Motion In Frequency Domain Research Articles

Hydroelastic analysis of offshore floating photovoltaic based on frequency-domain model

This paper presents a frequency-domain model for analyzing the hydroelastic response and the vulnerable area of floating photovoltaic structures under wave action. The structure is discretized into an array of modules connected by equivalent elastic beams, while the boundary element method is employed to solve the scattering and radiation problems of the modules. The structural stiffness matrix is assembled by employing coordinate transformations and matrix reorganization techniques. The hydrodynamic matrix and the structural stiffness matrix are combined to establish the frequency-domain motion equation for describing the flexibility of the structure. The maximum gradient index is introduced to evaluate the dynamics issues of floating photovoltaic structures. The vulnerable area of the structure is assessed using the equivalent stress based on the von Mises stress theory. The proposed numerical model is validated by comparing the results with benchmark experiment as well as classical numerical model results. With this method, the hydroelastic response of a 300m×300m offshore floating photovoltaic is investigated. The displacement and internal force of the structure under various wave conditions is analyzed. This work can deepen the understanding of the hydrodynamics of floating photovoltaic structures in marine environment.

A frequency-domain reduced order model for joints by hyper-reduction and model-driven sampling

The dynamic behavior of jointed assemblies exhibiting friction nonlinearities features amplitude-dependent dissipation and stiffness. To develop numerical simulations for predictive and design purposes, macro-scale High Fidelity Models (HFMs) of the contact interfaces are required. However, the high computational cost of such HFMs impedes the feasibility of the simulations. To this end, we propose a model-driven method for constructing hyper-reduced order models of such assemblies. Focusing on steady-state analysis, we use the Multi-Harmonic Balance Method (MHBM) to formulate the equations of motion in frequency domain. The reduction basis is constructed through solving a set of vibration problems corresponding to fictitious interface conditions. Subsequently, a Galerkin projection reduces the order of the model. Nonetheless, evaluating the nonlinear forces is prohibitively expensive given the necessary fineness of the discretization of the interfaces. For this reason, we implement an adapted Energy Conserving Weighing and Sampling (ECSW) technique for Hyper Reduction (HR), by which frictional contact nonlinearities are evaluated on a substantially smaller set of weighted elements, thereby allowing significant speedups for meshes of arbitrary fineness. This feature is particularly advantageous since analysts typically encounter a trade-off between accuracy and computational cost when deciding on the mesh size, whose estimation is particularly challenging for problems of this type. To assess the accuracy of our method without resorting to the HFM solution, we propose an error indicator with thresholds that have proven reliable in our analyses. Finally, the accuracy and efficiency of the method are demonstrated by two case studies.

Experimentally validated vibro-acoustic modeling of 3D bio-printed grafts for potential use in human tympanic membrane regeneration

Three-dimensional (3D) bioprinting is a pioneering field of tissue engineering obtaining a special role in most medical engineering fields. Otology is a medicine branch that needs bioprinting technology to receive aids for the reconstruction of aesthetic necessities of the ear and treating hearing loss diseases due to several pathological reasons such as tympanic membrane (TM) perforation. In this work, computational dynamic simulations of 3D printed TM grafts are presented. The main purpose of numerical modeling of these experimentally validated composite scaffolds is to demonstrate the worth of simulation in shortening the design time and decreasing testing costs of biomedical engineering projects. The simulated 3D printed TM grafts were fabricated in two main architectural categories using three different polymeric materials of polydimethylsiloxanes (PDMS), flex polylactic acid (PLA), and polycaprolactone (PCL) with uniform infilling of fibrincollagen composite hydrogels. As a numerical and dynamic validation study, firstly, a finite element (FE) simulation of the artificial TM grafts is carried out for a vibro-acoustic analysis by the COMSOL Multiphysics software package. Then a comparative study of results obtained from the dynamic modeling is performed with a set of existing data taken from experimental validation test results from digital optoelectronic holography (DOEH) and laser Doppler vibrometry (LDV). Observations show a good correlation between the acoustic behaviors of in vitro tested 3D printed TM grafts and computational models in both frequency domain motion and normalized velocity patterns. Satisfying correlation between acoustic properties of simulated TM grafts and experimental test results shows potential applications of printed TM grafts in tympanoplasty.

Ideal tooth profile modifications for improving nonlinear dynamic response of planetary gear trains

The ultimate goal in this study is to investigate the effects of tooth profile modifications (TPMs) on PGTs by performing parametric studies. For this purpose, firstly a nonlinear planetary gear dynamics model with time-varying stiffness is introduced. A time-varying stiffness function is included into the analysis by using loaded static transmission error (LSTE) for sun-planet and ring-planet gear meshes. In this analysis the computationally calculated values of LSTE are used; however, if an experimentally measured LSTE can be used, it will include all gear errors that exist in the gear pair, as well as time-varying mesh stiffness. Therefore, when this method is used with experimentally measured LSTE for dynamic modeling of planetary gear trains, one does not require any additional computational tool to estimate the time-varying mesh stiffness parameter. A drive-train simulation tool (Transmission3D), which combines analytical contact mechanics solutions with FE effectively, is used for verification purposes. The validity of the proposed model is shown by comparisons of the dynamic response of the proposed model with the response obtained through Transmission3D on an example PGT. A wide frequency range is selected to cover superharmonics of the natural frequencies in order to verify the accuracy of the dynamic model for speed ranges lower than the natural frequencies of the system, which are often encountered in practical applications. Harmonic balance method (HBM) is used to obtain the nonlinear algebraic equations of motion in frequency domain, which are solved by using Newton's method with arc length continuation. Parametric studies are performed by employing the mathematical model suggested important outcomes for application of TPMs in PGTs. The relationships between the distinct modal characteristics of PGTs and effectivity of TPMs are investigated in detail, leading to interesting outcomes. Moreover, different sensitivity characteristics are observed for linear and parabolic modification schemes. These outcomes; along with further evaluations on other aspects of design such as load intervals during operation, manufacturing tolerances, wear on gears, etc.; can be used in design guidelines for PGTs.

Spectral finite element method for wave propagation analysis in smart composite beams containing delamination

PurposeThe purpose of the study is to present a frequency domain spectral finite element model (SFEM) based on fast Fourier transform (FFT) for wave propagation analysis of smart laminated composite beams with embedded delamination. For generating and sensing high-frequency elastic waves in composite beams, piezoelectric materials such as lead zirconate titanate (PZT) are used because they can act as both actuators and sensors. The present model is used to investigate the effects of parametric variation of delamination configuration on the propagation of fundamental anti-symmetric wave mode in piezoelectric composite beams.Design/methodology/approachThe spectral element is derived from the exact solution of the governing equation of motion in frequency domain, obtained through fast Fourier transformation of the time domain equation. The beam is divided into two sublaminates (delamination region) and two base laminates (integral regions). The delamination region is modeled by assuming constant and continuous cross-sectional rotation at the interfaces between the base laminate and sublaminates. The governing differential equation of motion for delaminated composite beam with piezoelectric lamina is obtained using Hamilton’s principle by introducing an electrical potential function.FindingsA detailed study of the wave response at the sensor shows that the A0 mode can be used for delamination detection in a wide region and is more suitable for detecting small delamination. It is observed that the amplitude and time of arrival of the reflected A0 wave from a delamination are strongly dependent on the size, position of the delamination and the stacking sequence. The degraded material properties because of the loss of stiffness and density in damaged area differently alter the S0 and A0 wave response and the group speed. The present method provides a potential technique for researchers to accurately model delaminations in piezoelectric composite beam structures. The delamination position can be identified if the time of flight of a reflected wave from delamination and the wave propagation speed of A0 (or S0) mode is known.Originality/valueSpectral finite element modeling of delaminated composite beams with piezoelectric layers has not been reported in the literature yet. The spectral element developed is validated by comparing the present results with those available in the literature. The spectral element developed is then used to investigate the wave propagation characteristics and interaction with delamination in the piezoelectric composite beam.

A simplified derivation of the ordinary differential equations for the free-surface Green functions

Ordinary differential equations (ODEs) are derived for the free-surface Green functions and their gradients, in a fluid of infinite depth. The cases of harmonic time-dependence in the frequency domain and impulsive motion in the time domain are considered separately. These ODEs were derived originally by Clément, starting with fourth-oder equations in the time domain and using Fourier transforms to derive a second-order ODE in the frequency domain. In the present work a simpler procedure is followed independently in each domain, transforming the governing Laplace equation to an ordinary differential equation. The results are consistent with the ODEs derived using Clément’s method.

A new parameter to empirically describe and predict the non-linear seismic response of sites derived from the analysis of Kik-Net database

We evaluate the non-linear site response at the stations of the Japanese Kik-Net network by computing the ratio between the Fourier spectra of the recordings at the surface and at the downhole station. When the amplitude of the input signal increases, we observe a shift of the resonance peaks towards lower frequencies, characteristic of non-linear soil behavior. We propose a new parameter called fsp to characterize this shift. We observe that fsp is a good proxy for the shear modulus reduction by comparing fsp and the modulus reduction curve obtain by both laboratory test measurements and numerical approaches. The fsp is used to correct the linear site response and surface ground motion in frequency domain in order to take into account the non-linear soil behavior. We show that the procedure we established reduces the error in predicting the main frequency peak by 50% compared to an elastic evaluation of the site response during the 2016 Kumamoto earthquake (Mw = 7.1).

Motion in frequency domain for harmonic balance simulation of electrical machines

PurposeThe high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation without eddy-currents and hysteresis losses. The harmonic balance approach is known for efficient and accurate simulations of magnetic devices in the frequency domain. But it lacks an efficient method for the motion of the geometry.Design/methodology/approachThe high computational effort of steady-state simulations limits the optimization of electrical machines. Stationary solvers calculate a fast but less accurate approximation without eddy-currents and hysteresis losses. The harmonic balance approach is known for efficient and accurate simulations of magnetic devices in the frequency domain. But it lacks an efficient method for the motion of the geometry.FindingsThe three-phase symmetry reduces the simulated geometry to the sixth part of one pole. The motion transforms to a frequency offset in the angular Fourier series decomposition. The calculation overhead of the Fourier integrals is negligible. The air impedance approximation increases the accuracy and yields a convergence speed of three iterations per decade.Research limitations/implicationsOnly linear materials and two-dimensional geometries are shown for clearness. Researchers are encouraged to adopt recent harmonic balance findings and to evaluate the performance and accuracy of both formulations for larger applications.Practical implicationsThis method offers fast-frequency domain simulations in the optimization process of rotating machines and so an efficient way to treat time-dependent effects such as eddy-currents or voltage-driven coils.Originality/valueThis paper proposes a new, efficient and accurate method to simulate a rotating machine in the frequency domain.

A time domain discrete-module-beam-bending-based hydroelasticity method for the transient response of very large floating structures under unsteady external loads

A time domain method is developed for estimating the transient response of very large floating structures under unsteady external loads. The hybrid frequency-time domain approach based on Cummins equations is adopted. First, the discrete-module-beam-bending-based hydroelasticity method in which a flexible structure is discretised into several rigid submodules connected by beam elements is used to establish the equations of motion for a flexible structure in frequency domain. The equations of motion in frequency domain are transformed into time domain following the idea of Cummins equations. The unsteady external loads at any point of the flexible structure are transferred to the centre of gravity of each submodule using the hydrostatic analysis of a beam in calm water. Good agreements are obtained between the numerical and experimental data for a weight drop test and a moving point load test of a continuous flexible structure in calm water, which validates the present time domain method. Finally, the time domain method is used for simulating the transient response of an interconnected flexible structure under the combination of wave and unsteady external loads, which highlights the significant effects of moving point loads on both the vertical displacement and bending moment of the structure.

Frequency Domain Updating of Thin-Walled Workpiece Dynamics Using Reduced Order Substructuring Method in Machining

The structural dynamics of thin-walled parts vary as the material is removed during machining. This paper presents a new, computationally efficient reduced order dynamic substructuring method to predict the frequency response function (FRF) of the workpiece as the material is removed along the toolpath. The contribution of the removed mass to the dynamics of the workpiece is canceled by adding a fictitious substructure having the opposite dynamics of the removed material. The equations of motion of the workpiece are updated, and workpiece FRFs are evaluated by solving the hybrid set of assembled equations of motion in frequency domain as the tool removes the material between two consecutive dynamics update steps. The orders of the initial workpiece structure and the removed substructures are reduced using a model order reduction method with a newly introduced automatic master set selection criterion. The reduced order FRF update model is validated with peripheral milling tests and FRF measurements on a plate-shaped workpiece. It is shown that the proposed model provides ∼20 times faster FRF predictions than the full order finite element (FE) model.

Experimental and numerical study on coupled motion responses of a floating crane vessel and a lifted subsea manifold in deep water

The floating crane vessel in waves gives rise to the motion of the lifted object which is connected to the hoisting wire. The dynamic tension induced by the lifted object also affects the motion responses of the floating crane vessel in return. In this study, coupled motion responses of a floating crane vessel and a lifted subsea manifold during deep-water installation operations were investigated by both experiments and numerical calculations. A series of model tests for the deep-water lifting operation were performed at Ocean Engineering Basin of KRISO. For the model test, the vessel with a crane control system and a typical subsea manifold were examined. To validate the experimental results, a frequency-domain motion analysis method is applied. The coupled motion equations of the crane vessel and the lifted object are solved in the frequency domain with an additional linear stiffness matrix due to the hoisting wire. The hydrodynamic coefficients of the lifted object, which is a significant factor to affect the coupled dynamics, are estimated based on the perforation value of the structure and the CFD results. The discussions were made on three main points. First, the motion characteristics of the lifted object as well as the crane vessel were studied by comparing the calculation results. Second, the dynamic tension of the hoisting wire were evaluated under the various wave conditions. Final discussion was made on the effect of passive heave compensator on the motion and tension responses.

Frequency domain subpixel registration using HOG phase correlation

We present a novel frequency-domain image registration technique, which employs histograms of oriented gradients providing subpixel estimates. Our method involves image filtering using dense Histogram of oriented gradients (HOG), which provides an advanced representation of the images coping with real-world registration problems such as non-overlapping regions and small deformations. The proposed representation retains the orientation information and the corresponding weights in a multi-dimensional representation. Furthermore, due to the overlapping local contrast normalization characteristic of HOG, the proposed histogram of oriented gradients - phase correlation (HOG-PC) method improves significantly the estimated motion parameters in small size blocks. Experiments using sequences with and without ground truth including both global and local/multiple motions demonstrate that the proposed method outperforms the state-of-the-art in frequency-domain motion estimation, in the shape of phase correlation, in terms of subpixel accuracy and motion compensation prediction for a range of test material, block sizes and motion scenarios.

High speed on-chip multiple cosine transform generator

Speeding up video encoding process is an important issue nowadays due to the high demand of increasing the video transmission speed for real-time video applications. Many algorithms and hardware implementations have been proposed for achieving such demand using pixel domain motion estimation. Moreover, much savings in computations and hardware complexity can be achieved using frequency domain motion estimation (FDME). The key issues in the FDME encoder is to generate four different transforms that are used for deciding the best match motion vector in the motion estimation (ME) process. The related transformed-discrete cosine transform (RT-DCT) generator is responsible for generating such transforms in the FDME encoder. In this paper, a fast RT-DCT generator is proposed to speed up the FDME encoding time by reducing its complexity. That makes the proposed RT-DCT appropriated for real-time video applications with limited resources, such as mobile internet device, cellular phones, personal digital assistant (PDA), and ultra-mobile personal computer. Moreover, the proposed architecture does not scarify the resolution. By adding the proposed RT-DCT generator to the whole FDME system, implementation and simulation results show that the system performs ME for SDTV video sequence at 371 MHz.

Spectral finite element for wave propagation analysis of laminated composite curved beams using classical and first order shear deformation theories

A frequency domain spectral finite element formulation is presented for the wave propagation analysis of laminated composite curved beams using the first order shear deformation theory (FSDT) and the classical laminate theory (CLT). The elements are derived from the exact solution of the governing equation of motion in frequency domain, obtained through Fourier transformation of the time domain equation. The formulation is validated by comparing the results for natural frequencies with the published results. The new elements are then employed to perform dispersion and wave propagation analyses of curved composite beams. The numerical results reveal that the wavenumbers predicted by the CLT show large deviation from those of the FSDT even for thin beams, and the deviation increases and occurs at lower frequencies with the increase in the thickness to radius ratio. The orthotropy ratio of the composite has a significant effect on the wavenumbers for tangential and mid-surface rotation modes. The wave propagation response predicted by the CLT differs widely from the FSDT prediction, for thin and thick, and shallow and deeply curved beams at both low and high frequencies. Thus, the CLT should not be used for wave propagation analysis of even thin curved laminated beams.

High Speed Transform Coding on Chip for Wireless Video Surveillance Systems

Streaming video quality dependents in part upon the video encoding process. The Frequency Domain Motion Estimation process is commonly used to accelerate the entire video encoding process. It is used to reduce the encoding time by increasing the Motion Estimation Time Saving. The Combinational-Discrete Cosine Transform consumes most of the time of the Frequency Domain Motion Estimation video encoder. Its function is to generate four transform coefficients to be used by the Frequency Domain Motion Estimation process. Generating such transforms slows down the encoding speed. Consequently, Frequency Domain Motion Estimation may not be suitable for online video applications. Saving time in the Combinational-Discrete Cosine Transform generator will considerably speed up the Frequency Domain Motion Estimation process. This paper proposes a fast Combinational-Discrete Cosine Transform architecture. The proposed architecture achieves up to 50% and 39% savings in both area and power consumption, respectively, compared to recent state-of-the-art Combinational-Discrete Cosine Transform architectures. The proposed architecture can perform up to 60 fps motion estimation over a 4CIF video at 123.21 MHz when integrated in the frequency domain encoder. It can be generalized to be used even for higher video resolution transmission such as HDTV broadcasting and video surveillance systems.

System identification method by using inverse solution of equations of motion in frequency domain

In this paper a direct system identification method is presented for identification of general linear system physical parameters (structural mass, damping and stiffness matrices) using direct inverse solution of the equations of motion in the frequency domain. When the input and output (responses) measured data are noise free, the proposed method can identify physical parameters exactly. When the input and outputs are mixed with measurement noise, an optimization process has been added to the method in order to improve the accuracy of the identified physical parameters of the system. The validity and efficiency of the proposed method is tested on a multistory-non-proportional-damping-structure subjected to sweep harmonic forces at the first story. It is shown that the proposed method can estimate the system parameters with a high level of accuracy. In the case of Gaussian white noise root mean square (RMS) is equal to 3% of the RMS of the structure response, stiffness matrix will be identified with around 2% error. Therefore identified matrices could be used for the damage detection process. The sensitivity of the proposed method to the noise level and damping of structure has also been investigated.

Linearization of Quadratic Drag to Estimate CALM Buoy Pitch Motion in Frequency-Domain and Experimental Validation

The dynamics of an oil offloading catenary anchor leg mooring (CALM) buoy coupled with mooring and flow lines are directly related to the fatigue life of a mooring system, necessitating an accurate estimate of the buoy hydrodynamic response. Linear wave theory is used for modeling the surface boundary value problem, and the boundary element method is used to solve the fluid-structure interaction between the buoy hull and the incident waves in the frequency-domain. The radiation problem is solved to estimate the added mass and radiation damping coefficients, and the diffraction problem is solved to determine the linear wave exciting loading. The buoy pitch motion is investigated, and linearizations of the quadratic drag/damping term are performed in the frequency-domain. The pitch motion response is calculated by considering an equivalent linearized drag/damping. Quadratic, cubic, and stochastic linearizations of the nonlinear drag term are employed to derive the equivalent drag/damping. Comparisons between the linear and nonlinear damping effects are presented. Time-domain simulations of the buoy motions are performed in conjunction with Morison’s equation to validate the floating buoy response. The time- and frequency-domain results are finally compared with the experimental model test results for validations. The linearization methods applied result in good estimates for the peak pitch response. However, only the stochastic linearization method shows a good agreement for the period range of the incident wave where typical pitch response estimate has not been correctly estimated.

Fast mode decision for the H.264/AVC video coding standard based on frequency domain motion estimation

The H.264 video coding standard achieves high performance compression and image quality at the expense of increased encoding complexity. Consequently, several fast mode decision and motion estimation techniques have been developed to reduce the computational cost. These approaches successfully reduce the computational time by reducing the image quality and/or increasing the bitrate. In this paper we propose a novel fast mode decision and motion estimation technique. The algorithm utilizes preprocessing frequency domain motion estimation in order to accurately predict the best mode and the search range. Experimental results show that the proposed algorithm significantly reduces the motion estimation time by up to 97%, while maintaining similar rate distortion performance when compared to the Joint Model software.

Sub-Hexagonal Phase Correlation for Motion Estimation

We present a novel frequency-domain motion estimation technique, which operates on hexagonal images and employs the hexagonal Fourier transform. Our method involves image sampling on a hexagonal lattice followed by a normalised hexagonal cross-correlation in the frequency domain. The term subpixel (or subcell) is defined on a hexagonal grid in order to achieve floating point registration. Experiments using both artificially induced motion and actual motion demonstrate that the proposed method outperforms the state-of-the-art in frequency-domain motion estimation operating on a square lattice, in the shape of phase correlation, in terms of subpixel accuracy for a range of test material and motion scenarios.

Estimation of Subpixel Motion Using Bispectrum

Motion estimation techniques are widely used in today's video processing systems. The frequently used techniques are frequency-domain motion estimation methods, most notably phase correlation (PC). If the image frames are corrupted by Gaussian noises, then cross-correlation and related techniques do not work well. In this paper, however, we have studied this topic from a viewpoint different from the above. Our scheme is based on the bispectrum method for sub-pixel motion estimation of noisy image sequences. Experimental results show that our proposed method performs significantly better than PC technique.