• Title/Summary/Keyword: Added Mass Effect

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Effect of Austenitizing Temperature on the Hardenability and Tensile Properties of Boron Steels (오스테나이트화 온도에 따른 보론강의 경화능과 인장 특성)

  • Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.25 no.9
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    • pp.497-502
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    • 2015
  • The hardenability of boron steel specimens with different molybdenum and chromium contents was investigated using dilatometry and microstructural observations, and then was quantitatively measured at a critical cooling rate corresponding to 90 % martensite hardness obtained from a hardness distribution plotted as a function of cooling rate. Based on the results, the effect of an austenitizing temperature on the hardenability and tensile properties was discussed in terms of segregation and precipitation behavior of boron atoms at austenite grain boundaries. The molybdenum addition completely suppressed the formation of pro-eutectoid ferrite even at the slowest cooling rate of $0.2^{\circ}C/s$, while the chromium addition did at the cooling rates above $3^{\circ}C/s$. On the other hand, the hardenability of the molybdenum-added boron steel specimens decreased with an increasing austenitizing temperature. This is associated with the preferred precipitation of boron atoms since a considerable number of boron atoms could be concentrated along austenite grain boundaries by a non-equilibrium segregation mechanism. The secondary ion mass spectroscopy results showed that boron atoms were mostly segregated at austenite grain boundaries without noticeable precipitation at higher austenitization temperatures, while they formed as precipitates at lower austenitization temperatures, particularly in the molybdenum-added boron steel specimens.

An Approximate Analytical Method for Hydrodynamic Forces on Oscillating Inner Cylinder in Concentric Annulus (동심원내에서 진동하는 내부 실린더에 작용하는 유체유발력의 근사적 해법)

  • 심우건
    • Journal of KSNVE
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    • v.7 no.5
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    • pp.861-869
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    • 1997
  • An approximate analytical method has been developed for estimating hydrodynamic forces acting on oscillating inner cylinder in concentric annulus. When the rigid inner cylinder executes translational oscillation, fluid inertia and damping forces on the oscillating cylinder are generated by unsteady pressure and viscous skin friction. Considering the dynamic-characteristics of unsteady viscous flow and the added mass coefficient of inviscid fluid, these hydrodynamic forces including viscous effect are dramatically simplified and expressed in terms of oscillatory Reynolds number and the geometry of annular configuration. Thus, the viscous effect on the forces can be estimated very easily compared to an existing theory. The forces are calculated by two models developed for relatively high and low oscillatory Reynolds numbers. The model for low oscillatory Reynolds number is suitable for relatively high ratio of the penetration depth to annular space while the model for high oscillatory Reynolds number is applicable to the case of relatively low ratio. It is found that the transient ratio between two models is approximately 0.2~0.25 and the forcea are expressed in terms of oscillatory Reynolds number, explicity. The present results show good agreements with an existing numerical results, especially for high and low penetration ratios to annular gap.

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Consideration of Structural Damage of Fresh Water Tank for 2,600 TEU Container Vessel (2,600 TEU Container Vessel 의 Fresh Water Tank 구조손상 사례 고찰)

  • Shin Sung-Kwang;Ahn Hyung-Joon;Choi Eui-keol;Koh Myeong-Seob;Leem Hyo-Kwan
    • Special Issue of the Society of Naval Architects of Korea
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    • 2005.06a
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    • pp.216-221
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    • 2005
  • Many tanks such as a fresh water tank, an aft peak tank and oil tanks are arranged in the engine room and aft part areas of the ship. By added mass effect of the fluid inside the tanks, the natural frequency will be changed according to filling height of the tank. For this reason, there is possibility of occurrence of excessive vibration by resonance between natural frequencies of local structure and excitation frequencies of the propeller or main engine. Therefore, calculation of natural frequencies is required for structure for many types of tank which are contacting with water or oil to consider added mass effect for anti-resonance design at design stage. In this study, a case of structure damage on the fresh water tank for 2600 TEU container vessel is introduced. In addition, natural frequency analysis and vibration measurement have been performed to investigate vibration characteristics for excessive vibration control.

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Effect of Adding Al-Ca Fluoride on Sintering Behavior of Aluminum-Bronze Powder

  • Masuoka, Sachiko;Arami, Yoshiro;Nagai, Shozo
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.276-277
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    • 2006
  • In order to accelerate the sintering of Al-Bronze powder covered with passive oxide film, we focused on the way to add Al-Ca fluoride consisting of $AlF_3$ and $CaF_2$, examined the effect of the $CaF_2$ mixing rate in Al-Ca fluoride, the amount of the added Al-Ca fluoride and the sintering temperature on sintering properties of Al-Bronze powder and considered the mechanism of the sintering acceleration. Al-Bronze powder was sintered most effectively by adding Al-Ca fluoride with the $CaF_2$ mixing rate of 20mass%. If the amount of added fluoride was over 0.05mass% and the sintering temperature was over 1123K, the sintering acceleration of the Al-Bronze powder appears. Regarding the mechanism of the sintering acceleration, it was presumed that $Al_2O_3$ film on the surface of the Al-Bronze particles was removed in the process of the formation of gaseous AlOF by the reaction with $AlF_3$, and the reaction was accelerated further by the presence of the liquid phase which is formed in Al-Ca fluoride.

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A Negative Effect of Animation Character in Mass Culture of Korea (한국의 대중문화에 Animation Character가 미치는 부정적인 영향)

  • 김홍산;신정숙
    • Archives of design research
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    • v.14 no.2
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    • pp.147-154
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    • 2001
  • The Animation Character is high value-added industry in an aspect of economic value. Because Animation Character creates various synergic effects. First and most importantly, the value of animation character is role of communicator in mass culture. The diverse personality and behavior of Animation character affects masses's a way of thinking and act. But the personality and behavior of Animation character express an extreme inclination, for the most part. And presentation of role's model that is necessary for maintenance and continuance of mass society is Auctioning wrongfully.

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Natural Vibration Characteristics of Cantilever Plate Partially Submerged into Water (수중에 부분 몰수된 외팔보의 고유진동 특성)

  • Kwak, Moon K.;Yang, Dong-Ho;Lee, Jae-Ha
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2012.10a
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    • pp.229-230
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    • 2012
  • The free flexural vibration of a cantilever plate partially submerged in a fluid is investigated. The fluid is assumed to be inviscid and irrotational. The virtual mass matrix is derived by solving the boundary-value problem related to the fluid motion using elliptical coordinates. The introduction of the elliptical coordinates naturally leads to the use of the Mathieu function. Hence, the virtual mass matrix which reflects the effect of the fluid on the natural vibration characteristics is expressed in analytical form in terms of the Mathieu functions. The virtual mass matrix is then combined with the dynamic model of a thin rectangular plate obtained by using the Rayleigh-Ritz method. This combination is used to analyze the natural vibration characteristics of a partially submerged cantilever plate qualitatively. Also, the non-dimensionalized added virtual mass incremental factors for a partially submerged cantilever plate are presented to facilitate the easy estimation of natural frequencies of a partially submerged cantilever plate. The numerical results validate the proposed approach.

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Effect of Cu Addition on Oxide Growth of Al-7 mass%Mg Alloy at High Temperature

  • Seong-Ho Ha;Abdul Wahid Shah;Bong-Hwan Kim;Young-Ok Yoon;Hyun-Kyu Lim;Shae K. Kim
    • Archives of Metallurgy and Materials
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    • v.66 no.3
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    • pp.699-702
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    • 2021
  • Effect of Cu addition on oxide growth of Al-7 mass%Mg alloy at high temperature was investigated. As-cast microstructures of Al-7 mass%Mg and Al-7 mass%Mg-1 mass%Cu alloys showed α-Al dendrites and area of secondary particles. The 1 mass%Cu addition into Al-7 mass%Mg alloy formed Mg32(Al, Cu)49 ternary phase with β-Al3Mg2. The total fraction of two Mg-containing phases in Cu-added alloy was higher than the β-Al3Mg2 fraction in Cu-free alloy. From measured weight gains depending on time at 500℃ under an air atmosphere, it was shown that all samples exhibited significant weight gains depending on time. Al-7mass%Mg-1mass%Cu alloy showed the relatively increased oxidation rate when compared with Cu-free alloy. All the oxidized cross-sections throughout the entire oxidation time showed coarse and dark areas regarded as oxides grown from the surface to inside, but bigger oxidized areas were formed in the Al-7mass%Mg-1mass%Cu alloy containing higher fraction of Mg-based phases in the as-cast microstructure. As a result of compositional analysis on the oxide clusters, it was found that the oxide clusters contained Mg-based oxides formed through internal oxidation during a long time exposure to oxidizing environments.

A Study for the Effect of a Virtual Mass with a Low-Pass Filter on a Stability of a Haptic System (가상질량과 저주파통과필터에 의한 햅틱 시스템의 안정성 영역에 관한 연구)

  • Lee, Kyungno
    • Journal of Institute of Convergence Technology
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    • v.7 no.2
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    • pp.25-30
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    • 2017
  • This paper presents the effects of a virtual mass with a low-pass filter on the stability boundary of a virtual spring in the haptic system. In general, a haptic system consists of a haptic device, a sampler, a virtual impedance model and zero-order-hold. The virtual impedance is modeled as a virtual spring and a virtual mass. However the high-frequency noise due to the sampling time and the quantization error of sampled data may be generated when an acceleration is measured to compute the inertia force of the virtual mass. So a low-pass filter is needed to prevent the unstable behavior due to the high-frequency noise. A finite impulse response (FIR) filter is added to the measurement process of the acceleration and the effects on the haptic stability are simulated. According to the virtual mass with the FIR filter and the sampling time, the stability boundary of the virtual spring is analyzed through the simulation. The maximum available stiffness to guarantee the stable behavior is reduced, but simulation results still show that the stability boundary of the haptic system with the virtual mass is larger than that of the haptic system without the virtual mass.

3_D Time-Domain Analysis on the Motion of a Ship Advancing in Waves (파중 진행하는 선박의 3차원 시간영역 운동해석)

  • 홍도천;하태범;김대헌;송강현
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2001.10a
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    • pp.164-168
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    • 2001
  • The motion of a ship advancing in regular waves is analyzed in the time-domain using the convolution integral of the radiation forces. The memory effect functions and infinite frequency added masses are obtained from the solution of the three dimensional improved Green integral equation in the frequency domain by making use of the Fourier transformation. The ship motions in regular waves have been calculated by both the time and frequency domain methods. It has been shown that they agree very well with each other. The present time-domain method can be used to predict the time histories of unsteady motions in irregular waves. It can also be used to calculate the hydrostatic and Froude-Krylov forces over the instantaneous wetted surface of the ship hull to predict large ship motions, in a practical sense, advancing in large amplitude waves.

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Numerical Study on the Local Motion of an A-frame for Deep Sea ROV Mother Ship in Irregular Waves (심해잠수정 모선의 A-프레임 시간영역 국부운동해석)

  • Hong, Do-Chun;Lee, Pan-Mook
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2003.05a
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    • pp.105-108
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    • 2003
  • The local motion at the top of an A-frame fixed on a research vessel for deep sea ROV floating in irregular waves is studied in the time-domain. The motion is analyzed in the time-domain using the convolution integral of the radiation forces. The memory effect functions and infinite frequency added masses are obtained from the solution of the three dimensional improved Green integral equation in the frequency domain by making use of the Fourier transformation.

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