Non-optimal Configurations Research Articles

Generic Framework for the Optimal Implementation of Flexibility Mechanisms in Large-Scale Smart Grids

This paper aims to provide the smart grid research community with an open and accessible general mathematical framework to develop and implement optimal flexibility mechanisms in large-scale network applications. The motivation of this paper is twofold. On the one hand, flexibility mechanisms are currently a hot topic of research, which is aimed to mitigate variation and uncertainty of electricity demand and supply in decentralised grids with a high aggregated share of renewables. On the other hand, a large part of such related research is performed by heuristic methods, which are generally inefficient (such methods do not guarantee optimality) and difficult to extrapolate for different use cases. Alternatively, this paper presents an MPC-based (model predictive control) framework explicitly including a generic flexibility mechanism, which is easy to particularise to specific strategies such as demand response, flexible production and energy efficiency services. The proposed framework is benchmarked with other non-optimal control configurations to better show the advantages it provides. The work of this paper is completed by the implementation of a generic use case, which aims to further clarify the use of the framework and, thus, to ease its adoption by other researchers in their specific flexibility mechanism applications.

A multi-objective optimization method of inflow control device configuration

Inflow control device (ICD) restricts flows of certain sections to achieve a uniform push of water oil contact along a horizontal well. The efficiency of ICD depends on its configuration (location, number of nozzles, and nozzle sizes). Traditionally, optimal ICD configurations have been selected using a trial and error approach simulating different configurations. This method is time-consuming and the outcome can be limited by pre-set candidates, thus may result in non-optimal configurations. In this paper, a method involving several optimization objectives is proposed to obtain the optimal ICD configuration, in order to reach an optimal total production before water breakthrough. A flow coupling model (permeation flow – nozzle flow – inner tubing flow) of horizontal wells completed by ICDs is established to calculate the inflow profile and the pressure distribution along the horizontal wellbore. The production rate and the water breakthrough time are the optimization objectives, and the sand control condition (production pressure drawdown < critical pressure drawdown of sanding onset) is taken as one of the constraints of optimization. Then the NSGA-II algorithm is employed to search for the Pareto frontier based on the model of coupled flow. Selected by the TOPSIS method from the Pareto frontier, the optimal ICD configuration ensuring optimal total production and no sanding is acquired. The original data of well A1 in SL oilfield are used for case study. The optimal configuration is compared with single-objective optimization results and open hole completion in terms of production rate and water breakthrough time. By predicting the total productions of different configurations before water breakthrough, we think the optimization method is capable of determining the optimal configuration. This research can provide some theoretical support for the determination of ICD configuration in horizontal wells.

Interdisciplinary decision support model for grid-bound heat supply systems in urban areas

BackgroundIn the past two centuries, energy consumption per capita has significantly increased. At the same time the fundamentals of energy provision have continuously developed towards fossil energy sources. This extended use of finite, unequally distributed and emission-intensive energy sources poses a challenge to both the energy, the climate and therefore the socio-ecological systems. Consequently, solutions are needed to reduce the fossil energy demand while fulfilling our daily energy services. District heating systems powered by renewable energy can contribute to this societal mission.MethodsThis paper presents the co called Eco.District.Heat-kit, a novel planning model supporting future decision-making processes regarding grid-bound heating. The interdisciplinary approach assesses the feasibility of district heating systems at different locations from a qualitative and quantitative perspective. Given the lack of quick and simple planning tools in this field, the Eco.District.Heat-kit provides a time-efficient pre-evaluation on the basis of widely available input data.ResultsThe decision support model rates district heating networks regarding the thematic areas of (1) integrated spatial and energy planning (2) costs, (3) resources, and (4) environment and climate. In addition, it involves a long-term planning horizon by including spatial development and climate scenarios until 2050. Finally, the Eco.District.Heat-kit identifies parameters both positively and negatively influencing the overall rating. This enables end-users to sort out non-optimal configurations before entering a more detailed planning stage.ConclusionsDue to the straightforward methodological approach and the focus on basic parameters of district heating system planning, the Eco.District.Heat-kit supports energy suppliers, urban-planners and decision-makers at the beginning of planning processes. In order to increase both transparency and applicability of the model, its functionality and input parameters are disclosed within this paper, enabling the recreation and adaptation towards user-specific needs and local situations.

A comparison of upper body kinematics and muscle activation between sit and stand computer workstation configuration

Very few studies considered the movement constraints imposed by the computer workstation during office computer work. The impact of computer workstation on user’s muscle and joint coordination is not yet understood. This study examined three workstation configurations (sitting and standing with elbow desk height, and sitting with elevated desk) and analyzed their corresponding posture, muscle effort and inter-joint and muscle coordination. We found that sitting computer workstation with an elevated desk associated with more non-neutral postures and increased muscle load, particularly on the shoulders. Properly set up sitting and standing workstations resulted in similar median values for postures and muscle loads, but standing workstation allowed for greater muscle dynamic ranges and could be beneficial for short duration mouse tasks. Identifying effects of non-optimal configurations can lead to interventions to help decrease risks of developing musculoskeletal disorders.

Shape optimisation of the support section of a tunnel at great depths

The shape optimisation of a cavity is typically performed without considering the previous support, which may significantly reduce the practical significance of such analyses. Even when an excavation section is optimised, failure of the surrounding rock in a tunnel cannot be prevented in the presence of excessive in situ stress. Thus, a support should be established to protect the stability of a tunnel from the failure of the surrounding rock. This study examines the optimal shape of the support that satisfies the optimisation criterion, which minimises the largest tangential stress along the inner edge of the support, for a specific net tunnel size and support strength. The optimisation process is to solve a series of forward problems using the conformal mapping method for a plane elasticity complex function. The tangential stress along the inner edge of the support is selected as the objective function, and the coefficients of the mapping function are considered as the design variables. The minimum value of the objective function is calculated based on the mixed penalty function method and the optimal support shape that satisfies the given constraints can be obtained. The stress state of an optimally shaped tunnel support is significantly improved compared to non-optimal configurations, and the stress concentration along the inner edge of the support is minimised.

Network-wide energy optimization for adaptive embedded systems

This paper discusses network-wide energy optimization of embedded systems which can adapt by switching configurations. We model applications and their task chains in a network of embedded devices, including sleep modes and change of configuration, which provides a basic adaptation mechanism. We present a formal model of the energy consumption for such systems and apply it to automotive embedded systems. In particular, we develop new potential for network-wide energy savings as well as optimizations for adaptive systems. For instance, we show that non-optimal configurations may lead to a globally optimal system setup, if a system adapts regularly.

Vision Tape—A Flexible Compound Vision Sensor for Motion Detection and Proximity Estimation

In this paper, we introduce Vision Tape (VT), a novel class of flexible compound-eye-like linear vision sensor dedicated to motion extraction and proximity estimation. This novel sensor possesses intrinsic mechanical flexibility that provides wide-range adaptive shape, allowing adjustable field of view as well as integration with numerous substrates and curvatures. VT extracts Optic Flow (OF) of the visual scene to calculate the motion vector, which allows proximity estimation based on the motion parallax principle. In order to validate the functionality of VT, we have designed and fabricated an exemplary prototype consisting of an array of eight photodiodes attached to a flexible PCB that acts as mechanical and electrical support. This prototype performs image acquisition and processing with an integrated microcontroller at a frequency of 1000 fps, even during bending of the sensor. With this, the effect of VT shape on motion perception and proximity estimation is studied and, in particular, the effect of pixel-to-pixel angle is discussed. The results of these experiments allow estimating an optimal configuration of the sensor for OF extraction. Subsequently, a method that enhances the quality of extracted OF for non-optimal configurations is proposed. The experimental results show that, by applying the proposed method to VT in a suboptimal curvature, the quality of the OF can be increased by up to 176% and proximity estimation by 178%.

Locomotion modes of a novel piezo-driven microrobot: Analytical modeling and performance evaluation

This paper presents a novel, sliding, A-shaped microrobot with nanometric resolution for precision positioning applications. The microrobot is actuated near its natural frequency using a piezoelectric stack actuator to produce translational motion. The dynamic modeling of the mechanism is based on the assumptions of the linear piezoelectric behavior and the Coulomb friction model. Using this model the required condition for generating net motion is found. The suitability of three simple, friction-based locomotion modes for implementation on the proposed device is addressed. Influences of some important configuration parameters on the behavior of the microrobot, based on defined criteria, are investigated. Even with non-optimal configurations, simulations show a velocity of 1mm/s, a motion resolution of 180nm, and a power consumption of 1.5mW. Comparisons made with other microrobots of the same locomotion modes indicate good improvements in all criteria.

Process Optimization of Finish Turning of Hardened Steels

Process planning and optimization is crucial to help establish the economic and quality viability of hard turning processes with the presence of a wide spectrum of tooling and process parameters. A systematic methodology is discussed in this paper to design the optimal tool geometry and cutting conditions for hard turning, incorporating the consideration of part finish, tool wear, and material removal rate. Experimental demonstration of the optimization scheme is presented at two levels: the first level is to validate the process prediction results and the second is to validate the optimization results. Hardened AISI 1053 steel was selected as the workpiece material in this study and its material property related parameters, including the Johnson–Cook constants and wear coefficients, were determined based on the machining tests. It is seen that the cutting force and tool wear progression agrees well with the predictions from 3-D oblique cutting model, and the machined surface roughness can be predicted with a surface kinematic model incorporating the plowing effect. The experimental results also showed that the process configuration as derived from the analytical optimization procedure lends itself to superior results in comparison to other experimental results under non-optimal configurations.

A BRANCH AND BOUND ALGORITHM FOR TOPOLOGY OPTIMIZATION OF TRUSS STRUCTURES

An algorithm for the selection of a minimum weight truss, out of a set of possible candidate trusses, is presented. The trusses are subject to stress and deflection constraints. Multiple loading conditions are considered. Starling with a ground structure, a sequence of subtrusses called candidate trusses are generated and analyzed. Several criteria are used to rapidly discard non-optimal configurations. Sequential Quadratic Programming is used to solve a non-linearly constrained problem which is part of the algorithm. A technique, frequently used to keep second derivative approximations positive definite, is found to give numerical instabilities. Possible modifications to improve stability are discussed. Finally, three examples are given to demonstrate the algorithm.

Calculation of the Optimum Dimensions of Collimators for Neutron Diffraction

If the horizontal angular divergence and total width of the aperture are preset, the neutron intensity transmitted by a primary Soller collimator will vary with the number of channels. For a given set of collimator system dimensions there is an optimum number of collimating channels, and a corresponding maximum in the transmitted intensity. For a broad range of system dimensions, it is possible to calculate both of these quantities explicitly. This provides a simple and rapid means of comparing alternatives in collimator design and location, for both optimal and nonoptimal configurations.