ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employ... more ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employing instantaneous frequency (IF) extracted using Time-Frequency Representations (TF.R) of earthquake records. The study is, therefore, aimed to demonstrate the applicability of real-time modal frequency shift technique for the non-linear 'smart' pin-frame model, but it is also used to numerically assess the performance of the proposed frequency shift strategy. The results showed the potential use of this approach for vibration mitigation of structures.
The use of smart dampers to optimally control the response of structures is on the increase. To m... more The use of smart dampers to optimally control the response of structures is on the increase. To maximize the potential use of such damper systems, their accurate modeling and assessment of their performance is of vital interest. In this study, the performance of a controllable fluid dashpot damper, in terms of damper forces, damper dynamic range and damping force hysteretic loops, respectively, is studied mathematically. The study employs a damper Bingham-Maxwell (BingMax) model whose mathematical formulation is developed using a Fourier series technique. The technique treats this one-dimensional Navier-Stokes`s momentum equation as a linear superposition of initial-boundary value problems (IBVPs): boundary conditions, viscous term, constant Direct Current (DC) induced fluid plug and fluid inertial term. To hold the formulation applicable, the DC current level to the damper is supplied as discrete constants. The formulation and subsequent simulation are validated with experimental results of a commercially available magneto rheological (MR) dashpot damper (Lord model No`s RD-1005-3) subjected to a sinusoidal stroke motion using a `SCHENK` material testing machine in the Materials Laboratory at the University of Technology, Sydney.
ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employ... more ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employing instantaneous frequency (IF) extracted using Time-Frequency Representations (TF.R) of earthquake records. The study is, therefore, aimed to demonstrate the applicability of real-time modal frequency shift technique for the non-linear 'smart' pin-frame model, but it is also used to numerically assess the performance of the proposed frequency shift strategy. The results showed the potential use of this approach for vibration mitigation of structures.
Summary The paper presents a reliability approach to assess the impact of ship collision on the e... more Summary The paper presents a reliability approach to assess the impact of ship collision on the existing jacket platforms in the waters of Viet Nam. The approach adopts the limit state concept for boat impact energy and platform structural absorption energy capacity to assess the structural failures. Two boat impact energy spectra, representing the 50 th and 95 th percentiles of impact energy, are used to determine the probability of platform structural failure. In this paper, the platform structural absorption energy of one representative steel jacket type platform is determined using SACS “Collapse” module based on plasticity for structural members which will subsequently contribute to the loss of global structural stiff ness.
Journal of Mechanical Science and Technology, Oct 1, 2007
Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, s... more Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses ofpolarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each hearn-column connection and suhjected to two scaled earthquake excitations, namely EI-Centro 1940 and Northridge 1994, which respectively represent near-and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
Journal of Mechanical Science and Technology, 2007
Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, s... more Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses ofpolarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each hearn-column connection and suhjected to two scaled earthquake excitations, namely EI-Centro 1940 and Northridge 1994, which respectively represent near-and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
Modelling and simulation for controllable dashpot dampers using magneto-or electro-rheological fl... more Modelling and simulation for controllable dashpot dampers using magneto-or electro-rheological fluids have been carried out extensively, however, only few have considered shear dampers. Experiments at the University of Technology, Sydney (UTS) are being conducted to characterize the performance of a prototype shear damper. The damper performance in the quasi-static state is being assessed based on the shear strength, generated in the semi-solid plug formed when the controllable fluid is magnetized, versus damper displacement or velocity. Employing curve-fitting technique, validation of the proposed quasi-static parameteric model was carried out accordingly. Results indicate good agreement with the proposed model.
The use of adjustable Amplitude Frequency Characteristics (AFC) approach is a new concept in vibr... more The use of adjustable Amplitude Frequency Characteristics (AFC) approach is a new concept in vibration mitigation, which is developed from frequency detuning technique used in vibration protection against resonance. This non-constant AFC can be generated by Magnetorheological (MR) fluid-based pins, so called 'smart pins', which are mounted at beam-column connections. The paper presents a preliminary investigation of a 'smart'-pin-frame system, a single-storey, one bay, steel plane frame with a traditional pin and a 'smart' pin mounted at each beam-column end, whose frequencies can be adjusted by partially 'locking' or 'releasing' the smart pin. To do so, a maximum or zero DC current level is supplied to the smart pin, which respectively transforms the system into either pin-rigid (P-R) or pin-pin (P-P) beam in a frame structure. Experiments, conducted in the Structure Laboratory of the University of Technology, Sydney (UTS) using both a sudden release technique and a shake table, were used to investigate the non-linear dynamic properties and the system AFC prior to their 'proof-of-concept' testings. Preliminary AFC results showed the potential use of the system subjected to harmonic forced vibrations.
Journal of Mechanical Science and Technology, 2007
Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, s... more Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses ofpolarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each hearn-column connection and suhjected to two scaled earthquake excitations, namely EI-Centro 1940 and Northridge 1994, which respectively represent near-and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employ... more ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employing instantaneous frequency (IF) extracted using Time-Frequency Representations (TF.R) of earthquake records. The study is, therefore, aimed to demonstrate the applicability of real-time modal frequency shift technique for the non-linear 'smart' pin-frame model, but it is also used to numerically assess the performance of the proposed frequency shift strategy. The results showed the potential use of this approach for vibration mitigation of structures.
The use of smart dampers to optimally control the response of structures is on the increase. To m... more The use of smart dampers to optimally control the response of structures is on the increase. To maximize the potential use of such damper systems, their accurate modeling and assessment of their performance is of vital interest. In this study, the performance of a controllable fluid dashpot damper, in terms of damper forces, damper dynamic range and damping force hysteretic loops, respectively, is studied mathematically. The study employs a damper Bingham-Maxwell (BingMax) model whose mathematical formulation is developed using a Fourier series technique. The technique treats this one-dimensional Navier-Stokes`s momentum equation as a linear superposition of initial-boundary value problems (IBVPs): boundary conditions, viscous term, constant Direct Current (DC) induced fluid plug and fluid inertial term. To hold the formulation applicable, the DC current level to the damper is supplied as discrete constants. The formulation and subsequent simulation are validated with experimental results of a commercially available magneto rheological (MR) dashpot damper (Lord model No`s RD-1005-3) subjected to a sinusoidal stroke motion using a `SCHENK` material testing machine in the Materials Laboratory at the University of Technology, Sydney.
ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employ... more ABSTRACT: This paper presents the dynamic analysis of a 'smart' pin-frame system employing instantaneous frequency (IF) extracted using Time-Frequency Representations (TF.R) of earthquake records. The study is, therefore, aimed to demonstrate the applicability of real-time modal frequency shift technique for the non-linear 'smart' pin-frame model, but it is also used to numerically assess the performance of the proposed frequency shift strategy. The results showed the potential use of this approach for vibration mitigation of structures.
Summary The paper presents a reliability approach to assess the impact of ship collision on the e... more Summary The paper presents a reliability approach to assess the impact of ship collision on the existing jacket platforms in the waters of Viet Nam. The approach adopts the limit state concept for boat impact energy and platform structural absorption energy capacity to assess the structural failures. Two boat impact energy spectra, representing the 50 th and 95 th percentiles of impact energy, are used to determine the probability of platform structural failure. In this paper, the platform structural absorption energy of one representative steel jacket type platform is determined using SACS “Collapse” module based on plasticity for structural members which will subsequently contribute to the loss of global structural stiff ness.
Journal of Mechanical Science and Technology, Oct 1, 2007
Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, s... more Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses ofpolarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each hearn-column connection and suhjected to two scaled earthquake excitations, namely EI-Centro 1940 and Northridge 1994, which respectively represent near-and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
Journal of Mechanical Science and Technology, 2007
Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, s... more Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses ofpolarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each hearn-column connection and suhjected to two scaled earthquake excitations, namely EI-Centro 1940 and Northridge 1994, which respectively represent near-and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
Modelling and simulation for controllable dashpot dampers using magneto-or electro-rheological fl... more Modelling and simulation for controllable dashpot dampers using magneto-or electro-rheological fluids have been carried out extensively, however, only few have considered shear dampers. Experiments at the University of Technology, Sydney (UTS) are being conducted to characterize the performance of a prototype shear damper. The damper performance in the quasi-static state is being assessed based on the shear strength, generated in the semi-solid plug formed when the controllable fluid is magnetized, versus damper displacement or velocity. Employing curve-fitting technique, validation of the proposed quasi-static parameteric model was carried out accordingly. Results indicate good agreement with the proposed model.
The use of adjustable Amplitude Frequency Characteristics (AFC) approach is a new concept in vibr... more The use of adjustable Amplitude Frequency Characteristics (AFC) approach is a new concept in vibration mitigation, which is developed from frequency detuning technique used in vibration protection against resonance. This non-constant AFC can be generated by Magnetorheological (MR) fluid-based pins, so called 'smart pins', which are mounted at beam-column connections. The paper presents a preliminary investigation of a 'smart'-pin-frame system, a single-storey, one bay, steel plane frame with a traditional pin and a 'smart' pin mounted at each beam-column end, whose frequencies can be adjusted by partially 'locking' or 'releasing' the smart pin. To do so, a maximum or zero DC current level is supplied to the smart pin, which respectively transforms the system into either pin-rigid (P-R) or pin-pin (P-P) beam in a frame structure. Experiments, conducted in the Structure Laboratory of the University of Technology, Sydney (UTS) using both a sudden release technique and a shake table, were used to investigate the non-linear dynamic properties and the system AFC prior to their 'proof-of-concept' testings. Preliminary AFC results showed the potential use of the system subjected to harmonic forced vibrations.
Journal of Mechanical Science and Technology, 2007
Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, s... more Ibis paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses ofpolarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each hearn-column connection and suhjected to two scaled earthquake excitations, namely EI-Centro 1940 and Northridge 1994, which respectively represent near-and farfield excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
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Papers by Joko Widjaja