributed front-end workload, a two-node open queueing network model that estimates the capacity of databases serving both CPU and I/O-intensive query workloads and greedy algorithms for selecting best cloud locations based on latency and cost. We implement a prototype of our DBScale system on Amazon EC2’s distributed cloud. Our experiments with our prototype show up to a 66% improvement in response time when compared to local elasticity approaches.

Fractional Calculus Based FDTD Modeling of Layered Biological Media Exposure to Wideband Electromagnetic Pulses

Electromagnetic fields are involved in several therapeutic and diagnostic applications such as hyperthermia and electroporation. For these applications, pulsed electric fields (PEFs) and transient phenomena are playing a key role for understanding the biological response due to the exposure to non-ionizing wideband pulses. To this end, the PEF propagation in the six-layered planar structure modeling the human head has been studied. The electromagnetic field and the specific absorption rate (SAR) have been calculated through an accurate finite-difference time-domain (FDTD) dispersive modeling based on the fractional derivative operator. The temperature rise inside the tissues due to the electromagnetic field exposure has been evaluated using both the non-thermoregulated and thermoregulated Gagge’s two-node models. Moreover, additional parametric studies have been carried out with the aim to investigate the thermal response by changing the amplitude and duration of the electric pulses.

Extension of dual equivalent linearization to nonlinear analysis of thermal behavior of a two-node model for small satellites in Low Earth Orbit

The purpose of this study is to extend the dual equivalent linearization to the problem of thermal analysis of small satellites in Low Earth Orbit (LEO) using two-node model. The satellite is modeled as a body with two iso-thermal nodes, namely, outer and inner ones. The outer node represents for the shell of the satellite whereas the inner node stands for some inner equipment. In space environment, the outer node is subjected to three main thermal loadings including the solar irradiation, albedo and Earth’s infrared radiation. Also, the inner node is assumed to be undergone a constant heat dissipation level. To simplify the process of linearization, a preprocessing step in separating nonlinear terms of the original system is carried out to get an equivalent system in which each differential equation contains only one nonlinear term. Based on the dual criterion a closed form of linearization coefficients system is obtained and solved by a Newton–Raphson iteration procedure. It is shown that the solutions obtained from the dual criterion are in a good agreement with those obtained from the Grande’s approach and Runge–Kutta algorithm.

Toward better estimation of HVAC Loads: integrating a detailed human thermal model into building simulation

The transient nature of the occupant heat load is not fully addressed and implemented in a building simulation tool. In this paper, the effect of using dynamic occupant heat loads in building simulation on energy building performance and occupant thermal comfort has been studied. A two-node thermoregulatory model was integrated into ESP-r. The predictions of the integrated two-node model were compared to two commonly used approaches in building simulation: gains modelled as a basic fixed profile and gains modelled using a polynomial function of temperature and relative humidity. The variation in occupant thermal load demonstrated appreciable differences on both cooling and dehumidification loads.

Modelling hand skin temperature in relation to body composition

Skin temperature is a challenging parameter to predict due to the complex interaction of physical and physiological variations. Previous studies concerning the correlation of regional physiological characteristics and body composition showed that obese people have higher hand skin temperature compared to the normal weight people. To predict hand skin temperature in a different environment, a two-node hand thermophysiological model was developed and validated with published experimental data. In addition, a sensitivity analysis was performed which showed that the variations in skin blood flow and blood temperature are most influential on hand skin temperature. The hand model was applied to simulate the hand skin temperature of the obese and normal weight subgroup in different ambient conditions. Higher skin blood flow and blood temperature were used in the simulation of obese people. The results showed a good agreement with experimental data from the literature, with the maximum difference of 0.31°C. If the difference between blood flow and blood temperature of obese and normal weight people was not taken into account, the hand skin temperature of obese people was predicted with an average deviation of 1.42°C. In conclusion, when modelling hand skin temperatures, it should be considered that regional skin temperature distribution differs in obese and normal weight people.

Characterization of the pierce two-node model under exercise load by parameter optimization toward construction of a modified thermal model for persons with spinal cord injury.

In this study, we attempted to develop a thermal model for estimating a body temperature in persons with spinal cord injury (SCI) during exercise. To clarify requisites for the SCI thermal model, we compared actual body temperature of SCI subjects with that calculated with a standard thermal model, that is, the Pierce two-node model. Model optimization by the parameter search method was able to fit the model-estimated skin and core temperature with those in able-bodied subjects during repeated exercise and rest. However, there remained a phase shift between actual and model-estimated core temperature trends in SCI subjects even after the optimization. The comparison of the optimized parameter combinations revealed that the Pierce two-node model was able to express loss of sweating in the SCI subjects, but unable to express delay in heat accumulation and dissipation. These results suggest that SCI thermal model requires additional nodes that express the speed and extent of heat transfer in the body of SCI persons.

Forked queueing model with load dependent service rate and bulk arrivals

In this paper a forked two-node tandem queueing model with load dependent service rates having bulk arrivals is introduced and analysed under transient and equilibrium conditions. The system performance measures like probability of emptiness of the system, the probabilities of emptiness of marginal queues, the average number of customers in each queue, the average waiting time of the customer in each queue, the throughput of each node, the utility of servers and the variance of the number of customers in each queue are derived and analysed. The sensitivity analysis of a model reveals that the bulk size distribution parameters has a significant influence on system performance measures. Through numerical studies, it is observed that the load dependent service rates can reduce the congestion in queues and mean delay. A comparative study of the model with respect to equilibrium and transient conditions reveal that the time has significant influence on the performance measures. This model also includes some of the earlier models as particular cases for specific values of the parameters.

Modelling of Internet of Things units for estimating security-energy-performance relationships for quality of service and environment awareness

Complexity of Internet of Things IoT applications and difficulty to predict their behaviour in wireless communications make modelling of IoT units an important research topic. The IoT unit is considered here as the two-node IoT model that supports bi-directional wireless communications. There are many approaches to model security and energy awareness; however, little is known about the synergistic effect of those factors at the application level under the influence of environmental factors such as noise. The paper introduces a modelling framework to model the security-energy-environment issues as main attributes to allow defining quality of service QoS for the IoT-based applications. Among others, the healthcare ones are regarded as predominant now. We model IoT units using the feature-based modelling methodology adopted from the software engineering domain. The result of modelling is a set of feature models with valid configurations that describe the energy-security-environment-performance relationships and possible constraints to support various IoT applications. Having feature models, we can select a configuration that is best suited for a given IoT application with respect to QoS requirements. As feature models represent abstract relationships of domain factors, we need additionally to provide experiments to determine concrete values of modelled features. We describe the experimental system to measure energy consumption under the influencing factors. Both models abstract and concrete allow reasoning about QoS of the IoT applications. Copyright © 2016 John Wiley & Sons, Ltd.

Linear magnetoconductivity in an intrinsic topological Weyl semimetal

Searching for the signature of the violation of chiral charge conservation in solids has inspired a growing passion for the magneto-transport in topological semimetals. One of the open questions is how the conductivity depends on magnetic fields in a semimetal phase when the Fermi energy crosses the Weyl nodes. Here, we study both the longitudinal and transverse magnetoconductivity of a topological Weyl semimetal near the Weyl nodes with the help of a two-node model that includes all the topological semimetal properties. In the semimetal phase, the Fermi energy crosses only the 0th Landau bands in magnetic fields. For a finite potential range of impurities, it is found that both the longitudinal and transverse magnetoconductivity are positive and linear at the Weyl nodes, leading to an anisotropic and negative magnetoresistivity. The longitudinal magnetoconductivity depends on the potential range of impurities. The longitudinal conductivity remains finite at zero field, even though the density of states vanishes at the Weyl nodes. This work establishes a relation between the linear magnetoconductivity and the intrinsic topological Weyl semimetal phase.

Cardiovascular disease-induced thermal responses during passive heat stress: an integrated computational study.

The cardiovascular system plays a crucial role in human thermoregulation; cardiovascular diseases may lead to significantly degrading the thermoregulation ability for patients during exposure to heat stress. To evaluate the thermal responses of patients with common chronic cardiovascular diseases, we here propose an integrated computational model by coupling a two-node thermoregulation model with a closed-loop, multi-compartment, lumped-parameter cardiovascular model. This bioheat transfer model is validated, capable to predict cardiovascular functions and thermal responses under varying environmental conditions. Our results demonstrate that the cardiovascular disease-induced reduction in cardiac output and skin blood flow causes extra elevation in core temperature during hyperthermic challenges. In addition, a combination of aging, obesity, and cardiovascular diseases shows a pronounced increase in core temperature during heat exposure, which implies that such combined effect may increase the risk of heat-related morbidity and mortality. Copyright © 2016 John Wiley & Sons, Ltd.

Healthy ageing: differences between elderly and non-elderly in temperature sensation and dissatisfied

ABSTRACTThe key question in this study is: ‘To which extent is the difference in thermal comfort mathematically to describe by temperature sensation and the percentage of dissatisfied, between the elderly and non-elderly, related to the Fanger model?’. This study proves that it is possible to mathematically describe the difference in thermal comfort between elderly and non-elderly by means of a comparison between the calculation results of a thermophysiological two-node model, adjusted for individual characteristics, and different experimental studies. Since the various subgroups of elderly are increasing in number disproportionately to other age groups, adapting the existing thermophysiological human models, for predicting the thermal response of people depending on age and sex, is important. In this way, useful insights can be realized from modelling the thermal behaviour and response patterns of the elderly for the future design of buildings and climate installations.

Energy cooperation for throughput optimization based on save-then-transmit protocol in wireless communication system

Green communication and energy saving have been a critical issue in modern wireless communication systems. The concepts of energy harvesting and energy transfer are recently receiving much attention in academic research field. In this paper, we study energy cooperation problems based on save-then-transmit protocol and propose two energy cooperation schemes for different system models: two-node communication model and three-node relay communication model. In both models, all of the nodes transmitting information have no fixed energy supplies and gain energy only via wireless energy harvesting from nature. Besides, these nodes also follow a save-then-transmit protocol. Namely, for each timeslot, a fraction (referred to as save-ratio) of time is devoted exclusively to energy harvesting while the remaining fraction is used for data transmission. In order to maximize the system throughput, energy transfer mechanism is introduced in our schemes, i.e., some nodes are permitted to share their harvested energy with other nodes by means of wireless energy transfer. Simulation results demonstrate that our proposed schemes can outperform both the schemes with half-allocate save-ratio and the schemes without energy transfer in terms of throughput performance, and also characterize the dependencies of system throughput, transferred energy, and save-ratio on energy harvesting rate.

A novel updated Lagrangian complementary energy-based formulation for the elastica problem: force-based finite element model

This paper addresses the development of a novel updated Lagrangian variational formulation and its associated finite element model for the geometrically nonlinear quasi-static analysis of cantilever beams. The formulation is based on an incremental complementary energy principle. The proposed finite element model only contains nodal bending moments as degrees of freedom. The model is used for the analysis of problems modeled by the so-called elastica theory. Numerical solutions satisfying all equilibrium equations in a strong sense can be obtained for arbitrarily large displacements and rotations. A Newton–Raphson method is adopted to trace the post-buckling response. Numerical results are presented and compared with those produced by the standard total Lagrangian two-node displacement-based finite element model.

Regulatory logic and pattern formation in the early sea urchin embryo

We model the endomesoderm tissue specification process in the vegetal half of the early sea urchin embryo using Boolean models with continuous-time updating to represent the regulatory network that controls gene expression. Our models assume that the network interaction rules remain constant over time and the dynamics plays out on a predetermined program of cell divisions. An exhaustive search of two-node models, in which each node may represent a module of several genes in the real regulatory network, yields a unique network architecture that can accomplish the pattern formation task at hand – the formation of three latitudinal tissue bands from an initial state with only two distinct cell types. Analysis of an eight-gene model constructed from available experimental data reveals that it has a modular structure equivalent to the successful two-node case. Our results support the hypothesis that the gene regulatory network provides sufficient instructions for producing the correct pattern of tissue specification at this stage of development (between the fourth and tenth cleavages in the urchin embryo).