• Computers and Concrete
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• 제21권2호
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• pp.111-116
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• 2018

Establishment of test methods to assess the fresh properties of self-compacting concrete (SCC) are required to ensure the homogeneity in fresh and hardened states. This paper discusses the suitability of a simple test method for assessing the slump flow and stability of SCC by testing on self-compacting mortar (SCM) fraction. The proposed test method aims at investigating slump flow diameter test and sieve stability test of SCC by testing SCM fraction with a plunger penetration apparatus. A central composite modeling design was performed to evaluate the effects of water/cement ratio (W/C), superplasticizer dosage (SP) and powder marble content (MP) on slump flow diameter, stability and plunger penetration test of fresh SCC. The responses of the derived statistical models are slump flow (Sf), sieve stability (S) and plunger penetration (P). Relationships obtained in this study show acceptable correlations between plunger penetration test value and slump flow diameter test results and stability. It should note that the developed relationships are very useful to predict slump flow diameter and stability of studied SCC mixtures by carrying out a simple plunger penetration test on its mortar, which can save labour and time in laboratory experiments.

• Advances in concrete construction
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• 제7권2호
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• pp.97-105
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• 2019

In this paper, the workability and static stability were evaluated using a proposed test method. Workability and static stability represent a key property of self-compacting concrete (SCC) in fresh state. A number of standardized test methods were developed to assess these properties. However, no accelerated test method reliably predicts both workability and static stability of SCC. In the present work, a modified K-slump test method was developed to evaluate workability and static stability of SCC. In order to take implicit mixture variations of SCC constituents that can affect fresh SCC properties, a central composite design was adopted to highlight the effect of gravel to sand ratio (G/S), gravel 3/8 to gravel 8/15 ratio (G1/G2), water to cement ratio (W/C), marble powder to cement ratio (MP/C) and superplasticizer content (SP) on workability measured with slump and flow time (T50) tests and static stability measured with sieve stability test (Pi), segregation test index (SSI), Penetration test (Pd) and the proposed K-slump test (Km). The obtained results show that G/S ratio close to 1 and G1/G2 ratio close to 60% can be considered as optimal values to achieve a good workability while ensuring a sufficient static stability of SCC. Acceptable relationships were obtained between Slump flow, Pi, Pd and Km. Results show that the proposed K-slump test allow to assess both workability and static stability of fresh SCC mixtures.

• 한국항공운항학회지
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• 제15권4호
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• pp.142-147
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• 2007

When the aircraft is developed, several flight tests are performed including stability and controllability, performance and systems, above all the most important part of the flight test is stability test. Stability test is divided into two parts, static stability and dynamic stability. Static stability of the aircraft is typically defined in terms of its initial tendency to return to equilibrium after a disturbance and not included time concept. One of static stability, longitudinal static stability, was addressed here. The longitudinal static stability was studied from the basic theory to the flight test method and also explained data reduction method throughout the flight test. Finally showed how to meet the specifications such as ROC, FAR and MIL-specifications.

• Wind and Structures
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• 제10권4호
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• pp.367-382
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• 2007

A nonlinear numerical method was developed to assess the stability of suspension bridge catwalks under a wind load. A section model wind tunnel test was used to obtain a catwalk's aerostatic coefficients, from which the displacement-dependent wind loads were subsequently derived. The stability of a suspension bridge catwalk was analyzed on the basis of the geometric nonlinear behavior of the structure. In addition, a full model test was conducted on the catwalk, which spanned 960 m. A comparison of the displacement values between the test and the numerical simulation shows that a numerical method based on a section model test can be used to effectively and accurately evaluate the stability of a catwalk. A case study features the stability of the catwalk of the Runyang Yangtze suspension bridge, the main span of which is 1490 m. Wind can generally attack the structure from any direction. Whenever the wind comes at a yaw angle, there are six wind load components that act on the catwalk. If the yaw angle is equal to zero, the wind is normal to the catwalk (called normal wind) and the six load components are reduced to three components. Three aerostatic coefficients of the catwalk can be obtained through a section model test with traditional test equipment. However, six aerostatic coefficients of the catwalk must be acquired with the aid of special section model test equipment. A nonlinear numerical method was used study the stability of a catwalk under a yaw wind, while taking into account the six components of the displacement-dependent wind load and the geometric nonlinearity of the catwalk. The results show that when wind attacks with a slight yaw angle, the critical velocity that induces static instability of the catwalk may be lower than the critical velocity of normal wind. However, as the yaw angle of the wind becomes larger, the critical velocity increases. In the atmospheric boundary layer, the wind is turbulent and the velocity history is a random time history. The effects of turbulent wind on the stability of a catwalk are also assessed. The wind velocity fields are regarded as stationary Gaussian stochastic processes, which can be simulated by a spectral representation method. A nonlinear finite-element model set forepart and the Newmark integration method was used to calculate the wind-induced buffeting responses. The results confirm that the turbulent character of wind has little influence on the stability of the catwalk.

• International Journal of Control, Automation, and Systems
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• 제2권3호
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• pp.319-332
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• 2004

This paper proposes some further improvements on N.K. Bose's 2D stability test for polynomials with real coefficients by revealing symmetric properties of the polynomials, resultants occurring in the test and by generalizing Sturm's method. The improved test can be fulfilled by a totally algebraic algorithm with a finite number of steps and the computational complexity is largely reduced as it involves only certain real variable polynomials with degrees not exceeding half of their previous complex variable counterparts. Nontrivial examples for 2D polynomials having both numerical and literal coefficients are also shown to illustrate the computational advantage of the proposed method.

• Smart Structures and Systems
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• 제25권2호
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• pp.155-167
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• 2020

This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

• 동력기계공학회지
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• 제12권6호
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• pp.29-35
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• 2008

This study is conducted to provide the proper analysis method to evaluate the stability of a container crane under wind load. Two analysis method, namely structure analysis and fluid-structure interaction, are adopted to evaluate the stability of a container crane in this investigation. To evaluate the effect of wind load on the stability of the crane, 50-ton class container crane widely used in container terminals is adopted for analysis model and 19-values are considered for wind direction as design parameter. We conduct structure analysis and fluid-structure interaction for a container crane with respect to the wind direction using ANSYS and CFX. Then we compare the uplift forces yielded from two analysis with it yielded from wind tunnel test. The results are as follows: 1) A correlation coefficient between structure analysis and wind tunnel test is lower than 0.65(as $0.29{\sim}0.57$), but between fluid-structure interaction and wind tunnel test is higher than 0.65(as $0.78{\sim}0.86$). 2) There is low correlation between structure analysis and wind tunnel test but very high correlation between fluid-structure interaction and wind tunnel test.

• 한국항공우주학회지
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• 제31권6호
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• pp.45-51
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• 2003

본 논문에서는 소형 커나드 항공기인 Velocity-173의 가로안정성을 향상시키기 위한 방법에 대하여 연구하였다. Velocity-173의 세로안정성은 매우 우수한 반면, 가로안정성은 상대적으로 나쁘다. 가로안정성을 향상시키기 위해 수직미익의 면적을 증가시키는 작은 패널을 설계 및 제작하였다. 패널 설계 과정에서 AAA를 이용하여 패널 부착으로 인한 가로안정성의 변화를 예측하였다. 패널 부착 효과를 검증하기 위해 비행시험이 수행되었다. 또한, 비행시험 데이터로부터 안정/조종 미계수를 추출하기 위하여 최대공산추정법을 이용하였다. 본 연구를 통해 수직미익 아래에 부착된 패널의 효과를 확인할 수 있었다.

• 대한조선학회 특별논문집
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• 대한조선학회 2015년도 특별논문집
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• pp.74-78
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• 2015

When floating platform or drilling unit is located at operating station during its design life, it has to have the sufficient stability considering external environment. To evaluate whether offshore structure is complied with the required design criteria for intact stability, the factors which decrease the righting moment have to be considered. Wind heeling moment is one of main factors because the direction is opposite to the righting moment. According to 2009 MODU CODE (Code for the construction and equipment of Mobile Offshore Drilling Units, 2009), wind heeling moment derived from wind tunnel test on scale model of offshore structure enables to apply as alternative given formula and method in 2009 MODU CODE. However, there is no the specific method for applying data derived from wind tunnel test. Based on the following reasons, this paper presents that the calculation method of wind heeling moment utilizing non-dimensional coefficient relative to wind loads (wind forces and moments) and the comparison with each method applying an example.

• 항공우주시스템공학회지
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• 제15권4호
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• pp.40-46
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• 2021

At launch, satellites are exposed to various types of structural loads, such as quasi-static loads, sinusoidal vibrations, acoustic/random vibrations, and shocks. The launch environment test is aimed at verifying the structural stability of the test object against the launch environment. Various types of launch environments are simulated by simple vibration, acoustic, and shock tests considering possible test conditions in ground. However, the difference between the launch environment and the test environment is one of the causes of excessive testing. To prevent overtesting, a notching technique that adjusts the frequency range and the input load considering the design load is applied. For notching, specific procedures are established considering the satellite development concept, selected launch vehicle, higher system requirements, and test target level. In this study, the notching method, established procedure, and development of a notching toolkit for efficient testing are described.