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P. Canavan - One of the best experts on this subject based on the ideXlab platform.
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Design, Control and Human Testing of an Active Knee Rehabilitation Orthotic Device
Proceedings 2007 IEEE International Conference on Robotics and Automation, 2007Co-Authors: B. Weinberg, J. Nikitczuk, Constantinos Mavroidis, S. Patel, B. Patritti, P. Bonato, P. CanavanAbstract:This paper presents a novel, smart and portable active knee rehabilitation orthotic device (AKROD) designed to train stroke patients to correct knee hyperextension during stance and stiff-legged gait (defined as reduced knee flexion during swing). The knee brace provides variable damping controlled in ways that foster motor recovery in stroke patients. A resistive, variable damper, electro-rheological fluid (ERF) based component is used to facilitate knee flexion during stance by providing resistance to knee buckling. Furthermore, the knee brace is used to assist in knee control during swing, i.e. to allow patients to achieve adequate knee flexion for toe clearance and adequate knee extension in preparation to heel strike. The detailed design of AKROD, the first prototype built, closed loop control results and initial human testing are presented here
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ICRA - Design, Control and Human Testing of an Active Knee Rehabilitation Orthotic Device
Proceedings 2007 IEEE International Conference on Robotics and Automation, 2007Co-Authors: B. Weinberg, J. Nikitczuk, Constantinos Mavroidis, S. Patel, B. Patritti, P. Bonato, P. CanavanAbstract:This paper presents a novel, smart and portable active knee rehabilitation orthotic device (AKROD) designed to train stroke patients to correct knee hyperextension during stance and stiff-legged gait (defined as reduced knee flexion during swing). The knee brace provides variable damping controlled in ways that foster motor recovery in stroke patients. A resistive, variable damper, electro-rheological fluid (ERF) based component is used to facilitate knee flexion during stance by providing resistance to knee buckling. Furthermore, the knee brace is used to assist in knee control during swing, i.e. to allow patients to achieve adequate knee flexion for toe clearance and adequate knee extension in preparation to heel strike. The detailed design of AKROD, the first prototype built, closed loop control results and initial human testing are presented here
Tao Peng - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation on the suppression device of viv of a flexible riser
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Shixiao Fu, Leijian Song, Tao PengAbstract:Experimental investigations were conducted on a flexible riser with and without helical Strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of Strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical Strakes, and the suppression performance depends on the geometry of the helical Strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical Strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that Strake height has a greater influence on the VIV response than the Strake pitch, and the drag exerted on the riser increases with Strake pitch and height.Copyright © 2014 by ASME
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Strake Design and VIM-Suppression Study of a Cell-Truss Spar
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 6, 2010Co-Authors: Ying Wang, Jianmin Yang, Tao Peng, Haining LuAbstract:Along with the development of offshore technology, Spar platforms have been widely used in deep-sea oil and gas exploitation. Due to the deep draft cylinder hull piercing into the water, Spar platforms could be subjected to Vortex-Induced Motions (VIM) in certain current conditions. To mitigate VIM, helical Strakes are used on the Spar hulls, and they have been proved to be effective. Cell-Truss Spar is a new concept of Spar platform which has recently been put forward by State Key Laboratory of Ocean Engineering (SKLOE) of Shanghai Jiao Tong University. It combines some good qualities of the Cell Spar and Truss Spar designs, aiming to bring in the lighter truss section and heave plate damping feature of the Truss Spar to obtain satisfactory heave motion performances, while reduce manufacture and installation difficulties by means of cell concept. Since the Cell-Truss Spar is a new design concept that has physical characteristics which are different from the existing Spars, the global motion performance should be carefully studied and verified. Researches about the VIM performance of the Cell-Truss Spar have been carried out recently (see Wang Ying et al, 2008, etc). Since it is still at the concept design stage, the Cell-Truss Spar configuration is considered without detail Strake design in these studies. For the Cell-Truss Spar, which is still on concept design stage at the present time, the design and optimization of the helical Strakes is very important to control the VIM response and improve the hydrodynamic performance. In this paper, Strake design and VIM-Suppression Study of the Cell-Truss Spar is carried out. As a result of the unique characters on the hull, the outer surface of the Cell-Truss Spar does not form a regular cylinder. Hence, the Strakes should be designed more carefully. In this study, four different configurations of Strake groups are put forward and studied, and the one with the highest efficiency is chosen to be applied on the Cell-Truss Spar. The fluid field around the hard tank of the hull, the vortex disturbance near the Strakes, and the forces acting on the hard tank with different Strakes are simulated by CFD method, and the Strake efficiency is assessed through model test combining with CFD computation. The optimized Strake configuration is finally chosen, and the VIM performance of the Strake-equipped Spar is studied.© 2010 ASME
Tongming Zhou - One of the best experts on this subject based on the ideXlab platform.
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Experimental Evaluation of Vortex Induced Vibration Response of Straked Pipes in Tandem Arrangements
Volume 5: Ocean Engineering; CFD and VIV, 2012Co-Authors: Matthew Blumberg, Elizabeth Tellier, Dhyanjyoti Deka, Tongming ZhouAbstract:Vortex induced vibration (VIV) due to steady current flow can be a significant driver in the design of offshore riser systems, affecting riser global configuration, component details and overall subsea architecture. Helical Strakes are known to reduce VIV but the degree of effectiveness can vary considerably depending on Strake pitch, fin height and more importantly, current flow regime. In addition, the amplitude of VIV and the effectiveness of VIV suppression Strakes depends on the inclination of flow to the riser (incidence angle) and presence of wake effects from adjacent risers. Test and field data regarding suppression of riser VIV by Strakes is not extensively available in the public domain. This is primarily due to the proprietary nature of the tests conducted in industry. In this paper, a program of testing is devised to better understand Strake effectiveness as a function of current incidence angle and the presence of adjacent risers. Experiments have been conducted on single and tandem pipe arrangements in air in order to evaluate Strake suppression efficiency. Aluminium cylinders are tested in a wind tunnel in the structures laboratory of The University of Western Australia (UWA). Two sets of experiments are conducted: the first to evaluate cylinder VIV response at angles of incidence ranging from 30 to 90 degrees and the second to evaluate VIV response of the downstream pipe in a dual pipe arrangement with varying spacing between the pipes. In both cases the bare cylinders are first tested at varying flow speeds. Helical Strakes are then added to the single cylinder, and downstream cylinder in the tandem pipe test, and the vibration response is recorded at varying flow speeds. From the experimentation, it can be seen that downstream cylinder motions are amplified by wake induced instability. This phenomenon is of particular concern for tightly spaced top-tensioned risers (TTR) in wellbays of tension leg platforms (TLP) and deep draft floaters. The VIV motion of the downstream, bare, wake-affected pipe, is magnified to approximately 1.3-2 times the motion of a single bare pipe. When Strakes are added to the downstream cylinder, the magnification factor of the downstream cylinder response is largely increased due to the wake of the upstream bare cylinder. However, the actual VIV motions of the downstream cylinder are largely reduced when Strakes are incorporated. The present work demonstrates that helical Strakes provide an effective means of suppressing vortex induced vibrations of risers in riser arrays, though the degree of effectiveness is reduced in a downstream tubular compared to suppression levels for single pipes.
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On the study of vortex-induced vibration of a cylinder with helical Strakes
Journal of Fluids and Structures, 2011Co-Authors: Tongming Zhou, Siti Fatin Mohd Razali, Zhiyong Hao, Liang ChengAbstract:Abstract While the effect of helical Strakes on suppression of Vortex-Induced Vibrations (VIV) has been studied extensively, the mechanism of VIV mitigation using helical Strakes is much less well documented in the literature. In the present study, a rigid circular cylinder of diameter d =80 mm attached with three-strand helical Strakes of dimensions of 10 d in pitch and 0.12 d in height was tested in a wind tunnel. It was found that the helical Strakes can reduce VIV by about 98%. Unlike the bare cylinder, which experiences lock-in over the reduced velocity in the range of 5–8.5, the Straked cylinder does not show any lock-in region. In exploring the mechanism of VIV reduction by helical Strakes, measurements in stationary bare and Straked cylinder wakes using both a single X-probe at four different Reynolds numbers, i.e. Re=10 240, 20 430, 30 610 and 40 800, and two X-probes with variable separations in the spanwise direction at R e=20 430 were conducted. It was found that vortices shed from the Straked cylinder are weakened significantly. The dominate frequency varies by about 30% over the range of x / d =10–40 in the streamwise direction while that differs by about 37.2% of the averaged peak frequency over a length of 3.125 d in the spanwise direction. The latter is supported by the phase difference between the velocity signals measured at two locations separated in the spanwise direction. The correlation length of the vortex structures in the bare cylinder wake is much larger than that obtained in the Straked cylinder wake. As a result, the Straked cylinder wake agrees more closely with isotropy than the bare cylinder wake. Flow visualization on the plane perpendicular to the cylinder axis at Reynolds number of about 300 reveals small-scale vortices in the shear layers of the Straked cylinder wake. However, these vortices do not roll up and interact with each other to form the well-organized Karman-type vortices. Flow visualization on the plane parallel to the cylinder axis shows vortex dislocation and swirling flow, which should be responsible for the variations of the peak frequency in the streamwise as well as spanwise directions.
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Experimental Investigation on the Mechanism of VIV Reduction using Helical Strakes
2010Co-Authors: Siti Fatin Mohd Razali, Tongming Zhou, Liang ChengAbstract:In this study, the mechanism of vortex-induced vibration (VIV) mitigation using helical Strakes is further investigated complying with the recent literatures. A rigid circular cylinder of diameter d = 80 mm attached with three-strand helical Strakes of a dimension of 10d in pitch and 0.12d in height was tested in a wind tunnel. A bare cylinder was also tested to provide a benchmark for the Straked cylinder system. It was found that the helical Strakes reduce VIV by about 98%. Unlike the bare cylinder which experiences lock-in over the reduced velocity of 5 ~ 9, the Straked cylinder does not show any lock-in region. In exploring the mechanism of VIV reduction by helical Strakes, it was found that vortices shed from the Straked cylinder are weakened significantly. The cross-correlation coefficients in the bare cylinder wake were much larger than that obtained in the Straked cylinder wake, indicating that the correlation length of the former is larger than that of the latter. As a result, the Straked cylinder wake agrees more favorably with isotropy than the bare cylinder wake.
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Investigation on suppression of vortex-induced vibration using helical Strakes
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 6, 2010Co-Authors: Tongming Zhou, Siti Fatin Mohd Razali, Liang ChengAbstract:While the effect of helical Strakes on suppression of Vortex-Induced Vibrations (VIV) has been studied extensively, the mechanism of VIV mitigation using helical Strakes is less well documented in the literature. In the present study, experiments were conducted in a wind tunnel at four velocities, i.e. 1.92, 3.83, 5.74 and 7.65 m/s. Strakes with a dimension of 10d in pitch and 0.12d in height were fitted onto a rigid cylinder of diameter d = 80mm, and subjected to a transverse air flow. Hotwire techniques were used to measure the instantaneous velocity fluctuations at various locations to explore the mechanism for VIV mitigation by using helical Strakes. It was found that the helical Strakes reduce VIV by about 98%. Unlike the bare cylinder which experiences lock-in over the reduced velocity of 5 ∼ 9, the Straked cylinder does not show any lock-in region. In exploring the mechanism of VIV reduction by helical Strakes, it was found that vortices shed from the Straked cylinder are weakened significantly. The dominant frequency of the vortex structures along the spanwise direction of the bare cylinder was very stable. This is not the case for the Straked cylinder wake, which differs by about 36% of the averaged peak frequency over the length of 3.125d along the cylinder axial direction, indicating that the vortex shed from the latter is out-of-phase and mismatching. This is supported by the phase shift between the velocity signals measured at two locations separated in the spanwise direction. The cross-correlation coefficients in the bare cylinder wake were much larger than that obtained in the Straked cylinder wake, indicating that the correlation length of the former is much larger than that of the latter.Copyright © 2010 by ASME
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Experimental Studies of Vortex Structures in the Wake of a Cylinder With Helical Strakes
29th International Conference on Ocean Offshore and Arctic Engineering: Volume 6, 2010Co-Authors: Zhiyong Hao, Tongming Zhou, Xikun Wang, Soon Keat TanAbstract:This work is experimental studies of the turbulent vortex structures in the wake of a fixed cylinder with helical Strakes. The effect and mechanism of a triple helical Strake system on suppression of vortex induced vibrations (VIV) are investigated experimentally in a water tunnel. Strakes with a length of 25D in pitch and 0.1D & 0.2D in height are fitted onto a rigid cylinder of diameter D = 12mm, and subjected to a transverse water flow. PIV techniques are used to measure the vector field to identify the vortex structures. The hot-film techniques are also employed to identify the shedding frequency. Measurements for the bare cylinders are also conducted for comparison. The mechanism of the VIV reduction by helical Strakes is discussed in detail.Copyright © 2010 by ASME
Shixiao Fu - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation of the response performance of viv on a flexible riser with helical Strakes
Ships and Offshore Structures, 2016Co-Authors: Shixiao Fu, Yifan ChenAbstract:Experimental investigations were conducted on a flexible riser with and without helical Strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of Strakes with different heights and pitches was studied. The experimental results indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical Strakes, and the suppression performance depends on the geometry of the helical Strakes. The VIV responses in the cross-flow (CF) and in-line (IL) directions can be coupled via variations in the tensile force. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical Strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that the Strake height has a greater influence on the VIV response than the Strake pitch, and the drag exerted...
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viv response of a long flexible riser fitted with Strakes in uniform and linearly sheared currents
Applied Ocean Research, 2015Co-Authors: Shixiao Fu, Youming Xiong, Leijian SongAbstract:Abstract An experimental investigation was conducted on a flexible riser with and without various Strake arrangements. The aim of the present work was to further improve the understanding of the response performance of the vortex-induced vibration (VIV) of a riser with helical Strakes. Two current profiles, including uniform and linearly sheared flows, were simulated. The uniform current was simulated by towing the riser model in one direction using the towing carriage, and the linearly sheared current was simulated by fixing one end of the riser and using a driven cantilever to traverse a circular arc. Based on the modal superposition method, the displacement responses were obtained from the measured strain. Strakes with different heights and pitches were analysed, and response parameters such as the displacement response and fatigue damage were studied. The results of the bare model test show that the lock-in phenomenon displays multi-order characteristics, and the VIV displacement decreases with an increased order of the lock-in regime. The results of the Straked model test indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical Strakes, and the response performance depends closely on the geometry of the Strake configuration.
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experimental investigation on the suppression device of viv of a flexible riser
ASME 2014 33rd International Conference on Ocean Offshore and Arctic Engineering, 2014Co-Authors: Shixiao Fu, Leijian Song, Tao PengAbstract:Experimental investigations were conducted on a flexible riser with and without helical Strakes. A uniform current was obtained by towing a riser model in a tank, and the vortex-induced vibration (VIV) suppression of Strakes with different heights and pitches was studied. The results of the bare riser show that the characteristics of the synchronization of the VIV for a flexible riser have many orders, and the excited mode jumps from one to another abruptly. During the high order synchronization regime, the VIV response decreases with the increased order of the synchronization. The experimental results also indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical Strakes, and the suppression performance depends on the geometry of the helical Strakes. The fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser fitted with helical Strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. The experimental results also confirmed that Strake height has a greater influence on the VIV response than the Strake pitch, and the drag exerted on the riser increases with Strake pitch and height.Copyright © 2014 by ASME
B. Weinberg - One of the best experts on this subject based on the ideXlab platform.
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Design, Control and Human Testing of an Active Knee Rehabilitation Orthotic Device
Proceedings 2007 IEEE International Conference on Robotics and Automation, 2007Co-Authors: B. Weinberg, J. Nikitczuk, Constantinos Mavroidis, S. Patel, B. Patritti, P. Bonato, P. CanavanAbstract:This paper presents a novel, smart and portable active knee rehabilitation orthotic device (AKROD) designed to train stroke patients to correct knee hyperextension during stance and stiff-legged gait (defined as reduced knee flexion during swing). The knee brace provides variable damping controlled in ways that foster motor recovery in stroke patients. A resistive, variable damper, electro-rheological fluid (ERF) based component is used to facilitate knee flexion during stance by providing resistance to knee buckling. Furthermore, the knee brace is used to assist in knee control during swing, i.e. to allow patients to achieve adequate knee flexion for toe clearance and adequate knee extension in preparation to heel strike. The detailed design of AKROD, the first prototype built, closed loop control results and initial human testing are presented here
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ICRA - Design, Control and Human Testing of an Active Knee Rehabilitation Orthotic Device
Proceedings 2007 IEEE International Conference on Robotics and Automation, 2007Co-Authors: B. Weinberg, J. Nikitczuk, Constantinos Mavroidis, S. Patel, B. Patritti, P. Bonato, P. CanavanAbstract:This paper presents a novel, smart and portable active knee rehabilitation orthotic device (AKROD) designed to train stroke patients to correct knee hyperextension during stance and stiff-legged gait (defined as reduced knee flexion during swing). The knee brace provides variable damping controlled in ways that foster motor recovery in stroke patients. A resistive, variable damper, electro-rheological fluid (ERF) based component is used to facilitate knee flexion during stance by providing resistance to knee buckling. Furthermore, the knee brace is used to assist in knee control during swing, i.e. to allow patients to achieve adequate knee flexion for toe clearance and adequate knee extension in preparation to heel strike. The detailed design of AKROD, the first prototype built, closed loop control results and initial human testing are presented here
