Vibration Damping of Lightweight Sandwich Structures

Honeycomb-cored sandwich structures are widely used in transport for their high strength-to-mass ratio. Their inherent high stiffness and lightweight properties make them prone to high vibration cycles which can incur deleterious damage to transport vehicles. This PhD thesis investigates the performance of a novel passive damping treatment for honeycomb-cored sandwich structures, namely the Double Shear Lap-Joint (DSLJ) damper. It consists of a passive damping construct which constrains a viscoelastic polymer in shear, thus dissipating vibrational energy. A finite element model of such DSLJ damper inserted in the void of a hexagonal honeycomb cell is proposed and compared against a simplified analytical model. The damping efficiency of the DSLJ damper in sandwich beams and plates is benchmarked against that of the Constrained Layer Damper (CLD), a commonly used passive damping treatment. The DSLJ damper is capable of achieving a higher damping for a smaller additional mass in the host structure compared to the optimised CLD solutions found in the literature. The location and orientation of DSLJ inserts in honeycomb sandwich plates are then optimised with the objective of damping the first two modes using a simple parametric approach. This method is simple and quick but is not robust enough to account for mode veering occurring during the optimisation process. A more complex and computationally demanding evolutionary algorithm is subsequently adopted to identify optimal configurations of DSLJ in honeycomb sandwich plates. Some alterations to the original algorithm are successfully implemented for this optimisation problem in an effort to increase the convergence rate of the optimisation process. The optimised designs identified are manufactured and the modal tests carried out show an acceptable correlation in the trends identified by the numerical simulations, both in terms of damping per added mass and natural frequencies.Interreg IV-A and ERDF (Material for Energy Efficiency in Transport

Development of Pea (Pisum sativum L.) and Chickpea (Cicer arietinum L.) Snacks using Different Cooking Methods

The research objectives were: to evaluate the quality of a pea snack prepared using four different methods of cooking, namely, frying, baking, steaming and microwave; to determine the effect of blending dried green pea with chickpea dhal on the quality of a fried pea snack. Green pea and chickpea snacks were prepared according to a traditional Mauritian recipe by using dried green pea and chickpea dhal respectively. Instrumental colour (CIE L*a*b*) and texture (shear force) were measured. Moisture content was determined by the air-oven drying method and fat content was quantified by the soxhlet extraction method. Quantitative Descriptive Analysis was performed by 7 experienced assessors of CFTRI using 15 cm line scales. The fried green pea snack obtained highest score for “crispy” and lowest score for “moist” texture attributes compared to the nonfried snacks (p<0.05). Higher instrumental shear force values were recorded for fried snacks than those which were cooked by other methods (p<0.05). Shear force was lowest for the steamed green pea snack (4.33±0.07 N) and highest for the fried green pea snack (20.89±0.93 N) (p<0.05). The CIE L* (lightness) values of the snack surface showed that the fried snacks were darker than the non-fried snacks (p<0.05). The fried snacks were characterised by positive CIE a*, representing red colour, with the highest value obtained for the chickpea snack (9.77±0.18) (p<0.05). On the other hand, the CIE a* results for the nonfried snacks were negative, representing green colour, with the lowest value noted for the steamed green pea snack (-2.33±0.44) (p<0.05). The fried pea snack was found to have much higher fat content than the non-fried snacks: fried snack (27.94 % w/w, wet weight basis); non-fried snacks (1.20-2.75% w/w/, wet weight basis). The reverse trend was observed for the moisture content data: fried snack (39.86% w/w, wet weight basis); non-fried snacks (45.56-68.10% w/w, wet weight basis). The sensory scores for the snack prepared with equal proportion of green pea and chickpea radiated a picture which was intermediate between the trends for the fried green pea and fried chickpea snacks. Sensory scores for “fried oil” and “onion” flavour characteristics were highest for the fried green pea snack while the fried chickpea snack obtained highest score for “pulsey” flavour and lowest score for “greenish inner core” (p<0.05). Significant correlations were established between sensory scores for colour and texture, as well as colour and flavour characteristics. Correlations between instrumental and sensory data for colour and texture parameters were also significant. The fried and non-fried snacks were comparable in terms of overall quality scores given by assessors.Keywords: green pea, chickpea, snack, frying, steaming, baking, microwave cooking, sensory characteristics, qualit

A novel viscoelastic damping treatment for honeycomb sandwich structures

Journal ArticleCopyright © 2015 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Composite Structures. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Composite Structures Vol. 119 (2015), DOI: 10.1016/j.compstruct.2014.09.005Constrained layer dampers (CLD) are in widespread use for passive vibration damping, in applications including aerospace structures which are often lightweight. The location and dimensions of CLD devices on structures has been the target of several optimisation studies using a variety of techniques such as genetic algorithms, cellular automata, and gradient techniques. The recently developed double shear lap-joint (DSLJ) damper is an alternative method for vibration damping, and can be placed internally within structures. The performance of the DSLJ damper is compared in a parametric study with that of CLD dampers on beam and plate structures under both cantilever and simply supported boundary conditions, using finite element analysis. The objective was to determine which damper and in which configuration produced the highest modal loss factor and amplitude reduction for least added mass, as would be important for lightweight applications. The DSLJ tend to be more mass efficient in terms of loss factor and amplitude reduction for cantilevered beam and plate structure, and are competitive with CLD dampers in simply supported beam and plate structures. The DSLJ works well because it has the potential to magnify global flexural deformation into shear deformation in the viscoelastic more effectively than traditional CLD dampers.MEET project (Material for Energy Efficiency in Transport) in the context of the INTERREG IV A France (Channel) – England European cross-border co-operation programme, which is co-financed by ERDF

Navigating through peaks and valleys: Public space and water infrastructure as intervention tools for urban regeneration in Kigali, Rwanda

Current methods of urban regeneration, more specifically as practiced in Rwanda, are totally devoid of socially inclusive approaches, and highly lack contextual adaptability. In the aftermath of the genocide of 1994, which plundered the country's resources and human capita, Rwanda has undergone various states of reconstruction - socially, economically and architecturally. Over the past two decades, Kigali, Rwanda’s capital city, has been building up its momentum of development towards translating itself into a dynamic urban hub, aiming at attracting foreign investors to boost the local economy. In 2007, the government adopted the Kigali Conceptual Master Plan, branding Kigali as a city of character, vibrant economy and diversity. Since then, various alterations of the masterplan have been issued. Today, Kigali’s skyline is dominated by steel, glass and concrete megastructures, in the image of 'modernity'. However, these efforts at transforming Kigali into a city anchored on Western standards are completely disconnected from the current socio-cultural, ecological and economic dynamics. The masterplan promotes the annihilation of the informal areas within the city, which account for the dwelling area of 66% of Kigali's population. It also dismisses the undulating topography and communal significance of Kigali's wetlands to informal dwellers. Consequently, the latter remain deeply vulnerable, constantly living under the fear of being evicted or relocated, while the wetland valleys, currently under serious ecological threat, are destined to be converted into parks reserved for the elite. Through the critique of current methods and proposals of urban revitalisation, this thesis advocates for a more inclusive approach to urban planning, and promotes urban development lying in the interest of every strata of Rwandan society. The work dwells into how wetlands can be utilised as a backbone for urban revitalisation by optimising the potential of Kigali’s watershed to provide adequate infrastructure that consolidates existing community relationships. The juxtaposition of ecology, infrastructure and architecture opens the possibilities for various patterns of incremental growth, while remaining sensitive to the social, environmental and cultural dimensions of the urban fabric. The design strategy proposes a framework supporting enhanced livability based on the dimensions of society, economy, biodiversity, and sustainable development. The framework is explored through three nodes, each with its own specific challenges, and focusses primarily on restoring water quality and wetland ecology through a decentralised, human-centric set of interventions. This work also showcases how the framework allows for continuous growth in the medium and long term, remaining in complete synchronisation with the altering dynamics of Kigali's emerging society. In contexts like Rwanda, where peace and conflict are sensitive and controversial matters, this thesis demonstrates how design can not only build communities and trigger tenacious social relations, but also how it can act as a gentle and subversive form of questioning the status quo

Reinforcement Learning Experiments and Benchmark for Solving Robotic Reaching Tasks

Reinforcement learning has shown great promise in robotics thanks to its ability to develop efficient robotic control procedures through self-training. In particular, reinforcement learning has been successfully applied to solving the reaching task with robotic arms. In this paper, we define a robust, reproducible and systematic experimental procedure to compare the performance of various model-free algorithms at solving this task. The policies are trained in simulation and are then transferred to a physical robotic manipulator. It is shown that augmenting the reward signal with the Hindsight Experience Replay exploration technique increases the average return of off-policy agents between 7 and 9 folds when the target position is initialised randomly at the beginning of each episode

rl_reach: Reproducible reinforcement learning experiments for robotic reaching tasks

rl_reach is publicly available at this URL: https://github.com/PierreExeter/rl_reach[EN] Training reinforcement learning agents at solving a given task is highly dependent on identifying optimal sets of hyperparameters and selecting suitable environment input/output configurations. This tedious process could be eased with a straightforward toolbox allowing its user to quickly compare different training parameter sets. We present rl_reach, a self-contained, open-source and easy-to-use software package designed to run reproducible reinforcement learning experiments for customisable robotic reaching tasks. rl_reach packs together training environments, agents, hyperparameter optimisation tools and policy evaluation scripts, allowing its users to quickly investigate and identify optimal training configurations. rl_reach is publicly available at this URL: https://github.com/PierreExeter/rl_reachSIEuropean Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 713654

Optimised location and orientation of passive viscoelastic dampers for lightweight sandwich structures

PublishedPaper presented at 16th International Conference on Experimental Mechanics, 7th to 11th July 2014. University of Cambridge UKThe recently developed Double Shear Lap-Joint (DSLJ) damper technology is a new device which can be placed internally within lightweight structures. This work considers the optimal location and orientation of DSLJ dampers within a simplified honeycomb sandwich structure, as an example of a lightweight structure subject to vibration, under typical idealised boundary conditions. The Pareto Archived Evolutionary Strategy was used as a multi-objective algorithm to maximise the modal loss factor whilst minimising the additional mass of the DSLJ inserts. Optimal configurations of DSLJ insert arrays within the sandwich core were identified for several of the dominant vibration modes

Multi-objective optimisation of viscoelastic damping inserts in honeycomb sandwich structures

PublishedArticleAccepted ManuscriptThe Double-Shear Lap Joint (DSLJ) is a novel damping insert sited internally within a structure which is particularly well suited for lightweight sandwich structures with internal voids, such as honeycomb core sandwich panels. In high performance lightweight structures, the insertion of relatively more dense dampers of any type may increase the total mass substantially and alter the mass distribution significantly. The objective herein was to determine the optimum location, number and orientation of DSLJ inserts within a typical sandwich panel, and thereby to assess the efficacy of two different optimisation approaches to this problem; a parametric optimisation and the Adaptive Indicator-Based Evolutionary Algorithm (IBEA). Both approaches were used to maximise the damping while minimising the additional mass of the damping inserts applied to the structure. Although the parametric approach was faster and easier to implement, the Adaptive IBEA identified significantly better configurations in many cases, especially where veering occurred, in one case improving modal loss factors more than fourfold vs the parametric method. Solutions were identified with large increases in modal loss factors but only small increases in mass vs the empty structure.This work was supported by the MEET project (Material for Energy Efficiency in Transport) in the context of the INTERREG IV-A France (Channel) England European cross-border co-operation programme, which is co-financed by the ERDF