Power Density Function Research Articles

SEISMONOISY: A Quasi-Real-Time Seismic Noise Network Monitoring System.

This paper introduces SEISMONOISY, an application designed for monitoring the spatiotemporal characteristic and variability of the seismic noise of an entire seismic network with a quasi-real-time monitoring approach. Actually, we have applied the developed system to monitor 12 seismic networks distributed throughout the Italian territory. These networks include the Rete Sismica Nazionale (RSN) as well as other regional networks with smaller coverage areas. Our noise monitoring system uses the methods of Spectral Power Density (PSD) and Probability Density Function (PDF) applied to 12 h long seismic traces in a 24 h cycle for each station, enabling the extrapolation of noise characteristics at seismic stations after a Seismic Noise Level Index (SNLI), which takes into account the global seismic noise model, is derived. The SNLI value can be used for different applications, including network performance evaluation, the identification of operational problems, site selection for new installations, and for scientific research applications (e.g., volcano monitoring, identification of active seismic sequences, etc.). Additionally, it aids in studying the main noise sources across different frequency bands and changes in the characteristics of background seismic noise over time.

A modified Diesel cycle via isothermal heat addition, its endoreversible modelling and multi-objective optimization

A new model of thermal cycle, modified Diesel cycle, is constructed via isothermal heat addition. Endorebersible modelling is performed considering heat transfer loss. Power (P), efficiency (η), power density (Pd) and ecological function (E) are deduced and evaluated. Characteristic relationships are deduced by using the finite-time thermodynamics theory. Cycle performances under the conditions of the maximum E, the maximum Pd, the maximum η, and the maximum P are compared. Under the same conditions, four performance functions of modified Diesel cycle and traditional Diesel cycle are compared. Based on the algorithm of NSGA-II, taking four performance indictors as the optimization objectives and the compression ratio as the optimization variable, multi-objective optimizations of the modified and traditional Diesel cycles under different objective combinations are carried out. Three decision-making method are used to select a group of optimal solutions. Compared with traditional Diesel cycle, performances P, η, Pd and E of modified Diesel cycle are improved at least by 8.69 %, 0.97 %, 8.23 %, and 8.64 %, respectively. Modified Diesel cycle with Pd and E for two-objective optimization is optimal, and the minimum deviation index is 0.1336, while the traditional Diesel cycle with P, η and Pd for three-objective optimization is optimal, and the minimum deviation index is 0.1339.

A Piezo‐Tribovoltaic Nanogenerator with Ultrahigh Output Power Density and Dynamic Sensory Functions

AbstractTribovoltaic nanogenerator (TVNG) mainly collects energy from sliding motions of two semiconducting materials, but it cannot effectively react to the pressure change in the vertical direction. Here, a piezo‐tribovoltaic nanogenerator (P‐TVNG) is proposed by integrating piezoelectric and tribovoltaic effects to collect energy from both the sliding motion and the variation of applied pressure. Hence, this P‐TVNG can gain extra performance improvement on the top of the original output limit of TVNG. The maximum output power density of P‐TVNG is up to 3.61 W m−2, which is 28.9 % higher than the highest record of the TVNG using similar materials. Additionally, the piezo‐module can work as a separated sensory component by switching the circuit, which can monitor and analyze various working parameters of TVNG. A series of dynamic characteristics of TVNG during its operation have been identified, including the hysteresis between output current and applied pressure, the influence and incompatibility of interface stress to output performance, and so on. As a multifunction of devices, this P‐TVNG system is possible to be applied in semiconductor industry, smart manufacturing, and many other fields. This work improves the performance of the TVNGs while extending its functionality, which broadens the application field of TVNG devices.

Fractal and structural analysis of the different sculptured Mn-based nanostructures

Surface morphology and fractal properties of 3D nanostructures of the circular helical, square helical, and chevron were investigated. The nanostructures were deposited on the glass substrate using the oblique angle deposition technique. The surface properties of the nanostructures were investigated by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The autocorrelation function (ACF), height-height correlation function (H(r)), power density function (PSDF), and Minkowski function are used for fractal characterization. The results showed that the circular helical nanostructure has more surface roughness, roughness exponent, and grain size compared to the square helical and chevron nanostructures. The fractal dimension of the surface of all three nanostructures showed that the chevron nanostructure with Df=2.88 has higher spatial complexity. The Minkowski functionals showed similar behavior for all three nanostructures. However, more negative and positive Minkowski connectivity was obtained for the circular helical nanostructure compared to the other two nanostructures.

An effective method for modelling wireless communication systems

Statement of the problem. To describe the multipath propagation of radio signals using two models: the ray tracing method and the method of stochastic simulation. Let us consider the stochastic model as the most general one that allows to describe various scenarios and factors influencing signal propagation such as multipath, arrival time variance, distance loss, atmospheric conditions, etc. Under real-world conditions, channel variation does not follow a Gaussian distribution. Coloured non-Gaussian noise has to be taken into account in the design and modelling of the wireless communication system. The complexity of the stochastic channel modelling method is that the variation of PSD power spectral density function and PDF probability density function of a random variable are strongly related to each other. To remove the limitations of existing methods, the Gaussian random variable filtering method is used. But in contrast to the applied simulation techniques, we will use Global Search Optimization (GSE) algorithm. Objective. To investigate a possibility of generation of colored non-Gaussian noise which satisfies the specified requirements by the filtering method based on the global search optimization algorithm. Results. The method based on the global search optimization algorithm for generating colored non-Gaussian noise, which satisfies specified requirements of the Spectral Power Density function and the Probability Density function, is proposed. Numerical simulation results confirm its effectiveness. The advantage of the new method is that the complexity of calculating the required pre-distortion for the filter is replaced by a simple search method. Once the required coefficients are found, non-Gaussian noise generation can be accomplished by secondary filtering and inverse transform. Practical Significance. Compared to methods based on block structures or other analytical methods, the proposed method is more suitable for real-time wireless channel simulation.

Combining spectral analysis and geochemical tracers to investigate surface water–groundwater interactions: A case study in an intensive agricultural setting (southern Guatemala)

An increase in the frequency of severe hydrological events has highlighted the importance of sustainable water management in intensive agricultural regions. In a warming climate, improved understanding and stewardship of water resources are needed to guarantee water supply, ensure food security, and build resilience against extreme events. In this study, we evaluate a framework that combines spectral analysis and geochemical tracers as a potential tool for (1) gaining valuable insights into surface water (SW)–groundwater (GW) interactions, and (2) providing guidance for improved water management in an intensive agricultural basin in southern Guatemala. The framework proves to be useful in revealing important water dynamics, exposing key feedback mechanisms for water availability and quality. With the use of power density functions and hydrochemistry (T, pH, EC, and major ions), two specific interaction regimes (influent and effluent) were identified and delimited for the main watercourse. These segments are estimated to interact at high rates with the shallow aquifer in the river channel proximities and would lose influence towards the basin flanks. Furthermore, the δ2H and δ18O values indicate that regional groundwater flow systems play an essential role in the basin groundwater recharge. Lastly, we established three influence zones that depict the spatial extent of the SW-GW interactions within the basin. With these zones, we provide recommendations that will allow for further investigation and application into better water management strategies regulating groundwater development and land use activities within the agricultural context of the area.

Sensorless Speed Control of a Brushless DC Motor Using Particle Filter (PF)

The equivalent of electricity has recently been used to replace all the wear-prone moving mechanical components that produce faults. The electronic unit that substitutes the mechanical commutation unit in Brushless Direct Current (BLDC) motors improves dynamic properties, noise level, and efficiency. This work describes a method for estimating the BLDC machine's rotor speed and position by using Extended Kalman Filter (EKF) and Particle Filter (PF). The BLDC is a non-linear system with nonlinear measurements. To perform the EKF, Jacobian linearization of the motor model and the observation are needed. Linearization leads to a decrease in the accuracy of filter estimation. In PF, the relative likelihood of each particle is computed according to the measurements. Resampling gives set particles are distributed according to power density function (pdf). Then the PF can compute any desired statistical measure of this pdf. A sensorless drive has an accurate good throughout a wide speed range and with varied load torque, according to the simulation's results. The results show that the velocity inaccuracy rate at PF is approximately 0.01% and that at EKF it is approximately 1%. According to the findings, the PF outperformed the EKF in a comparison between them.

Energy, exergy and ecology performance prediction of a novel SOFC-AMTEC-TEG power system

• A novel triple-cycle power system is proposed. • Energy, exergy and ecology performance are analyzed. • Effectiveness and generic performance characteristics are demonstrated. • There is an optimum thermoelectric element number to optimize performance. In order to realize the cascade utilization of the waste heat for the solid oxide fuel cell, a novel triple-cycle system including a solid oxide fuel cell, an alkali metal thermal electric converter and a thermoelectric generator is proposed. In this system, the alkali metal thermal electric converter powered by the waste heat of the solid oxide fuel cell can drive the thermoelectric generator. The proposed system can efficiently generate electricity in a green and noiseless way, and Thomson effect is considered in the thermoelectric generator model. The results show that improving the number of the thermoelectric generator stages is not conducive to the improvement of the system performance. The maximum power density and ecology function density can result in 42.0% and 53.5% improvement over those of the sole solid oxide fuel cell system, respectively. Further sensitivity analysis confirms that there is an optimum element number of the thermoelectric generator to optimize the performance of the triple-cycle system. This work proves the feasibility of the triple-cycle system, and hints the broad prospect of high-grade heat recovery through an alkali metal thermal electric converter-thermoelectric generator unit.

Four-Objective Optimization for an Irreversible Porous Medium Cycle with Linear Variation in Working Fluid's Specific Heat.

Considering that the specific heat of the working fluid varies linearly with its temperature, this paper applies finite time thermodynamic theory and NSGA-II to conduct thermodynamic analysis and multi-objective optimization for irreversible porous medium cycle. The effects of working fluid’s variable-specific heat characteristics, heat transfer, friction and internal irreversibility losses on cycle power density and ecological function characteristics are analyzed. The relationship between power density and ecological function versus compression ratio or thermal efficiency are obtained. When operating in the circumstances of maximum power density, the thermal efficiency of the porous medium cycle engine is higher and its size is less than when operating in the circumstances of maximum power output, and it is also more efficient when operating in the circumstances of maximum ecological function. The four objectives of dimensionless power density, dimensionless power output, thermal efficiency and dimensionless ecological function are optimized simultaneously, and the Pareto front with a set of solutions is obtained. The best results are obtained in two-objective optimization, targeting power output and thermal efficiency, which indicates that the optimal results of the multi-objective are better than that of one-objective.

Nonlinear dynamics investigation of contact force in a cam–follower system using the Lyapunov exponent parameter, power spectrum analysis, and Poincaré maps

AbstractThe aim of this article is to detect the detachment between the cam and the follower using the largest Lyapunov exponent parameter, the power density function of fast Fourier transform, and Poinaré maps due to the nonlinear dynamics phenomenon of the follower. The detachment between the cam and the follower was investigated for different cam speeds and different internal distances of the follower guide from inside. This study focuses on the use of the cam–follower system with a bionic quadruped robot through a linkage mechanism. Multishock absorber (spring–damper–mass) systems at the very end of the follower were used to improve the dynamic performance and to reduce the detachment between the cam and the follower. The SolidWorks program was used in the numerical solution, while a high‐speed camera at the foreground of the OPTOTRAK 30/20 equipment was used to identify the follower position. The friction and impact were considered between the cam and the follower and between the follower and its guide. In general, when the cam and the follower are in permanent contact, there is no loss in potential energy, and no impact or restitution. The detachment between the cam and the follower increases with increasing coefficient of restitution in the presence of the impact.

Nonlinear dynamics phenomenon detection in a polydyne cam with an offset flat-faced follower mechanism using multi shocks absorbers systems

The influences of the internal distance of the guide from inside (I.D.), the constant speeds of the cam (N), and the followers' offsets (O) on the chaotic phenomena are studied in this research. The chaotic phenomena is investigated using Phase-plane portrait with Poincare’ Maps, Power Density Function of Fast Fourier Transform (FFT), and Largest Lyapunov Exponent. The chaos analysis of the offset flat-faced follower due to the contact with the polydyne cam profile is controlled using multi linear and nonlinear shocks absorbers systems. The suspensions of the shocks absorbers are described using (spring-damper-mass) systems. The nonlinear response of the flat-faced follower due to the offset shift is calculated at different internal distance of the follower guide (I.D), different speeds of the cam (N), and different followers’ offsets (O). The analytic solution of the nonlinear follower motion is done using the second-order ordinary differential equation. The numerical results of the nonlinear response of the follower is determined using SolidWorks program, while OPTOTRAK 30/20 equipment with high speed camera is used in the experiment inspection. Largest Lyapunov exponent has a maximum values when the follower offsets to the right, while the largest Lyapunov exponent has a minimum values when the follower offsets to the left. The transition to chaos when the follower offsets to the left is faster than when the follower offsets to the right at (O = 50 mm). The chaos phenomenon in cam follower system in the presence of follower offset is increased with the increasing of (I.D.), (N), and (O).

Nonlinear Dynamics Suppression of Bending Deflection in a Composite Laminated Plate Using a Beam Stiffener Due to Critical Buckling Load and Shear Force

In this paper, the nonlinear dynamics behavior of the bending deflection of a stiffened composite laminated plate is suppressed using beam stiffeners at different fiber volume fractions and different aspect ratios. The non-periodic motion and chaos in a stiffened composite laminated plate is detected using the largest Lyapunov exponent parameter and power density function of a fast Fourier transform (FFT). The critical buckling load is calculated at different thickness ratios, numbers of stiffeners, lamination angles and stiffener–depth ratios based on different boundary conditions. The nonlinear response of the bending deflection is analyzed analytically, numerically and experimentally. The analytic solution has been derived using Levy and Navier solutions of classical laminate plate theory at different boundary conditions (CLPT). The numerical simulation was conducted using the ANSYS program while the experiment test was carried out using a strain gauge through a strain meter device. Experimentally, a Southwell plot is used to investigate the value of the critical buckling load. The combined loading are the in-plane compression mechanical load and shear force. All the values of the largest Lyapunov exponent are positive, which gives indication to non-periodic motion and chaos. The nonlinear dynamics behavior of the bending deflection is decreased with the increasing of number of stiffeners in which the value of largest Lyapunov exponent has been decreased. The nonlinear dynamics behavior is increased with the increasing of aspect ratios and fiber volume fractions. The system with an aspect ratio (2.5) and fiber volume fraction (υf = 80%) for an un-stiffened plate is more chaotic than the other systems.

Detachment Detection in Cam Follower System Due to Nonlinear Dynamics Phenomenon

The detachment between the cam and the follower was investigated for different cam speeds (N) and different internal distance of the follower guide from inside (I.D.). The detachment between the cam and the follower were detected using largest Lyapunov exponent parameter, power density function of Fast Fourier Transform (FFT), and Poincare’ maps due to the nonlinear dynamics phenomenon of the follower. The follower displacement and the contact force between the cam and the follower were used in the detection of the detachment heights. Multi-degrees of freedom (spring-damper-mass) systems at the very end of the follower were used to improve the dynamic performance and to reduce the detachment between the cam and the follower. Nonlinear response of the follower displacement was calculated at different cam speeds, different coefficient of restitution, different contact conditions, and different internal distance of the follower guide from inside. SolidWorks program was used in the numerical solution while high speed camera at the foreground of the OPTOTRAK 30/20 equipment was used to catch the follower position. The friction and impact were considered between the cam and the follower and between the follower and its guide. The peak of nonlinear response of the follower displacement was reduced to (15%, 32%, 45%, and 62%) after using multiple degrees of freedom systems.

Wind farm site selection considering turbulence intensity

Selecting a suitable site is a critical step in wind energy projects. In this regard, using appropriate decision criteria plays a significant role. Turbulence intensity is one of the main characteristics of airflow that affects the power production and lifespan of wind turbines. Therefore, it is considered as a wind site selection criterion in this paper.The present paper formulates the effect of turbulence on both power production and lifespan of wind turbines via an equivalent wind power density (WPDeq) function, to use it in the wind site selection process. To implement the proposed methodology, 88 wind sites in Iran have been studied. The results reveal the significant effect of turbulence on the site selection process as some sites have changed their rank up to 8 grades considering turbulence intensity in the siting process.To consider the turbulence intensity as an independent criterion to use it in multi-criteria decision-making methods, its relative importance (weight) have to be calculated. Sensitivity analysis shows that, on average, the relative importance of turbulence intensity over wind power density can be approximated as 1/5. Researchers can quickly consider turbulence intensity in siting process incorporating its weight in the pairwise comparison matrix of multi-criteria decision–making.

Overall and component basis performance evaluations for turbojet engines under various optimal operating conditions

An evaluation using various operating conditions such as the maximums of: power, power density, ECOP and ECOL optimization functions for the analysis of turbojet engines is reported. Although, these well-known optimization functions were applied for various cycle types by researchers, the application of these methods for aircraft turbojet engines have not been explored. To this effect, a Brayton cycle including diffuser and nozzle together with the compressor, combustion chamber and turbine with various irreversibilities was considered. Engine irreversibilities are taken into account through appropriate efficiencies for each component. Different parameters influencing the cycle performance are examined such as compressor pressure ratio, cycle temperature ratio, compressor and turbine efficiencies, altitude and flight Mach number. The cycle performance was assessed utilizing the maximum power (MP), power density (MPD), Ecological Coefficient of Performance (ECOP) and Ecological Function (ECOL) conditions. In addition, the size variation of individual engine components and their contribution to the overall performance was also assessed under maximum power, power density, ECOP and ECOL conditions. The comparisons show that the design parameters at the maximum ECOL and maximum ECOP conditions may lead to smaller, more efficient and lower fuel consumption for turbojet engines than those at maximum power and maximum power density. However, on a component basis (compressor, combustion chamber, turbine and nozzle) the engine power, thrust, thermal efficiency, size and TSFC can be enhanced when utilizing the MP, MPD, ECOP and ECOL optimization functions.

Four-Objective Optimizations for an Improved Irreversible Closed Modified Simple Brayton Cycle.

An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, the cycle performance is optimized by taking four performance indicators, including the dimensionless power output, thermal efficiency, dimensionless power density, and dimensionless ecological function, as the optimization objectives. The impacts of the irreversible losses on the optimization results are analyzed. The results indicate that four objective functions increase as the compressor and turbine efficiencies increase. The influences of the latter efficiency on the cycle performances are more significant than those of the former efficiency. Then, the NSGA-II algorithm is applied for multi-objective optimization, and three different decision methods are used to select the optimal solution from the Pareto frontier. The results show that the dimensionless power density and dimensionless ecological function compromise dimensionless power output and thermal efficiency. The corresponding deviation index of the Shannon Entropy method is equal to the corresponding deviation index of the maximum ecological function.

Levenberg–Marquardt Algorithm for Acousto-Electric Tomography based on the Complete Electrode Model

The inverse problem in acousto-electric tomography concerns the reconstruction of the electric conductivity in a body from knowledge of the power density function in the interior of the body. This interior power density results from currents prescribed at boundary electrodes, and it can be obtained through electro-static boundary measurements together with auxiliary acoustic probing. Previous works on acousto-electric tomography used the continuum model for the electrostatic boundary conditions; however, from Electrical Impedance Tomography, it is known that the complete electrode model is much more realistic and accurate. In this paper, the inverse problem of acousto-electric tomography is posed using the (smoothened) complete electrode model, and a reconstruction method based on the Levenberg–Marquardt iteration is formulated in appropriate function spaces. This results in a system of partial differential equations to be solved in each step. To increase the computational efficiency and stability, a strategy based on both the complete electrode model and the continuum model is proposed. The method is implemented numerically for a two-dimensional scenario, and the algorithm is tested on two different numerical phantoms, a heart and lung model and a human brain model. Several numerical experiments are carried out confirming the feasibility, accuracy and stability of the developed method.

Log-Exponential Power Distribution for Accelerated Failure Time Model in Survival Analysis and Its Application

We proposed the log-exponential power density function as baseline distribution for accelerated failure time model (AFT) used in analysis of survival data with covariates. This model generalizes the log-normal and some exponential family due to flexibility at the tail region. It has log-concavity property, accommodates the four basic shapes of hazard function which is an attractive property ive to some existing models was tested using data from chronic liver disease patients monitored at Obafemi Awolowo University Teaching Hospital, Ile-Ife.

Power, Efficiency, Power Density and Ecological Function Optimization for an Irreversible Modified Closed Variable-Temperature Reservoir Regenerative Brayton Cycle with One Isothermal Heating Process

One or more isothermal heating process was introduced to modify single and regenerative Brayton cycles by some scholars, which effectively improved the thermal efficiency and significantly reduced the emissions. To analyze and optimize the performance of this type of Brayton cycle, a regenerative modified Brayton cycle with an isothermal heating process is established in this paper based on finite time thermodynamics. The isothermal pressure drop ratio is variable. The irreversibilities of the compressor, turbine and all heat exchangers are considered in the cycle, and the heat reservoirs are variable-temperature ones. The function expressions of four performance indexes; that is, dimensionless power output, thermal efficiency, dimensionless power density and dimensionless ecological function are obtained. With the dimensionless power density as the optimization objective, the heat conductance distributions among all heat exchangers and the thermal capacitance rate matching among the working fluid and heat reservoir are optimized. Based on the NSGA-II algorithm, the cycle’s double-, triple- and quadruple-objective optimization are conducted with the total pressure ratio and the heat conductance distributions among heat exchangers as design variables. The optimal value is chosen from the Pareto frontier by applying the LINMAP, TOPSIS and Shannon entropy methods. The results show that when the pressure ratio in the compressor is less than 12.0, it is beneficial to add the regenerator to improve the cycle performance; when the pressure ratio is greater than 12.0, adding the regenerator will reduce the cycle performance. For single-objective optimization, the four performance indexes could be maximized under the optimal pressure ratios, respectively. When the pressure ratio is greater than 9.2, the cycle is simplified to a closed irreversible simple modified Brayton cycle with one isothermal heating process and coupled to variable-temperature heat reservoirs. Therefore, when the regenerator is used, the range of pressure ratio is limited, and a suitable pressure ratio should be selected. The triple objective (dimensionless power output, dimensionless power density and dimensionless ecological function) optimization’ deviation index gained by LINMAP or TOPSIS method is the smallest. The optimization results gained in this paper could offer some new pointers for the regenerative Brayton cycles’ optimal designs.

Parameter Estimation for Two-Dimensional Incoherently Distributed Source with Double Cross Arrays.

A direction of arrival (DOA) estimator for two-dimensional (2D) incoherently distributed (ID) sources is presented under proposed double cross arrays, satisfying both the small interval of parallel linear arrays and the aperture equalization in the elevation and azimuth dimensions. First, by virtue of a first-order Taylor expansion for array manifold vectors of parallel linear arrays, the received signal of arrays can be reconstructed by the products of generalized manifold matrices and extended signal vectors. Then, the rotating invariant relations concerning the nominal elevation and azimuth are derived. According to the rotating invariant relationships, the rotating operators are obtained through the subspace of the covariance matrix of the received vectors. Last, the angle matching approach and angular spreads are explored based on the Capon principle. The proposed method for estimating the DOA of 2D ID sources does not require a spectral search and prior knowledge of the angular power density function. The proposed DOA estimation has a significant advantage in terms of computational cost. Investigating the influence of experimental conditions and angular spreads on estimation, numerical simulations are carried out to validate the effectiveness of the proposed method. The experimental results show that the algorithm proposed in this paper has advantages in terms of estimation accuracy, with a similar number of sensors and the same experimental conditions when compared with existing methods, and that it shows a robustness in cases of model mismatch.