Flow Theory Research Articles

Layout Optimization of Wave Energy Park Based on Multi-Objective Optimization Algorithm

Abstract In this paper, both semi-analytical method and numerical simulation is applied to investigate the hydrodynamic behavior of large arrays of point-absorber wave energy converters (WECs). To analyze wave interactions among multiple WECs within an array, a semi-analytical model is developed based on the potential flow theory and the matched eigen-function expansions method. The fluid domain is divided into two kinds of regions: interior regions underneath the cylinders and an exterior region surrounding all the cylinders. The matched eigenfunction expansions method is employed to solve the radiation potential problem in each domain, and the hydrodynamic coefficients and motion response of the cylinders in the array are evaluated. To validate the accuracy of the semi-analytical method, WAMIT is adopted to simulate the wave energy park numerically and compared with the results by the semi-analytical model. The hydrodynamic characteristics and power absorption performance of the WECs within the wave energy park are analyzed. The power performance of a wave energy park is studied as functions of layout geometry, incident wave direction and separation distance between WECs respectively. Finally, MOPSO based on a surrogate model is used to optimize the layout of wave energy array.

Performance assessment of a Triple Coaxial-Cylinder Wave-Energy Converter (TCWEC)

We propose a novel Triple Coaxial-cylinder Wave-Energy Converter (TCWEC) system, as an evolution of the commonly deployed dual-coaxial cylinder WEC (DCWEC). TCWEC consists of one inner cylinder and two concentric outer cylinders, characterized by two coupled resonant frequencies, improving wave power absorption. A semi-analytical model, based on potential flow theory and matched eigenfunction expansions, is developed to analyze the 3-Degrees of Freedom (DOF) system. The viscous drag coefficients are determined by Computational Fluid Dynamics (CFD) simulations and employed as equivalent linear damping. Analysis of impact of the viscous flow-separation factor fvis on the capture width indicates that the higher energy-absorption capability of TCWEC is not merely attributed to a smaller fvis value, but rather a planned split of the outer cylinder in DCWEC design into two cylinders in TCWEC, so as to produce an effectively broader resonance property. Under identical sea conditions, it is found that, compared to DCWEC, the optimal capture width of TCWEC is increased by as much as 77% in regular waves. In irregular waves, the optimal capture width is increased up to 40% across the entire frequency range. These findings suggest that the energy absorption efficiency of TCWEC is promising and its potential for real-world applications.

Comparative study of analytical models with linear and quadratic pressure drop conditions on a perforated plate in water waves

Proper pressure drop conditions are essential in predicting hydrodynamic performance of perforated structures in the framework of a potential flow theory. In this study, we investigate water waves passing through a perforated plate with various pressure drop models to examine how pressure drop conditions affect the hydrodynamic performance of perforated structures. We derive the analytical solutions of waves across the perforated plate by adopting three commonly pressure drop conditions, including one linear pressure drop condition (LPDC), and two quadratic pressure drop conditions (QPDCs). A series of laboratory experiments are conducted to validate the present theoretical results. We compare the hydrodynamic performance between the experimental data and the theoretical solutions with the three different pressure drop models, typically for wave reflection coefficients, dynamic pressures, and velocity fields measured by the technique of particle image velocimetry in the experiments. It is found that the existing pressure drop models can predict well wave reflection coefficients, dynamic pressure, and velocity profiles at certain conditions. However, the linear wave solutions associated with LPDC or QPDCs generally underpredict the amplitude of particle velocity near the free surface on the perforated plate. This underestimation increases largely as the wave steepness increases. The LPDC performance relies much on the selection of empirical coefficients. For the QPDCs, the analytical models show deviated results from the experimental data for wave reflection coefficients when the wave steepness is relatively low.

Determinants of E-Learning Acceptance in Indonesia Post-COVID-19 and Its Impact on Students’ Technopreneurship

Objective: This research aims to address the gaps in country-specific e-learning studies by examining the key factors influencing e-learning adoption in Indonesia. Grounded in a comprehensive literature review on flow theory, service quality, and technology acceptance models, the study develops a research model that includes four independent variables (instructor characteristics, teaching materials, content design, and enjoyment), two belief variables (perceived usefulness and perceived ease of use), and one dependent variable (intention to use e-learning). Method: Data were collected from 404 respondents, comprising students and lecturers at state Islamic universities in Indonesia, using convenience sampling. The study employed SEM-PLS for data analysis, validating the research instrument's reliability and validity. Results: The results offer insights into the managerial implications and suggest directions for future research in e-learning adoption. Its results confirm six hypotheses. Novelty: This study fills a gap in e-learning adoption research by focusing on Indonesia and integrating flow theory, service quality, and technology acceptance models. It highlights the roles of perceived playfulness, ease of use, and instructional content design in influencing e-learning adoption while challenging the expected impact of instructor characteristics. This research provides fresh insights into technology-driven learning in the context of developing countries.

Струйный эффект при возникновении присоединенной каверны от системы импульсивных давлений

We consider the plane problem of the emergence of an attached cavity caused by the sudden action of impulsive pressures at some initial time. It is assumed that these pressures are distributed on the upper part of the boundary of a stationary circular cylinder immersed in liquid. A problem with unilateral constraints is formulated, on the basis of which the flow of liquid at the initial moment of time and the initial zone of separation of liquid particles are determined. At the next moments of time, an attached cavity is formed, the shape of which is determined based on the solution of the dynamic initial-boundary value problem of the theory of potential flows of an ideal incompressible fluid with free boundaries. The main unknowns in it are the velocity potential, the shape of the cavity, the dynamics of the separation points, and the perturbation of the external free boundary of the liquid. It is required to study the posed problem at short times, focusing on the behavior of the internal free boundary of the liquid near the separation points. When studying this problem, pressure in the cavern, which is created artificially, plays an important role. At low pressures, the internal free boundary of the liquid near the separation point is located on opposite sides of this point. In this case, the end part of the cavity resembles a stream of gas directed along the boundary of the cylinder towards the liquid.

Particle-resolved direct numerical simulation and bottom-up statistical analysis on solid-phase pressure in particle–fluid systems

Solid-phase stress is a major factor shaping the complex behaviors of particle–fluid systems. However, uncertainties and inconsistencies can be found among the various models proposed. This work pays attention to the effect of mesoscale structures, that is, the heterogeneity of particle distribution at a scale of statistical meaning but no significant flow field variation, on the solid-phase normal stress, or pressure. Using a bottom-up statistical method, the solid-phase pressure in liquid- and gas–solid flows is investigated by particle-resolved direct numerical simulation (PR-DNS). It is found that, in almost uniform liquid–solid flows, the solid-phase pressure is not well predicted by classical kinetic theory of granular flow (KTGF) due to the presence of interphase force, although KTGF applies much better to single-phase granular flows. In gas–solid flows, with increasing heterogeneity described by structural functions, the statistical solid-phase pressure becomes significantly larger than that in corresponding homogeneous flows. It reveals that mesoscale structures strongly affect solid-phase pressure, and suggests the deviation from classical KTGF in heterogeneous gas–solid flows can be attributed to both the interphase forces (mainly drag) and mesoscale structures. The coefficients in the solid-phase pressure models in KTFG are modified, fitting the statistical results of both homogeneous and heterogeneous particle–fluid flows.

A Study on the Optimization of the Pokémon Gym Battle System Based on Game Flow Theory

A Study on the Optimization of the Pokémon Gym Battle System Based on Game Flow Theory

A frequency domain analysis method for the dynamic response of a submerged floating tunnel under wave action

To investigate the dynamic response of a submerged floating tunnel (SFT) under the action of waves, a modal superposition method in the frequency domain was established, and the amplitudes of the modals were determined using the generalized wave loads and hydrodynamic coefficients of the structural modals. In this model, the SFT was simplified as a constant-cross-section Euler–Bernoulli beam with multiple anchor cables, and its structural modals were resolved using the finite element method (FEM). The generalized wave loads and generalized hydrodynamic coefficients were obtained using the Fourier expansion strategy of the modal function, by which the hydrodynamic problem can be converted into 2D problems with the modified Helmholtz controlling equation and solved using the matched higher-order boundary element method (HOBEM) and eigenfunction expansion. The effects of the diameter of the anchor cables and length of the SFT on the stiffness of the structure and the dynamic response of an SFT with anchor cables under wave action were investigated. Furthermore, the effects of different added mass calculation methods on the structural response were studied. In addition, the wave exciting forces were calculated using potential flow theory or linearized Morison equations according to the wave scale. Finally, the effects of the incident wave frequencies and incident angles were investigated in detail to reveal the combined resonance mechanism.

The Moderating Role of Interest in the Relationship between Perceived Task Difficulty and Invested Mental Effort

Including motivational variables such as interest in the cognitive load framework is an ongoing process. Of particular interest is the question of how motivational variables influence the investment of mental effort. In this study, we investigated how topic interest affects the investment of mental effort in simple tasks. A total of 1543 students’ judgments regarding invested mental effort, perceived task difficulty, and topic interest for 32 tasks of a chemistry test were analyzed at the task level based on item response theory parameters. Additionally, objective task difficulty was calculated. The Rasch parameters were used for correlation and moderated regression analyses. The results indicated that when perceived task difficulty was low, students invested more mental effort in solving tasks of low topic interest compared to tasks of high topic interest. With increasing perceived task difficulty, the amount of invested mental effort rose for tasks of low as well as high topic interest. However, the difference between tasks of low and high topic interest in the amount of invested mental effort decreased as perceived task difficulty increased and even vanished when perceived task difficulty roughly corresponded to students’ performance capability. These results are in line with flow theory and the expectancy-value-cost model of motivation. When solving tasks that match their performance capability, students can experience a flow situation. However, when solving rather easy tasks of low interest, students can experience motivational costs in terms of additional effort, such as an increased need for motivational self-regulation. The results of this study provide a basis for systematically investigating and better understanding the relationship between interest, task difficulty, invested mental effort, flow experience, and emotional costs.

CFD modeling of gas–solid flow in a two‐stage jetting fluidized bed with an overflow standpipe

AbstractThe two‐fluid model–kinetic theory of granular flow (TFM–KTGF) model and the sub‐grid‐scale (SGS) model are used to conduct a three‐dimensional numerical simulation study on the hydrodynamic characteristics of a two‐stage fluidized bed with an integrated overflow pipe. Using various drag models, the gas–solid flows, bed expansions, pressure drop distributions, and equilibrium conditions in the two‐stage bed are compared, and the conditions for the formation of a stable overflow in the two‐stage bed are thoroughly investigated. In addition, during the simulation of the secondary distribution in the bed, the porous media model simulates the momentum loss caused by the redistribution plate to avoid the direct simulation of the redistribution plate, which requires extensive grid division work and calculation costs. This work can provide technical direction for the industrialization of one‐step coal to multistage fluidized bed natural gas technology.

Bilevel low-carbon coordinated operation of integrated energy systems considering dynamic tiered carbon pricing methodology

The coordinated operation and management of energy and carbon emissions in an integrated energy system (IES) can effectively promote overall energy efficiency and reduce carbon emissions. However, allocating carbon emission responsibilities between transmission-level integrated energy system (TIES) and regional integrated energy system (RIES) is difficult. On the basis of carbon emission flow theory, a model for allocating carbon emission responsibility for IES is developed in this paper. Moreover, the Shapley value method is adopted to obtain the carbon emissions responsibility intervals at the RIES. A dynamic tiered carbon pricing methodology is proposed for the RIES on the basis of equitable carbon emission responsibility intervals. In addition, a bilevel coordinated operation model that imposes carbon price to more fully excavate the low-carbon benefits obtained from operating an IES is proposed. The upper-level model, namely, the TIES, explores the optimal low-carbon schedule for energy networks by imposing fixed carbon price on the energy production costs. The lower-level model, namely, the RIES, investigates the optimal low-carbon energy supply scheme of multienergy coupling equipment and imposes dynamic tiered carbon pricing to adjust the amount of electricity and natural gas consumed. After the whole bilevel model is solved iteratively, equilibrium is reached. Case studies verify the potential and efficacy of the proposed bilevel model, demonstrating superior effectiveness in reducing carbon emissions compared with existing methods.

Asymptotic safe nonassociative quantum gravity with star R-flux products, Goroff–Sagnotti counter-terms, and geometric flows

Nonassociative modifications of general relativity, GR, defined by star products with R-flux deformations in string gravity consist an important subclass of modified gravity theories, MGTs. A longstanding criticism for elaborating quantum gravity, QG, argue that the asymptotic safety does not survive once certain perturbative terms (in general, nonassociative and noncommutative) are included in the projection space. The goal of this work is to prove that a generalized asymptotic safety scenario allows us to formulate physically viable nonassociative QG theories using effective models defined by generic off-diagonal solutions and nonlinear symmetries in nonassociative geometric flow and gravity theories. We elaborate on a new nonholonomic functional renormalization techniques with parametric renormalization group, RG, flow equations for effective actions supplemented by certain canonical two-loop counter-terms. The geometric constructions and quantum deformations are performed for nonassociative phase spaces modelled as R-flux deformed cotangent Lorentz bundles. Our results prove that theories involving nonassociative modifications of GR can be well defined both as classical nonassociative MGTs and QG models. Such theories are characterized by generalized G. Perelman thermodynamic variables which are computed for certain examples of nonassociative geometric and RG flows.

Effective lateral dispersion of momentum, heat and mass in bubbling fluidized beds

The lateral dispersion of bed material in a bubbling fluidized bed is a key parameter in the prediction of the effective in-bed heat transfer and transport of heterogenous reactants, properties important for the successful design and scale-up of thermal and/or chemical processes. Computational fluid dynamics simulations offer means to investigate such beds in silico and derive effective parameters for reduced-order models. In this work, we use the Eulerian-Eulerian two-fluid model with the kinetic theory of granular flow to perform numerical simulations of solids mixing and heat transfer in bubbling fluidized beds. We extract the lateral solids dispersion coefficient using four different methods: by fitting the transient response of the bed to (1) an ideal heat or (2) mass transfer problem, (3) by extracting the time-averaged heat transfer behavior and (4) through a momentum transfer approach in an analogy with single-phase turbulence. The method (2) fitting against a mass transfer problem is found to produce robust results at a reasonable computational cost when assessed against experiments. Furthermore, the gas inlet boundary condition is shown to have a significant effect on the prediction, indicating a need to account for nozzle characteristics when simulating industrial cases.

Application of Seagull Optimization Algorithm-BP Neural Network in Oil-Water Two-Phase Flow Pattern Forecasting

With the ongoing increase in global energy demand, the significance of innovations in oil exploration and development technologies is rising, especially in relation to the development of unconventional reservoirs. The application of horizontal wells is becoming increasingly important in this particular situation. However, accurately monitoring and analyzing fluids in horizontal wells remains challenging due to the complex and fluctuating flow patterns of oil-water two-phase flow within the wellbore. Several elements, including well slope angle, flow rate, and water content, are involved. This study aimed to explore and develop an effective method for forecasting flow patterns, improving the precision of the dynamic monitoring of oil-water two-phase flow in horizontal wells. By analyzing the flow patterns in different experimental conditions, a predictive model using the SOA-BP neural network was developed, providing a scientific basis for dynamic monitoring in actual production scenarios. Initially, the simulated experiment for oil-water two-phase flow was carried out at room temperature and pressure utilizing a multiphase flow simulator. An optically transparent wellbore, with a diameter comparable to that of a real downhole well, was utilized, and No. 10 industrial white oil and tap water were employed as the experimental fluids. The experiment considered multiple contributing factors, including different well deviation, total flow, and water cut. The flow characteristics of oil and water were observed via visual monitoring and high-definition video, followed by detailed analysis. After collecting the experimental data, flow regimes for various scenarios were classified based on the established theory of oil-water two-phase flow in horizontal wells; then, detailed flow distribution diagrams were drawn. These data and diagrams presented offer a visual representation of the behavioral patterns exhibited by oil-water two-phase flow under varying situations and form the basis for subsequent model training and testing. Subsequently, based on the experimental data, this study combined the Seagull Optimization Algorithm (SOA) with a BP neural network to effectively learn and predict the experimental data. The SOA optimized the weights and biases of the BP neural network, improving the model’s convergence speed and prediction accuracy. Through rigorous training and testing, an oil-water two-phase flow pattern forecasting model was established, effectively predicting flow patterns under different well deviation, total flow, and water cut conditions. Finally, to validate the efficiency of the established model, a total of 15 data points were chosen from a sample well for validation. By comparing the flow patterns predicted by the model with actual logging data, the results indicate that the model’s accuracy in identifying flow pattern was 86.67%. This demonstrates that the flow pattern prediction model based on the SOA-BP neural network achieved a high level of accuracy under different complicated working conditions. This model effectively fulfills the requirements for dynamic monitoring in actual production. This indicates that the SOA-BP neural network-based flow pattern forecasting method is highly valuable due to its practical application value and provides an efficient technical approach for the development of unconventional reservoirs and the dynamic monitoring of horizontal wells in the future.

Heat transfer efficiency in gas–solid fluidized beds with flat and corrugated walls

Abstract Gas–solid fluidized bed reactors exhibit improved heat and mass transfer performance as compared to packed beds. Corrugated walls installed in narrow gas–solid bubbling fluidized bed (CWBFB) enclosures have been observed to decrease minimum bubbling velocity, reduce bubble size, improve gas distribution, provide stable operation, and minimize particle carryover or loss. Thorough analyses of the wall-to-bed heat transfer coefficient in flat- (FWBFB) and corrugated- (CWBFB) wall bubbling fluidized beds have been performed for a variety of operating conditions and geometric parameters. Fast-response self-adhesive heat flux probes and thermocouples were used to simultaneously measure the wall-to-bed heat flux, surface and bed temperatures, and were used to determine the heat transfer coefficient (HTC) at various axial and lateral locations. For a given set of parameters, a significant increase in HTC was observed at lower gas flow rates in CWBFB as compared to FWBFB. It was shown that CWBFB inventory required lower U mb (gas flow rate) as compared to FWBFB. Full 3-D transient Euler–Euler CFD simulations using the kinetic theory of granular flow were also performed, which confirmed the experimental results.

Abyssal Slope Currents

Abstract Realistic computational simulations in different oceanic basins reveal prevalent prograde mean flows (in the direction of topographic Rossby wave propagation along isobaths; a.k.a. topostrophy) on topographic slopes in the deep ocean, consistent with the barotropic theory of eddy-driven mean flows. Attention is focused on the Western Mediterranean Sea with strong currents and steep topography. These prograde mean currents induce an opposing bottom drag stress and thus a turbulent boundary-layer mean flow in the downhill direction, evidenced by a near-bottom negative mean vertical velocity. The slope-normal profile of diapycnal buoyancy mixing results in down-slope mean advection near the bottom (a tendency to locally increase the mean buoyancy) and up-slope buoyancy mixing (a tendency to decrease buoyancy) with associated buoyancy fluxes across the mean isopycnal surfaces (diapycnal downwelling). In the upper part of the boundary layer and nearby interior, the diapycnal turbulent buoyancy flux divergence reverses sign (diapycnal upwelling), with upward Eulerian mean buoyancy advection across isopycnal surfaces. These near-slope tendencies abate with further distance from the boundary. An along-isobath mean momentum balance shows an advective acceleration and a bottom-drag retardation of the prograde flow. The eddy buoyancy advection is significant near the slope, and the associated eddy potential energy conversion is negative, consistent with mean vertical shear flow generation for the eddies. This cross-isobath flow structure differs from previous proposals, and a new one-dimensional model is constructed for a topostrophic, stratified, slope bottom boundary layer. The broader issue of the return pathways of the global thermohaline circulation remains open, but the abyssal slope region is likely to play a dominant role.

Research progress on operation control and optimal scheduling of irrigation canal systems

AbstractOpen canals are a common water transfer method used in water transfer projects and agricultural irrigation and drainage projects. With the emergence of drawbacks in traditional canal control models and the increasingly severe shortage of water resources, accurate transport and distribution of water in the canal system of the irrigation district, rational allocation of water resources, reduction in water loss, improvement in the efficiency and benefit of water resource utilization, and satisfaction of the water demand of different water users are needed. Many scholars have conducted extensive research on canal operation control and optimal scheduling. This paper systematically reviews and summarizes the relevant research progress, including the theory of unsteady flow in open canals, the operation mode of the canal system, the operation control model and algorithm of canal systems, and the optimization of water distribution in canal systems. By summarizing the research progress already achieved, the existing problems and future development directions are identified according to actual needs, providing a reference for the ongoing modernization of irrigation districts and the research and application of digital twin irrigation district technology.

Dynamic analysis of multi-module floating photovoltaic platforms with composite mooring system by considering tidal variation and platform configuration

Floating Photovoltaics (FPV) are emerging as an innovative technology to utilizing solar energy which advances the exploration of renewable energy technologies in the deep sea. This investigation proposes a novel methodology to verify the feasibility of the designed models in time-domain analysis via the motion responses, the mooring analysis based on the finite element method (FEM) and the airgap analysis, considering a comparison of dynamic responses between the regular hexagon shape and rectangle shape semi-submersible floating photovoltaic platform (FPVP) both combinate the cables and the tensioners mooring system to adapt the tidal variation. Initially, the response amplitude operators (RAOs) of the two configurations of the FPVP numerical models established in AQWA are derived from the frequency-domain analysis. Then, the method of rectifying the RAOs by incorporating additional damping essential to compensating the fluid viscosity due to the limitation of the potential flow theory is verified through comparison with the Computational Fluid Dynamics (CFD) solver. Subsequently, the motion responses of the two conceptualized FPVPs with the composite mooring system under different depths of water are assessed in time-domain analysis through OrcaFlex which regards the cables and tensioners as Morison type based on the FEM theory. Simultaneously, the variations in the air gap of platforms with dissimilar stiffness tensioners are compared to assess the safety of FPV systems under different water depths. The long-term extreme forecast of effective tension force for various return periods derived from the Weibull distribution model is verified. Finally, considering the factors that influence the design and safety of multi-module floating photovoltaics in variable-depth water, this study provides essential guidance for the safe construction technology of semi-submersible FPVPs, serves as a valuable reference for promoting reliable and cost-effective FPV technologies for offshore environments.

Research on dynamic responses of multi-float systems during wet towing

Very large floating structures (VLFS) are substantial in scale, typically comprising dozens to hundreds of interconnected modules. This paper utilizes a multi-float towing approach to enhance transport efficiency. A numerical model of multi-float system, based on potential flow theory and multi-body hydrodynamic interaction, is developed and validated. The dynamic responses for six towing configurations under various wave periods and environmental load directions are investigated by using this model. In addition, a selection method is proposed to determine the optimal towing configuration that meets the towing stability criteria while maximizing efficiency, cost-effectiveness, and minimizing environmental impact. Results indicate that during towing multi-float systems, the rear module's vertical motion caused by the combination of heave and pitch is significantly greater than that of the front module, especially in long wave periods. When the number of longitudinal tandem modules reaches four, the low-frequency motion modes with sway and yaw as the main motions are excited, leading to a significant lateral displacement and horizontal rotation of the multi-float system. This also results in uneven tensions of the symmetrical cables. Additionally, the dynamic behaviors of the towing configurations are more pronounced in oblique or lateral waves than in forward waves. As the current direction shifts from forward to lateral, the sway amplitude of the system with four longitudinal tandem modules decreases. Furthermore, an optimal towing configuration is determined by the selection method, which has good stability in moderate sea conditions. The findings of this paper provide valuable insights for towing multi-float systems and have implications for future VLFS construction.

Experimental and numerical study of a hinged floating bridge under waves and moving loads

ABSTRACT As an important means of water transportation, floating bridges have broad application prospects. In this paper, a numerical calculation model of the floating bridge considering the combined actions of waves and moving loads is established based on the potential flow theory, and model tests are carried out to verify the accuracy of the numerical method. The effects of motorcade loads and wave parameters on the dynamic responses of the floating bridge were further investigated. The results show that the larger vertical displacements of the floating bridge are affected by both the increase in the number of vehicles and the decrease in vehicle distances. The wave frequency and wave amplitude ranges dominated by the waves and vehicle loads were provided. The extreme dynamic responses of the hinged floating bridge under the combined effect of the waves and moving loads are less than the linear superposition of the individual effect.