Non-uniform Conditions Research Articles

PV output power enhancement using meta-heuristic crow search algorithm under uniform and shading condition

In uniform condition, the power-voltage (P_V) curve has unique global peak and no local peaks. But in non-uniform or shading condition P_V curve has many local peaks with a unique global peak. Therefore, tracking the global peak is key factor to improve the photo voltaic (PV) performance under uniform and shading conditions. To track global peak, maximum power point tracking (MPPT) controller is mandatory requirement. Numerous soft computing algorithms are developed and explained in past decades. But the ability to track global maximum peak (GMP) is not assured under shading conditions due to trapping with local peaks instead of global peaks. In this research article, a new meta–heuristic crow search algorithm (CSA) is developed and extracted GMP under uniform and shading conditions of PV module. The highlight of CSA is it works on dual mode search ability namely intensification and diversification. Because of this dual mode operation, the local peak convergence problem is solved and it tracks GMP very fast. The experimental outcomes show that the CSA technique provides higher efficiency and faster tracking time.

Topology optimization of regenerative cooling channel in non-uniform thermal environment of hypersonic engine

Regenerative cooling technology is widely used in the active thermal protection system of hypersonic airbreathing engine. However, the overall efficiency of active cooling with limited total coolant quantity needs to be improved due to flow non-uniformity, hydrocarbon fuel pyrolysis and other factors. This paper presents a fluid–structure coupled topology optimization design of the regenerative cooling channel to improve heat transfer efficiency. To further verify the advantages of topology-optimized cooling channels under real operating conditions, detailed three-dimensional numerical simulations were conducted to investigate the supercritical flow and heat transfer processes of hydrocarbon fuel in the topology-optimized channels. Results reveal that compared to the traditional straight cooling channel, the topology-optimized channel has improved the heat transfer efficiency and flow distribution significantly. Many micro-channels perpendicular to the mainstream direction which can be termed as “capillary-like” zone in the optimized channel distribute the inlet fuel to the adiabatic walls, thus significantly improving the overall heat transfer. Remarkable cooling capacity robustness of the topology-optimized cooling channels has been found under different non-uniform heat flux conditions. Comparing to the straight channels, the averaged temperature of the heated wall in the optimized channels can be decreased up to 5.8% and the pressure drop can be decreased up to 20.6%. The uniformity of the fuel temperature distribution is about 2 times better than that of the straight channel. However, although overall heat transfer efficiency is high, complex flow and heat transfer phenomenon occurs in the topology-optimized cooling channel, such as the reverse flow phenomenon induced by adverse pressure gradient near the entrance and the stagnated flow in the “capillary-like” zone near the exit, which impair the local heat transfer and cause the existence of high temperature regions.

Experiments on and numerical calculations of debris flows passing through narrowed and widened channel regions

We clarified the dynamics of debris flows in areas wherein the topography changes abruptly. First, the dynamics of debris flow through a constriction were investigated by experimentally generating non-uniform flow conditions. Then, numerical calculations were performed using an erosion/deposition rate equation that considers the pressure gradient in a constriction, and compared with the experimental data.

An Efficient Honey Badger Optimization Based Solar MPPT Under Partial Shading Conditions

Due to the enormous utilization of solar energy, the photovoltaic (PV) system is used. The PV system is functioned based on a maximum power point (MPP). Due to the climatic change, the Partial shading conditions have occurred under non-uniform irradiance conditions. In the PV system, the global maximum power point (GMPP) is complex to track in the P-V curve due to the Partial shading. Therefore, several tracking processes are performed using various methods like perturb and observe (P & O), hill climbing (HC), incremental conductance (INC), Fuzzy Logic, Whale Optimization Algorithm (WOA), Grey Wolf Optimization (GWO) and Flying Squirrel Search Optimization (FSSO) etc. Though, the MPPT is not so efficient when the partial shading is increased. To increase the efficiency and convergences in MMPT, the Honey Badger optimization (HBO) algorithm is presented. This HBO model is motivated by the excellent foraging behaviour of honey badgers. This HBO model is used to achieve the best solution in GMPP tracking and speed convergence. The HBO methodology is also compared with prior P&O, WOA and FSSO methods using MATLAB. Therefore, the experiment shows that the HBO method is performed a higher tracking than all prior methods.

Reducing Uncertainty in Collective Perception Using Self-Organizing Hierarchy

In collective perception, agents sample spatial data and use the samples to agree on some estimate. In this paper, we identify the sources of statistical uncertainty that occur in collective perception and note that improving the accuracy of fully decentralized approaches, beyond a certain threshold, might be intractable. We propose self-organizing hierarchy as an approach to improve accuracy in collective perception by reducing or eliminating some of the sources of uncertainty. Using self-organizing hierarchy, aspects of centralization and decentralization can be combined: robots can understand their relative positions system-wide and fuse their information at one point, without requiring, e.g., a fully connected or static communication network. In this way, multi-sensor fusion techniques that were designed for fully centralized systems can be applied to a self-organized system for the first time, without losing the key practical benefits of decentralization. We implement simple proof-of-concept fusion in a self-organizing hierarchy approach and test it against three fully decentralized benchmark approaches. We test the perceptual accuracy of the approaches for absolute conditions that are uniform time-invariant, time-varying, and spatially nonuniform with high heterogeneity, as well as the scalability and fault tolerance of their accuracy. We show that, under our tested conditions, the self-organizing hierarchy approach is generally more accurate, more consistent, and faster than the other approaches and also that its accuracy is more scalable and comparably fault-tolerant. Under spatially nonuniform conditions, our results indicate that the four approaches are comparable in terms of similarity to the reference samples. In future work, extending these results to additional methods, such as collective probability distribution fitting, is likely to be much more straightforward in the self-organizing hierarchy approach than in the decentralized approaches.

전기차 배터리 냉각을 위한 3차원 진동형 히트파이프의 패턴에 따른 유동 가시화 연구

Heat pipes using oscillating characteristics of vapor or liquid flow in a tube called an oscillating heat pipe (OHP) have been visualized and presented. Unlike ordinary planar type oscillating heat pipes, in the present study, 3-D oscillating heat pipes was designed, and tried to shape and verify the operability of upper heating OHP rather than lower heating OHP. Unlike the lower heating method, since the motion of the internal working fluid is directly affected by gravity, structural characteristics were studied to overcome gravity and create oscillation characteristics. In this study, it was observed that the supplied heat to the upper evaporator created the pressure difference as the internal space of the upper region was heated, and then eventually, internal working fluid was circulated by creating a pressure difference in the OHP, which was one of the anti-gravity heat pipes. It was observed that the internal working fluid is heated in the internal space of the upper part according to the heating in the evaporator, creating a pressure difference between the liquid and the lower part, and thus oscillating normally. In this study, the operating conditions of OHP using non-traditional heating and cooling modes were experimentally verified. Future electric vehicles are also suggested to use OHP in a few promising and innovative ways. The fundamental OHP operating mechanism for non-uniform working conditions are planned to be presented in this study.

Homomorphic filtering for the image enhancement based on fractional-order derivative and genetic algorithm

The main aim of image enhancement is to improve the visual quality or appearance of an image. This article presents an image enhancement method based on Grunwald-Letnikov, Riemann-Liouville fractional-order derivatives and genetic algorithm to boost the homomorphic filtering performance. Homomorphic filtering is used to attenuate the contribution made by the illumination and amplify the reflectance components of an image. This work uses a fractional-order derivative to enhance the mid- and high-frequencies and preserve the low-frequencies. The enhancement of the image depends on the parameters required for the homomorphic filter function and fractional-order value, which are not the same for all types of images. Hence, the genetic algorithm is applied, which automatically determines these parameters by optimizing the fitness function. The capability of the proposed approach is evaluated using performance metrics such as information entropy, average gradient, and contrast improvement index on different sizes of images. An average improvement in information entropy of 6.5%, average gradient of 52%, and contrast improvement index of 75%, respectively, are achieved for standard, medical images and images with low contrast and non-uniform illumination conditions. Also, the proposed method outperforms the existing methods by producing a better visual appearance of the image.

Jellyfish search algorithm based optimal thermoelectric generation array reconfiguration under non-uniform temperature distribution condition

Thermoelectric generators (TEGs) can convert heat to electricity based on the temperature difference between their hot and cold sides. However, during practical operations, low thermoelectric conversion efficiency is usually caused by non-uniform temperature difference (NTD) conditions; thus, reliable and effective maximum power point tracking (MPPT) under NTD conditions is imperative for TEG arrays. Therefore, in this study, a jellyfish search (JS) algorithm-based TEG array reconfiguration strategy is proposed to realise MPPT under NTD conditions, upon which the overall power loss is effectively decreased, the energy conversion efficiency is efficiently enhanced, and the MPPT speed is improved. In particular, the simulation results demonstrate that the JS algorithm-based TEG array reconfiguration using a random pattern can enhance the maximum output power by 23.32% for 9 × 9 symmetric TEG arrays and 15.78% for 10 × 15 asymmetric TEG arrays. Finally, a hardware-in-the-loop (HIL) test was conducted on the RTLAB platform to verify its feasibility for hardware implementation.

Effects of physical properties and operating parameters on numerically developed flat-tube solid oxide fuel cell performance

Fuel cells are promising as a clean energy conversion device in the era of global warming threat. Solid oxide fuel cells stand out among other fuel cell types because they are especially feasible for high-temperature applications. Besides the operating parameters, which are frequently encountered problems in SOFCs, physical parameters also directly affect cell performance. For this reason, careful examination of the effects of the parameters while designing the SOFC will contribute to the increase of the maximum power to be provided from the cell in applications. In this study, a solid oxide fuel cell (SOFC) created in flat-tube geometry is numerically modeled. The effect of the electrode and electrolyte layers on the performance is investigated parametrically on the created geometry. In addition, the effect of temperature on cell power is investigated comparatively by making analyzes at different temperatures for each case. In the analyzes, performance values are investigated for electrode layer thicknesses of 0.75 mm, 0.5 mm, and 0.25 mm, and electrolyte layer thicknesses of 1.25 mm, 1 mm, and 0.75 mm, respectively. As a result of the study, the highest cell power is obtained at 0.25 mm of the anode layer thickness. The maximum predicted average cell power of the flat tubular solid oxide fuel cell (FT-SOFC) is approximately 68.2 mW/cm2 for the operating temperature of 1273 K. In the study, the effect of electrolyte conductivity on the performance of the developed cell is also investigated. It is observed that the cell with a conductivity value of 100 S/m at 1073 K operating temperature has the best performance. In addition, in the last part of the study, the performance of SOFC under non-uniform operating temperature conditions is also examined and a comparison is made for this situation, which is frequently experienced in practice. The results show that small changes in fuel cell operating temperature affect the cell performance in positive and negative directions depending on the increasing and decreasing temperature values.

Experimental and numerical investigation on the pressure pulsation in reactor coolant pumps under different inflow conditions

A reactor coolant pump (RCP) is essential for transporting coolant in the primary loop of pressurized water reactors. In the advanced passive reactor, the absence of a long pipeline between the steam generator and RCP serves as a transition section, resulting in a non-uniform flow field at the pump inlet. Therefore, the characteristics of the pump should be investigated under non-uniform flow to determine its influence on the pump. In this study, the pressure pulsation characteristics were examined in the time and frequency domains, and the sources of low-frequency and high-amplitude signals were analyzed using wavelet coherence analysis and numerical simulation. From computational fluid dynamics (CFD) results, non-uniform inflow has a great effect on the flow structures in the pump's inlet. The pressure pulsation in the pump at the rated flow increased by 78–128.7% under the non-uniform inflow condition in comparison with that observed under the uniform inflow condition. Furthermore, a low-frequency signal with a high amplitude was observed, whose energy increased significantly under non-uniform flow. The wavelet coherence and CFD analysis verified that the source of this signal was the low-frequency pulsating vortex under the steam generator.

Design and Implementation of a New Fast and Efficient MPPT Controller under Different Solar Irradiance Conditions

The power-voltage (P-V) characteristic curve of solar photovoltaic (PV) systems operating in partial shading conditions (PSC) is nonlinear and has multiple local maximum peak power (LMPP) points, rendering many of the maximum power point tracking (MPPT) algorithms ineffective at locating global maximum peak power (GMPP) points. This work proposes a novel slime mould algorithm- (SMA-) based MPPT controller to utilise maximum peak power (MPP) from solar PV systems during uniform irradiance conditions (UC) and nonuniform irradiance conditions (NUC). On the basis of the MPP they tracked, tracking time, and power efficiency, MPPT controller performance is assessed through MATLAB simulations and implemented experimentally with dSPACE MicroLabBox under various irradiance conditions. The effective performance of the proposed controller is validated and demonstrated in comparison to existing popular MPPT controllers.

Power maximization in standalone photovoltaic system: an adaptive PSO approach

A control strategy for power maximization which is an important mechanism to extract maximum power under changing environmental conditions using Adaptive Particle Swarm Optimization (APSO) is proposed in this paper. An Adaptive Inertia Weighting Factor (AIWF) is utilized in the velocity update equation of traditional PSO for the improvement in speed of convergence and precision in tracking Maximum Power Point (MPP) in standalone Photovoltaic system. Adaptation of weights based on the success rate of particles toward maximum power extraction is the most promising feature of AIWF. The inertia weight is kept constant in traditional PSO for the complete duration of optimization process. The MPPT in PV system poses a dynamic optimization problem and the proposed APSO approach paves way not only to track MPP under uniform irradiation conditions, but also to track MPP under non-uniform irradiation conditions. Simulations are done in MATLAB/Simulink environment to verify the effectiveness of proposed technique in comparison with the existing PSO technique. With change in irradiation and temperature, the APSO technique is found to provide better results in terms of tracking speed and efficiency. Hardware utilizing dSPACE DS1104 controller board is developed in the laboratory to verify the effectiveness of APSO method in real time.

Power optimization of a photovoltaic system with artificial intelligence algorithms over two seasons in tropical area

Power output from the PV module changes continuously with time depending upon the climatic condition. This changes are most important in tropical area like Senegal due to the variation of the seasons (dry and rainy). Furthermore, different types of maximum power point tracking (MPPT) algorithm are presented in literature in order to get maximum output from the PV system. They can be summarized in two categories: classical and intelligent methods. The classical methods in no uniform weather condition are not efficient and an important loss of energy is showed. However, faced to this problematics like energy loss and no uniform weather conditions an Adaptative methods is used to optimize the PVs energy. In this study, two intelligent controllers based on artificial neural networks (ANN) and Adaptive Neuro Fuzzy Inference System (ANFIS) are proposed to optimize the PVs production in non-uniform weather conditions and compared in order to show the most powerful model. For the ANN, the main challenge is to find the optimal neural in the hidden layer and in the paper, it is obtained using evaluator factor like mean squared error (MSE). These techniques using artificial intelligence (AI) algorithms are used for power optimization of a photovoltaic system are trained and validated with real data from a photovoltaic micro power plant in dry and rainy season installed at polytechnic high school of Dakar. The performances of the controllers to optimize the PVs power are evaluated during the dry and rainy seasons. Simulation results show that the ANFIS MPPT controller is more efficient and robust than ANN in non-uniform weather conditions. They have the ability of generalization and adaption to each meteorological conditions. These bullet summarize the applied methodology•A real electrical characteristics of photovoltaic panel are used for learning and validation of the controllers.•A comparative study of the methods in two different season is done.•ANFIS gives best performance in weather conditions compared to the ANN.

Topological shadowing methods in arnold diffusion: weak torsion and multiple time scales

Consider a map which possesses a normally hyperbolic invariant manifold of any even dimension with transverse homoclinic channels. We develop a topological shadowing argument to prove the existence of Arnold diffusion along the invariant manifold, shadowing some iterations of the inner dynamics carried by the invariant manifold and the outer dynamics induced by the stable and unstable foliations. In doing so, we generalise an idea of Gidea and de la Llave (2006 Discrete Contin. Dyn. Syst. 14 295), based on the method of correctly aligned windows and a so-called transversality-torsion argument. Our proof permits that the dynamics on the invariant manifold satisfy only a non-uniform twist condition, and, most importantly for applications, that the splitting of separatrices be small in certain directions and thus the associated drift in actions very slow; diffusion occurs in the directions of the manifold having non-small splitting. Furthermore we provide estimates for the diffusion time.

Experimental and theoretical study on the onset of nucleate boiling in non-uniform heating tube bundle channel

The transverse non-uniform heating tube bundle exists in steam generator and will affect the heat transfer and flow conditions in the shell side. It is important for the operational performance of the steam generator. In this study, a non-uniform heating tube bundle channel experimental device was set up. The channel consisted of two groups of heating tube bundles which were non-uniform heating in the transverse direction and uniform heating in the axial direction. Experiments and theoretical analysis were conducted to evaluate the influence of transverse non-uniform heating on the Onset of Nucleate Boiling (ONB). The locations of ONB during the experiments were determined from the heat transfer coefficient variations and the tube wall temperature variations. Experimental results at ONB were compared with existing well-known correlations under uniform heating conditions. And then under non-uniform heating conditions, the experimental wall superheat at ONB were furthermore compared with results predicted by the verified existing correlation. It was found that the correlation can’t predict the experimental wall superheats well under transverse non-uniform heating conditions. Therefore, the influence of transverse non-uniform heating on ONB was theoretically analyzed. Correction factors were theoretically introduced and a new correlation was proposed. This new correlation was examined with experimental data and the result showed the correction factors need to be further studied.

Buckling analyses of thin-walled cylindrical shells subjected to multi-region localized axial compression: Experimental and numerical study

Thin-walled cylindrical shell is a fundamental engineering structure which has efficient load-carrying capacity. In practical application, this structure is more easily subjected to localized axial compression loads and is prone to buckling. However, until now there is only limited studies on the buckling problems of multi-region localized axial compression loaded cylindrical shells. To elucidate the buckling behaviors of cylindrical shell under such kind of non-uniform loading condition, experimental and numerical studies are carried out in this paper. Twenty cylindrical shell test specimens with different types of localized axial compression loads are fabricated and tested. The corresponding finite element model considering the measured initial geometric imperfections is established for buckling analysis, and good agreement between the numerical and experimental results is validated. Then the buckling failure mode and axial load-carrying capacity of cylindrical shells are investigated in details. Finally, the imperfection sensitivity of thin-walled cylindrical shell under multi-region localized axial compression is discussed. It is found that the number of loading regions and the total loading area have significant effects on buckling failure mode and axial load-carrying capacity of cylindrical shells. The results obtained from experimental and numerical studies can provide some important guidance or suggestions for the design of thin-walled cylindrical shell structures in actual engineering.

Studying the advantages of equal curvature curved fin to enhance phase change heat storage

Strengthening the heat storage process is the most important means for its application of the phase change heat storage system. By adding fins to the phase change material, the heat transfer area can be expanded and consequently effectively accelerates the heat storage rate. Therefore, this paper proposed a new fin optimization method: the combination of fins of different structures under non-uniform arrangement conditions. This study proposed an equal-curvature curved fin structure based on straight fin. Then, under the same amounts of fins and heat transfer area, the heat storage system with curved fin and straight fin were studied and analyzed. Moreover, by comparing with straight fin, the effect of the combined curved and straight fins on the performance of heat storage system with different arrangements was exhibited and discussed. The results indicated that curved fins have the effect of enhancing heat transfer by comparing with a straight fin. However, the combined curved fin and straight fin with uniform arrangement has no obvious advantage over straight fin model. Compared with the uniform arrangement, under the condition of non-uniform arrangement, the melting performance of the curved fin and straight fin combination models was improved by 24.5 % at most and at least 9.2 %, the melting performance of the straight fin model is improved by 7.7 %. Finally, the results of the optimization method proposed by other scholars are compared to prove that the optimization method proposed in this study is feasible. This work provides the new ideas for fins design with different structures and non-uniform arrangement of heat storage system.

Extended search pigeon-inspired optimized MPPT controller for solar quadcopter

PurposeThe purpose of this paper is to propose a novel maximum power point track (MPPT) controller for a type of solar quad-copter to solve the problem of tracking the maximum power point (MPP) when it works in nonuniform environment conditions.Design/methodology/approachThe influence of uniform and nonuniform illumination and different temperatures results in the output characteristics of the solar array arising multiple local MPPs. To track the global MPP of the solar array on the designed solar quadcopter, a type of MPPT controller based on an improved pigeon-inspired optimization (PIO) algorithm is proposed.FindingsA novel type of MPPT controller based on extended search PIO (ESPIO) algorithm, called ESPIO–MPPT controller, is introduced emphatically, which is used to extend the solar quadcopter’s flight time. The simulation experiments show that the ESPIO–MPPT controller can find the global MPP (GMPP) with smaller amplitudes of oscillation and less time cost.Practical implicationsThe proposed solar quadcopter with ESPIO–MPPT controller has satisfactory flight performance which can greatly broaden its mission scope.Originality/valueA type of efficient MPPT algorithm based on ESPIO is proposed for GMPP tracking of solar quadcopters in nonuniform environment conditions.

Hybrid MPPT approach using Cuckoo Search and Grey Wolf Optimizer for PV systems under variant operating conditions

Photovoltaic (PV) systems are adversely affected by partial shading and non-uniform conditions. Meanwhile, the addition of a bypass shunt diode to each PV module prevents hotspots. It also produces numerous peaks in the PV array’s power-voltage characteristics, thereby trapping conventional maximum power point tracking (MPPT) methods in local peaks. Swarm optimization approaches can be used to address this issue. However, these strategies have an unreasonably long convergence time. The Grey Wolf Optimizer (GWO) is a fast and more dependable optimization algorithm. This renders it a good option for MPPT of PV systems operating in varying partial shading. The conventional GWO method involves a long conversion time, large steady-state oscillations, and a high failure rate. This work attempts to address these issues by combining Cuckoo Search (CS) with the GWO algorithm to improve the MPPT performance. The results of this approach are compared with those of conventional MPPT according to GWO and MPPT methods based on perturb and observe (P&O). A comparative analysis reveals that under non-uniform operating conditions, the hybrid GWO CS (GWOCS) approach presented in this article outperforms the GWO and P&O approaches.

Responses of an axially rotated tube versus twisted tube design as two solutions to enhance the thermal performance under a non-uniform heat flux condition: A numerical study

• Heat transfer in rotating and twisted tubes are studied and compared numerically. • A maximum increase of 137% in Nusselt number occurs at N=10.5 for the 3-meter pipe. • Pipe rotation eliminates the liquid stratification phenomenon in the pipe. • A maximum increase of 2.5% in outlet temperature occurs at twist ratio S=0.1. • A maximum loss in the pressure coefficient reaches 32.8% at twist ratio S=0.1. Enhancement of heat transfer in tubes exposed to non-uniform heat flux applications is a key factor in increasing such applications' efficiency. In the present study, heat transfer in an axially rotating pipe with concentrated heat flux at the lower section of the pipe is numerically investigated and compared to the twisting technique in such applications. The effects of pipe’s length (1, 2, and 3 meters) and rotation rate (N=0-10.5), which is the ratio between the rotational and axial Reynold’s numbers, are studied numerically using ANSYS Fluent while the effect of the twist ratio (S=0.1-1) is studied in the twisted tube. The numerical analysis reveals that the pipe axial rotation has a negative impact on the average outlet temperature where a maximum decrease of 7.7% is reached in the 3-meter pipe at a rotation rate of N=10.5 with respect to the stationary pipe while the effect of the twisting technique was significant as the outlet temperature has a maximum increase of 9.3% at S=0.1. On the other hand, the pipe rotation increases the temperature homogeneity between the liquid layers thus reducing the liquid stratification phenomenon in the pipe. The average reduction percentage in the temperature difference between the pipe wall and the fluid center is 69.7% at N=10.5, however; this reduction reached a maximum value of only 11% at twist ratio S=0.1. This is evidenced by the increase in the Nusselt number where the numerical results show a maximum increase of 137% in the Nusselt number at N=10.5 for the 3-meter pipe whereas this increase reached 9.8% at a twist ratio of S=0.1 compared to the plain tube. Therefore, pipe axial rotation increases the temperature homogeneity by reducing the temperature gap between the pipe wall and the fluid center by reducing the pipe wall temperature thus making the pipe capable of absorbing greater heat amounts at larger lengths while the twisting technique increases the outlet temperature taking into consideration that this is a passive technique that does not consume power.