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Wp-2 basic investigation of transition effect
No full textAn important goal of the TFAST project was to study the effect of the location of transition in relation to the shock wave on the separation size, shock structure and unsteadiness of the interaction area. Boundary layer tripping (by wire or roughness) and flow control devices (Vortex Generators and cold plasma) were used for boundary layer transition induction. As flow control devices were used here in the laminar boundary layer for the first time, their effectiveness in transition induction was an important outcome. It was intended to determine in what way the application of these techniques induces transition. These methods should have a significantly different effect on boundary layer receptivity, i.e. the transition location. Apart from an improved understanding of operation control methods, the main objective was to localize the transition as far downstream as possible while ensuring a turbulent character of interaction. The final objective, involving all the partners, was to build a physical model of transition control devices. Establishing of such model would simplify the numerical approach to flow cases using such devices. This undertaking has strong support from the industry, which wants to include these control devices in the design process. Unfortunately only one method of streamwise vortices was developed and investigated in the presented study
Wp-1 reference cases of laminar and turbulent interactions
No full textIn order to be able to judge the effectiveness of transition induction in WP-2, reference flow cases were planned in WP-1. There are two obvious reference cases—a fully laminar interaction and a fully turbulent interaction. Here it should be explained that the terms “laminar” and “turbulent” interaction refer to the boundary layer state at the beginning of interaction only. There are two basic configurations of shock wave boundary layer interaction and these are a part of the TFAST project. One is the normal shock wave, which typically appears at the transonic wing and on the turbine cascade. The characteristic incipient separation Mach number range is about M = 1.2 in the case of a laminar boundary layer and about M = 1.32 in the case of turbulent boundary layer. The second typical flow case is the oblique shock wave reflection. The most characteristic case in European research is connected to the 6th FP IP HISAC project concerning a supersonic business jet. The design speed of this airplane is M = 1.6. Therefore the TFAST consortium decided to use this Mach number as the basic case. Pressure disturbance at this Mach number is not very high and can be compared to the disturbance of the normal shock at the incipient separation Mach number mentioned earlier. As mentioned earlier, shock reflection at M = 1.6 may be related to incipient separation. Therefore two additional test cases were planned with different Mach numbers. ITAM conducted an M = 1.5 test case, and TUD an M = 1.7 test case. These partners have also previously made very specialized and successful contributions to the UFAST project
Failure of a pre-cracked epoxy sandwich layer in shear
No full textAdhesive joints are frequently used in automotive, maritime and construction applications, yet joint reliability remains a concern. The purpose of this study is to develop a fracture mechanics methodology for the failure of an elastic-brittle lap-shear joint comprising a thick adhesive layer (an epoxy, of thickness on the order of 10 mm) sandwiched between thick steel adherends. This configuration is of practical application to ship-building, such as the bonding of a superstructure to the underlying hull. A modified thick-adherend shear test (TAST) is designed, and specimens are fabricated, with a range of interfacial pre-crack length and a range of adhesive layer thickness. The failure of samples with no pre-crack is governed by a critical value of corner singularity, whereas the failure of samples with long pre-cracks is governed by a critical value of interfacial stress intensity factor. Predictions for the dependence of failure load upon layer thickness and pre-crack length are obtained by analysing the elastic stress state for both a corner singularity and for an interfacial crack. Both the experimental results and the theoretical framework are useful in the design and fabrication of reliable lap-shear joints that comprise a thick elastic adhesive layer
Generating minimal Pareto sets in multi-objective topology optimisation: an application to the wing box structural layout
No full textMulti-objective topology optimisation problems are often tackled by compromising the cost functions according to the designer’s knowledge. Such an approach however has clear limitations and usually requires information which especially at the preliminary design stage could be unavailable. This paper proposes an alternative multi-objective approach for the generation of minimal Pareto sets in combination with density-based topology optimisation. Optimised solutions are generated integrating a recently revised method for a posteriori articulation of preferences with the Method of Moving Asymptotes. The methodology is first tested on an academic two-dimensional structure and eventually employed to optimise a full-scale aerospace structure with the support of the commercial software Altair OptiStructⓇ. For the academic benchmark, the optimised layouts with respect to static and dynamic objectives are visualised on the Pareto frontier and reported with the corresponding density distribution. Results show a progressive and consistent transition between the two extreme single-objective layouts and confirm that the minimum number of evaluations was required to fill the smart Pareto front. The multi-objective strategy is then coupled with Altair OptiStruct and used to optimise a full-scale wing box, with the clear purpose to fill a gap in multi-objective topology optimisation applied to the wing primary structure. The proposed methodology proved that it can generate efficiently non-dominated optimised configurations, at a computational cost that is mainly driven by the model complexity. This strategy is particularly indicated for the preliminary design phase, as it releases the designer from the burden to assign preferences. Furthermore, the ease of integration into a commercial design tool makes it available for industrial applications
A conceptual study of a high gradient trapped field magnet (HG-TFM) toward providing a quasi-zero gravity space on Earth
No full textIn this work, we propose a new concept of a high gradient trapped field magnet (HG-TFM). The HG-TFM is made from (RE)BaCuO bulk superconductors, in which slit ring bulks (slit-TFMs) are tightly stacked with TFM cylinders (full-TFMs), and state-of-the-art numerical simulations were used to investigate the magnetic and mechanical properties in detail during and after magnetization. A maximum value of the magnetic field gradient product of = 6040 T2 m-1 was obtained after conventional field cooled magnetization (FCM) with an applied field, B app, of 10 T of the HG-TFM with 60 mm in outer diameter and 10 mm in inner diameter. This value may be the highest value ever reported compared to any other magnetic sources. The value increased with decreasing inner diameter of the HG-TFM and with increasing B app during FCM. The electromagnetic stress in the HG-TFM during the FCM process mainly results from the hoop stress along the circumferential direction. The simulations suggested that there is no fracture risk of the bulk components during FCM from 10 T in a proposed realistic configuration of the HG-TFM where both TFM parts are mounted in Al-alloy rings and the whole HG-TFM is encapsulated in a steel capsule. A quasi-zero gravity space can be realized in the HG-TFM with a high value in an open space outside the vacuum chamber. The HG-TFM device can act as a compact and cryogen-free desktop-type magnetic source to provide a large magnetic force and could be useful in a number of life/medical science applications, such as protein crystallization and cell culture
Erratum: A new benchmark problem for electromagnetic modelling of superconductors: The high-T<inf>c</inf> superconducting dynamo (Superconductor Science and Technology (2020) 33 (105009) DOI: 10.1088/1361-6668/abae04)
No full textSince publication, we have realized that the results from the minimum electromagnetic entropy (MEMEP) method (see section 3.3 in the original paper [1]) used a different voltage definition, causing a slight discrepancy with the results obtained from the other methods in figures 3 and 4. Instead of Veq (t) = −LEave (t), as given by equation (5) in [1], we used −∆V(t) as defined by equation (22) in [2]: ∆V ≈ L· [∂tAav,J + Eave (J)] . Although both definitions result in the same DC voltage, the instantaneous signal differs, as shown in figure 1 in this corrigendum. Indeed, the used ∆V for the MEMEP method in [1] adds an extra contribution, ∂tAav,J, the vector potential due to the superconducting current. As a result, the new curve has much better qualitative and quantitative agreement with the waveforms calculated by the other methods shown in figure 3 of the original article [1]. In the original article [1], we also used the −∆V(t) definition above instead of Veq (t) to calculate the cumulative time-averaged equivalent voltage, defined from equation (6) in [1] as t Vcumul (t) = 1t Veq (t) dt. 0 The new results, using Veq (t) , present only small changes compared to the original calculations, as shown in figure 2 in this corrigendum. This curve also has very good qualitative and quantitative agreement with the waveforms calculated by the other methods, as shown in figure 4 in the original article [1]. The data related to the new calculations for this corrigendum are available at the University of Cambridge data repository (https://doi.org/10.17863/CAM.60437)
Scalar fluctuation and its dissipation in turbulent reacting flows
No full textThe dissipation rate of a scalar variance is related to the mean heat release rate in turbulent combustion. Mixture fraction is the scalar of interest for non-premixed combustion, and a reaction progress variable is relevant for premixed combustion. A great deal of work is conducted in past studies to understand the spectra of passive scalar transport in turbulent flows. A very brief summary of these studies to bring out the salient characteristics of the passive scalar spectrum is given first. Then, the classical analysis of the reactive scalar spectrum is revisited in the lights of recent understanding gained through analyzing the scalar spectrum deduced from direct numerical simulation data of both non-premixed and premixed combustion. The analysis shows that the reactive scalar spectral density in premixed combustion has a dependence on Karlovitz and Damköhler numbers, which comes through the mean scalar dissipation rate appearing in the spectral expression. In premixed combustion, the relevant scale for the scalar dissipation rate is shown to be of the order of the chemical length scale, and the dissipation rate is not influenced by the scales in the inertial-convective range unlike for the passive scalar dissipation rate. The scalar fluctuations produced near the chemical scales cascade exponentially to larger scales. These observations imply that the passive scalar models cannot be extended to premixed combustion
Capacity planning and optimization for integrated energy system in industrial park considering environmental externalities
No full textThe integrated energy system (IES) is developing rapidly duo to its high energy efficiency and environmental protection. Environmental protection is an advantage of IES, and the costs of environmental externalities should be considered in the construction cost of IES in industrial parks. This paper considered the environmental externalities of coal, wind and photovoltaic power generation of industrial park IES (IP-IES) as a part of the unit cost of IP-IES, and constructed a capacity planning and optimization model, whose objective function is to minimize the cost per unit power generation. Subsequently, particle swarm optimization (PSO) is adopted into the model, and the model results are compared to the actual values, in order to determine the reasonable ratios of various types of capacity. Case study results show that: (1) considering environmental externality costs, photovoltaic and wind power have an advantage over thermal power. (2) Reasonable capacity planning can reduce the unit power generation cost
Characterisation of Strain-Hardening Cementitious Composite (SHCC) Under Cyclic Loading Conditions for Self-healing Applications
No full textThe ground shaking in an earthquake often imposes cyclic loadings on infrastructures placing them in danger. Concrete is quasi-brittle in tension and easy to crack under cyclic loadings. Fibre reinforced strain-hardening cementitious composites (SHCC) featuring high ductility, high energy absorbing capacity and controlled multiple cracking have been proposed for seismic-resistant applications. The fine cracks have been proved to not only improve the durability but also enhance the autogenous self-healing ability. This study focuses on investigating the material behaviour and self-healing potential of SHCC under cyclic flexural loading conditions. Four-point flexural tests (including monotonic and cyclic tests) were performed to study its mechanical properties and cracking behaviour. The surface crack widths were measured by optical microscopy. Results showed that 28-day air cured specimens exhibited a deflection capacity of up to 9.6 mm and an average crack width of 28 μm under monotonic flexural loading. Regarding the flexural stress-deflection curves, the envelops of cyclic testing results were close to monotonic results with both elastic and hardening phases. SHCC could still maintain fine crack widths (below 60 μm) under cyclic loading conditions. SEM/EDX test was conducted to investigate the fibre-matrix interface
Simulating the molecular density distribution during multi-phase fluid intrusion in heterogeneous media
No full textA computational recovery of multi-phase intrusion was discussed with the modified multi-relaxation time Lattice Boltzmann method (MRT-LBM). Originally proposed dual-matrix computation is developed to address the different phase separation and interface tracking for the multi-phase problem. A comprehensive validation is performed with the previously theorized observation of the mercury-water system. Results show that the dual-matrix computation is feasible to provide converged output under narrowed density difference down to 18%. The wetting and non-wetting behaviour resulted from form solid–fluid interaction is realized with arbitrary boundaries, in which the contact variance is up to 4.14%. The linear relations described by Laplace's law and Washburn's equation were three-dimensionally recovered with determination coefficients of 96.34% and 94.19%, respectively. A third fluid intrusion status of partial-intrusion is captured in addition to complete-intrusion and non-occupation in porous boundary, demonstrating the advanced function of the phase-separation and interface tracking in problems with further increased heterogeneity