Dynamic Stability Research On the DCT Marine Propulsion System with Unsymmetrical Load

2021 ◽  
Author(s):  
Jianghai Xu ◽  
Chunxiao Jiao ◽  
Donglin Zou ◽  
na ta ◽  
Zhushi Rao
Keyword(s):  
Large Scale ◽  
Excitation Frequency ◽  
Load Ratio ◽  
Coupled System ◽  
Propulsion System ◽  
System Stability ◽  
Unstable State ◽  
Finite Width ◽  
Gear Pair ◽  
The Stability

Abstract The DCT (double-cylinder turbines) propulsion system is widely applied to large-scale ships, while the instability mechanism of the system lacks theoretical and scientific research. Based on gear transmission principle and finite width journal bearings theory, the lateral-torsional-axial model of the system considering multiple nonlinear and time-varying factors is established. The effects of the unsymmetrical load parameters on the stability of the coupled system have been explored and quantified. Results indicate that the phenomenon of instability gradually occurs with the increase of excitation frequency, the decrease of load ratio between the two inputs or the decrease of input load value, and the vibration of the gear pair on the low load side is more severe. Furthermore, the vibration amplitude is not only related to the load parameters but also the distance between the gear pair and the load input disc. Finally, the influence of the oil whip on the system stability is crucial, especially when the system is in an unstable state. This study provides a theoretical reference for the optimization and adjustment of such propulsion system.

scholarly journals Large Photovoltaic Power Plants Integration: A Review of Challenges and Solutions

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3798 ◽  
Author(s):  
Mansouri ◽  
Lashab ◽  
Sera ◽  
Guerrero ◽  
Cherif
Keyword(s):  
System Integration ◽  
Power Plants ◽  
Large Scale ◽  
System Stability ◽  
Pv System ◽  
Pv Systems ◽  
Large Scale Integration ◽  
Voltage Limit ◽  
The Stability ◽  
Scale Integration

Renewable energy systems (RESs), such as photovoltaic (PV) systems, are providing increasingly larger shares of power generation. PV systems are the fastest growing generation technology today with almost ~30% increase since 2015 reaching 509.3 GWp worldwide capacity by the end of 2018 and predicted to reach 1000 GWp by 2022. Due to the fluctuating and intermittent nature of PV systems, their large-scale integration into the grid poses momentous challenges. This paper provides a review of the technical challenges, such as frequency disturbances and voltage limit violation, related to the stability issues due to the large-scale and intensive PV system penetration into the power network. Possible solutions that mitigate the effect of large-scale PV system integration on the grid are also reviewed. Finally, power system stability when faults occur are outlined as well as their respective achievable solutions.

Analysis on Stability of POGO and Parameters of Propulsion System in Liquid Rocket

2014 ◽  
Vol 664 ◽  
pp. 158-162
Author(s):  
Hou Wang Li ◽  
Cong Wang ◽  
Xiao Shi Zhang
Keyword(s):  
Natural Frequency ◽  
Damping Ratio ◽  
Coupled System ◽  
Propulsion System ◽  
Suction Line ◽  
Liquid Rocket ◽  
The Stability ◽  
Critical Damping

To explore effective methods of avoiding POGO instability, this paper starts with a thorough study on influence of parameters on natural frequency of propulsion system in liquid rocket. By adopting the method of critical damping ratio, stability of coupled structure-propulsion system is analyzed. The results show that installing an accumulator in suction line can effectively decrease natural frequency of propulsion system, which can improve the stability of coupled system. When cavitation and inertance of accumulator increases or installation position gets closer to top of pump, the influence of accumulator on the natural frequency becomes more significant.

scholarly journals SIMULATION AND BIFURCATION ANALYSIS OF GEOTECHNICAL SYSTEM STABILITY UNDER VIBRATION

2020 ◽  
Vol 61 (3) ◽  
pp. 92-100
Author(s):  
Nikolai V. Dorofeev ◽  
◽  
Anastasia V. Grecheneva ◽  
Ekaterina S. Pankina ◽  
Roman V. Romanov ◽  
...  
Keyword(s):  
Control Systems ◽  
Bifurcation Analysis ◽  
System Stability ◽  
Structure Stability ◽  
Unstable State ◽  
Automated Control ◽  
Geotechnical Stability ◽  
Geotechnical System ◽  
Vibration Action ◽  
The Stability

The automation of control processes for the stability of geotechnical systems is a great challenge involving the development of methods for multivariate analyzing and forecasting the stability with the subject to the nonlinearity of material stiffness parameters. The aim of the study is to improve the efficiency of automated control systems for geotechnical stability by developing an approach to detect negative changes in bifurcation diagrams of vibration displacement parameters of object structures. The authors present a mathematical model of the dynamic behavior of structural elements of an object as an elementary unit of a geotechnical system that describes a response to an external vibration action. An algorithm of bifurcation analysis is presented, which allows authors to determine the initial transition stage of the object structure to an unstable state by the acceleration values of forced oscillations exceeding the model parameters. A bifurcation diagram of stability changes in the structure of object at the displacement resulting from the load increase under vibration action has been constructed. This diagram, which type of codimension-one bifurcations is merging, enabled to determine the critical load values resulting in an unstable state transition of a system due to the influence of a combination of vibration factors. The efficiency evaluation of the proposed approach was carried out by the comparison with the results of construction stability calculations obtained by the use of the dynamic coefficient. The difference between the values of the maximum object displacement without loss of the stability under vibration action, obtained by the standard calculation method and using the developed model, is 32.5%, and it is significant in the theory of structure stability. When exogenous vibration noise is used as a source of a sounding signal, the application of the developed approach in automated control systems for geotechnical stability enable to change the permissible stability thresholds of objects being exploited depending on the level and combination of influencing factors.

The Mechanics and Stability of Gold Nanoparticle-Oligo-Ligand-DNA Systems

2013 ◽  
Vol 1513 ◽  
Author(s):  
Letisha A. McLaughlin ◽  
Mohammed A. Zikry
Keyword(s):  
Gold Nanoparticles ◽  
Dislocation Density ◽  
Large Scale ◽  
Mechanical Stability ◽  
Compressive Loading ◽  
High Stress ◽  
System Stability ◽  
Interfacial Behavior ◽  
Thiol Ligands ◽  
The Stability

ABSTRACTSystems in which DNA is adsorbed onto gold nanoparticles have the potential for applications in gene regulation therapies, drug delivery, sensing, and DNA scaffolding. However, the mechanical stability of gold nanoparticles (AuNPs) and interfacial behavior between the gold nanoparticles and thiol ligands are not well understood or quantified. The stability of DNA-AuNP) systems is, therefore, examined using a large-scale specialized finite-element approach with a dislocation-density based crystalline plasticity framework to model the AuNPs and an elastic description to model thiol ligands, DNA, and the ionic solution. For compressive loading conditions, the system exhibited morphological instabilities in the nanoparticles, as well as high stress and dislocation-density gradients at the thiol-nanoparticle attachment sites, which can affect system stability and attachment strength.

scholarly journals Impedance-Based Stability Analysis of Paralleled Grid-Connected Rectifiers: Experimental Case Study in a Data Center

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 2109 ◽  
Author(s):  
Henrik Alenius ◽  
Tomi Roinila
Keyword(s):  
Stability Analysis ◽  
Data Center ◽  
Large Scale ◽  
Real Life ◽  
System Stability ◽  
Limited Information ◽  
Impedance Measurements ◽  
Grid Connected Converters ◽  
The Stability

Grid-connected systems often consist of several feedback-controlled power-electronics converters that are connected in parallel. Consequently, a number of stability issues arise due to interactions among multiple converter subsystems. Recent studies have presented impedance-based methods to assess the stability of such large systems. However, only few real-life experiences have been previously presented, and practical implementations of impedance-based analysis are rare for large-scale systems that consist of multiple parallel-connected devices. This work presents a case study in which an unstable high-frequency operation, caused by multiple paralleled grid-connected rectifiers, of a 250 kW data center in southern Finland is reported and studied. In addition, the work presents an experimental approach for characterizing and assessing the system stability by using impedance measurements and an aggregated impedance-based analysis. Recently proposed wideband-identification techniques based on binary injection and Fourier methods are applied to obtain the experimental impedance measurements from the input terminals of a single data center rectifier unit. This work provides a practical approach to design and implement the impedance-based stability analysis for a system consisting of multiple paralleled grid-connected converters. It is shown that the applied methods effectively predict the overall system stability and the resonant modes of the system, even with very limited information on the system. The applied methods are versatile, and can be utilized in various grid-connected applications, for example, in adaptive control, system monitoring, and stability analysis.

Stability Analysis and Improvement of Virtual Wall Model

2011 ◽  
Vol 464 ◽  
pp. 183-186
Author(s):  
Jia Lu Li ◽  
Ai Guo Song ◽  
Xiao Rui Zhang
Keyword(s):  
Haptic Rendering ◽  
System Stability ◽  
Unstable State ◽  
Prototype System ◽  
Sampled Data ◽  
Wall Model ◽  
Passive Behavior ◽  
Energy Conversation ◽  
The Stability ◽  
Main Factor

Sampled-data system’s nature is the main factor that causes virtual wall to demonstrate active (non-passive) behavior, destroying the illusion of reality. To enhance the stability of haptic rendering by virtual wall model, a novel spring-impulse model based on energy conversation and momentum conversation is proposed. In the model, an impulse in the opposite direction of avatar’s velocity is exerted on avatar at the instant from inner of virtual wall back to balance position during unstable state. This resistant forces eliminate extra work to reduce the non-passive behaviors of the haptic system, which lead to improved realistic rigid perceptions and system stability. The experiments have verified the effectiveness of our spring-impulse method in a virtual stiff-wall prototype system via a Phantom Omni haptic device.

Dynamic Interaction Analysis of a 2D Propulsion Shaft-Ship Hull System Subjected by Sea Wave

2014 ◽  
Author(s):  
Zhe Tian ◽  
Xinping Yan ◽  
Zhixiong Li ◽  
Cong Zhang
Keyword(s):  
Large Scale ◽  
Interaction Analysis ◽  
Coupled System ◽  
Ship Hull ◽  
Propulsion System ◽  
Coupling Mechanism ◽  
Sea Waves ◽  
Ship Propulsion ◽  
Large Ship ◽  
Sea Wave

Since there is an evident tendency of development of large scale ships, the interaction between the propulsion shaft and ship hull becomes severe due to the tremendously increased ship size. As a result the reliability of the vessels has been put in an important position by the companies and the governments all over the world. The excited forces caused by severe sea waves have considerable effects on the hull deformation which could have further impact on the shaft propulsion system. This paper aims to investigate the coupling dynamics between the large ship propulsion system and hull subjected by sea wave in 2-dimensional circumstance. To look into the coupling mechanism between the ship propulsion shaft, hull and sea waves, a 2-dimensional novel model of large ship propulsion-hull coupling system is presented in this work to analyze the dynamic interactions of the ship propulsion system and hull. According to the dynamic equations of the coupling model, the dynamical responses of the ship shaft and hull are obtained under different stiffness of the support bearings. The analysis indicates that choosing the suitable stiffness of bearings have an important effect on the coupled system.

Extensive Experimental Study on the Stability of Rotor System With Spline Coupling

2018 ◽  
Author(s):  
Zezeng Dai ◽  
Jianping Jing ◽  
Changmin Chen ◽  
Jiqing Cong
Keyword(s):  
Experimental Study ◽  
High Reliability ◽  
Influence Factors ◽  
Coupled System ◽  
Transmission Error ◽  
Rotor System ◽  
System Stability ◽  
Spline Coupling ◽  
The Stability ◽  
Turboshaft Engine

Spline couplings which have simple structure, high reliability and can compensate torque transmission error are widely used in rotating machineries, such as aeroengine and gasturbine, etc. Recent efforts show that it is potential to make the rotor system losing its stability. Nevertheless, the experimental study of rotor system with spline coupling is rare and inadequate. This indicates a need to study the factors that affect the stability of rotor system with spline coupling experimentally. In this paper, a specially designed spline connection rotor test rig has been built and used to simulate a multi rotor system of turboshaft engine. The experimental instability characteristics of spline connected rotor system are presented. The instability speed and critical speed under different conditions such as lubrication conditions, external damping, load torque, spline tooth error and fit type of internal and external spline are measured. Based on the above-mentioned results, the effect rules of the influence factors on spline connected rotor system stability are studied. Results show that lubrication can effectively weaken the vibration of the system. The increased external damping makes the stability better when the spline coupling is unlubricated. With the increasing of load, the subharmonic vibration decreases after the system loses its stability, the system stability becomes better. The stability of spline coupled system with larger tooth error is better than that with normal one. Normal fit-up spline coupling improves the system stability under the conditions of lubrication and small external damping. This study may be helpful to get the favorable parameter setting of spline connected rotor system for avoiding instability and reducing vibration.

scholarly journals Development and Characterization of Two Types of Surface Displayed Levansucrases for Levan Biosynthesis

Catalysts ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 757
Author(s):  
Huiyi Shang ◽  
Danni Yang ◽  
Dairong Qiao ◽  
Hui Xu ◽  
Yi Cao
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Molecular Weight ◽  
Large Scale ◽  
Surface Display ◽  
Yeast Surface Display ◽  
Fusion Partner ◽  
Whole Cell ◽  
Food Industries ◽  
Yeast Surface ◽  
The Stability

Levan has wide applications in chemical, cosmetic, pharmaceutical and food industries. The free levansucrase is usually used in the biosynthesis of levan, but the poor reusability and low stability of free levansucrase have limited its large-scale use. To address this problem, the surface-displayed levansucrase in Saccharomyces cerevisiae were generated and evaluated in this study. The levansucrase from Zymomonas mobilis was displayed on the cell surface of Saccharomyces cerevisiae EBY100 using a various yeast surface display platform. The N-terminal fusion partner is based on a-agglutinin, and the C-terminal one is Flo1p. The yield of levan produced by these two whole-cell biocatalysts reaches 26 g/L and 34 g/L in 24 h, respectively. Meanwhile, the stability of the surface-displayed levansucrases is significantly enhanced. After six reuses, these two biocatalysts retained over 50% and 60% of their initial activities, respectively. Furthermore, the molecular weight and polydispersity test of the products suggested that the whole-cell biocatalyst of levansucrase displayed by Flo1p has more potentials in the production of levan with low molecular weight which is critical in certain applications. In conclusion, our method not only enable the possibility to reuse the enzyme, but also improves the stability of the enzyme.

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