Long-range sediment transport in the world’s oceans by stably stratified turbidity currents

Peer reviewedPublisher PD

Sustained gravity currents in a channel

Gravitationally driven motion arising from a sustained constant source of dense fluid in a horizontal channel is investigated theoretically using shallow-layer models and direct numerical simulations of the Navier–Stokes equations, coupled to an advection–diffusion model of the density field. The influxed dense fluid forms a flowing layer underneath the less dense fluid, which initially filled the channel, and in this study its speed of propagation is calculated; the outflux is at the end of the channel. The motion, under the assumption of hydrostatic balance, is modelled using a two-layer shallow-water model to account for the flow of both the dense and the overlying less dense fluids. When the relative density difference between the fluids is small (the Boussinesq regime), the governing shallow-layer equations are solved using analytical techniques. It is demonstrated that a variety of flow-field patterns are feasible, including those with constant height along the length of the current and those where the height varies continuously and discontinuously. The type of solution realised in any scenario is determined by the magnitude of the dimensionless flux issuing from the source and the source Froude number. Two important phenomena may occur: the flow may be choked, whereby the excess velocity due to the density difference is bounded and the height of the current may not exceed a determined maximum value, and it is also possible for the dense fluid to completely displace all of the less dense fluid originally in the channel in an expanding region close to the source. The onset and subsequent evolution of these types of motions are also calculated using analytical techniques. The same range of phenomena occurs for non-Boussinesq flows; in this scenario, the solutions of the model are calculated numerically. The results of direct numerical simulations of the Navier–Stokes equations are also reported for unsteady two-dimensional flows in which there is an inflow of dense fluid at one end of the channel and an outflow at the other end. These simulations reveal the detailed mechanics of the motion and the bulk properties are compared with the predictions of the shallow-layer model to demonstrate good agreement between the two modelling strategies.</jats:p

Multi-objective Optimization of a Ridesharing System Performance

Ridesharing is a shared vehicle service with the potential to meet the growing travel demand due to population increase, economic growth, and shortage in transportation infrastructure capacity. Compared to the current system of predominantly using personal vehicles, ridesharing services reduce the number of vehicles while providing mobility services to the same number of people with no additional investment in the transportation infrastructure. One of the big challenges in implementing ridesharing services is matching drivers and riders. Conflicts between matching-objectives to comply with the interests of diverse stakeholders influence the efficiency of ridesharing in a transportation system. This study investigates the conflicts between two ridesharing matching-objectives minimization of systemwide Trip Time (TT) and minimization of systemwide Vehicle Miles Traveled (VMT) by adopting a multi-objective optimization technique. The optimization results indicate that it is possible to have an acceptable reduction in TT and VMT by optimizing the conflicts between conflicting objectives in a ridesharing system. Tradeoff analysis indicates the benefits of a multi-objective optimization model in a ridesharing system by optimizing ridesharing system performance considering multiple conflicting matching-objectives

Modeling, Stability Analysis, and Control of Distributed Generation in the Context of Microgrids

One of the consequences of competitive electricity markets and international commitments to green energy is the fast development and increase in the amount of distributed generation (DG) in distribution grids. These DGs are resulting in a change in the nature of distribution systems from being "passive", containing only loads, to "active", including loads and DGs. This will affect the dynamic behavior of both transmission and distribution systems. There are many technical aspects and challenges of DGs that have to be properly understood and addressed. One of them is the need for adequate static and dynamic models for DG units, particularly under unbalanced conditions, to perform proper studies of distribution systems with DGs (e.g., microgrids). The primary objective of this thesis is the development and implementation of dynamic and static models of various DG technologies for stability analysis. These models allow studying systems with DGs both in the long- and short-term; thus, differential and algebraic equations of various DGs are formulated and discussed in order to integrate these models into existing power system analysis software tools. The presented and discussed models are generally based on dynamic models of different DGs for stability studies considering the dynamics of the primary governor, generators, and their interfaces and controls. A new comprehensive investigation is also presented of the effects of system unbalance on the stability of distribution grids with DG units based on synchronous generator (SG) and doubly-fed induction generator (DFIG) at different loading levels. Detailed steady-state and dynamic analyses of the system are performed. Based on voltage and angle stability studies, it is demonstrated that load unbalance can significantly affect the distribution system dynamic performance. Novel, simple, and effective control strategies based on an Unbalanced Voltage Stabilizer (UVS) are also proposed to improve the system control and the stability of unbalanced distribution systems with SG- and DFIG-based DGs

The Journey to Trustworthy AI- Part 1: Pursuit of Pragmatic Frameworks

This paper reviews Trustworthy Artificial Intelligence (TAI) and its various definitions. Considering the principles respected in any society, TAI is often characterized by a few attributes, some of which have led to confusion in regulatory or engineering contexts. We argue against using terms such as Responsible or Ethical AI as substitutes for TAI. And to help clarify any confusion, we suggest leaving them behind. Given the subjectivity and complexity inherent in TAI, developing a universal framework is deemed infeasible. Instead, we advocate for approaches centered on addressing key attributes and properties such as fairness, bias, risk, security, explainability, and reliability. We examine the ongoing regulatory landscape, with a focus on initiatives in the EU, China, and the USA. We recognize that differences in AI regulations based on geopolitical and geographical reasons pose an additional challenge for multinational companies. We identify risk as a core factor in AI regulation and TAI. For example, as outlined in the EU-AI Act, organizations must gauge the risk level of their AI products to act accordingly (or risk hefty fines). We compare modalities of TAI implementation and how multiple cross-functional teams are engaged in the overall process. Thus, a brute force approach for enacting TAI renders its efficiency and agility, moot. To address this, we introduce our framework Set-Formalize-Measure-Act (SFMA). Our solution highlights the importance of transforming TAI-aware metrics, drivers of TAI, stakeholders, and business/legal requirements into actual benchmarks or tests. Finally, over-regulation driven by panic of powerful AI models can, in fact, harm TAI too. Based on GitHub user-activity data, in 2023, AI open-source projects rose to top projects by contributor account. Enabling innovation in TAI hinges on the independent contributions of the open-source community.Comment: Updates: Fixed typos. Fixed NIST checkmarks in table 1. Added new subsections: copyright (4.6) and risks on webcrawled datasets (5.2.1). Updated figure 3 to show EU-AI Act passin

Applications of Particle Swarm Optimization Algorithm to Solving the Economic Load Dispatch of Units in Power Systems with Valve-Point Effects

Reduction of operating costs in power system in order to return the investment costs and more profitability has vital importance in power industry. Economic Load Dispatch (ELD) is one of the most important issues in reducing operating costs. ELD is formulated as a nonlinear optimization problem with continuous variables within the power plants. The main purpose of this problem is optimal planning of power generation in power plants with minimum cost by total units, regarded to equality and inequality constraints including load demand and the range of units' power productivity. In this article, Economic Load Dispatch problem has been modeled by considering the valve-point loading effects with power plants' constraints such as: the balance of production and consumption in system, the forbidden zones, range of production, increasing and decreasing rates, reliability constraints and network security. To solve the problem, Particle Swarm Optimization (PSO) Algorithms has been employed. To evaluate the effectiveness of the proposed method, the problem has been implemented on a power system with 15 generating units and the results have been evaluated.DOI:http://dx.doi.org/10.11591/ijece.v4i6.672

Modelling Heat Transfer in an Extruder for Recycling Plastics into Filaments for use in Additive Manufacturing

Global production of plastic increased by 500% over the last 30 years and it is expected to continue to grow to 850 million tons/year by 2050. Plastic use results in a substantial environmental burden due to both land and water pollution as plastics take 10 to 450 years to decompose in landfills. This has resulted in increased calls for innovative ways to recycle plastics, one of which is a decentralised solution where wasted plastics are recycled into filaments for 3D printing. This has been identified as a promising solution, especially for low-income communities in the global south where waste management infrastructure is inadequate. However, studies have highlighted the need for more research and development in the extruder design and operation, especially in terms of optimising temperature distribution and the cooling rate in order to prevent poor filament quality and inconsistent filament diameter. This paper describes the modelling of the temperature distribution and cooling rate of an extruder. The innovation is that the extruder is designed to be built and operated in low-income settings of the global south using locally available materials and skills. The aim of the work is to develop a mathematical model for evaluating the thermal distribution in the extruder as well as optimise the cooling rate conditions. The model is useful for optimising the operating conditions such as ambient temperature, extrusion temperature, extrusion speed, cooling rate and spooling mechanism

Optimising tibia implants : comparative study of lattice designs and material performance under gait cycles

This study advances orthopaedic implant design by examining the impact of lattice structures on gait cycles and integrating biomimicry principles for superior patient outcomes. Using Finite Element Analysis (FEA), three lattice designs; Face Centred Cubic (FCC), Body Centred Cubic (BCC), and a hybrid Face-Body Centred Cubic (FBCC) were evaluated with materials including Ni-Ti Shape Memory Alloy, TNTZ Alloy, and AZ91D Alloy for its suitability in orthopaedic implants. AZ91D emerged as the optimal material based on compression analysis, offering the best balance of strength and weight. Tibia bone implants made from AZ91D were tested under various gait cycle conditions, including loading-level knee bending, 20% bending, and 30% bending, where the FBCC structure outperformed others due to its enhanced load transfer capabilities. Porosity effects were analysed by varying strut diameters between 0.3 mm and 0.6 mm, resulting in a 40% stiffness difference compared to natural bone, affirming its suitability for biomimetic applications. This innovative approach achieves an ∼86% weight reduction compared to titanium-based implants, significantly enhancing comfort, reducing physical strain, and improving mobility for amputees. By leveraging advanced topology optimisation and material science, this research provides valuable insights into lightweight and high-performance orthopaedic implant development

On the causes of pulsing in continuous turbidity currents

Velocity pulsing has previously been observed in continuous turbidity currents in lakes and reservoirs, even though the input flow is steady. Several different mechanisms have been ascribed to the generation of these fluctuations, including Rayleigh‐Taylor (RT) instabilities that are related to surface lobes along the plunge line where the river enters the receiving water body and interfacial waves such as Kelvin‐Helmholtz instabilities. However, the understanding of velocity pulsing in turbidity currents remains limited. Herein we undertake a stability analysis for inclined flows and compare it against laboratory experiments, direct numerical simulations, and field data from Lillooet Lake, Canada, and Xiaolangdi Reservoir, China, thus enabling an improved understanding of the formative mechanisms for velocity pulsing. Both RT and Kelvin‐Helmholtz instabilities are shown to be prevalent in turbidity currents depending on initial conditions and topography, with plunge line lobes and higher bulk Richardson numbers favoring RT instabilities. Other interfacial wave instabilities (Holmboe and Taylor‐Caulfield) may also be present. While this is the most detailed analysis of velocity pulsing conducted to date, the differences in spatial scales between field, direct numerical simulations, and experiments and the potential complexity of multiple processes acting in field examples indicate that further work is required. In particular, there is a need for simultaneous field measurements at multiple locations within a given system to quantify the spatiotemporal evolution of such pulsing