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Continuum mechanics is widely used to analyse the response of materials and structures to external loading conditions. Without paying attention to atomistic details, continuum mechanics can provide us very accurate predictions as long as continuum approximation is valid. There are various continuum mechanics formulations available in the literature. The most common formulation was proposed by Cauchy 200 years ago and the equation of motion for a material point is described by using partial differential equations. Although these equations have been successfully utilised for the analysis of many different challenging problems of solid mechanics, they encounter difficulties when dealing with problems including discontinuities such as cracks. In such cases, a new continuum mechanics formulation, peridynamics, can be more suitable since the equations of motion in peridynamics are in integro-differential equation form and do not contain any spatial derivatives. In nano-materials, material properties close to the surfaces can be different than bulk properties. This variation causes surface stresses. In this study, modified core–shell model is utilised to define the variation of material properties in the surface region by considering surface effects. Moreover, directional effective material properties are obtained by utilising analytical and peridynamic solutions.

A study has been conducted to evaluate the mechanical and fatigue crack propagation properties of wire + arc additively manufactured ER70S-6 components. A parallel-built deposition strategy was employed to fabricate the additively manufactured wall. The hardness values were slightly higher at the bottom and top of the wall due to the presence of Widmanstätten ferrite and carbides. The characterization of mechanical properties in both orientations; parallel and perpendicular to the deposition direction showed a marginal difference in yield strength and ultimate tensile strength. The crack growth rates were correlated with linear elastic fracture mechanics parameter ΔK and compared with an oscillation-built deposition strategy from the literature. The crack growth rates of both deposition strategies were found to be very similar to each other. Furthermore, it has been demonstrated that the variability in the crack growth histories can be reasonably well captured by using the NASGRO crack growth equation.

Interface creep cracking is very common to be seen in various kinds of welded components which are used widely in engineering practice. In the present paper, the interface creep crack tip field by considering material mismatch effect is studied. The interface creep crack is found to be close to the HRR field which can produce the faster creep crack growth rate. A material mismatch constraint parameter is proposed based on the validation of the local mismatch effect on the interface creep crack tip field which also maintains the self-similarity. An averaged material mismatch constraint M avg ∗ is presented to represent the material mismatch constraint effect. It reveals that the material mismatch constraint effect for interface creep crack decreases with the increase of the local mismatch factor. The physical meaning of the material mismatch constraint effect for the interface creep crack and its future application to engineering failure analysis is also discussed and presented.

The matrix component of composite structures is generally brittle. In any damage occurrence, fracture propagates rapidly through the structure. This study proposes a novel toughening enhancement model for unidirectional (UD) composites to overcome these damage-propagation issues. The toughening mechanism is established by introducing the so-called micro defects/cracks for increasing the toughness of the matrix constituent of the composite structure. Mechanical simulations are performed utilizing a non-local continuum formulation known as Peridynamics (PD). The PD formulation facilitates modeling material discontinuities such as complex crack/defect formations with arbitrary size, orientation, and location features in composite structures. Here, the toughening enhancement models are established by allocating various micro-crack formations in three different fiber orientations (0°, 45°, 90°) of UD composite plates. The toughening effects of micro-crack clusters are thoroughly analyzed by making comprehensive comparisons of the propagation speed of an initially introduced macro-crack and its tip strain energy density. As a result, various micro-crack distributions are established to provide an augmented toughness to the brittle composite materials, and their key features are assessed in detail.

One of the key challenges of uncertainty analysis in model updating is the lack of experimental data. The definition of an appropriate uncertainty quantification metric, which is capable of measuring as sufficient as possible information from the limited and sparse experimental data, is significant for the outcome of model updating. This work is dedicated to the definition and investigation of a general-purpose uncertainty quantification metric based on the sub-interval similarity. The discrepancy between the model prediction and the experimental observation is measured in the form of intervals, instead of the common probabilistic distributions which require elaborate experimental data. An exhaustive definition of the similarity between intervals under different overlapping cases is proposed in this work. A sub-interval strategy is developed to compare the similarity considering not only the range of the intervals, but more importantly, the distributed positions of the available observation samples within the intervals. This sub-interval similarity metric is developed to be capable of different model updating frameworks, e.g. the stochastic Bayesian updating and the interval model updating. A simulated example employing the widely known 3-dof mass-spring system is presented to perform both stochastic Bayesian updating and interval updating, to demonstrate the universality of the proposed sub-interval similarity metric. A practical experimental example is followed to demonstrate the feasibility of the proposed metric in practical application cases.

The design of an adsorption solar air conditioning system is investigated by using a model with an activated carbon–methanol working pair. This system is analysed with the solar insolation levels and ambient temperatures of Singapore. The proposed design mainly consists of two tubular reactor heat exchangers (TRHEXs) operating out of phase and driven by heat from an evacuated tube solar collector (ETSC). The pair of TRHEXs act as a thermal compressor and contain about 2.275 kg of activated carbon per reactor. The evacuated tube solar collector (ETSC) has better performance and is more cost effective than the flat plate solar collector (FPSC), even though it has a higher cost per unit. On the hottest day of the year, the proposed adsorption system has a maximum cooling power of 2.6 kW and a COP of 0.43 at a maximum driving temperature of 139 °C with a 9.8 m2 ETSC area. The system has a total estimated cost of EUR 10,550 corresponding to about SGD 14,800 with a 7-year payback time. At similar cooling capacities, the adsorption air conditioning system is expected to be more cost effective than the conventional system beyond an expected period of 7 years, with an expected lifetime of 15 to 20 years. Published version

The results of a study of environmental ageing on the apparent interfacial shear strength of glass fibre – vinyl ester microbond samples are presented. The scale related issues of estimating water absorption levels in microbond samples are reviewed and discussed and a solution based on Fickian diffusion is given. Interphase strength of microdroplets aged in water at 23 °C was relatively stable up to 6 days exposure after which strength degradation was fairly rapid. Immersion in water at 50 °C resulted in an immediate 20-30% irreversible loss of strength. Further exposure beyond 2 days led to total loss of integrity of the microbond samples. Electron microscope images of aged microdroplets appeared to show the development of a bi-phasic microstructure. The presence of two phases in small scale vinyl ester polymer samples was confirmed by DMA on thin films.

This paper provides a systematic approach to study the influence of electrical steel grade on electric vehicle traction motor performance. A permanent magnet assisted synchronous reluctance motor, an interior permanent magnet motor and an induction motor are considered to systematically quantify the influence of lamination thicknesses from 0.1 to 0.35mm, and materials with 3% and 6.5% silicon contents. Laminations with low silicon steel are better candidates in terms of peak and continuous torque production for low-speed operations. 0.1mm 6.5% silicon steel - 10JNEX900 can achieve higher efficiency and better flux-weakening capability above 400 Hz. Its higher mechanical strength is beneficial for complex rotor structure with bridges under stress from centrifugal forces. Therefore, grade choice relies on a compromise between low and high speed performance, propulsion system cost estimation and manufacturing challenges. Application related priorities define which grade is best suited.

In this paper, an Advanced Dynamic Model Predictive Control (AMPC) based on a Nonlinear Model Predictive Control (NMPC) framework with a multi-objective cost function driven by dynamic weights is proposed to improve the energy performance of fuel cell hybrid electric vehicles whilst prolonging their component lifetime. By the use of dynamic weights, the cost function is effectively formulated as the combination of fuel consumption, rate of change of fuel cell power, battery power, the fuel cell efficiency, state of charge of the battery, and their temperatures. In order to enhance the adaptability of the AMPC, a Fuzzy Cognitive Map (FCM) is then newly designed to regulate online the dynamic weights to adjust the importance of each cost component according to the conditions prevailing during driving. A comparative study between the proposed AMPC, a constant weight based NMPC and a conventional NMPC having cost function with fewer objectives has been carried out by means of simulation using a FCHEV model from the simulation tool ADVISOR to illustrate the efficacy of the proposed AMPC.

An accurate battery model is essential for battery management system (BMS) applications. However, existing models either don't describe battery physics or are too computationally intensive for practical applications. This paper presents a non-linear equivalent circuit model with diffusion dynamics (NLECM-diff) which phenomenologically describes the main electrochemical behaviours, such as ohmic, charge-transfer kinetics, and solid-phase diffusion. A multisine approach is applied to identify the elements for high frequency dynamics, as well as a distributed SoC dependent diffusion model block is optimised to account for long time dynamics. The model identification procedure is conducted on a three-electrode experimental cell, such that NLECM-diff models are developed for each electrode to then obtain the full cell voltage. Results imply that the NLECM-diff reduces the voltage root mean square error (RMSE) by 49.6% compared to a conventional ECM in the long duration discharge and has comparable accuracy to a parameterised SPMe in the NEDC driving cycle. Additionally, the variation of diffusion-related characteristics of the negative electrode under different currents is determined as the primary reason of the battery models' large low-SoC-range error. Furthermore, the diffusion process is determined as the dominant voltage loss contributor in the long duration discharge and the ohmic voltage loss is identified as the dominant dynamic under NEDC driving profile.

We present the large-scale, computational fluid dynamics (CFD) simulation of a full gas-turbine engine compressor, demonstrating capability towards overcoming current limitations for virtual certification of aero-engine design. The simulation is carried out through a performance portable codebase on multi-core/many-core HPC clusters with a CFD-to-CFD coupled execution, combining an industrial CFD solver linked using custom coupler software. The application innovates in its design for performance portability through the OP2 domain specific library for the CFD components, allowing the automatic generation of highly optimized platform-specific parallelizations for both multi-core (CPU) and many-core (GPU) clusters via a single high-level source. The code is used for the simulation of a 4.58B node, full-annulus 10-row production-grade test compressor (DLR’s Rig250), using a coupled sliding-plane setup on the ARCHER2 and Cirrus supercomputers at EPCC. The OP2 generated multiple parallelizations, together with optimized coupler configurations on heterogeneous/hybrid settings achieve, for the first time, execution of 1 revolution in less than 6 hours on 512 nodes of ARCHER2 (65k cores), with a parallel scaling efficiency of over 80% compared to a 107 node run. Results indicate a speed up of the CFD suite by an order of a magnitude (≈ 30×) relative to current production capability. Benchmarking and performance modelling project a time-to-solution of less than 5 hours on a cluster of 488×NVIDIA V100 GPUs, about 3×– 4× speedup over CPU clusters. The work demonstrates a stepchange towards achieving virtual certification of aircraft engines with the requisite fidelity and tractable time-to-solution that was previously out of reach under production settings.

The Covid-19 pandemic disrupted the normal mode of teaching and a remote learning model was substituted in the academic year of 2020-21. As part of the move, a series of additional summative assessments were introduced in many modules of the host department of this study to ensure students' engagement and provide them with feedback while they were learning remotely. Coursework, online quizzes and online exams were used to assess students' learning in this academic year. A student workload model was used to predict the effect of assessments and ensure students have enough time to study all their modules. Surveys were used to determine how different forms of assessment contributed to students learning as well as their impact on students’ workload. Questionnaires were designed to collect information on the number of hours students spent on different forms of assessments, how they perceived the effect of those assessments on their learning and how well they have learned different subjects. Irrespective of the weighting of the assessments and their types, students have treated all summative assessments very seriously and spent considerable time on even small pieces of assessments such as weekly online quizzes with a very low weighting. They perceived completing harder and longer assessments contributed relatively less to their learning. Amongst all three types of assessment, students reported reviewing for online exams helped them the most to enhance their learning.

This paper aims to design and manufacture an Android-controlled robotic arm for the purpose of picking and placing objects in constrained environments. The motivation of the research is to assess the feasibility of controlling complex real-time operating systems using a personal handheld device, with a future scope to control larger scale operations in the same way. Our robotic arm is produced using rapid prototyping techniques and controlled by an Arduino based development board. It receives control commands from a bespoke Bluetooth app, allowing to select different servo operating modes. The system will be fully controllable from the Android device, allowing the user to manually adjust the position of the arm or running predefined algorithms in automatic mode. Experimental tests are conducted to evaluate the practical limitations of the robotic arm design coupled with the PCB circuitry used as a shield to control the system. The test results show that the system is capable of lifting weights up to 80g with a current draw of 970mA. The automatic control algorithm is found to operate for up to 12 minutes before encountering system bugs or overheating and proves to be a highly repeatable test system with a high level of adaptability. However, the 3D printed PETG is seen to wear over time; and therefore, a more suitable material is recommended to be utilized for fabrication.

This study investigates the mechanical behaviour of elastomeric bearings with a low shape factor (LSF). Such bearings can offer an effective solution for three-dimensional seismic isolation of structures, that is, isolation in vertical as well as horizontal directions. They could also be employed for developing low-cost isolation systems for developing countries due to their reduced weight and manufacturing cost. The first part of the study describes tests carried out at Tun Abdul Razak Research Centre (TARRC) on low-damping rubber double-shear test pieces and LSF bearings. The material tests are used to inform the development of a finite element (FE) model of the bearings, which is validated against the bearing test results. It is shown that the proposed FE model can be used to describe accurately the global non-linear horizontal force-displacement behaviour of the compressed bearings, while providing an insight into the local distribution of stresses and strains. It can also be used to investigate the bearing response under boundary conditions that differ from the one considered in the tests. The second part of the study illustrates the numerical simulations of shaking table tests carried out at the University of Naples Federico II on a structural prototype mounted on the low-damping LSF bearings. Useful insights are provided into the effect of the vertical bearing flexibility on the response and the attainment of critical conditions of zero tangent horizontal stiffness under horizontal displacements.

How actors react to change is a crucial question for social scientists interested in global energy system transformation (EST). The global oil industry's response to the challenges associated with climate change and EST is a particular topic of discussion. Here, we argue for an interdisciplinary approach, bringing together insights from multiple disciplines within the social sciences that study oil companies, to further our understanding of what they are doing and why they are doing it. Although research on the political economy and socio-technical nature of EST has led to important insights, it tends to treat the global oil industry as a monolith with common interests and strategic objectives. We argue that the analytical and conceptual tools provided by the management and business literature can help unpack this ‘black box’. We explain how this is the case by exploring some of these tools and applying them to a novel heuristic, the ‘Transition Strategy Continuum’ that helps categorise and analyse the emerging strategies of the publicly-traded ‘International Oil Companies’ (IOCs). As such, we respond to the call for interdisciplinarity raised in the inaugural issue of this Journal. Ultimately, we want social scientists working on energy to take serious insights from other fields of inquiry that help illuminate the complexities of the task of transformation ahead for the IOCs and other related stakeholders.

The hot ductility of V containing high Al, TWIP steels was determined at a 1000°C, when no dynamic recrystallisation occurred, and precipitation was too coarse to influence ductility. A change in grain size from ∼1250 to 500 µm caused the reduction of the area to increase by ∼25%, intimating that the improvement in ductility on adding boron is due to its segregation to the boundaries causing grain refinement on solidification. Fine VC precipitation was mainly responsible for deteriorating ductility. In these steels, the ductility of un-recrystallised austenite decreases gradually with increasing temperature from 700°C to 1000°C and this in combination with fine precipitation can markedly change the shape of the hot ductility curve from ductility decreasing to increasing with temperature.

This article proposes a method to decentralize the navigation burden and improve the fault tolerance for a spacecraft constellation. The constellation body reference system is introduced, which is the perifocal frame of one satellite in the constellation. The structure of the proposed navigation method is constructed to enable each spacecraft to estimate its own orbit in this body reference system. This step is essentially the relative orbit determination (OD) based on inter-satellite range measurements. Thereafter, the approach to transfer an orbit from the constellation body reference system to an inertial reference system is developed. The essential requirements on absolute measurements to realize the coordinate transfer are presented. By dividing the absolute OD into relative OD and coordinate transfer, each navigation subsystem operated in a spacecraft can be independent with others, and the absolute measurements collected by any spacecraft can contribute to the absolute OD of the whole constellation. The proposed method applies to constellations in any geometric configuration. A Walker constellation is taken as an example for numerical simulations. The results show that the proposed method has a lower computation burden compared to an integrated navigation system. With the same type of absolute measurements, the proposed method has higher accuracy and convergence velocity than conventional decentralized algorithms. When a spacecraft occurs with fault, the orbit results of other spacecraft are not affected using the proposed method, which is beyond the ability of conventional methods.

Communication between people is commonly thought to play a major role in determining the success or failure of collaborative design projects. We conducted eight weeks of observation and 62 interviews in three design companies. Our findings indicate that communication is blamed for causing many problems which are not of an obviously technical nature. However, such problems are more often symptomatic of underlying factors related to information, representation, individual, team, and organisational issues. Examples of factors influencing communication at interfaces are people's understanding of the ‘sequence of tasks’ or ‘goals and objectives’ in the design process. With a system-theory informed conceptualisation of communication, we propose that awareness of such factors could assist design practitioners in targeting interventions and researchers in generating hypotheses about communication and design performance.

Vertical axis wind turbine (VAWT) array design requires adequate modelling of the turbine wakes to model the flow throughout the array and, therefore, the power output of turbines in the array. This paper investigates how accurately different turbulence models using 2D computational fluid dynamics (CFD) simulations can estimate near and far wakes of VAWTs to determine an approach towards accurate modelling for array design. Three experiments from the literature are chosen as baselines for validation, with these experiments representing the near to far wake of the turbine. Five URANS turbulence models were chosen due to their common and potential usage for VAWT CFD: models k–ω SST, k–ω SST LRN, k–ω SSTI, transition SST, and k–kl–ω. In addition, the lifting line-free vortex wake (LLFWV) model was tested as an alternative to CFD for the far turbine wake where it was appropriate for use. The results for turbulent kinetic energy and vorticity were compared for the first experiment, whilst streamwise and cross-stream velocity were used for the other two experiments. It was found that none of the turbulence models tested or LLFVW produced adequate estimations within the methodology tested, however, transition SST produced the closest estimations. Further adjustments to the methodology are required to improve accuracy due to their large impact on results including use of 3D CFD, adjustment of surface roughness, and inlet flow characteristics.

Moisture buffering describes the use of materials with high water-vapour sorption capacity to provide humidity control in interior spaces. Established models of the moisture dynamics of buffering are derived from conventional Fickian vapour-diffusion equations. We describe an alternative analysis using a Sharp-Front formulation. This yields a similar expression for the moisture effusivity, several consistent scalings and a new definition of the moisture penetration depth. Features of the model are compared with some published experimental data. A new sorption buffer index is a measurable experimental property that describes the water-vapour buffer strength of the material.

The relaxation dynamics of thermal capillary waves for nanoscale liquid films on anisotropic-slip substrates are investigated using both molecular dynamics (MD) simulations and a Langevin model. The anisotropy of slip on substrates is achieved using a specific lattice plane of a face-centered cubic lattice. This surface’s anisotropy breaks the simple scalar proportionality between slip velocity and wall shear stress and requires the introduction of a slip-coefficient tensor. The Langevin equation can describe both the growth of capillary wave spectra and the relaxation of capillary wave correlations, with the former providing a time scale for the surface to reach thermal equilibrium. Temporal correlations of interfacial Fourier modes, measured at thermal equilibrium in MD, demonstrate that (i) larger slip lengths lead to a faster decay in wave correlations and (ii) unlike isotropic-slip substrates, the time correlations of waves on anisotropic-slip substrates are wave-direction-dependent. These findings emerge naturally from the proposed Langevin equation, which becomes wave-direction-dependent, agrees well with MD results, and allows us to produce experimentally verifiable predictions.\ud \ud

Subspace identification methods, such as canonical variate analysis (CVA), are non-iterative tools suitable for the state-space modelling of multi-input, multi-output (MIMO) processes, e.g. industrial processes, using input-output data. To learn nonlinear system behavior, kernel subspace techniques are commonly used. However, the issue of kernel design must be given more attention because the type of kernel can influence the kind of nonlinearities that the model can capture. In this paper, a new kernel design is proposed for CVA based identification, which is a mixture of a global and local kernel to enhance generalization ability and includes a mechanism to vary the influence of each process variable into the model response. During validation, model hyper-parameters were tuned using random search. The overall method is called Feature-Relevant Mixed Kernel Canonical Variate Analysis (FR-MKCVA). Using an evaporator case study, the trained FR-MKCVA models show a better fit to observed data than those of single-kernel CVA, linear CVA, and neural net models under both interpolation and extrapolation scenarios. This work provides a basis for future exploration of deep and diverse kernel designs for system identification.

Aluminium alloys are increasingly used to fabricate cooling channels for the thermal management of Li-ion batteries. Cooling channel fabrication involves a number of manufacturing operations including material extrusion, forming and joining/welding. In general, welding of aluminium alloys is challenging as they are both highly reflective and thermally conductive. To address the joining challenges, this paper is focused on developing an optimised joining process to connect a thin, flanged cooling channel to the thick module manifold of the battery thermal management system to create a watertight joint with high mechanical strength. As continuous seam welding was required, laser welding was the preferred as it is a non-contact process combining high speed and precision. For this application, 0.4 mm Al cooling channel was welded with 1.5 mm Al endplate/module manifold using a wobble head integrated with 1 kW CW fibre laser system. The effect of process parameters including line energy, incident angle, laser power, welding speed and beam offset were investigated to optimise both the weld geometry and strength. Microstructure, micro-hardness and grain formation analyses were carried out to understand the metallurgical behaviour of the weld. Beam offset had the most significant effect on the responses such as weld strength, throat thickness and modified throat thickness, and laser power had a significant influence on two key geometric features of the fusion zone, i.e. penetration depth and weld width. Weld strength was optimised using a developed surrogate model and a maximum load of 646.89 N was achieved using 0.2 mm beam offset, 331.82 W laser power and 659.10 mm/min welding speed. Using this optimum combination, a leak-proof cooling channel and module manifold joint were produced for battery thermal management.

Constructing an appropriate membership function is significant in fuzzy logic control. Based on the multi-model control theory, this article constructs a novel kernel function which can implement the fuzzification and defuzzification processes and reflect the dynamic quality of the nonlinear systems accurately. Then we focus on the identification problems of the nonlinear systems based on the kernel functions. Applying the hierarchical identification principle, we present the hierarchical stochastic gradient algorithm for the nonlinear systems. Meanwhile, the one-dimensional search methods are proposed to solve the problem of determining the optimal step sizes. In order to improve the parameter estimation accuracy, we propose the hierarchical multi-innovation forgetting factor stochastic gradient algorithm by introducing the forgetting factor and using the multi-innovation identification theory. The simulation example is provided to test the proposed algorithms from the aspects of parameter estimation accuracy and prediction performance.

Copyright © 2021 The Author(s). The microstructure characteristics in early stage shear localization of near-α Ti−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar (SHPB) tests using hat-shaped specimens. The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction (EBSD) method. It is found that the nucleation and expansion of adiabatic shear band (ASB) are affected by both geometric and structural factors. The increase of dislocation density, structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions. In addition to the dislocation slips, the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect. Interestingly, the sandwich structure imposes a crucial influence on ASB, which finally becomes a mature wide ASB in the dynamic deformation. However, due to much larger width, the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation. Pre-research Project of Equipment Development Department of China (No. 41422010505); Technology Innovation Leading Program of Shanxi Province, China (No. 2019CGHJ-21).

IF=5.673; International audience; In this article, we address the simultaneous estimation problem of the lateral speed, the steering input, and the effective engine torque, which play a fundamental role in vehicle handling, stability control, and fault diagnosis of autonomous ground vehicles. Due to the involved longitudinal-lateral coupling dynamics and the presence of unknown inputs (UIs), a new nonlinear observer design technique is proposed to guarantee the asymptotic estimation performance. To this end, we make use of a specific Takagi-Sugeno (TS) fuzzy representation with nonlinear consequents to exactly model the nonlinear vehicle dynamics within a compact set of the vehicle state. This TS fuzzy modeling not only allows reducing significantly the real-time computational effort in estimating the vehicle variables but also enables an effective way to deal with unmeasured nonlinearities. Moreover, via a generalized Luenberger observer structure, the UI decoupling can be achieved without requiring a priori UI information. Using Lyapunov stability arguments, the UI observer design is reformulated as an optimization problem under linear matrix inequalities, which can be effectively solved with standard numerical solvers. The effectiveness of the proposed TS fuzzy UI observer design is demonstrated with real-time hardware-in-the-loop experiments.

A new inter-module connection was developed, adopting structural topology optimisation (STO) and the inter-locking method of joining. The structural performance of the connection was assessed through a series of monotonic and cyclic FE analyses. Results revealed that the structural behaviour of the new connection was comparable to that of other inter-module joints in the literature, while managing to tackle their limitations by introducing both an easy-to-install and easy-to-disassemble configuration with promising opportunities for reuse, demonstrating that inter-locking joints can be worthy competitors for traditional means of attachment in the future of modular construction.

Defect-free welds between A-516 ferritic and 316L austenitic stainless steel were achieved using inertia friction welding (IFW) under varying friction and forge pressures. The microstructural evolution and the associated mechanical properties were characterised across different weld regimes. The welds were free from microcracks and demonstrated higher strength and hardness than the parent metal (PM), indicating enhanced properties. Carbide precipitates were not observed at the weld interface, implying no occurrence of sensitisation in the stainless steel. The presence of refined grains coupled with low grain orientation spread (GOS) values was the indication of continuous dynamic recrystallisation (CDRX) occurring during IFW.

Seaports are global players in the maritime industry with the responsibility of promoting the well-being of employees and customers in the workplace. However, over the past years safety performance of seaports operating within the West African sub-region has become a major concern due to the lack of enforcement of national occupational health and safety regulations. This has compelled some seaports to adopt the occupational health and safety management system (OHSMS) ISO 45001:2018 standard. The aim of this study is therefore to assess the progress seaports have made in the implementation of ISO 45001:2018 standard and discuss the challenges that need to be overcome when implementing ISO 45001:2018 standard in seaports. Through the use of questionnaire, observations and review of institutional document, data was gathered from workers and senior managers of export, container depot and the stevedoring sections of seaports operating in Ghana. The findings of this study revealed that seaports within Ghana have made some progress with regards to workers’ awareness of occupational health and safety issues, usage of personal protective equipment (PPEs) and safe working procedures. However, it was also established that a lot more needs to be done to improve the current levels of communication, safety training and resources in relation to health and safety management. The findings of this research are useful to maritime institutions wishing to migrate from OHSAS 18001:2007 certification to ISO 45001:2018 certification or seeking to improve on already existing system.

The present investigation focuses on developing cost-effective Carbon/Glass/Kevlar fiber-reinforced polymer hybrid composite laminates for achieving its synergistic effect on flexural and impact performance. It investigates the effect of stacking sequence induced by the use of different fiber types (Kevlar = K, glass = G, and carbon = C) on the flexural and impact performance of the composites. Five hybrid composites (labelled as A = [G2K3G2], B = [KG2CG2K], C = [CKGCGKC], D = [CGKCKGC], E = [CK2CK2C]) and three plain (i.e., non-hybrid) composites (F = [K]7, G = [G]7, H = [C]7) have been fabricated through manual pre-preg lay-up manufacturing techniques. The flexural strength and modulus, hardness, and Izod impact strength have been evaluated for the fabricated composites and compared. The results showed that the D-type hybrid composite achieves the maximum positive hybrid effect as compared to other hybrid composites, possesses a hardness of 59 BHN, a flexural strength of 380 MPa, and modulus of 36 GPa, and impact strength of 80 KJ/m2. The fracture surfaces of the hybrid composite specimen have been analysed using scanning electron microscopy, and compared against the properties achieved for enabling correlations. Furthermore, the cost-efficiency of the hybridization in terms of flexural strength/cost, modulus/cost, and impact strength/cost ratio were evaluated for potential engineering and design applications.

This paper aims to maximize the total power generation for wind farms subject to strong wake effects and stochastic inflow wind speeds. A data-driven control method that only requires the accessible measurements of every turbine in the farm is proposed via deep reinforcement learning (DRL). We employ a grouping strategy to mitigate the high computational complexity induced by DRL and enhance our method’s applicability to large-scale wind farms. Based on the levels of aerodynamic interactions among turbines, this grouping strategy divides the whole farm into small sub-groups. Therefore, one can execute DRL on these sub-groups instead of carrying on a complicated learning process for the entire farm. Simulations verify the advantages of the proposed DRL-based wind farm control method over the commonly employed greedy strategy. Results also show that the proposed method can significantly reduce the overall computing cost compared with the direct execution of DRL on the whole wind farm.

According to the Food and Agriculture Organization, fishing at sea is a risky activity with the highest mortality rate due to accidents. Many ship accidents are experienced by small ships, especially on boats with a length of smaller than 24 metres. With a large number of small fishing boats in Indonesia, the risk of potential ship accidents is high. Therefore, an operability analysis must be carried out for various loading conditions to address any safety issues due to severe vessel motion in advance. The operation of fishing vessels is different from that of merchant ships. The net cargo of merchant ships tends to remain unchanged during a voyage. By contrast, the net cargo of a fishing boat, which is fish caught, will change during its operation at sea. This change will also affect the ship’s seakeeping characteristics. This study aims to determine the effect of changes in load and their effect on a traditional fishing boat’s operability in Indonesia, taking into account the ship’s intact stability. In addition, this study also highlights the response of the ship roll motion to prevent stability failure. The stability curve is used to relate ship stability analysis to seakeeping analysis. Percentage operability and Operability Robustness Index are used to assess the root mean square (RMS) roll response and the ship's expected maximum roll motion. In this study, it is shown that the percentage operability of the fishing boat satisfying all pre-determined seakeeping criteria varies between 61% to 74%. Among all criteria, the limiting boundary for RMS roll motions and RMS pitch motion are relatively low, affecting the overall operability.

Loss models are used to evaluate the aerodynamic performance of axial turbines at the preliminary design stage. The commonly used loss models were derived for air and steam turbines and have not been sufficiently investigated for turbines working with non-conventional working fluids, relevant to new power systems, such as organic fluids and supercritical CO (sCO). Thus, the aim of this study is to explore the deviation between the performance predictions of different loss models, namely Dunham and Came, Kacker and Okapuu, Craig and Cox and Aungier, for non-conventional working fluids where turbines may differ in design and operation than conventional air or steam turbines. Additionally, this paper aims to investigate the effect of the turbine scale on the trends in the performance predictions of these models. Three different case-studies are defined for air, organic Rankine cycle (ORC) and sCO turbines and each one is evaluated at two different scales. It is found that the selected loss models resulted in varying loss predictions; particularly for predicting the losses due to the clearance gap for all small scale designs. Furthermore, large variations were found in predicting the effect of the flow regime on the turbine performance for all models.

This work proposes a distribution-free stochastic model updating framework to calibrate the joint probabilistic distribution of the multivariate correlated parameters. In this framework, the marginal distributions are defined as the staircase density functions and the correlation structure is described by the Gaussian copula function. The first four moments of the staircase density functions and the correlation coefficients are updated by an approximate Bayesian computation, in which the Bhattacharyya distance-based metric is proposed to define an approximate likelihood that is capable of capturing the stochastic discrepancy between model outputs and observations. The feasibility of the framework is demonstrated on two illustrative examples and a followed engineering application to the updating of a nonlinear dynamic system using observed time signals. The results demonstrate the capability of the proposed updating procedure in the very challenging condition where the prior knowledge about the distribution of the parameters is extremely limited (i.e., no information on the marginal distribution families and correlation structure is available).

The microbond test has been widely adopted by researchers seeking to characterise the fibre-matrix interface in polymer composites. This test requires the preparation of polymer droplets with a mass as little as 20 ng. This brings with it the possibility of scaling issues causing unanticipated significant differences to the properties and performance of these droplets in comparison to macroscale samples. This paper reviews a number of these potential scaling issues in a range of polymer systems which users of the microbond test should be aware of. Some of these phenomena can affect the magnitude of the test results obtained much more than the fibre-matrix interface effects which the test is used to detect. It is concluded that in many cases the structure and properties of the polymer in such microdroplets is not representative of the same polymer, with the same thermal and environmental exposure history, prepared on the macroscale.

In this study, combustion synthesis involving mechanical milling and subsequent sintering process was utilised to fabricate Cu/AlxCuy/Al2O3 in-situ composite through the aluminothermic reduction of CuO powders. First, CuO and Al powders were mixed, and ball milled for 30–150 min to facilitate self-propagating high-temperature synthesis (SHS). Then, mechanically activated Al-CuO powders were mixed with elemental Cu powders and experienced subsequent cold compaction and sintering processes. The reactions during synthesis were studied utilising differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Densification and hardness of green and sintered bodies were also obtained. The results indicated that despite the negative free energy of the aluminothermic reaction, an initial activation energy supply is required, and mixed Al-CuO powders did not show significant progress in the combustion synthesis method. The aluminothermic reaction became probable whenever the activation energy was entirely provided by high-energy ball milling or by the sintering of ball-milled Al-CuO mixed powders. DTA results showed that the aluminothermic reaction temperature of Al-CuO decreased with milling times, whereas after 150 min of ball milling, the reaction was completed. XRD patterns revealed that the formation of Al2Cu and Al2O3 reinforcing phases resulted from CuO reduction with Al. Al4Cu9, Cu solid solution, and Al oxide phases were observed in sintered samples. The relative density of the samples was reduced compared to the green compacted parts due to the nature of the Cu-Al alloy and the occurrence of the swelling phenomenon. The hardness results indicated that in-situ formation of reinforcing phases in samples that experienced thermally assisted thermite reaction yielded superior hardness.

Commercial Li-ion cell electrodes comprise a random mix of the constituent materials largely unchanged for more than three decades. During fast charge/discharge, electrode-scale Li-ion concentration gradients develop, along with a spatially heterogeneous distribution of overpotential, utilization and degradation of active material, which ultimately restricts the range of realizable energy-power combinations. We expand energy-power characteristics and reduce cell degradation rate using electrodes that are compositionally graded at the microscale to homogenize active material utilization. Trapezoidal-graded composition LiFePO4 cathodes, enabled by a layer-by-layer deposition technique, are compared with conventional electrodes: at an energy density of 500 Wh L−1 the best graded electrode design increased power density from approximately 100 W L−1 to 630 W L−1, while at a power density of 300 W L−1, the energy density increased from approximately 420 Wh L−1 to 600 Wh L−1. The results highlight the potential for new manufacturing approaches and electrode designs to provide performance enhancements for existing and future Li ion battery chemistries.

The aim of this paper is to investigate the potential of using shallow geothermal energy in Lebanon for cooling a power cycle. The study includes ground temperature measurement, operating system management, and pressure drop assessment. Temperatures were monitored at six positions underground reaching to a depth of 2 m in Bekaa-Lebanon during the whole of 2020. The temperature sensors were placed at depths of 0.3, 0.6, 1, 1.3, 1.6, and 2 m underground. At 2 m depth, the ground temperature showed high stability with an annual temperature difference of 7 °C, while that of high and low ambient temperatures were 40 °C and 33 °C, respectively. Based on the comparison between ambient and ground temperatures, the ground cooling system can operate 207 days/year partially with full operations of 51 days. This shows that shallow geothermal energy has a great potential to activate a ground-based cooling system in this region. However, to avoid heat accumulation, use of another heat exchanger is recommended to support the ground cooling system. This heat exchanger can also provide coolth compensation when the power cycle is turned off. The pressure drop inside the heat exchangers was found to be highly significant, hence, it was essential to add an intermediate water loop between the power cycle and the ground loop.

This paper proposes two significant developments of the Wittrick–Williams (W–W) algorithm for an exact wave propagation analysis of lattice structures based on analytical dynamic stiffness (DS) model for each unit cell of the structures. Based on Bloch's theorem, the combination of both the DS and the W–W algorithm makes the wave propagation analysis exact and efficient in contrast to existing methods such as the finite element method (FEM). Any number or order of natural frequencies can be computed within any desired accuracy from a very small-size DS matrix; and the W–W algorithm ensures that no natural frequency of the structure is missed in the computation. The proposed method is then applied to analyze the band gap characteristics and mode shapes of hexagonal honeycomb lattice structures and the results are validated and contrasted against the FE results. The effects of different primitive unit cell configurations on band diagrams and iso-frequency contours are thoroughly investigated. It is demonstrated that the proposed method gives exact eigenvalues and eigenmodes with the advantage of at least two orders of magnitude in computational efficiency over other methods. This research provides a powerful, reliable analysis and design tool for the wave propagations of lattice structures.

Peridynamics (PD) has been introduced to account for long range internal force/moment interactions and to extend the classical continuum mechanics (CCM). PD equations of motion are derived in the form of integro-differential equations and only few analytical solutions to these equations are presented in the literature. The aim of this paper is to present analytical solutions to PD beam equations for both static and dynamic loading conditions. Applying trigonometric series, general solutions for the deflection function are derived. For several examples in the static case including simply supported beam and cantilever beam, the coefficients in the series are presented in a closed analytical form. For the dynamic case, the solution is derived for a simply supported beam applying the variable separation with respect to the time and the axial coordinate. Several numerical cases are presented to illustrate the derived solutions. Furthermore, PD results are compared against results obtained from the classical beam theory (CBT). A very good agreement between these two different approaches is observed for the case of the small horizon sizes (HSs), which shows the capability of the current approach.

A novel approach for predicting the intermetallic compound (IMC) formation during friction stir welding (FSW) of AA6061 to commercially pure copper has been developed, in addition to their effect on mechanical properties. The temperature distribution of the aluminium to copper weld nugget determined by a finite element model, the use of an Al–Cu phase diagram and the elemental concentration of copper and aluminium in the weld nugget have been combined to predict and validate several IMCs present in the different zones of the weldment. The results of performing butt-welding of these dissimilar metals using the FSW process demonstrated that the highest ultimate tensile strength of 194.5 MPa was achieved at 1500 rev min −1 tool rotational speed, 100 mm min −1 traverse speed and a zero-tool offset.

Microchannel resonators containing a miniaturized volume of a solution can have various applications in different fields. In this study, a microchannel cantilever was loaded with a solution containing a very small number of Pseudomonas fluorescens bacteria suspended in M9 growth medium. The liquid-filled microchannel cantilever was irradiated with a 532-nm laser. The shift in the frequency of the cantilever due to varying bacterial loads is less reliable; therefore, it could not be used for monitoring the bacterial concentration. The energy loss of the cantilever extracted from the quality factor exhibited reliable results and a very strong correlation with the bacterial concentration. The results showed a linear relation between the damping factor of the cantilever and the bacterial concentration. Accordingly, these findings were expected because the bacteria inside the solution can be considered as particles acting against the cantilever motion due to the solution’s viscosity. Thus, more bacteria caused more damping, in agreement with the experimental observations. A semiquantitative experiment was conducted with a heat source (i.e., laser beam) that focused at the cantilever tip to demonstrate the redistribution of the bacterial load within the solution due to the thermal gradient.

The flexural ultrasonic transducer has traditionally been limited to proximity measurement applications, such as car-parking systems and industrial metrology. Principally, their classical form is unsuitable for environments above atmospheric 1 bar pressure, due to an internal air cavity which creates a pressure imbalance across the transducer’s vibrating membrane. This imbalance leads to physical deformation and degradation of the transducer’s structure, restricting the membrane’s capacity to vibrate at resonance to transmit and receive ultrasound. There is a requirement for ultrasonic sensors which can withstand environments of elevated pressure, for example in ultrasonic gas metering. Recent research demonstrated the dynamic performance of flexural ultrasonic transducers with vented structures, allowing the pressure to balance across the transducer membrane. However, a hermetically sealed transducer is a more practical and robust solution, where the internal components of the transducer, such as the piezoelectric ceramic disc, will be protected from harmful environmental fluids. In this research, the design and fabrication of a new form of flexural ultrasonic transducer for environments of elevated pressure is demonstrated, where the internal air cavity is filled with an incompressible fluid in the form of a non-volatile oil. Dynamic performance is measured through acoustic microphone measurements, electrical impedance analysis, and pulse-echo ultrasound measurement. Together with finite element analysis, stable ultrasound measurement is achieved above 200 bar in air, opening the possibility for reliable ultrasound measurement in hostile environments of elevated pressure.\ud

We study the dynamic behaviour of a hybrid system where manufacturing and remanufacturing operations occur simultaneously to produce the same serviceable inventory for order fulfilment. Such a hybrid system, commonly found in the photocopier and personal computer industries, has received considerable attention in the literature. However, its dynamic performance and resulting bullwhip effect, under push and pull remanufacturing policies, remain unexplored. Relevant analysis would allow considering the adoption of appropriate control strategies, as some of the governing rules in a push-based environment may break down in pull-driven systems, and vice versa. Using nonlinear control theory and discrete-time simulation, we develop and linearise a nonlinear stylised model, and analytically assess bullwhip performance of push- and pull-controlled hybrid systems. We find the product return rate to be the key influencing factor of the order variance performance of pull-controlled hybrid systems, and thus, to play an important role towards push or pull policy selection. Product demand frequency is another important factor, since order variance has a U-shaped relation to it. Moreover, the product return delay shows a supplementary impact on the system's dynamics. In particular, the traditional push-controlled hybrid system may be significantly influenced by this factor if the return rate is high. The results highlight the importance of jointly considering ordering structure and product demand characteristics for bullwhip avoidance.

The effects of surface topography, processing, and environment conditions during tribological contact between Ti6Al4V titanium alloy and UHMWPE friction pairs were systematically evaluated. Hence, in this research the polyethylene samples (blocks) having a constant surface roughness were rubbed against counter-bodies (rollers) made of titanium alloy with different roughness of surfaces. The counter-samples were manufactured using either dry machining and/or minimum quantity lubrication (MQL) conditions. Such cutting conditions are harmless to humans and the environment. Simulated body fluid (SBF) and distilled water was used to simulate the tribological trials. We have noted that the lubricant applied to protect the integrity of machined parts, the rollers, have only minor impact on the tribological features of the friction pairs tested. Further, the samples produced with dry machining demonstrated a slightly lower momentary friction coefficient and temperature. In contrast, the MQL method enable reduced friction surface and significant wear accumulation. Further, it was found that the minimum and maximum values of the Sa texture parameter associated to tribological parameters do not exceed 21% and 4%, when is used dry and MQL methods, respectively. Nevertheless, the distilled water revealed a much better wear resistance when comparing to SBF, and the later one trigger as well as an accentuated wear progress with different patterns. The results of the study are important in the design of new biomedical components produced by finish turning.

Monocular Visual Simultaneous Localisation and Mapping (VSLAM) systems are widely utilised for intelligent mobile robots to work in unknown environments. However, complex and varying illuminations challenge the accuracy and robustness of VSLAM systems significantly. Existing feature-based VSLAM methods often fail due to the insufficient feature points that can be extracted in those challenging illumination environments. Therefore, this paper proposes an improved ORB-SLAM algorithm based on adaptive FAST threshold and image enhancement (AFE-ORB-SLAM), which works in the environments with complex lighting conditions. An improved truncated Adaptive Gamma Correction (AGC) is combined with unsharp masking to reduce the effect caused by different illuminations. What is more, an improved ORB feature extraction method with the adaptive FAST threshold is proposed and adopted to obtain more reliable feature points. To verify the performance of the AFE-ORB-SLAM, three public datasets (the extended Imperial College London and National University of Ireland Maynooth (ICL-NUIM) dataset with different lighting conditions, Onboard Illumination Visual-Inertial Odometry (OIVIO) dataset and the European Robotics Challenge (EuRoC) dataset) are utilised. The results are compared with other state-of-the-art monocular VSLAM methods. The experimental results demonstrate that the AFE-ORB-SLAM could achieve the highest average localisation accuracy with robust performance in the environments with complex lighting conditions while keeping similar performance in the normal lighting scenarios.

The curing performance of two epoxy resin systems has been investigated using the microbond test and FTIR spectroscopy. A novel sample preparation technique involving curing epoxy droplets on thin steel filaments allowed for high-throughput determination of microbond droplet cure state using a conventional benchtop spectrometer. Parity between steel filament and glass fibre microbond samples was confirmed by infrared microspectroscopy. It is shown that cure schedules used in the manufacture of composite parts produced microbond droplets with degrees of cure lower than that of bulk matrix specimens subjected to an identical thermal history. For a commercial resin system, testable microbond droplets could only be produced when a room temperature pre-curing time of at least 2 hours was introduced. It is concluded that microbond testing be supported by some method of droplet cure state characterisation to ensure that interfacial effects are not artefacts of droplet sample preparation.

Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge-transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility. Films are analyzed by X-ray scattering and Mueller matrix polarimetry to characterize the microscale organization of the polycrystalline ensembles. Carrier mobilities of organic field-effect transistors are five times higher when the crystals are grown with the smallest pitches (most twisted), compared to those with the largest pitches, along the fiber elongation direction. A tenfold increase is observed along the perpendicular direction. Simulation of electrical potential based on scanning electron microscopy images and density functional theory suggests that the twisting-enhanced mobility is mainly controlled by the fiber organization in the film. A greater number of tightly packed twisted fibers separated by numerous smaller gaps permit better charge transport over the film surface compared to fewer big crystallites separated by larger gaps.

Epoxy is an important class of thermosetting material which have been used in many fields such as aerospace, automobile and energy sectors. cured epoxy, however, exhibits poor resistance to crack initiation and growth, thus low toughness and brittleness at failure. To improve the mechanical properties, in numerous studies the epoxy matrix in polymer composites has been modified by various techniques such as the inclusion of a second phase (e.g. core-shell rubber, thermoplastics or nanofillers). Inclusion of these materials in epoxy improves toughness and the impact resistance properties, but very few studies have focused on offering an ‘active toughening’ mechanism, meaning an increase in toughness activated by a stimulation (mechanical, electrical, thermal etc.) in high-performance rigid structures. In this study, aerospace grade epoxy resin modified with tetragonal barium titanate (BaTiO3) nanoparticles has been prepared, and its instantaneous toughening behaviour has been analysed under contact-less electromagnetic fields. For this reason, different wt.% of BaTiO3 nanoparticles (1, 5, 10 wt%) have been functionalised with silane coupling agents and dispersed uniformly into epoxy Araldite LY1564, a diglycidyl ether of bisphenol A (DGEBA) associated with its curing agent Aradur 3487. Real-time strain measurement (Tensile measurements) of the modified epoxy along with in-situ Raman shift study have been carried out in situ under an electric field stimulation. The results demonstrate that the activation of dipole displacements in BaTiO3 via an electromagnetic field introduces an interfacial compressive stress onto its surrounding rigid (fully cured) epoxy that enhances the toughness of the nanocomposite via suppressing the coalesce of inherent or process induced microcracks in the epoxy. The mechanism provides an effective route for mechanical property tailoring, specifically toughening of thermoset composites, under an electric field. The in-situ Tensile and Raman (during the stimulation) along with the materials characterisation (post stimulation) provides a unique quantitative framework for design of a toughening mechanism.