• Gradient-based optimization method for producing a contoured beam with single-fed reflector antenna

      Lian, Peiyuan; Wang, Congsi; Xiang, Binbin; Shi, Yu; Xue, Song; Xidian University; University of Chester; Chinese Academy of Sciences (IEEE, 2019-03-07)
      A gradient-based optimization method for producing a contoured beam by using a single-fed reflector antenna is presented. First, a quick and accurate pattern approximation formula based on physical optics (PO) is adopted to calculate the gradients of the directivity with respect to reflector's nodal displacements. Because the approximation formula is a linear function of nodal displacements, the gradient can be easily derived. Then, the method of the steepest descent is adopted, and an optimization iteration procedure is proposed. The iteration procedure includes two loops: an inner loop and an outer loop. In the inner loop, the gradient and pattern are calculated by matrix operation, which is very fast by using the pre-calculated data in the outer loop. In the outer loop, the ideal terms used in the inner loop to calculate the gradient and pattern are updated, and the real pattern is calculated by the PO method. Due to the high approximation accuracy, when the outer loop is performed once, the inner loop can be performed many times, which will save much time because the integration is replaced by matrix operation. In the end, a contoured beam covering the continental United States (CONUS) is designed, and simulation results show the effectiveness of the proposed algorithm.
    • Modelling impact damage in composite laminates: A simulation of intra- and inter-laminar cracking

      Pinna, Christophe; Soutis, Constantinos; Shi, Yu; University of Chester; University of Sheffield; University of Manchester (Elsevier, 2014-04-12)
      In this work, stress- and fracture mechanics-based criteria are developed to predict initiation and evolution, respectively, of intra- and inter-laminar cracking developed in composite laminates subjected to a relatively low energy impact (⩽15 J) with consideration of nonlinear shear behaviour. The damage model was implemented in the finite element (FE) code (Abaqus/Explicit) through a user-defined material subroutine (VUMAT). Delamination (or inter-laminar cracking) was modelled using interface cohesive elements while splitting and transverse matrix cracks (intralaminar cracking) that appeared within individual plies were also simulated by inserting cohesive elements along the fibre direction (at a crack spacing determined from experiments for computing efficiency). A good agreement is obtained when the numerically predicted results are compared to both experimentally obtained curves of impact force and absorbed energy versus time and X-ray radiography damage images, provided the interface element stiffness is carefully selected. This gives confidence to selected fracture criteria and assists to identify material fracture parameters that influence damage resistance of modern composite material systems.
    • Surface adjustment strategy for a large radio telescope with adjustable dual reflectors

      Lian, Peiyuan; Wang, Congsi; Xue, Song; Xu, Qian; Shi, Yu; Jia, Yu; Xiang, Binbin; Wang, Yan; Yan, Yuefei; Xidian University; University of Chester; Chinese Academy of Sciences (IET, 2019-08-15)
      With the development of large-aperture and high-frequency radio telescopes, a surface adjustment procedure for the compensation of surface deformations has become of great importance. In this study, an innovative surface adjustment strategy is proposed to achieve an automated adjustment for the large radio telescope with adjustable dual reflectors. In the proposed strategy, a high-precision and long-distance measurement instrument is adopted and installed on the back of the sub-reflector to measure the distances and elevation angles of the target points on the main reflector. Here, two surface adjustment purposes are discussed. The first purpose is to ensure that the main reflector and sub-reflector are always positioned at their ideal locations during operation. The second purpose is to adjust the main reflector to the location of the best fitting reflector, and the sub-reflector to the focus of the best fitting reflector. Next, the calculation procedures for the adjustments of the main reflector and the sub-reflector are discussed in detail, and corresponding simulations are carried out to verify the proposed method. The results show that the proposed strategy is effective. This study can provide helpful guidance for the design of automated surface adjustments for large telescopes.
    • Modelling transverse matrix cracking and splitting of cross-ply composite laminates under four point bending

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (Elsevier, 2015-11-30)
      The transverse matrix cracking and splitting in a cross-ply composite laminate has been modelled using the finite element (FE) method with the commercial code Abaqus/Explicit 6.10. The equivalent constraint model (ECM) developed by Soutis et al. has been used for the theoretical prediction of matrix cracking and results have been compared to those obtained experimentally and numerically. A stress-based traction–separation law has been used to simulate the initiation of matrix cracks and their growth under mixed-mode loading. Cohesive elements have been inserted between the interfaces of every neighbouring element along the fibre orientation for all 0° and 90° plies to predict the matrix cracking and splitting at predetermined crack spacing based on experimental observations. Good agreement is obtained between experimental and numerical crack density profiles for different 90° plies. In addition, different mechanisms of matrix cracking and growth processes were captured and splitting was also simulated in the bottom 0° ply by the numerical model.
    • Enhancement in Interfacial Adhesion of Ti/Polyetheretherketone by Electrophoretic Deposition of Graphene Oxide

      Pan, Lei; Lv, Yunfei; Nipon, Roy; Wang, Yifan; Duan, Lixiang; Hu, Jingling; Ding, Wenye; Ma, Wenliang; Tao, Jie; Shi, Yu; et al. (Wiley, 2019-03-24)
      This article discusses about the significance of graphene oxide (GO) deposition on the surface of a titanium plate by electrophoretic deposition (EPD) method to improve the adhesive strength of Ti/polyetheretherketone (PEEK) interfacial adhesive. Firstly, the anodic EPD method was applied to a water dispersion solution of GO, and then the morphology and the properties of titanium plate surface were characterized by scanning electron microscopy and contact angle measurements before and after GO deposition. Furthermore, the changes in the properties of GO after heating at 390°C were characterized by Raman and Fourier transform infrared spectroscopies. According to the results of single lap tensile shear test, the adhesion strength of Ti/PEEK interface after the anodization and deposition of GO was 34.94 MPa, an increase of 29.2% compared with 27.04 MPa of sample with only anodization. Also, the adhesion strengths were 58.1 and 76.5% higher compared with the samples of only GO deposited (22.1 MPa) and pure titanium (19.8 MPa), respectively.
    • Multiphysics vibration FE model of piezoelectric macro fibre composite on carbon fibre composite structures

      Jia, Yu; Wei, Xueyong; Xu, Liu; Wang, Congsi; Lian, Peiyuan; Xue, Song; Alsaadi, Ahmed; Shi, Yu; University of Chester; Xi'an Jiaotong University; Xidian University (Elsevier, 2018-12-21)
      This paper presents a finite element (FE) model developed using commercial FE software COMSOL to simulate the multiphysical process of pieozoelectric vibration energy harvesting (PVEH), involving the dynamic mechanical and electrical behaviours of piezoelectric macro fibre composite (MFC) on carbon fibre composite structures. The integration of MFC enables energy harvesting, sensing and actuation capabilities, with applications found in aerospace, automotive and renewable energy. There is an existing gap in the literature on modelling the dynamic response of PVEH in relation to real-world vibration data. Most simulations were either semi-analytical MATLAB models that are geometry unspecific, or basic FE simulations limited to sinusoidal analysis. However, the use of representative environment vibration data is crucial to predict practical behaviour for industrial development. Piezoelectric device physics involving solid mechanics and electrostatics were combined with electrical circuit defined in this FE model. The structure was dynamically excited by interpolated vibration data files, while orthotropic material properties for MFC and carbon fibre composite were individually defined for accuracy. The simulation results were validated by experiments with <10﹪ deviation, providing confidence for the proposed multiphysical FE model to design and optimise PVEH smart composite structures.
    • Multimodal Shear Wave Deicing Using Fibre Piezoelectric Actuator on Composite for Aircraft Wings

      Shi, Yu; Jia, Yu; University of Chester
      The formation and accretion of ice on aircraft wings during flight can be potentially disastrous and existing in-flight deicing methods are either bulky or power consuming. This paper investigates the use of shear wave deicing driven by a macro fibre piezoelectric composite actuator on a composite plate typically used for aircraft wings. While the few existing research on this novel deicing approach focused on either theoretical studies or single frequency mode optimization that required high-excitation amplitudes, this study revealed that the use of multimodal excitation through broadband frequency sweeps has the potential to promote the chance of shear stress induced deicing at a relatively small excitation amplitude. The results reported here form the foundation for a pathway towards low power and lightweight deicing mechanism for in-flight aircraft wings.
    • Vibration Energy Harvesting of Multifunctional Carbon Fibre Composite Laminate Structures

      alsaadi, Ahmed; University of Chester
      A sustainable power supply for a wide range of applications, such as power- ing sensors for structural health monitoring and wireless sensor nodes for data transmission and communication used in unmanned air vehicles, automobiles, renewable energy sectors, and smart city technologies, is targeted. This pa- per presents an experimental and numerical study that describes an innovative technique to harvest energy resulted from environmental vibrations. A piezo- electric energy harvester was integrated onto a carbon fibre reinforced polymer (CFRP) laminate structure using the co-curing method. The integrated com- posite with the energy harvester was lightweight, flexible and provided robust and reliable energy outcomes, which can be used to power different low-powered wireless sensing nodes. A normalised power density of 97 μW cm −3 m −2 s 4 was obtained from resonance frequency of 46 Hz sinusoidal waves at amplitude of 0.2 g; while the representative environmental vibration waves in various appli- cations (aerospace, automotive, machine and bridge infrastructure) were ex- perimentally and numerically investigated to find out the energy that can be harvested by such a multifunctional composite structure. The results showed the energy harvested at different vibration input from various industrial sectors could be sufficient to power an autonomous structural health monitoring system and wireless communications by the designed composite structure.
    • Modelling low velocity impact induced damage in composite laminates

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (Springer, 2017-07-26)
      The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction.
    • Low-velocity impact of composite laminates: damage evolution

      Shi, Yu; Pinna, Christophe; Soutis, Constantinos; University of Chester; University of Sheffield; University of Manchester (Woodhead Publishing, 2016-02-19)
      This chapter presents modelling procedures used to simulate damage evolution in composite laminates used in aircraft structures when subjected to low-energy-level impact (≤15 J). Damage models for both initiation and evolution are first introduced by considering the individual damage modes of composite laminates in the form of intra- and inter-laminar damage mechanisms. The implementation of these damage criteria into the user subroutine Vumat of the finite element code Abaqus is then described for the simulation of damage development during low-velocity impact tests. Finite element prediction is then compared to experimental load-time measurements and damage extent obtained using X-rays as a non-destructive technique (NDT). Further development of the model is then presented by simulating matrix cracking evolution and splitting using a fracture mechanics-based criterion approach implemented into a cohesive zone element (CZE) formulation. Results from the extended model show clear improvement in terms of the accuracy of damage prediction, with experimental observations of the damage modes operating at ply-level providing further validation of the model. This can be used at an early stage of the design process of optimising laminate configurations used in aircraft structural applications.
    • A Numerical Feasibility Study of Kinetic Energy Harvesting from Lower Limb Prosthetics

      Jia, Yu; Wei, Xueyong; Pu, Jie; Xie, Pengheng; Wen, Tao; Wang, Congsi; Lian, Peiyuan; Xue, Song; Shi, Yu; Aston University; University of Chester; Xidian University; Xi'an Jiaotong University (MDPI, 2019-10-10)
      With the advancement trend of lower limb prosthetics headed towards bionics (active ankle and knee) and smart prosthetics (gait and condition monitoring), there is an increasing integration of various sensors (micro-electromechanical system (MEMS) accelerometers, gyroscopes, magnetometers, strain gauges, pressure sensors, etc.), microcontrollers and wireless systems, and power drives including motors and actuators. All of these active elements require electrical power. However, inclusion of a heavy and bulky battery risks to undo the lightweight advancements achieved by the strong and flexible composite materials in the past decades. Kinetic energy harvesting holds the promise to recharge a small on-board battery in order to sustain the active systems without sacrificing weight and size. However, careful design is required in order not to over-burden the user from parasitic effects. This paper presents a feasibility study using measured gait data and numerical simulation in order to predict the available recoverable power. The numerical simulations suggest that, depending on the axis, up to 10s mW average electrical power is recoverable for a walking gait and up to 100s mW average electrical power is achievable during a running gait. This takes into account parasitic losses and only capturing a fraction of the gait cycle to not adversely burden the user. The predicted recoverable power levels are ample to self-sustain wireless communication and smart sensing functionalities to support smart prosthetics, as well as extend the battery life for active actuators in bionic systems. The results here serve as a theoretical foundation to design and develop towards regenerative smart bionic prosthetics.
    • An Analytical and Numerical Study of Magnetic Spring Suspension with Energy Recovery Capabilities

      Jia, Yu; Li, Shasha; Shi, Yu; University of Chester; China National Intellectual Property Administration (MDPI, 2018-11-12)
      As the automotive paradigm shifts towards electric, limited range remains a key challenge. Increasing the battery size adds weight, which yields diminishing returns in range per kilowatt-hour. Therefore, energy recovery systems, such as regenerative braking and photovoltaic cells, are desirable to recharge the onboard batteries in between hub charge cycles. While some reports of regenerative suspension do exist, they all harvest energy in a parasitic manner, and the predicted power output is extremely low, since the majority of the energy is still dissipated to the environment by the suspension. This paper proposes a fundamental suspension redesign using a magnetically-levitated spring mechanism and aims to increase the recoverable energy significantly by directly coupling an electromagnetic transducer as the main damper. Furthermore, the highly nonlinear magnetic restoring force can also potentially enhance rider comfort. Analytical and numerical models have been constructed. Road roughness data from an Australian road were used to numerically simulate a representative environment response. Simulation suggests that 10’s of kW to >100 kW can theoretically be generated by a medium-sized car travelling on a typical paved road (about 2–3 orders of magnitude higher than literature reports on parasitic regenerative suspension schemes), while still maintaining well below the discomfort threshold for passengers (<0.315 m/s2 on average).
    • Integration and Characterisation of Piezoelectric Macro-Fibre Composite on Carbon Fibre Composite for Vibration Energy Harvesting

      Shi, Yu; Piao, Chenghe; Fadlaoui, Dounia; Alsaadi, Ahmed; Jia, Yu; University of Chester (IOPScience, 2019-11-01)
      Carbon fibre composite is a strong and a lightweight structural material with applications in automotive, aerospace, medical and industrial applications. The integration of piezoelectric transducer films onto the composite stack can add vibration energy harvesting capabilities to enable net-zero-power autonomous sensing for an otherwise purely mechanical structure. A PZT macro-fibre composite is co-cured with a carbon/epoxy pre-preg in order to manufacture the multi-functional composite plate. Without noticeably increasing profile, adding weight or compromising mechanical integrity, the resultant mechanical plate can recover power from vibrational excitations. With a volume of 13.5 cm3, a peak average power of 9.25 mW was recorded at 2.66 ms −2 . The normalised power density of 97 µW cm −3 m −2 s4 is comparable to some of the state-of-the-art PZT generators reported in the literature.
    • Evaporation of liquid nitrogen droplets in superheated immiscible liquids

      Rebelo, Neville; Zhao, Huayong; Nadal, Francois; Garner, Colin; Williams, Andy; Loughborough University; University of Chester (Elsevier, 2019-08-22)
      Liquid nitrogen or other cryogenic liquids have the potential to replace or augment current energy sources in cooling and power applications. This can be done by the rapid evaporation and expansion processes that occur when liquid nitrogen is injected into hotter fluids in mechanical expander systems. In this study, the evaporation process of single liquid nitrogen droplets when submerged into n-propanol, methanol, n-hexane, and n-pentane maintained at 294 K has been investigated experimentally and numerically. The evaporation process is quantified by tracking the growth rate of the resulting nitrogen vapour bubble that has an interface with the bulk liquid. The experimental data suggest that the bubble volume growth is proportional to the time and the bubble growth rate is mainly determined by the initial droplet size. A comparison between the four different bulk liquids indicates that the evaporation rate in n-pentane is the highest, possibly due to its low surface tension. A scaling law based on the pure diffusion-controlled evaporation of droplet in open air environment has been successfully implemented to scale the experimental data. The deviation between the scaling law predictions and the experimental data for 2-propanol, methanol and n-hexane vary between 4% and 30% and the deviation for n-pentane was between 24% and 65%. The more detailed bubble growth rates have been modelled by a heuristic one-dimensional, spherically symmetric quasi-steady-state confined model, which can predict the growth trend well but consistently underestimate the growth rate. A fixed effective thermal conductivity is then introduced to account for the complex dynamics of the droplet inside the bubble and the subsequent convective processes in the surrounding vapour, which leads to a satisfactory quantitative prediction of the growth rate.
    • Rapid, Chemical-Free Generation of Optically Scattering Structures in Poly(ethylene terephthalate) Using a CO2 Laser for Lightweight and Flexible Photovoltaic Applications

      Academic Editor: Yan, Yanfa; Hodgson, Simon D.; Gillett, Alice R. (Hindawi, 2018-12-16)
      Highly light scattering structures have been generated in a poly(ethylene terephthalate) (PET) film using a CO2 laser. The haze, and in some cases the transparency, of the PET films have been improved by varying the processing parameters of the laser (namely, scanning velocity, laser output power, and spacing between processed tracks). When compared with the unprocessed PET, the haze has improved from an average value of 3.26% to a peak of 55.42%, which equates to an absolute improvement of 52.16% or a 17-fold increase. In addition to the optical properties, the surfaces have been characterised using optical microscopy and mapped with an optical profilometer. Key surface parameters that equate to the amount and structure of surface roughness and features have been analysed. The CO2 laser generates microstructures at high speed, without affecting the bulk properties of the material, and is inherently a chemical-free process making it particularly applicable for use in industry, fitting well with the high-throughput, roll to roll processes associated with the production of flexible organic photovoltaic devices.
    • Interface Cohesive Elements to Model Matrix Crack Evolution in Composite Laminates

      Shi, Yu; Pinna, Christophe; Soutis, Constantinos; University of Chester; University of Sheffield; University of Manchester (Springer, 2013-10-02)
      In this paper, the transverse matrix (resin) cracking developed in multidirectional composite laminates loaded in tension was numerically investigated by a finite element (FE) model implemented in the commercially available software Abaqus/Explicit 6.10. A theoretical solution using the equivalent constraint model (ECM) of the damaged laminate developed by Soutis et al. was employed to describe matrix cracking evolution and compared to the proposed numerical approach. In the numerical model, interface cohesive elements were inserted between neighbouring finite elements that run parallel to fibre orientation in each lamina to simulate matrix cracking with the assumption of equally spaced cracks (based on experimental measurements and observations). The stress based traction-separation law was introduced to simulate initiation of matrix cracking and propagation under mixed-mode loading. The numerically predicted crack density was found to depend on the mesh size of the model and the material fracture parameters defined for the cohesive elements. Numerical predictions of matrix crack density as a function of applied stress are in a good agreement to experimentally measured and theoretically (ECM) obtained values, but some further refinement will be required in near future work.
    • Predicting the critical heat flux in pool boiling based on hydrodynamic instability induced irreversible hot spots

      Zhao, Huayong; Williams, Andrew; Loughborough University; University of Chester (Elsevier, 2018-03-07)
      A new model, based on the experimental observation reported in the literature that CHF is triggered by the Irreversible Hot Spots (IHS), has been developed to predict the Critical Heat Flux (CHF) in pool boiling. The developed Irreversible Hot Spot (IHS) model can predict the CHF when boiling methanol on small flat surfaces and long horizontal cylinders of different sizes to within 5% uncertainty. It can also predict the effect of changing wettability (i.e. contact angle) on CHF to within 10% uncertainty for both hydrophilic and hydrophobic surfaces. In addition, a linear empirical correlation has been developed to model the bubble growth rate as a function of the system pressure. The IHS model with this linear bubble growth coefficient correlation can predict the CHF when boiling water on both flat surfaces and long horizontal cylinders to within 5% uncertainty up to 10 bar system pressure, and the CHF when boiling methanol on a flat surface to within 10% uncertainty up to 5 bar. The predicted detailed bubble grow and merge process from various sub-models are also in good agreement with the experimental results reported in the literature.
    • A micromachined device describing over a hundred orders of parametric resonance

      Jia, Yu; Du, Sijun; Arroyo, Emmanuelle; Seshia, Ashwin A.; University of Cambridge; University of Chester (AIP Publishing, 2018-04-24)
      Parametric resonance in mechanical oscillators can onset from the periodic modulation of at least one of the system parameters, and the behaviour of the principal (1st order) parametric resonance has long been well established. However, the theoretically predicted higher orders of parametric resonance, in excess of the first few orders, have mostly been experimentally elusive due to the fast diminishing instability intervals. A recent paper experimentally reported up to 28 orders in a micromachined membrane oscillator. This paper reports the design and characterisation of a micromachined membrane oscillator with a segmented proof mass topology, in an attempt to amplify the inherent nonlinearities within the membrane layer. The resultant oscillator device exhibited up to over a hundred orders of parametric resonance, thus experimentally validating these ultra-high orders as well as overlapping instability transitions between these higher orders. This research introduces design possibilities for the transducer and dynamic communities, by exploiting the behaviour of these previously elusive higher order resonant regimes.
    • Evidence for the Perception of Time Distortion During Episodes of Alice in Wonderland Syndrome

      Jia, Yu; Miao. Ying; University of Chester; Aston University (Lippincott Williams & Wilkins, 2018-05-17)
      Alice in Wonderland syndrome (AIWS) is a rare perceptual disorder associated with sensation of one or several visual and/or auditory perceptual distortions including size of body parts, size of external objects, or passage of time (either speeding up or slowing down). Cause for AIWS is yet to be widely agreed, and the implications are widely varied. One of the research difficulties is the brevity of each episode, typically not exceeding few tens of minutes. This article presents a male adult in late 20s who has apparently experienced AIWS episodes since childhood, and infection has been ruled out. Reaction speed tests were conducted during and after AIWS episodes, across a span of 13 months. Statistically significant evidence is present for delayed response time during AIWS episodes when the patient claims to experience a sensation of time distortion: where events seem to move faster and people appear to speak quicker.
    • A finite element analysis of impact damage in composite laminates

      Shi, Yu; Soutis, Constantinos; University of Chester; University of Manchester (Cambridge University Press, 2012-12-01)
      In this work, stress-based and fracture mechanics criteria were developed to predict initiation and evolution, respectively, of intra- and inter-laminar cracking developed in composite laminates subjected to low velocity impact. The Soutis shear stress-strain semi-empirical model was used to describe the nonlinear shear behaviour of the composite. The damage model was implemented in the finite element (FE) code (Abaqus/Explicit) by a user-defined material subroutine (VUMAT). Delamination (or inter-laminar cracking) was modelled using interface cohesive elements and the splitting and transverse matrix cracks that appeared within individual plies were also simulated by inserting cohesive elements between neighbouring elements parallel to the fibre direction in each single layer. A good agreement was obtained when compared the numerically predicted results to experimentally obtained curves of impact force and absorbed energy versus time. A non-destructive technique (NDT), penetrant enhanced X-ray radiography, was used to observe the various damage mechanisms induced by impact. It has been shown that the proposed damage model can successfully capture the internal damage pattern and the extent to which it was developed in these carbon fibre/epoxy composite laminates.