Frequency-domain Finite Element Analysis Research Articles

Characterization of Bonding Defects in Fiber-Reinforced Polymer-Bonded Structures Based on Ultrasonic Transmission Coefficient.

This research delves into the characterization of the ultrasonic transmission coefficient pertaining to various types of bonding defects in Fiber-Reinforced Polymer (FRP)-bonded structures. Initially, an ultrasonic transmission coefficient calculation model for FRP-bonded structures in a water immersion environment is established. This model is used to analyze the variation in the ultrasonic transmission coefficient under different defect types, namely intact bonding, interfacial slip, and debonding defects. Subsequently, a frequency domain finite element analysis model of FRP-bonded structures with different defect types is constructed. The simulation validates the accuracy of the theoretical analysis results and concurrently analyzes the variation in the transmission signal when the defects alter. Lastly, an experimental platform for water immersion ultrasonic transmission measurement is set up. The transmission signals under different defect types are extracted through experiments and evaluated in conjunction with theoretical calculations to assess the types of bonding defects.

Fast Estimation of Harmonic Losses Caused by Inverter Carrier in Interior Permanent-Magnet Synchronous Motors by Using Combination of Time- and Frequency-Domain Finite-Element Analyses

This article describes a fast calculation method for harmonic losses caused by inverter carrier in interior permanent-magnet synchronous motors (IPMSMs) under a large number of driving conditions. In the proposed method, the harmonic loss caused by the largest component of the harmonic voltages is calculated by the linear frequency-domain finite-element analysis (FEA) with the differential permeability distribution obtained by the time-domain FEA. The total carrier loss is predicted by the variation in this largest harmonic component and sum of the square of harmonic voltages. The proposed method is applied to the efficiency-map calculation of an IPMSM. It is clarified that the total computational time is reduced to be 1/20th when compared with the conventional method.

A biopotential optrode array: operation principles and simulations

We propose an optical electrode ’optrode’ sensor array for biopotential measurements. The transduction mechanism is based on deformed helix ferroelectric liquid crystals which realign, altering the optrode’s light reflectance properties, relative to applied potential fields of biological cells and tissue. A computational model of extracellular potential recording by the optrode including the electro-optical transduction mechanism is presented, using a combination of time-domain and frequency-domain finite element analysis. Simulations indicate that the device has appropriate temporal response to faithfully transduce neuronal spikes, and spatial resolution to capture impulse propagation along a single neuron. These simulations contribute to the development of multi-channel optrode arrays for spatio-temporal mapping of electric events in excitable biological tissue.

Development and verification of a time-domain approach for determining forces and moments in structural components of floaters with an application to floating wind turbines

Structural design of the floater is an important aspect in developing cost efficient and reliable floating wind turbines. It is difficult to well account for the effect of strong non-linear dynamic characteristics and transient loading events, e.g. wind turbine faults, of floating wind turbines in a frequency-domain finite element analysis. The time-domain approach which implements the Morison's formula cannot accurately account for the hydrodynamic loads on the hull of floating wind turbines. While, the conventional hybrid frequency-time domain approach (based on the potential flow theory) fails to capture structural responses of the hulls since a rigid-body global model rather than a finite element model of the hull is employed. The present paper deals with the development and verification of a time-domain approach that can be easily implemented in various state-of-the-art computer codes for wind turbine analysis, e.g. Simo/Riflex/Aerodyn, OrcaFlex and FAST + CHARM3D, to extend their capabilities to analyze global forces and moments in structural components of a generic floater subject environmental loads from e.g. wind and waves. The global forces and moments in the structural components might be used as inputs of design formulas for structural strength design checks and/or used as boundary conditions in a sub-model finite element analysis to determine structural responses such as stresses. The proposed approach focuses on modeling of the inertia and external loads on the hull and mapping of the loads in the finite element model of the hull. In the proposed approach, floating wind turbines are considered as a system of several structural components, e.g. blades, rotational shaft, nacelle, tower, mooring lines, columns, pontoons and braces, rather than one rigid-body, while a finite element model for the hull is developed to represent the global stiffness of the structural components. The external and inertial loads on the hull are modeled as distributed loads rather than the integrated forces and moments. The conventional hybrid frequency-time domain approach, which is available in the state-of-the-art computer codes, is implemented to model the hydrodynamic loads on each structural component with essential modifications with respect to the corresponding hydrodynamic coefficients, e.g. added mass and potential damping coefficients and wave excitation forces. Approaches for modeling the hydrostatic pressure forces, gravity loads, drag forces and inertial loads on each structural component are also illustrated. Second order and higher order terms of the hydrostatic and hydrodynamic loads and the hydroelasticity effects are not accounted for in the present paper but can be further included. So far, the proposed approach has been implemented in the computer code Simo/Riflex/Aerodyn to analyze global forces and moments in the hull of a semi-submersible wind turbine. Good agreement between the reference values and the simulation results has been observed and indicates that the developed time-domain numerical models are reliable. The simulation results show that the low-frequency aerodynamic loads and fluctuations of hydrostatic pressure forces on and gravity of the floating wind turbine are important contributions to the structural responses, in particular, in the low-frequency range.

Modal content-based damage indicators for disbonds in adhesively bonded composite structures

Adhesive bonding is a promising joining method for composite materials. This article focuses on the use of modal content-based damage indicators to improve the sensitivity of guided waves to disbonds in the adhesive. Wave-defect interaction is modeled using frequency-domain finite element analysis in order to identify modes sensitive to adhesive degradation in joints between carbon fiber–reinforced polymer laminates. Phased array transducers and multielement array sensors designed for structural health monitoring are employed to enable preferential mode excitation and modal content extraction, respectively. The domains in dispersion curve space predicted to have good, intermediate, and no sensitivity to disbond were experimentally found to have good, intermediate, and limited sensitivity using a feature of the received signals associated with the modal amplitude or a modal amplitude ratio. Furthermore, the modal amplitude was found to decrease monotonically with increasing disbond size, demonstrating that it has potential to quantitatively size disbonds.

Electrothermal Characterization of Doped-Si Heated Microcantilevers Under Periodic Heating Operation

This paper reports the frequency-dependent electrothermal behaviors of a freestanding doped-silicon heated microcantilever probe operating under periodic (ac) Joule heating. We conducted a frequency-domain finite-element analysis (FEA) and compared the steady periodic solution with 3ω experiment results. The computed thermal transfer function of the cantilever accurately predicts the ac electrothermal behaviors over a full spectrum of operational frequencies, which could not be accomplished with the 1D approximation. In addition, the thermal transfer functions of the cantilever in vacuum and in air were compared, through which the frequency-dependent heat transfer coefficient of the air was quantified. With the developed FEA model, design parameters of the cantilever (i.e., the size and the constriction width of the cantilever heater) and their effects on the ac electrothermal behaviors were carefully investigated. Although this work focused on doped-Si heated microcantilever probes, the developed FEA model can be applied for the ac electrothermal analysis of general microelectromechanical systems.

Folded dipole plasmonic resonators

A class of folded ordered plasmonic dipole nanoresonators based on insulator-metal-insulator (IMI) slab waveguides is proposed and studied. This work is motivated by the development of a novel fabrication process that avoids the need for direct write nanolithography and instead relies on accessible UV lithography and other top-down parallel fabrication techniques that result in metallic dolmen structures with nanometre sized gaps. In this context, the dolmen geometry consists of two vertical segments supporting a flat horizontal slab. It is shown using frequency domain finite element analysis that such structures, which are essentially folded dipole antennas, resonate in a similar manner to their linear unfolded counterparts. The effect of the likely fabrication features is also studied.

Frequency domain analysis of guided resonances and polarization selectivity in photonic crystal membranes

Microstructured photonic crystal membranes are of great interest as compact filters in a variety of fields, including telecommunication and sensing. Here we present an analysis of the transmission and resonance behavior of a dielectric membrane featuring periodically arranged holes using the frequency domain finite element analysis. We solve both the source as well as eigenvalue problem for a given geometry. Applying symmetry considerations, we discard modes that cannot be excited by incident transverse electro-magnetic (TEM) light simultaneously. We relate the results of the source problem to the modal analysis and obtain strong correspondence in both frequency and resonance quality factor. We find that the sharp resonances can be related to the eigenmodes of a rectangular dielectric resonator formed by the membrane and the holes of the photonic crystal. Analyzing noncircular holes for polarization-dependent transmittivity, the modal analysis presented herein constitutes a powerful tool to understand and identify occurrence of pronounced wideband polarization selectivity.

Poroelastic behaviour of cortical bone under harmonic axial loading: A finite element study at the osteonal scale

Bone fluid flow and its induced effects on the bone cells are important players in triggering and signalling bone formation and bone remodelling. This study aims to numerically investigate the behaviour of interstitial fluid flows in cortical bone under axial cyclic harmonic loads that mimics in vivo bone behaviour during daily activities like walking. Here, bone tissue is modelled as a fluid-saturated anisotropic poroelastic medium which consists of a periodic group of osteons. By using a frequency-domain finite element analysis, the fluid velocity field is quantified for various loading conditions and bone matrix parameters.

A system identification approach to the modelling of pulsed eddy-current systems

The purpose of this article is to present a novel approach in the modelling of pulsed eddy-current systems. Frequency-domain finite element analysis is used to build up a z-domain, finite impulse response (FIR) model. The FIR model allows excitation to be varied without need for the field analysis to be performed again. Furthermore, the proposed approach to the modelling of the system function allows unequal spacing of the frequency samples. This enables greater accuracy of the modelling in the frequency range where the magnitude or phase response of the system varies greatly. The proposed approach was validated on a pulsed remote-field eddy-current system in a ferromagnetic tube. Excellent agreement between predicted and measured response was achieved.