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Key enablers for the evolution of aerospace ecosystems
No full textThe aerospace industry is experiencing an unprecedented scenario. The air travel drifted from years of constant growth and positive expectations to a place where the uncertainty is the most predominant distinctive. Consequently, the aerospace ecosystem needs to adapt to cope with challenges never faced before. Understanding the evolution of the aerospace ecosystem is thus essential to foster its progression. This research aims at the identification and categorisation of key enablers that have been linked to the growth of aerospace ecosystems. To this extent, key enablers are first identified and then categorised using interpretive structural modelling (ISM) and cross-impact matrix multiplication applied to classification (MICMAC) methodologies. An analysis is elaborated for a developed aerospace ecosystem, the United Kingdom, and an emergent aerospace ecosystem, Mexico. Results evidence a contrasting categorisation of key enablers among both ecosystems. On the other hand, the automotive ecosystem and geopolitical factors are considered as underpinning enablers for both aerospace ecosystems evolution
How natural flood management helps downstream urban drainage in various storm directions
No full textThe wider benefits of natural flood management are increasingly used to engage local stakeholders and justify physical implementation. Previous studies have highlighted the potential for upstream natural flood management interventions to contribute to water level management strategies by mitigating downstream water levels and promoting free discharge at surface drainage outfalls from urban areas. The study reported in this paper extended the scope of this possible benefit by examining the potential for upstream interventions to de-synchronise rural and urban responses under various storm tracks, thereby improving the performance of downstream surface drainage networks. The methodology used a coupled modelling approach. Five design events, each applied with eight different storm tracks, were used to evaluate how catchment-scale natural flood management in the upper Calder River, UK, might influence performance of surface drainage in the downstream town of Todmorden. The results suggested that all the storm tracks considered had substantial influence on whether urban rainfall occurs during the period when outfalls are inundated. While upstream natural flood management interventions create modest flow attenuation, a slight delay in rural response can significantly improve drainage performance and reduce instances of nuisance flooding
Finite element modeling of buildings with structural and foundation rocking on dry sand
No full textAllowing structures to rock during an earthquake can effectively provide base isolation at a relatively small cost. Rocking limits the base shear demand and provides self-centering, but the rocking response depends on energy dissipation caused by interaction with the soil and impacts during re-centering. This paper addresses the computational modeling of buildings that have either been designed to rock on the soil beneath their foundation (foundation rocking) or at the foundation–structure interface (structural rocking). Within OpenSees, foundation and structural rocking were modeled using a beam-on-a-nonlinear-Winkler-foundation model (BNWF) combined with flat-slider elements for footing–soil and superstructure–footing interactions, respectively. The modified with flat-slider elements BNWF model (mBNWF) involves an uplift-dependent stiffness and viscous damping for both vertical and horizontal directions, and a friction–vertical force coupling. The proposed computational model was used to simulate an extensive set of centrifuge tests involving both structural rocking and foundation rocking with sequential excitations. Generally, the proposed modeling approach, without calibration of built-in parameters, adequately captured the response observed in centrifuge experiments. More specifically, the modeling captured the response amplitude and waveform of story accelerations and building rocking angle in most cases, but including potential nonlinear behavior caused by previous ground excitations was in some cases critical to obtain reasonable predictions. This was more profound for foundation rocking due to its inherent dependency on the soil strength and energy dissipation; for structural rocking previous nonlinear response primarily affected the transition time between full contact and rocking, but had a smaller effect on the prediction of maximum response
Gaussian Process Regression for Materials and Molecules.
No full textWe provide an introduction to Gaussian process regression (GPR) machine-learning methods in computational materials science and chemistry. The focus of the present review is on the regression of atomistic properties: in particular, on the construction of interatomic potentials, or force fields, in the Gaussian Approximation Potential (GAP) framework; beyond this, we also discuss the fitting of arbitrary scalar, vectorial, and tensorial quantities. Methodological aspects of reference data generation, representation, and regression, as well as the question of how a data-driven model may be validated, are reviewed and critically discussed. A survey of applications to a variety of research questions in chemistry and materials science illustrates the rapid growth in the field. A vision is outlined for the development of the methodology in the years to come
Crack-resistant cement–bentonite cut-off wall materials incorporating superabsorbent polymers
No full textPreserving the integrity of cement–bentonite cut-off walls, particularly in aggressive environments, is critical to their serviceability in polluted sites. The hardened cement–bentonite material in cut-off walls is highly susceptible to desiccation and wet–dry cycles, commonly leading to cracking. The objective of the work presented in this paper was to develop crack-resistant cement–bentonite cut-off wall materials subject to wet–dry cycles. Superabsorbent polymers (SAPs), which are cross-linked polymers that can absorb and retain a large amount of water and swell as a result, were employed for this purpose. It is found that the added SAPs increased the compressive strength by decreasing the water-to-cement ratio and that the strain at failure also increased due to energy dissipative and reinforcement effects. In addition, crack resistance was greatly improved under the imposed wet–dry cycles as the matrix suction was reduced as a result of the reduction of the contact between the free pore water and cement–bentoniteparticlesandtheincreaseoftheporesizeinthematrix. The morphology and microstructure of the interconnected foam network formed by the SAP films in the matrix were identified with SEM-EDX and micro-CT scan analyses. The results demonstrated the significant potential for SAPs in the development of crack-resistant cement–bentonite cut-off wall materials
Numerical and experimental investigation of turbulent n-heptane jet-in-hot-coflow flames
No full textA turbulent n-heptane jet flame in a jet-in-hot-coflow burner is numerically and experimentally investigated, revealing distinct features of this fuel in a jet-in-hot-coflow burner. The RANS k-ε turbulence model is adopted in combination with a dynamic partially-stirred reactor (PaSR) combustion model. The simulation results are used to support newly-obtained experimental measurements of mean temperature, OH number density and normalised CH2O-PLIF signal values at several axial locations. The simulations capture the transitional phenomenon observed experimentally for the low coflow oxygen concentration case, which is determined to be due to the two chemical pathways which exist for the n-heptane fuel. The predicted flame weak-to-strong transition heights based on the streamwise (axial) gradient of OH number density show non-monotonic behaviour. Furthermore, an investigation on negative heat release rate region shows that the absolute value of negative heat release rate increases with reduced coflow oxygen content, in contrast to the suppression phenomenon seen in laminar opposed-flow flames
AC loss of Bi-2212 round wire at wide frequency ranges up to 500 kHz
No full textThe Bi-2212 round wire has a multifilamentary structure, and the use of numerical method to study ac loss of such multifilamentary superconducting wire requires a long calculation time and large memory. Adopting a homogenization method at low frequency to study the ac loss of multifilamentary structural wire/tape has been proven to have high enough accuracy and can save a lot of calculation time. With the expansion of the application range of superconducting materials, however, superconducting power devices exceeding the frequency of tens of kHz have huge potential applications in the future such as wireless power transfer. Therefore, it is necessary to study the applicability of the homogenization model at high frequencies. This article mainly presents an ac loss numerical study of Bi-2212 round wire at wider frequency (50 Hz-500 kHz) by homogenization method. The homogenization is achieved by two different methods. The first method is to treat the superconducting bundle and the Ag matrix between the bundles as a superconducting domain (bundle-matrix homogenized model, BHM). The second method is to regard the Ag matrix between the superconducting filaments and the filaments as a superconducting domain (filament-matrix homogenized model, FHM). In order to evaluate the feasibility of the two different homogenization methods, we compare the calculation results of the two different homogenization models with the original model, OM. The results show that the FHM can effectively improve the calculation speed while satisfying the high calculation accuracy. This conclusion can be used to quickly evaluate the ac energy loss of large-scale superconducting devices at wider frequencies
The Objective-Conflict-Resolution Approach: A Novel Approach for Developing Radical and Frugal Innovation
No full textDespite the interest in frugal innovation, both in research and in business practice, little is known about methods, approaches, or procedures that specifically support the systematic development of frugal innovations. In this article, we propose a novel approach that can be applied for developing frugal innovations, which also appears to be suitable for developing radical innovations. We present one in-depth case study that shows how the approach can be applied for successful concept development of a frugal and even radical innovation. The study follows an exploratory action research method conducted in a U.S. engineering company over 19 months. The action research resulted in a novel approach that we call objective-conflict-resolution (OCR). Applying this approach in the company led to the development of a frugal innovation - for which a patent application was submitted - that is significantly less expensive, requires fewer resources, and offers greater ease-of-use than previous solutions. The OCR approach has two main advantages over existing approaches. It can be applied for developing frugal and radical innovations when established approaches result in rather incremental solutions (such as value engineering) and is less complex and easier to implement than existing approaches that are deliberately used for developing radical solutions (such as TRIZ)
Extracting Information from Axle-Box Acceleration: On the Derivation of Rail Roughness Spectra in the Presence of Wheel Roughness
No full textRailhead roughness increases over time, leading to increased environmental noise and vibration. The use of axle-box acceleration (ABA) measurements on in-service railway vehicles to monitor rail roughness is potentially more cost-effective than other techniques. The measured acceleration requires signal processing to derive suitable metrics of railhead condition. A transfer function may be calibrated with direct roughness and ABA measurements made on a reference track, which may then be used to derive roughness spectra from subsequent ABA measurements. However, this approach is affected by variations in track dynamic behaviour, as well as variations in wheel roughness, which is inherently combined with rail roughness in the ABA measurement. This paper proposes an improved approach that (i) extracts the track’s dynamic stiffness parameters from the ABA measurements, enabling the derivation of the roughness-ABA transfer function for each section of track, and (ii) separates the wheel and rail roughness by synchronous averaging over several wheel revolutions. By accounting for variations in track properties and removing the influence of wheel roughness, initial modelling indicates that reliable measurements of rail roughness spectra can be obtained in practice
Examining the value of flexible logistics offerings
No full textIn the order fulfilment and retail industry, the provision of fast and low cost delivery services has received significant focus over the last decade. What is often neglected is other factors that contribute to a customer's overall experience like customisation and flexibility of deliveries, especially in cases when a customer's needs and plans change between order placement and order delivery. This paper explores the value of a flexible type of logistics offering in which the customer is able to change the order requirements (such as delivery date) after the order has been placed. In particular, we focus on the interactions between a retailer and a customer in agreeing and executing such logistics orders. We examine the benefits of this type of flexible logistics offerings because flexibility and customisation are critical factors for the success of omni-channel commerce. Such offerings are clearly connected with recent developments in digital technologies as these technologies are essential for the implementation. Our results indicate that flexible logistics offerings can be beneficial both for retailers and for customers. They also highlight the importance of receiving orders that do not fully meet the requirements of a customer