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Sher Afghan Khan - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of Stability Derivatives in Newtonian Limit for Oscillating Cone
    IOP Conference Series: Materials Science and Engineering, 2018
    Co-Authors: Aysha Shabana, Asha Crasta, Renita Sharon Monis, Sher Afghan Khan
    Abstract:

    Stability derivatives in Newtonian limit for an oscillating cone are obtained. Stiffness derivative decreases with Pivot Position for the entire range of cone angles. For cone angles in the range 20 to 30 degrees there is substantial increase in the stiffness derivative. Damping derivative decreases with Pivot Position for various cone angles and attains a minima at h = 0.75 and then again with increase in Pivot Position there is non-linear increment in damping derivatives. There is considerable change in the magnitude, for higher cone angles in the range of 20 degrees and above as the centre of pressure has further moved towards the trailing edge of the cone at Pivot Position around h = 0.88. Stiffness derivative increases with cone angle for various Pivot Positions. Damping derivative with cone angle for various fixed Pivot Positions is seen to increase linearly with cone angle, it is also observed that this trend of linear increment tend to become non-linear for cone angles in the range 20 degrees and beyond. Damping derivative decreases with Pivot Position h = 0.8 for the entire range of cone angles, however, for Pivot Position h = 1.0, shows almost constant values up to cone angle of 20 degrees. For cone angle 30 degrees value of damping derivative coincides irrespective of Pivot Position being at h = 0.8 or 1.0 and this trend is attributed to the 3-D effect of the flow field.

  • Supersonic flow analysis and evaluation of damping derivative
    IOSR Journal of Mechanical and Civil Engineering, 2016
    Co-Authors: Renita Sharon Monis, Asha Crasta, Ayesha Shabana, Sher Afghan Khan
    Abstract:

    The emphasis of this paper is to examine the variation of damping derivative with incidence angle and Mach number with varying Pivot Position. The damping derivative decreases with Mach number and increases with the incidence angle. It is also seen that for a given Mach number the damping derivatives are decreasing and reaches a minimum value and then again increases and attains the same value which was at h = 0, for Pivot Position h = 0 to h = 1.0 and at h = 0.5 it attains a minimum value and then increases for h = 0.6 to h = 1. The Damping derivative decreases with Mach number for the varying Pivot Position.

  • Analysis of variation of stiffness derivative with Mach number and angle of attack for a supersonic flow
    IOSR Journal of Mechanical and Civil Engineering, 2016
    Co-Authors: Asha Crasta, Aysha Shabana, Renita Sharon Monis, Sher Afghan Khan
    Abstract:

    In this paper unified supersonic theory is used to derive the expressions of Stiffness derivative of a wedge in Hypersonic flow. This paper demonstrates the effects of Pivot Position on the stffness derivative with Mach number and incidence angle. From the above discussion it is seen that behaviour of the stiffness derivative is the same for h = 0 to 0.4 and also for h = 0.8, 0.9, and 1.0. Due to the Pivot Position variations there is a significant variation of Stiffness derivative with Mach number and incidence angle.

  • Effect of angle of attack on damping derivatives of delta wing with full sine wave curved leading edge
    2015
    Co-Authors: Asha Crasta, Sher Afghan Khan
    Abstract:

    In the Present paper effect of angle of incidence on Damping derivative of a delta wing with Curved leading edges (for a full sine wave) for attached shock case in Supersonic Flow has been studied. A Strip theory is used in which strips at different span wise location are independent of each other. This combines with similitude to give a piston theory which gives closed form solutions for damping derivatives at low to high supersonic Mach numbers. From the results it is seen that with the increase in the Mach number, there is a progressive decrease in the magnitude of damping derivatives for all the Mach numbers of the present studies; however, the decrease in the magnitude is variable at different inertia level. It is seen that with the increase in the angle of attack the damping derivative increases linearly, nevertheless, this linear behavior limit themselves for different Mach numbers. For Mach number M = 2, this limiting value of validity is fifteen degrees, for Mach 2.5 & 3, it is twenty five degrees, whereas, for Mach 3.5 & 4 it becomes thirty five degrees, when these stability derivatives were considered at various Pivot Positions; namely at h = 0.0, 0.4, 0.6, and 1.0. After scanning the results it is observed that with the shift of the Pivot Position from the leading edge to the trailing edge, the magnitude of the damping derivatives continue to decrease throughout. Results have been obtained for supersonic flow of perfect gases over a wide range of angle of attack and Mach number. The effect of real gas, leading edge bluntness of the wing, shock motion, and secondary wave reflections are neglected.

  • Estimation of Damping Derivative in Pitch of a Supersonic Delta Wing with Curved Leading Edges
    2015
    Co-Authors: Asha Crasta, Sher Afghan Khan
    Abstract:

    In the Present paper effect of angle of incidence on Damping derivative of a delta wing with Curved leading edges for attached shock case in Supersonic Flow has been studied. A Strip theory is used in which strips at different span wise location are independent of each other. This combines with similitude to give a piston theory which gives closed form solutions for damping derivatives at low to high supersonic Mach numbers. From the results it is seen that with the increase in the Mach number, there is a progressive decrease in the magnitude of damping derivatives for all the Mach numbers of the present studies; however, the decrease in the magnitude is variable at different inertia level. It is seen that with the increase in the angle of attack the damping derivative increases linearly, nevertheless, this linear behavior limit themselves for different Mach numbers. For Mach number M = 2, this limiting value of validity is fifteen degrees, for Mach 2.5 & 3, it is twenty five degrees, whereas, for Mach 3.5 & 4 it becomes thirty five degrees, when these stability derivatives were considered at various Pivot Positions; namely at h = 0.0, 0.4, 0.6, and 1.0. After scanning the results it is observed that with the shift of the Pivot Position from the leading edge to the trailing edge, the magnitude of the damping derivatives continue to decrease throughout. Results have been obtained for supersonic flow of perfect gases over a wide range of angle of attack and Mach number. The effect of real gas, leading edge bluntness of the wing, shock motion, and secondary wave reflections are neglected.

Asha Crasta - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of Stability Derivatives in Newtonian Limit for Oscillating Cone
    IOP Conference Series: Materials Science and Engineering, 2018
    Co-Authors: Aysha Shabana, Asha Crasta, Renita Sharon Monis, Sher Afghan Khan
    Abstract:

    Stability derivatives in Newtonian limit for an oscillating cone are obtained. Stiffness derivative decreases with Pivot Position for the entire range of cone angles. For cone angles in the range 20 to 30 degrees there is substantial increase in the stiffness derivative. Damping derivative decreases with Pivot Position for various cone angles and attains a minima at h = 0.75 and then again with increase in Pivot Position there is non-linear increment in damping derivatives. There is considerable change in the magnitude, for higher cone angles in the range of 20 degrees and above as the centre of pressure has further moved towards the trailing edge of the cone at Pivot Position around h = 0.88. Stiffness derivative increases with cone angle for various Pivot Positions. Damping derivative with cone angle for various fixed Pivot Positions is seen to increase linearly with cone angle, it is also observed that this trend of linear increment tend to become non-linear for cone angles in the range 20 degrees and beyond. Damping derivative decreases with Pivot Position h = 0.8 for the entire range of cone angles, however, for Pivot Position h = 1.0, shows almost constant values up to cone angle of 20 degrees. For cone angle 30 degrees value of damping derivative coincides irrespective of Pivot Position being at h = 0.8 or 1.0 and this trend is attributed to the 3-D effect of the flow field.

  • Supersonic flow analysis and evaluation of damping derivative
    IOSR Journal of Mechanical and Civil Engineering, 2016
    Co-Authors: Renita Sharon Monis, Asha Crasta, Ayesha Shabana, Sher Afghan Khan
    Abstract:

    The emphasis of this paper is to examine the variation of damping derivative with incidence angle and Mach number with varying Pivot Position. The damping derivative decreases with Mach number and increases with the incidence angle. It is also seen that for a given Mach number the damping derivatives are decreasing and reaches a minimum value and then again increases and attains the same value which was at h = 0, for Pivot Position h = 0 to h = 1.0 and at h = 0.5 it attains a minimum value and then increases for h = 0.6 to h = 1. The Damping derivative decreases with Mach number for the varying Pivot Position.

  • Analysis of variation of stiffness derivative with Mach number and angle of attack for a supersonic flow
    IOSR Journal of Mechanical and Civil Engineering, 2016
    Co-Authors: Asha Crasta, Aysha Shabana, Renita Sharon Monis, Sher Afghan Khan
    Abstract:

    In this paper unified supersonic theory is used to derive the expressions of Stiffness derivative of a wedge in Hypersonic flow. This paper demonstrates the effects of Pivot Position on the stffness derivative with Mach number and incidence angle. From the above discussion it is seen that behaviour of the stiffness derivative is the same for h = 0 to 0.4 and also for h = 0.8, 0.9, and 1.0. Due to the Pivot Position variations there is a significant variation of Stiffness derivative with Mach number and incidence angle.

  • Effect of angle of attack on damping derivatives of delta wing with full sine wave curved leading edge
    2015
    Co-Authors: Asha Crasta, Sher Afghan Khan
    Abstract:

    In the Present paper effect of angle of incidence on Damping derivative of a delta wing with Curved leading edges (for a full sine wave) for attached shock case in Supersonic Flow has been studied. A Strip theory is used in which strips at different span wise location are independent of each other. This combines with similitude to give a piston theory which gives closed form solutions for damping derivatives at low to high supersonic Mach numbers. From the results it is seen that with the increase in the Mach number, there is a progressive decrease in the magnitude of damping derivatives for all the Mach numbers of the present studies; however, the decrease in the magnitude is variable at different inertia level. It is seen that with the increase in the angle of attack the damping derivative increases linearly, nevertheless, this linear behavior limit themselves for different Mach numbers. For Mach number M = 2, this limiting value of validity is fifteen degrees, for Mach 2.5 & 3, it is twenty five degrees, whereas, for Mach 3.5 & 4 it becomes thirty five degrees, when these stability derivatives were considered at various Pivot Positions; namely at h = 0.0, 0.4, 0.6, and 1.0. After scanning the results it is observed that with the shift of the Pivot Position from the leading edge to the trailing edge, the magnitude of the damping derivatives continue to decrease throughout. Results have been obtained for supersonic flow of perfect gases over a wide range of angle of attack and Mach number. The effect of real gas, leading edge bluntness of the wing, shock motion, and secondary wave reflections are neglected.

  • Estimation of Damping Derivative in Pitch of a Supersonic Delta Wing with Curved Leading Edges
    2015
    Co-Authors: Asha Crasta, Sher Afghan Khan
    Abstract:

    In the Present paper effect of angle of incidence on Damping derivative of a delta wing with Curved leading edges for attached shock case in Supersonic Flow has been studied. A Strip theory is used in which strips at different span wise location are independent of each other. This combines with similitude to give a piston theory which gives closed form solutions for damping derivatives at low to high supersonic Mach numbers. From the results it is seen that with the increase in the Mach number, there is a progressive decrease in the magnitude of damping derivatives for all the Mach numbers of the present studies; however, the decrease in the magnitude is variable at different inertia level. It is seen that with the increase in the angle of attack the damping derivative increases linearly, nevertheless, this linear behavior limit themselves for different Mach numbers. For Mach number M = 2, this limiting value of validity is fifteen degrees, for Mach 2.5 & 3, it is twenty five degrees, whereas, for Mach 3.5 & 4 it becomes thirty five degrees, when these stability derivatives were considered at various Pivot Positions; namely at h = 0.0, 0.4, 0.6, and 1.0. After scanning the results it is observed that with the shift of the Pivot Position from the leading edge to the trailing edge, the magnitude of the damping derivatives continue to decrease throughout. Results have been obtained for supersonic flow of perfect gases over a wide range of angle of attack and Mach number. The effect of real gas, leading edge bluntness of the wing, shock motion, and secondary wave reflections are neglected.

Georg N. Duda - One of the best experts on this subject based on the ideXlab platform.

  • Author Correction: Weight Bearing Activities change the Pivot Position after Total Knee Arthroplasty
    Scientific Reports, 2020
    Co-Authors: Philippe Moewis, Hagen Hommel, Adam Trepczynski, Leonie Krahl, Philipp Roth, Georg N. Duda
    Abstract:

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

  • Weight Bearing Activities change the Pivot Position after Total Knee Arthroplasty
    Scientific Reports, 2019
    Co-Authors: Philippe Moewis, Hagen Hommel, Adam Trepczynski, Leonie Krahl, Philipp Roth, Georg N. Duda
    Abstract:

    The knee joint center of rotation is altered in the absence of the anterior cruciate ligament, which leads to substantially higher variance in kinematic patterns. To overcome this, total knee arthroplasty (TKA) designs with a high congruency in the lateral compartment have been proposed. The purpose of this study was to analyze the influence of a lateral Pivot TKA-design on in-vivo knee joint kinematics. Tibiofemoral motion was retrospectively addressed in 10 patients during unloaded flexion-extension and loaded lunge using single plane fluoroscopy. During the unloaded flexion-extension movement, the lateral condyle remained almost stationary with little rollback at maximum flexion. The medial condyle exhibited anterior translation during the whole flexion cycle. During the loaded lunge movement, a higher degree of rollback compared to the unloaded activity was observed on the lateral condyle, whereas the medial condyle remained almost stationary. The results showed a clear lateral Pivot during the unloaded activity, reflective of the implant’s geometric characteristics, and a change to a medial Pivot and a higher lateral rollback during the weight-bearing conditions, revealing the impact of load and muscle force. It remains unclear if the kinematics with a lateral TKA design could be considered as physiological, due to the limited knowledge available on native knee joint kinematics.

  • Tibio-Femoral Contact Force Distribution is Not the Only Factor Governing Pivot Location after Total Knee Arthroplasty
    Nature Publishing Group, 2019
    Co-Authors: Adam Trepczynski, Philippe Moewis, I. Kutzner, P. Schütz, J. Dymke, R. List, P. Von Roth, G. Bergmann, W. R. Taylor, Georg N. Duda
    Abstract:

    Abstract Total knee arthroplasty aims to mimic the natural knee kinematics by optimizing implant geometry, but it is not clear how loading relates to tibio-femoral anterior-posterior translation or internal-external Pivoting. We hypothesised that the point of Pivot in the transverse plane is governed by the location of the highest axial force. Tibio-femoral loading was measured using an instrumented tibial component in six total knee arthroplasty patients (aged 65–80y, 5–7y post-op) during 5–6 squat repetitions, while knee kinematics were captured using a mobile video-fluoroscope. In the range of congruent tibio-femoral contact the medial femoral condyle remained approximately static while the lateral condyle translated posteriorly by 4.1 mm (median). Beyond the congruent range, the medial and lateral condyle motions both abruptly changed to anterior sliding by 4.6 mm, and 2.6 mm respectively. On average, both the axial loading and Pivot Position were more medial near extension, and transferred to the lateral side in flexion. However, no consistent relationship between Pivoting and load distribution was found across all patients throughout flexion, with R2 values ranging from 0.00 to 0.65. Tibio-femoral kinematics is not related to the load distribution alone: medial loading of the knee does not necessarily imply a medial Pivot location

Philippe Moewis - One of the best experts on this subject based on the ideXlab platform.

  • Author Correction: Weight Bearing Activities change the Pivot Position after Total Knee Arthroplasty
    Scientific Reports, 2020
    Co-Authors: Philippe Moewis, Hagen Hommel, Adam Trepczynski, Leonie Krahl, Philipp Roth, Georg N. Duda
    Abstract:

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

  • Weight Bearing Activities change the Pivot Position after Total Knee Arthroplasty
    Scientific Reports, 2019
    Co-Authors: Philippe Moewis, Hagen Hommel, Adam Trepczynski, Leonie Krahl, Philipp Roth, Georg N. Duda
    Abstract:

    The knee joint center of rotation is altered in the absence of the anterior cruciate ligament, which leads to substantially higher variance in kinematic patterns. To overcome this, total knee arthroplasty (TKA) designs with a high congruency in the lateral compartment have been proposed. The purpose of this study was to analyze the influence of a lateral Pivot TKA-design on in-vivo knee joint kinematics. Tibiofemoral motion was retrospectively addressed in 10 patients during unloaded flexion-extension and loaded lunge using single plane fluoroscopy. During the unloaded flexion-extension movement, the lateral condyle remained almost stationary with little rollback at maximum flexion. The medial condyle exhibited anterior translation during the whole flexion cycle. During the loaded lunge movement, a higher degree of rollback compared to the unloaded activity was observed on the lateral condyle, whereas the medial condyle remained almost stationary. The results showed a clear lateral Pivot during the unloaded activity, reflective of the implant’s geometric characteristics, and a change to a medial Pivot and a higher lateral rollback during the weight-bearing conditions, revealing the impact of load and muscle force. It remains unclear if the kinematics with a lateral TKA design could be considered as physiological, due to the limited knowledge available on native knee joint kinematics.

  • Tibio-Femoral Contact Force Distribution is Not the Only Factor Governing Pivot Location after Total Knee Arthroplasty
    Nature Publishing Group, 2019
    Co-Authors: Adam Trepczynski, Philippe Moewis, I. Kutzner, P. Schütz, J. Dymke, R. List, P. Von Roth, G. Bergmann, W. R. Taylor, Georg N. Duda
    Abstract:

    Abstract Total knee arthroplasty aims to mimic the natural knee kinematics by optimizing implant geometry, but it is not clear how loading relates to tibio-femoral anterior-posterior translation or internal-external Pivoting. We hypothesised that the point of Pivot in the transverse plane is governed by the location of the highest axial force. Tibio-femoral loading was measured using an instrumented tibial component in six total knee arthroplasty patients (aged 65–80y, 5–7y post-op) during 5–6 squat repetitions, while knee kinematics were captured using a mobile video-fluoroscope. In the range of congruent tibio-femoral contact the medial femoral condyle remained approximately static while the lateral condyle translated posteriorly by 4.1 mm (median). Beyond the congruent range, the medial and lateral condyle motions both abruptly changed to anterior sliding by 4.6 mm, and 2.6 mm respectively. On average, both the axial loading and Pivot Position were more medial near extension, and transferred to the lateral side in flexion. However, no consistent relationship between Pivoting and load distribution was found across all patients throughout flexion, with R2 values ranging from 0.00 to 0.65. Tibio-femoral kinematics is not related to the load distribution alone: medial loading of the knee does not necessarily imply a medial Pivot location

Tiesheng Zheng - One of the best experts on this subject based on the ideXlab platform.

  • Linear Stability Analysis of a Tilting-Pad Journal Bearing System
    Journal of Tribology, 2006
    Co-Authors: Guang Qiao, Liping Wang, Tiesheng Zheng
    Abstract:

    This paper describes a mathematical model to study the linear stability of a tilting-pad journal bearing system. By employing the Newton-Raphson method and the pad assembly technique, the full dynamic coefficients involving the shaft degrees of freedom as well as the pad degrees of freedom are determined. Based on these dynamic coefficients, the perturbation equations including self-excited motion of the rotor and rotational motion of the pads are derived. The complex eigenvalues of the equations are computed and the pad critical mass identified by eigenvalues can be used to determine the stability zone of the system. The results show that some factors, such as the preload coefficient, the Pivot Position, and the rotor speed, significantly affect the stability of tilting-pad journal bearing system. Correctly adjusting those parameter values can enhance the stability of the system. Furthermore, various stability charts for the system can be plotted.