Fire accidents might be caused by liquid fuel leakage, which can accumulate in a prescribed area under the action of physical barriers. Therefore, pool fires could be of an arbitrary geometry in less ...ideal configurations. The current objective is to uncover the underlying physics of flame structure and dynamics in pool fires of different geometries. In this work, pool fires with seven different geometries were examined. Flame base structure and instantaneous flame height in pool fires of different geometries were recorded. Temperature, velocity/vorticity fields and coherent vortical structures were further presented by Large Eddy Simulation (LES). Results show that mean flame height of circular pool fire is the highest, while that of right triangle fires is the lowest. Mean flame height of the other noncircular geometries lies in these two extremes. The presence of vertices and hypotenuses has a dramatic influence on the formation and development of vortical structures. Triangular pool fires have the highest oscillation frequency, followed by quadrangular and circular geometries. To account for the physics of air entrainment and vortex dynamics due to pool fire geometry, pool perimeter is used as a characteristic length scale to propose new scaling relations for describing flame height and oscillation frequency.
•Fuel geometry effect on flame structure and dynamics of pool fires is studied.•Flame length scales and oscillation frequencies of pool fires are compared.•Cross-sectional temperature, velocity and vorticity profiles are numerically revealed.•Results present the vortex dynamics of pool fires in different geometries.•Relations of flame height and oscillation frequency in different geometries are proposed.
•By analyzing the mechanism of SSCI, the AHCC method, consisting of a subsynchronous frequency detection part and harmonic current compensation part, is applied to the RSC current inner loop.•The ...frequency detection part of the AHCC method can real-time identify the SSCI frequency, ensuring its applicability in SSCI suppression under various operating conditions. Compared to the structural complexity of the suppression strategies, it is simpler and more achievable.•Considering various influencing factors such as wind speed, the number of wind turbines, and the degree of series compensation, multiple simulations with oscillation frequency variation were constructed to verify the robustness and adaptability of the proposed control strategy.
In this paper, an adaptive harmonic current compensation (AHCC) method is proposed to mitigate subsynchronous oscillation (SSO) in series-compensated doubly-fed induction generator (DFIG)-based wind farms. The AHCC method, which consists of the subsynchronous frequency detection part and harmonic current compensation part, possesses the ability to mitigate SSO with wide-band frequency variation. The frequency detection part adopts the triple spectral line interpolation FFT method to detect and track oscillation frequency. The harmonic current compensation part adopts a quasi-proportional integral resonant (Q-PIR) controller. The Q-PIR adds a damped remodeling branch of oscillation frequency and blocks the sub-synchronous component's propagation. The center frequency of Q-PIR is adaptively adjusted according to the oscillation frequency to ensure stable operation under various conditions. Simulation results demonstrate the effectiveness and robustness of the AHCC method in mitigating SSO and enhancing the stability of wind power systems.
•Flame height and oscillation frequency of rectangular pool fires at different distances from a wall.•Length scale for flame height correlation is different from length scale for oscillation ...frequency correlation.•These length scales are modified, owing to air entrainment restrictions, as the distance from the wall changes.•Dimensionless correlations of flame height and oscillation frequency are proposed.
This manuscript presents an experimental investigation on the effect of varying separation distances from a facade wall on the flame height and oscillation frequency of a rectangular-source fire. Four sets of burners, each with the same area but different aspect ratios, were utilized. The burner aspect ratio, separation distance from the facade wall, and fire heat release rate were considered as test conditions. The flame oscillation frequency, determined based on flame height, was recorded and analyzed using Fast Fourier Transform (FFT). The results demonstrate that the flame oscillation frequency of the rectangular-source fire increases as the separation distance from the facade wall increases, while remaining unaffected by the heat release rate of the fire source. The factors influencing the flame oscillation frequency under different separation distances from the facade wall are analyzed. It is revealed that the air entrainment from the facade side is constrained, which affects the length scales used to determine the flame scale and flame oscillation frequency. The controlling correlation length scale for flame height is found to be related to the perimeter of the rectangular-source fires, whereas for oscillation frequency, it is related to the hydraulic diameter of the rectangular-source fires. These length scales are adjusted as the distance from the facade wall changes. Furthermore, the effective heat release rate in the flame height modeling is modified to account for changes in the distance from the wall. Based on these new developments, similarity correlations for flame height and oscillation frequency well reproduce the experimental results.
The results of a series of bench-scale pool fire experiments to explore the burning characteristics under a sealed environment are presented in this work.Although the oxygen fraction in the space ...gradually decreases by burning consumingin comparison to open conditions, the transient heat release rate can still be calculated using the PER approach using the in-situ measured oxygen fraction. The dimensionless flame height can still be calculated using the McCaffrey's model for open conditions, but a greater coefficient should be used because the flame burns in a ‘hunger’ mode when the oxygen fraction is low. The current non-sealed fire model for centerline temperature rise of pool fires is unsuitable for the sealed environment: the centerline temperature rise decreases more quickly than that predicted by Nasr's model developed for cases with a limited ventilation in the middle and later stages of the fire. A new engineering model has been developed in this study by curve fitting sealed fire test results. Pagni's law can still be suitable to describe the relationship between the frequency of flame oscillation and the diameter of a pool fire in a sealed environment, but the modified coefficients are required.
•A series of pool fire experiments in sealed ship engine room were conducted.•New model of characteristics concerned sealed pool fires was developed.•Differences of combustion parameters between sealed and open spaces were compared.•Abundant experimental data of sealed pool fires were collected.
Terahertz (THz) silicon-based electronics is undergoing rapid developments. In order to keep this momentum high, an accurate and optimized on-wafer characterization procedure needs to be developed. ...While evaluating passive elements, the measured s-parameter data can be verified by a direct use of EM simulation tools. However, this verification requires to precisely introduce part of the measurement environment such as the probes, pads, and access lines to accurately predict the impact of calibration and layout for on-wafer measurements. Unfortunately, this procedure is limited to passive elements. Hence, in this work, we propose a new procedure to emulate the measurement of active devices using an electromagnetic SPICE cosimulation. By this method, one can clearly highlight that a measurement artifact that was observed for the transistor measurement can be reproduced. One of the most representative examples of measurement artifact involves the measurement and estimation of <inline-formula> <tex-math notation="LaTeX">{f}_{\text {MAX}} </tex-math></inline-formula> which is not constant over all frequency bands. Also, the measurement is difficult to perform above 40 GHz. This typical problem is now undoubtedly attributed to the probe-to-substrate coupling and probe-to-probe coupling which are strongly dependent on the probe geometry. Finally, this cosimulation procedure evidently underlines the need for an optimized deembedding procedure above 200 GHz.
Biodiesel is an emblematic energy of green power and developing vigorously, which is conducive to an important strategic significance covering the sustainable development of the global economy, the ...promotion of energy substitution, the reduction of environmental pressure, and the control of atmospheric contamination. In order to study the biodiesel energy burning characteristics, a series of experiments were carried out in an ISO9705 full-scale room, and the effects of pool size on the burning rate, flame height, flame oscillation frequency, and flame radiation fraction of biodiesel energy fire were systematically analyzed. This study uses genetic algorithm-back propagation neural network (GA-BPNN) algorithms for real-time prediction of transient fire mass loss rates. Three parameters (pool size, liquid depth, and burning time) are paired with the fuel mass loss rate and trained using a GA-BPNN algorithms model. The results show that the GA-BPNN algorithms predictions have a good correlation with the validated experimental values and the relative is less than 15%. Furthermore, the ratio of intermittent flame height and continuous flame height to their mean value is calculated respectively at about 1.72 and 0.58. The flame oscillation frequency decreases following the increase in oil pool size, the correlation can be calculated by f=0.3(D/g′)1/2. Finally, a new correlation χrad=0.2Q˙*−2/3 is proposed to predict the flame radiation fraction by increasing the flame viewing factor coefficient. The proposed correlation can be used to describe its evolution under different oil pool sizes, which can be essential to estimate the flame radiation impact on surroundings for such biodiesel energy fires.
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•The combustion characteristics of biodiesel pool fire is investigated.•GA-BPNN algorithm is used to predict the real-time biodiesel burning rate.•A new correlation of flame radiation fraction prediction is introduced.
In this paper, the challenges of designing distributed amplifiers at frequencies close to <inline-formula> <tex-math notation="LaTeX">f_{\text {max}} </tex-math></inline-formula> of transistors are ...tackled. By using bandpass transmission lines, the maximum operation frequency of the distributed amplifier is increased compared to low-pass transmission lines. Moreover, a novel gain-boosted cascode structure with an internal feedback is employed to cancel a part of the loss in the input line and boost the bandwidth and the highest operation frequency of the amplifier. The proposed amplifier operates up to frequencies as high as 0.67 <inline-formula> <tex-math notation="LaTeX">f_{\text {max}} </tex-math></inline-formula> of the transistors. Two proof-of-concept prototypes are fabricated in a 0.13-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> SiGe process with <inline-formula> <tex-math notation="LaTeX">f_{\text {max}} </tex-math></inline-formula> of 210 GHz. The first prototype shows an average gain of 14.4 dB from 52 to 142 GHz (bandwidth of 90 GHz at the center frequency of 97 GHz) while the second one achieves an average gain of 18.6 dB from 48 to 135 GHz (bandwidth of 87 GHz at the center frequency of 91.5 GHz).
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