Separation Point Research Articles

Two-degree-of-freedom flow-induced vibrations of a D-section prism

This paper presents a comprehensive study of flow-induced vibrations of a D-section prism with various angles of attack $\alpha$ ( $= 0^{\circ }\unicode{x2013}180^{\circ }$ ) and reduced velocity $U^*$ (= 2–20) via direct numerical simulations at a Reynolds number ${Re} = 100$ . The prism is allowed to vibrate in both streamwise and transverse directions. Based on the characteristics of vibration amplitudes and frequencies, the responses are classified into nine different regimes: typical VIV regime ( $\alpha = 0^{\circ }\unicode{x2013}30^{\circ }$ ), hysteretic VIV regime ( $\alpha = 35^{\circ }\unicode{x2013}45^{\circ }$ ), extended VIV regime ( $\alpha = 50^{\circ }\unicode{x2013}55^{\circ }$ ), first transition response regime ( $\alpha = 60^{\circ }\unicode{x2013}65^{\circ }$ ), dual galloping regime ( $\alpha = 70^{\circ }$ ), combined VIV and galloping regime ( $\alpha = 75^{\circ }\unicode{x2013}80^{\circ }$ ), narrowed VIV regime ( $\alpha = 85^{\circ }\unicode{x2013}145^{\circ }$ ), second transition response regime ( $\alpha = 150^{\circ }\unicode{x2013}160^{\circ }$ ) and transverse-only galloping regime ( ${\alpha = 165^{\circ }\unicode{x2013}180^{\circ }}$ ). In the typical and narrowed VIV regimes, the vibration frequencies linearly increase with increasing $U^*$ . In the hysteretic and extended VIV regimes, the vibration amplitudes are large in a wider range of $U^*$ as a result of the closeness of the vortex shedding frequency to the natural frequency of the prism because of the shear layer reattachment and separation point movement. In the two galloping regimes, the transverse amplitude keeps increasing with $U^*$ while the streamwise amplitude stays small or monotonically increases with increasing $U^*$ . In the combined VIV and galloping regime, the vibration amplitude is relatively small in the VIV region while drastically increasing with increasing $U^*$ in the galloping region. In the transition response regimes, the vibration frequencies are galloping-like but the divergent amplitude cannot persist at high $U^*$ . Furthermore, a wake mode map in the examined parametric space is offered. Particular attention is paid to physical mechanisms for hysteresis, dual galloping and flow intermittency. Finally, we probe the dependence of the responses on Reynolds numbers, mass ratios and degrees of freedom, and analyse the roles of the shear layer reattachment and separation point movement in the appearance of multiple responses.

Using combative and imitative active video games to increase the physical activity levels of university students on campus

This study aimed to investigate the effects of combative and imitative active video games (AVGs) on the physical activity levels of university students on campus. University students (n = 10; mean age: 20.30 ± 1.57 years), participated in this study. Measurements were taken from each participant at two separate time points on a university campus. During these visits, the physiological responses were recorded for two AVGs and resting conditions for measurement of physical activity level. The AVGs were randomly played for 15 minutes using an Xbox One device on the university campus. Physiological responses were measured continuously using the computerized, breath-by-breath analysis system, also the heart rate was recorded continuously. Data were analyzed using a one-way repeated measures ANOVA. The findings demonstrate that active video imitative and combative games significantly increased physiological responses, the energy expenditure from 0.019 ± 0.002 (rest) to 0.102 ± 0.019 and 0.131 ± 0.017 kcal.kg−1.min−1, respectively. The MET values of games (imitative: 5.937 ± 1.03; combative: 7.547 ± 0.94) were significantly higher than the rest (1.120 ± 0.11). The HR values significantly increased from 72.4 ± 9.96 beat.min-1 for rest to 132.2 ± 21.10 beat.min-1 for the imitative game, and 153.1 ± 19.76 beat.min-1 for the combative game. The highest physiological responses were determined for active video combative games which were significantly higher than active video imitative game responses (p < 0.01) and rest (p < 0.001). In conclusion, both combative and imitative AVGs, which can be integrated into campus and physical education classes, could serve as effective tools for increasing the physical activity levels of university students.

Effects of energy conversion under shock wave on the effective liquefaction efficiency in the nozzle during natural gas dehydration

Shock wave induces boundary layer separation when back pressure is set at the nozzle outlet. However, the effects of the complex flow characteristics on energy conversion mechanisms and the non-equilibrium phase transitions are not fully understood. This study developed a physical model for the homogeneous condensation of water vapour. The accuracy of the model was verified through flow and condensation experiments. The findings indicate that vortex clusters enhance energy transfer near the shear layer when the boundary layer separates. The separation point represents the region with the highest entropy generation. The peak entropy value near the wall with an increase of 7.07% as back pressure decreases from 0.75 to 0.1 MPa. The significant discovery that shock wave has minimal influence on droplet evaporation when the back pressure is 0.15 MPa, and the liquefaction efficiency at the outlet peaks at 79.42%. Moreover, over-expansion of the gas mixture at the back pressure of 0.15 MPa can lower the total pressure loss from 72.89% to 62.96% compared with the back pressure of 0.25 MPa. These findings provide an effective theoretical basis for determining optimal back pressures to reduce total pressure loss and enhance the liquefaction efficiency of the nozzle.

Direct numerical simulation of turbulent convection in a channel roughened with circular-arc ribs

Turbulent flows through a channel roughened with circular-arc ribs of different pitch-to-height ratios (P/H=3.0, 5.0 and 7.5) at a fixed Reynolds number are studied using direct numerical simulations (DNS). It is interesting to observe that in contrast to the classical channel flow over transverse square bars, the flow separation point in a channel roughened with circular-arc ribs is sensitive to the testing conditions and varies along the rib arc. The influences of the pitch-to-height ratio on the flow separation, statistical moments of the velocity field, and the anisotropy of turbulence stresses are investigated. The dynamics of coherent structures are studied by examining the skewness of the flow field, characteristics of the joint probability density functions (JPDF) of velocity fluctuations, quadrant analysis of Reynolds stresses, instantaneous velocity field, swirling strength, and temporal–spatial two-point auto-correlations. It is found that the flow anisotropy becomes suppressed as the value of P/H increases due to significant enhancement of the spanwise Reynolds normal stress 〈w′w′〉. It is also interesting to observe that the lifespan of turbulence structures becomes increasingly shortened at the midspan between two adjacent ribs as the pitch-to-height ratio increases.

Numerical study on the flow and heat transfer characteristics in a high-temperature gas-cooled reactor core

In the high-temperature gas-cooled reactor (HTGR), the core operation heavily relies on the heat transfer process facilitated by the coolant that withdraws the heat released by fuel particles. Therefore, it is imperative to carefully study the flow and heat transfer characteristics between the fuel particle and coolant. Additionally, under high core temperature conditions, the fuel particle tends to incur damage. In this study, we have designed a new type of HTGR using hydrogen as a coolant, and performed numerical simulations to explore the flow and heat transfer conditions in the core under various working conditions. Our results indicate that under high velocity inlet and low temperature inlet conditions, the system provides a high heat transfer rate. Furthermore, interesting relationships were observed between the flow and heat transfer characteristics of the model through the Reynolds number (Re), n, and Tr. Since the density of the coolant changes as the temperature varies, the hydrogen is susceptible to compression. Notably, poor thermal conductivity on the fuel particle surface generates hotspots at the points of flow stagnation, flow separation, and flow convergence. Our study on the new reactor core's flow and heat transfer characteristics provides an important reference for improving the core outlet temperature and the fuel particle's structure.

NUMERICAL SOLUTION OF NON-SIMILAR BOUNDARY-LAYER FLOW OVER A CYLINDER

This paper presents а numerical solution of a non-similar two-dimensional boundary-layer flow over a cylinder. The assumptions and related two-dimensional flow equations are presented. The fourth-order Runge-Kutta method with the backward differentiation formula (BDF) method to separation point is implemented in the numerical solution using MATLAB software. Numerical solution results are compared with well-known analytic solutions. Shear stress diagram, friction ratio based on θ and x, and output results are illustrated. The results of numerical solution demonstrate good consistency with analytic solutions.

On the surface flow patterns and associated aerodynamics of an asymmetrical flat-box section

In this study, wind tunnel experiments were carried out in smooth flow to examine the nexus between flow patterns around a flat-box section and its aerodynamics with the variation of the wind angle of incidence (α). The model cross section closely represents the overall asymmetric geometry and attendant aerodynamics of a class of flat-box decks frequently employed in long-span bridges. To explore the flow around and associated aerodynamic properties of this model that are distinct from a typical symmetric section (e.g., rectangular), detailed wind tunnel tests involving smoke-wire based flow visualizations and synchronous multipoint pressure measurements were carried out. Experimental results were analyzed to identify flow patterns, pressure distributions and associated Strouhal numbers, power spectral densities, aerodynamic force coefficients, proper orthogonal decomposition (POD) analyses, and span-wise correlation. Three typical flow patterns previously observed around symmetric bluff bodies with varying α were also observed in the asymmetric cross section, i.e., the trailing-edge vortex shedding (TEVS), the impinging leading-edge vortices (ILEV), and the alternate-edge vortex shedding (AEVS). However, due to the chordwise asymmetry of the section, the three flow patterns identified are distinct from the classical ones associated with symmetric sections in terms of flow separation points, the static “stall” angle of the section, and characteristics of leading-edge vortices. The roles played by these flow patterns in the aerodynamics of the flat-box section have been identified. It is observed that, if the ILEV or AEVS governs the flow topology, the aerodynamic force coefficients vary nonlinearly with the increase in α, in contrast with the linear variation in the TEVS-dominant case. For cases in which the TEVS dominates, the POD mode participation factors of the fluctuating pressure field display energy in higher modes. In this case, the reconstruction process requires that higher POD modes are retained. Finally, in the TEVS flow pattern, a weaker spanwise correlation of the fluctuating forces is noted as compared to the ILEV and AEVS-type flows. This study is limited to the fundamental examination of asymmetric section aerodynamics in smooth flows, which should be extended in case the influences of turbulence and aeroelastic effect are of interest.

A Method for Extracting the Tree Feature Parameters of Populus tomentosa in the Leafy Stage

With the advancement of 3D information collection technology, such as LiDAR scanning, information regarding the trees growing on large, complex landscapes can be obtained increasingly more efficiently. Such forestry data can play a key role in the cultivation, monitoring, and utilization of artificially planted forests. Studying the tree growth of artificially planted trees during the leafy period is an important part of forestry and ecology research; the extraction of tree feature parameters from the point clouds of leafy trees, obtained via terrestrial laser scanning (TLS), is an important area of research. The separation of foliage and stem point clouds is an important step in extracting tree feature parameters from data collected via TLS. By modeling the separated stem point clouds, we can obtain parameters such as a tree’s diameter at breast height (DBH), the number of branches, and the relationship between these and other parameters. However, there are always problems with the collected foliated tree point clouds; it is difficult to separate the point clouds into foliage and stems, yielding poor separation results. To address this challenge, the current study uses a deep learning-based method to train a mixture of non-foliated and foliated point clouds from artificially planted trees to semantically segment the foliage labels from the stem labels of these trees. And this study focused on a Chinese white poplar (Populus tomentosa Carr.) plantation stand. At the same time, the method of this study greatly reduces the workload of labeling foliated point clouds and training models; an overall segmentation accuracy of 0.839 was achieved for the foliated Populus tomentosa point clouds. By building the Quantitative Susceptibility Mapping (QSM) model of the segmented point clouds, a mean value of 0.125 m for the tree diameter at breast height, and a mean value of 14.498 m for the height of the trees was obtained for the test set. The residual sum of squares for the diameter at breast height was 0.003 m, which was achieved by comparing the calculated value with the measured value. This study employed a semantic segmentation method that is applicable to the foliated point clouds of Populus tomentosa trees, which solves the difficulties of labeling and training models for the point clouds and improves the segmentation precision of stem-based point clouds. It offers an efficient and reliable way to obtain the characteristic parameters and stem analyses of Populus tomentosa trees.

Drag reduction of a cylinder by using spiral protuberances to generate three-dimensional surface flow

The air flow around a circular cylinder with 12 spiral protuberances was investigated via wind tunnel static force and surface pressure measurement tests to study drag reduction. A comparison with the flow characteristics of a smooth cylinder is presented herein. Kármán vortex shedding was suppressed and drag reduction of approximately 33% was observed within the Reynolds number (Re) range of 1.3×104 to 3.1×104. This drag reduction was associated with the three-dimensional surface flow caused by the guiding effect of the protuberances. The guiding effect became more significant with an increasing Re and helped delay the separation points. Therefore, upon the suppression of vortex shedding, Re dependence phased out, and instead, the flow was controlled by the spiral protuberances, and a constant dimensionless drag was achieved.

Application of Authority Control Process in Koha Cataloguing System

This study suggests a pragmatic approach to the authority control process in library cataloguing systems in order to develop a better database that facilitates speedy information retrieval from library OPACs. The authority control method also creates a unified bibliographic database with separate access points for both library users and library professionals. To review the authority control procedure for the sake of this study, we used free and open-source library management software, namely Koha. Different methods are followed by the Koha administration and its cataloguing module. The bibliographic and authority frameworks are very helpful and conducive to all the libraries and information centers. The originality of this study has been successfully demonstrated by library cataloguers’ observations on frequent strategies for carrying out the authority control processes.

Study on flow and heat transfer characteristics in rectangular channels with lantern-shaped pin fin array: Part I- effect of sphere diameter

Featuring high heat transfer capacity and low pressure loss, pin fin arrays have become one of the important cooling methods for the trailing edge cooling channel of modern gas turbines. To improve the heat transfer efficiency of the channel, a lantern-shaped pin consisting of a cylinder and a sphere is proposed in Part I of this study. The flow and heat transfer characteristics in rectangular channels containing eight rows of staggered lantern-shaped pins with different sphere-to-pin diameter ratios, R/D, are investigated and compared by numerical simulations in the Re range of 3,000 to 30,000. The calculations indicate that the spheres trigger a pair of counter-rotating vortices behind the pins, which significantly enhance the Nusselt number and pressure loss. The pair of vortices also change the distributions of the endwall and pin Nusselt number. The endwall Nusselt numbers behind the fins and the pin Nusselt numbers at the leading edge and trailing edge of the pins are substantially enhanced. After the third row, the endwall Nusselt number augmentation Nu e/Nu 0 of the lantern-shaped pin with R/D = 1.0 decreases with the increased Re. However, the result of a slight increase in the Nu e/Nu 0 with the increased Re for R/D = 1.7 is diametrically opposite to that for R/D = 1.0. Meanwhile, with the increasing R/D, the separation and transition points are closer to the trailing edge. The increased Re makes the separation point moves closer to the leading edge while the transition point remains near 130 degrees. The endwall, pin, total area-averaged Nusselt numbers, and pressure loss rapidly boost with the increased R/D. The thermal performance index of the lantern-shaped pin with R/D = 1.7 ranges from 1.72 to 1.21. At Re = 10,000, the lantern-shaped pin with R/D = 1.7 shows the most significant percentage increase in thermal performance index of 4.39% compared to R/D = 1.0.

Wall pressure fluctuations in wall heated and cooled shock wave and turbulent boundary layer interactions

Wall pressure fluctuations in shock wave and turbulent boundary layer interactions on heated and cooled walls are investigated by performing direct numerical simulations. The objectives of this study are to identify flow dynamics causing low- and high-frequency wall pressure fluctuations and evaluate wall heating and cooling effects on the wall pressure fluctuations. The wall pressure spectra highlight two characteristic low-frequency spectral peaks at the separation point and below the expansion waves. Conditional analysis reveals that the two spectral peaks originate from the oscillations of the reflected shock and expansion waves, coupled with the expansion and contraction motions of the separated turbulent shear layer. Regarding wall temperature effects, wall cooling enhances the magnitude of the wall pressure fluctuations regardless of the low- and high-frequency components. Furthermore, influences of the expansion waves are also enhanced by wall cooling, which increases the wall pressure fluctuations locally after the separation.

Multiple traveling salesperson problem with drones: General variable neighborhood search approach

A key factor to consider in the development of new technologies in a number of fields is the use of unmanned aerial vehicles. This rapidly developing technology is used in military, communication, health, mapping, agriculture and transportation fields. The importance of cargo transportation has grown due to the growth of e-commerce. Currently, with advancing technology, and the effect of the pandemic, purchases are increasingly made over the internet. For cargo transporters, this situation leads to an increase in the number of destination points, in distances traveled, and in the delivery frequency, and a decrease in the package sizes. As a result, the planning of transportation has become increasingly complex. One solution is to make greater use of unmanned aerial vehicles in this sector, and to reduce reliance on trucks through appropriate planning. This involves two aspects: the unmanned aerial vehicle delivering to a point, while the cargo truck delivers to a separate point. In this study, we consider a multiple traveling salesperson problem simultaneously using multiple trucks and unmanned aerial vehicles for package delivery. We develop a general variable neighborhood search algorithm, and compare the results with the existing studies in the literature. Computational experiments show that our approach is able to find highly satisfactory solutions in reasonable time, and outperforms the existing methods in terms of best solution, average solution and solution time in majority of the instances.

Weight cutting in female UFC fighters.

It is common practice for fight sport athletes to use a variety of weight manipulation strategies to compete in desired weight classes. Although numerous studies have highlighted rapid weight loss (RWL) strategies and the magnitude of weight loss, few have focused specifically on weight loss in female fighters. The purpose of this study was to provide descriptive information on professional UFC female fighters engaging in RWL in all women's UFC weight divisions: strawweight (52.2 kg): flyweight (56.7 kg); bantamweight (61.2 kg); featherweight (65.8 kg). All fighter's weights were obtained at five separate time points: 72 hrs. pre-weigh-in, 48 hrs. pre-weigh-in, 24hrs. pre-weigh-in, official weigh-in, and 24 hrs. post-weigh-in (competition weight). Mixed effects models and random effects analysis were used to assess changes in weight and differences between weight divisions. All statistics were analyzed, and significance was set atp ≤0.05. Significant changes in weight between all time points were reported. No statistical differences between weight divisions were observed. Female fighters lost 4.5-6.6% of their weight prior to the official weigh-in. Females engaged in RWL practices lose weight in a similar fashion irrespective of weight class.

Impact of Resource Planning and Information Management Services based on Sustainable Development Goals (SDGs) - The Eco-Environmental and Economic Behavior for the Chemical Industries in China

The Chinese economy and the global supply chain both heavily rely on the chemical industry. These services strive to optimize resource utilization, decrease environmental contamination, and support environmentally friendly and commercially successful operations in the chemical sector by incorporating sustainable practices and utilizing technical breakthroughs .Sustainable development goals (SDGs) are a necessity that has only lately come to light on a global scale, but they are a dynamic phenomenon that calls for ongoing analysis and is the subject of current study and policy. As more people become aware of environmental issues, businesses are under pressure to manage their supply chains in an environmentally sustainable manner. This quantitative study analyses the effects of resource planning and information management services on eco-environmental and economic behavior in China's chemical industries with a focus on the Sustainable Development Goals (SDGs). The study used a longitudinal research design with data collected at two separate time points due to low response rates. The study employs a 5-point Likert scale questionnaire for data collection, and SPSS Macros is used for statistical analysis. The author has also investigated the moderating effects of resource availability and the use of resource theory. The findings of this study contribute valuable insights to the field of sustainable development and industrial practices. The implications of these research findings are twofold. First, they provide valuable guidance for the chemical industries in China to enhance their eco-environmental and economic performance through efficient resource planning and data-driven information management. Second, the study's identification of key sustainable development factors can assist policymakers in formulating targeted strategies to advance the SDGs within the chemical sector. The findings support sustainable behavior in the chemical industry by offering useful insights into how to include SDGs into resource planning and information management systems.

Flight control of a flying wing aircraft based on circulation control using synthetic jet actuators

To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft (FWA), a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actuators was proposed without the movement of rudders. Effects on the longitudinal aerodynamic characteristics of a small-sweep FWA were investigated. Then, flight tests were carried out to verify the control abilities, providing a novel technology for the design of a future rudderless FWA. Results show that synthetic jets could narrow the dead zone area, improve the flow velocity near the trailing edge, and then move the trailing-edge separation point and the leading-edge stagnation point downwards, which make the effective Attack of Angle (AOA) increase, thereby enhancing the pressure envelope area. Circulation control based on synthetic jets could improve the lift, drag and nose-down moment. The variations of lift and nose-down moment decrease with the growth of AOA caused by the improved reverse pressure gradient and the weakened circulation control efficiency. Finally, synthetic jet actuators were integrated into the trailing edge of a small-sweep FWA, which could realize the roll and pitch control without deflections of rudders during the cruise stage, and the maximum roll and pitch angular velocity are 12.64 (°)/s and 8.51 (°)/s, respectively.

Furcation area and root proximity of molars as a risk indicator of periodontitis: a cone‑beam computed tomography-based study.

This study assessed the root proximity in molars and the furcation area (FA) in the first root separation point (RSP) using cone‑beam computed tomography (CBCT) and evaluated the association between the furcation area of molars and periodontal status of the patients. A total of 264 molar teeth in 66 participants were included in the study. The control group consisted of 110 molar teeth of participants, and 154 molar teeth were included in periodontitis group, which consisted of only stage II and III periodontitis patients. FA, RSP, and root proximities were measured in axial slices, and bone resorption rates were measured in sagittal slices. Both maxillary and mandibular molar groups had significantly less FA in periodontitis group than in controls (p < 0.005), and there were significant relationships between the degree of bone resorption in molars and FA and furcation grades (p < 0.001). According to regression analysis, the risk of periodontitis increased by 1.011 times as total FA decreased (p < 0.001), and periodontitis risk of maxillary molar was 1.693 times higher than mandibular molars but not found to be statistically significant (p = 0.152). When assessing the root proximity between molar teeth, maxillary molars showed significantly higher root proximity in CEJs than mandibular molars in both periodontitis and control groups (p < 0.05). The results indicate that the association between FA and the degree of bone resorption and root proximity of maxillary molars might be considered as a risk indicator for bone resorption in molars and might play a role during disease progression.

Separation of near-boiling mixtures (acetic acid and water) enhanced by ionic liquid

Acetic acid aqueous solution is a common and typical near-boiling mixture in the petroleum, chemical, polymer, pharmaceutical and food industries. Because of the large number of ideal plates for separating acetic acid and water by ordinary distillation, the energy consumption and production cost are high. Designable ionic liquids (ILs) and deep eutectic solvents (DESs) are environmentally-friendly entrainers for extractive distillation. Many azeotropic systems enhanced by adding ILs or DESs have been studied, but the near-boiling water/acetic acid system is rarely discussed.In this study, an IL 1,2,3-trimethylimidazolium dimethylphosphate ([TMIM]+[Me2PO4]−) with easy synthesis, low production cost and good thermal stability was employed as the rectification entrainer for water/acetic acid system, while the DESs were easy to react in acetic acid aqueous solution and was abandoned. First, the relative volatility of water (1) and acetic acid (2) at the more difficult separation point (x1′ = 0.9) was measured using a modified Othmer still at 101.32 kPa. When the mole fraction of entrainers was 0.071, these relative volatilities were 2.80 (n,n-dimethylformamide), 2.88 (1-methyl-2-pyrrolidinone), 4.82 ([TMIM]+[Me2PO4]−) respectively. The separation performance of [TMIM]+[Me2PO4]− was 67% higher than that of 1-methyl-2-pyrrolidinone. Then, the effect of [TMIM]+[Me2PO4]− concentration on the relative volatility was investigated. The relative volatility was dramatically increased from 1.60 to 6.85 with 0–0.103 mol fraction of [TMIM]+[Me2PO4]− and was 4.28 times that in an IL-free system. After that, isobaric vapor–liquid equilibrium (VLE) data of water + acetic acid, water + [TMIM]+[Me2PO4]− and water + acetic acid + [TMIM]+[Me2PO4]− ([TMIM]+[Me2PO4]− at ∼ 5, 15, and 25 mass%) systems were determined at 101.32 kPa. Also, Based on the chemical theory and Hayden–O’Connell method, the binary energy parameters of the NRTL (Non-Random-Two-Liquid) model for these systems were regressed and the predicted values were found to fit the experimental VLE data quite well..For the first time, we have found that [TMIM]+[Me2PO4]− as an entrainer is superior to conventional volatile solvents for water/acetic acid distillation in terms of performance, which provides more choices and imagination for industry. At the same time, it promotes understanding of the influence of IL structure on water/acetic acid separation performance, and is also an important inspiration for the distillation of other near-boiling systems.

Simulation of Drag Crisis in Flow Past a Circular Cylinder using 2D Computations

The unsteady incompressible 2D Navier-Stokes equations are solved using a finite element method with Streamline-Upwind/Petrov-Galerkin (SUPG) and Pressure-Stabilizing/Petrov- Galerkin (PSPG) stabilization terms for high Reynolds number (105 to I06) flow past a cylinder to stimulate drag-crisis. The mean drag coefficient for various Re are compared with experimental data. It is observed that the low at Re =106 separates much later, from the cylinder surface as compared to that at Re =105. The wake at Re =106 is narrower than that at Re = 105. The time-averaged flow field shows a standing bubble just downstream of the flow separation point for the Re = 105 flow. The bubble is not observed for the flow at Re = 106. The energy spectrum of the flow exhibits the characteristics of 2D isotropic turbulence.

Enhancing the Performance of a Renewable Energy System Using a Novel Predictive Control Method

The current study concerns improving the performance of a renewable energy system using systematically designed control algorithms. The performance of the system under study is evaluated under two operating scenarios: the first in which the system consists of only a wind-driven synchronous generator connected to the utility grid; in the second scenario, the generator is combined with a photo-voltaic solar system and a battery for supplying a load. Each system component is modeled and thoroughly described. To maximize the benefits of solar and wind energies, two separate maximum power point tracking procedures are adopted. Furthermore, to enhance the generator’s dynamics, a novel predictive control scheme is designed and validated by comparing its performance with traditional predictive control. The novel predictive controller utilized a simple and unique cost function to avoid the shortages of traditional predictive controllers. For standalone operation, an effective procedure is adopted to ensure the power balance between the generation, storage, and isolated load units. To evaluate the effectiveness of the designed controllers under different operating regimes, Matlab/Simulink is utilized for this task. The obtained results confirm the superiority of the novel predictive scheme used with the synchronous generator over the classic control approach for the two operating scenarios. This has been shown in the form of reduced ripples and reduced current harmonics. The obtained results are also confirming the validity of the adopted maximum power tracking strategies with solar panels and wind turbines as well. Furthermore, balanced power delivery is achieved thanks to the adopted management strategy for standalone operation, which enhances the overall system performance.