• Title/Summary/Keyword: Energy stability

Search Result 3,238, Processing Time 0.038 seconds

DEVELOPMENT OF PREDICTABLE STABILITY TEST FOR ASSESSMENT OF OPTIMUM LOADING TIME IN DENTAL IMPLANT

  • Kim, Seong-Kyun;Heo, Seong-Joo;Koak, Jai-Young;Lee, Joo-Hee;Kwon, Ji-Yong
    • The Journal of Korean Academy of Prosthodontics
    • /
    • v.46 no.6
    • /
    • pp.628-633
    • /
    • 2008
  • STATEMENT OF PROBLEM: The application of a simple, clinically applicable noninvasive test to assess implant stability are considered highly desirable. So far there is still a controversy about correlation of various tests and implant stability. PURPOSE: In order to assess implant stability, the development of a new method is critical. It's possible to assess implant stability by calculating energy and angular momentum during implant installation. The purpose of this study is to evaluate the correlation of energy and implant stability. MATERIAL AND METHODS: Twenty three implants were installed in two different types of pig bone. Type I bone was retrieved from the distal aspect of the rib, with more cortical bone. Type II bone came from a more proximal region with less cortical components and a higher content of bone marrow and spongeous trabeculae. Insertion torque, removal torque, ISQ values and angular momentum and energy were measured. Pearson Correlation test was done to analyze the relation between RFA, maximum insertion torque, mean insertion torque, bone type, energy and removal torque. RESULTS: Type I bone showed higher removal torque than type II bone. Energy value was significantly correlated with maximum insertion torque and mean insertion torque. RFA values were related with insertion torques but the significance was lower than Energy value. CONCLUSION: Within the limitation of this study energy values were considered clinically predictable method to measure the implant stability.

Energy Stability Analysis on the Onset of Buoyancy-Driven Convection in a Horizontal Fluid Layer Subject to Evaporative Cooling

  • Kim, Min Chan
    • Korean Chemical Engineering Research
    • /
    • v.57 no.1
    • /
    • pp.142-147
    • /
    • 2019
  • The onset of buoyancy-driven convection in an initially isothermal and quiescent horizontal fluid layer was analyzed theoretically. It is well-known that at the critical Rayleigh number $Ra_c=669$ convective motion sets in with a constant-heat-flux cooling through the upper boundary. Here, based on the momentary instability concept, the dimensionless critical time ${\tau}_m$ to mark the onset of convective motion for Ra > 669 was analyzed theoretically. The energy method under the momentary stability concept was used to find the critical conditions as a function of the Rayleigh number Ra and the Prandtl number Pr. The predicted critical conditions were compared with the previous theoretical and experimental results. The momentary stability criterion gives more reasonable wavenumber than the conventional energy method.

Transient Stability assessment in the real power system using Energy Function. (에너지함수를 이용한 실계통에의 과도 안정도 평가 적용)

  • Kwon, Tae-Won;Lee, Kyung-Jae;Lee, Byung-Ha;Ham, Wan-Kyun
    • Proceedings of the KIEE Conference
    • /
    • 1992.07a
    • /
    • pp.153-156
    • /
    • 1992
  • Transient stability analysis of Korea Electric power Corporation(KEPCO) system is conducted by time simulation method, and the method is robust and reliable. But, time simulation consumes enormous computing resources and engineering time, and it does not provide a measure of the degree of stability of the system. Therefore, this method does not apply to every changed condition appropriately and quickly in planning and operating. And Transient Energy Function (TEF) method whis can assess quickly and quantatively the degree of stability of the system and which judges the stability and the instability to analyse transient dynamic charater of the system by mutual changing kinetic energy and potential energy, is developed. TEF method analyses the first Swing transient stability of the system by using the thought that if after disturbance happening, the increase of all the rotator kinetic energy changes into the potential energy after diturbance clearing, the system is stable, otherwise the system is unstable. This paper represents the availabiIity of the TEF method by comparing with time simulation method on the two cases.

  • PDF

A Study on the Stability of the Flywheel System During the Storage and Generation of Energy (플라이휠 시스템의 에너지 저장/발생시 동역학적 안전성연구)

  • Jang, Ung-Jae;Lee, Su-Hun
    • Journal of the Korean Society for Precision Engineering
    • /
    • v.17 no.12
    • /
    • pp.151-156
    • /
    • 2000
  • A vibration in a high-speed machine may lead to machinery malfunction and even catastrophic failure. So solving the vibration problem is a fundamental requirement for the stability of the high-speed machine. The flywheel energy storage system using superconducting magnetic bearings is a device to store electrical energy as rotational kinetic energy by motor and to convert it to electrical by generator when necessary. The high-speed rotating flywheel has large amplitude at a critical speed. And it has an unstable behavior by the electric torque at the first stage of the energy generation. In this paper, the stability analysis is performed with an analytical model and equations of motion-which is considered the effect of the electric torque-to identify the stable driving condition and the dynamic behavior.

  • PDF

A Study on Power System Voltage Stability Analysis by the Direct Lyapunov Function (Luapunov 직접법에 의한 전력계통 전압안정도 해석)

  • 문영현;박능수;이태식
    • The Transactions of the Korean Institute of Electrical Engineers
    • /
    • v.43 no.5
    • /
    • pp.693-702
    • /
    • 1994
  • This paper deals with direct voltage stability analysis using a power system energy function. The structure preserved energy function is proposed as an energy function for voltage stability analysis. With the use of the proposed energy function voltage collapse conditions are derived, which yields the exactly same results with the Jacobian matrix approach. The voltage collapse phenomenon is analyzed by several methods, which shows that all of the methods produce the same voltage condition. This study also investigates the voltage collapse dynamics by using the proposed energy function. As a result, it has been found that the voltage collapse can be classified into two categories: static and dynamic instablilties which have quite different behaviors. In addition a new method is presented to calculate the power capacity limit of transmission lines with respect to voltage stability. The proposed method is tested for a 2-bus sample system, which shows the characteristics of voltage collapse phenomenon via the energy function.

Effect of Surfactant on the Dispersion Stability of Slurry for Semiconductor Silicon CMP (계면활성제가 반도체 실리콘 CMP용 슬러리의 분산안정성에 미치는 영향)

  • Yun, Hye Won;Kim, Doyeon;Han, Do Hyung;Kim, Dong Wan;Kim, Woo-Byoung
    • Journal of Powder Materials
    • /
    • v.25 no.5
    • /
    • pp.395-401
    • /
    • 2018
  • The improvement of dispersion stability for the primary polishing slurry in a CMP process is achieved to prevent defects produced by agglomeration of the slurry. The dispersion properties are analyzed according to the physical characteristics of each silica sol sample. Further, the difference in the dispersion stability is confirmed as the surfactant content. The dispersibility results measured by Zeta potential suggest that the dispersion properties depend on the content and size of the abrasive in the primary polishing slurry. Moreover, the optimum ratio for high dispersion stability is confirmed as the addition content of the surfactant. Based on the aforementioned results, the long-term stability of each slurry is analyzed. Turbiscan analysis demonstrates that the agglomeration occurs depending on the increasing amount of surfactant. As a result, we demonstrate that the increased particle size and the decreased content of silica improve the dispersion stability and long-term stability.

Effect of Activation Energy and Crystallization Kinetics of Polyethylenes on the Stability of Film Casting Processes

  • Lee, Joo-Sung;Cho, Joon-Hee
    • Korea-Australia Rheology Journal
    • /
    • v.21 no.2
    • /
    • pp.135-141
    • /
    • 2009
  • Effect of activation energy and crystallization kinetics of polyethylenes (PEs) on the dynamics and stability has been investigated by changing rheological properties and crystallization rate in film casting process. The effect of changes of these properties has been shown using a typical example of short-chain branching (SCB) in linear polyethylenes. SCBs in linear polymers generally lead to the increase of the flow activation energy, and to the decrease of the crystallization rate, making polymer viscosity lower in the case of equivalent molecular weight. In general, the increment of the crystallinity of polymers under partially crystallized state helps to enhance the process stability by increasing tension, and lower fluid viscoelasticity possesses the stabilizing effect for linear polymers. It has been found that the fluid viscoelasticity plays a key role in the control of process stability than crystallization kinetics which critically depends on the cooling to stabilize the film casting process of short-chain branched polymers operated under the low aspect ratio condition.

A Novel Method for Clustering Critical Generator by using Stability Indices and Energy Margin (안정도 지수와 에너지 마진을 이용한 불안정 발전기의 clustering 법)

  • Chang Dong-Hwan;Jung Yun-Jae;Chun Yeonghan;Nam Hae-Kon
    • The Transactions of the Korean Institute of Electrical Engineers A
    • /
    • v.54 no.9
    • /
    • pp.441-448
    • /
    • 2005
  • On-line dynamic security assessment is becoming more and more important for the stable operation of power systems as load level increases. The necessity is getting apparent under Electricity Market environments, as operation of power system is exposed to more various operating conditions. For on-line dynamic security assessment, fast transient stability analysis tool is required for contingency selection. The TEF(Transient Energy Function) method is a good candidate for this purpose. The clustering of critical generators is crucial for the precise and fast calculation of energy margin. In this paper, we propose a new method for fast decision of mode of instability by using stability indices. Case study shows very promising results.

A New Algorithm for Unstable Mode Decision in the On-line Transient Stability Assessment (온라인 과도안정도 평가를 위한 새로운 불안정모드 선정 알고리즘)

  • Chang, Dong-Hwan;Kim, Jung-Woo;Chun, Yeong-Han
    • The Transactions of The Korean Institute of Electrical Engineers
    • /
    • v.57 no.7
    • /
    • pp.1123-1128
    • /
    • 2008
  • The necessity of online dynamic security assessment is getting apparent under Electricity Market environments, as operation of power system is exposed to more various operating conditions. For on-line dynamic security assessment, fast transient stability analysis tool is required for contingency selection. The TEF(Transient Energy Function) method is a good candidate for this purpose. The clustering of critical generators is crucial for the precise and fast calculation of energy margin. In this paper, we propose a new method for fast decision of mode of instability by using stability indices and energy margin. The method is a new version of our previous paper.[1] Case studies are showing very promising results.

Study of stability and evolution indexes of gobs under unloading effect in the deep mines

  • Fu, Jianxin;Song, Wei-Dong;Tan, Yu-Ye
    • Geomechanics and Engineering
    • /
    • v.14 no.5
    • /
    • pp.439-451
    • /
    • 2018
  • The stress path characteristics of surrounding rock in the formation of gob were analysed and the unloading was solved. Taking Chengchao Iron Mine as the engineering background, the model for analysing the instability of deep gob was established based on the mechanism of stress relief in deep mining. The energy evolution law was investigated by introducing the local energy release rate index (LERR), and the energy criterion of instability of surrounding rock was established based on the cusp catastrophe theory. The results showed that the evolution equation of the local energy release energy of the surrounding rock was quartic function with one unknown and the release rate increased gradually during the mining. The calculation results showed that the gob was stable. The LERR per unit volume of the bottom structure was relatively smaller, which mean the stability was better. The LERR distribution showed that there was main energy release in the horizontal direction and energy concentration in the vertical direction which meet the characteristics of deep mining. In summary, this model could effectively calculate the stability of surrounding rock in the formation of gob. The LERR could reflect the dynamic process of energy release, transfer and dissipation which provided an important reference for the study of the stability of deep mined out area.