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Inter-organisational governance in megaprojects: a systematic review and an agenda for future research
Get PDFThe review analysed 4,536 titles. 781 papers were selected for the title and abstract review after applying exclusion criteria and 81 papers were identified for the full review. Gioia method was applied to extract the first-order and second-order concepts and aggregate dimensions. The thematic analysis illustrates that megaprojects are delivered through multi-party settings and the governance is regarded as dynamic, processual and anchored in multiple levels. Megaproject governance mechanisms include informal and informal approaches. Committed leadership, collaboration, stakeholder management and culture are key components to enable the governance mechanisms.
The main challenges in the implementation of a complex infrastructure project are not technical but are rather those related to how to govern the work in a complex inter-organisational setting that brings together a diverse set of actors who differ in their values, culture and goals
Design optimisation of separate-jet exhausts with CFD in-the-loop and dimensionality reduction techniques
Get PDFFor Ultra-High Bypass Ratio aero-engines, the exhaust system is likely to play a significant role on the aerodynamics and performance of the aircraft. For this reason, relatively rapid methods for the aerodynamic design and optimisation of exhaust systems are required to inform design decisions at early stages of the design process. Previous exhaust optimisation works encompassed Response Surface Model (RSM) based optimisations of nozzle configurations that were parametrised with a significant number of design variables. The RSM were constructed with a large database of designs that were assessed with fine computational meshes and well resolved boundary layers. However, the large number of design variables and the computational cost required to evaluate each exhaust design limited the optimisation capabilities. This work develops a relatively more rapid exhaust optimisation method based on CFD in-the-loop and dimensionality reduction. The methodology is based on coarse meshes and wall functions to guide the optimisation process and is coupled with methods for the identification of the dominant design variables. For an UHBR aero-engine exhaust design space of 16 design variables, it was found that the velocity coefficient could be characterised with only seven parameters. Based on these results, various optimisation methods were developed and applied. These targeted the maximisation of the velocity coefficient by optimising just the 7 dominant design variables. With these approaches, a similar benefit in exhaust performance relative to the baseline optimisation method was obtained approximately 4 times faster.AIAA SCITECH 2024 Forum 202
Analysis of scaling relationships for flood parameters and peak discharge estimation in a tropical region
Get PDFRelationships between peak discharges and catchment size (e.g., flood scaling) in a catchment have the potential to support new river flood forecasting approaches but have not been tested in tropical regions. This study determined flood scaling relationships between peak discharge and nested drainage areas in the La Sierra catchment (Mexico). A statistical power law equation was applied to selected rainfall–runoff events that occurred between 2012 and 2015. Variations in flood scaling parameters were determined in relation to catchment descriptors and processes for peak downstream discharge estimation. Similar to studies in humid temperate regions, the results reveal the existence of log-linear relationships between the intercept (α) and exponent (θ) parameter values and the log–log power–law relationships between α and the peak discharge observed from the smallest headwater catchments. The flood parameter values obtained were then factored into the scaling equation (QP = αAθ) and successfully predicted downstream flood peaks, especially highly recurrent flood events. The findings contribute to a better understanding of the nature of flood wave generation and support the development of new flood forecasting approaches in unregulated catchments suitable for non-stationarity in hydrological processes with climate change.Hydrology Researc
An experimental investigation into the effect two-phase flow induced vibrations have on a J-shaped flexible pipe
Get PDFMultiphase flow inside of pipes occurs in a wide variety of engineering applications, including offshore deep-water oil and gas transport. Vibrations induced by the flow inside of the pipe can lead to its mechanical failure and thus lead to uncontrolled release of the fluids being transported. In subsea applications, flexible J-risers are often employed to deliver the produced fluids from the seafloor to the host platform. Despite the potentially significant liabilities associated with subsea hydrocarbon leaks, there has been a distinct lack of investigations into how flow induced vibrations in large scale, pressurised flexible J-risers can lead to system integrity loss. Previous investigations have generally focused on the response of rigid pipes or small scale, unpressurised flexible risers. This study presents an investigation into the response of a 10 m long, 50.8 mm internal diameter composite riser containing a tensile armour helical structure to a variety of two-phase, water-nitrogen flows at 10.8 barg of pressure and ambient temperature. High speed cameras were used to investigate the structure of the flow at either end of the flexible riser, whilst synchronised surface mounted strain gauges and accelerometers were used to investigate the response of the pipe. Time-averaged data were acquired to assess the general response of the pipe, whilst a statistical analysis of the fluctuations highlighted the movement of the pipe. One-dimensional and computational fluid dynamics simulations were used to define the experimental test matrix and provide further insight into the structure of the flow inside the J-riser. Single-phase gas flow was found not to cause the J-riser to move significantly, whilst multiphase flow led to significant in-plane movement of the pipe. Increasing the liquid flow rate (or decreasing the gas flow rate) increased the mean strain experienced by the pipe. At low gas flow rates, the pipe oscillated smoothly about its mean position, but at higher gas flow rates a violent intermittent whipping motion was observed. The latter produced large in-plane and out-of-plane movement of the pipe which could pose a threat to system integrity. This work offers new insights into fluid-structure interactions in large scale engineering applications, contributing to improved system design and control.Journal of Fluids and Structure
Quasi-2D thermal network based heat soakage model for gas turbine transient performance modification
Get PDFTo overcome the limitations of traditional heat soakage analysis, a novel quasi-2D thermal network based heat soakage model is established with the consideration of component internal thermal resistance, combustor temperature profile, cooling technologies and thermal barrier coating. The method has been integrated into Turbomatch, a gas turbine performance software developed by Cranfield University, to offer a more realistic estimation of the heat soakage effect during the gas turbine transient manoeuvre. The accuracy of the heat soakage model has been validated against results obtained from GasTurb. Furthermore, a parametric analysis has been conducted to evaluate the effects of combustor temperature profile, cooling technologies, and thermal barrier coating. It is found that the combustor temperature profile will cause a significant increase in heat flow rate, which is approximately four times the conventional lumped parameter method based model. The implementation of cooling technologies and thermal barrier coating will reduce the heat flow rate by 48.97%. More importantly, the change in heat flow rate causes a further delay in engine transient response. Corrected rotational speed was decreased by 0.89%, and thrust was reduced by 2.24%. Moreover, a delay of 8s (233% increase) in the transient acceleration time was found when comparing the quasi-2D thermal network based heat soakage model with the traditional lumped parameter method based model. These highlight the significance of accurately evaluating the heat soakage effects during gas turbine transient simulation.Applied Thermal Engineerin
Design and control of a 7-degree-of-freedom symmetric manipulator module for in-orbit operations
Get PDFThis paper proposes a modular redesign of multi-armed robotic systems with application to in-orbit operations. The manipulators that the robot includes are made independent and the connection to the central body is achieved through additional standard interfaces (SI). This grants the system the ability to self-repair through self-reconfiguration. The arms are also upgraded, giving rise to symmetrical manipulators of 7 degrees of freedom (DOF) capable of locomoting by themselves. The models of the new manipulator design are presented along with its nominal workspace. In addition to this, a novel algorithm for the control of the arm is developed based on the F ABRIK approach. This programme is tested using diverse target poses as input and the consequent results are shown too. All the models and sketches were created in SolidWorks; the algorithm was coded in MATLAB.2023 11th International Conference on Control, Mechatronics and Automation (ICCMA
Stepwise model parametrisation using satellite imagery and hemispherical photography: tuning AquaCrop sensitive parameters for improved winter wheat yield predictions in semi-arid regions
Get PDFCrop models are complex with many parameters, which has limited their application. Here we present an approach which both removes the model complexity through reducing the parameter dimensionality through sensitivity analysis, and presents a subsequent efficient approach to model parameterisation using swarm optimisation. We do this for two key model outputs, crop canopy and yield, and for two types of observational data, hemispheric photographs and Landsat7 imagery. Importantly we compare the usefulness of these two sources of data in terms of accurate yield prediction. The results showed that the dominant model parameters that predict canopy cover were generally consistent across the fields, with the exception of those related water stress. Although mid-season canopy cover extracted from Landsat7 was underestimated, good agreement was found between the simulated and observed canopy cover for both sources of data. Subsequently, less accurate yield predictions were achieved with the Landsat7 compared to the hemispherical photography-based parametrizations. Despite the small differences in the canopy predictions, the implications for yield prediction were substantial with the parametrization based on hemispherical photography providing far more accurate estimates of yield. There are, however, additional resource implications associated with hemispherical photography. We evaluate these trade-offs, providing model parametrization sets and demonstrating the potential of satellite imagery to assist AquaCrop, particularly on large scales where ground measurements are challenging.This work is part of the SAFA (Sustainable Agriculture For Africa) project which is funded by OCP, Morocco.Field Crops Researc
Numerical study of premixed PODE3-4/CH4 flames at engine-relevant conditions
Get PDFPolyoxymethylene dimethyl ether (PODEn, n ≥ 1) is a promising alternative fuel to diesel with higher reactivity and low soot formation tendency. In this study, PODE3-4 is used as a pilot ignition fuel for methane (CH4) and the combustion characteristics of PODE3-4/CH4 mixtures are investigated numerically using an updated PODE3-4 mechanism. The ignition delay time (IDT) and laminar burning velocity (LBV) of PODE3-4/CH4 blends were calculated at high temperature and high pressure relevant to engine conditions. It is discovered that addition of a small amount of PODE3-4 has a dramatic promotive effect on IDT and LBV of CH4, whereas such a promoting effect decays at higher PODE3-4 addition. Kinetic analysis was performed to gain more insight into the reaction process of PODE3-4/CH4 mixtures at different conditions. In general, the promoting effect originates from the high reactivity of PODE3-4 at low temperatures and it is further confirmed in simulations using a perfectly stirred reactor (PSR) model. The addition of PODE3-4 significantly extends the extinction limit of CH4 from a residence time of ~0.5 ms to that of ~0.08 ms, indicating that the flame stability is enhanced as well by PODE3-4 addition. It is also found that NO formation is reduced in lean or rich flames; moreover, NO formation is inhibited by too short a residence time.Fuel
What drives the green development behavior of local governments? A perspective of grounded theory
Get PDFAlthough the elements that lead local governments to adopt sustainable development behaviors have been examined, the underlying processes that local governments adopt to accomplish green development behavior (GDB) lack systematic theoretical analysis. This study aims to investigate the determinants influencing local governments’ implementation of GDB from the organizational internal and external perspectives. This study employed grounded theory to analyze the data and develop an influencing factor model of local government green development behavior (GDB-LG) after interviewing 53 Chinese local officials. Additionally, through integrating process organization research with new institutional theory, the mechanism that explains how these elements influence GDB was investigated. The results of the study demonstrate that the influencing factors model could give municipal governments clear guidance when creating sensible green development policies, further enhancing the efficacy of GDB.Heliyo
Multi-agent reinforcement learning-based passenger spoofing attack on Mobility-as-a-Service
Get PDFCyber-physical systems, such as smart transportation, face security threats from both digital and physical realms. Recently, Mobility-as-a-Service (MaaS) has emerged as a novel transportation concept, offering passengers access to diverse mobility services via a unified platform. Central to this system is the smart MaaS coordinator, tasked with tailoring services to passengers based on their profiles and behaviors. However, the coordination of heterogeneous passengers introduces vulnerabilities, enabling malicious entities to exploit the system by impersonating priority passengers with falsified information. Effective detection mechanisms require a deep understanding of the spoofing process. This paper investigates threats to the smart MaaS coordinator, unveiling a new reinforcement learning-based attack named the passenger spoofing attack, which aims to mitigate the risk of inadvertently exposing MaaS vulnerabilities post-deployment. This attack leverages feedback from actions and experiences to manipulate system profitability and passenger satisfaction by generating false passenger information. Furthermore, our research reveals that multi-agent reinforcement learning, accounting for spatial distribution among malicious agents and passengers, strengthens the attack. Through simulations based on datasets from New York City and synthetic sources, we demonstrate that the attack can significantly reduce 70% of profit and 50% of passenger satisfaction. Spatial analysis indicates an effective distance of approximately two nodes from the origin or destination. This study enriches our comprehension of the vulnerabilities inherent in smart coordinators within MaaS, enabling the development of robust countermeasures against malicious actors.This work was supported by EPSRC MACRO - Mobility as a service: Managing Cybersecurity Risks across Consumers, Organisations and Sectors (EP/V039164/1)IEEE Transactions on Dependable and Secure Computin