Browsing by Author "Asproulis, N."

Now showing 1 - 7 of 7
  • Thumbnail Image
    ItemOpen Access
    Computational nanoscience and molecular modelling of shock wave interactions with biological membranes
    (Cranfield University, 2011) Sourmaidou, Damiani; Asproulis, N.; Drikakis, Dimitris
    Lateral diffusion of membrane components (lipids and proteins) is an important membrane property to measure since the essential process of absorption of anti-cancer and other drugs -some of which are not soluble in lipids and therefore would not be able to penetrate the cell membrane through passive diffusion- lies on it. In particular, the procedure of diffusion into the cell cytoplasm is reliant on free volumes in the membrane (passive diffusion) as well as carrier proteins (facilitated diffusion). By enhancing the mobility of lipids and/or proteins, the possibility of the carrier protein to "encapsulate" pharmacological components maxim- izes, as a "scanning" of the proteins gets performed due to the fluid phase of a biological membrane. At the same time, the increased mobility of the lipids facilitates the passage of lipid-soluble molecules into the cell. Thus, given that the success of anticancer treatments heavily depends on their absorption by the cell, a significant enhancement of the cell mem- brane permeability (permeabilisation) is rendered vital to the applicability of the technique. For this reason, there is augmented interest in combined methods such as Nanotechnology based drug delivery that is focused on the development of optimally designed therapeutic agents along with the application of shock waves to enhance the membrane permeability to the agents. This study examines the impact of shock waves on a numerical model of a biological membrane. Cont/d.
  • Thumbnail Image
    ItemOpen Access
    High-order methods on mixed-element unstructured meshes for aeronautical applications
    (Cranfield University, 2012-11) Antoniadis, Antonis F.; Drikakis, Dimitris; Asproulis, N.
    Higher resolution and reliability are the desiderata for Computational Fluid Dynamics and main drivers for the development, implementation and validation of highorder accurate methods. Complex fluid dynamic phenomena such as shock-wave boundary-layer interactions, turbulent separated flows and fluid problems involving multiple scales are adequately resolved with high-order schemes. The spatial representation of the flow field by an unstructured mesh provides flexibility, automation, fast and effortless grid generation and exceptional load balance on multiple processor computers. This plethora of advantages is mirrored by the unprecedented popularity of unstructured-based schemes. The objective of this PhD project is the implementation of two high-order schemes for the compressible Navier-Stokes equations in the context of the finite volume “kexact” framework: the MUSCL-TVD and WENO. The schemes are formulated in two and three space dimensions for mixed-element unstructured meshes; in addition, the Spalart-Allmaras turbulence model is implemented into the developed numerical framework. A wide range of applications are considered spanning from low-speed flows (M = 0.08) to supersonic conditions (M = 5.0); inviscid and viscous simulations in a broad spectrum of Reynolds numbers ranging from Re = 500 up to Re = 37×106. The applications include: the Taylor-Green vortex, the ONERA-M6 wing, flat plate, the NACA-0012 and the MD 30P-30N aerofoils, and a shock-wave boundary-layer interaction. For the examined cases, WENO schemes demonstrate superior accuracy, numerical dissipation and non-oscillatory behaviour over the MUSCL-TVD. High-order schemes inherit low numerical dissipation properties while turbulence models induce dissipation, this disequilibrium has adverse effects on the stability, convergence and accuracy of the simulation; therefore, turbulence model re-calibration would be required in order to accommodate high-order discretisation methods.
  • Thumbnail Image
    ItemOpen Access
    Hybrid molecular and continuum fluid dynamics models for micro and nanofluidic flows
    (Cranfield University, 2009-12) Asproulis, N.; Drikakis, Dimitris
    From molecules to living organisms and from atoms to planets a variety of physical phe- nomena operate at different temporal and spatial scales. Understanding the nature of those phenomena is crucial for advancing new technologies in many disciplines. In micro and nanofluidics as the operational dimensions are downsized to smaller scales the surface-to- volume ratio increases and the surface phenomena become dominant. Numerical modelling is the key for obtaining a better insight into the processes involved. The Achilles heel of fine grain microscopic numerical simulations is their computational cost. Simulating a multiscale phenomenon with an accurate microscopic description is extremely demand- ing computationally. On the contrary, simulations of multiscale phenomena based only on macroscopic descriptions cannot fully capture the physics of the multiscale systems. In order to confront this dilemma multiscale frameworks, called hybrid codes, have been de- veloped to couple the microscopic and macroscopic description of a system and to facilitate the exchange of information. The aim of this research project is to establish and implement a robust hybrid molecular- continuum method for micro- and nano-scale fluid flows. Towards that direction a hybrid multiscale method named as Point Wise Coupling (PWC) has been developed. PWC aims to circumvent the limitations of the existing hybrid continuum/atomistic approaches and deliver a modular and applicable methodology. In the PWC, the whole domain is covered with the macroscopic solver and the microscale model enters as a local refinement. Ad- ditionally, numerical techniques based on neural networks are employed to minimise the cost of the molecular solver and reduce the outcomes’ variability induced by the fluctuating nature of the atomistic data. Molecular studies have been performed (i) to obtain a better insight of the interfacial phenomena in the solid/liquid interfaces, and (ii) to study the parametrisation of the molec- ular models and mapping of atomistic information to hybrid frameworks. Specifically, the impact of parameters, such as surface roughness and stiffness, to slip process is studied. PWC framework has been employed to study a number of fundamental test cases in- cluding Poiseuille flow of polymeric fluids, isothermal slip Couette flow and slip Couette flow with heat transfer. Attention is drawn to the boundary condition transfer from the continuum solver to the atomistic description. In the performed hybrid studies the effects of the numerical optimisation techniques (linear interpolation, neural networks) to simu- lations’ accuracy, stability and efficiency are studied. The outcomes of the simulations suggest that the neural networks scheme enhance the simulation’s efficiency by minimising the number of atomistic simulations and at the same time act as a smoothing operator for reducing the oscillations’ strength of the atomistic outputs.
  • Thumbnail Image
    ItemOpen Access
    The impact of hydraulic retention time on the performance of two configurations of anaerobic pond for municipal sewage treatment
    (Taylor & Francis, 2021-07-06) Cruddas, P. H.; Asproulis, N.; Antoniadis, Antonis F.; Best, D.; Collins, G.; Porca, E.; Jefferson, Bruce; Cartmell, E; McAdam, Ewan J.
    Anaerobic ponds have the potential to contribute to low carbon wastewater treatment, however are currently restricted by long hydraulic residence time (HRT) which leads to large land requirements. A two-stage anaerobic pond (SAP) design was trialled against a single-stage control (CAP) over four HRTs down to 0.5 days, to determine the lowest HRT at which the ponds could operate effectively. No statistical differences were observed in particulate removal between the ponds over all four HRTs, suggesting solids loading is not a critical factor in AP design. Significantly higher biogas production rates were observed in the SAP than the CAP at 1.5 d and 1.0 d HRT, and microbial community profiling suggests the two-stage design may be facilitating spatial separation of the anaerobic digestion process along reactor length. Hydrogenotrophic methanogensis dominated over aceticlastic, with acetate oxidisation a likely degradation pathway. Experimental tracer studies were compared to CFD simulations, with the SAP showing greater hydraulic efficiency, and differences more pronounced at shorter HRTs. Greater flow recirculation between baffles was observed in CFD velocity profiles, demonstrating baffles can dissipate preferential flow patterns and increase effective pond volume, especially at high flow rates. The study demonstrates the potential of APs to be operated at shorter HRTs in psychrophilic conditions, presenting an opportunity for use as pre-treatments (in place of septic tanks) and primary treatment for full wastewater flows. Two-stage designs should be investigated to separate the stages of the anaerobic digestion process by creating preferential conditions along the pond length.
  • Thumbnail Image
    ItemOpen Access
    Life cycle assessment of composites and aluminium use in aircraft systems
    (Cranfield University, 2013-10) Liu, Ziqian; Asproulis, N.; Kolios, Athanasios
    As a consequence of the gradually expanding aviation network, civil aircrafts are occupying an increasingly high proportion of the transport industry. Air transport now dominates the intercity rapid transit, long-distance passenger transport, international passenger and freight transport, and specific regional transport, advantaged as it is by fast, convenient, comfortable and safe options. Nevertheless, the potential adverse impact on the environment of air transport, specifically, in the case of this research, the pollutants generated during aircraft production remain a concern. Using the A319 as the main research object, this thesis will conduct a life cycle assessment research about its environmental impact. Moreover, it will focus on the impact brought by the application of composite materials to the entire life cycle environmental influence of the aircraft, particularly the material production and disposal process. At the same time, a contrast with the B737-800 aircraft will be made due to their different composite material use rate. Firstly, the inventory list is formed by collecting data about the weight and material of every component in the aircraft, the input and output information of the composite material manufacturing process, the disposal situation of the aircraft and the treatment of composite material. Secondly, the impact assessment of the aircraft is conducted to examine their environmental influence. During the assessment, each life stage and the whole life cycle of the aircrafts is assessed, and a comparison between these two aircraft types is made. Finally, according to the impact assessment result, the environment load increase brought by the manufacturing of composite material and the decrease of the environment impact due to the weight reduction character of composite material is calculated and compared. From this research, the conclusion that the use of composite material has a positive effect on decreasing the environmental impact of the whole life cycle of the aircraft is obtained. This will enable aircraft manufacturers to target these reas for improvement, to produce more comfortable, environment friendly and market competitive aircraft.
  • Thumbnail Image
    ItemOpen Access
    Molecular studies of confined liquids and nanofluids for passive thermal management
    (2015-03) Frank, Michael; Drikakis, Dimitris; Asproulis, N.; Murray, Angus;
    The constant technological advances in integrated circuits and electronic systems experienced over the last few years have resulted in large temperature gradients. These can damage electronic devices. Current cooling methods are unable to cope with highly demanding applications such as military systems. Furthermore, for applications in which failure is not an option, a lack of sufficient thermal management can be a limiting factor in the design and addition of functionality. The aim of this research project is to provide possible solutions to the overheating of electronics. Following an in depth review of the state-of-the-art in cooling technologies, we have identified nanofluidics and nanofluids as promising candidates for thermal management. However, systems characterised by such small dimensions are governed by surface phenomena. Sometimes, continuum computational methods such as Computational Fluid Dynamics (CFD) are inadequate in providing a detailed description of such effects. Instead, molecular methods, such as Molecular Dynamics (MD), study systems at a higher resolution and can potentially provide a more accurate understanding of such systems. This thesis uses MD to understand how the thermodynamic properties of liquids and nanofluids are modified by spatial restrictions. An important finding is that heat is transferred differently in confined and unconfined liquids. Following this realisation, an analysis of the system parameters is carried out to understand how to optimise the heat conductance of such systems. We also consider confined nanofluids. Different materials are modelled and compared with respect to their possible practical use as thermal management agents. The thermodynamic behaviour discovered has not been described elsewhere and has potentially high practical importance. Although in its infancy, we believe that it can eventually provide a framework for the design of efficient cooling devices.
  • Thumbnail Image
    ItemOpen Access
    Wind farm and environmental aerodynamics assessment using computational engineering
    (Cranfield University, 2011-08) Zoumprouli, Argyro; Asproulis, N.
    The aim of this thesis is the application of computational engineering software for the study of wind resource assessment of a wind farm as well as for establishing the range of influence of different numerical and physical parameters, including turbulence modeling , surface roughness and wakes. Simulations were performed for a wind farm which is in operation since 2006, called Panachaiko, located at the west part of Greece and encompassing an energy capacity of 34.85 MW. Simulations were performed using three variants of the k-ε model. Moreover, the effects of surface roughness and wake on the efficiency of wind farm operation were investigated. Comparisons were performed between linear and non-linear computational fluid dynamics (CFD) modeling, in the framework of the available engineering (commercial) software. Both qualitative and quantitative assessment of the results is presented. The study revealed the dependence of the results on the CFD (linear vs non-linear) model employed. The results of the present study provide useful guidance regarding the applicability of CFD models for wing resource assessment.