Cellular buckling in stiffened plates

An analytical model based on variational principles for a thin-walled stiffened plate subjected to axial compression is presented. A system of nonlinear differential and integral equations is derived and solved using numerical continuation. The results show that the system is susceptible to highly unstable local--global mode interaction after an initial instability is triggered. Moreover, snap-backs in the response showing sequential destabilization and restabilization, known as cellular buckling or snaking, arise. The analytical model is compared to static finite element models for joint conditions between the stiffener and the main plate that have significant rotational restraint. However, it is known from previous studies that the behaviour, where the same joint is insignificantly restrained rotationally, is captured better by an analytical approach than by standard finite element methods; the latter being unable to capture cellular buckling behaviour even though the phenomenon is clearly observed in laboratory experiments.Comment: 22 pages, 9 figures, 1 table, accepted for publication. Proceedings of the Royal Society A, 201

Localized and cellular buckling in stiffened plates

Nonlinear buckling behaviour of a thin-walled simply-supported stiffened panel that has uniformly spaced longitudinal stiffeners is studied. The structure is made from a linear elastic, isotropic and homogeneous material. The panel is subjected to pure compression applied at the centroid of whole cross-section. In such structures, the nonlinear interaction can occur between a global (Euler) buckling and local plate ( i.e. the stiffener or the main plate) buckling modes. The interactive buckling behaviour is usually more unstable than when the modes are triggered individually. This can lead to a significant reduction of the load-carrying capacity. The current work focuses on the case where the stiffening is only on one side of the main plate. An analytical model of a perfect thin-walled stiffened plate is formulated based on variational principles by minimizing the total potential energy. The equations of equilibrium are then solved numerically using the continuation and bifurcation software Auto to determine the post-buckling behaviour. Cellular buckling (or snaking) is revealed analytically in such a component arising from nonlinear local global interactive buckling, perhaps for the first time. In addition, the effect of varying the rigidity at the main plate -stiffener junction is studied; a rapid erosion of the cellular buckling response is revealed by increasing the joint rigidity. The initial model is then developed by including more degrees of freedom within the stiffened panel and the introduction of global and local imperfections. The results from the analytical model are validated by the finite element (FE) method using the commercial software Abaqus as well as by comparing against some experimental results taken from the literature. To obtain a greater understanding of the drivers of the structural behaviour, parametric studies are conducted for a variety of different plate and stiffener geometries as well as an investigation into the heightened sensitivity to geometric imperfections. The worst forms of local imperfection are identified in terms of the initial amplitude, number of waves and the degree of localization. The imperfection sensitivity and the parametric studies are conducted for two limiting cases, where the main plate- stiffener joint is assumed to be fully pinned or fully rigid. A framework for establishing the zone where structural designers need to consider mode interaction carefully is presented.Open Acces

Elevated Intraocular Pressure after Pars Plana Vitrectomy: A Review

Intraocular pressure (IOP) elevation is a well-known complication after pars plana vitrectomy with or without tamponade. The mechanism of increase in IOP can be open angle, closed angle or both. Oxidative stress is hypothesized to have a significant role in the pathogenesis of post vitrectomy elevated IOP and the presence of the lens probably has a protective role. The use of silicone oil and intraocular gases as tamponade is related to higher risk of post-operative elevated IOP and causes longer-term IOP elevation. Anti-inflammatory agents, mydriatics, anti-glaucoma medications especially aqueous suppressants, glaucoma surgery and laser procedures might be used for controlling post vitrectomy elevated IOP. Glaucoma shunt implantation and cyclodestructive procedures are the most important surgeries performed for treatment of uncontrolled intraocular pressure after vitrectomy

Industry 5.0 transition for an advanced service provision

The current service provision for high-value manufactured equipment is transitioning from a purely product-focused business model to a service-focused one, known as servitization. Businesses aim to continuously improve their service offerings to sustain customer satisfaction in order to maintain their competitive edge within the industry. On the other hand, Industry 5.0 is characterized by bringing industries’ focus towards collaboration for sustainable value co-creation rather than producing goods and services for profit. This research investigates the possible enablers to design and deploy a highly effective advanced service provision. Advanced service provision refers to providing service solutions that fulfil the desirable availability, capability, and reliability in product-service contracts. The research outcomes are presented in the form of a transition framework and a set of recommendations towards the desired future state, with phased timings for implementing the key enablers with a potential 2035 vision to support the Industry 5.0 transition. The validity of the framework was tested by collecting experts’ opinion who currently work within servitization contracts. The outcome of this study can be generalized for industries in high-value manufacturing

An agent-based approach to quantify the uncertainty in product-service system contract decisions: a case study in the machine tool industry

Product-service system (PSS) business models appraise the relationship between different stakeholders and focus on a partnership based on profit. Existing literature discusses servitization and the associated cost-benefit analysis (CBA) models mostly from the perspective of original equipment manufacturers. Additionally, CBA is typically conducted using top-down approaches and standard activity-based costing, with limited available data and without considering uncertainty. As a result, inadequate and under-priced contract decisions may be made. To address the problem, this paper extends the current literature by proposing a novel framework for quantifying uncertainty in cost and benefit estimates of PSS contracts. The framework offers a bottom-up costing approach using the agent-based simulation technique. The framework comprises a stochastic CBA model for PSS. It is developed by considering through-life cost and benefit of products and services with aggregate uncertainty in terms of service costs, service lead-times, and their occurrences. The framework has been tested successfully on a real-world case study with a bespoke service provider in the machine tool industry. The model is applied to include spare-parts and availability-based servitization contracts. The simulation results are validated by real-world measurements and expert knowledge. The results involve a comprehensive stochastic analyses of a through-life CBA under probabilistic uncertainty and provide the opportunity to quantify the uncertainty in PSS contract decisions. Moreover, the results highlight that servitization is more beneficial for bespoke service providers in long-term contracts, and for relatively new or retrofitted products. Further research works are required to apply the model on capability-based contract

An agent-based model for flexible customization in product-service systems

Product-Service System (PSS) models offer an integrated service solution to create value for businesses. In the high-value manufacturing sector, value creation for maintaining market competitiveness and improving customer satisfaction is a challenging task. Designing an effective PSS solution depends on integrated service, and product requirements and constraints. Thereby, PSS contract decisions can be significantly influenced by customers’ requirements, and also product and service features. However, existing literature primarily focuses on the impact of service requirements on the PSS contract decisions. Moreover, the existing insights for PSS customization mainly consider hysteretic customer requirements rather than forecasting the requirements under product and service uncertainties. In this paper, an agent-based cost-benefit analysis simulation model is implemented for the PSS contract decisions context. Moreover, a sensitivity analysis is conducted on service costs. Additionally, the effect of product remaining life on service contract decisions is analyzed. The simulation model considers stochastic uncertainty to study PSS contracts customization. The presented model supports PSS customization process by providing a quantitative tool that measures contracts’ profitability as early as the requirement elicitation phase. Furthermore, the bottom-up nature of the model, and the integration of probabilistic uncertainties enhance the flexibility of PSS customization. A case study of PSS contract decision in the machine tool industry is considered for assessing the validity of the presented model. Studies on different forms of service uncertainty highlight that the product failure rate has the most influence on the profitability of a service contract. Moreover, the impact of product age on profitability in an availability-based contract is more significant compared to a spare-parts contract

Toward an integrated sustainability assessment in through-life engineering services

Through-life Engineering Services (TES) is comprised of develop, prepare, utilize and retire phases for complex engineering assets with a focus on maximizing their availability, predictability and reliability at the lowest possible life-cycle cost. TES employs a set of technologies and solutions to improve asset performance efficiently. On the other hand, optimal solutions for minimizing waste in terms of service time and resources is crucial for designing the right service at the right time. Thereby, specifying the possible TES opportunities within the economic, social and environmental sustainability dimensions can be an added value across different manufacturing sectors when deploying TES. However, due to the complexities and immensity of TES approaches, it is challenging to perceive such opportunities. To this end, the existing literature is limited to the effect of TES on economic sustainability and mostly focuses on investigating how TES has modified the service design to improve productivity and profitability. However, a comprehensive study on integrated sustainability has not been yet conducted. This paper presents a holistic view of the potential TES opportunities associated with the sustainability triple bottom line following a systematic review of empirical and theoretical advancements and methodological approaches in the literature. The outcome from this research raises the awareness of TES contribution in the design of sustainable service solutions and technologies, and offers a benchmark and reference point for future research in the field. Finally, this paper provides a set of recommendations that call for the further development of an integrated sustainability assessment framework for TES.Cranfield Universit

Cognitive Performance as a Predictor of Functional Capacity in Schizophrenia

Introduction: Schizophrenia is a severe mental illness characterized by cognitive deficits as well as vocational impairment and interpersonal difficulties. This study examined the link between Continues Performance and everyday living skills. Methodes: Sample was 20 Schizophrenia (11 male and 9 female) selected using convenience sampling among individual with Schizophrenia diagnostic and 20 (10 male and 10 female) were matched with them as control group considering sex, age, marriage and education . Instruments were used in this study include: UCSD Performance-Based Skills Assessment Test (UPSA) and Continues Performance Test (CPT). Results: MANOVA showed a significant main effect for five domain of UPSA and four domain of UPSA. CPT predicted UPSA in schizophrenia. Conclusions: Individuals with schizophrenia would perform significantly worse in everyday living skills and on CPT. In fact poorer performance in CPT predicted basic skills performance in schizophrenia. This will help to determine what specifically needs to be targeted in rehabilitation of cognitive symptoms for those with schizophrenia, and that may reveal remediation in functional capacity as well. DOI: 10.5901/mjss.2015.v6n2s1p14

A multi-objective approach for resilience-based system design optimisation of complex manufacturing systems

Disruptive events in complex manufacturing systems (CMS), characterised by labour-intensive processes and repetitive activities, render these systems vulnerable. In order to tackle this challenge, an approach for resilience-based system design optimisation is proposed. The approach: (i) introduces a dynamic multi-dimensional resilience metric; and (ii) formulates the resilience as a multi-objective optimisation problem to improve CMSs resilience by finding an optimal human resource allocation model, considering design factors including redundancy, resources capacity and roles. The case study, selected to test the validity of the presented approach, show improvement in resilience and efficiency, in terms of throughput, resources utilisation and restoration time

Digital twin-enabled automated anomaly detection and bottleneck identification in complex manufacturing systems using a multi-agent approach

Digital twin (DT) models are increasingly being used to improve the performance of complex manufacturing systems. In this context, DTs automatically enabling anomaly detection, such as increase in orders, and bottleneck identification, such as shortage of products, can significantly enhance decision-making to mitigate the consequences of the identified bottlenecks. The existing literature has mainly focused on implementing top-down approaches for analysing the bottlenecks without considering the emergent behaviour of micro-level agents, including inventory levels and human resources, and their impact on the macro-level system’s performance. In order to handle the aforementioned challenges, this paper extends the current literature by proposing a novel DT integrated in a multi-agent cyber physical system (CPS) for detecting anomalies in sensor data, while identifying and removing bottlenecks that emerge during the operation of complex manufacturing systems. An extended 5 C CPS architecture, using multi-agent approach, is implemented to allow DT integration. The agent-based simulation technique enables capturing the probabilistic variability, and aggregate parallelism and dynamism of parallel dynamic interactions within the DT-CPS. A new single agent at the exo-level of the multi-level agent-based modelling structure, called the ‘monitoring agent’, is introduced in this research. The agent detects anomalies and identify bottlenecks through communicating with other agents in different levels automatically. The DT-CPS provides feedback automatically to the physical space to remove and mitigate the identified bottlenecks. The proposed DT based multi-agent CPS has been tested successfully on a real case study in a cryogenic warehouse shop-floor from the cell and gene therapy industry. The performance of the studied cryogenic warehouse is continuously measured using real-time sensor data. The analyses of the results show that the proposed DT-CPS improves the utilisation rates of human resources, on average, by 30% supporting decision making and control in complex manufacturing systems.Innovate UK: 104515. Engineering and Physical Sciences Research Council (EPSRC): EP/R032718/