Search results

The high probability of the occurrence of separation bubbles or shocks and early transition to turbulence on surfaces of airfoil makes it very difficult to design high-lift and high-speed Natural-Laminar-Flow (NLF) airfoil for high-altitude long-endurance unmanned air vehicles. To resolve this issue, a framework of uncertainty-based design optimization (UBDO) is developed based on an adjusted polynomial chaos expansion (PCE) method.

The γ ̄Re-θt transition model combined with the shear stress transport k-ω turbulence model is used to predict the laminar-turbulent transition. The particle swarm optimization algorithm and PCE are integrated to search for the optimal NLF airfoil. Using proposed UBDO framework, the aforementioned problem has been regularized to achieve the optimal airfoil with a tradeoff of aerodynamic performances under fully turbulent and free transition conditions. The tradeoff is to make sure its good performance when early transition to turbulence on surfaces of NLF airfoil happens.

The results indicate that UBDO of NLF airfoil considering Mach number and lift coefficient uncertainty under free transition condition shows a significant deterioration when complicated flight conditions lead to early transition to turbulence. Meanwhile, UBDO of NLF airfoil with a tradeoff of performances under both fully turbulent and free transition conditions holds robust and reliable aerodynamic performance under complicated flight conditions.

In this work, the authors build an effective uncertainty-based design framework based on an adjusted PCE method and apply the framework to design two high-performance NLF airfoils. One of the two NLF airfoils considers Mach number and lift coefficient uncertainty under free transition condition, and the other considers uncertainties both under fully turbulent and free transition conditions. The results show that robust design of NLF airfoil should simultaneously consider Mach number, lift coefficient (angle of attack) and transition location uncertainty.

In recent years, the airfoil sections with blunt trailing edge (called flatback airfoils) have been proposed for the inboard regions of large wind‐turbine blades because they provide several structural and aerodynamic performance advantages. The purpose of this paper is to optimize the shape of these airfoils for optimal performance using a multi‐objective genetic algorithm.

A multi‐objective genetic algorithm is employed for shape optimization of flatback airfoils to achieve two objectives, namely the generation of maximum lift as well as the maximum lift to drag ratio. The commercially available software FLUENT is employed for calculation of the flow field using the Reynolds‐Averaged Navier‐Stokes (RANS) equations in conjunction with a two‐equation Shear Stress Transport (SST) turbulence model and a three‐equation k‐kl‐ω turbulence model.

It is shown that the multi‐objective genetic algorithm based optimization can generate superior flatback airfoils compared to those obtained by using a single objective genetic algorithm.

The method of employing genetic algorithms for shape optimization of flatback airfoils could be considered as an excellent example for the optimization of other types of wind turbine blades such as DU FX and S series airfoils.

This paper is the first to employ the multi‐objective genetic algorithm for shape optimization of flatback airfoils for wind‐turbine blades to achieve superior performance.

The purpose of this paper is to identify the cognitive biases of consumer and explain how they are creating barriers in transition towards circular economy (CE).

This is a conceptual paper which adopts a consumer-centric conceptualization of CE by focussing on cognitive biases as an underlying and unifying mechanism which is creating barriers in the adoption of CE. This conceptualization explains consumers’ non-adoption of circular business model, highlight synergies across disconnected theories and streams of research originating in different disciplines and at the individual, societal and cultural levels of analysis.

The findings of this paper suggest that circular business models are not fulfilling the psychological, social and cultural needs of the consumers and that in turn lead to barriers in diffusion of the CE. Consumers have a negative connotation with the different circular business model due to their cognitive biases.

The paper details about key implications to design effective interventions to modify consumer behaviour in the desired direction for hassle-free transition to CE from the linear economy.

This paper offers a shift in CE research from a deterministic approach to conceptualising consumers to a positivist approach to conceptualising consumers.

The main purpose of this paper is to investigate the effects of icing on unmanned aerial vehicles (UAVs) at low Reynolds numbers and to highlight the differences to icing on manned aircraft at high Reynolds numbers. This paper follows existing research on low Reynolds number effects on ice accretion. This study extends the focus to how variations of airspeed and chord length affect the ice accretions, and aerodynamic performance degradation is investigated.

A parametric study with independent variations of airspeed and chord lengths was conducted on a typical UAV airfoil (RG-15) using icing computational fluid dynamic methods. FENSAP-ICE was used to simulate ice shapes and aerodynamic performance penalties. Validation was performed with two experimental ice shapes obtained from a low-speed icing wind tunnel. Three meteorological conditions were chosen to represent the icing typologies of rime, glaze and mixed ice. A parameter study with different chord lengths and airspeeds was then conducted for rime, glaze and mixed icing conditions.

The simulation results showed that the effect of airspeed variation depended on the ice accretion regime. For rime, it led to a minor increase in ice accretion. For mixed and glaze, the impact on ice geometry and penalties was substantially larger. The variation of chord length had a substantial impact on relative ice thicknesses, ice area, ice limits and performance degradation, independent from the icing regime.

The implications of this manuscript are relevant for highlighting the differences between icing on manned and unmanned aircraft. Unmanned aircraft are typically smaller and fly slower than manned aircraft. Although previous research has documented the influence of this on the ice accretions, this paper investigates the effect on aerodynamic performance degradation. The findings in this work show that UAVs are more sensitive to icing conditions compared to larger and faster manned aircraft. By consequence, icing conditions are more severe for UAVs.

Atmospheric in-flight icing is a severe risk for fixed-wing UAVs and significantly limits their operational envelope. As UAVs are typically smaller and operate at lower airspeeds compared to manned aircraft, it is important to understand how the differences in airspeed and size affect ice accretion and aerodynamic performance penalties.

Earlier work has described the effect of Reynolds number variations on the ice accretion characteristics for UAVs. This work is expanding on those findings by investigating the effect of airspeed and chord length on ice accretion shapes separately. In addition, this study also investigates how these parameters affect aerodynamic performance penalties (lift, drag and stall).

Product development in most industries is often done today in a global engineering network (GEN). More recently, there has been a clear shift to using development resources from the so‐called “emerging countries” (ECs) that have growing domestic market, highly skilled workforce, and low labor cost base. The integration of resources from ECs, whether from the company's own businesses there or from external suppliers, poses a new challenge for collaborative work in a GEN. This paper aims to describe these challenges. Further, the process of transition to the use of resources from ECs is fraught with business risks. Further, seeks to discuss these risks and how they can be mitigated and to propose a model, derived from practice, to manage the transition process. The model comprises a set of foundation elements and location‐dependent transformation processes.

Product development teams in three businesses were studied – an automotive supplier, a manufacturer of made‐to‐order electrical equipment and a developer of automation software – over three years. These businesses were in the process of relocating some development activities to ECs. Two of the teams were assisted in this transition and the third observed and the model presented is an outcome of this involvement.

Successfully starting a global development team strategy requires clarity and transparency of strategy, good communication, proper organization of effort and focus on product and process standardization. Further, a set of change management processes needs to be launched at participating locations for competence build‐up and team building.

This model can be used by organizations setting up such EC‐IC teams to avoid the possibility of failure of such critical collaborative efforts.

There is considerable literature on distributed product development and virtual teams. The coverage includes management challenges, technology enablers and organizational and multi‐cultural challenges. However, the specific challenge of teams comprising membership from advanced and ECs is not covered. Further, while the literature deals with the operation of such teams it does not cover the sensitive transition or start‐up phase. This paper deals with this issue.

The High Density Packaging Users Group conducted a substantial study of the solder joint reliability of high‐density packages using lead‐free solder. The design, material, and assembly process aspects of the project are addressed in this paper. The components studied include many surface mount technology package types, various lead, and printed circuit board finishes and paste‐in‐hole assembly.