A wave rotor optimizes the use of energy resources by enhancing thermodynamic cycles, and further optimization of wave rotor geometry is emerging as an attractive research area. Among the geometric features, the stagger angle of channels lacks sufficient study in spite of its important effects. To address this question, this work developed and applied the velocity triangle models to modify the basic geometry of wave rotors for different stagger angles, and investigated the flow fields with two-dimensional numerical methods. Results showed that: (1) different stagger angles worked out similar unsteady pressure wave systems and kept nearly constant compression and expansion ratios of the wave rotor; (2) increased stagger angle made the inlet and outlet flows turn toward the axial direction, which was beneficial to compact and light-weighted integration of the wave rotor to a gas turbine; (3) increased stagger angle made the wave rotor consume more shaft power, but even the maximum shaft... [more]

The development of dynamic models for control purposes is characterised by the challenge of finding a compromise between the minimum necessary information about the system dynamics contained in the model and a model with a low level of complexity such that the model-based control system design becomes comfortable. To achieve this balance, a modified dynamic model for the drivetrain of a wind turbine is proposed in this contribution. The main idea is to introduce the tip-speed ratio as a state variable so that an interval observer can be designed in such a way that its estimates can be used in the torque control during the partial load operation as well as for the estimation of the effective wind speed. During the runtime, the observer’s matrix gain is recalculated to adapt the behaviour to the current operational state, which changes all the time with the wind speed. Besides the theoretical formulation, a numerical example of a 20 MW reference wind turbine illustrates the utility of th... [more]

To operate, radial turbines used in turbochargers require a minimum tip gap between the rotor blades and the stationary wall casing (shroud). This gap generates leakage flow driven by the pressure difference between the pressure and suction side. The tip leakage flow is largely unturned, which translates into a reduction of the shaft work due to the decrease in the total pressure. This paper investigates the flow through the rotor blade tip gap and the effects on the main flow when the turbine operates at a lower and higher pressure ratio with the presence of supersonic regions at the rotor trailing edge for two rotational speeds using computational fluid dynamics (CFD). The rotor tip gap has been decreased and increased up to 50% of the original tip gap geometry given by the manufacturer. Depending on the operational point, the results reveal that a reduction of 50% of the tip gap can lead to an increase of almost 3% in the efficiency, whereas a rise in 50% in the gap penalty the effi... [more]

The operational characteristics during transients are significantly influenced by magnetic saturation in electrical equipment. For the computation of steady-state rated operation in multiphase induction machines, the assumption of linear magnetic behavior of the iron core in classical machine models may be sufficient. The mathematical models of the considered models differ in terms of the existence or absence of dynamic cross-saturation effects. The approach that is most frequently used to examine the impact of magnetic saturation is based on the state-space variable representation of the mathematical model in dynamic axes (d−q). The purpose of this research is to investigate the effects of magnetic saturation on six-phase induction machines. In this study, a d−q transformation-based model of a six-phase induction machine (SPIM), including the magnetic saturation effect, is developed. The cross-saturation and the common mutual leakage inductance between the two sets of stators’ winding... [more]

In China, sandstone geothermal reservoirs are large in scale and widely distributed, but their exploitation is hindered by low recharge efficiency. In this paper, an unblocking and permeability enhancement technology using a rotary water jet for low recharge efficiency wells in sandstone geothermal reservoirs is proposed to solve this problem. This paper presents a series of studies about the proposed technology, including experiments, simulation and field application. Firstly, an experiment was carried out to verify the scale removal effect of a high-pressure water jet on the inner wall of the screen tube and its impact on sandstone. Secondly, the numerical models of the rotary jet flow field in the wellbore were established by ANSYS Fluent to study the influence of parameters. Finally, based on the simulation and experiment results, a rotary jet tool applicable to unblocking and descaling low-efficiency wells was designed, and a field application for low-efficiency wells in sandstone... [more]

Today’s research on concentrated photovoltaic (CPV) cells focuses on creating multi-junction semiconductor solar cells capable of withstanding high temperatures without losing their properties. This paper investigated silicon low concentrated photovoltaic (LCPV) devices using Fresnel lenses. The parameters of the silicon CPV cell were measured to simulate its operation based on a single-diode model with four and five parameters. The most optimal position of the Fresnel lens relative to the solar cell was shown, and the dependence of the CPV efficiency on the concentration ratio, incident solar power, and temperature was studied. Experiments on heating of a solar cell were conducted to build a model of heating of a solar cell under different solar radiation based on machine learning. Additionally, a cooling system was developed, and experiments were conducted for one LCPV cell. The resulting LCPV model was used to predict electrical power output and temperature change pattern using clea... [more]

The use of simulation and modelling has been proposed for determining the excitations to be applied in the procedures of laboratory testing of a car’s structural components, without the need to test the complete vehicle. The paper presents the general concept as well as an example of the procedure. It covers determining the spectrum and time-domain realization of a load on a selected node of the vehicle structure under durability tests. The author used both the mathematical and physical model of the tractor-semitrailer unit, where the input was considered as a random process resulting from the road profile. He calculated the transmittance modules and the power spectral densities of the vertical force on the joint between the tractor’s fifth wheel and the kingpin of the semitrailer and the extreme values of the dynamic components of this force. The inverse discrete Fourier transform makes it possible to generate the realization of the said force. It can be used in durability studies. Th... [more]

The gas and water flow behavior in rough-walled hydrophilic fractures at the pore scale is crucial for understanding the gas production characteristics of naturally fractured formations. This paper presents a systematic analysis of the gas and water flow characteristics in both the single-fracture and Y-shaped junction fracture models using the volume of fluid (VOF) method. Numerical simulations showed that the gas/water rate ratio is the most significant factor influencing gas bubble/slug geometry, phase distribution, and saturation. The effect of fracture roughness and tortuosity is less significant than the gas/water ratio, whereas the total fluid rate has a negligible effect. For Y-shaped junction models, the phase distribution and referential pathways are predominantly controlled only by the channel aperture ratio, whereas the effect of the intersecting angle and fluid flow rate can be neglected.

Horizontal axis wind turbines (HAWTs) experience yaw misalignments due to the physical limitations of yaw controllers and various novel active yaw controls. Moreover, the motion of floating offshore wind turbines (FOWTs) accelerates yaw misalignment. The blade element momentum (BEM) method is widely used due to its computational efficiency for the design of HAWTs. Momentum theory, the basis of BEM, assumes steady flow and uniform induction field at the disc. Those assumptions are relaxed by engineering models to capture yaw and unsteady effects. Current yaw engineering models, however, are inaccurate since they do not capture the asymmetric wake expansion effect. Dynamic inflow models have been developed for non-yawed flow. Furthermore, the AVATAR project shows that BEM using fully coupled engineering models, the current yaw, dynamic inflow and various engineering models, suffers from significant deficiencies. This purpose of this paper, therefore, is to investigate dynamic effects for... [more]

The subject of the model research contained in this paper is an application of a motion energy−harvesting device on a crane-hoisting mechanism to power independent measurement devices. Numerical experiments focused on the selected motion energy−harvesting device (M-EHS) and its configuration properties in the context of energy-harvesting efficiency in the case of using it on a crane. The results of the computer simulations were limited to the initial specified conditions for the harvester and the movement of the conditions of the crane-hoisting mechanism. The article compares the energy efficiency for the selected construction and parameters of the harvester for specific hoisting speed and the arm length of the motion conversion system. For this purpose, the initial conditions for the crane and the configuration of parameters of the energy harvester were assumed. The results are visualized on the diagram of RMS voltage induced on piezoelectric elements, showing the impact of individual... [more]

Despite offering promising opportunities for wind energy harvesting in urban environments, vertical axis wind turbines face limitations in terms of poor starting characteristics. In this study, we focus on analyzing improvements offered by dual-stage turbines for a range of wind velocities. Numerical simulations are performed for different phase angles between the rotors (a measure of relative angular positions of the blades in the two rotors) to quantify the response time for their starting behavior. These simulations rely on a through sliding mesh technique coupled with flow-induced rotations. We find that for U∞=4m/s, the phase angles of 30∘ and 90∘ substantially reduce starting time in comparison to a single-stage turbine. Dual-stage turbines with a phase angle of 90∘ exhibit similar or better starting behavior for other wind speeds. The phase angle of 0∘ in double-rotor turbines shows the poorest starting response. Moreover, it is revealed that stabilization of shear layers genera... [more]

The design and implementation of an asynchronous coilgun’s structure is relatively simple compared with other types of linear induction launchers. In order to drive rotating electrical machines, multilevel converter structures have attracted much attention in recent decades as a result of their unique advantages. A linear induction launcher has an identical theoretical background to rotating electrical machines; therefore, multilevel converter structures can be applied to them as well. The stator of a launcher can be excited by generators or capacitor groups whose voltage and frequency might be fixed or changeable by a power conditioner. The aim of this study is to design and simulate a novel power conditioner as a multilevel converter topology for the power source of an asynchronous coilgun. Cascaded H-Bridge multilevel converter topology constitutes the proposed power conditioner in which a level-shifted pulse-width modulation method is used to generate appropriate pulses for the pow... [more]

Sea wave energy is being increasingly regarded as one of the most promising sources of renewable energy. This paper deals with the modeling and simulation of an onshore wave energy converter system designed by UMBRA GROUP SpA. Several topics are addressed. Starting from the multibody modeling strategy, this paper delves more deeply into the mechanical efficiency evaluation of the ball-screw in the elastohydrodynamic lubrication regime, the core of the energy conversion process, as well as the thermal characterization of the power take-off module, based on the lumped-parameter and finite element method models. High values of ball-screw indirect efficiency have been observed, ranging from 73% to 97%; these results appear even more encouraging when compared to the performance of alternative energy-consuming technologies. Thermal analysis, on the other hand, provided a maximum temperature increase of 40 °C, allowing for the aversion of any structural collapse and the realistic identificati... [more]

Compression by shock waves is a specific way of compressing gases. It has been practically applied for many years in supersonic flying objects. The idea of using this method in rotary engines is extremely appealing because one disk can replace several or a dozen disks of an axial compressor, significantly reducing the weight and production costs of the engine and lowering the fuel consumption due to possible increased compression ratio. This paper presents a review of existing technical solutions and the results of published research devoted to the construction of shock wave compression rotary engines: patents, scientific publications describing various research methods, numerical calculations, and the experimental results of unusual technical solutions. The characteristic solutions and problems that arose during the implementation of these methods are presented and described. Judging from the presented overview, these have wide application possibilities, and an enormous intellectual a... [more]

Vertical axis wind turbines are an emerging and in-development wind energy technology which are characterized by their complicated aerodynamics. Detached flow conditions, which are typically developed at operational tip speed ratios, demand a rigorous characterization of the airfoils for an accurate prediction of the turbine performance. In this work, a custom-built, three-component external strain gauge balance, specifically developed for airfoil testing, is validated. The physical reasons responsible for discrepancies with reference data are also analyzed. Two- and three-dimensional flat plates, as well as the DU06-W-200 airfoil, are tested in a wind tunnel. Lift and drag coefficients and pitching moments are obtained for a wide angular range at Re = 200,000. The results are compared with data from the bibliography and CFD simulations, performed with the recently developed GEKO (generalized k-omega) turbulence model, achieving remarkable agreement. Instantaneous forces are also analy... [more]

Drying is a complex process of simultaneous heat, mass, and momentum transport phenomena with continuous phase changes. Numerical modelling is one of the most effective tools to mechanistically express the different physics of drying processes for accurately predicting the drying kinetics and understanding the morphological changes during drying. However, the mathematical modelling of drying processes is complex and computationally very expensive due to multiphysics and the multiscale nature of heat and mass transfer during drying. Physics-informed machine learning (PIML)-based modelling has the potential to overcome these drawbacks and could be an exciting new addition to drying research for describing drying processes by embedding fundamental transport laws and constraints in machine learning models. To develop such a novel PIML-based model for drying applications, it is necessary to have a fundamental understanding of heat, mass, and momentum transfer processes and their mathematica... [more]

The methods used in chemical engineering are strongly reliant on having a solid grasp of the thermodynamic features of complex systems. It is difficult to define the behavior of ions and molecules in complex systems and to make reliable predictions about the thermodynamic features of complex systems across a wide range. Deep learning (DL), which can provide explanations for intricate interactions that are beyond the scope of traditional mathematical functions, would appear to be an effective solution to this problem. In this brief Perspective, we provide an overview of DL and review several of its possible applications within the realm of chemical engineering. DL approaches to anticipate the molecular thermodynamic characteristics of a broad range of systems based on the data that are already available are also described, with numerous cases serving as illustrations.

Emissions from wood burning for heating in secondary homes or cabins is an important part in the development of high-resolution emissions in specific areas. Norway is used as case study as 20% of the national wood consumption for heating occurs in cabins. Our study first shows a method to estimate emissions from cabins based on traffic data to derive cabin occupancy, which combined with heating need allows for the spatial and temporal distribution of emissions. The combination of residential (RWC) and cabin wood combustion (CWC) emissions shows large spatial and temporal differences, and a temporally “cabin population” can in areas be orders of magnitude larger than the registered population. While RWC emissions have been steadily reduced, CWC have kept relatively constant or even increased, which results in an increase in the cabin share to total heating emissions up to 25−35%. When comparing with regional emission inventories, our study shows that the gradient between rural and urban... [more]

In recent years, there has been great interest in Wankel-type rotary engines, which are one of the most suitable power sources for unmanned aerial vehicle (UAV) applications due to their high power-to-size and power-to-weight ratios. The purpose of the present study was to investigate the potential of a hydrogen enrichment strategy for the improvement of the performance and reduction of the emissions of Wankel engines. The main motivation behind this study was to make Wankel engines, which are already very advantageous for UAV applications, even more advantageous by applying the hydrogen enrichment technique. In this study, hydrogen addition was implemented in a spark-ignition rotary engine model operating at a constant engine speed of 6000 rpm. The mass fraction of hydrogen in the intake gradually increased from 0% to 10%. Simulation results revealed that addition of hydrogen to the fuel accelerated the flame propagation and increased the burning speed of the fuel, the combustion temp... [more]

The smart city has been a growing utopia, a brilliant image of a city of the future, in the past twenty years. Since its birth, at the end of the previous century, several changes have been seen in urban areas, both aligned and detached from this concept. On the one side, digital implementation seems to be growing in all the major cities, especially in the service sector, which are experiencing a proliferation of new solutions, tools and modalities of interactions. On the other side, new concepts are rising such as the “digital twin”, the “15-minute city”, and the “metaverse city”, evidencing both the necessity to continuously innovate and reach higher levels of digitalization but also the need to focus on people’s life. This paper aims to provide a contribution to the understanding of the concept’s evolution at the forefront of climate change with the aim to detect the elements of innovation, focusing on implementation roadmaps and trends but also searching for evolutions in research... [more]

This article introduces a single-phase five-level multilevel inverter based on six switches and two transformers. The proposed converter requires a single dc input source with low voltage. The disposition of switches makes it possible to build the converter with a transistors six-pack module off-the-shelves, traditionally used to build three-phase inverters, which simplifies the manufacturing process. The converter increases the voltage with two transformers; for that reason, it does not require an auxiliary step-up converter. The use of transformers (with the transformer’s turns ratio) allows for using the same topology for several input voltage levels. To verify the operation of the proposed multilevel inverter, a computer-based simulation was performed with PSIM, a software that considers parasitic components. The results show that the proposed converter can work properly.

Undersaturated oil viscosity is one of the most important PVT parameters to be measured and/or predicted in a fluid sample. Since direct experimental measurements are expensive and time-costly, prediction methods are essential. In this work, viscosity data from more than five hundred fluid reports are utilized, and all correlation methods available in the literature and implemented in commercial software for reservoir and production engineering calculations, including fracked systems, are evaluated against the dataset. The results of this work are intended to set up workflows that give insight as to which method should be selected when running flow simulations, with emphasis on complex simulations such as in the case of EOR. The developed workflows provide the optimal choice of the viscosity correlation for the case of distinct viscosity ranges, as well as when overall performance is sought. A surprising result is that one of the oldest known correlations from the literature gives the... [more]

Direct contact heat exchangers can be smaller, cheaper, and have simpler construction than the surface, shell, or tube heat exchangers of the same capacity and can operate in evaporation or condensation modes. For these reasons, they have many practical applications, such as water desalination, heat exchangers in power plants, or chemical engineering devices. This paper presents a comprehensive review of experimental and numerical activities focused on the research about direct condensation processes and testing direct contact condensers on the laboratory scale. Computational Fluid Dynamics (CFD) methods and CFD solvers are the most popular tools in the numerical analysis of direct contact condensers because of the phenomenon’s complexity as multiphase turbulent flow with heat transfer and phase change. The presented and developed numerical models must be carefully calibrated and physically validated by experimental results. Results of the experimental campaign in the laboratory scale... [more]

Asal rift is an aerial rift segment resulting from the westward propagation of the Aden ridge into the Afar Depression. Geothermal manifestations such as hot springs and fumaroles, fault creep, conductivity anomaly, and high geothermal gradient were observed both at the surface and in the subsurface. Despite many scientific works conducted in Asal to understand the rifting mechanisms, the hydrothermal fluid circulation still needs to be evaluated since it is based on simplified conceptual models. To further contribute and progress toward a quantitative evaluation of fluid circulation, a 2D numerical model perpendicular to the rift axis was developed with the objective of better understanding the role of subsurface anisotropy in fluid flow and heat transfer in the Asal rift. Numerical modeling of multiphase flow and heat transfer was carried out with an equivalent porous medium intersected by fault zones having greater permeability. Horizontal anisotropic permeability and magmatic fluid... [more]

High-speed EMUs (electric multiple-units) frequently pass through the phase-separation zone during operation. Overvoltage generated during the operation of the vehicle-mounted circuit breaker has a long duration and high waveform steepness, which accelerates the service life of the vehicle-mounted equipment and is likely to cause insulation failures. For the above-mentioned problems, the operating overvoltage characteristics of high-speed EMU were obtained by traction substation-catenary-EMUs system (SCES) analysis and experiments, thus deriving the influences of the closed phase angle and the residual magnetism of the vehicle-mounted transformer on operating overvoltage. The results showed that the voltage phase of the catenary significantly affected the operating overvoltage, and the closed switching overvoltage was small at 0−40°, 140−210° and 320−350°. The voltage on the primary side of the vehicle-mounted transformer was 60.78 kV, with the transient impact of high-frequency oscill... [more]