| 1. |
- Thompson, David, et al.
(författare)
-
Assessment of measurement-based methods for separating wheel and track contributions to railway rolling noise
- 2018
-
Ingår i: Applied Acoustics. - : Elsevier. - 0003-682X .- 1872-910X. ; 140, s. 48-62
-
Tidskriftsartikel (refereegranskat)abstract
- The noise produced during a train pass-by originates from several different sources such as propulsion noise, noise from auxiliary equipment, aerodynamic noise and rolling noise. The rolling noise is radiated by the wheels and the track and is excited by the wheel and rail unevenness, usually referred to as roughness. The current TSI Noise certification method, which must be satisfied by all new mainline trains in Europe, relies on the use of a reference track to quantify the noise from new vehicles. The reference track is defined by an upper limit of the rail roughness and a lower limit of the track decay rate (TDR). However, since neither the rail roughness nor the track radiation can be completely neglected, the result cannot be taken as representing only the vehicle noise and the measurement does not allow separate identification of the noise radiated by wheel and track. It is even likely that further reductions in the limit values for new rolling stock cannot be achieved on current tracks. There is therefore a need for a method to separate the noise into these two components reliably and cheaply. The purpose of the current study is to assess existing and new methods for rolling noise separation. Field tests have been carried out under controlled conditions, allowing the different methods to be compared. The TWINS model is used with measured vibration data to give reference estimates of the wheel and track noise components. Six different methods are then considered that can be used to estimate the track component. It is found that most of these methods can obtain the track component of noise with acceptable accuracy. However, apart from the TWINS model, the wheel noise component could only be estimated directly using three methods and un- fortunately these did not give satisfactory results in the current tests.
|
|
| 2. |
- Afzal, Mohammad, 1987-, et al.
(författare)
-
A formulation of the Jacobian matrixfor 3D numerical friction contact model applied to turbine blade shroud contact
-
Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modelling that eciently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for thecalculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3Drelative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite dierence method, with many points at the contact interface. Therefore,it also significantly reduces the overall computation time for the solution of the equations of motion,since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite dierence approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for aperiodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.
|
|
| 3. |
- Afzal, Mohammad, 1987-, et al.
(författare)
-
Adaptive control of normal load at the friction interface of bladed disks using giant magnetostrictive material
-
Ingår i: Journal of Vibration and Control. - 1077-5463 .- 1741-2986.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A novel application of magnetostrictive actuators in underplatform dampers of bladed disks is proposed for adaptive control of the normal load at the friction interface in order to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on many parameters such as rotational speed, engine excitation order, nodal diameter, contact stiffness, friction coefficient and normal contact load. However, all these parameters have a fixed value at an operating point. On the other hand, the ability to vary some of these parameters such as the normal contact load is desirable in order to obtain an optimum damping in the bladed disk at different operating conditions. Under the influence of an external magnetic field, magnetostrictive materials develop an internal strain that can be exploited to vary the normal contact load at the friction interface, which makes them a potentially good candidate for this application. A commercially available magnetostrictive alloy, Terfenol-D is considered in this analysis that is capable of providing magnetostrain up to 0.002 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a DC application, is employed to compute the output displacement and the blocked force of the actuator. A nonlinear finite element contact analysis is performed to compute the normal contact load between the blade platform and the underplatform damper as a result of magnetostrictive actuation. The contact analysis is performed for different mounting configurations of the actuator and the obtained results are discussed. The proposed solution is potentially applicable to adaptively control vibratory stresses in bladed disks and consequently to reduce failure due to high-cycle fatigue. Finally, the practical challenges in employing magnetostrictive actuators in underplatform dampers are discussed.
|
|
| 4. |
- Afzal, Mohammad, 1987-, et al.
(författare)
-
Adaptive control of normal load at the friction interface of bladed disks using giant magnetostrictive material
- 2020
-
Ingår i: Journal of Intelligent Materials Systems and Structures. - : SAGE Publications. - 1045-389X .- 1530-8138. ; 31:8, s. 1111-1125
-
Tidskriftsartikel (refereegranskat)abstract
- A novel application of magnetostrictive actuators in underplatform dampers of bladed disks is proposed for adaptive control of the normal load at the friction interface to achieve the desired friction damping in the structure. Friction damping in a bladed disk depends on operating parameters, such as rotational speed, engine excitation order, nodal diameter normal contact load, and contact interface parameters, such as contact stiffness and friction coefficient. The operating parameters have a fixed value, whereas the contact interface parameters vary in an unpredictable way at an operating point. However, the ability to vary some of these parameters such as the normal contact load in a controlled manner is desirable to attain an optimum damping in the bladed disk at different operating conditions. Under the influence of an external magnetic field, magnetostrictive materials develop an internal strain that can be exploited to vary the normal contact load at the friction interface, which makes them a potentially good candidate for this application. A commercially available magnetostrictive alloy, Terfenol-D is considered in this analysis that is capable of providing magnetostrain up to 2 × 10-3 under prestress and a blocked force over 1500 N. A linearized model of the magnetostrictive material, which is accurate enough for a direct current application, is employed to compute the output force of the actuator. A nonlinear finite element contact analysis is performed to compute the normal contact load between the blade platform and the underplatform damper as a result of magnetostrictive actuation. The nonlinear contact analysis is performed for different actuator mounting configurations and the obtained results are discussed. The proposed solution is potentially applicable to adaptively control vibratory stresses in bladed disks and consequently to reduce failure due to high-cycle fatigue. Finally, the practical challenges in employing magnetostrictive actuators in underplatform dampers are discussed.
|
|
| 5. |
- Afzal, Mohammad, et al.
(författare)
-
An analytical calculation of the Jacobian matrix for 3D friction contact model applied to turbine blade shroud contact
- 2016
-
Ingår i: Computers & structures. - : Elsevier. - 0045-7949 .- 1879-2243. ; 177, s. 204-217
-
Tidskriftsartikel (refereegranskat)abstract
- An analytical expression is formulated to compute the Jacobian matrix for 3D friction contact modeling that efficiently evaluates the matrix while computing the friction contact forces in the time domain by means of the alternate frequency time domain approach. The developed expression is successfully used for the calculation of the friction damping on a turbine blade with shroud contact interface having an arbitrary 3D relative displacement. The analytical expression drastically reduces the computation time of the Jacobian matrix with respect to the classical finite difference method, with many points at the contact interface. Therefore, it also significantly reduces the overall computation time for the solution of the equations of motion, since the formulation of the Jacobian matrix is the most time consuming step in solving the large set of nonlinear algebraic equations when a finite difference approach is employed. The equations of motion are formulated in the frequency domain using the multiharmonic balance method to accurately capture the nonlinear contact forces and displacements. Moreover, the equations of motion of the full turbine blade model are reduced to a single sector model by exploiting the concept of cyclic symmetry boundary condition for a periodic structure. Implementation of the developed scheme in solving the equations of motion is proved to be effective and significant reduction in time is achieved without loss of accuracy.
|
|
| 6. |
- Afzal, Mohammad, 1987-, et al.
(författare)
-
Numerical analysis of multiple friction contacts in bladed disks
-
Ingår i: International Journal of Mechanical Sciences. - 0020-7403 .- 1879-2162.
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The damping potential of multiple friction contacts in a bladed disk, tip shroud and strip damper is investigated, showing that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations and a highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the approximate steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.
|
|
| 7. |
- Afzal, Mohammad, et al.
(författare)
-
Numerical analysis of multiple friction contacts in bladed disks
- 2018
-
Ingår i: International Journal of Mechanical Sciences. - : Elsevier. - 0020-7403 .- 1879-2162. ; 137, s. 224-237
-
Tidskriftsartikel (refereegranskat)abstract
- The damping potential of multiple friction contacts in a bladed disk is investigated. Friction contacts at tip shrouds and strip dampers are considered. It is shown that friction damping effectiveness can be potentially increased by using multiple friction contact interfaces. Friction damping depends on many parameters such as rotational speed, engine excitation order and mode family and therefore it is not possible to damp all the critical resonances using a single kind of friction contact interface. For example, a strip damper is more effective for the low nodal diameters, where blade/disk coupling is strong. The equations of motion of the bladed disk with multiple friction contacts are derived in the frequency domain for a cyclic structure with rotating excitations. A highly accurate method is used to generate the frequency response function (FRF) matrix. Furthermore, a finite element contact analysis is performed to compute the normal contact load and the contact area of the shroud interface at operating rotational speed. The multiharmonic balance method is employed in combination with the alternate frequency time domain method to find the steady state periodic solution. A low-pressure turbine bladed disk is considered and the effect of the engine excitation level, strip mass, thickness and the accuracy of FRF matrix on the nonlinear response curve are investigated in detail.
|
|
| 8. |
- Afzal, Mohammad, 1987-
(författare)
-
On efficient and adaptive modelling of friction damping in bladed disks
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work focuses on efficient modelling and adaptive control of friction damping in bladed disks. To efficiently simulate the friction contact, a full-3D time-discrete contact model is reformulated and an analytical expression for the Jacobian matrix is derived that reduces the computation time drastically with respect to the classical finite difference method. The developed numerical solver is applied on bladed disks with shroud contact and the advantage of full-3D contact model compared to a quasi-3D contact model is presented. The developed numerical solver is also applied on bladed disks with strip damper and multiple friction contacts and obtained results are discussed. Furthermore, presence of higher harmonics in the nonlinear contact forces is analyzed and their effect on the excitation of the different nodal diameters of the bladed disk are systematically presented. The main parameters that influence the effectiveness of friction damping in bladed disks are engine excitation order, contact stiffnesses, friction coefficient, relative motion at the friction interface and the normal contact load. Due to variation in these parameters during operation, the obtained friction damping in practice may differ from the optimum value. Therefore, to control the normal load adaptively that will lead to an optimum damping in the system despite these variations, use of magnetostrictive actuator is proposed. The magnetostrictive material that develops an internal strain under the influence of an external magnetic field is employed to increase and decrease the normal contact load. A linearized model of the magnetostrictive actuator is used to characterize the magnetoelastic behavior of the actuator. A nonlinear static contact analysis of the bladed disk reveals that a change of normal load more than 700 N can be achieved using a reasonable size of the actuator. This will give a very good control on friction damping once applied in practice.
|
|
| 9. |
- Amiri, A., et al.
(författare)
-
A replacement model to simulate the nonlinear dynamics of electro-responsive liquid crystal coatings
- 2023
-
Ingår i: AIP Advances. - : AIP Publishing. - 2158-3226. ; 13:3
-
Tidskriftsartikel (refereegranskat)abstract
- An electric circuit replacement model is proposed to simulate the key nonlinear dynamics of electro-responsive liquid crystal polymer networks (LCNs). LCNs are known for having great potential to be integrated into smart functional surfaces due to their ability to generate various surface patterns. However, due to their complex molecular dynamics, low-order dynamic models that can accurately describe and predict their dynamic behavior are still lacking. In light of this research gap, we develop a lumped-parameter replacement model based on the observed dynamics in the experimental data and the physics of LCN dielectric properties. The unique assembly of lumped parameters in its simplest form describes the transformation of a high-frequency input voltage to a relatively slow increase in the local height of the LCN coating in between the electrodes, serving as an excitation mechanism to induce height change. The nonlinear dynamics of this height increase, as a function of both excitation frequency and voltage, is described by the proposed model. Furthermore, the comparison of the simulation results with the experimental data from LCN shows that key LCN response characteristics are captured well by the model. This model makes it possible to accurately predict and control the response of the electro-responsive LCN surfaces to obtain a predefined desired deformation pattern, which is a vital requirement for integrating them in haptic and smart surface devices.
|
|
| 10. |
- Amlinger, Hanna, et al.
(författare)
-
Impact of PWM switching frequency on the radiated acoustic noise from a traction motor
- 2017
-
Ingår i: 2017 20th International Conference on Electrical Machines and Systems, ICEMS 2017. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538632468
-
Konferensbidrag (refereegranskat)abstract
- The radiated acoustic noise from a traction motor at low speeds is dominated by the noise of electromagnetic origin. For a motor operated from pulse width modulated (PWM) converters, the switching frequency of the converter will have a large impact on the noise. The total harmonic distortion of the motor phase currents and thus also the exciting forces, will decrease with increasing switching frequency. Furthermore, changing the switching frequency will shift the frequencies of the exciting forces, hence have an influence on the coincidence with structural resonances of the motor. Tests have been performed on a traction motor and a decrease in sound pressure level with increasing switching frequency has been quantified and analyzed.
|
|
