DSpace collection: 期刊論文

A comprehensively validated three-step global mechanism for high-fidelity simulation of oblique detonation waves in n-decane–air mixtures

Fri, 06 Mar 2026 04:06:32 GMT

title: A comprehensively validated three-step global mechanism for high-fidelity simulation of oblique detonation waves in n-decane–air mixtures abstract: This study presents a new three-step global chemical mechanism for n-decane/air combustion, specifically optimized for efficient simulation of oblique detonation waves (ODWs). The parameters in the global mechanism were specially formulated to enable predictions of essential features in ODWs, including ignition delays, heat release distribution, and detonation velocity with substantially reduced computational cost while preserving fidelity. Comprehensive validations are conducted through extensive numerical simulations, supported by direct comparisons with experimental shock tube data and a skeletal mechanism (Skel40). The proposed mechanism was found to demonstrate predictive robustness across a wide range of combustor conditions, spanning initial temperatures from 600 to 1600 K, pressures from 10 to 1000 kPa, and equivalence ratios from 0.5 to 1.6. As demonstrated in two-dimensional simulations of ODWs, the proposed three-step mechanism predicts key features consistent with those from Skel40 but with a 56-fold improvement in computational efficiency. This new capability provides a reliable and convenient alternative for system-level detonation modeling.

Shock-like Magnetic Enhancements Generated by Kelvin–Helmholtz Instability above Weakly Magnetized Bodies

Fri, 06 Mar 2026 04:06:27 GMT

title: Shock-like Magnetic Enhancements Generated by Kelvin–Helmholtz Instability above Weakly Magnetized Bodies abstract: Shock-like magnetic field structures above weakly magnetized bodies such as the Moon have been reported for more than half a century and represent a key long-standing feature of their solar-wind interactions. Yet their physical origin has remained without a satisfactory explanation, particularly regarding their steepened profiles and high-altitude extension. Here we show that a long-overlooked nonlinear branch of the Kelvin–Helmholtz instability (KHI) naturally produces these localized external magnetic enhancements. Using magnetohydrodynamic simulations constrained by Lunar Prospector (LP) observations, we demonstrate that velocity shear at the solar-wind–crustal-anomaly interface can trigger a KHI whose nonlinear evolution generates outwardpropagating fast-mode shocks that are distinct from the familiar vortex-type KHI waves. These KHI-driven shocks reproduce the LP-observed amplitude and morphology of lunar magnetic enhancements extending hundreds of kilometers above the surface. Two distinct nonlinear KHI regimes, one shock-dominated and one vortex-dominated, together provide a unified framework that explains both the morphological diversity and the wide range of amplitudes of localized magnetic enhancements observed above the Moon and can be applied to other weakly magnetized bodies, revealing a previously unrecognized mechanism governing solar-wind interactions with crustal magnetic anomalies across the solar system.

Power transmission of whistlers in the lunar ionosphere

Wed, 14 Jan 2026 04:05:50 GMT

title: Power transmission of whistlers in the lunar ionosphere abstract: This study investigates the power transmission ratio of lunar whistlers below 10 Hz for the first time by solving full wave equations that incorporate collisional effects for waves propagating upward from the surface to 100 km high in an ionosphere with four dominant ion species at temperatures of 150 K and 400 K in the lunar crustal field environment. The results indicate that increasing wave frequencies lead to decreasing power transmission ratios. This trend is consistent with the satellite observations near the Moon, which predominantly detect peak wave intensities at lower frequencies. Stronger magnetic field intensities and larger angles between the field and the surface led to an increase in power transmission ratios. This finding is consistent with the increased detection of waves in regions with higher field intensities and the more frequent occurrence rate of broadband whistlers linked to larger angles. As the temperature increases, the power transmission ratio increases, consistent with the higher occurrence rates of broadband whistlers at regions with smaller solar zenith angles. Incorporating the Doppler shift effect from solar wind on the observed wave frequency, the selenographic distribution of power transmission ratios exceeding −3 dB within the instrumentally detectable frequency range shows a heightened northern–southern asymmetry, aligning with the established patterns of wave intensities and occurrence rates. The preference to measure harmonic whistlers at lower altitudes can be attributed to the attenuation of the higher-frequency component at higher altitudes. The fact that the intensities of left-hand polarized components are more pronounced can also be interpreted.

Rain-induced vibration energy harvesting using nonlinear plates with piezoelectric integration and power management

Tue, 16 Dec 2025 04:05:25 GMT

title: Rain-induced vibration energy harvesting using nonlinear plates with piezoelectric integration and power management abstract: Vibration energy offers promising potential for renewable energy harvesting, especially in conditions where conventional sources such as solar power may be limited or intermittent. This study proposes a rain energy harvester (REH) that converts the kinetic energy of raindrops into electrical energy using nonlinear thin plates, integrated with piezoelectric elements. Two plate configurations—fully hinged (H-H-H-H) and clamped–hinged–free–hinged (C-H-F-H)—are investigated. Theoretical modeling and simulation results are compared with experimental data, with special attention paid to the role of slapping forces in improving prediction accuracy. A power management system is also introduced to stabilize and regulate the harvested voltage. Results confirm the feasibility of rain-induced energy harvesting, showing potential for application in rain-prone areas and integration with existing infrastructure such as solar panels, tents, or canopies.

Application of machine learning in vibration energy harvesting from rotating machinery using jeffcott rotor model

Tue, 16 Dec 2025 04:05:20 GMT

title: Application of machine learning in vibration energy harvesting from rotating machinery using jeffcott rotor model abstract: This study presents a machine learning-based framework for predicting the electrical output of a vibration energy harvesting system (VEHS) integrated with a Jeffcott rotor model. Vibration induced by rotor imbalance is converted into electrical energy via piezoelectric elements, and the system’s dynamic response is simulated using the fourth-order Runge–Kutta method across varying mass ratios, rotational speeds, and eccentricities. The resulting dataset is validated experimentally with a root-mean-square error below 5%. Three predictive models—Deep Neural Network (DNN), Long Short-Term Memory (LSTM), and eXtreme Gradient Boosting (XGBoost)—are trained and evaluated. While DNN and LSTM yield a high predictive accuracy (R2 > 0.9999), XGBoost achieves comparable accuracy (R2 = 0.9994) with significantly lower computational overhead. The results demonstrate that among the tested models, XGBoost provides the best trade-off between speed and accuracy, achieving R2 > 0.999 while requiring the least training time. These results demonstrate that XGBoost might be particularly suitable for real-time evaluation and edge deployment in rotor-based VEHS, offering a practical balance between speed and precision.

A Bio-Inspired Vibration Energy Harvesting System with Internal Resonance and Slapping Mechanism for Enhanced Low-Frequency Power Generation

Tue, 16 Dec 2025 04:05:13 GMT

title: A Bio-Inspired Vibration Energy Harvesting System with Internal Resonance and Slapping Mechanism for Enhanced Low-Frequency Power Generation abstract: This study presents the development and validation of a bio-inspired vibration energy harvesting system, termed the Bio-Inspired Epiphytic-Plant Slapping Vibration Energy Harvesting System (BIS-VEHS). Inspired by the swaying and slapping behavior of epiphytic plants, the system integrates a circular plate, an elastic beam, a surface-bonded piezoelectric patch (PZT), and a lever-type slapping mechanism to enhance energy conversion. A nonlinear beam model is established and analyzed using the method of multiple scales, through which a 1:3 internal resonance between the first and third bending modes is identified as a key mechanism for promoting energy transfer from higher to lower modes. Time responses are obtained via numerical simulation using the Runge–Kutta method, and the model is validated experimentally. The results confirm that both internal resonance and the slapping mechanism significantly increase the harvested voltage compared with non-resonant and non-slapping configurations. Comparative tests under different excitation modes and plate configurations show good agreement between theory and experiment, with most discrepancies within 10%. These findings demonstrate that the BIS-VEHS is a promising candidate for sustainable low-frequency vibration energy harvesting, particularly for autonomous low-power sensor applications.

Impact of Intermediate Species in Simulating Oblique Detonation with Pre-Vaporized N-Decane/air Mixtures Substituting for Kerosene/Air Mixtures

Tue, 21 Oct 2025 04:05:27 GMT

title: Impact of Intermediate Species in Simulating Oblique Detonation with Pre-Vaporized N-Decane/air Mixtures Substituting for Kerosene/Air Mixtures abstract: A renewed two-step n-decane mechanism is presented to improve reliable and robust simulation results, substituting for kerosene. This mechanism demonstrates that effective control of ignition delay time and heat release, based on the Chapman – Jouguet condition, enables successful simulation of oblique detonation waves. Chain reactions influence the overall reaction heat and explosion temperature, especially in simplified mechanisms with few steps. Therefore, carbon monoxide (CO) generation is crucial for balancing the overall reaction heat and reducing species sensitivity to pressure, a factor previously not discussed in simplified models. The computational time for solving detailed chemical kinetics increases exponentially with species count, driving the pursuit for further reduction in kinetic mechanism size. The sensitive interaction between density and temperature during the fuel/air mixture explosion process affects initiation zone formation and cellular structure. Analyzing the distribution of CO can provide insights into structural details. The study considers applying the Rankine – Hugoniot curve to confirm detonation speeds, temperatures, and kinetic energy changes induced by chemical reactions.

High-Fidelity Simulation of CJ-ODW Initiation and Wave Interactions in JP-10/Air Mixtures Using a Robust Combustion Modelling Method

Tue, 21 Oct 2025 04:05:19 GMT

title: High-Fidelity Simulation of CJ-ODW Initiation and Wave Interactions in JP-10/Air Mixtures Using a Robust Combustion Modelling Method abstract: Jet Propellant 10 (JP-10), a high-energy-density fuel with a complex molecular structure, is widely utilised in advanced propulsion systems owing to its favourable volumetric energy content and thermal stability. This study employs high-fidelity numerical simulations to examine ODWs formed in JP-10/air mixtures, utilising a skeletal mechanism, a reduced mechanism, and a three-step model to analyze shock-induced ignition, heat release rates, and wave interactions. Key features, including the Chapman – Jouguet ODW (CJ-ODW), are investigated to clarify CJ-ODW initiation characteristics. Although CJ-ODWs exhibit lower strength than conventional ODWs, they still achieve the critical CJ conditions for initiation. Moreover, interactions between the first transverse wave and the second oblique shock wave distort the CJ plane, while combustion waves continue heating the reactive mixture. JP-10’s endothermic behaviour during initial breakdown strongly influences this process, creating a characteristic V-shaped temperature gap and altering the reaction front

Enhancing rotor performance of a small-scale drag-type vertical-axis wind turbine with vertical guide vanes through Taguchi optimization

Fri, 19 Sep 2025 04:06:30 GMT

title: Enhancing rotor performance of a small-scale drag-type vertical-axis wind turbine with vertical guide vanes through Taguchi optimization abstract: This study used FlowVision, a commercial CFD software, to simulate the operation of a small-scale drag-type vertical-axis wind turbine with vertical guide vanes. The simulations were conducted ranging from 4 m/s to 8 m/s, which reflects typical conditions for small-scale wind turbines. The rotor blades and guide vanes were optimized using the Taguchi method to improve the rotor performance. In the Taguchi optimization, the control factors investigated were the blade diameter, number of blades, and number of guide vanes. How these factors affect the rotor’s performance was discussed. The results indicated that the number of guide vanes most significantly influenced the rotor rotation of the investigated control factors. The blades and the guide vanes exhibited significant interactions. The guide vanes functioned as flow augmenters, directing and accelerating incoming airflow into the rotor. They also shield incoming airflow to prevent it from affecting the returning blades. However, using an excessive number of guide vanes may result in low rotor speed. The optimum wind turbine configuration was 8 blades, blades with D/Dr = 0.25 in diameter, and 6 guide vanes. The maximum power coefficient CP,max for the optimum configuration was 55.56% higher than that for the worst configuration.

Impact of Intermediate Species in Simulating Oblique Detonation with Pre-Vaporized N-Decane/air Mixtures Substituting for Kerosene/Air Mixtures

Thu, 20 Mar 2025 01:30:05 GMT

Development of a Less Dissipative Interface Variable Reconstruction to Solve the Euler Equations by Q Learning Method

Thu, 20 Mar 2025 01:30:01 GMT

title: Development of a Less Dissipative Interface Variable Reconstruction to Solve the Euler Equations by Q Learning Method abstract: In this study, we propose a blend of the average of THINC-EM and MUSCL (ATM) methods based on the AUSMD scheme for solving detonation wave problems. It is well known that the simulation of the detonation problems can produce incorrect shock information or strong spurious due to the stiff source term. Accurate simulation of detonation problems plays a crucial role in the design of detonation engines. The proposed ATM method combines the MUSCL and THINC-EM methods with different weighting functions, the optimized parameters of which are determined by the Q-learning method in order to accurately capture detonation waves, shock waves, and expansion fans. To validate the proposed numerical method, one and two-dimensional shock tube and the detonation tube and nozzles are chosen as benchmark test cases. Our numerical results show that the proposed the ATM type AUSMD scheme has great potential for handling more complex detonation problems and pulse detonation engine flow problems.

A Magneto-Electric Device for Fluid Pipelines with Vibration Damping and Vibration Energy Harvesting

Thu, 20 Mar 2025 01:29:58 GMT

title: A Magneto-Electric Device for Fluid Pipelines with Vibration Damping and Vibration Energy Harvesting abstract: This study introduces an innovative energy harvesting system designed for industrial applications such as fluid pipelines, air conditioning ducts, sewer systems, and subsea oil pipelines. The system integrates magneto-electric flow coupling and utilizes a dynamic vibration absorber (DVA) to mitigate the vibrations induced by fluid flow while simultaneously harvesting energy through magnetic dipole–dipole interactions in a vibration energy harvester (VEH). The theoretical models, based on Hamilton’s Principle and the Biot–Savart Law, were validated through comprehensive experiments. The results indicate the superior performance of the small-magnet system over the largemagnet system in both damping and power generation. The study analyzed the frequency response and energy conversion efficiency across different parameters, including the DVA mass, spring constant, and placement location. The experimental findings demonstrated significant vibration reduction and increased voltage output, validating the theoretical model. This research offers new avenues for energy harvesting systems in pipeline infrastructures, potentially enhancing energy efficiency and structural integrity.

Application of Deep Learning Models to Predict Panel Flutter in Aerospace Structures

Thu, 20 Mar 2025 01:29:55 GMT

title: Application of Deep Learning Models to Predict Panel Flutter in Aerospace Structures abstract: This study investigates the application of deep learning models—specifically Deep Neural Networks (DNN), Long Short-Term Memory (LSTM), and Long Short-Term Memory Neural Networks (LSTM-NN)—to predict panel flutter in aerospace structures. The goal is to improve the accuracy and efficiency of predicting aeroelastic behaviors under various flight conditions. Utilizing a supersonic flat plate as the main structure, the research integrates various flight conditions into the aeroelastic equation. The resulting structural vibration data create a large-scale database for training the models. The dataset, divided into training, validation, and test sets, includes input features such as panel aspect ratio, Mach number, air density, and decay rate. The study highlights the importance of selecting appropriate hidden layers, epochs, and neurons to avoid overfitting. While DNN, LSTM, and LSTM-NN all showed improved training with more neurons and layers, excessive numbers beyond a certain point led to diminished accuracy and overfitting. Performance-wise, the LSTM-NN model achieved the highest accuracy in classification tasks, effectively capturing sequential features and enhancing classification precision. Conversely, LSTM excelled in regression tasks, adeptly handling long-term dependencies and complex non-linear relationships, making it ideal for predicting flutter Mach numbers. Despite LSTM’s higher accuracy, it required longer training times due to increased computational complexity, necessitating a balance between accuracy and training duration. The findings demonstrate that deep learning, particularly LSTM-NN, is highly effective in predicting panel flutter, showcasing its potential for broader aerospace engineering applications. By optimizing model architecture and training processes, deep learning models can achieve high accuracy in predicting critical aeroelastic phenomena, contributing to safer and more efficient aerospace designs.

Utilizing the Taguchi Method to Optimize Rotor Blade Geometry for Improved Power Output in Ducted Micro Horizontal-Axis Wind Turbines

Wed, 31 Jul 2024 04:09:56 GMT

title: Utilizing the Taguchi Method to Optimize Rotor Blade Geometry for Improved Power Output in Ducted Micro Horizontal-Axis Wind Turbines abstract: This numerical study utilized the Taguchi method to systematically optimize the blade geometry of a ducted micro horizontal-axis wind turbine (HAWT) for moving vehicles to enhance the output power coefficient. Three geometric parameters of the rotor, namely, the number of blades, rotor solidity, and blade pitch angle, were investigated. The optimum parameter design includes eight blades, rotor solidity of 60%, and a pitch angle of 30°, where the blade pitch angle had the most significant effect on the rotor performance. This result confirms that high rotor solidity is more suitable for micro HAWT. The CP,max value achieved with the optimum geometry was 0.432, which was 39.4% higher than that achieved with the worst blade geometry. The aerodynamic characteristics of this wind turbine were also investigated. Compared with the worst blade geometry, the rotor with the optimum blade geometry drew more airflow into the duct and exhibited a higher CP,max due to a greater pressure difference between the windward and leeward sides of the blades. The optimum blade geometry achieved a CT,max of 0.43, which was 38.7% higher than the worst blade geometry. The investigated untwisted blades exhibited low torque near their tips; therefore, the use of twisted blades is recommended for further increasing the torque generated at the blade tip and thus the turbine's output power. This study facilitates insight into blade geometry effects on rotor performance and helps improve wind energy efficiency, contributing to sustainable development goals (SDGs) like SDG 7 (affordable and clean energy).

Development of a Lagrangian–Eulerian approach-based five-equation two-fluid model for simulation of multiphase reactive flows

Wed, 10 Jul 2024 04:05:15 GMT

title: Development of a Lagrangian–Eulerian approach-based five-equation two-fluid model for simulation of multiphase reactive flows abstract: The purpose of the current study is to develop numerical capability to analyze the flow structures of the scramjet engine in which many complex physical phenomena are involved, such as shock waves, breakup, atomization, and chemical reactions. To understand these complex physical phenomena, we first proposed the five-equation multiphase flow model coupling with the Lagrangian method to reproduce the process of fuel atomization and evaporation in a flow over a side jet problem. Shock waves, recirculation zones, and breakup processes of droplet particles were well captured in the computational works. It was shown that the five-equation multiphase model achieved better resolution of the shock-capturing comparing with the single-phase Navier–Stokes equation coupling with the Lagrangian approach. In addition, the single-step reaction model was performed with the current five-equation multiphase model to simulate the detonative cell in the detonation flow problem. The detonation waves under various operating conditions were discussed. Finally, a preliminary simulation is applied to the flow phenomena through DLR scramjet. The current works have achieved satisfactory agreement compared to the experimental data no matter in reacting flow case or nonreacting flow case.

Bulge formation of liquid film at the trailing edge: Scaling laws and particle removal assessment

Tue, 12 Mar 2024 04:05:48 GMT

title: Bulge formation of liquid film at the trailing edge: Scaling laws and particle removal assessment abstract: We present numerical simulations and laboratory experiments to study bulge formation at the trailing edge of an inclined surface and its inhibitory effect on particle removal during surface cleaning. We investigate the spatial variations in liquid films near the trailing edge and find that the Weber number can be used as a dominant parameter to determine bulge occurrence over the trailing edge. We divide the film region near the trailing edge at which the bulge occurs into two: the region where the surface linearly grows and the surface tension is negligible, and the region where the surface tension force becomes dominant and the film surface is curved. In the investigated cases in which the Reynolds number is O(10) or greater, the viscous forces are negligible, which allows for the derivation of the scaling laws for the length of the two regions according to the condition that the bulge height scales with the capillary length. In the resulting scaling law, the length scales depend on the Froude number and the inclination angle. The proposed scaling law allows for the prediction of the bulge shape and the prediction agrees with the simulation results, particularly at low Weber numbers (i.e., We < 0.5). Moreover, we construct a particle removability map to assess the removal of particles of different sizes at specific locations on the substrate. The map reveals a reduction of the removability for small-size particles or particles located in the bulge.

Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling

Tue, 12 Mar 2024 04:05:43 GMT

title: Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling abstract: This paper presents a single-pressure-field two-fluid model with finite-volume discretization to solve the equations of motion of compressible multiphase flows. To capture the discontinuities caused by shock waves and fluid interfaces, we propose a generalized discontinuity sharpening technique that combines the conventional monotonic upstream scheme for conservation law (MUSCL) and tangent of hyperbola interface capturing (THINC) schemes. In addition, a slope ratio-weighted parameter, ζ, is used to control the proportion of values reconstructed by MUSCL and THINC, and we show that the present method can retain sharp interfaces when the value of the parameter β in the THINC scheme is set ranging from 1.6 to 3.0. Fluxes across various interfaces are evaluated using a hybrid AUSMD-type flux algorithm, where the mass flux and pressure induced on the cell faces are calculated using an approximate Riemann solver. The accuracy and robustness of the proposed method are validated by solving a series of one- and two-dimensional single-phase flows. Furthermore, complex wave patterns arising from two-dimensional shock bubble/water-column interactions are examined, which indicate that compared with the existing schemes applied to two-fluid modeling, the proposed scheme significantly sharpens the interfaces and captures more details of the flow features. Finally, simulations of a three-dimensional example of the liquid jet crossflow are conducted. The proposed scheme shows more details of the fluid interface, including the interfacial instabilities on the windward side of the liquid jet and droplet formation due to the breakup phenomenon in the downstream of the crossflow, than the existing schemes.

An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions

Wed, 06 Mar 2024 04:05:15 GMT

title: An Experimental and Numerical Study on the Cavitation and Spray Characteristics of Micro-Orifice Injectors under Low-Pressure Conditions abstract: A fuel injector plays a crucial role in an internal combustion engine, and the occurrence of cavitation inside the injector may affect the engine’s spray characteristics, atomization characteristics, and combustion efficiency. Most literature investigated the cavitation characteristics for a micro-orifice injector under high injection pressure (P_inj) or a large-orifice injector under low P_inj, i.e., under high Reynolds number (Re). In this study, a micro-turbojet engine with a 0.3-mm-diameter micro-orifice fuel injector was developed for operation under low P_inj. The cavitation and spray characteristics of water and kerosene fuel in this injector were experimentally and numerically investigated. The results indicated that the water and kerosene also exhibited no cavitation, cavitation, super-cavitation, and hydraulic flip phenomena. However, the discharged jet was unaffected by the internal flows, and the jet angles remained approximately constant, implying that the cavitation in micro-orifice injectors under low Re is less important than that under high Re. Since the cavitation in micro-orifice injectors under low Re is not beneficial to the atomization and spray, the selection of geometry of the micro-injector is important. A micro-orifice injector with a small length-to-diameter (L/D) ratio of the injector nozzle has a rounded-edge inlet and a small taped angle due to the limitation of electrical discharge machining, which results in a high discharge coefficient and increases the difficulty of hydraulic flip. Thus, an L/D ratio of 3 is recommended for the injector of the developed micro-turbojet engine. This study provides some insights for the design of micro-turbojet engines.

Analysis of a wind-driven power generation system with root slapping mechanism

Fri, 01 Mar 2024 04:05:44 GMT

title: Analysis of a wind-driven power generation system with root slapping mechanism abstract: This study introduces a groundbreaking slap-type Vibration Energy Harvesting (VEH) system, leveraging a rotating shaft with magnets to induce vibrations in an adjacent elastic steel sheet through magnetic repulsion. This unique design causes the elastic sheet to vibrate, initiating the oscillation of a seesaw-type rigid plate lever. The lever then slaps a piezoelectric patch (PZT) at the elastic steel sheet’s root, converting vibrations into electrical energy. Notably, the design enables the PZT to withstand deformation and flapping forces simultaneously, enhancing power conversion efficiency. The driving force for the rotating shaft is harnessed from the downstream flow field generated by moving objects like rotorcraft, fixed-wing aircraft, motorcycles, and bicycles. Beyond conventional vibration energy harvesting, this design taps into additional electric energy generated by the PZT’s slapping force. This study includes mathematical modeling of nonlinear elastic beams, utilizing the Method of Multiple Scales (MOMS) for in-depth vibration mode analysis. Experimental validation ensures the convergence of theory and practice, confirming the feasibility and superior voltage generation efficiency of this slap-type VEH concept compared to traditional VEH systems.

Energy harvesting analysis of the magneto-electric and fluid-structure interaction parametric excited system

Wed, 25 Oct 2023 04:05:27 GMT

title: Energy harvesting analysis of the magneto-electric and fluid-structure interaction parametric excited system abstract: This research proposes an innovative design of a fluid-solid coupling vibration energy harvesting system (VEH system) that includes a downstream waterwheel driven by the flow field, which, in turn, drives gears and connecting rods to rotate a wheel equipped with magnets to generate electricity by changing the magnetic field. A piezoelectric patch (PZT) is installed upstream of the pipeline with a magnet attached to it. The repulsive force between the magnet on the wheel and the magnet on the PZT generates additional force while also creating vibration through fluid-solid coupling of the pipeline. The study derives a theoretical model of the nonlinear vibrating beam and couples it with the piezoelectric and magneto-electric equations to simulate the vibration of the fixed-fixed elastic pipe. The method of multiple scales (MOMS), fixed points plots, phase plots, and Poincar´e maps are employed to verify the theoretically predicted parametric excitation properties of the system. The study uses the Biot-Savart Law to calculate the theoretical magnetic force and combines it with the fluid-conveying nonlinear beam and the PZT to create a magnetoelectric coupling fluid pipeline vibration energy harvesting model. The study conducts a simple experiment to verify the feasibility of the theoretical model and demonstrates that the repulsive force of the magnet significantly enhances the electric generation benefit of the system. Regardless of whether the PZT is located in the curved or flat area (straight part) of the nonlinear beam, the addition of magnets to the system significantly increases voltage generation efficiency by more than 190 % when compared to systems without magnets.

Predicting Multiple Numerical Solutions to the Duffing Equation Using Machine Learning

Wed, 25 Oct 2023 04:05:23 GMT

title: Predicting Multiple Numerical Solutions to the Duffing Equation Using Machine Learning abstract: This study addresses the problem of predicting convergence outcomes in the Duffing equation, a nonlinear second-order differential equation. The Duffing equation exhibits intriguing behavior in both undamped free vibration and forced vibration with damping, making it a subject of significant interest. In undamped free vibration, the convergence result oscillates randomly between 1 and −1, contingent upon initial conditions. For forced vibration with damping, multiple variables, including initial conditions and external forces, influence the vibration patterns, leading to diverse outcomes. To tackle this complex problem, we employ the fourth-order Runge–Kutta method to gather convergence results for both scenarios. Our approach leverages machine learning techniques, specifically the Long Short-Term Memory (LSTM) model and the LSTM-Neural Network (LSTM-NN) hybrid model. The LSTM-NN model, featuring additional hidden layers of neurons, offers enhanced predictive capabilities, achieving an impressive 98% accuracy on binary datasets. However, when predicting multiple solutions, the traditional LSTM method excels. The research encompasses three critical stages: data preprocessing, model training, and verification. Our findings demonstrate that while the LSTM-NN model performs exceptionally well in predicting binary outcomes, the LSTM model surpasses it in predicting multiple solutions.

Enhancing Electrical Generation Efficiency through Parametrical Excitation and Slapping Force in Nonlinear Elastic Beams for Vibration Energy Harvesting

Wed, 25 Oct 2023 04:05:19 GMT

title: Enhancing Electrical Generation Efficiency through Parametrical Excitation and Slapping Force in Nonlinear Elastic Beams for Vibration Energy Harvesting abstract: This study aims to enhance conventional vibration energy harvesting systems (VEHs) by repositioning the piezoelectric patch (PZT) in the middle of a fixed–fixed elastic steel sheet instead of the root, as is commonly the case. The system is subjected to an axial simple harmonic force at one end to induce transversal vibration and deformation. To further improve power conversion, a baffle is strategically installed at the point of maximum deflection, introducing a slapping force to augment electrical energy harvesting. Employing the theory of nonlinear beams, the equation of motion for this nonlinear elastic beam is derived, and the method of multiple scales (MOMS) is used to analyze the phenomenon of parametric excitation. This study demonstrates through experiments and theoretical analysis that the second mode yields better power generation benefits than the first mode. Additionally, the voltage generation benefits of the enhanced system with the added baffle (slapping force) surpass those of traditional VEH systems. Overall, the proposed model proves feasible and holds promising potential for efficient vibration energy harvesting applications in various industrial sectors.

Experimental study on air extraction performance of novel rooftop natural ventilators

Mon, 04 Sep 2023 04:05:10 GMT

title: Experimental study on air extraction performance of novel rooftop natural ventilators abstract: The air extraction performance of novel rooftop natural ventilators was experimentally investigated and compared to the conventional turbine ventilator. The newly developed ventilator integrates a vertical-axis wind turbine with a static ventilator, where the wind turbine, equipped with 8 C-type rotors and 6 rotor guide vanes, serves to drive the rotation of the static ventilator. The static ventilator is an exhaust cowl with curved guide vanes inside. The wind turbine, including 8 C-rotors and 6 flat guide vanes, is 10 cm in height with a diameter of 21 cm. The dimensions of static ventilation are 7 cm in height, and 26 cm and 21 cm in bottom and top diameters, respectively, with curved guide vanes inside. Various heights of guide vanes (0.5 cm and 3 cm) and numbers of guide vanes (0, 6, and 12) were investigated. An open wind tunnel system was used to simulate the condition where the wind blows over the rooftop ventilator. The ventilator air extraction rates were determined using the mean air velocities, measured using a hot-wire anemometer at an open slot in a ventilation pipe connected to the ventilator. The results indicated that the rotating and non-rotating novel ventilators exhibited superior air extraction rates at most tested wind speeds compared to the rotating conventional turbine ventilator. The curved guide vanes inside the static ventilator played the most important role in the air extraction rate. This study suggests that a static ventilator with an adequate guide-vane design may be more suitable for rooftop ventilation than a conventional turbine ventilator.

Simulation of the effects of dilution gas for the formation of CJ plane during the oblique detonation

Wed, 26 Jul 2023 04:05:18 GMT

title: Simulation of the effects of dilution gas for the formation of CJ plane during the oblique detonation abstract: This study aims to properly simulate transition patterns (the initiation structure between oblique shock wave and oblique detonation wave) to better understand the performance of oblique detonation wave engines under practical operating conditions. The former two cases are observed in a stoichiometric hydrogen-air mixture, the oblique detonation originates from the impact shock region where the pre-combustion hot gas near the wall interacts with the oblique shocks. In the second case, different proportions of dilution gas are tested. It is noted that a thermal choking condition due to strong compression waves during a sufficient duration results in the turning transverse waves and the inhomogeneous Chapman–Jouguet (CJ) plane. Therefore, the deformed CJ plane, the nonuniform combustion structures, and the overheated oblique detonation wave (ODW) with the excessive pressure rise are shown. Finally, it is concluded that the chemical equilibrium shift and the stability of ODW in the combustor are significantly affected by the expanding flow of dilution gases.

Accurate simulation of discontinuities induced by detonations

Wed, 26 Jul 2023 04:05:15 GMT

title: Accurate simulation of discontinuities induced by detonations abstract: In this study, we propose the HMSTH (Hybrid MUSCL with THINC-EM) [6, 11] type AUSMD [5] flux scheme to solve the stiff Euler equations to achieve an accurate simulation of the detonation waves. When the detonation wave propagates downstream after being ignited in the combustion, it produces a supersonic wave through the nozzle to achieve the thrust cycle called the Pulse Detonation Engine (PDE). [10] The PDE has a great advantage in energy efficiency according to many studies, so its development is important in the future. To overcome the applicant issue making the PDE work smoothly. We work to build an appropriate numerical method. To verify it, one and two-dimensional shock tube problems and the PDE combustion are chosen as the benchmark cases. The numerical results show that the proposed HMSTH-type AUSMD scheme has great potential in simulating further complicated detonation waves and PDE problems.

Development of a Lagrangian–Eulerian approach-based five-equation two-fluid model for simulation of multiphase reactive flows

Wed, 26 Jul 2023 04:05:11 GMT

An assessment of whistlers generated from tree-like gigantic jets

Fri, 28 Apr 2023 09:22:09 GMT

title: An assessment of whistlers generated from tree-like gigantic jets abstract: The characteristics of whistlers generated from an observed gigantic jet (GJ) are assessed and possible locations to detect these waves are deduced. Modeling is based on disturbances in the electric field, as measured by NCKU ELF/VLF station, associated with a tree-like GJ event over typhoon Lionrock. The power spectrum of GJ differs from that of common cloud-to-ground lightning; therefore, this study also investigates differences between GJ-generated signals and common lightning-generated whistlers. Detectability is evaluated by considering the absorption of amplitudes resulted from collisional damping associated with the propagation of generated waves. Our results show that in the ionosphere the waves are subject to greater attenuation as the frequency increases; however, a reversal occurs at lower frequencies of a few hundred Hz. The calculated waveforms show that the whistlers generated by the tree-like GJs are preceded by small fluctuations at high frequencies generated by the initiating lightning. Overall, the amplitudes increase with the passage of time; however, they are more randomly-distributed over time for whistlers generated from common lightning. The amplitudes decrease again when lower-frequency components below a few hundred Hz arrive. The amplitudes drop to the order of 1 mV/m as the waves propagate in the ionosphere, which puts them within a range detectable by the instruments on most satellites. Based on the locations of tree-like GJ events observed by ISUAL (Imager of Sprites and Upper Atmospheric Lightning), regions of the western and southeastern Pacific Ocean, as well as northern Africa region are the most likely locations to detect these whistlers.

Numerical study of optimum parameter design for film cooling effectiveness by Taguchi method

Fri, 28 Apr 2023 09:22:03 GMT

title: Numerical study of optimum parameter design for film cooling effectiveness by Taguchi method abstract: The present numerical study investigated a novel film cooling scheme that combines a cylindrical hole with an upstream Barchan-dune ramp and a triangular tab over the hole. Simulations revealed that this arrangement can induce an additional anti-kidney vortex pair on the outside of the original primary kidney vortices to suppress the penetration of the high-temperature mainstream by the cooling flow, increasing cooling effectiveness. Compared with schemes employing only a triangular tab or a Barchan-dune ramp, the novel film cooling scheme achieved superior cooling performance. An optimum parameter design is determined through the Taguchi method. Three parameters were investigated, namely, the Barchan-dune-shaped ramp height, triangular tab length, and blowing ratio, under various incoming temperatures. Analysis of variance revealed that the blowing ratio has the greatest influence on cooling effectiveness. An average cooling effectiveness of 34.1% was achieved by the optimum parameter design.

Analysis of double inverted flag energy harvesting system in pipe flow

Fri, 28 Apr 2023 09:22:00 GMT

title: Analysis of double inverted flag energy harvesting system in pipe flow abstract: This technical note numerically and experimentally studies a vibration energy harvester (VEH) consisting of a set of two parallel elastic steel sheets (ESSs) and piezoelectric patches (PZTs) in pipe flow. The roots of the elastic steel sheets are fixed on the base with the PZTs to form a double inverted flag vibration energy harvesting system (DIF-VEHS). In this note, a semi-circular receiving device (receiver) was added to the free end of the elastic steel, and a cylinder was installed upstream to generate a periodic oscillating flow field in the pipeline to obtain better electric energy generation efficiency. This study reveals the effect of different factors on the energy harvesting system, such as the distance between the ESSs, the diameter of the cylinder, etc. This study uses ANSYS software to simulate the fluid–structure interaction vibration of ESSs to determine the feasibility of this design. An experimental setup is then implemented to find the most effective combination of factors for the system. The results of this study show that with all parameters configured properly, the electric energy generation reaches a maximum average value of 1.6657 V per minute. In the future, such devices could be installed in sewers, pipes or rivers, allowing the flow energy of the fluid to be recycled to generate more energy.

Analysis of a Clapping Vibration Energy Harvesting System in a Rotating Magnetic Field

Fri, 28 Apr 2023 09:21:56 GMT

title: Analysis of a Clapping Vibration Energy Harvesting System in a Rotating Magnetic Field abstract: This technical note proposes a clapping vibration energy harvesting system (CVEH system) installed in a rotating system. This device includes a rotating wheel, a drive shaft that rotates the wheel, and a double elastic steel sheet fixed on the drive shaft. One of the free ends of the steel is fixed with a magnet, and the free end of the other elastic steel is fixed with a PZT patch. We also install an array of magnets on the periphery (rim) of the wheel. The rim magnets repulse the magnet on the elastic steel sheet of the transmission shaft, causing the elastic steel to oscillate periodically, and slap the piezoelectric patch installed on the other elastic steel sheet to generate electricity. In this study, the authors’ previous study on the voltage output was improved, and the accurate nonlinear natural frequency of the elastic steel was obtained by the dimensional analysis method. By adjusting the rotation speed of the wheel, the precise frequency was controlled to accurately excite the energy harvesting system and obtain the best output voltage. A simple experiment was also performed to correlate with the theoretical model. The voltage and power output efficiencies of the nonlinear frequency to linear frequency excitation of the CVEH system can reach 15.7% and 33.5%, respectively. This study confirms that the clapping VEH system has practical power generation benefits, and verifies that nonlinear frequencies are more effective than linear frequencies to excite the CVEH system to generate electricity.

Vibration reduction of continuous moving loads on a nonlinear simple beam resting on an elastic foundation

Fri, 28 Apr 2023 09:21:52 GMT

title: Vibration reduction of continuous moving loads on a nonlinear simple beam resting on an elastic foundation abstract: This technical note investigates a hinged-hinged nonlinear Euler-Bernoulli beam resting on an elastic foundation subjects to moving loads. The method of multiple scales (MOMS) is employed to analyze this nonlinear beam model. The fixed points plots are made to identify the system’s internal resonance. The frequency ratio plot is proposed to predict the system internal resonance conditions. This study improved the author’s earlier work for a wider range of prediction on internal resonance conditions. The continuous concentrated moving loads are applied to this nonlinear beam model. The dynamic vibration absorber (DVA) is attached on the beam to reduce vibration and prevent internal resonance. The mass, spring constant and location of the DVA are studied to obtain the best damping effect on the nonlinear beam with moving loads. The results are verified by numerical results and ANSYS simulations.

Accurate hybrid AUSMD type flux algorithm with generalized discontinuity sharpening reconstruction for two-fluid modeling

Thu, 10 Mar 2022 04:11:24 GMT

Variation of Osculating Orbit Elements Using Low-Thrust Photonic Laser Propulsion in the Two-Body Problem

Tue, 15 Feb 2022 04:11:47 GMT

title: Variation of Osculating Orbit Elements Using Low-Thrust Photonic Laser Propulsion in the Two-Body Problem abstract: This study investigated the variation of the osculating orbit elements of a spacecraft propelled by photonic laser propulsion (PLP) under the two-body problem assumption. The PLP thrusting system can produce continuous and constant thrust. This paper first reviewed its basics and then studied its influences on the variation of osculating orbit elements given a small PLP thrust. Gauss’s equations, perturbation theory, and normalization were introduced to investigate this problem. Our work approached the problem by studying the influences of small planar and out-of-plane PLP thrusts, respectively. Bounds on the variation of orbit elements were derived, and a sufficient condition that traps the mission spacecraft in the vicinity of the mother ship was also found. Numerical simulations are also presented to verify our results, including the bounds and the sufficient conditions. The results obtained in this paper are directly applicable to the usage of PLP thrust, a new type of thrusting system, in the future, and are potentially helpful to various space missions, especially interplanetary travel.

Flutter speed prediction by using deep learning

Fri, 19 Nov 2021 04:10:20 GMT

title: Flutter speed prediction by using deep learning abstract: Deep learning technology has been widely used in various field in recent years. This study intends to use deep learning algorithms to analyze the aeroelastic phenomenon and compare the differences between Deep Neural Network (DNN) and Long Short-term Memory (LSTM) applied on the flutter speed prediction. In this present work, DNN and LSTM are used to address complex aeroelastic systems by superimposing multi-layer Artificial Neural Network. Under such an architecture, the neurons in neural network can extract features from various flight data. Instead of time-consuming high-fidelity computational fluid dynamics (CFD) method, this study uses the K method to build the aeroelastic flutter speed big data for different flight conditions. The flutter speeds for various flight conditions are predicted by the deep learning methods and verified by the K method. The detailed physical meaning of aerodynamics and aeroelasticity of the prediction results are studied. The LSTM model has a cyclic architecture, which enables it to store information and update it with the latest information at the same time. Although the training of the model is more time-consuming than DNN, this method can increase the memory space. The results of this work show that the LSTM model established in this study can provide more accurate flutter speed prediction than the DNN algorithm.

Drag Reduction Optimization for Hypersonic Blunt Body with Aerospikes

Thu, 11 Nov 2021 04:10:41 GMT

title: Drag Reduction Optimization for Hypersonic Blunt Body with Aerospikes abstract: Orion MPCV (Multi-Purpose Crew Vehicle) is one of the state-of-the-art manned space vehicles nowadays which will engage in the deep space missions in the near future. Besides, Orion spacecraft is a kind of blunt body, thus the phenomena concerning the high levels of pressure drag and aerodynamic heating are experienced during the atmospheric re-entry process. Pressure drag and aeroheating stirred by the shock wave is the main challenge of hypersonic flight. Therefore, both aerospikes and aerodisks can be efficiently utilised as the approach for drag reduction. In this thesis, we would research the effect of different geometric shapes of aerospikes with different disk gap widths on drag reduction. Accordingly, we implemented a series of Computational Fluid Dynamics (CFD) simulation work to investigate the behaviour as to hypersonic flow over aerospiked blunt bodies. Moreover, the drag reduction efficiency of spiked blunt bodies would be acquired via Kriging method. For the models we studied, we found that the drag on the spiked blunt bodies is much lower than the spike off one. The drag reduction efficiency especially would be predominated by the scale of recirculation zone, which increases as both the spike length and the gap size of aerodisk increase.

An Investigation of Civil Aircraft Performance Parameters via the Hilbert-Huang Transform Method

Thu, 11 Nov 2021 04:10:38 GMT

title: An Investigation of Civil Aircraft Performance Parameters via the Hilbert-Huang Transform Method abstract: Flight Operational Quality Assurance (FOQA) flight data and flapping wings results were examined by the aid of Hilbert-Huang Transform (HHT) method. The purpose of applying HHT is to find the hidden frequency-based (Intrinsic Mode Functions) IMF patterns from the origin signal. From flight data of three normal flights and one abnormal flight, a case of engine No.1 failure during cruise was extracted from a twin-engine turboprop airliner. Several important alignment results of different flight phases were found in the parameter of this flight indicates the existence of potential risk factors before the event flight. The alignment results of FOQA engine failure during operation in flight are vague, and are mainly due to the fact that engine failure usually appears to be a sudden change within milliseconds. The sampling rate of engine related parameters was 1 Hz, thus is considered as the congenital missing of data that leads to lacking of precise measures. For FOQA data alignments, the pattern finding probability is approximately 55.13%. An empirical system and procedure for pattern searching is needed to handle a population of data. The hidden patterns were found in both cases and the concept of data homology was illustrated.

Analysis of double elastic steel wind driven magneto-electric vibration energy harvesting system

Tue, 09 Nov 2021 04:10:19 GMT

title: Analysis of double elastic steel wind driven magneto-electric vibration energy harvesting system abstract: This research proposes an energy harvesting system that collects the downward airflow from a helicopter or a multi-axis unmanned rotary-wing aircraft and uses this wind force to drive the magnet to rotate, generating repulsive force, which causes the double elastic steel system to slap each other and vibrate periodically in order to generate more electricity than the traditional energy harvesting system. The design concept of the vibration mechanism in this study is to allow the elastic steel carrying the magnet to slap another elastic steel carrying the piezoelectric patch to form a set of double elastic steel vibration energy harvesting (DES VEH) systems. The theoretical DES VEH mechanism of this research is composed of a pair of cantilever beams, with magnets attached to the free end of one beam, and PZT attached to the other beam. This study analyzes the single beam system first. The MOMS method is applied to analyze the frequency response of this nonlinear system theoretically, then combines the piezoelectric patch and the magneto-electric coupling device with this nonlinear elastic beam to analyze the benefits of the system’s converted electrical energy. In the theoretical study of the DES VEH system, the slapping force between the two elastic beams was considered as a concentrated load on each of the beams. Furthermore, both SES and DES VEH systems are studied and correlated. Finally, the experimental data and theoretical results are compared to verify the feasibility and correctness of the theory. It is proven that this DES VEH system can not only obtain the electric energy from the traditional SES VEH system but also obtain the extra electric energy of the steel vibration subjected to the slapping force, which generates optimal power to the greatest extent.

Transverse vibration energy harvesting of double elastic steel

Thu, 07 Oct 2021 04:10:19 GMT

title: Transverse vibration energy harvesting of double elastic steel abstract: This study uses the piezoelectric technology to collect vibration energy from the fixed-fixed nonlinear elastic beams attached with the piezo-patch between the two ends. Both single elastic steel sheet (SESS) and double elastic steel sheet (DESS) systems are investigated and correlated. To simulate the power generation of the vibration energy harvester (VEH) of both the SESS and the DESS in different engineering elements, the simple harmonic external force generated by a shaker at the location of the piezo-patch is used as the source. With this, more vibration converted electric energy is derived from the transverse deformation and flapping from the DESS than the SESS beam. The equation of a nonlinear Euler-Bernoulli beam is coupled with the electric energy equation of the piezo-patch to simulate the SESS VEH system. The flapping force from the DESS VEH system can be considered the concentrated external load applied on the SESS beam model. The method of multiple scales (MOMS) is employed to analyze this nonlinear problem. The fixed points plots and the numerical results confirm this theory presented for the two beam systems, which can be used for evaluating similar engineering systems. Experiments are also performed in this study. The Taguchi method is used to analyze the optimum locations of the shaker and piezo-patch, as well as the confidence level of the factors. The method of nonlinear analysis presented in this study demonstrates its accuracy compared with the linear case. The transverse DESS VEH model proposed is proved to be feasible and more effective than the SESS system.

General Solution to the Spectator-First Tantalizer Problem

Fri, 11 Jun 2021 04:11:53 GMT

title: General Solution to the Spectator-First Tantalizer Problem abstract: This paper investigates a topic inspired by a magic trick called the “Tantalizer”, which is a card game resembling the well-known Josephus Problem. We study the spectator-first Tantalizer problem with a deck of n-cards and investigate which card is left in the end after a series of dealing operations. A formula and an algorithm with a running time complexity based on the binary form of n are proposed to solve this problem.

On the Drag Reduction Optimization of the DrivAer Fastback Model Car with Digital Side Mirror

Thu, 10 Jun 2021 04:10:26 GMT

title: On the Drag Reduction Optimization of the DrivAer Fastback Model Car with Digital Side Mirror abstract: The traditional side mirrors on automobile could create substantial part of drag in the total car aerodynamic design consideration. On some concept cars, digital side mirrors have been installed which are aiming to reduce the total drag, thus the optimization study of digital side mirrors configuration becomes an important task. In this study the benchmark DrivAer fastback model is employed for optimization work of digital side mirrors via computation fluid dynamics software, and simulated with realistic moving ground and rotating wheel conditions. In order to validate the lift and drag coefficients with existing experimental data, the wheel rotation is implemented by three different kinds of rotating methods: Moving Wall, Multiple Reference Frame and Sliding Mesh, while the Sliding Mesh method provides the most accurate results. For optimization work, a concept of digital side mirror configuration is created, and the objective is aiming the best drag reduction via various installation positions by using the surrogate method which is based on Kriging model. The results show for the best achieved side mirror location, it is observed that a positive effect of drag reduction from increasing the intensity of some specific vortices, and its wake region can be weaker than the original configuration.