This paper established a numerical simulation model to analyze the pressure transient and rate transient behaviors in reservoir with complex fracture network. Firstly, the fractures are introduced into the coordinate system through the position, angle, and length. Secondly, a mathematical model is established by using unstable seepage model. Thirdly, the central difference method was used to solve the model and local grid refinement method is introduced to describe the network fractures. Finally, we compared the results obtained from this paper’s model with the production data. The results show acceptable and reasonable matches for typical well. Meanwhile, the sensitivity of two properties is discussed. The model solution is verified with an analytical method thoroughly. The novelty of this paper is to introduce each fracture in fracture network into the coordinate system. Then, the grid refinement is achieved according to the fracture information. The presented new model simplifies th... [more]

The 660 MW ultra-supercritical circulating fluidized bed (CFB) boiler, which is the maximum capacity and largest scale boiler in the world has entered construction stage in China. This study established a full-scale dynamic simulation model of the 660 MW ultra-supercritical at 100% boiler maximum continuous rating (BMCR) condition. The model consists of an air-flue gas system, a water-steam system, and an ash circulation system. The “core-annulus” of the gas-solid two-phase flow structure and “six-equation” model of water-steam two-phase flow were applied to simulate the behaviors of the gas-solid phase and water-steam system, respectively. The model was calibrated and verified at 100% BMCR condition, and the steady-state simulation results presented a high accuracy compared with the designed parameters. A dynamic simulation of three typical conditions were carried out as well, including a 5% feed water decrease, 5% air decrease, and 5% coal decrease, respectively. The results showed t... [more]

The “Clean Energy for all Europeans” package highlights the need to create a resilient critical energy infrastructure in the European Union. Resilience is an emerging term to describe the energy system’s ability to withstand shocks caused by natural hazards, technical accidents, or intentional threats. In this paper, a framework to assess the resilience of energy systems using quantitative indicators is presented. Two main groups of resilience indicators are proposed that depend on what is being measured within the energy system: capacity (attribute-based) indicators or performance in the presence of disruption (performance-based) indicators. This study concentrates on the first resilience phase, when the energy system has to absorb the impact of the shock. The approach considers various disruptions (both internal and external) as triggering events. There is a particular focus on future shocks affecting the prospective energy system, which will have changed with respect to the current... [more]

The increase in energy efficiency, reducing energy demand, greenhouse gas emissions and the use of waste, renewable and recycled heat from low-temperature sources are significant challenges today and are key parts of the idea of the 4th Generation District Heating (4GDH) [...]

With an increase in mining depth, the problem of heat damage in metal mine working face has become increasingly prominent. In order to effectively reduce the temperature of the working face and provide a comfortable working environment for the miners, based on the concept of “cooling on demand”, a mobile refrigeration system for high-temperature working face was designed, and a field test was carried out in Dahongshan Copper Mine, Yunnan Province. At the same time, based on the experimental conditions, the parameter optimization research of the mobile refrigeration system was carried out. The results showed that: (1) The mobile refrigeration system could reduce the wet bulb temperature of the working face at the test site to below 30 °C, which is in line with the “Safety Regulations for Metal and Non-Metallic Mines” (GB16423-2020); (2) when the diameter of the air supply pipe was 600 mm and the air supply velocity was 12 m/s, the target cooling area could meet the continuous operation... [more]

Problems with inaccurate prediction of electricity generation from photovoltaic (PV) farms cause severe operational, technical, and financial risks, which seriously affect both their owners and grid operators. Proper prediction results are required for optimal planning the spinning reserve as well as managing inertia and frequency response in the case of contingency events. In this work, the impact of a number of meteorological parameters on PV electricity generation in Poland was analyzed using the Pearson coefficient. Furthermore, seven machine learning models using Lasso Regression, K−Nearest Neighbours Regression, Support Vector Regression, AdaBoosted Regression Tree, Gradient Boosted Regression Tree, Random Forest Regression, and Artificial Neural Network were developed to predict electricity generation from a 0.7 MW solar PV power plant in Poland. The models were evaluated using determination coefficient (R2), the mean absolute error (MAE), and root mean square error (RMSE). It w... [more]

In this study, we conducted experiments and numerical analysis on a 270 kW industrial-scale centrifugal compressor used in the fuel supply system of an LNG carrier in order to improve the lumped-parameter surge model by considering the viscosity in the pipeline and to confirm whether the improved model would be applicable. The steady and unsteady compressor performance curves were constructed using measurements and predictions, respectively. The flow through the pipeline was assumed to be both steady and unsteady, and each governing equation under the assumptions was derived in accordance with the lumped-parameter model. In the steady flow case, the surge behavior of the modified model was in a good agreement with the lumped-parameter model at surge parameter B = 4.8716. In the unsteady flow case, however, the modified model showed a deviation from the lumped-parameter model, and the simulation from the modified model described the surge behavior 5% more accurately than the lumped-para... [more]

Ventilation design of the scattering room and sample room in the Chinese Spallation Neutron Source (CSNS) is of great significance to maintain good indoor air quality and ensure the health of radiation workers. Based on the computational fluid dynamics (CFD) theory, the three-dimensional models of the scattering and sample rooms were established and fourteen layout schemes were simulated. Subsequently, the best schemes were selected among three typical layout schemes. On this basis, the paper presents research about the influence of changing the height of the outlet on the ventilation quality. The results show that the trend of numerical simulation is consistent with experimental data, which verifies the reliability of the numerical method. The change of the exhaust port position has an apparent influence on indoor ventilation, which reduces the air age by 4−27%. When the position of the outlet descends 0.5 m, the air age decreases by 2−11%, and this study provides guidance and suggest... [more]

Biomass pyrolysis is considered as a thermochemical conversion system that is performed under oxygen-depleted conditions. A large body of literature exists in which thermodynamic equilibrium (TE) and kinetic approaches have been applied to predict pyrolysis products. However, the reliability, accuracy and predictive power of both modeling approaches is an area of concern. To address these concerns, in this paper, two new simulation models based on the TE and kinetic approaches are developed using Aspen Plus, to analyze the performance of each approach. Subsequently, the results of two models are compared with modeling and experimental results available in the literature. The comparison shows that, on the one hand, the performance of the TE approach is not satisfactory and cannot be used as an effective way for pyrolysis modeling. On the other hand, the results generated by the new model based on the kinetic approach suggests that this approach is suitable for modeling biomass pyrolysis... [more]

The open-source code DualSPHysics, based on the Smoothed Particle Hydrodynamics method for solving fluid mechanics problems, defines a complete numerical environment for simulating the interaction of floating structures with ocean waves, and includes external libraries to simulate kinematic- and dynamic-type restrictions. In this work, a full validation of the SPH framework using experimental data available for an experimental test campaign on a 1:37-scale floating offshore wind turbine tension-leg platform (TLP) is presented. The first set of validation cases includes a surge decay test, to assess the quality of the fluid−solid interaction, and regular wave tests, which stimulate the mooring system to a large extent. During this phase, tendons (tension legs) that are simulated by MoorDyn+ are validated. Spectral comparison shows that the model is able to capture the surge and pitch dynamic amplification that occurs around the resonant fundamental mode of vibration. This work concludes... [more]

Through new core wettability simulation technology and the single-sided unidirectional imbibition experimental method, the influence of core wettability on oil imbibition characteristics was studied by using artificial cores with wettability index in the range of −0.9~0.95. Results show that for the cores with permeability from ultra-low to medium−high, the imbibition time shows a monotonically decreasing law with the increase in the wettability index. In the weak water-wet range, the imbibition time increases significantly with the weakening of water-wet. Oil imbibition rate goes up with the increase in wettability index. In the strong water-wet range, the imbibition rate will change significantly with wettability. In the water-wet zone, there is a positive correlation between imbibition oil limit recovery and wettability index, according to which a power exponent model of them is established. The imbibition−displacement ratio, which characterizes the contribution rate of oil recovery... [more]

The increasing use of high-voltage transmission wires requires more and more high-voltage pylons, and sometimes, constructing pylons in mining areas is very urgent. To ensure the safe operation of pylons, coal pillars with large side lengths are usually used to provide sufficient support; however, this results in a huge waste of coal. Eight high-voltage pylons are arranged on the ground surface corresponding to the location of working face 1110 of Sima Coal Mine in Shanxi Province, China, which cannot be mined by traditional methods. Taking this as the engineering background, the failure mode of high-voltage pylon is first analyzed. Using FLAC3D numerical simulations, the influence of five different mining plans on ground surface deformation in working face 1110 is evaluated, and the vertical settlement and horizontal deformation in different areas of the ground surface, as well as the variation law of horizontal strain and slope are analyzed. According to the numerical simulation resu... [more]

The development and utilization of marine renewable energy is an important measure for achieving energy conservation, emissions reduction and carbon neutrality. Ocean thermal energy is the most stable energy among all the types of marine renewable energy. This paper built a simulation model of an ocean thermal energy conversion system based on actual device specifications by Aspen and MATLAB and put forward a corresponding control strategy. The opening control signal of the control valve at the turbine inlet was the condenser inlet pressure in this paper, and the frequency control of the working fluid pump depended on the evaporating pressure and flow rate of the working fluid. This paper analyzed the key operating parameter changes of the system under different working conditions. According to the analysis results, the turbogenerator in this system was able to generate 50 kW power for about 8 months per year. The highest net output power of the Organic Rankine Cycle was 47.3 kW; the h... [more]

The aim of this paper is to develop an experimental procedure to measure contact friction between granular particles. The contact friction is a micro-property needed in the micromechanical modeling of a granular medium. The proposed method can measure the interparticle friction of idealized spherical particles using the conventional direct shear apparatus in soil testing. In preparation for the test, the test specimen is made of four steel balls embedded halfway in a sulfaset paste plate positioned in a statically determinant configuration to provide point contacts among the steel balls. The upper half of the shear box contains one steel ball, which is supported by three steel balls in the lower shear box, ensuring contact points at all times during the test. Shear force and shear displacement are measured under a specific normal force during the test. An analytical equation is developed based on the geometrical configuration of the balls to calculate the interparticle friction angle.... [more]

With the wide application of motors in deep sea exploration, deep-sea motors require a higher power density and a longer lifetime. Motor lifetime mainly depends on the thermo-mechanical stress (TMS) load on its stator insulation. Unlike normal motors, deep-sea motors are usually filled with oil to compensate for the high pressure generated by seawater, which leads to high additional viscous drag loss. This, combined with the high pressure, will greatly change the TMS distribution and further influence motor insulation lifetime. Thus, the insulation degradation analysis of deep-sea oil-filled (DSOF) motors due to TMS has become important. This paper presents a TMS analytical model of DSOF motor insulation, considering the joint effects of high pressure and motor temperature. The CFD method is adopted to perform motor thermal analysis, considering temperature effects on viscous drag loss. The FEA method is adopted for thermo-mechanical analysis and to verify the analytical model accuracy... [more]

Computational Fluid Dynamics (CFD) have been frequently applied to model the growth conditions in photobioreactors, which are affected in a complex way by multiple, interacting physical processes. We review common photobioreactor types and discuss the processes occurring therein as well as how these processes have been considered in previous CFD models. The analysis reveals that CFD models of photobioreactors do often not consider state-of-the-art modeling approaches. As a comprehensive photobioreactor model consists of several sub-models, we review the most relevant models for the simulation of fluid flows, light propagation, heat and mass transfer and growth kinetics as well as state-of-the-art models for turbulence and interphase forces, revealing their strength and deficiencies. In addition, we review the population balance equation, breakage and coalescence models and discretization methods since the predicted bubble size distribution critically depends on them. This comprehensive... [more]

Recent growing energy crisis in Europe, coupled with the rising energy prices worldwide, is a clear indication of the many difficulties awaiting the transition of modern societies away from fossil fuels [...]

This paper treats a parallel 12-pulse rectifier as the study subject. The influence of unbalanced terminal voltage, the triggering angle, as well as the commutation angle of a thyristor-controlled rectifier circuit are considered in switching functions. Then, a frequency-domain harmonic coupled admittance matrix under the effect of positive sequence and negative sequence voltages are proposed, respectively. With the integration of the above matrices, a harmonic coupled admittance matrix model of a parallel 12-pulse rectifier under unbalanced voltage is proposed. On this basis, a simplified harmonic model of a 12-pulse rectifier is established, which only considers the effect of major elements through analyzing the elements’ distribution and magnitude of the harmonic coupled admittance matrix, as well as the AC current harmonic producing mechanism. All the models proposed in this paper are verified with high accuracy through simulation in MATLAB/Simulink. The models proposed in this pap... [more]

Due to its enhancement in the flame speed, ozone added in lean premixed syngas turbulent jet flame was investigated by the three-dimensional direct numerical simulation method in the near field of the flame. In the present study, numerical simulations were conducted in the lean premixed syngas turbulent jet flame configuration to explore the effects of ozone addition on freely-propagating turbulent flames. It was seen that turbulence began to significantly affect the flame surface to produce wrinkles in lean premixed gas flame with ozone added after 4D; ozone started to affect the composition field and temperature field after 8D; it accelerated the generation of intermediate products, OH and O radicals; and it will promote the production of CO2 in the near field range. Ozone will increase the flame surface area of the lean premixed syngas flame during the ignition period and can promote the ignition process and make the combustion occur earlier. The flame surface of the case with ozone... [more]

Understanding the phase behaviour of (CO2 + water + permanent gas) systems is critical for implementing carbon capture and storage (CCS) processes, a key technology in reducing CO2 emissions. In this paper, phase behaviour data for (H2O + N2) and (CO2 + H2O + N2) systems are reported at temperatures from 323 to 473 K and pressures up to 20 MPa. In the ternary system, the mole ratio between CO2 and N2 was 1. Experiments were conducted in a newly designed analytical apparatus that includes two syringe pumps for fluid injection, a high-pressure equilibrium vessel, heater aluminium jacket, Rolsi sampling valves and an online gas chromatograph (GC) for composition determination. A high-sensitivity pulsed discharge detector installed in the GC was used to measure the low levels of dissolved nitrogen in the aqueous phase and low water levels in the vapour phase. The experimental data were compared with the calculation based on the γ-φ and SAFT-γ Mie approaches. In the SAFT-γ Mie model, the li... [more]

The AQWA software is often used to perform hydrodynamic analysis, and it is highly convenient for performing frequency domain simulations of Pelamis-like wave energy converters. However, hydraulic power take-off (PTO) must be simplified to a linear damping model or a Coulomb torque model when performing a time domain simulation. Although these simulation methods can reduce the computational complexity, they may not accurately reflect the energy capture characteristics of the hydraulic PTO. By analyzing system factors such as the flow and pressure of each branch of the hydraulic PTO, the output torque of the hydraulic cylinder to the buoy, and the electromagnetic torque of the generator, a relatively complete hydraulic PTO model is obtained, and the model is applied to AQWA using the FORTRAN language. Comparing and analyzing the simulation results of the linear damping model, the Coulomb torque model, and the hydraulic PTO, we found that the simulation results obtained by the linear dam... [more]

In this paper, the design and analysis of a 30 kW, 30,000 r/min high-speed permanent magnet motor (HSPMM) for compressor application are provided. In order to provide a reasonable electromagnetic design scheme, the electromagnetic performances of the HSPMM under different structures are analyzed and compared by the finite element method (FEM). The thermal performances and cooling system of the HSPMM are, respectively, analyzed and designed by computational fluid dynamics (CFD). Finally, the HSPMM’s rotor strength is studied by both FEM and analytical methods, and the influencing factors of which are also researched in this paper.

Exhaust is generated by engine flows through a turbocharger, front exhaust pipe, and selective catalytic reduction (SCR) post-treatment device. The structure of the front exhaust pipe affects the temperature, velocity, and turbulent kinetic energy of exhaust and the Sauter Mean Diameter (SMD) of urea water solution (UWS). A high temperature and turbulent kinetic energy in the exhaust will promote the decomposition of UWS, and further accelerate the evaporation and atomization effect of the UWS droplets. Therefore, in order for the exhaust to reach a high temperature and turbulent kinetic energy, a double-layered pipe structure with air insulation was designed. The flow field and the atomization of UWS in the double-layered pipe based on hydroforming processing was investigated through numerical simulation. The thermal insulation simulation was verified by the temperature measurement system and the temperature drops between the double-layered pipe and the volcanic rock-wrapped pipe were... [more]

This study aims to analyze the actual heating energy consumption according to the location and size of apartment houses. The study shows the variation in heating energy consumption in accordance with the living pattern of residents in such apartments. By calculating the average annual heating energy consumption and distribution of the measured heating energy of two years, it was found that the outdoor temperature was inversely proportional to the average heating energy consumption. Moreover, the lowest/highest floors and corner houses were the most vulnerable since they had a lot of area exposed to the outside air and, thus, consume a huge amount of heating energy. According to this study, the heating load had relevance to the factors such as wall loss, window loss, ventilation loss, and solar radiation gain that were analyzed in accordance with the growth in house size. Based on the survey outcome on the living pattern and number of residents, a simulation was conducted to analyze the... [more]

A novel hybrid machine learning technique is proposed for the protection of three-phase power transformers in this study. Here, the developed model was tested across several types of current signal fault cases from different fault conditions and examined based on a laboratory-constructed transformer system, in which internal and external faults were created. The data gathered on signals were used to develop a novel hybrid model. A process for optimal feature identification was put forward, with machine learning classifiers being trained to classify faults. The methods used included orthogonal matching pursuit and discrete wavelet transform for extraction of statistical characteristics from unprocessed data. Following this, the bees algorithm (BA) was used to create an optimized subset, minimizing the amount of data needed and making the model more accurate. In order to distinguish normal operational conditions (inrush current) from faults, an optimized feature set was used as an input... [more]