Michael Ian Friswell

Swansea University | SWAN · College of Engineering

This paper investigates the dynamical responses and performances of mono-, bi-, and tri-stable nonlinear energy sinks in simultaneous vibration suppression and energy harvesting as well as solely vibration mitigation. To this end, a realizable multi-stable nonlinear energy sink composed of a bimorph cantilever beam and arrays of magnets is consider...

Model updating using multivalued Frequency Response Curves (FRCs) is an important approach to construct a strongly nonlinear model. Residues between the predicted and measured FRCs are usually computed for updating, while the updating precision may be impacted by the measurement noise at local DOFs. In this paper, based on multivalued Global Shape...

In the field of aerospace engineering, the design and manufacturing of high aspect ratio composite wings has become a focal point of innovation and efficiency. These long, slender wings, constructed with advanced materials such as carbon fiber and employing efficient manufacturing methods such as vacuum bagging, hold the promise of significantly li...

This paper reviews the various control algorithms and strategies used for fixed-wing morphing aircraft applications. It is evident from the literature that the development of control algorithms for morphing aircraft technologies focused on three main areas. The first area is related to precise control of the shape of morphing concepts for various f...

Data-driven discovery of governing laws for complex nonlinear structural dynamic systems remains a challenging issue of paramount importance. This work addresses the above issue by leveraging the available noisy data and integrating sparse Bayesian machine learning (ML) techniques to discover the governing equations. The problem of discovery is re-...

The present study investigates the free vibration behavior of rotating beams made of functionally graded materials (FGMs) with a tapered geometry. The material properties of the beams are characterized by an exponential distribution model. The stiffness and mass matrices of the beams are derived using the principle of virtual energy. These matrices...

Rotor bearing systems are a crucial component in many engineering applications, with bearings are typically classified as either rolling contact or sliding contact. In this context, we focus specifically on sliding contact bearings, and more specifically on fluid film journal bearings. The fluid film between the rotor and stator in such bearings ca...

This study examines the vibration of rotating beams with double tapered geometry utilizing BFGMs. Material properties of the beams are power law distributed in the x and z directions. The stiffness and mass matrices are derived employing the Reddy formulation, also known as the Third-order Shear Deformation Theory (TSDT). Our main goal is to analyz...

The coupling between the frictional energy dissipation and the dynamic response at the joint interface leads to mechanisms that are challenging to identify relying mainly on numerical data. The need for experimental analyses of such mechanisms is vital for better understanding of the inherent features in the contact interface dynamic response and f...

Understanding the mechanical behavior of nanoscale structures is crucial in the development of advanced nanotechnologies. In this study, a novel approach to investigate the thermal lateral vibration of cracked nanobeams immersed in an elastic matrix is investigated. For this purpose, Reddy’s third-order shear deformation theory (TSDT) is considered...

The paper introduces a Bayesian framework in conjunction with Markov Chain Monte Carlo (MCMC) sampling for parameter estimation in nonlinear stochastic dynamic systems. The proposed methodology is applied to both numerical and experimental cases. The paper commences by introducing Bayesian inference and its constituents: the likelihood function, pr...

The study presents a novel approach for stochastic nonlinear model updating in structural dynamics, employing a Bayesian framework integrated with Markov Chain Monte Carlo (MCMC) sampling for parameter estimation by using an approximated likelihood function. The proposed methodology is applied to both numerical and experimental cases. The paper com...

This study focuses on stochastic modelling of 2D aeroelastic model to quantify the uncertainties in the parameters of aeroelastic models, specifically the plunging and torsional stiffness. To measure the frequency response, a simulation of an aeroelastic model in a wind tunnel is considered. The excitation is provided by Gust. The frequency-velocit...

This study examines the vibration of rotating beams with double tapered geometry utilizing BFGMs. Material properties of the beams are power law distributed in the x and z directions. The stiffness and mass matrices are derived employing the Reddy formulation, also known as the Third-order Shear Deformation Theory (TSDT). Our main goal is to analyz...

Rotor bearing systems are a crucial component in many engineering applications, with bearings are typically classified as either rolling contact or sliding contact. In this context, we focus specifically on sliding contact bearings, and more specifically on fluid film journal bearings. The fluid film between the rotor and stator in such bearings ca...

Material properties, geometrical dimensions, and environmental conditions can greatly influence the characteristics of bistable composite laminates. In the current work, to understand how each input feature contributes to the curvatures of the stable equilibrium shapes of bistable laminates and the snap-through force to change these configurations,...

A recent consideration in aircraft design is using hinged wing tip devices to increase the aspect ratio, improving aircraft performance. Moreover, numerical studies have suggested using the wingtips during flight to provide additional gust load alleviation ability. This work aims to experimentally validate aeroelastic models of a wing with fixed an...

Model updating using multivalued responses is an important approach to construct strongly nonlinear models. During updating, swept frequency tests are usually used to measure the multivalued responses, but the measured responses only contain the stable branches. Accordingly,updating mainly uses these stable responses for the nonlinear model constru...

This research investigates the feasibility of mass sensing in piezoresistive MEMS devices based on catastrophic bifurcation and sensitivity enhancement due to the orientation adjustment of the device with respect to the crystallographic orientation of the silicon wafer. The model studied is a cantilever microbeam at the end of which an electrostati...

Inerter-based periodic structures have attracted significant interest among the research community due to their wide range of applications. However, existing studies on quasiperiodic structures, especially with inerters, are limited. Therefore, this timely work investigates the dynamics of novel one-dimensional inerter-based quasiperiodic lattices...

In this paper, a probabilistic-based evolution Markov chain algorithm is used for updating finite element models. The Bayesian approaches are well-known algorithms used for quantifying uncertainties associated with structural systems and several other engineering domains. In this approach, the unknown parameters and their associated uncertainties a...

A parameter study is presented to determine effects of planet gear design parameters on the global modal behaviour of planetary geared rotor systems. The modal sensitivity analysis is conducted using a three-dimensional dynamic model of a planetary geared rotor system for the number of planet gears, planet mistuning, mass of planet gears, gear mesh...

Time simulation has been widely used when investigating the nonlinear response of rotating machines, due to its relative simplicity. However, this approach is computationally inefficient due to large transient decay times and the need to repeat the analysis for multiple drive speeds and initial conditions, and is incomplete because of its inability...

This article demonstrates the possibility of energy harvesting by mistuned pendulums with torsional coupling. Two pendulums of different lengths with coils and magnets at the pivots are used as electromagnetic harvesters. The ambient energy source to the system is considered in the form of harmonic base excitations. Torsional coupling is achieved b...

The complex dynamics of a frictional contact interface have been the subject of many research investigations. However, a comprehensive model has not been proposed that can be easily solved and considers the effect of all parameters of interest, i.e., the variation in contact pressure, the interaction of normal and tangential direction mechanisms, a...

This paper analytically and experimentally investigates the potential of a tuned mass damper (TMD) with an integrated piezoelectric layer for simultaneous energy harvesting and vibration suppression. The system investigated is composed of a main beam that is excited by a shaker. A TMD comprising a unimorph piezoelectric beam is attached to the main...

Modelling the uncertainties at the joint interface is crucial as it affects the dynamics of the whole system. But modelling the interface using only a physics-based (mathematical) model may lead to large differences between predictions and observations as the physics of the actual system is only partially known. The research focuses on the Bayesian...

Vibration-based energy harvesting represents a clean power technology that can be of interest for application in civil engineering structures. This study focuses on energy harvesting using cantilever piezoelectric devices excited by operational and ambient bridge vibration. The optimal design and analysis of energy harvesters is usually performed u...

Uncertainties arising in the parameters and modelling of complex systems need to be considered for credible predictions of their dynamic response. For most practical systems, the detailed information regarding these two types of uncertainties is not available. In this paper, the Wishart random matrix model is presented to quantify the total uncerta...

Physics-informed neural networks have received considerable attention for the solution and data-driven discovery of physical systems governed by differential equations. Despite their immense success, it has been observed that the first-generation PINNs suffer from a drawback arising from the regularization of the loss function. The motivation of th...

This work develops a morphing concept that utilises a metamaterial as the passive morphing device for helicopter blades. The metamaterials are created with bend-twist coupling, which enable the blade twist under prescribed bending loads. Finite element analysis (FEA) is performed to investigate the influence of the unit cell configurations on the c...

This work explores the closed-loop response of the MODFLEX flexible wing in the presence of 1-cosine gusts. The ultimate aim of the project is to investigate the effects of gusts on a structurally nonlinear system and to apply linear/nonlinear active control, aiming to mitigate the vibration of the system which would reduce the loads introduced int...

A common issue with morphing structures is that the actuators must work against significant structural and aerodynamic stiffness. The concept of passive energy balancing (PEB) aims to ameliorate this, and thereby reduces system mass, by connecting negative stiffness elements to the actuated degrees of freedom. However, these devices can be complex...

Despite all the efforts made to investigate the dynamics of jointed structures, they still remain as one of the uncertain dynamical systems in structural dynamics. Modelling the dynamic behaviour of bolted joint contact interfaces is one of the most challenging tasks in structural dynamics. The multi-frequency response of nonlinear systems, particu...

In jointed structures, both stiffness and damping properties are affected by the way that the contact interfaces behave. The overall behaviour of the contact interface is the result of different parameters; among them are the contact surface quality and interface pressure distribution. Small changes in these parameters result in a considerable chan...

The idea of morphing a helicopter blade by using compliant structures promises augmented capabilities in terms of manoeuvrability and fuel efficiency. To achieve morphing, compliant structures work by elastically deforming to achieve the desired response, and therefore actuation must work against the inherent structural stiffness in addition to ext...

A vane-type gust generator has been designed and characterized in the Swansea University wind tunnel to enable the validation of the response of aircraft models to gust loads. The experimental results reveal the complexity of the flow between the gust vanes and the aircraft model location. Previous studies have shown that generating a predetermined...

The development of lighter and more efficient transport aircraft has led to an increased focus on gust load alleviation. A recent consideration in aircraft design is using hinged wing tip devices to increase the aspect ratio, improving aircraft performance. Moreover, numerical studies have suggested using the wing tips during flight to provide addi...

In this paper, the effect of a nonlinear energy sink (NES) device on the aeroelastic and gust response of an aircraft wing with a hardening stiffness structural nonlinearity is investigated. The structural dynamics of the wing is simulated using a 2-DOF typical section which undergoes pitch and heave (plunge) motions. Furthermore, the wing is subje...

The present study performs a set of static tests to demonstrate a novel passive morphing concept. The concept introduces a bend-twist coupled composite spar to rotor blades, allowing for twist morphing to be achieved by imposing a lagwise bending moment using centrifugal forces produced by a movable mass at the blade tip. First, three composite spa...

An understating on interaction between a rotating flexible member and a stationary element has a wide range of industrial applications. The focus of this study was to understand the modal interactions using a conceptual model. The conceptual model of the system consists of multiple disc rotors with a localised conduit. A theoretical model of the sy...

A vane type gust generator has been designed and characterized in the Swansea University wind tunnel to enable the validation of the response of aircraft models to gust loads. The experimental results reveal the complexity of the flow between the gust vanes and the aircraft model location. Previous studies have shown that generating a predetermined...

View Video Presentation: https://doi.org/10.2514/6.2022-0172.vid A common issue with morphing structures is that the actuators must work against significant structural and aerodynamic stiffness. The concept of Passive Energy Balancing (PEB) aims to ameliorate this, and thereby reduce system mass, by connecting negative stiffness elements to the act...

In recent years, the development of lighter and more efficient transport aircraft has led to an increased focus on gust load alleviation. A recent strategy is based on the use of folding wingtip devices that increase the aspect ratio and therefore improve the aircraft performance. Moreover, numerical studies have suggested such a folding wingtip so...

Testing nonlinear structures to characterise their internal nonlinear forces is challenging. Often nonlinear structures are excited by harmonic forces and yield a multi-harmonic response. In many systems, particularly ones with strong nonlinearities, the effect of higher harmonics in the force and responses cannot be ignored. Even if the intended e...

Parametric excitation is introduced to amplify the external harmonic excitation and extend the capabilities of a nonlinear piezoelectric energy harvester device. To investigate the efficiency of the parametrically amplified energy harvester, the time responses of the voltage and power are computed using the state space formulation. It is assumed th...

Parametric excitation is introduced to amplify the external harmonic excitation and extend the capabilities of a nonlinear piezoelectric energy harvester device. To investigate the efficiency of the parametrically amplified energy harvester, the time responses of the voltage and power are computed using the state space formulation. It is assumed th...

The dynamics of elastic cantilevered smart pipes conveying fluid with non-uniform flow velocity profiles is presented for optimal power generation. The Navier-Stokes equations are used to model the incompressible flow in the circular smart pipe, and flow profile modification factors are formulated based on the Reynolds number and Darcy friction fac...

Analytically obtained bearing dynamic characteristics have been a major source of error in the modelling and analysis of large turbo-generators. An experimental estimation algorithm for bearing dynamic characterisation by using unbalance response measurements is presented for flexible rotor-bearing systems. The algorithm estimates the bearing dynam...

This paper addresses the influence of manufacturing variability of a helicopter rotor blade on its aeroelastic responses. An aeroelastic analysis using finite elements in spatial and temporal domains is used to compute the helicopter rotor frequencies, vibratory hub loads, power required and stability in forward flight. The novelty of the work lies...

A vane-type gust generator has been designed and characterised in the Swansea University wind tunnel to validate the response of aircraft models to gust loads. Experimental results reveal the complex dynamics of the airflow in the wake of the two gust generator vanes. More specifically, imposing '1-cos' vane rotation does not produce an exact '1-co...

Rotating machines are intrinsically susceptible to expensive and high-risk faults such as rotor–stator rub. During a rub event normal and tangential forces are generated by the contact and friction that cause wear at the contacting interfaces. In the present work, such forces are computed by assuming linear elastic contact and Coulomb friction at m...

With increasing demand for rotor blades in applications such as wind turbines, helicopters, and unmanned aircrafts , improving the performance of such structures using morphing blades has received considerable attention. Resonant passive energy balancing is a relatively new concept introduced to minimize the required actuation energy. This study in...

We demonstrate that the consideration of material uncertainty can dramatically impact the optimal topological micro‑structural configuration of mechanical metamaterials. The robust optimization problem is formulated in such a way that it facilitates the emergence of extreme mechanical properties of metamaterials. The algorithm is based on the bi‑di...

Periodic structures attenuate wave propagation in a specified frequency range, such that a desired bandgap behaviour can be obtained. Most periodic structures are produced by additive manufacturing. However, it is recently found that the variability in the manufacturing processes can lead to a significant deviation from the desired behaviour. This...

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 k...

A novel passive twist morphing concept is examined for helicopter blades. The concept is demonstrated using a thin-walled rectangular composite beam created with symmetric layup to obtain bend-twist property. The twist of a rotor blade is proposed to be actuated though a movable mass at the blade tip which is able to provide a range of lagwise bend...

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 diffe...

The dynamic response of individual components in an assembled structure shows high accuracy compared to experimental measurements of the system response. However, when it comes to assemblies, the conventional linear approaches fail to deliver good accuracy, due to the uncertain linear and nonlinear mechanisms in the contact interface of the joints....

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...

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 discretisa...

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 equation...

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 reconstructio...

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 simula...

A rotor can contact a stator thereby inducing some very strong non-linearities that can result in a plethora of vibration phenomena. Synchronous motions, chaotic motion, backward whirl, forward whirl are some of the reported phenomena in the literature. This article presents an experimental approach based on a very flexible rotor rig designed with...

This paper characterizes the stochastic dynamic response of periodic structures by accounting for manufacturing variabilities. Manufacturing variabilities are simulated through a probabilistic description of the structural material and geometric properties. The underlying uncertainty propagation problem has been efficiently carried out by functiona...

The optimum position and minimum restraint stiffness of a flexible point support to raise a natural frequency of a thin bending plate is investigated, with the inclusion of the corresponding additional support mass. First the derivatives of the natural frequencies of the plate structure are derived with respect to the support movement using a finit...

Parametric excitation is introduced to amplify the external harmonic excitation and extend the capabilities of a nonlinear piezoelectric energy harvester device. To investigate the efficiency of the parametrically amplified energy harvester, the time responses of the voltage and power are computed using the state space formulation. It is assumed th...

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...

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...

Robust design optimization (RDO) of large-scale engineering systems is computationally intensive and requires significant CPU time. Considerable computational effort is still required within conventional meta-model assisted RDO frameworks. The primary objective of this article is to minimize further the computational requirements of meta-model assi...

This paper presents an extensive review of the developments in the aeroelasticity of morphing aircraft that occurred in the last decade (from 2009 to 2020). It focuses mainly on fixed-wing aircraft and highlights some representative examples from rotary-wing aircraft. Morphing wings are usually associated with significant changes in the aerodynamic...

Bayesian methods have become very popular in the area of finite element model updating (FEMU) in the last decade, where these methods are considered as powerful tools in quantifying the uncertainties associated with the modelling and the experimental processes. Based on Bayes’ theorem, the posterior distribution function can be employed to describe...

In this study, the aeroelastic instability of a wing with an initial out-of-plane curvature is determined. The structural dynamics of the wing is modelled by using the geometrically exact beam equations, and the aerodynamic loads are determined using an incompressible unsteady aerodynamic model. The wing is considered to have initial out-of-plane c...

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 rot...

The steady-state response of a strongly nonlinear system often has multiple solutions under harmonic excitation, which includes both multiple response amplitudes and multiple phases. Taking advantage of the force dropout phenomenon of electrodynamic shakers near resonance, a fixed frequency test method was proposed previously to measure the multiva...

In this paper, the dynamics of a tailored composite rotating blade with curved tips are investigated, with a view to improving the dynamic behaviour of the blade in flight. The blade tip is curved either in the out-of-plane or in the in-plane directions. The composite blade is modelled by using the exact beam formulation, and the cross-sectional pr...

A passive energy balancing concept for linear actuation is investigated in the current work by adopting a negative stiffness mechanism. The proposed negative stiffness mechanism uses a pre-tensioned spring to produce a passive torque and therefore to transfer the passive torque through a crankshaft for linear motion. The proposed passive energy ba...