Steady-state Calculation Method Research Articles

Numerical Simulation and Experimental Verification of Rotor Airflow Field Based on Finite Volume Method and Lattice Boltzmann Method

The primary focus of research in agricultural unmanned aerial vehicle (UAV) pesticide application technology is the investigation of droplet drift and deposition. The influence of the rotor airflow on droplets is particularly significant, making numerical simulations a crucial tool for airflow field analysis. Among existing numerical simulation methods, the Finite Volume Method (FVM) and the Lattice Boltzmann Method (LBM) are commonly used, but there is limited research that compares the two approaches. Therefore, this paper conducts numerical simulations of the rotor airflow of an agricultural UAV using Fluent, representing the FVM, and XFlow, representing the LBM. This research aims to reveal the distribution patterns of airflow field numerical simulations under different theoretical methods, validate them through practical experiments, and select the optimal method for simulating rotor airflow. The ultimate goal is to establish an effective airflow field model to enhance the precision of pesticide application by an agricultural UAV. The results indicate that the lift error calculated by XFlow in this paper is 2.57% smaller than that by Fluent. The wind field of Fluent entered the “stable state” earlier than XFlow, and the speed value of Fluent was smaller than that of XFlow. The difference between the two speed values became larger and larger as the distance from the rotor was longer. Compared with XFlow, Fluent changes more obviously in the core region, and the center region gradually disappears with the distance from the rotor. However, in the velocity field calculated by XFlow, there are still more turbulent flows outside the core region, indicating that the transient calculation method based on the LBM can better show the details of fluid flow than the steady-state calculation method based on the FVM. Through comparison with the actual test data, it is found that the relative error of the velocity value of XFlow at 0.2 m and 0.4 m is small, while that of Fluent at 0 and 0.2 m is small. It shows that XFlow simulation has higher accuracy for external turbulent flow, while Fluent simulation has higher accuracy for steady laminar flow. The research results provide data comparison and a basis for further analysis of the wind field model of the rotor wing of the plant protection UAV, and they lay a foundation for further research on precision application technology.

The new method for hydraulic calculations of a district heating (DH) network

How to estimate the exact value of pressure losses within a district heating (DH) network been in service for decades, which a pump at pumping station should compensate to achieve maximum benefits and the lowest costs relative to the scenario of the started process of transition to 4th generation district heating (4GDH)? Geographic Information System (GIS) software Zulu© was used to model a DH network and evaluate how specific location will affect hot water flow rates. Pressure, roughness and hydraulic resistance profiles were plotted using hydraulic optimisation software ZuluThermo©– GIS Zulu© add-in. While the new arrangement does not reduce pressure losses themselves, the corrected arrangement provides economic advantage due to lower operation costs and more stable hydraulic profiles. That means that end sections of DH network between the transmission line and consumers become more effective. By calculating pressure loss and temperature degradation the method also allows to detect an optimum location to connect a new consumer where the minimum modernisation is needed. Working with data-driven network models makes it possible to obtain a lot of positive effects at the same time including the main - the DH utility sells more heat and becomes more profitable as the losses are lower. • To ensure low-temperature energy supply, its consumption for pumping is assessed. • Steady-state calculation method is used to evaluate pressure and flow distribution. • To verify, portable ultrasonic flow rate meter&traditional pressure sensors are used. • Electricity consumption is decreased by 394.74 kW, the saving effect is up to 6%. • Effect is achieved by lowering losses, clarifying friction factor&relative roughness.

Draught perception in intermittent ventilation at neutral room temperature

This study questions the extent which steady-state calculation methods for the draught rate according to ISO 7730 are applicable to intermittent ventilation, especially with pulse durations shorter than 30 s. 37 subjects were exposed to intermittent ventilation in a cooling scenario at neutral room temperature, i.e.in an ambient that was neither warm nor cool. Two displacement air diffusers supplied the air alternatingly, 50% of the time from each side. The operation profile of each diffuser thus corresponded to a square waveform. The diffuser supply air temperature was at 19 °C while the room temperature was controlled to thermally neutral conditions at 22 °C. Two subjects sat directly in front of large air diffusers and were therefore located in the core region of a free jet with the cool air blowing from behind. The subjects were asked to evaluate their thermal comfort for nine conditions with air velocities between 0.2 ms−1and0.6 ms−1 and pulse durations between 10 s and 30 s. In intermittent ventilation, the discomfort was higher than in steady ventilation at the same maximum velocity. Draught perception increased with increasing velocity and with increasing pulse duration. Due to the enhanced mixing with ambient air in intermittent ventilation, the average air temperature 25 cm in front of the diffusers could be increased by 0.5 K.

Applicability of different energy efficiency calculation methods of residential buildings in severe cold and cold zones of China

With the accelerated development of dynamic energy consumption simulation software, the accuracy and feasibility of steady-state calculation method for energy efficiency designs of residential buildings in severe cold and cold zones should be investigated. A six-story residential building model as a case study is introduced to be calculated and simulated by steady-state calculation method elaborated in ‘Design standard for energy efficiency of residential buildings in severe cold and cold zones’ and dynamic energy consumption simulation of EnergyPlus software respectively, in order to compare and analyze the differences between these two methods in five typical cities of China (Xi’an, Lhasa, Xining, Harbin and Hailar). The findings indicate that the index of heat loss of building obtained from both methods is different to typical cities with varied difference ratios. Especially in cities of high altitude, strong radiation and greater diurnal range, namely Lhasa and Xining, the difference ratio is as high as 43.83% and 16.63%. Thus, dynamic energy consumption simulation should be used for counting residential building energy efficiency instead of steady-state calculation method in above mentioned zones by analyzing main factors concerning the differences.

Numerical study on heat blocking efficiency of non-recirculating air curtain and its optimal discharge velocity

From the point of view to reduce energy consumption, door open while air conditioner running on buildings have a problem. To solve the problem, many facilities for entrance with vestibule, revolving door, and air curtain are utilized. Among the facilities, the air curtain cuts off the indoor and outdoor air by discharging the wide air surrounding the opening, thereby preventing the heat loss from the indoor. The purpose of this study is to evaluate the heat blocking efficiency of non-recirculating air curtain and to evaluate its optimal discharge velocity. To achieve this goal, the infiltration rate across the single-side opening were investigated with air temperature differences between areas by transient CFD simulation and the results were compared with the steady-state calculation method. In addition, to evaluate the heat blocking efficiency of non-recirculating air curtain, the calculation model was set up and several cases with discharge velocity were compared. The results show that the discharged air from the air curtain causes a deflection from the high temperature area to the low temperature area, and the deflection decreases with increasing the discharge air velocity. In this study, the safety factor for deflection modulus of the non-recirculating air curtain was calculated 2.75.

On the limits of the quasi-steady-state method to predict the energy performance of low-energy buildings

The recent European energy policies progressively introduced more restrictive energy performance requirements aimed at achieving the nearly zero-energy building target for all new buildings and major renovations. To check compliance with these requirements, the building energy performance can be evaluated through different calculation methods, as widely presented in literature. The present article is aimed at identifying in which boundary conditions (e. g. climate, use category, building size, thermal insulation level) a simplified steady-state calculation method can predict with sufficient accuracy the energy performance of low-energy buildings if compared with a dynamic simulation model. The analysis was performed on two building types, representative of the Italian residential typology, located in three different climatic zones and characterised by two insulation levels. The insulation levels fit the U-values of the notional reference building, established by the Italian legislation for checking compliance with energy performance requirements in two different steps; the first level is in force until 2020, while the second level is that of a reference nearly zero-energy building in force from 2021 onwards. The building energy performance, in terms of net energy needs for space heating and space cooling, was assessed by means of both the monthly calculation method of CEN standards and the detailed simulation model of EnergyPlus. Consistency options were applied to the models to guarantee that their outputs could be comparable. The quasi-steady-state method demonstrated to predict the cooling energy need quite well, but to lose in accuracy when the weight of the thermal transfer in the energy balance increases.

Practise-oriented consideration of the dynamic fast fault current of power park modules in grid protection analysis

Protection design in distribution grids is usually undertaken by simple to handle practice-oriented steady-state calculation methods. For the calculation of the minimal short-circuit current models and methods are described in IEC 60909. In the revised version from 2016 constant current sources for modelling of reactive current infeed of converter-based generators due to mandatory grid support in Germany are considered, though the infeed is voltage dependent. Moreover, the dynamic settling process of the reactive current infeed can affect the functionality of the protection, which is not taken into account in steady-state calculations. This study outlines a possibility to estimate the influence of these new dynamic effects on grid protection behaviour in steady-state calculation methods. Different types of decentralised generation (DG) units as well as other influences, e.g. grid topologies, distribution of DG or protection concepts are taken into account. The authors will show that suitable steady-state calculations are sufficient for practical protection analysis. The risk of undesirable reactions of the grid protection can be minimised by the use of the derived general recommendations.

Unsteady-state human-body exergy consumption rate and its relation to subjective assessment of dynamic thermal environments

Few examples studied applicability of exergy analysis on human thermal comfort. These examples relate the human-body exergy consumption rate with subjectively obtained thermal sensation votes and had been based on steady-state calculation methods. However, humans are rarely exposed to steady-state thermal environments. Therefore, the first objective of the current paper was to compare a recently introduced unsteady-state model with previously used steady-state model using data obtained under both constant and transient temperature conditions. The second objective was to explore a relationship between the human-body exergy consumption rate and subjective assessment of thermal environment represented by thermal sensation as well as to extend the investigation towards thermal acceptability votes. Comparison of steady-state and unsteady-state model showed that results from both models were comparable when applied to data from environments with constant operative temperature. In contrast, when applied to data with temperature transients the prediction of particular models differed significantly and the unsteady-state model resulted in better prediction of mean skin temperature. The results of the present study confirmed previously indicated trends that lowest human body exergy consumption rate is associated with thermal sensation close to neutrality. Moreover, higher acceptability was in general associated with lower human body exergy consumption rate.

Evaluation of the Reference Numerical Parameters of the Monthly Method in ISO 13790 Considering S/V Ratio

Many studies have investigated the accuracy of the numerical parameters in the application of the quasi steady-state calculation method. The aim of this study is to derive the reference numerical parameters of the ISO 13790 monthly method by reflecting the surface-to-volume (S/V) ratio and the characteristics of the structures. The calculation process was established, and the parameters necessary to derive the reference numerical parameters were calculated based on the input data prepared for the established calculation processes. The reference numerical parameters were then derived through regression analyses of the calculated parameters and the time constant. The parameters obtained from an apartment building and the parameters of the international standard were both applied to the Passive House Planning Package (PHPP) and EnergyPlus programs, and the results were analyzed in order to evaluate the validity of the results. The analysis revealed that the calculation results based on the parameters derived from this study yielded lower error rates than those based on the default parameters in ISO 13790. However, the differences were shown to be negligible in the case of high heat capacity.

Determination of enzymatic reaction enthalpy by simultaneous calorimetry and spectrophotometry

A synchronized calorimetric and spectrophotometric method for measuring enzymatic reaction enthalpy was described. The spectrophotometric method was used to determine the amounts of reactant or product changes during the reaction, and calorimetry was used to determine the thermal changes associated with the reaction. Both methods used a same reaction system to simultaneously measure the progress of reaction. By the synchronized calorimetric–spectrophotometric determination, enthalpy values were obtained as 92.17 ± 3.06 kJ mol−1 by the initial velocity calculation method and 100.9 ± 1.81 kJ mol−1 by the steady-state calculation method for a catalase-catalyzed hydrogen peroxide reaction at 298.15 K and pH 7.0. When comparing with the theoretical values, the results showed that the synchronized method with the steady-state method was in alignment and demonstrated greater stability.

Evaluation of the accuracy of the implementation of dynamic effects in the quasi steady-state calculation method for school buildings

The quasi steady-state calculation method (based on EN ISO 13790) is commonly used for energy performance checking. This method attempts to accurately represent the building's energy use. However, intermodal comparison of dynamic and static calculations reveals quite some discrepancies often caused by the inaccuracy of the gain utilization factor and the temperature setback approach used for intermittently heated buildings. This paper tries to improve the method for schools buildings focusing on the gain utilization factor ηH,gn and the parameters a0 and τ0 in particular. These parameters will be adapted to the Flemish climate and the typical characteristics of school buildings. The Monte Carlo analysis technique is applied to cover the broad spectrum of influential parameters. Based on the comparison of dynamic and static calculation results, a regression analysis is performed to determine the correlation between the heat-balance ratio γH and the gain utilization factor ηH,gn. Although more accurate results are found using the adapted dynamic parameters a0=1.4 and τ0=185, the quasi steady-state method for school buildings remains unreliable as the accuracy of the method is simultaneously determined by the value of the gain utilization factor and by the assessment of the adjusted set-point temperature.

Optimization Study of Shaft Tubular Turbine in a Bidirectional Tidal Power Station

The shaft tubular turbine is a form of tidal power station which can provide bidirectional power. Efficiency is an important turbine performance indicator. To study the influence of runner design parameters on efficiency, a complete 3D flow-channel model of a shaft tubular turbine was developed, which contains the turbine runner, guide vanes, and flow passage and was integrated with hybrid grids calculated by steady-state calculation methods. Three aspects of the core component (turbine runner) were optimized by numerical simulation. All the results were then verified by experiments. It was shown that curved-edge blades are much better than straight-edge blades; the optimal blade twist angle is 7°, and the optimal distance between the runner and the blades is 0.75–1.25 times the diameter of the runner. Moreover, the numerical simulation results matched the experimental data very well, which also verified the correctness of the optimal results.

Transient Analysis of Cold Winds on Exposed Skin: Reflections on the Assessment of Wind Chill Equivalent Temperatures

Abstract A transient analysis of the human–environment thermal interaction in cold and windy environments is presented. The site selected to represent this interaction is the head–face, which is depicted as a hollow cylinder wherein heat is conducted in the radial direction. Environmental radiation effects, which are small relative to the wind-driven convection effects, as well as metabolic heat and blood perfusion effects, are not accounted for at this stage. The model is solved analytically by an integral transform. Results are used to calculate the wind chill equivalent temperatures (WCETs) for different environmental temperatures and wind speeds. The temporal variations of the calculated WCETs are contrasted against the steady-state values that are published by the weather services in North America. The inherently transient nature of this parameter is clearly demonstrated. This observation should form a basis for modifying the heretofore employed steady-state calculation method of this useful weather predictor.

A multitime circuit formulation for closely spaced frequencies

Verifying circuits with two or more closely-spaced driving frequencies is important in RF and wireless communications, for example, in the design of down-conversion mixers. Existing steady-state calculation methods, like harmonic balance, rely on Fourier series expansions to find the difference-frequency components typically of interest. Time-domain methods are, however, better suited for circuits with strong nonlinearities such as switching. Towards this end, we present a purely time-domain method for direct computation of difference tones in closely-spaced multitone problems. Our approach is based on multiple artificial time scales for decoupling the tones driving the circuit. Our method relies on a novel multitime reformulation that expresses circuit equations directly in terms of time-scales corresponding to difference tones. We apply the new technique to an RF-CMOS mixer to predict baseband bit-streams and down-conversion gain and distortion, in two orders of magnitude less CPU time than traditional time-stepping simulation. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

Effect of Exfiltration on the Hygrothermal Behaviour of a Residential Wall Assembly

The hygrothermal behaviour of timber frame wall is analysed using a steady-state calculation method and a two-dimensional heat, air, and moisture transport computer model. The conditions associated with exfiltration of warm and humid indoor air are examined. The physical quantities investigated included the amount of moisture accumulated in the wall cavity during the heating season and the heat loss across the wall. Several interesting correlations between moisture accumula tion in a cavity and parameters such as leakage rate, vapour permeance characteristics of the exterior boundary, additional thermal resistance offered by an exterior sheath ing, and indoor humidity level emerge. These correlations show the advantage of us ing the analytical methods in deriving design guidelines for building components. The results from the analysis are used to identify and quantify various parameters that govern the performance of air barrier systems.

Method for calculating wing loading during maneuvering flight along a three-dimensional curved path

The aerodynamic forces due to the nonsteady motion of a lifting surface along a three-dimensional path are analyzed. For this purpose, available steady-state calculation methods, based on potential theory, were modified by retaining the nonsteady terms in the governing equations. The surface motion is limited to such cases where the linear analysis can be applied. As an example, the time-dependent forces and moments of a slender wing in various nonsteady motions were studied.