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In this paper, a site-specific optimization procedure aimed at finding the optimal substructures of a 10 MW Floating Offshore Wind Turbine (FOWT) is presented. An in-house developed Frequency Domain (FD) model is adopted for the simulation of the coupled system. Two Mediterranean sites have been chosen for the characterization of the metocean environments. 20-year databases have been used to obtain the joint distributions of wind speed, significant wave height and peak spectral period. The optimizations, performed adopting a Genetic Algorithm (GA), are aimed at reducing the costs of the floating substructure, controlling the maximum system response under both extreme and fatigue wind-wave loads. Results show that the optimized solution significantly reduces the system cost with an acceptable increase of the loads, opening interesting perspectives for the reduction of the Levelized Cost of Energy (LCOE) in sites characterized by mild sea states and low wind resource. • A site-specific optimization procedure for a 10 MW semisubmersible wind turbine is proposed. • Simulations are performed using a 7-DoF coupled frequency-domain model. • Optimizations are performed considering two installation sites in the Mediterranean Sea. • Objective functions are: maximum tower load, manufacturing cost and fatigue damage. • Results show the existence of improved solutions compared to an upscaled configuration. [ABSTRACT FROM AUTHOR]

Rational function approximation is commonly used to fit the transmission line impedance over a wide frequency range. Nevertheless, it is computationally costly and challenging to implement in practical applications due to the high number of approximations required to fit the impedance curve for the high-frequency range. Therefore, a novel fitting method of multiconductor transmission line (MTL) based on the analytical impedance equation of a transmission line using the impedance frequency response measurement is presented in this paper. The proposed fitting method is a function of the transmission line length since it is based on the analytical impedance equation of a finite transmission line. Furthermore, the proposed model uses a constant set of equations and calculated parameters to fit the impedance frequency response for a wide range of frequencies. Moreover, the proposed model parameters are calculated using derived resonance equations and the impedance frequency response measurement. In addition, an algorithm is developed to further fit the proposed model to the impedance frequency response measurement of the transmission line. MTL impedance frequency response is measured using a real-time digital simulator (RTDS). To ensure the accuracy of the proposed model, a comparison between the proposed model and vector fitting (VF) is presented. [ABSTRACT FROM AUTHOR]

This article proposes a model for a three-phase variable frequency drive in frequency domain for balanced harmonic condition. The model is represented by a frequency coupling matrix and is obtained through simulations in MATLAB and experimentation on a commercial drive. Two different model approaches, i.e., average model and lookup table-based model are attempted and difference in their performance is investigated. The model is validated for 70 voltage waveforms recorded at different industrial locations. The results obtained from the model match with the time domain simulation results. The proposed model is very fast with respect to the time of execution. A method to obtain the model in presence of grid impedance is proposed and the impact of variation of the grid impedance on the model parameters is also investigated. Further the application of the model is discussed using case studies. [ABSTRACT FROM AUTHOR]

In this paper, an optimization procedure is proposed to find platform and mooring system configurations which most effectively reduce the dynamic response of a semisubmersible 10 MW Floating Offshore Wind Turbine (FOWT). This is done by developing an efficient frequency domain simulation model able to account for the viscous drag forces and the contributions to the equation of motion stemming from turbine and mooring lines. The objective function is the value of the Response Amplitude Operator (RAO) at the eigenfrequency of the selected degree of freedom (DoF) of the system. Both parked and power production states are investigated. Feasibility constraints related to mean displacements and moorings layout are considered. Results show that optimized configurations can be found with better performances and smaller platform dimensions with respect to the configuration obtained by scaling up the 5 MW geometry. [ABSTRACT FROM AUTHOR]

This paper presents a frequency domain transfer function methodology for thermal characterization and design for energy flexibility of zones with hydronic radiant heating/cooling systems and significant thermal mass. The modeling methodology is validated with experiments in an environmental chamber. Using the developed frequency domain model of the zone, key transfer functions are calculated for a case study. By means of transfer functions, the effect of different levels of thermal mass on the zone thermal response and quantification of the energy flexibility in response to grid signals is studied. The model is used to evaluate different design and operation options on a relative basis to enhance energy flexibility for different scenarios. It is shown how transfer function analysis provides insight into the building thermal dynamics without the need for simulations. The transfer function that relates the radiant floor heat source at the bottom of the slab to the zone air temperature is derived and the delay between the heat input of the radiant slab and zone air temperature is calculated. Experimental measurements in an environmental chamber are used to validate the key design parameters obtained from the frequency domain transfer function regarding the operational strategies for energy flexibility of the thermal zone. Finally, it is shown how to utilize the quantified energy flexibility that is possible with the floor thermal mass through application of appropriate control strategies while maintaining satisfactory comfort conditions. • Frequency domain model gives lots of insight into the building thermal dynamics without any need for simulation. • Thermal mass energy flexibility will help reducing grid peak demand. • Optimum concrete thickness in terms of zone air fluctuations can be obtained through studying the relevant transfer functions. • Transfer function Z 1,aux can calculate the delay between the heat input of the radiant floor and air temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new probability density model is proposed. • The new model is composed of an exponential distribution and a Weibull distribution. • Comparative studies on the model accuracy are carried out. • The stochastic vibration fatigue test is carried out. In order to improve the fatigue life prediction of engineering structures under bimodal vibration response stress power spectra, a new probability density model of stress amplitude is proposed in this paper, which is composed of an exponential distribution and a two-parameter Weibull distribution. Under ideal bimodal response stress power spectra with different bandwidths, the connection between the first three order moments of rain-flow amplitude distributions and the spectral parameters is found. Then, according to the equations between the first three order moments of stress amplitude distributions of the model and those of rain-flow amplitude distributions, combined with the numerical optimization method, the relationship between model parameters and spectral parameters is established. Through comparative studies, the model in this paper leads to more accurate stress amplitude distributions and fatigue damage, which is very close to those obtained from time domain approach. Through the stochastic vibration fatigue test of aluminum alloy notched specimens, the high accuracy of the proposed model for estimating fatigue life is further verified. [ABSTRACT FROM AUTHOR]

Using frequency domain approach, this paper focuses on a zero-sequence harmonic filter model. The model is based on electromagnetic arrangement created through a three-legged core construction and zigzag windings that provide a low-priced, robust and efficient equipment to reduce zero-sequence fundamental and harmonic distortion. The methodology adopted here provides a useful technique for evaluating the steady-state operation of the filter with emphasis on its efficiency at reducing harmonics and at identifying the main constructive and electrical parameters of influence on the product performance. The representation is based on sequence harmonic transmittances that were found helpful in estimating the filter operational characteristics under both ideal and non-ideal conditions. Furthermore, the effectiveness of the filter and its representation are fully validated using an equipment prototype and laboratory results. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• A frequency domain model based on artificial neural networks is developed. • The bandwidth parameters are used as input neurons of the developed model. • The model is applicable for the wideband random fatigue life prediction. • The model exhibits better prediction accuracy than existing frequency domain models. In this paper, a novel artificial neural network (ANN) model is developed to achieve fatigue lifetime prediction under wideband random loads. Many power spectral density (PSD) samples with different spectral shapes and a wide range of material parameters related to fatigue life are used to improve the generalization ability of the model. The bandwidth parameters are used as the input neurons for the first time, compensating for the defect that the existing neural network models have too many input neurons. Numerous numeric simulations demonstrate that the developed model is more accurate in life prediction than the existing frequency domain models. [ABSTRACT FROM AUTHOR]

Primary space conditioning can be provided through active building-integrated thermal energy storage (BITES) systems, such as radiant space heating through concrete slabs. This approach can reduce peak space conditioning demand and energy costs while satisfying thermal comfort. However, thermal charging rates need to be predictively controlled due to the slow thermal response of BITES systems. This paper presents a charge control strategy using frequency domain models and room air temperature set-point profile as input. The models were previously verified with full-scale experiment data. The calculation procedures are demonstrated on active BITES systems with and without airflow to zone. Results show that the calculated charging rates satisfy the desired room air temperature set-point profiles. This control strategy is important for integrating the design and operation of active BITES systems because frequency domain models also provide important design information. [ABSTRACT FROM AUTHOR]

A methodology is presented for integrating the design and operation of active building-integrated thermal energy storage (BITES) systems to enhance their thermal and energy performance. A bounding-condition based design approach is proposed in conjunction with predictive control strategies. The predictive control uses frequency domain models and room air temperature set-point profile as input. The set-point profiles and BITES design are improved in a holistic manner according to the thermal dynamic response of active BITES systems and their thermal zones. The dynamic response is obtained from the transfer functions of frequency domain models. The methodology is demonstrated on ventilated systems. The results show that the methodology can significantly improve the design and operation of active BITES systems, and hence improve their thermal and energy performance. The dynamic response of different sizes of systems is presented to provide useful information for design selection. It is shown that concrete thickness of 0.2–0.3 m is a good value to initiate design. Other important application considerations are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents the mixed-mode effect on motor common mode current (CMC) in an adjustable speed drive (ASD). It is expected that the motor CMC is lower than inverter output CMC. However, the measurement result of the ASD shows that the AC motor input CMC is higher than the inverter output CMC in a frequency range. By using a mixed-mode (MM) 6-port networks, it is proven that the AC motor input CMC is higher due to an MM CMC which is generated from differential mode current. [ABSTRACT FROM AUTHOR]

In this paper, an optimal semisubmersible platform is sought considering two key geometry variables: the diameter of the outer cylinders and their radial distance from the platform centre. The goal is to identify a platform configuration able to most efficiently contrast the combined wind-wave action, keeping the platform dimensions as small as possible. The amplitude of the Response Amplitude Operator (RAO) peaks and the integral area of the RAOs in a range of excited frequencies for the selected degrees of freedom are chosen as targets to be minimised. Through an efficient frequency domain simulation approach, we show that upscaling techniques proposed in the literature may lead to overdesigned platforms and that smaller and more performing platforms can be identified. In particular, the optimised platform shows a reduction of about 51% in parked and 54% in power production of the heave RAO peak, and a reduction of about 37% in parked and 50% in power production of the pitch RAO. [ABSTRACT FROM AUTHOR]