The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
T. Pritz - One of the best experts on this subject based on the ideXlab platform.
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Relation of bulk to shear Loss Factor of solid viscoelastic materials
Journal of Sound and Vibration, 2009Co-Authors: T. PritzAbstract:The relation between the bulk and shear Loss Factors of isotropic, homogeneous, linear solid viscoelastic materials is investigated in this paper by means of the complex modulus concept. It is shown that the bulk and shear Loss Factors can be related through the dynamic Poisson's ratio provided that the shear Loss is low enough. Bounds on the ratio of the bulk to shear Loss Factor are derived, and the respective lower bounds are given as a function of the dynamic Poisson's ratio. The ratio of the bulk to shear Loss Factor is predicted to decrease with the increase of dynamic Poisson's ratio, and it is shown that the decrease may obey a simple power law if the Poisson's ratio is close to either 0 or 0.5. Experimental data on solid polymeric materials are presented which support the theoretical findings.
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The Poisson's Loss Factor of solid viscoelastic materials
Journal of Sound and Vibration, 2007Co-Authors: T. PritzAbstract:The complex Poisson's ratio plays an important role in characterizing the linear dynamic behaviour of solid materials, and occurs in a number of equations used for acoustical and vibration calculus. The ratio of the imaginary part to the real part of complex Poisson's ratio is referred to as Poisson's Loss Factor. The magnitude of the Poisson's Loss Factor is investigated in this paper for homogeneous, isotropic, linear solid viscoelastic materials with positive Poisson's ratio. The relation of the Poisson's Loss Factor to the material damping is determined. It is shown that the magnitude of the Poisson's Loss Factor is approximately proportional to the difference between the shear and bulk Loss Factors, and is a rational fractional function of the dynamic Poisson's ratio. In addition, relationships are developed which enable one to determine the approximate magnitude of the Poisson's Loss Factor from knowledge only of the shear Loss Factor and the dynamic Poisson's ratio. It is shown that the Poisson's Loss Factor is smaller than the shear Loss Factor usually by one order of magnitude at least. Moreover, it is pointed out that the Poisson's Loss Factor of a high Loss and a low Loss material may be about the same. Experimental data on two rubbers and a hard plastic are presented to verify the theoretical conclusions.
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Loss Factor PEAK OF VISCOELASTIC MATERIALS: MAGNITUDE TO WIDTH RELATIONS
Journal of Sound and Vibration, 2001Co-Authors: T. PritzAbstract:The Loss Factor of viscoelastic materials as a function of frequency has at least one peak. The relation between the magnitude and width of the Loss Factor peak is investigated in this paper by means of the fractional derivative Zener model with special reference to polymeric materials used for sound and vibration damping. It is shown that the magnitude and width are interrelated through the dispersion of dynamic modulus and the rate of frequency variation of Loss Factor. Moreover, it is proved that the relation between the magnitude and width of the Loss Factor peak is not unequivocal; either proportionality or inverse proportionality may exist between them. The important consequence of prediction on the proportionality is that, in contrast to the common belief concerning polymers, it is physically possible to increase the Loss Factor while simultaneously broadening the peak. The validity of model predictions is discussed and it is proved that the predictions are of a general nature, because they obey fundamental physical principles. Experimental data supporting the theoretical predictions are presented.
Hiroaki Kato - One of the best experts on this subject based on the ideXlab platform.
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Optimum Loss Factor for a Perfectly Matched Layer in Finite-Difference Time-Domain Acoustic Simulation
IEEE Transactions on Audio Speech and Language Processing, 2010Co-Authors: Parham Mokhtari, Hironori Takemoto, Ryouichi Nishimura, Hiroaki KatoAbstract:A perfectly matched layer (PML) is commonly used in finite-difference time-domain (FDTD) simulation to absorb outgoing waves and thereby reduce artifactual reflections from the computational domain boundaries. However, previous two-dimensional studies have noted that increasing the PML Loss Factor does not monotonically improve the PML's performance. This paper evaluates the PML in three-dimensional FDTD acoustic simulations. It confirms the existence of an optimum Loss Factor, with higher values degrading PML performance. An empirical formula is offered for estimating the optimum Loss Factor for a linear or a quadratic profile, that depends on the PML depth, sound speed, and grid resolution.
Parham Mokhtari - One of the best experts on this subject based on the ideXlab platform.
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Optimum Loss Factor for a Perfectly Matched Layer in Finite-Difference Time-Domain Acoustic Simulation
IEEE Transactions on Audio Speech and Language Processing, 2010Co-Authors: Parham Mokhtari, Hironori Takemoto, Ryouichi Nishimura, Hiroaki KatoAbstract:A perfectly matched layer (PML) is commonly used in finite-difference time-domain (FDTD) simulation to absorb outgoing waves and thereby reduce artifactual reflections from the computational domain boundaries. However, previous two-dimensional studies have noted that increasing the PML Loss Factor does not monotonically improve the PML's performance. This paper evaluates the PML in three-dimensional FDTD acoustic simulations. It confirms the existence of an optimum Loss Factor, with higher values degrading PML performance. An empirical formula is offered for estimating the optimum Loss Factor for a linear or a quadratic profile, that depends on the PML depth, sound speed, and grid resolution.
Alejandro Zaleta-aguilar - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamic characterization of the power Loss Factor in steam turbines
Energy Conversion and Management, 2002Co-Authors: Alejandro Zaleta-aguilar, Luis F Vega, Armando Gallegos-muñoz, Abel Hernandez-guerreroAbstract:Abstract Erosion, roughness, steam path damage etc., are Factors that reduce the power capacity in a steam turbine (ST). Any power Loss occurring locally in intermediate stages of a ST results in more available energy in the downstream stages. This effect is well known as the Loss Factor (LF) [Steam Turbines and Their Cycles, Krieger, NY, USA, 1974; Steam and Gas Turbines, McGraw-Hill, NY, USA, 1927; Steam Turbines Theory and Design, McGraw-Hill, NY, USA, 1984]. Currently, it is calculated by graphical methods [Evaluting and Improving Steam Turbine Performance, Gilson, NY, USA, 1993]. In this work, a new thermodynamic expression for the LF is introduced in order to improve applications to evaluate malfunctions in the first and intermediate stages of STs. The proposed thermodynamic expression for the LF is based on second law analysis and concepts like the internal parameter θ , and the dissipation temperature T d [Las Ecuaciones Caracteristicas, Doctoral Thesis, University of Zaragoza, 1992]. To show the main features and easiness of application of the proposed method, a 158 MW conventional power plant is analyzed, comparing the classical graphical method [Evaluating and Improving Steam Turbine performance, Gilson, NY, USA, 1993; Simplified Performance Test of Steam Turbines, ASME, NY, USA, 1970] and the proposed expression of the LF. Special emphasis is made on the thermoeconomical deviations that could arise by an imprecise application of the LF Method during an energy audit of the steam turbine internal parts.
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Thermodynamic Model of the Loss Factor Applied to Steam Turbines
International Journal of Thermodynamics, 2001Co-Authors: Alejandro Zaleta-aguilar, Javier Royo, Antonio ValeroAbstract:Erosion, roughness, steam path damage, etc., are Factors that reduce power capacity in a steam turbine. Any power Loss occurring locally in intermediate stages of a steam turbine results in more available energy in the downstream stages, this effect is well known as the Loss Factor (Salisbury, 1974; Stodola, 1927; Husain, 1984). Currently, the Loss Factor is been calculated by graphical methods (Cotton, 1996). In this work a new thermodynamic expression for the Loss Factor (LF) is introduced, in order to improve applications to evaluate malfunctions in the first and intermediate stages of steam turbines. The new thermodynamic expression for the Loss Factor, is based on Second Law Analysis; and concepts like the internal parameter θ, and the dissipation temperature Td; (Royo, 1992). An Example of a steam turbine in a conventional power plant of 158 MW is analyzed by comparing a classical graphical method (ASME/ANSI PTC-6, 1970; and Cotton, 1993), and the proposed expression of the Loss Factor (LF). Special emphasis is made on the thermoeconomical deviations that could arise by an imprecise application of the Loss Factor Method, during an energy audit of the steam turbine internal parts.
Yongqing Deng - One of the best experts on this subject based on the ideXlab platform.
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Inversion of Oil-Immersed Paper Resistivity in Transformer Based on Dielectric Loss Factor
IEEE Access, 2019Co-Authors: Jiangjun Ruan, Yu Tian, Yongqing DengAbstract:The aging of the transformer oil-paper insulation distributes spatially, which results in changes in paper resistivity in different regions. This paper establishes an iterative inversion algorithm using the finite element method to calculate the oil-immersed paper resistivity in different regions of a transformer. This algorithm sets the transformer dielectric Loss Factor tan δ at low frequency, the dielectric parameters of the transformer oil as inputs and the oil-immersed paper resistivity as output. The resistivity obtained from inversion can be used as a reference to access the insulation state of the oil-paper insulation. This paper aims at achieving the nondestructive detection of the partial state of the oil-paper insulation.
