Rob Hewson

Development of anti-icing materials by chemical tailoring of hydrophobic textured metallic surfaces

Ice on surfaces can have dramatic consequences for human activities. Over the last decades, the design of new materials with anti-icing properties has generated significant research efforts for the prevention of ice accretion. Here we investigate water freezing temperatures on untreated and negatively charged hydrophobic stainless steel surfaces and use these temperatures to evaluate icephobicity. Supercooled water microdroplets are deposited and undergo a slow controlled cooling until spontaneous freezing occurs. Textured hydrophobic stainless steel surfaces functionalized with anionic polyelectrolytes brushes display unexpectedly lower freezing temperatures, at least 7 °C lower than polished untreated steel. On the basis of the entropy reduction of the crystalline phase near a charged solid surface, we used a modification of the classical heterogeneous nucleation theory to explain the observed freezing temperatures lessening. Our results could help the design of new composite materials that more efficiently prevent ice formation.

Multifidelity metamodel building as a route to aeroelastic optimization of flexible wings

High-fidelity aeroelastic simulations of the response of flexible wings to a sudden gust can result in a huge computing effort, making the search for the best wing design prohibitively expensive. As an alternative, a cost-effective multifidelity metamodelling-based optimization strategy, where a metamodel of a high-fidelity aeroelastic simulation response is built by tuning a lower fidelity aeroelastic simulation response, is proposed. In order to address and validate such an approach, both linear and non-linear aeroelastic equations for an aerofoil employing different levels of complexity for expressing the aerodynamic load are used for the high- and low-fidelity models. An aeroelastic gust response evaluation problem is formulated for the flexible wing of a small unmanned air vehicle, whose characteristic size makes it particularly susceptible to gusts. Three different approaches to tune the low-fidelity model, both explicit and implicit, are investigated and compared. Good agreement between the high-fidelity model and the corrected low-fidelity one shows that the proposed approach is indeed suitable for optimization of the aeroelastic gust performance of flexible wings.

Robotic platforms for general and colorectal surgery

Surgeons are increasingly turning to new technologies to help them overcome the barriers imposed by minimally invasive surgery (MIS). Robotics is an enabling technology with obvious applications to MIS. This manuscript looks at robotic platforms for general surgical application and explores the advantages, limitations and possible future roles.

Reviewing the technological challenges associated with the development of a laparoscopic palpation device

Minimally invasive surgery (MIS) has heralded a revolution in surgical practice, with numerous advantages over open surgery. Nevertheless, it prevents the surgeon from directly touching and manipulating tissue and therefore severely restricts the use of valuable techniques such as palpation. Accordingly a key challenge in MIS is to restore haptic feedback to the surgeon. This paper reviews the state‐of‐the‐art in laparoscopic palpation devices (LPDs) with particular focus on device mechanisms, sensors and data analysis. It concludes by examining the challenges that must be overcome to create effective LPD systems that measure and display haptic information to the surgeon for improved intraoperative assessment. Copyright

Design Methodology for Magnetic Field-Based Soft Tri-Axis Tactile Sensors.

Tactile sensors are essential if robots are to safely interact with the external world and to dexterously manipulate objects. Current tactile sensors have limitations restricting their use, notably being too fragile or having limited performance. Magnetic field-based soft tactile sensors offer a potential improvement, being durable, low cost, accurate and high bandwidth, but they are relatively undeveloped because of the complexities involved in design and calibration. This paper presents a general design methodology for magnetic field-based three-axis soft tactile sensors, enabling researchers to easily develop specific tactile sensors for a variety of applications. All aspects (design, fabrication, calibration and evaluation) of the development of tri-axis soft tactile sensors are presented and discussed. A moving least square approach is used to decouple and convert the magnetic field signal to force output to eliminate non-linearity and cross-talk effects. A case study of a tactile sensor prototype, MagOne, was developed. This achieved a resolution of 1.42 mN in normal force measurement (0.71 mN in shear force), good output repeatability and has a maximum hysteresis error of 3.4%. These results outperform comparable sensors reported previously, highlighting the efficacy of our methodology for sensor design.

An Investigation of Freezing of Supercooled Water on Anti-Freeze Protein Modified Surfaces

This work investigates how functionalization of aluminium surfaces with natural type III Anti-Freeze Protein (AFP) affects the mechanism of heterogeneous ice nucleation. First the bulk ice nucleation properties of distilled water and aqueous solution of AFP were evaluated by differential scanning calorimetry. Then the modified surface was characterized by Secondary Ions Mass Spectroscopy (SIMS), Fourier Transform InfraRed (FTIR) spectroscopy and contact angle measurement. Freezing experiments were then conducted in which water droplets underwent a slow controlled cooling. This study shows that compared to uncoated aluminium, the anti-freeze proteins functionalized surfaces exhibit a higher and narrower range of freezing tempera-ture. It was found that these proteins that keep living organisms from freezing in cold environment act in the opposite way once immobilized on surfaces by promoting ice nucleation. Some suggestions regarding the mechanism of action of the observed phenomena were proposed based on the Classical Nucleation Theory (CNT).

A Multiscale Framework for EHL and Micro-EHL

In this article, a heterogeneous multiscale method is introduced to analyze the microelastohydrodynamic lubrication (micro-EHL) of bearings with topological features. Two scales are adopted in the analysis: the large-scale simulations describe the entire bearing domain, and the small-scale simulations describe the fluid–structure interaction (FSI) at the small-scale features. Conservation of mass and momentum of the lubricant and the bearings elastic deformation are solved for. The relationship between the pressure gradient and mass flow is obtained from homogenized small-scale FSI simulations and applied on a global scale via a scattered data interpolation method. When the micro structure is periodic the exact model at micro scale is replaced by an effective derived equation, i.e., homogenized model. The elastic deformation of the textured bearing surface is addressed at both the large and small scales, by decomposing the displacement influence matrix into the diagonal terms and nondiagonal terms (sorted at the small scale and large scale, respectively). The multiscale method was demonstrated as being capable of modeling the global pressure and film thickness for a bearing with surface texture while maintaining the accuracy of the small-scale modeling features. The illustrative geometry was that of a linear converging pad bearing in two dimensions. The solutions were compared with those obtained using lubrication theory for the smooth surface case, and good agreement was obtained. The method was then demonstrated for geometries incorporating topographical features.

Metamodelling Based on High and Low Fidelity Models Interaction for UAV Gust Performance Optimization

The size of small flexible winged Unmanned Air Vehicles (UAVs) makes them particularly susceptible to gusts. Accordingly, a gust performance evaluation problem is formulated where the simulation of the gust response is treated as an aeroelastic problem. Generally, a high-fidelity simulation can result in a large computing effort that, being multiplied by a large number of calls for the aeroelastic simulation in the design optimization process, could make the latter prohibitively computationally expensive. Therefore, a multifidelity technique is employed, where a metamodel of the high-fidelity simulation response is built based on a tuned lower fidelity aeroelastic model. In order to address and validate such a multifidelity modelling approach, the linear aeroelastic equations of a 2D airfoil employing quasi-static aerodynamics are used for the lowfidelity model and solved analytically, whereas the nonlinear aeroelastic equations of a 2D airfoil employing unsteady aerodynamics are used for the high-fidelity model and solved numerically. Three different approaches to the low-fidelity model tuning are investigated and compared, both explicit and implicit. An application of the Moving Least Squares Method (MLSM) to the low-fidelity model tuning is also investigated. Good agreement between the high-fidelity model and the corrected low-fidelity model shows that a multifidelity model-based strategy is suitable for use in optimising the gust performance of small UAVs even in the presence of large structural deformations of their wings.

Aerodynamic Drag Reduction of Emergency Response Vehicles

This paper presents the first experimental and computational investigation into the aerodynamics of emergency response vehicles and focuses on reducing the additional drag that results from the customary practice of adding light-bars onto the vehicles’ roofs. A series of wind tunnel experiments demonstrate the significant increase in drag that results from the light bars and show these can be minimized by reducing the flow separation caused by them. Simple potential improvements in the aerodynamic design of the light bars are investigated by combining Computational Fluid Dynamics (CFD) with Design of Experiments and metamodelling methods. An aerofoil-based roof design concept is shown to reduce the overall aerodynamic drag by up to 20% and an analysis of its effect on overall fuel consumption indicates that it offers a significant opportunity for improving the fuel economy and reducing emissions from emergency response vehicles. These benefits are now being realised by the UK’s ambulance services.

Influence of material properties and operating conditions on the predicted performance of poroelastic faced bearings

A new lubrication model of poroelastic lubrication of materials with low Young’s modulus and permeability is presented based on Darcy’s law and linear elastic solid mechanics and a contact model. A rotating bearing surface moving against a flat surface is considered and the effect of material parameters and operating conditions is analyzed. The results show that the material parameters (permeability (k), Young’s modulus (E), and viscosity (μ)) and operating conditions (angular velocity (ω) and material deformation (δ)) have significant effects on the lubrication performance of the poroelastic bio-inspired materials. It is also observed that the load ratio (the ratio of pressure-borne load to the applied load along the contact boundary) increases as k and E decrease, and as μ, ω, and δ increase. Conversely maximum solid stress decreases with decreasing of E, μ, ω, δ and with increasing of k. The relationship of the load ratio, contact stress, and deformation relative to E and k has been illustrated in this paper.