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Response of a frame structure on a canyon site to spatially varying ground motions
Kaiming Bi,Hong Hao,Weixin Ren 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.1
This paper studies the effects of spatially varying ground motions on the responses of a bridge frame located on a canyon site. Compared to the spatial ground motions on a uniform flat site, which is the usual assumptions in the analysis of spatial ground motion variation effects on structures, the spatial ground motions at different locations on surface of a canyon site have different intensities owing to local site amplifications, besides the loss of coherency and phase difference. In the proposed approach, the spatial ground motions are modelled in two steps. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function and an empirical spatial ground motion coherency loss function. Then, power spectral density function of ground motion on surface of the canyon site is derived by considering the site amplification effect based on the one dimensional seismic wave propagation theory. Dynamic, quasi-static and total responses of the model structure to various cases of spatially varying ground motions are estimated. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effects, to spatial ground motions without considering coherency loss or phase shift are also calculated. Discussions on the ground motion spatial variation and local soil site amplification effects on structural responses are made. In particular, the effects of neglecting the site amplifications in the analysis as adopted in most studies of spatial ground motion effect on structural responses are highlighted.
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An Adaptive Tuned Heave Plate (ATHP) for suppressing heave motion of floating platforms
Kaiming Bi,Ruisheng Ma,Haoran Zuo 국제구조공학회 2023 Smart Structures and Systems, An International Jou Vol.31 No.3
Structural stability of floating platforms has long since been a crucial issue in the field of marine engineering. Excessive motions would not only deteriorate the operating conditions but also seriously impact the safety, service life, and production efficiency. In recent decades, several control devices have been proposed to reduce unwanted motions, and an attractive one is the tuned heave plate (THP). However, the THP system may reduce or even lose its effectiveness when it is mistuned due to the shift of dominant wave frequency. In the present study, a novel adaptive tuned heave plate (ATHP) is proposed based on inerter by adjusting its inertance, which allows to overcome the limitation of the conventional THP and realize adaptations to the dominant wave frequencies in real time. Specifically, the analytical model of a representative semisubmersible platform (SSP) equipped with an ATHP is created, and the equations of motion are formulated accordingly. Two optimization strategies (i.e., <i>J</i><sub>1</sub> and <i>J</i><sub>2</sub> optimizations) are developed to determine the optimum design parameters of ATHP. The control effectiveness of the optimized ATHP is then examined in the frequency domain by comparing to those without control and controlled by the conventional THP. Moreover, parametric analyses are systematically performed to evaluate the influences of the pre-specified frequency ratio, damping ratio, heave plate sizes, peak periods and wave heights on the performance of ATHP. Furthermore, a Simulink model is also developed to examine the control performance of ATHP in the time domain. It is demonstrated that the proposed ATHP could adaptively adjust the optimum inertance-to-mass ratio by tracking the dominant wave frequencies in real time, and the proposed system shows better control performance than the conventional THP.
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Kaiming Bi,Hong Hao 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.5
Previous major earthquakes revealed that most damage of the buried segmented pipelines occurs at the joints of the pipelines. It has been proven that the differential motions between the pipe segments are one of the primary reasons that results in the damage (Zerva et al. 1986, O’Roueke and Liu 1999). This paper studies the combined influences of ground motion spatial variations and local soil conditions on the seismic responses of buried segmented pipelines. The heterogeneous soil deposits surrounding the pipelines are assumed resting on an elastic half-space (base rock). The spatially varying base rock motions are modelled by the filtered Tajimi-Kanai power spectral density function and an empirical coherency loss function. Local site amplification effect is derived based on the one-dimensional wave propagation theory by assuming the base rock motions consist of out-of-plane SH wave or combined in-plane P and SV waves propagating into the site with an assumed incident angle. The differential axial and lateral displacements between the pipeline segments are stochastically formulated in the frequency domain. The influences of ground motion spatial variations, local soil conditions, wave incident angle and stiffness of the joint are investigated in detail. Numerical results show that ground motion spatial variations and local soil conditions can significantly influence the differential displacements between the pipeline segments.
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Bi, Kaiming,Hao, Hong Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.44 No.5
Previous major earthquakes revealed that most damage of the buried segmented pipelines occurs at the joints of the pipelines. It has been proven that the differential motions between the pipe segments are one of the primary reasons that results in the damage (Zerva et al. 1986, O'Roueke and Liu 1999). This paper studies the combined influences of ground motion spatial variations and local soil conditions on the seismic responses of buried segmented pipelines. The heterogeneous soil deposits surrounding the pipelines are assumed resting on an elastic half-space (base rock). The spatially varying base rock motions are modelled by the filtered Tajimi-Kanai power spectral density function and an empirical coherency loss function. Local site amplification effect is derived based on the one-dimensional wave propagation theory by assuming the base rock motions consist of out-of-plane SH wave or combined in-plane P and SV waves propagating into the site with an assumed incident angle. The differential axial and lateral displacements between the pipeline segments are stochastically formulated in the frequency domain. The influences of ground motion spatial variations, local soil conditions, wave incident angle and stiffness of the joint are investigated in detail. Numerical results show that ground motion spatial variations and local soil conditions can significantly influence the differential displacements between the pipeline segments.
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Jiang, Kaiming,Pham, Thanh-Truc,Kang, Sung Gu,Men, Yong,Shin, Eun Woo Elsevier 2018 Journal of alloys and compounds Vol.739 No.-
<P><B>Abstract</B></P> <P>In this study, we investigated the changes of the structural and optical properties of NiTiO<SUB>3</SUB> materials modified by transition metal doping. Cobalt (Co) or tungsten (W)-doped NiTiO<SUB>3</SUB> materials were successfully prepared by a modified Pechini method via solvothermal treatment. Raman, FTIR, and XRD spectroscopic analyses showed that the Co<SUP>2+</SUP> ions were selectively doped into Ni<SUP>2+</SUP> sites in the NiTiO<SUB>3</SUB> lattice while maintaining an ilmenite structure, resulting in a solid solution of triple transition metal oxides. The size similarity between Co and Ni induced the formation of a solid solution, Co<SUB>x</SUB>Ni<SUB>1-x</SUB>TiO<SUB>3</SUB>, in the ilmenite structure. In contrast, W doping into the NiTiO<SUB>3</SUB> ilmenite structure resulted in an irregularity of the materials due to the characteristics of the heavy transition metal dopant. Along with increasing the W content, the crystallite size in the ilmenite structure decreased from 90.2 to 74.5 nm and new Raman bands at 831 and 892 cm<SUP>−1</SUP> for WO<SUB>x</SUB> appeared at high W contents. However, the PL emission intensities gradually decreased with increasing doping content, implying that the recombination process was inhibited in the NiTiO<SUB>3</SUB> materials by the dopants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co (W)-doped NiTiO<SUB>3</SUB> materials were successfully prepared by a modified Pechini method. </LI> <LI> Selective Co<SUP>2+</SUP> ion doping into Ni<SUP>2+</SUP> sites in the NiTiO<SUB>3</SUB> lattice formed a solid solution. </LI> <LI> W doping into the NiTiO<SUB>3</SUB> lattice resulted in an irregularity in the lattice structure. </LI> <LI> The PL emission intensities gradually decreased with increasing dopant concentration. </LI> <LI> The recombination process in the NiTiO<SUB>3</SUB> materials was inhibited by the metal dopants. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Response of a frame structure on a canyon site to spatially varying ground motions
Bi, Kaiming,Hao, Hong,Ren, Weixin Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.1
This paper studies the effects of spatially varying ground motions on the responses of a bridge frame located on a canyon site. Compared to the spatial ground motions on a uniform flat site, which is the usual assumptions in the analysis of spatial ground motion variation effects on structures, the spatial ground motions at different locations on surface of a canyon site have different intensities owing to local site amplifications, besides the loss of coherency and phase difference. In the proposed approach, the spatial ground motions are modelled in two steps. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function and an empirical spatial ground motion coherency loss function. Then, power spectral density function of ground motion on surface of the canyon site is derived by considering the site amplification effect based on the one dimensional seismic wave propagation theory. Dynamic, quasi-static and total responses of the model structure to various cases of spatially varying ground motions are estimated. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effects, to spatial ground motions without considering coherency loss or phase shift are also calculated. Discussions on the ground motion spatial variation and local soil site amplification effects on structural responses are made. In particular, the effects of neglecting the site amplifications in the analysis as adopted in most studies of spatial ground motion effect on structural responses are highlighted.
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Haoran Zuo,Kaiming Bi,Hong Hao 국제구조공학회 2020 Smart Structures and Systems, An International Jou Vol.26 No.4
To effectively extract the vast wind resource, offshore wind turbines are designed with large rotor and slender tower, which makes them vulnerable to external vibration sources such as wind and wave loads. Substantial research efforts have been devoted to mitigate the unwanted vibrations of offshore wind turbines to ensure their serviceability and safety in the normal working condition. However, most previous studies investigated the vibration control of wind turbines in one direction only, i.e., either the out-of-plane or in-plane direction. In reality, wind turbines inevitably vibrate in both directions when they are subjected to the external excitations. The studies on both the in-plane and out-of-plane vibration control of wind turbines are, however, scarce. In the present study, the NREL 5 MW wind turbine is taken as an example, a detailed three-dimensional (3D) Finite Element (FE) model of the wind turbine is developed in ABAQUS. To simultaneously control the in-plane and out-of-plane vibrations induced by the combined wind and wave loads, another carefully designed (i.e., tuned) spring and dashpot are added to the perpendicular direction of each Tuned Mass Damper (TMD) system that is used to control the vibrations of the tower and blades in one particular direction. With this simple modification, a bi-directional TMD system is formed and the vibrations in both the out-of-plane and in-plane directions are simultaneously suppressed. To examine the control effectiveness, the responses of the wind turbine without control, with separate TMD system and the proposed bi-directional TMD system are calculated and compared. Numerical results show that the bi-directional TMD system can simultaneously control the out-of-plane and in-plane vibrations of the wind turbine without changing too much of the conventional design of the control system. The bi-directional control system therefore could be a cost-effective solution to mitigate the bi-directional vibrations of offshore wind turbines.
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Heat transfer characteristics in regenerator cell for gaseous organic compound treatment
Fulin Liu,Kaiming Ren,Junyan Pei,Xuze Zhao,Xiaowen Hao 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.2
Regenerative combustion technology can efficiently decompose organic gases with high thermal efficiency. This capability is attributed to the regenerator and the periodic gas switching technology. However, published findings regarding the regenerator were inconsistent with some important parameters, and investigations into the regenerative chamber did not provide a comprehensive explanation of the heat transfer characteristics. Therefore, a regenerator cell was investigated in this study. The temperature distribution pattern inside the cell was simulated after model verification. The effects of the superficial velocity, switching time, side width, and wall thickness of the regenerator cell on the outlet temperature, energy recovery ratio, and heat-transfer coefficient were investigated. The outlet temperature, heat transfer, and energy recovery ratio of the regenerator cells varied monotonically during each period. The average energy recovery ratio and heat transfer coefficient indicated that the side width of the regenerator cell was the most significant factor. Meanwhile, the switching time and wall thickness did not significantly affect the energy recovery ratio. The superficial velocity and wall thickness did not significantly affect the heat transfer coefficient.
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