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Prof. Michael Friswell
Swansea University, Swansea, UK

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Research Keywords & Expertise

0 Condition Monitoring
0 Energy Harvesting
0 Nonlinear Dynamics
0 Piezoelectric
0 Rotor Dynamics

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Vibration
finite element model
Piezoelectric
Energy Harvesting
morphing aircraft
Structural Health Monitoring
Condition Monitoring
Morphing Structures
Nonlinear Dynamics
Sensitivity Analysis

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Swansea University

University Educator/Researcher

01 January 2009 - 01 September 2021




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Original paper
Published: 23 June 2021 in Nonlinear Dynamics
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Nonlinearities in rotating systems have been seen to cause a wide variety of rich phenomena; however, the understanding of these phenomena has been limited because numerical approaches typically rely on “brute force” time simulation, which is slow due to issues of step size and settling time, cannot locate unstable solution families, and may miss key responses if the correct initial conditions are not used. This work uses numerical continuation to explore the responses of such systems in a more systematic way. A simple isotropic rotor system with a smooth nonlinearity is studied, and the rotating frame is used to obtain periodic solutions. Asynchronous responses with oscillating amplitude are seen to initiate at certain drive speeds due to internal resonance, in a manner similar to that observed for nonsmooth rotor–stator contact systems in the previous literature. These responses are isolated, in the sense that they will only meet the more trivial synchronous responses in the limit of zero damping and out of balance forcing. In addition to increasing our understanding of the responses of these systems, the work establishes the potential of numerical continuation as a tool to systematically explore the responses of nonlinear rotor systems.

ACS Style

Mehmet Selim Akay; Alexander D. Shaw; Michael I. Friswell. Continuation analysis of a nonlinear rotor system. Nonlinear Dynamics 2021, 1 -19.

AMA Style

Mehmet Selim Akay, Alexander D. Shaw, Michael I. Friswell. Continuation analysis of a nonlinear rotor system. Nonlinear Dynamics. 2021; ():1-19.

Chicago/Turabian Style

Mehmet Selim Akay; Alexander D. Shaw; Michael I. Friswell. 2021. "Continuation analysis of a nonlinear rotor system." Nonlinear Dynamics , no. : 1-19.

Original article
Published: 22 June 2021 in Mechanics of Advanced Materials and Structures
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This study develops a comprehensive vibrational analysis of rotating nanobeams on visco-elastic foundations with thermal effects based on the modified couple stress and Eringen’s nonlocal elasticity theories. This approach accurately simulates the nonlocal stress and size effects. Higher-order shear deformation beam theory and the generalized differential quadrature method are used to obtain the numerical results. The effects of nonlocal parameters, length scale, Winkler–Pasternak coefficients, thermal gradient, slenderness ratios, rotating velocity, and viscoelastic coefficient are demonstrated and discussed in detail. Mode switching and the importance of the correct choice of theory and associated size effect parameters are highlighted.

ACS Style

Arash Rahmani; Shirko Faroughi; Michael I. Friswell; Alireza Babaei. Eringen’s nonlocal and modified couple stress theories applied to vibrating rotating nanobeams with temperature effects. Mechanics of Advanced Materials and Structures 2021, 1 -26.

AMA Style

Arash Rahmani, Shirko Faroughi, Michael I. Friswell, Alireza Babaei. Eringen’s nonlocal and modified couple stress theories applied to vibrating rotating nanobeams with temperature effects. Mechanics of Advanced Materials and Structures. 2021; ():1-26.

Chicago/Turabian Style

Arash Rahmani; Shirko Faroughi; Michael I. Friswell; Alireza Babaei. 2021. "Eringen’s nonlocal and modified couple stress theories applied to vibrating rotating nanobeams with temperature effects." Mechanics of Advanced Materials and Structures , no. : 1-26.

Review article
Published: 18 May 2021 in Aerospace Science and Technology
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Gust and turbulence events are of primary importance for the analysis of flight incidents, for the design of gust load alleviation systems and for the calculation of loads in the airframe. Gust and turbulence events cannot be measured directly but they can be obtained through direct or optimisation-based methods. In the direct method the discretisation of the Fredholm Integral equation is associated with an ill conditioned matrix. In this work the effects of regularisation methods including Tikhonov regularisation, Truncated Single Value Decomposition (TSVD), Damped Single Value Decomposition (DSVD) and a recently proposed method using cubic B-spline functions are evaluated for aeroelastic gust identification using in flight measured data. The gust identification methods are tested in the detailed aeroelastic model of FFAST and an equivalent low-fidelity aeroelastic model developed by the authors. In addition, the accuracy required in the model for a reliable identification is discussed. Finally, the identification method based on B-spline functions is tested by simultaneously using both low-fidelity and FFAST aeroelastic models so that the response from the FFAST model is used as measurement data and the equivalent low-fidelity model is used in the identification process.

ACS Style

Davide Balatti; Hamed Haddad Khodaparast; Michael I. Friswell; Marinos Manolesos; Andrea Castrichini. Aircraft turbulence and gust identification using simulated in-flight data. Aerospace Science and Technology 2021, 115, 106805 .

AMA Style

Davide Balatti, Hamed Haddad Khodaparast, Michael I. Friswell, Marinos Manolesos, Andrea Castrichini. Aircraft turbulence and gust identification using simulated in-flight data. Aerospace Science and Technology. 2021; 115 ():106805.

Chicago/Turabian Style

Davide Balatti; Hamed Haddad Khodaparast; Michael I. Friswell; Marinos Manolesos; Andrea Castrichini. 2021. "Aircraft turbulence and gust identification using simulated in-flight data." Aerospace Science and Technology 115, no. : 106805.

Journal article
Published: 16 May 2021 in Composite Structures
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Bistable composite laminates are advanced composite structures which are potential candidates for morphing structure applications. The geometrical dimensions, material properties, ambient temperature and moisture have significant effects on the bistable behaviour, and the effect of uncertain parameters should be quantified. Reliability analysis is well established for the quantitative assessment of the probability of an event due to parameter uncertainty. Thus, subset simulation is applied to the reliability and sensitivity analysis of bistable composite plates with multiple random parameters. The bistability probability is estimated using the principle of minimum energy; the Rayleigh-Ritz method is used to develop the equations of motion and the limit state function. The results indicate that the stacking sequence has a large effect on bistability probability, and cross-ply composite laminates are most likely to be bistable. Moreover, moisture absorption by the laminate can dramatically reduce this probability. The sensitivity reliability analysis demonstrates that for bistable laminates subject to humidity, the coefficient of thermal and moisture expansions have the greatest influence on the bistability probability. However, for bistable laminates without moisture the thickness is the most important factor. The accuracy and efficiency of the subset simulation method is validated by Monte Carlo simulation.

ACS Style

Saeid Saberi; Azam Abdollahi; Michael I. Friswell. Probability analysis of bistable composite laminates using the subset simulation method. Composite Structures 2021, 271, 114120 .

AMA Style

Saeid Saberi, Azam Abdollahi, Michael I. Friswell. Probability analysis of bistable composite laminates using the subset simulation method. Composite Structures. 2021; 271 ():114120.

Chicago/Turabian Style

Saeid Saberi; Azam Abdollahi; Michael I. Friswell. 2021. "Probability analysis of bistable composite laminates using the subset simulation method." Composite Structures 271, no. : 114120.

Journal article
Published: 02 April 2021 in Aerospace
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In this paper, the effect of distributed electric propulsion on the aeroelastic stability of an electric aircraft wing was investigated. All the electric propulsors, which are of different properties, are attached to the wing of the aircraft in different positions. The wing structural dynamics was modelled by using geometrically exact beam equations, while the aerodynamic loads were simulated by using an unsteady aerodynamic theory. The electric propulsors were modelled by using a concentrated mass attached to the wing, and the motor’s thrust and angular momentum were taken into account. The thrust of each propulsor was modelled as a follower force acting exactly at the centre of gravity of the propulsor. The nonlinear aeroelastic governing equations were discretised using a time–space scheme, and the obtained results were verified against available results and very good agreement was observed. Two case studies were considered throughout the paper, resembling two flight conditions of the electric aircraft. The numerical results show that the tip propulsor thrust, mass, and angular momentum had the most impact on the aeroelastic stability of the wing. In addition, it was observed that the high-lift motors had a minimal effect on the aeroelastic stability of the wing.

ACS Style

Mohammadreza Amoozgar; Michael Friswell; Seyed Fazelzadeh; Hamed Haddad Khodaparast; Abbas Mazidi; Jonathan Cooper. Aeroelastic Stability Analysis of Electric Aircraft Wings with Distributed Electric Propulsors. Aerospace 2021, 8, 100 .

AMA Style

Mohammadreza Amoozgar, Michael Friswell, Seyed Fazelzadeh, Hamed Haddad Khodaparast, Abbas Mazidi, Jonathan Cooper. Aeroelastic Stability Analysis of Electric Aircraft Wings with Distributed Electric Propulsors. Aerospace. 2021; 8 (4):100.

Chicago/Turabian Style

Mohammadreza Amoozgar; Michael Friswell; Seyed Fazelzadeh; Hamed Haddad Khodaparast; Abbas Mazidi; Jonathan Cooper. 2021. "Aeroelastic Stability Analysis of Electric Aircraft Wings with Distributed Electric Propulsors." Aerospace 8, no. 4: 100.

Research article
Published: 09 March 2021 in Shock and Vibration
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A novel approach for mode shape feature extraction and model updating of axisymmetric structures based on radial Tchebichef moment (RTM) descriptors is proposed in this study. The mode shape features extracted by RTM descriptors can effectively compress the full-field modal vibration data and retain the most important information. The reconstruction of mode shapes using RTM descriptors can accurately describe the mode shapes, and the simulation shows that the RTM function is superior to Zernike moment function in terms of its mathematical properties and its shape reconstruction ability. In addition, the proposed modal correlation coefficient of the RTM amplitude can overcome the main disadvantage of using the modal assurance criterion (MAC), which has difficulty in identifying double or close modes of symmetric structures. Furthermore, the model updating of axisymmetric structures based on RTM descriptors appears to be more efficient and effective than the normal model updating method directly using modal vibration data, avoids manipulating large amounts of mode shape data, and speeds up the convergence of updating parameters. The RTM descriptors used in correlation analysis and model updating are demonstrated with a cover of an aeroengine rig. The frequency deviation between the test and the FE model was reduced from 17.13% to 1.23% for the first 13 modes via the model updating process. It verified the potential to industrial application with the proposed method.

ACS Style

C. Zang; H. B. Lan; D. D. Jiang; M. I. Friswell. Mode Shape Description and Model Updating of Axisymmetric Structures Using Radial Tchebichef Moment Descriptors. Shock and Vibration 2021, 2021, 1 -19.

AMA Style

C. Zang, H. B. Lan, D. D. Jiang, M. I. Friswell. Mode Shape Description and Model Updating of Axisymmetric Structures Using Radial Tchebichef Moment Descriptors. Shock and Vibration. 2021; 2021 ():1-19.

Chicago/Turabian Style

C. Zang; H. B. Lan; D. D. Jiang; M. I. Friswell. 2021. "Mode Shape Description and Model Updating of Axisymmetric Structures Using Radial Tchebichef Moment Descriptors." Shock and Vibration 2021, no. : 1-19.

Journal article
Published: 01 March 2021 in ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering
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To reduce the computational cost of assembled stochastic linear structural dynamic systems, a three-staged reduced order model-based framework for forward uncertainty propagation was developed. First, the physical domain was decomposed by constructing an equivalent reduced order numerical model that limited the cost of a single deterministic simulation. This was done in two phases: (1) reducing the system matrices of the subcomponents using component mode synthesis and (2) solving the resulting reduced system with the help of domain decomposition in an efficient manner. Second, functional decomposition was carried out in the stochastic space by employing a multioutput machine learning model that reduced the number of eigenvalue analyses to be performed. Thus, a multilevel framework was developed that propagated the dynamic response from the subcomponent level to the assembled global system level efficiently. Subsequently, reliability analysis was performed to assess the safety level and failure probability of linear stochastic dynamic systems. The results achieved by solving a two-dimensional (2D) building frame and a three-dimensional (3D) transmission tower model illustrated good performance of the proposed methodology, highlighting its potential for complex problems.

ACS Style

Tanmoy Chatterjee; Sondipon Adhikari; Michael I. Friswell. Multilevel Decomposition Framework for Reliability Assessment of Assembled Stochastic Linear Structural Systems. ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering 2021, 7, 04021003 .

AMA Style

Tanmoy Chatterjee, Sondipon Adhikari, Michael I. Friswell. Multilevel Decomposition Framework for Reliability Assessment of Assembled Stochastic Linear Structural Systems. ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering. 2021; 7 (1):04021003.

Chicago/Turabian Style

Tanmoy Chatterjee; Sondipon Adhikari; Michael I. Friswell. 2021. "Multilevel Decomposition Framework for Reliability Assessment of Assembled Stochastic Linear Structural Systems." ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering 7, no. 1: 04021003.

Journal article
Published: 29 January 2021 in Applied Mathematical Modelling
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In this work, a comprehensive vibrational behavior analysis is performed on anti-symmetric laminated composite plates resting on visco-elastic foundations undergoing thermal effects. Here, the governing equations of motion are developed through Hamilton's principle and Reddy's plate theory as higher-order shear deformation theory (HSDT) is employed to capture high accuracy. Also, the generalized differential quadrature method (GDQM) is used to predict the vibration response and the natural frequencies. The effects of temperature change, Winkler-Pasternak and damping coefficients for the elastic foundation, the elastic ratio, the arrangement of different anti-symmetric laminates, and the aspect and slenderness ratios are observed and discussed in detail. The results are extracted for fully clamped boundary conditions and the effects of other boundary conditions are also illustrated.

ACS Style

A. Rahmani; S. Faroughi; M.I. Friswell. Vibration analysis for anti-symmetric laminated composite plates resting on visco-elastic foundation with temperature effects. Applied Mathematical Modelling 2021, 94, 421 -445.

AMA Style

A. Rahmani, S. Faroughi, M.I. Friswell. Vibration analysis for anti-symmetric laminated composite plates resting on visco-elastic foundation with temperature effects. Applied Mathematical Modelling. 2021; 94 ():421-445.

Chicago/Turabian Style

A. Rahmani; S. Faroughi; M.I. Friswell. 2021. "Vibration analysis for anti-symmetric laminated composite plates resting on visco-elastic foundation with temperature effects." Applied Mathematical Modelling 94, no. : 421-445.

Journal article
Published: 28 January 2021 in Aerospace Science and Technology
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Morphing aircraft structures usually introduce greater compliance into aerodynamic sections, and therefore will affect the aeroelasticity with the potential risk of increased flutter. A low-fidelity model of an active camber morphing wing and its aeroelastic model are developed in order to investigate the potential critical speed by exploiting its chord-wise dimension and flexibility. Such a model may be used for conceptual design, where low fidelity models are used to explore and optimise a wide range of configurations. The morphing camber concept is implemented using a continuous representation of a two-segment structure with a rigid segment and a deformable part. The aeroelastic model is developed based on both steady and unsteady aerodynamic models, so that different parameters can be easily modified to examine changes in the flutter solutions. Of particular interest are the ratio of the morphing segment length to the chord, and its relative stiffness, as such morphing camber is potential operated using the deformable part as a flap. By comparing the results of the quasi-steady and unsteady aerodynamic models, it is shown that the quasi-steady aerodynamic model gives a more conservative prediction of the flutter speed. In addition, responses in phase space are simulated to show the fundamental aeroelastic behaviour of the morphing camber wing. It is also shown that the active compliant segment can be used to stabilise the morphing aircraft by using feedback control. This paper provides a system-level insight through mathematical modelling, parameter analysis and feedback control into dynamics applications of morphing camber.

ACS Style

Jiaying Zhang; Alexander D. Shaw; Chen Wang; Huaiyuan Gu; Mohammadreza Amoozgar; Michael I. Friswell; Benjamin K.S. Woods. Aeroelastic model and analysis of an active camber morphing wing. Aerospace Science and Technology 2021, 111, 106534 .

AMA Style

Jiaying Zhang, Alexander D. Shaw, Chen Wang, Huaiyuan Gu, Mohammadreza Amoozgar, Michael I. Friswell, Benjamin K.S. Woods. Aeroelastic model and analysis of an active camber morphing wing. Aerospace Science and Technology. 2021; 111 ():106534.

Chicago/Turabian Style

Jiaying Zhang; Alexander D. Shaw; Chen Wang; Huaiyuan Gu; Mohammadreza Amoozgar; Michael I. Friswell; Benjamin K.S. Woods. 2021. "Aeroelastic model and analysis of an active camber morphing wing." Aerospace Science and Technology 111, no. : 106534.

Book chapter
Published: 24 November 2020 in The Engineering of Sport
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ACS Style

Michael Friswell; M.G. Smart; S. M. Hamblyn; G. Horwood. The validation and updating of dynamic models of golf clubs. The Engineering of Sport 2020, 323 -331.

AMA Style

Michael Friswell, M.G. Smart, S. M. Hamblyn, G. Horwood. The validation and updating of dynamic models of golf clubs. The Engineering of Sport. 2020; ():323-331.

Chicago/Turabian Style

Michael Friswell; M.G. Smart; S. M. Hamblyn; G. Horwood. 2020. "The validation and updating of dynamic models of golf clubs." The Engineering of Sport , no. : 323-331.

Journal article
Published: 13 October 2020 in Eng
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The device under investigation in this paper consists of a float used to capture tidal energy, which is tethered by multiple flexible cables to a large barge-like reactor. The proposed float is made of a continuously wound glass-reinforced composite shell with stainless steel bolting plates integrated into the float walls to allow the connection of 5 stainless steel cables. Numerical computations are required to assess whether a delamination of the composite layers in the float is likely. The manufacturing of the device has various potential uncertainties that should be investigated, such as the number of the plies, the bond strength between the composite layers, and the fibre orientations of the composite material relative to the applied load. This paper provides a multi-level strategy to optimise the composite float system, which is manufactured from glass-reinforced plastic (GRP). In contrast to previous publications on the topic, the current work uses an efficient link between ANSYS Workbench and MATLAB through an in-house code that has been developed over 3 years. This allowed the whole process to be fully automated and to reduce the time and cost of the simulations. Previously, ANSYS APDL was linked to MATLAB, but limitations in terms of the geometry and boundary conditions made it impractical when compared to ANSYS Workbench for the simulation of complex features. This makes the current approach unique and rare when compared to the published work in the field. This approach allows the use of a huge number of trials and is able to reduce the number of parameters to be studied by selecting the most sensitive ones. Additionally, the developed tools may be used for the efficient, robust optimisation of the proposed structure. The current study has focused on exploring the effects of the fibre orientations and the optimum number of plies on the overall performance of the structure.

ACS Style

Nada Aldoumani; Cinzia Giannetti; Zakaria Abdallah; Fawzi Belblidia; Hamed Haddad Khodaparast; Michael I. Friswell; Johann Sienz. Optimisation of the Filament Winding Approach Using a Newly Developed In-House Uncertainty Model. Eng 2020, 1, 122 -136.

AMA Style

Nada Aldoumani, Cinzia Giannetti, Zakaria Abdallah, Fawzi Belblidia, Hamed Haddad Khodaparast, Michael I. Friswell, Johann Sienz. Optimisation of the Filament Winding Approach Using a Newly Developed In-House Uncertainty Model. Eng. 2020; 1 (2):122-136.

Chicago/Turabian Style

Nada Aldoumani; Cinzia Giannetti; Zakaria Abdallah; Fawzi Belblidia; Hamed Haddad Khodaparast; Michael I. Friswell; Johann Sienz. 2020. "Optimisation of the Filament Winding Approach Using a Newly Developed In-House Uncertainty Model." Eng 1, no. 2: 122-136.

Journal article
Published: 22 September 2020 in Applied Mathematical Modelling
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For the first time, the structural dynamics and vibrational stability of a viscoelastic axially functionally graded (AFG) beam with both spinning and axial motions subjected to an axial load are analyzed, with the aim to enhance the performance of bi-gyroscopic systems. A detailed parametric study is also performed to emphasize the influence of various key factors such as material distribution type, viscosity coefficient, and coupled rotation and axial translation on the dynamical characteristics of the system. The material properties of the system are assumed to vary linearly or exponentially in the longitudinal direction with viscoelastic effects. Adopting the Laplace transform and a Galerkin discretization scheme, the critical axial and spin velocities of the system are obtained. An analytical approach is applied to identify the instability thresholds. Stability maps are examined, and for the first time in this paper, it is demonstrated that the stability evolution of the system can be altered by fine-tuning of axial grading or viscosity of the material. The variation of density and elastic modulus gradient parameters are found to have opposite effects on the divergence and flutter boundaries of the system. Furthermore, the results indicate that the destabilizing effect of the axial compressive load can be significantly alleviated by the simultaneous determination of density and elastic modulus gradation in the axial direction of the system.

ACS Style

A. Ebrahimi-Mamaghani; A. Forooghi; H. Sarparast; A. Alibeigloo; M.I. Friswell. Vibration of viscoelastic axially graded beams with simultaneous axial and spinning motions under an axial load. Applied Mathematical Modelling 2020, 90, 131 -150.

AMA Style

A. Ebrahimi-Mamaghani, A. Forooghi, H. Sarparast, A. Alibeigloo, M.I. Friswell. Vibration of viscoelastic axially graded beams with simultaneous axial and spinning motions under an axial load. Applied Mathematical Modelling. 2020; 90 ():131-150.

Chicago/Turabian Style

A. Ebrahimi-Mamaghani; A. Forooghi; H. Sarparast; A. Alibeigloo; M.I. Friswell. 2020. "Vibration of viscoelastic axially graded beams with simultaneous axial and spinning motions under an axial load." Applied Mathematical Modelling 90, no. : 131-150.

Journal article
Published: 03 September 2020 in Vibration
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The experimental characterisation of a nonlinear structure is a challenging process, particularly for multiple degree of freedom and continuous structures. Despite attracting much attention from academia, there is much work needed to create processes that can achieve characterisation in timescales suitable for industry, and a key to this is the design of the testing procedure itself. This work proposes a passive testing method that seeks a desired degree of resonance between forcing and response. In this manner, the process automatically seeks data that reveals greater detail of the underlying nonlinear normal modes than a traditional stepped sine method. Furthermore, the method can target multiple harmonics of the fundamental forcing frequency, and is therefore suitable for structures with complex modal interactions. The method is presented with some experimental examples, using a structure with a 3:1 internal resonance.

ACS Style

Alexander D. Shaw; Thomas L. Hill; Simon A. Neild; Michael I. Friswell. Multiharmonic Resonance Control Testing of an Internally Resonant Structure. Vibration 2020, 3, 217 -234.

AMA Style

Alexander D. Shaw, Thomas L. Hill, Simon A. Neild, Michael I. Friswell. Multiharmonic Resonance Control Testing of an Internally Resonant Structure. Vibration. 2020; 3 (3):217-234.

Chicago/Turabian Style

Alexander D. Shaw; Thomas L. Hill; Simon A. Neild; Michael I. Friswell. 2020. "Multiharmonic Resonance Control Testing of an Internally Resonant Structure." Vibration 3, no. 3: 217-234.

Correction
Published: 28 August 2020 in Nonlinear Dynamics
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On the title page, author Oleg Shiryavev should be spelled as Oleg Shiryayev.

ACS Style

Mohammad A. Al-Shudeifat; Michael Friswell; Oleg Shiryayev; C. Nataraj. Correction To: On post-resonance backward whirl in an overhung rotor with snubbing contact. Nonlinear Dynamics 2020, 102, 1 -1.

AMA Style

Mohammad A. Al-Shudeifat, Michael Friswell, Oleg Shiryayev, C. Nataraj. Correction To: On post-resonance backward whirl in an overhung rotor with snubbing contact. Nonlinear Dynamics. 2020; 102 (1):1-1.

Chicago/Turabian Style

Mohammad A. Al-Shudeifat; Michael Friswell; Oleg Shiryayev; C. Nataraj. 2020. "Correction To: On post-resonance backward whirl in an overhung rotor with snubbing contact." Nonlinear Dynamics 102, no. 1: 1-1.

Journal article
Published: 01 August 2020 in AIP Advances
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Mechanical coupling in similar energy harvesters has the potential to enhance their broadband harvesting capability. However, often the performance of one harvester dominates the other, and the coupling transfers energy from the high frequency harvester to the low frequency harvester, thus reducing the capability of the high frequency harvester. Hence, researchers have proposed using the high frequency harvester only as an auxiliary oscillator to save the material cost. This paper investigates the possibility of enhancing the energy harvesting capability of both coupled harvesters. A torsionally coupled electromagnetic pendulum harvester system is considered, which is suitable for low frequency (<5 Hz) applications. The harmonic balance method is used to identify possible multiple solutions, and high magnitude solutions are observed to coexist with low magnitude solutions. These high energy solutions, which are often missed in the numerical simulation, can be attained by a careful choice of initial conditions or energy input. The simulation results show that more energy can be harvested over a wider range of frequencies by ensuring that the response occurs in the high energy orbits. The results show an enhancement of the bandwidth by 54% and 140% for the low and high frequency harvesters, respectively, with the optimum initial conditions. Moreover, an isolated frequency island is reported, which occurs due to the coupling of the nonlinear harvesters.

ACS Style

P. V. Malaji; M. I. Friswell; S. Adhikari; G. Litak. Enhancement of harvesting capability of coupled nonlinear energy harvesters through high energy orbits. AIP Advances 2020, 10, 085315 .

AMA Style

P. V. Malaji, M. I. Friswell, S. Adhikari, G. Litak. Enhancement of harvesting capability of coupled nonlinear energy harvesters through high energy orbits. AIP Advances. 2020; 10 (8):085315.

Chicago/Turabian Style

P. V. Malaji; M. I. Friswell; S. Adhikari; G. Litak. 2020. "Enhancement of harvesting capability of coupled nonlinear energy harvesters through high energy orbits." AIP Advances 10, no. 8: 085315.

Journal article
Published: 31 July 2020 in Journal of Engineering for Gas Turbines and Power
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A strongly nonlinear rotor-bearing system often has multiple solutions under harmonic excitations and jump phenomena. For example, a hardening nonlinearity may include a jump-down in the acceleration process and jump-up in the deceleration process. It is challenging to measure all of these multiple responses and establish an accurate dynamic model from experimental data to predict these phenomena. This paper used a fixed frequency test method to measure all of these multiple responses under harmonic excitations and developed a novel strategy to characterize and identify nonlinearities in a strongly nonlinear rotor-bearing system based on reconstructing constant response tests from fixed frequency test data. The fixed frequency tests are achieved by monotonically increasing the voltage applied to the exciter at a fixed frequency and using the force drop-out phenomenon through the resonance to control the force applied to the structure. This test method could measure multivalued response curves of a strongly nonlinear rotor-bearing system in a nonrotating state. The constant response tests could be reconstructed from these multivalued response curves. The relationship of equivalent stiffness versus displacement can be established, and hence, the nonlinear stiffness is characterized and identified from constant response tests. A rotor-bearing system with a strongly nonlinear support is used to demonstrate the method, and the nonlinear support stiffness parameters are identified and validated in a nonrotating state. The identified nonlinear rotor-bearing model also could predict the jump phenomena in the acceleration or deceleration process. The results demonstrate the feasibility and effectiveness of the approach, and also show the potential for practical applications in engineering.

ACS Style

Gengbei Zhang; Chaoping Zang; Michael I. Friswell. Parameter Identification of a Strongly Nonlinear Rotor-Bearing System Based on Reconstructed Constant Response Tests. Journal of Engineering for Gas Turbines and Power 2020, 142, 1 .

AMA Style

Gengbei Zhang, Chaoping Zang, Michael I. Friswell. Parameter Identification of a Strongly Nonlinear Rotor-Bearing System Based on Reconstructed Constant Response Tests. Journal of Engineering for Gas Turbines and Power. 2020; 142 (8):1.

Chicago/Turabian Style

Gengbei Zhang; Chaoping Zang; Michael I. Friswell. 2020. "Parameter Identification of a Strongly Nonlinear Rotor-Bearing System Based on Reconstructed Constant Response Tests." Journal of Engineering for Gas Turbines and Power 142, no. 8: 1.

Original paper
Published: 04 July 2020 in Nonlinear Dynamics
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Rotordynamic systems are central to many aerospace and heavy-duty industrial applications. The vibrational response of such systems is usually associated with forward whirl (FW) and backward whirl (BW) precessions. It is well known in the literature that the BW precession generally precedes the passage through the critical FW resonance precession. Therefore, it can be named as a pre-resonance BW frequency (Pr-BW). However, another kind of BW has been recently observed to be immediately excited after the passage through the critical FW resonance frequency in cracked rotors with anisotropic supports during run-up and coast-down operations. Consequently, this kind of BW can be named as a post-resonance backward whirl (Po-BW) precession. The Pr-BW and Po-BW phenomena are investigated here with an overhung rotor system that exhibits snubbing contact and stiffness anisotropy in the supports. Incorporating the snubbing moment couple into the equations of motion of the considered overhung rotor model yields a piecewise and strongly nonlinear system. Full-spectrum analysis is employed to capture the BW zones of rotational speeds in the whirl response. Wavelet transform spectrum analysis is also employed to determine the frequency content in the Pr-BW and the Po-BW zones. Three cases are considered in this numerical study to explore the effect of the support stiffness isotropy and anisotropy with active and inactive snubbing contact on the Po-BW excitation. For all cases, the Po-BW zones of rotational speeds are found. Moreover, the broadness and recurrence of the Po-BW zones of rotational speeds are more prominent for the cases of active snubbing contact. Even though the Pr-BW and Po-BW zones are excited at different shaft rotational speeds, they are found to possess nearly similar BW frequencies which are less than the FW resonance frequency of the considered system.

ACS Style

Mohammad A. Al-Shudeifat; Michael Friswell; Oleg Shiryayev; C. Nataraj. On post-resonance backward whirl in an overhung rotor with snubbing contact. Nonlinear Dynamics 2020, 101, 741 -754.

AMA Style

Mohammad A. Al-Shudeifat, Michael Friswell, Oleg Shiryayev, C. Nataraj. On post-resonance backward whirl in an overhung rotor with snubbing contact. Nonlinear Dynamics. 2020; 101 (2):741-754.

Chicago/Turabian Style

Mohammad A. Al-Shudeifat; Michael Friswell; Oleg Shiryayev; C. Nataraj. 2020. "On post-resonance backward whirl in an overhung rotor with snubbing contact." Nonlinear Dynamics 101, no. 2: 741-754.

Journal article
Published: 04 July 2020 in Aerospace
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The current research investigates the novel approach of coupling separate energy harvesters in order to scavenge more power from a stochastic point of view. To this end, a multi-body system composed of two cantilever harvesters with two identical piezoelectric patches is considered. The beams are interconnected through a linear spring. Assuming a stochastic band limited white noise excitation of the base, the statistical properties of the mechanical response and those of the generated voltages are derived in closed form. Moreover, analytical models are derived for the expected value of the total harvested energy. In order to maximize the expected generated power, an optimization is performed to determine the optimum physical and geometrical characteristics of the system. It is observed that by properly tuning the harvester parameters, the energy harvesting performance of the structure is remarkably improved. Furthermore, using an optimized energy harvester model, this study shows that the coupling of the beams negatively affects the scavenged power, contrary to the effect previously demonstrated for harvesters under harmonic excitation. The qualitative and quantitative knowledge resulting from this analysis can be effectively employed for the realistic design and modelling of coupled multi-body structures under stochastic excitations.

ACS Style

Hamidreza Masoumi; Hamid Moeenfard; Hamed Haddad Khodaparast; Michael I. Friswell. On the Effects of Structural Coupling on Piezoelectric Energy Harvesting Systems Subject to Random Base Excitation. Aerospace 2020, 7, 93 .

AMA Style

Hamidreza Masoumi, Hamid Moeenfard, Hamed Haddad Khodaparast, Michael I. Friswell. On the Effects of Structural Coupling on Piezoelectric Energy Harvesting Systems Subject to Random Base Excitation. Aerospace. 2020; 7 (7):93.

Chicago/Turabian Style

Hamidreza Masoumi; Hamid Moeenfard; Hamed Haddad Khodaparast; Michael I. Friswell. 2020. "On the Effects of Structural Coupling on Piezoelectric Energy Harvesting Systems Subject to Random Base Excitation." Aerospace 7, no. 7: 93.

Original paper
Published: 21 May 2020 in Nonlinear Dynamics
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A nonlinear micro-piezoelectric–electrostatic energy harvester is designed and studied using mathematical and computational methods. The system consists of a cantilever beam substrate, a bimorph piezoelectric transducer, a pair of tuning parallel-plate capacitors, and a tip–mass. The governing nonlinear mathematical model of the electro-mechanical system including nonlinear material and quadratic air-damping is derived for the series connection of the piezoelectric layers. The static and modal frequency curves are computed to optimize the operating point, and a parametric study is performed using numerical methods. A bias DC voltage is used to adapt the system to resonate with respect to the frequency of external vibration. Furthermore, to improve the bandwidth and performance of the harvester (and achieve a high level of harvested power without sacrificing the bandwidth), a nonlinear feedback loop is integrated into the design.

ACS Style

S. Amir Mousavi Lajimi; Michael I. Friswell. Design, analysis, and feedback control of a nonlinear micro-piezoelectric–electrostatic energy harvester. Nonlinear Dynamics 2020, 100, 3029 -3042.

AMA Style

S. Amir Mousavi Lajimi, Michael I. Friswell. Design, analysis, and feedback control of a nonlinear micro-piezoelectric–electrostatic energy harvester. Nonlinear Dynamics. 2020; 100 (4):3029-3042.

Chicago/Turabian Style

S. Amir Mousavi Lajimi; Michael I. Friswell. 2020. "Design, analysis, and feedback control of a nonlinear micro-piezoelectric–electrostatic energy harvester." Nonlinear Dynamics 100, no. 4: 3029-3042.

Journal article
Published: 30 April 2020 in Mechanical Systems and Signal Processing
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Recent theory has predicted the onset of asynchronous bouncing motion at speeds beyond those of internal resonance in multi-degree-of-freedom rotating systems with intermittent contact. This paper provides the first attempt to experimentally validate the theory. Vibrations incorporating rotor-stator contact are recorded from a vertically ounted rotordynamics test rig comprising two rigid shaft-disk assemblies that are axially joined by a bellows coupling. The upper rotor has an elastic bearing whereas the lower one is free but has a snubber ring located on its lower shaft, with clearance about 2.5% of the entire system’s length. Nonlinear vibrations are excited by a small measured eccentricity of about 20% of the clearance. Measurements are taken by a wireless accelerometer and processed to produce an experimental bifurcation diagram, for small steps in the rotor speed, allowing the transients to decay. Evidence is found of bistability between quiescent and violent motion over a wide range of rotational speeds, including those representing both fundamental and internal resonances. The results are shown to qualitatively match numerical simulations from a differential equation model that incorporates rigid impacts.

ACS Style

Rafael Sánchez Crespo; Alexander D. Shaw; Michael I. Friswell; Alan R. Champneys. Experimental characterisation of asynchronous partially contacting motion in a multiple-degree-of-freedom rotor system. Mechanical Systems and Signal Processing 2020, 145, 106904 .

AMA Style

Rafael Sánchez Crespo, Alexander D. Shaw, Michael I. Friswell, Alan R. Champneys. Experimental characterisation of asynchronous partially contacting motion in a multiple-degree-of-freedom rotor system. Mechanical Systems and Signal Processing. 2020; 145 ():106904.

Chicago/Turabian Style

Rafael Sánchez Crespo; Alexander D. Shaw; Michael I. Friswell; Alan R. Champneys. 2020. "Experimental characterisation of asynchronous partially contacting motion in a multiple-degree-of-freedom rotor system." Mechanical Systems and Signal Processing 145, no. : 106904.