The Experts below are selected from a list of 2535 Experts worldwide ranked by ideXlab platform

Ga Thomas - One of the best experts on this subject based on the ideXlab platform.

  • An experimental investigation on slamming kinematics, impulse and energy transfer for high-speed catamarans equipped with Ride Control Systems
    'Elsevier BV', 2019
    Co-Authors: Alavimehr J, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    High‐speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112‐m highspeed catamaran using a 2.5‐m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T‐Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model‐scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112‐m INCAT vessel, enabling isolation and measurement of a center bow force and Bending Moments at two cross sections along the demi‐hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60‐mm model‐scale waves it significantly reduced the peak slam force by 90% and the average slam‐Induced Bending Moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high‐speed catamaran vessels

  • The effect of centre bow and wet-deck geometry on wet-deck slamming loads and vertical Bending Moments of wave-piercing catamarans
    'Elsevier BV', 2018
    Co-Authors: Shabani B, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    An experimental study was performed to determine the influence of centre bow length and tunnel height on the magnitude of the wave slamming loads and Bending Moments acting on a 112 m Incat wave-piercer catamaran vessel. A 2.5 m hydroelastic segmented catamaran model was tested in regular head sea waves at a high model speed in multiple test series, whilst five centre bow (CB) and wet-deck configurations were considered, designated here as the parent, low, high, long and short CBs. The model global motions, centre bow slam loads, accelerations, and slam Induced vertical Bending Moments of the catamaran model in waves were measured. It was found that the slamming force, the centre bow entry force and slam Induced Bending Moment all increase as the centre bow length increases. Increasing the wet-deck height increased the motions but reduced the maximum slam load in moderate waves. It was seen that the short CB was the best design for the alleviation of slam loads. The high CB was the second best choice for operation in moderate waves but it was the worst configuration in terms of heave and pitch motions among various CB configurations tested

  • An experimental investigation of ride control algorithms for high-speed catamarans Part 2: Mitigation of wave impact loads
    'The Society of Naval Architects and Marine Engineers', 2017
    Co-Authors: Alavimehr J, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    High‐speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112‐m highspeed catamaran using a 2.5‐m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T‐Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model‐scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112‐m INCAT vessel, enabling isolation and measurement of a center bow force and Bending Moments at two cross sections along the demi‐hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60‐mm model‐scale waves it significantly reduced the peak slam force by 90% and the average slam‐Induced Bending Moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high‐speed catamaran vessels

Y K Chow - One of the best experts on this subject based on the ideXlab platform.

  • pile behavior due to excavation Induced soil movement in clay ii collapsed wall
    Journal of Geotechnical and Geoenvironmental Engineering, 2006
    Co-Authors: C F Leung, Dominic Ek Leong Ong, Y K Chow
    Abstract:

    A series of centrifuge model tests has been conducted to investigate the behavior of a single pile behind a retaining wall that eventually fails due to soil excavation in front of the wall. All the piles are located at 3 m behind the wall where the soil experiences large shear strain (>2%). The Induced Bending Moment and deflection on the pile as well as the soil and wall movements are monitored at regular intervals throughout the tests. It is found that the pile performance depends greatly on the degree of wall instability. After a critical excavation depth, active wedge slip plane and tension cracks developed in the vicinity of the pile. The limiting soil pressure profile deduced from the measured maximum Induced pile Bending Moment profile is established to be much lower than that of a conventional laterally loaded pile. Using the measured soil movements at the pile location as the input data, the calculated pile Bending Moment obtained using an existing numerical model generally show fair agreement with the measured values when the back-analyzed limiting soil pressures acting on the pile are employed in the back-analysis. The practical implications of the findings are discussed in the paper.

  • pile behavior due to excavation Induced soil movement in clay i stable wall
    Journal of Geotechnical and Geoenvironmental Engineering, 2006
    Co-Authors: Dominic Ek Leong Ong, C E Leung, Y K Chow
    Abstract:

    A series of centrifuge model tests has been conducted to investigate the behavior of a single pile subjected to excavation-Induced soil movements behind a stable retaining wall in clay. The results reveal that after the completion of soil excavation, the wall and the soil continue to move and such movement induces further Bending Moment and deflection on an adjacent pile. For a pile located within 3 m behind the wall where the soil experiences large shear strain (>2%) due to stress relief as a result of the excavation, the Induced pile Bending Moment and deflection reach their maximum values sometime after soil excavation and thereafter decrease slightly with time. For a pile located 3 m beyond the wall, the Induced pile Bending Moment and deflection continue to increase slightly with time after excavation until the end of the test. A numerical model developed at the National University of Singapore is used to back-analyze the centrifuge test data. The method gives a reasonably good prediction of the Induced Bending Moment and deflection on a pile located at 3 m or beyond the wall. For a pile located at 1 m behind the wall where the soil experiences large shear strain (>2%) due to stress relief resulting from the excavation, the calculated pile response is in good agreement with the measured data if the correct soil shear strength obtained from postexcavation is used in the analysis. However, if the original soil shear strength prior to excavation is used in the analysis, this leads to an overestimation of the maximum Bending Moment of about 25%. The practical implications of the findings are also discussed in this paper.

Shabani B - One of the best experts on this subject based on the ideXlab platform.

  • The effect of centre bow and wet-deck geometry on wet-deck slamming loads and vertical Bending Moments of wave-piercing catamarans
    'Elsevier BV', 2018
    Co-Authors: Shabani B, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    An experimental study was performed to determine the influence of centre bow length and tunnel height on the magnitude of the wave slamming loads and Bending Moments acting on a 112 m Incat wave-piercer catamaran vessel. A 2.5 m hydroelastic segmented catamaran model was tested in regular head sea waves at a high model speed in multiple test series, whilst five centre bow (CB) and wet-deck configurations were considered, designated here as the parent, low, high, long and short CBs. The model global motions, centre bow slam loads, accelerations, and slam Induced vertical Bending Moments of the catamaran model in waves were measured. It was found that the slamming force, the centre bow entry force and slam Induced Bending Moment all increase as the centre bow length increases. Increasing the wet-deck height increased the motions but reduced the maximum slam load in moderate waves. It was seen that the short CB was the best design for the alleviation of slam loads. The high CB was the second best choice for operation in moderate waves but it was the worst configuration in terms of heave and pitch motions among various CB configurations tested

  • The effects of tunnel height and centre bow length on motions and slam loads in large wave piercing catamarans
    2017
    Co-Authors: Shabani B
    Abstract:

    An above water centre bow in wave piercing catamarans provides additional reserve buoyancy for minimising deck diving in following seas. The centre bow entry in waves, however, contributes to the severity of the wet-deck arch slam loads and slam Induced Bending Moments. In this thesis, the effects of the centre bow length and wet-deck height/tunnel clearance on the motions and slam loads in large wave piercing catamarans are investigated through model tests to establish a framework for the preliminary design analysis. The model tests were performed in regular waves in head seas using a 2.5 m hydroelastic segmented catamaran model designed with an adjustable wet-deck and a changeable centre bow segment. Five different centre bow and wet-deck configurations were considered and over 500 towing tests were performed at two model speeds, in three wave heights and for various wave encounter frequencies. The catamaran model was comprehensively instrumented to measure the pitch and heave, centre bow loads, centre bow accelerations, wet-deck arch slam pressures and the vertical Bending Moments at two segment cuts located in each port and starboard demihull. Motion analyses showed that both heave and pitch increased over a wide range of encounter wave frequency as the wet-deck height of the catamaran model increased. Increasing the length of the centre bow showed an increase in the pitch but a decrease in the heave for a particular range of encounter wave frequency. The vertical motions along the model length indicated that the position of minimum vertical displacements and accelerations were aft of the LCG, between 20% and 38% of the overall length from the transom. The increase in wet-deck and consequently the archways clearance also resulted in an increase in relative vertical displacement in the centre bow area. This indicated that although the wet deck height had been increased, the consequent increase in motion still caused slamming to occur. In dynamic analyses, the maximum force acting on the centre bow segment during a slam event was decomposed into a bow entry force and a slam force. It was found that the slamming force, the centre bow entry force and slam Induced Bending Moment increase as the centre bow length increases. Increasing the wet-deck height reduced the maximum slam load and pressure in moderate waves, but not in large waves. A correlation analysis between the slam force and slam pressure showed that the slam loads increase in the longer centre bows because of the increase in the impact area. The location of maximum pressures along the centre bow length was more related to the encounter wave frequency rather than the centre bow configurations. The distribution of the peak pressures within the centre bow archways showed that the inboard peak pressures were higher than the top arch and outboard peak pressures. The slam occurrence and severity for different centre bow and wet-deck configurations were analysed by considering the centre bow immersion depth and relative velocity at slam using the undisturbed water profile. It was found that the undisturbed immersion depth for severe slam loads was greater than the immersion depth at the wet-deck level. Therefore, the cross structure between the demihulls and the centre bow can be modified to reduce the slamming pressure. The results obtained by the comparison of the various centre bow and wet-deck configurations demonstrate the significance of considering the effect of the centre bow and archway slamming in structural design and suggest that the class rules currently available for wave piercing catamarans with a flat deck structure could be modified accordingly. Amongst the tested centre bow configurations, the shortest centre bow was the best design for slam load alleviation. Ideally, a trade-off amongst the centre bow buoyancy in waves, slam load and the catamaran motions should be made to optimise the centre bow design according to the vessel‟s operating conditions

Ds Holloway - One of the best experts on this subject based on the ideXlab platform.

  • An experimental investigation on slamming kinematics, impulse and energy transfer for high-speed catamarans equipped with Ride Control Systems
    'Elsevier BV', 2019
    Co-Authors: Alavimehr J, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    High‐speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112‐m highspeed catamaran using a 2.5‐m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T‐Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model‐scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112‐m INCAT vessel, enabling isolation and measurement of a center bow force and Bending Moments at two cross sections along the demi‐hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60‐mm model‐scale waves it significantly reduced the peak slam force by 90% and the average slam‐Induced Bending Moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high‐speed catamaran vessels

  • The effect of centre bow and wet-deck geometry on wet-deck slamming loads and vertical Bending Moments of wave-piercing catamarans
    'Elsevier BV', 2018
    Co-Authors: Shabani B, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    An experimental study was performed to determine the influence of centre bow length and tunnel height on the magnitude of the wave slamming loads and Bending Moments acting on a 112 m Incat wave-piercer catamaran vessel. A 2.5 m hydroelastic segmented catamaran model was tested in regular head sea waves at a high model speed in multiple test series, whilst five centre bow (CB) and wet-deck configurations were considered, designated here as the parent, low, high, long and short CBs. The model global motions, centre bow slam loads, accelerations, and slam Induced vertical Bending Moments of the catamaran model in waves were measured. It was found that the slamming force, the centre bow entry force and slam Induced Bending Moment all increase as the centre bow length increases. Increasing the wet-deck height increased the motions but reduced the maximum slam load in moderate waves. It was seen that the short CB was the best design for the alleviation of slam loads. The high CB was the second best choice for operation in moderate waves but it was the worst configuration in terms of heave and pitch motions among various CB configurations tested

  • An experimental investigation of ride control algorithms for high-speed catamarans Part 2: Mitigation of wave impact loads
    'The Society of Naval Architects and Marine Engineers', 2017
    Co-Authors: Alavimehr J, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    High‐speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112‐m highspeed catamaran using a 2.5‐m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T‐Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model‐scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112‐m INCAT vessel, enabling isolation and measurement of a center bow force and Bending Moments at two cross sections along the demi‐hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60‐mm model‐scale waves it significantly reduced the peak slam force by 90% and the average slam‐Induced Bending Moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high‐speed catamaran vessels

Lavroff J - One of the best experts on this subject based on the ideXlab platform.

  • An experimental investigation on slamming kinematics, impulse and energy transfer for high-speed catamarans equipped with Ride Control Systems
    'Elsevier BV', 2019
    Co-Authors: Alavimehr J, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    High‐speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112‐m highspeed catamaran using a 2.5‐m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T‐Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model‐scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112‐m INCAT vessel, enabling isolation and measurement of a center bow force and Bending Moments at two cross sections along the demi‐hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60‐mm model‐scale waves it significantly reduced the peak slam force by 90% and the average slam‐Induced Bending Moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high‐speed catamaran vessels

  • The effect of centre bow and wet-deck geometry on wet-deck slamming loads and vertical Bending Moments of wave-piercing catamarans
    'Elsevier BV', 2018
    Co-Authors: Shabani B, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    An experimental study was performed to determine the influence of centre bow length and tunnel height on the magnitude of the wave slamming loads and Bending Moments acting on a 112 m Incat wave-piercer catamaran vessel. A 2.5 m hydroelastic segmented catamaran model was tested in regular head sea waves at a high model speed in multiple test series, whilst five centre bow (CB) and wet-deck configurations were considered, designated here as the parent, low, high, long and short CBs. The model global motions, centre bow slam loads, accelerations, and slam Induced vertical Bending Moments of the catamaran model in waves were measured. It was found that the slamming force, the centre bow entry force and slam Induced Bending Moment all increase as the centre bow length increases. Increasing the wet-deck height increased the motions but reduced the maximum slam load in moderate waves. It was seen that the short CB was the best design for the alleviation of slam loads. The high CB was the second best choice for operation in moderate waves but it was the worst configuration in terms of heave and pitch motions among various CB configurations tested

  • An experimental investigation of ride control algorithms for high-speed catamarans Part 2: Mitigation of wave impact loads
    'The Society of Naval Architects and Marine Engineers', 2017
    Co-Authors: Alavimehr J, Lavroff J, Ds Holloway, Davis Mr, Ga Thomas
    Abstract:

    High‐speed craft frequently experience large wave impact loads due to their large motions and accelerations. One solution to reduce the severity of motion and impact loadings is the installation of ride control systems. Part 1 of this study investigates the influence of control algorithms on the motions of a 112‐m highspeed catamaran using a 2.5‐m model fitted with a ride control system. The present study extends this to investigate the influence of control algorithms on the loads and internal forces acting on a hydroelastic segmented catamaran model. As in Part 1, the model active control system consisted of a center bow T‐Foil and two stern tabs. Six motion control feedback algorithms were used to activate the model‐scale ride control system and surfaces in a closed loop system: local motion, heave, and pitch control, each in a linear and nonlinear application. The loads were further determined with a passive ride control system and without control surfaces fitted for direct comparison. The model was segmented into seven parts, connected by flexible links that replicate the first two natural frequencies and mode shapes of the 112‐m INCAT vessel, enabling isolation and measurement of a center bow force and Bending Moments at two cross sections along the demi‐hulls. The model was tested in regular head seas at different wave heights and frequencies. From these tests, it was found that the pitch control mode was most effective and in 60‐mm model‐scale waves it significantly reduced the peak slam force by 90% and the average slam‐Induced Bending Moment by 75% when compared with a bare hull without ride controls fitted. This clearly demonstrates the effectiveness of a ride control system in reducing wave impact loads acting on high‐speed catamaran vessels