Non-uniform Power Research Articles

Parametric Evaluation of SiC/SiC Composite Cladding with UO2 Fuel for LWR Applications: Fuel Rod Interactions and Impact of Nonuniform Power Profile in Fuel Rod

SiC/SiC composites are candidates for accident tolerant fuel cladding in light water reactors. In the extreme nuclear reactor environment, SiC-based fuel cladding will be exposed to neutron damage, significant heat flux, and a corrosive environment. To ensure reliable and safe operation of accident tolerant fuel cladding concepts such as SiC-based materials, it is important to assess thermo-mechanical performance under in-reactor conditions including irradiation and realistic temperature distributions. The effect of non-uniform dimensional changes caused by neutron irradiation with spatially varying temperatures, along with the closing of the fuel–cladding gap, on the stress development in the cladding over the course of irradiation were evaluated. The effect of non-uniform circumferential power profile in the fuel rod on the mechanical performance of the cladding is also evaluated. These analyses have been performed using the BISON fuel performance modeling code and the commercial finite element analysis code Abaqus. A constitutive model is constructed and solved numerically to predict the stress distribution in the cladding under normal operating conditions. The dependence of dimensions and thermophysical properties on irradiation dose and temperature has been incorporated into the models. Initial scoping results from parametric analyses provide time varying stress distributions in the cladding as well as the interaction of fuel rod with the cladding under different conditions of initial fuel rod-cladding gap and linear heat rate. It is found that a non-uniform circumferential power profile in the fuel rod may cause significant lateral bowing in the cladding, and motivates further analysis and evaluation.

Dynamic Strategy for Efficiency Estimation in a CCM-Operated Front-End PFC Converter for Electric Vehicle Onboard Charger

This paper presents a method for efficiency estimation of boost-derived continuous conduction mode power factor correction (CCM-PFC) converters for electric vehicle (EV) onboard chargers. The proposed methodology incorporates converter nonidealities, especially caused by magnetic components. The value of magnetizing inductance in an inductor or transformer core does not remain constant over variable current levels, which causes nonuniform power losses at different current levels. The method proposed in this paper considers a time-variant inductance over various current levels and accordingly establishes a dynamic model of loss estimation. As a proof-of-concept verification, the approach is applied to three different PFC topologies for EV applications and the estimated conversion efficiencies exhibit good agreement with experimentally obtained efficiency values over a wide range of load power from 400 W to 4.6 kW. The deviation of the efficiency predicted from the experimental data is considerably lower in comparison with the existing estimation methods with fixed inductance assumption.

Integrated Circuit Cooling Using Heterogeneous Micropin-Fin Arrays for Nonuniform Power Maps

As microelectronic system density continues to increase, cooling with conventional technologies continues to become more challenging and is often a limiter of performance and efficiency. The challenge arises due to both large heat fluxes generated across entire chips and packages, and localized hotspots with even higher heat flux. In this paper, nonuniform micropin-fin heat sinks are investigated for the cooling of integrated circuits with nonuniform power maps. Four heterogeneous micropin-fin samples were fabricated and tested in single-phase experiments with deionized water to investigate the effectiveness of local micropin-fin clustering for the cooling of hotspots. Cylindrical and hydrofoil micropin-fins were tested, as well as two types of heterogeneous arrays: those with pin-fins clustered directly over the hotspot and those with the high density cluster spanning the entire width of the channel to prevent flow bypass around the cluster. Samples were tested with a uniform nominal heat flux of 250 W/cm2 as well as a hotspot heat flux of 500 W/cm2. Local micropin-fin clustering was found to be an effective method of reducing local thermal resistance with a modest pressure drop penalty.

Application of IR thermography and thermal inverse modelling to evaluate power losses in ferromagnetic strips

The authors deal with the problem of determining the local properties and power loss in ferromagnetic material subjected to mechanical cutting. They use an IR camera to record local temperature rise on the surface of ferromagnetic strips including in the punched region. Next, the temperature measured is used in the numerical models that allow estimation of the power loss density distribution. A simple inverse thermal model for a ferromagnetic strip with non-uniform power loss is presented. The correctness of the results obtained from the simple inverse model is verified using the 3D thermal Finite Element Model (FEM) and compared with the results from the literature.

Characteristics of electromechanical disturbance propagation in non‐uniform power systems

A disturbance in anywhere of an interconnected power system will cause system oscillation that propagates in the entire power grid in the form of a wave. A disturbance propagation model for power systems is proposed to investigate the dispersion relation of the discrete model. Then, the reflection and transmission phenomena are discussed in the non-uniform power system model, and the influences of disturbance oscillation frequency on the reflection and transmission coefficients are analysed. Finally, a chain system and a New England benchmark test system are used to validate the correctness of the theoretical analysis. This work is meaningful to analyse the electromechanical dynamics of power systems and control the disturbance propagation.

Comparative Modular Exponentiation with Randomized Exponent to Resist Power Analysis Attacks

We present a secure variant of modular exponentiation implemented in RSA and CRT-RSA to resist power analysis attacks. For speeding up the computation, modular exponentiation is generally done through “squaring and multiplication” according to the binary bit of the secret exponent. This is popularly known as straight forward method. However, such computation leaves behind distinct traces of power consumption leading to power analysis attacks. These attacks were so powerful that they could reveal the secret exponent or the key challenging the vulnerability of any cryptosystem. In this work, we have enhanced the security of modular exponentiation by first randomizing the exponent or the secret key and then executing comparative bitwise squaring and multiplication. Our proposed work could be implemented in left-to-right or right-to-left without any modification of the algorithm which removed the dependency of “squaring and multiplication” on the bits of the key. As RSA decryption has more security privilege, we have implemented our proposed work only while decrypting the message. However, it can be used during encryption too. The randomized key, bit-independent squaring–multiplication and comparative modular exponentiation would generate non-uniform and random power traces resisting it from power analysis attacks.

A nonuniform distributed power amplifier in 0.18-mm CMOS technology

A nonuniform distributed power amplifier in 0.18-mm CMOS technology

Laser particle counter validation for aeolian sand transport measurements using a highspeed camera

Abstract Measuring aeolian sand transport rates in the field has been a long-standing challenge. In this paper, we present the results of a laboratory experiment to test the ability of a laser particle counter sensor (Wenglor) to accurately count sand grains of various grain size classes and stainless steel beads. We compared the count data collected by the Wenglor with images from a Highspeed camera which revealed the actual number of grains passing the laser beam. A Silicon photodiode was used to record the laser intensity reduction induced by the sand grain passage through the laser beam to derive the minimal necessary reduction for the Wenglor to count grains. For the two possible settings of the Wenglor, i.e., Minimal Teach-in or Normal Teach-in, a minimum of 18% and 78% blocking of the laser beam was required for recording a count. This implies that the minimum grain size that can be observed by the Wenglor is 210 ± 3 μ m and 495 ± 10 μ m for the two settings respectively, which is considerably coarser than previously assumed. Due to the non-uniform power distribution of the laser sensor intensity, at the detection limit of 210 μm, only grains passing through the centre of the beam will be counted.

Design of Filtering Microstrip Antenna Array With Reduced Sidelobe Level

For the requirements of efficient integration and simple fabrication, a new codesign approach for a microstrip filter with an antenna array with reduced sidelobe level is introduced in this communication. The microstrip patch antennas and the stub-loaded resonators are used to illustrate the synthesis of a bandpass filtering antenna array. By controlling the coupling strength between the resonators, a uniform or nonuniform power divider network can be obtained. A nonuniform power division is used to reduce the sidelobe level. The equivalent lumped circuit model is developed and analyzed in detail. Two types of eight-element filtering antenna array with uniform and tapered power-distribution among the elements have been designed. Simulated and measured results provide a good verification for the theoretical concepts.

Performance Evaluation of Space Shift Keying in Free-Space Optical Communication

In this paper, we study the performance of a space shift keying (SSK) scheme in a free-space optical (FSO) communication system under indoor and outdoor conditions. For the outdoor N t χ 1 FSO-SSK system, where N t is the number of transmitters (Txs), a novel closed-form mathematical expression for the probability density function (pdf) of the difference between two weighted gamma-gamma random variables is derived. Using this pdf, a new analytical expression is obtained for the tight upper bound of the average bit error rate (ABER) of this system. We also study the analytical bit error rate (BER) of an indoor N t χ 1 FSO-SSK system experiencing a deterministic channel. For this system, optimized values of transmit power weights are obtained by minimizing the analytical BER; it is observed that the optimized nonuniform power distribution is better than the uniform power distribution. However, for the outdoor FSO-SSK system, the best error performance can be achieved by employing uniform transmit power. An asymptotic BER analysis of uniformly weighted general outdoor FSO-SSK with an arbitrary number of Tx and receiver (Rx) apertures is also performed. Furthermore, the analytical coding gain and diversity order of the considered system are found based on the derived analytical BER expression. An interesting result observed from the coding gain analysis is that the performance of the outdoor FSO-SSK system remains unaltered from a moderate to a strong atmospheric turbulence regime, which makes the considered system nearly independent of turbulence. In addition, it is found by simulation and analysis that the considered system performs more poorly under the weak turbulence regime as compared to the other (strong and moderate) turbulence regimes. Our analysis also shows that the diversity order of the outdoor FSO-SSK system is N r /2, where N r is the number of Rx apertures, irrespective of the number of optical sources and turbulence conditions. In addition, it is observed that the performance of the FSO-SSK system degrades with an increasing number of optical sources under both indoor and outdoor conditions. Therefore, a trade-off between spectral efficiency and ABER is observed.

Flow regimes and convective heat transfer of refrigerant flow boiling in ultra-small clearance microgaps

Understanding two-phase convective heat transfer under extreme conditions of high heat and mass fluxes and confined geometry is of fundamental interest and practical significance. In particular, next generation electronics are becoming thermally limited in performance, as integration levels increase due to the emergence of ‘hotspots’ featuring up to ten-fold increase in local heat fluxes, resulting from non-uniform power distribution. An ultra-small clearance, 10μm microgap, was investigated to gain insight into physics of high mass flux refrigerant R134a flow boiling, and to assess its utility as a practical solution for hotspot thermal management. Two configurations – a bare microgap, and inline micro-pin fin populated microgap – were tested in terms of their ability to dissipate heat fluxes approaching 1.5kW/cm2. Extreme flow conditions were investigated, including mass fluxes up to 3000kg/m2s at inlet pressures up to 1.5MPa and exit vapor qualities approaching unity. Dominant flow regimes were identified and correlated to two phase heat transfer coefficients which were obtained using model-based data reduction for both device configurations. The results obtained were compared to predictions using correlations from literature, with the maximum heat transfer coefficient reaching 1.5MW/m2K in the vapor plume regime in the case of the finned microgap.

Numerical investigation of supercritical water flow in a vertical pipe under axially non-uniform heat flux

The authors conducted a numerical investigation of water flow in a vertical pipe during the transition from sub-to supercritical conditions when non-uniform power is applied axially at the wall. The Computational Fluid Dynamics calculations were first assessed with experimental results found in literature, where uniform heat flux was applied. Next, the model was used to perform calculations of four various cases with non-uniform heat flux distribution along the axis, however, the average value is equal to the value of the reference axially uniform-heated case. Results showed high dependency of the wall temperature distributions on the shape of the power distribution curve applied at the wall. It was found that if the peak value of heat flux is close or behind occurrence of heat transfer deterioration (HTD) phenomenon, the wall temperature increases rapidly to higher than in the reference case. However, if the peak is moved to the front part of the pipe, it is possible to achieve lower temperatures than when uniform heat flux was applied. Calculations of convective heat transfer i.e. Nusselt number show that currently, only two correlations were able to follow the trend of the results i.e. the Bishop's and Ornatsky's formulas. From the sensitivity calculations, it was found that the wall temperature is much more dependent on the mass flux than the operating pressure since the temperature variation is much higher and it is followed by the change of the position where HTD occurs.

Bandwidth Efficiency Maximization for Single-Cell Massive Spatial Modulation MIMO: An Adaptive Power Allocation Perspective

The concept of massive spatial modulation aided multiple-input multiple-output (SM-MIMO) systems, where the base station (BS) is equipped with a large number of antennas and simultaneously serves several multi-antenna users that employ SM for their uplink transmission, has recently attracted substantial research interest. In this paper, we investigate the uplink bandwidth efficiency (BE) of single-cell massive SM-MIMO systems, and derive a new BE lower bound when the BS employs maximum ratio combining for uplink user detection. The proposed BE bound takes into account the impact of spatial correlations at the transmitter, of imperfect channel estimation, and of non-uniform power allocation among each user’s antennas (i.e., different antennas are allocated with different levels of transmit power). These bounds are shown to be tight even when a moderate number of antennas is used by the BS. Based on this bound, a gradient ascent method-based optimization is carried out to find the optimal power allocation among the transmit antennas (TAs) of each user, so that the uplink BE can be maximized. More specifically, the optimal power allocation is found to be typically dependent both on the TAs’ spatial correlation and on the large-scale attenuation of each user. Aided by this new power allocation scheme, a substantial BE gain can be achieved over the conventional uniform power allocation schemes, which is substantiated by our simulation results.

Modeling the Power Variability of Core Speed Scaling on Homogeneous Multicore Systems

We describe a family of power models that can capture the nonuniform power effects of speed scaling among homogeneous cores on multicore processors. These models depart from traditional ones, which assume that individual cores contribute to power consumption as independent entities. In our approach, we remove this independence assumption and employ statistical variables of core speed (average speed and the dispersion of the core speeds) to capture the comprehensive heterogeneous impact of subtle interactions among the underlying hardware. We systematically explore the model family, deriving basic and refined models that give progressively better fits, and analyze them in detail. The proposed methodology provides an easy way to build power models to reflect the realistic workings of current multicore processors more accurately. Moreover, unlike the existing lower-level power models that require knowledge of microarchitectural details of the CPU cores and the last level cache to capture core interdependency, ours are easier to use and scalable to emerging and future multicore architectures with more cores. These attributes make the models particularly useful to system users or algorithm designers who need a quick way to estimate power consumption. We evaluate the family of models on contemporary x86 multicore processors using the SPEC2006 benchmarks. Our best model yields an average predicted error as low as 5%.

Optimization of the printed circuit boards placement at thermal design of the units with natural air cooling

It is considered an influence of printed circuit boards placement on temperature distribution in electronic equipment units with natural air cooling. Modeling of the temperature distribution in the unit and research of mass-dimension characteristics were carried out by means of CADs and engineering analysis. There are developed simplified geometric and thermal models of the unit. Here we analyze specificities of heat exchange in the units of radio electronic equipment with natural air cooling. It is developed an algorithm for optimization of printed circuit boards placement in radio electronic equipment with natural air cooling taking into account non-uniform power distribution between printed circuit boards. Proposed algorithm can be used as one of the stage of optimization of size, carrying or mass-dimension factors of the unit in case where unit powers are distributed non-uniformly.

Design of a Microstrip Series Power Divider for Sequentially Rotated Nonuniform Antenna Array

This paper deals with the design of a microstrip series power divider for circularly polarized sequential rotational antenna array. The theoretical description of the design is firstly proposed, comprising the cases of nonuniform weighted antenna arrays. A more flexible open octagon shape instead of the classical open ring is suggested, highlighting benefits in the case of nonuniform power distribution. A design example of an ultra-high frequency (UHF) band 4×4 sequentially rotated Tschebischeff antenna array finally demonstrates the effectiveness of the proposed implementation.

1-D dynamic stability analysis of mixed-spectrum supercritical water reactor core

The supercritical water reactor (SCWR) is one of the most prominent Generation IV reactors due to its high efficiencies. However, the stability issues, which are mainly caused by the great changes of thermodynamic properties and transport properties of supercritical water near the pseudo-critical temperature, are a challenge to the system safety and must be studied carefully. This paper is focused on 1-D dynamic stability analysis of mixed-spectrum SCWR (SCWR-M) reactor core. To this end, a frequency-domain model has been developed for linear stability analysis, and marginal stability boundaries under both the fixed inlet flow boundary conditions and the fixed external pressures boundary conditions are generated, which indicate that the system normal operational condition is in stable regions. Parametric sensitivity studies in frequency domain have been carried out. Increasing the wall thermal conductivity and mass flows can increase system stability. The system is more stable if the thermal zone has a lower power fraction. System with the designed non-uniform axial power distribution is also more stable than with the uniform distribution. A time-domain model has also been developed for nonlinear analysis, and the system marginal stability boundaries calculated by this method is consistent with those by frequency domain method. The existence of transitional stable region has been observed. A more reasonable definition for system logarithmic decay ratio has been achieved. The SCWR-M core has a subcritical bifurcation characteristic under fixed external pressures boundary conditions, thus its dynamic behaviors are not only related to systematic parameters, but also to the amplitudes of perturbations.

New models of droplet deposition and entrainment for prediction of liquid film flow in vertical annuli

Droplet deposition and entrainment significantly affect dryout occurrences in annular two-phase flow. Currently, most of the correlations for droplet deposition and entrainment are derived from flows in tubes. However, the main challenge in thermal-hydraulic analyses of BWRs is the prediction of dryout occurrence in the rod bundle geometry of fuel assemblies. In the work reported here, the applicability of several tube-based droplet deposition and entrainment correlations to the annular geometry (effectively a “one-rod” bundle) is checked. It is found that the prediction values from all those correlations deviate from the experimental measurements. Therefore, a set of simple and easy-to-implement models for deposition and entrainment rates in annuli is developed based on the tube-based Hewitt-Govan correlations (Hewitt and Govan, 1990), with considering the liquid film flow characteristics in annuli and the geometry effect of the annulus. The present models are verified by comparison with experimental data for developing liquid films in adiabatic annuli. By using these models to predict dryout in heated annuli, we find that these new relationships have good capability in predicting dryout occurrence in annuli with uniform as well as non-uniform axial power distribution.

Experimental study of the self-regulating performance of an R744 two-phase thermosyphon loop

The two-phase thermosyphon loop (TPTL) is an efficient solution for use in air-conditioning systems in data centers. The typical TPTL system pattern in data centers is the multi-evaporator TPTL. When the heat generated from the evaporators varies, the TPTL will self-regulate according to its own rules. In the current study, an experiment on a double-evaporator R744-based TPTL was conducted. Uniform, non-uniform, and variable heating power conditions were investigated, and a theoretical analysis was performed. The experimental results show that the mass flow rate of the high-power evaporator is higher than that of the low-power evaporator, but the self-regulating ability of the TPTL is very limited. The mass flow rate ratio (Mmax/Mmin) was between 1 and 1.5, with the heating power ratio (Qmax/Qmin) changing from 1 to 3; even when Qmax/Qmin is as high as 15, Mmax/Mmin is only 1.67. If the heating power of the two evaporators is different, the operating conditions of the evaporators will be affected. Therefore, when a TPTL is designed, more attention should be paid to the load of each single evaporator and the load of the other evaporators in parallel. In practical applications, significant differences between the heat transfer loads of parallel evaporators should be avoided as much as possible.

Soil moisture estimation based on BeiDou B1 interference signal analysis

BeiDou Navigation Satellite System reflectometry (BDS-R) is an emerging area of BD (BeiDou) applications that uses multipath reflected signals in microwave remote sensing. Soil moisture estimation is one of the potential important applications of BDS-R. This study aims to investigate the feasibility of soil moisture estimation based on BD B1 band interference signals, which are composed of direct and reflected BD signals and can be readily captured using low-cost commercial BDS receivers. In this paper, a theoretical background for soil estimation from interference signals was introduced, and an analysis of field experimental data was conducted. First, a cosine model for the interference signal power was built, and a non-uniform power spectrum analysis was performed on the received interference signals to determine its main frequency. Then, a least squares curve fitting was applied on the interference signal power to extract its phase. The relationship between the soil moisture and the phase was then determined. Two months of experimental data were collected at BaoXie, Wuhan and analyzed for further inversion. Experimental results show that the phase of the interference signals increases with the increase of soil moisture. The correlation coefficient between the phase and the in-situ soil moisture value is approximately 0.8. Finally, the relationship between the phase and soil moisture is employed to estimate soil moisture. Results show that using BDS-R to measure soil moisture is feasible, which demonstrates a great potential of new application of the BD system.