Harmonic Point Research Articles

Electricity Generation Characteristics of Energy-Harvesting System with Piezoelectric Element Using Mechanical-Acoustic Coupling

This paper describes the electricity generation characteristics of a new energy-harvesting system with piezoelectric elements. The proposed system is composed of a rigid cylinder and thin plates at both ends. The piezoelectric elements are installed at the centers of both plates, and one side of each plate is subjected to a harmonic point force. In this system, vibration energy is converted into electrical energy via electromechanical coupling between the plate vibration and piezoelectric effect. In addition, the plate vibration excited by the point force induces a self-sustained vibration at the other plate via mechanical-acoustic coupling between the plate vibrations and an internal sound field into the cylindrical enclosure. Therefore, the electricity generation characteristics should be considered as an electromechanical-acoustic coupling problem. The characteristics are estimated theoretically and experimentally from the electric power in the electricity generation, the mechanical power supplied to the plate, and the electricity generation efficiency that is derived from the ratio of both power. In particular, the electricity generation efficiency is one of the most appropriate factors to evaluate a performance of electricity generation systems. Thus, the effect of mechanical-acoustic coupling is principally evaluated by examining the electricity generation efficiency.

Financial Performance of Top 20 Airlines

This empricial research article intends to analyse the financial performance of the top 20 airlines in the Word for the period of year 2011 and 2014. In order to measure the financial performance of the airlines on a uniqie base,an hormonic index is propesed by considering performance areas of profitability, operating, efficiency and liquidity. Next, each performance area is defined by using a various of performance ratios. Finally, all airlines companies examined are listed by their harmonic index scores. The total assets of the 20 biggest airlines are amounted over $457 billion in 2014 and Delta Airlines with an assest size of $54 billion is the biggest ailines. On the other hand, the highest revenue generated by Luftansa in 2011, 2012 and 2013 over $40 billion per year The empricial results show that the worst scores of harmonic index refer American Airlines in 2011, Soutwest in 2012, China Eastern Airlines in 2013 and Quantas Airways in 2014, while the best scores of harmonic index point Delta in 2011, Hainan Airlines in 2012 and EasyJet in 2013 and 2014. This analysis supports that the measurement of financial performance based upon total revenuue or profitability is somehow weak and may be extented by including other indicators.

Simplified dynamic analysis of stepped thickness rectangular plate structures by the assumed mode method

In this article, the assumed mode method is applied to simplified dynamic analysis of stepped thickness rectangular Mindlin plates and stiffened panels with arbitrary boundary conditions. The natural and frequency responses of stepped thickness plate structures subjected to harmonic point excitation force and enforced acceleration at boundaries, respectively, are considered. Potential and kinetic energies of the system are formulated and used to derive eigenvalue problem utilizing Lagrange’s equation of motion, and mode superposition method is further used for forced response assessment. Characteristic orthogonal polynomials having the property of Timoshenko beam functions are used for the assumed modes. Numerical examples analysing vibration of stepped thickness plate structures with different topologies and various sets of boundary conditions are provided. Numerical results are compared with the results from the relevant literature and finite element solutions obtained by a general finite element tool, and a very good agreement is achieved. Hence, it is expected that stepped rectangular plate structures satisfying the prescribed criteria regarding natural and frequency responses can be efficiently designed based on the proposed method.

Predictive coupled-cluster isomer orderings for some SinCm (m, n ≤ 12) clusters: A pragmatic comparison between DFT and complete basis limit coupled-cluster benchmarks.

The accurate determination of the preferred Si12C12 isomer is important to guide experimental efforts directed towards synthesizing SiC nano-wires and related polymer structures which are anticipated to be highly efficient exciton materials for the opto-electronic devices. In order to definitively identify preferred isomeric structures for silicon carbon nano-clusters, highly accurate geometries, energies, and harmonic zero point energies have been computed using coupled-cluster theory with systematic extrapolation to the complete basis limit for set of silicon carbon clusters ranging in size from SiC3 to Si12C12. It is found that post-MBPT(2) correlation energy plays a significant role in obtaining converged relative isomer energies, suggesting that predictions using low rung density functional methods will not have adequate accuracy. Utilizing the best composite coupled-cluster energy that is still computationally feasible, entailing a 3-4 SCF and coupled-cluster theory with singles and doubles extrapolation with triple-ζ (T) correlation, the closo Si12C12 isomer is identified to be the preferred isomer in the support of previous calculations [X. F. Duan and L. W. Burggraf, J. Chem. Phys. 142, 034303 (2015)]. Additionally we have investigated more pragmatic approaches to obtaining accurate silicon carbide isomer energies, including the use of frozen natural orbital coupled-cluster theory and several rungs of standard and double-hybrid density functional theory. Frozen natural orbitals as a way to compute post-MBPT(2) correlation energy are found to be an excellent balance between efficiency and accuracy.

Structure-Borne Noise Source Characterization from a Bayesian Point of View

In this paper, a local method of structure-borne noise source characterization is presented. It is based on measurements of transverse displacement and local structural operator knowledge and allows to localize and quantify sources without any need of boundary condition information. To fix the instability caused by measurement noise, the regularization step inherent to inverse problem is realized with a probabilistic approach, within the Bayesian framework. When a priori distributions about noise and sources are considered as Gaussian, the Bayesian regularization is equivalent to the well-known Tikhonov regularization. The optimization of the regularization is then performed by the Gibbs Sampling (GS) algorithm, which is part of Markov Chain Monte Carlo (MCMC) techniques. The whole probability of the regularized solution is inferred, providing access to confidence intervals. Both simulation and measurements of a beam excited by an harmonic point source are realized to validate this approach.

An analytical model for vibration prediction of a tunnel embedded in a saturated full-space to a harmonic point load

The dynamic response of a tunnel embedded in a saturated poroelastic full-space under a vertical harmonic load was investigated by a semi-analytical method. The tunnel was modeled as a thin cylindrical shell surrounded by soil of infinite radial extent. The soil was modeled as a saturated poroelastic full-space. Biot's theory was applied to characterize the soil medium, taking the solid skeleton-pore fluid coupling effects into account. Combined with the boundary conditions at tunnel–soil interface, the coupled equations of the system were solved in the frequency domain with the aid of Fourier decomposition and Fourier transform in the circumferential and longitudinal direction, respectively. Dynamic responses of the tunnel and soil generated by a unit harmonic load applied at the tunnel invert are presented. It is found that the soil permeability and the load frequency have significant influence on the displacements, the stresses and the pore pressure in the saturated soil. In the free field, an increase of the soil permeability leads to a decrease of the soil displacement and pore pressure response. An equivalent single-phase material was used to model the saturated soil and it is found only applicable for soil with lower permeability.

A theoretical investigation on influences of slab tracks on vertical dynamic responses of railway viaducts

A railway viaduct model consisting of infinite spans of elastically-supported girders carrying a slab track of infinite length is established to investigate the influence of the slabs on the vertical dynamic response of the viaduct, when a moving harmonic point load or a moving sprung wheel is applied. The infinite rail, the discontinuous slabs and girders of identical span lengths are idealized as Euler–Bernoulli beams. The rail fasteners, the cushion layer beneath the slab and the elastic bearings at the girder supports are represented by discretely distributed springs of hysteretic damping. Due to the repetitive nature of the girders, the model can be divided into periodic three-beam units by the span length of the girder, and then solved analytically in the frequency domain using the property of periodic structure. Besides the first natural frequency of the girder with elastic bearings, it is found that the resonance frequency of the slab on the cushion layer has a significant influence on the dynamic response of the track and the girder. Parametric excitations due to the moving wheel periodically passing the discontinuous slabs contribute significantly to the wheel/rail interactions.

Compressed sensing from a harmonic analysis point of view

This paper gives an easy and purely harmonic analysis approach of the compressed sensing theory of Candes, Romberg and Tao. It contains an application to the determination of a lacunary trigonometric series whose sum is known on an interval, and a critical appreciation of this application.

Free and forced vibrations of shear deformable functionally graded porous beams

This paper investigates the free and forced vibration characteristics of functionally graded (FG) porous beams with non-uniform porosity distribution whose elastic moduli and mass density are nonlinearly graded along the thickness direction. Both symmetric and asymmetric porosity distributions are considered. The relationship between coefficients of porosity and mass density is determined based on the typical mechanical property of an open-cell metal foam. Within the framework of Timoshenko beam theory to include the effect of transverse shear strain and by employing Lagrange equation method together with Ritz trial functions, the equation of motion is derived then solved by using Newmark-β method in the time domain. Natural frequencies and transient dynamic deflections are obtained for porous beams under different loading conditions, including a harmonic point load, an impulsive point load and a moving load with constant velocity. A detailed numerical study is conducted to examine the effects of varying porosity distribution, porosity coefficient, slenderness ratio and boundary condition, shedding important insights into the design of functionally graded porous beams to achieve improved dynamic behavior.

Royden Decomposition for Harmonic Maps with Finite Total Energy

We prove the harmonic map version of the Royden decomposition in the sense that given any bounded C1-map f with finite total energy on a complete Riemannian manifold into a Cartan-Hadamard manifold, there exists a unique bounded harmonic map with finite total energy from the manifold into the Cartan-Hadamard manifold taking the same boundary value at each harmonic boundary point as that of f.

The Role of Reactive Energy in the Radiation by a Dipole Antenna

The spatio-temporal distribution of the near field around an antenna is of fundamental importance in understanding its radiative properties, since it can affect the radiated power flow emitted by the device. In this work, we consider the simplest case of a harmonic point dipole antenna activated at some point in time, and study the distribution of the energy flow velocity and reactive energy in space and time. We discuss how the reactive energy building up around the radiator affects quite strongly the flow of energy in the vicinity of the dipole, while in the far field, the expected radiation features are restored. The reactive energy in the near field decelerates or even inverts the overall energy flow, resulting in partial standing waves near the feed. We also investigate the transient response of the stored reactive energy and identify the convergence to steady state, which is demonstrated through time-averaged quantities. Our results shed interesting observations on the radiation properties of antennas in their near field, as time progresses.

Frequency response of rectangular plate structures in contact with fluid subjected to harmonic point excitation force

Numerical procedure for the forced vibration analysis of bottom and vertical rectangular plate structures in contact with fluid, subjected to internal point harmonic excitation force is developed. The procedure is based on the assumed mode method for free vibration calculation and mode superposition method for forced vibration analysis. Structural model covers Mindlin rectangular plates and stiffened panels. Lagrange's equation of motion is utilized to formulate the eigenvalue problem taking into account potential and kinetic energies of a plate and reinforcements, and fluid kinetic energy which is calculated according to potential flow theory, respectively. From the boundary conditions for the fluid and structure the fluid velocity potential is derived and it is utilized for the calculation of added mass using the assumed modes. The developed theoretical model and in-house code are verified with extensive numerical examples related to forced vibration of bare plates and stiffened panels in contact with different fluid domains. Comparisons of the results with those obtained by a general purpose finite element (FE) software confirmed high accuracy of the presented numerical procedure.

Power Quality Analysis for Photovoltaic System Considering Unbalanced Voltage

Background/Objectives: Voltage unbalance is one of the most important power quality problems in distribution network. In this way, three phase Photo Voltaic (PV) system can increase voltage unbalance. Methods/Statistical Analysis: In this paper a three phase photovoltaic system with Maximum Power Point Tracking (MPPT) has been installed in an unbalance distribution network due to reduce Voltage Unbalance Factor (VUF). Also, a Dynamic Voltage Regulator (DVR) has been used to get better outcomes. Results: Results show that in the case in which load is balance and only network is unbalance, the system comprised of PV, MPPT and DVR can diminish VUF by 10%. Moreover, THD analysis is done and is obtained around 2.27%. This system is modeled in MATLAB/ SIMULINK. Conclusion/Application: Considering the benefits of using PV system for sustainable energy, utilizing MPPT and DVR can lessen voltage unbalance in distribution networks inclusive photovoltaic systems. First, output voltage waveform of three-phase photovoltaic system simulated in this paper with regard to existing controlling structure in PV system is balanced to radiation change (500 –1000W/m2) in a good approximation and acts like a balanced three-phase source. Second, when this photovoltaic system approaches an unbalanced load which is located in an unbalanced network, the voltage imbalance decreases in that bus. Also when PV system gets further from the considered load, the impact of voltage imbalance reduction decreases in that load and also whatever the used photovoltaic system in the network is nearer to a special load, the imbalance compensating effect becomes more sensible. Also according to the performed simulations if there is a load which is sensible to the imposed voltage imbalance from network, PV-DVR system can be used for modify the observed voltage imbalance from network. It is worth noting that the PV-DVR system hasn’t the ability to modify observed imbalance from network due to imbalance load. PV-DVR system in this paper has the ability to compensate voltage imbalance up to 10% and for more, the capabilities of both photovoltaic system and DVR must be added. In addition, or proposed network, FFT analysis is done. Therefore harmonic load flow illustrates the suggested photovoltaic system using PV-DVR is acceptable from harmonic distortion point of view. THD is obtained around 2.27% that is good value for PV-DVR system in comparison with 5% allowable standard value.

In-plane stress analysis of cracked layers under harmonic loads

Stress analysis is carried out in an isotropic layer weakened by multiple cracks under time-harmonic loading. The viscous damping is used to model energy dissipation in the material. The analysis is based on the stress fields caused by climb and glide of an edge dislocation in the layer. The solution for dislocation is obtained by means of the integral transform method. Furthermore, stress analysis in the intact layer under self-equilibrating harmonic point loads is carried out. These solutions are employed to derive a set of Cauchy singular integral equations for analyzing cracks parallel/perpendicular to the layer boundary. The numerical solution of these equations yields dislocation densities on a crack surface which are used to determine dynamic stress intensity factors over a range of frequency. The natural frequencies of layers with horizontal cracks are obtained and the interaction of multiple cracks is studied.

A Benchmark Model for Three-Dimensional Sound Propagation in an Ideal Wedge-Shaped Waveguide

A benchmark model is developed to compute the three-dimensional acoustic field excited by a harmonic point source in a homogeneous wedge-shaped waveguide with impenetrable boundaries. A derivation of the exact solution is presented based on Fourier synthesis, which reduces the three-dimensional ideal wedge problem to a sequence of two-dimensional line-source ideal wedge problems, to which the analytical solution is well established. The details of the numerical implementation of this solution are also provided. Our numerical results indicate that this model is efficient and capable of providing accurate three-dimensional acoustic fields for arbitrary receiver locations, and hence can serve as a benchmark model for sound propagation in a continental shelf environment.

Characterization of the Spatio-temporal Response of Optical Fiber Sensors to Incident Spherical Waves

A theoretical framework is presented for calculating the opto-acoustic response of optical fiber ultrasound sensors with several layers of coating. A harmonic point source generating a spherical wavefront with arbitrary position and frequency is assumed. The fiber is acoustically modeled by a layered cylinder on which spherical waves are scattered. The principle strains on the fiber axis are calculated from the scattering of the acoustic waves and used in a strain-optic model to calculate the phase shift of the guided modes. The theoretical results are compared to experimental data obtained with a sensing element based on a π-phase-shifted fiber Bragg grating and with photoacoustically generated ultrasonic signals.

Energy flow analysis of out-of-plane vibration in coplanar coupled finite Mindlin plates

In this paper, an Energy Flow Analysis (EFA) for coplanar coupled Mindlin plates was performed to estimate their dynamic responses at high frequencies. Mindlin plate theory can consider the effects of shear distortion and rotatory inertia, which are very important at high frequencies. For EFA for coplanar coupled Mindlin plates, the wave transmission and reflection relationship for progressing out-of-plane waves (out-of-plane shear wave, bending dominant flexural wave, and shear dominant flexural wave) in coplanar coupled Mindlin plates was newly derived. To verify the validity of the EFA results, numerical analyses were performed for various cases where coplanar coupled Mindlin plates are excited by a harmonic point force, and the energy flow solutions for coplanar coupled Mindlin plates were compared with the classical solutions in the various conditions.

A 3-D elasticity theory based model for acoustic radiation from multilayered anisotropic plates.

A theoretical model built upon three-dimensional elasticity theory is developed to investigate the acoustic radiation from multilayered anisotropic plates subjected to a harmonic point force excitation. Fourier transform technique and stationary phase method are combined to predict the far-field radiated sound pressure of one-side water immersed plate. Compared to equivalent single-layer plate models, the present model based on elasticity theory can differentiate radiated sound pressure between dry-side and wet-side excited cases, as well as discrepancies induced by different layer sequences for multilayered anisotropic plates. These results highlight the superiority of the present theoretical model especially for handling multilayered anisotropic structures.

Predictive modulation schemes to reduce common‐mode voltage in three‐phase inverters‐fed AC drive systems

Pulse width modulation controlled inverters produce common-mode voltage, which has been reported to cause many system drawbacks. This voltage along with high d v /d t raises leakage currents which can result in serious problems such as motor damage and electromagnetic interference to the surrounding equipment. Also common-mode voltage is responsible for bearing failure and overvoltage stress to the winding insulation of an AC motor. Therefore knowledge of reducing common-mode voltage is essential to provide a correct insight into the design of the drive system. Previous methods for common-mode voltage reduction cause extra harmonic in output currents, since they are based on voltage control. This study proposes new modulation strategies based on predictive current control (PCC) for three-phase pulse width modulation inverters-fed AC motor drive systems which mitigate the common-mode voltage and moreover, decrease the harmonic contents of output currents. As PCC can be employed in low voltage and medium voltage drive applications, the proposed strategies have been implemented on two-level and three-level neutral-point clamped inverter. A comparative study of proposed techniques with traditional ones has been carried out from the output current total harmonic distortion point of view. Simulation results and mathematical analyses, along with experimental tests for two-level inverter using Texas Instrument DSP model TMS320F28335, confirm that the new strategies improve behavior of drive systems in comparison with previous methods.

Sound Energy Field in a System of Coupled Rooms

The paper presents a theoretical basis of calculations of the sound intensity in enclosed spaces and shows results of numerical visualization of the active intensity in a room with absorptive walls formed by two coupled rectangular subrooms. The study was focused on the low-frequency range, therefore to describe the active and reactive intensities, the modal theory of room acoustics was applied. Space distribution of eigenfunctions, modal frequencies and modal damping coe cients were calculated numerically using the forced oscillator method (FOM) and the nite di erence time-domain (FDTD) method. Based on theoretical and numerical results, the computer program has been developed to simulate the active intensity vector eld when the room is excited by a harmonic point source. Calculation data have shown that the active intensity was extremely sensitive to position of the source since at a xed source frequency, di erent source locations always generate di erent distributions of characteristic objects of the active sound eld such as energy vortices and stagnation points. Because of complex room shape, the vortex centers are in most cases positioned irregularly inside the room. Almost regular arrangement of vortices was found only in the case when the source frequency was tuned to the frequencies of modes which were strongly localized in one of the subrooms.