Specific Power Spectral Density Research Articles

Comparative dynamic analyses under HELB-induced jet impingement loads

While ANSI/ANS 58.2 has been widely adopted as a standard to protect nuclear power plants against effects of postulated piping rupture, there are still arguments in determination of dynamic fluid characteristics and application to structural integrity assessment. To solve non-conservativeness of jet impingement loads in the current standard, a numerical approach was proposed that is promising from computational fluid dynamics analyses standpoint but further elaboration seems necessary for FE (Finite Element) analyses due to its implicit feature. This study is to investigate appropriate dynamic FE methods and to quantify differences with the previous one under postulated high energy line break conditions. In detail, modal analyses were performed to assess the vibration characteristic of integrated component and structure as well as individual components. Subsequent vibration analyses were carried out by using the modal analyses results of the integrated full model and specific power spectral density data depend on the jet direction and target area. From the comparative study, the dynamic FE analyses provided approximately 47% higher von Mises stresses and 14% larger radial displacements than the implicit FE analyses at the critical location.

Contactless approach to determine pavement skid resistance for Pavement Management System

Standard method to assess the pavement profile is to calculate the MPD (Mean Profile Depth) index based on results obtained usually by usage of laser techniques. In analysis the models of the surface pavements have been used in order to calculate the s1, s2, s3 parameters values corresponding to mega-, macro- and microtexture respectively. The values of the developed parameters s1, s2, s3 are calculated from the specific power spectral density values of surface roughness obtained for the threshold pavement roughness wavelength equal to 0.1, 0.05, 0.005 and 0.0005 m. The skid resistance has been correlated to the s1, s2, s3 parameters using 11 varied cases related to asphalt and concrete pavements. Skid resistance tests have been performed using CSR (Continuous Skid Resistance) device with fixed slip ratio equal to 13%. Three different test speed values 45, 65 and 95 km/h have been used. The obtained results lead to factorial correlation equations between developed parameters and skid resistance indices. Correlation results for uncontaminated pavement surface can be characterized by the coefficient of determination values in range between 0.55 and 0.94. The results can be used for contactless determination of pavement skid resistance in Pavement Management System.

Effects of quantum statistics of phonons on the thermal conductivity of silicon and germanium nanoribbons

We present molecular dynamics simulation of phonon thermal conductivity of semiconductor nanoribbons with an account for phonon quantum statistics. In our semiquantum molecular dynamics simulation, dynamics of the system is described with the use of classical Newtonian equations of motion where the effect of phonon quantum statistics is introduced through random Langevin-like forces with a specific power spectral density (color noise). The color noise describes interaction of the molecular system with the thermostat. The thermal transport of silicon and germanium nanoribbons with atomically smooth (perfect) and rough (porous) edges are studied. We show that the existence of rough (porous) edges and the quantum statistics of phonon change drastically the low-temperature thermal conductivity of the nanoribbon in comparison with that of the perfect nanoribbon with atomically smooth edges and classical phonon dynamics and statistics. The rough-edge phonon scattering and weak anharmonicity of the considered lattice produce a weakly pronounced maximum of thermal conductivity of the nanoribbon at low temperature.

Semiquantum molecular dynamics simulation of thermal properties and heat transport in low-dimensional nanostructures

We present a detailed description of semi-quantum molecular dynamics simulation of stochastic dynamics of a system of interacting particles. Within this approach, the dynamics of the system is described with the use of classical Newtonian equations of motion in which the effects of phonon quantum statistics are introduced through random Langevin-like forces with a specific power spectral density (the color noise). The color noise describes the interaction of the molecular system with the thermostat. We apply this technique to the simulation of thermal properties and heat transport in different low-dimensional nanostructures. We describe the determination of temperature in quantum lattice systems, to which the equipartition limit is not applied. We show that one can determine the temperature of such system from the measured power spectrum and temperature- and relaxation-rate-independent density of vibrational (phonon) states. We simulate the specific heat and heat transport in carbon nanotubes, as well as the heat transport in molecular nanoribbons with perfect (atomically smooth) and rough (porous) edges, and in nanoribbons with strongly anharmonic periodic interatomic potentials. We show that the effects of quantum statistics of phonons are essential for the carbon nanotube in the whole temperature range T<500K, in which the values of the specific heat and thermal conductivity of the nanotube are considerably less than that obtained within the description based on classical statistics of phonons.

Generation of Non-Gaussian Wide-Sense Stationary Random Processes with Desired PSDs and PDFs

This paper describes a new method to generate discrete signals with arbitrary power spectral density (PSD) and first order probability density function (PDF) without any limitation on PDFs and PSDs. The first approximation has been achieved by using a nonlinear transform function. At the second stage the desired PDF was approximated by a number of symmetric PDFs with defined variance. Each one provides a part of energy from total signal with different ratios of remained desired PSD. These symmetric PDFs defined by sinusoidal components with random amplitude, frequency and phase variables. Both analytic results and examples are included. The proposed scheme has been proved to be useful in simulations involving non-Gaussian processes with specific PSDs and PDFs.

On the Evaluation of MB-OFDM UWB Interference Effects on a WiMAX Receiver

The European Commission has recently adopted specific power spectral density masks for ultra wideband (UWB) devices, with detect and avoid capabilities, for coexistence with licensed standards. Under these regulations, a novel approach for analyzing the UWB interference effects on the WiMAX downlink is provided in this paper by means of a novel theoretical computation of the bit error rate (BER), simulation results, and measurements in a conducted modality. New analytical BER expressions for both uncoded and coded WiMAX systems, impaired by a single multiband-OFDM (MB-OFDM) UWB interference signal, are obtained in this paper for a Rayleigh fading channel. The BER is expressed in terms of the characteristic function of the interference signal. The maximum permissible interference levels and the signal-to-interference (SIR) values, which allow the UWB interference effects to be considered negligible, are estimated in this paper from simulation and measurement results. The analysis considers a WiMAX receiver operating at its minimum sensitivity level. The BER, the symbol error probability (SEP), and the error vector magnitude (EVM) of the WiMAX link are the metrics employed to characterize the interference effects for both frequency hopping and nonfrequency hopping UWB interferers.

Gaussian noise generator with specific autocorrelation properties

This paper deals with a new method for the design and implementation of a gaussian pseudorandom generator with a specific power spectral density or autocorrelation function. The method is based on the central limit theorem. The mathematical analysis of the generator, which consists of a digital white-noise generator and correlation-shaping transversal filter, is given. Computer simulation and experimental results show that the required process is generated with high accuracy.