Anastasia Bushueva, Olga Vlasova, Denis Polezhaev^*

FDMP-Fluid Dynamics & Materials Processing, Vol.20, No.4, pp. 847-857, 2024, DOI:10.32604/fdmp.2024.048271

Abstract The steady flow in a Hele-Shaw cell filled with fluids with a high viscosity contrast in the presence of fluid oscillations is experimentally studied. The control of oscillatory dynamics of multiphase systems with interfaces is a challenging technological problem. We consider miscible (water and glycerol) and immiscible (water and high-viscosity silicone oil PMS-1000) fluids under subsonic oscillations perpendicular to the interface. Observations show that the interface shape depends on the amplitude and frequency of oscillations. The interface is undisturbed only in the absence of oscillations. Under small amplitudes, the interface between water and glycerol widens due to mixing. When the… More >

Victor Kozlov^1,*, Vladimir Saidakov¹, Nikolai Kozlov²

FDMP-Fluid Dynamics & Materials Processing, Vol.20, No.4, pp. 693-703, 2024, DOI:10.32604/fdmp.2024.048068

Abstract The behavior of two immiscible low-viscosity liquids differing in density and viscosity in a vertical flat layer undergoing modulated rotation is experimentally studied. The layer has a circular axisymmetric boundary. In the absence of modulation of the rotation speed, the interphase boundary has the shape of a short axisymmetric cylinder. A new effect has been discovered, under the influence of rotation speed modulation, the interface takes on a new dynamic equilibrium state. A more viscous liquid covers the end boundaries of the layer in the form of thin films, which have the shape of round spots of almost constant radius;… More >

Wei Chen, Nan Qiu^*, Xusheng Yang

Energy Engineering, Vol.121, No.4, pp. 987-1005, 2024, DOI:10.32604/ee.2023.045475

Abstract During the operation of a DC microgrid, the nonlinearity and low damping characteristics of the DC bus make it prone to oscillatory instability. In this paper, we first establish a discrete nonlinear system dynamic model of a DC microgrid, study the effects of the converter sag coefficient, input voltage, and load resistance on the microgrid stability, and reveal the oscillation mechanism of a DC microgrid caused by a single source. Then, a DC microgrid stability analysis method based on the combination of bifurcation and strobe is used to analyze how the aforementioned parameters influence the oscillation characteristics of the system.… More >

Chongyang Zhao, Wei Chai, Beibei Rui, Lin Chen^*

Energy Engineering, Vol.120, No.11, pp. 2683-2705, 2023, DOI:10.32604/ee.2023.029620

Abstract At present, the direct drive permanent magnet synchronous generator (DD-PMSG) grid connected system based on virtual synchronous generator (VSG) control will experience power oscillation at sub synchronous frequencies. The mechanism and characteristics of this new type of sub-synchronous interaction (SSI) are not yet clear, and the system cannot recover to steady state solely based on the characteristics of VSG itself. Especially when connected to a weak current network, oscillations are more pronounced, affecting the stability of the system. In severe cases, the system may trigger shutdown protection and be disconnected from the network. Existing research has only analyzed the oscillation… More >

Jun Zeng¹, Fucheng Tian^1,*

The International Conference on Computational & Experimental Engineering and Sciences, Vol.27, No.2, pp. 1-1, 2023, DOI:10.32604/icces.2023.09636

Abstract Instability in dynamic fracture suppresses crack velocity from reaching theoretical limit predicted by the classical linear elastic fracture mechanics (LEFM). In thin systems, crack can accelerate to near the theoretical limiting velocity without micro-branching instability. A dynamic oscillatory instability is observed at such extreme crack speed. This sinusoidal oscillation was further found to be governed by intrinsic nonlinear scale. Using a dynamic phase-field model (PFM) with no attenuation of wave speed, we successfully reproduce the oscillations in the framework of non-linear deformation. The used PFM model based on Griffith's theory and derived from the nonconservative Lagrange's equation. To deal with… More >

Denis Benka^*, Sabína Vašová, Michal Kebísek, Maximilián Strémy

Intelligent Automation & Soft Computing, Vol.37, No.3, pp. 2519-2535, 2023, DOI:10.32604/iasc.2023.040799

Abstract Pattern recognition algorithms are commonly utilized to discover certain patterns, particularly in image-based data. Our study focuses on quasiperiodic oscillations (QPO) in celestial objects referred to as cataclysmic variables (CV). We are dealing with interestingly indistinct QPO signals, which we analyze using a power density spectrum (PDS). The confidence in detecting the latter using certain statistical approaches may come out with less significance than the truth. We work with real and simulated QPO data of a CV called MV Lyrae. Our primary statistical tool for determining confidence levels is sigma intervals. The aforementioned CV has scientifically proven QPO existence, but… More >

Yubing Li^a , Mo Yang^a,*, Jian Li^b , Zhiyun Wang^a

Frontiers in Heat and Mass Transfer, Vol.13, pp. 1-8, 2019, DOI:10.5098/hmt.13.11

Abstract Thermalsolutal convection induced by mass and heat source in horizontal cavity is investigated numerically based on SIMPLE algorithm with QUICK scheme. The high-concentration heat source is placed in the square cavity, and the cavity wall is low temperature and low concentration. The smoke is used as the diffusion medium, and the flow field, temperature and concentration of the fluid under different Rayleigh number, buoyancy ratio Nc, Soret numbers and Dufour numbers are analyzed systematically. Parameter study demonstrates that heat and mass transfer of thermosolutal convection are enhanced with increasing Rayleigh number or buoyancy ratio, and the couple-diffusive interaction has a… More >

Chao Zhu¹, Zhuopei Liu², Hao Chen^2,3, Yangyang Li^2,3,*

Energy Engineering, Vol.120, No.5, pp. 1081-1105, 2023, DOI:10.32604/ee.2023.026000

Abstract Experiments were conducted on a diesel-methanol dual-fuel (DMDF) engine modified by a six-cylinder, turbo-charged, inter-cooled diesel engine. According to the number of diesel injection, the experiments are divided to two parts: the single injection mode and double injection mode. The results show that, at the double injection mode, the maximum of pressure rise rate is small and the engine runs smoothly, however, knock still occurs when the co-combustion ratio (CCR) is big enough. Under knock status, the power density of the block vibration concentrating at some special frequencies rises dramatically, and the special frequency of single injection mode (about 4.1… More >

Lei Wang¹, Tiecheng Li¹, Hui Fan², Xuekai Hu¹, Lin Yang³, Xiaomei Yang^3,*

Energy Engineering, Vol.120, No.4, pp. 851-867, 2023, DOI:10.32604/ee.2023.025383

Abstract In recent years, subsynchronous resonance (SSR) has frequently occurred in DFIG-connected series-compensated systems. For the analysis and prevention, it is of great importance to achieve wide area monitoring of the incident. This paper presents a Hankel dynamic mode decomposition (DMD) method to identify SSR parameters using synchrophasor data. The basic idea is to employ the DMD technique to explore the subspace of Hankel matrices constructed by synchrophasors. It is analytically demonstrated that the subspace of these Hankel matrices is a combination of fundamental and SSR modes. Therefore, the SSR parameters can be calculated once the modal parameter is extracted. Compared… More >

Hui Fang¹, Jingsen Zhou¹, Haozheng Wang^2,*, Yanxu Wang², Hongji Xiang¹, Yechun Xin²

Energy Engineering, Vol.120, No.4, pp. 831-850, 2023, DOI:10.32604/ee.2023.025171

Abstract Recently, high-frequency oscillation of the modular multilevel converter (MMC) based high-voltage direct current (HVDC) projects has attracted great attentions. In order to analyze the small-signal stability, this paper uses the harmonic state-space (HSS) method to establish a detailed frequency domain impedance model of the AC-side of the HVDC transmission system, which considers the internal dynamic characteristics. In addition, the suggested model is also used to assess the system's high-frequency oscillation mechanism, and the effects of the MMC current inner loop control, feedforward voltage links, and control delay on the high-frequency impedance characteristics and the effect of higher harmonic components. Finally,… More >