This article describes an aging study of a foam-vacuum insulation panel (VIP) composite insulation board installed on a test wall in a natural exposure test facility through a 30-month period. Silica-based VIPs with a polymeric barrier film were used in this study. The study results showed the effectiveness of a VIP-based insulation to reduce the heat gains and losses through a wall compared to regular rigid foam insulation of the same thickness. However, the long-term performance monitoring indicated a gradual decline in the thermal performance of the foam-VIP composite. In addition, one-dimensional numerical models were created to simulate the in situ behavior of the foam-VIP composite. One model utilized constant thermal conductivities of the test wall components and another utilized temperature-dependent thermal conductivities; the latter used measurements of conductivity over temperatures ranging from −15 to 55 °C. The results of the simulations emphasized the need to use both tem... [more]

Germany has experienced rapid growth in onshore wind capacities over the past two decades. Substantial capacities of offshore wind turbines have been added since 2013. On a local, highly-resolved level, this analysis evaluated if differences in wind speed forecast errors exist for offshore and onshore locations regarding magnitude and variation. A model based on the Extra Trees algorithm is proposed and found to be a viable method to transform local wind speeds and capacities into aggregated wind energy feed-in. This model was used to analyze if offshore and onshore wind power expansion lead to different distributions of day-ahead wind energy forecast errors in Germany. The Extra Trees model results indicate that offshore wind capacity expansion entails an energy forecast error distribution with more frequent medium to high deviations, stemming from larger and more variable wind speed deviations of offshore locations combined with greater geographical concentration of offshore wind tur... [more]

Currently, in most countries, the electricity sector is liberalized, and electricity is traded in deregulated electricity markets. In these markets, electricity demand is determined the day before the physical delivery through (semi-)hourly concurrent auctions. Hence, accurate forecasts are essential for efficient and effective management of power systems. The electricity demand and prices, however, exhibit specific features, including non-constant mean and variance, calendar effects, multiple periodicities, high volatility, jumps, and so on, which complicate the forecasting problem. In this work, we compare different modeling techniques able to capture the specific dynamics of the demand time series. To this end, the electricity demand time series is divided into two major components: deterministic and stochastic. Both components are estimated using different regression and time series methods with parametric and nonparametric estimation techniques. Specifically, we use linear regress... [more]

According to the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report in 2013 (IPCC, 2013) [...]

hHoneycomb, a self-reconfigurable cleaning robot, is designed based on tiling theory, to overcome the significant challenges experienced by the fixed morphology cleaning robot. It consists of four regular hexagonal units and the units are connected by a planar revolute joint which helps in reconfiguration. This platform attains six distinct configurations (bar, bee, arch, wave, worm, and pistol) and these configurations have circular arcs and irregular concave and convex boundary that would help in accessing various obstacles in the cleaning space. This work addresses the mechanical design, system-level modeling, reconfiguration of the platform via hinged joint mechanism, mobility of the platform, polyhex based tiling set, and power consumption during reconfiguration. The strength of the mechanical structure is studied based on the structural analysis of the system using finite element method. Based on the natural frequency and deformation pattern, the proposed design is validated and... [more]

Contributed by the low cost, the simulation method is considered an attractive option for the optimization and design of the supersonic combustor. Unfortunately, accurate and satisfactory modeling is time-consuming and cost-consuming because of the complex processes and various working conditions. To address this issue, a mathematical modeling for the combustor on the basis of the clustering algorithm, machine learning algorithm, and model migration strategy is developed in this paper. A general framework for the migration strategy of the combustor model is proposed among the similar combustors, and the base model, which is developed by training the machine learning model with data from the existing combustion processes, is amended to fit the unexampled combustor using the model migration strategy with a few data. The simulation results validate the effectiveness of the development strategy, and the migrated model is proved to be suitable for the new combustor in higher accuracy with l... [more]

Quadruped robots can be used to transport loads or conduct rescue missions on tough terrain. In addition to flexibility and adaptability to complex terrain, the hydraulic driven quadruped robots also have the important characteristic of energy consumption. This paper studies the trot gait motions of the quadruped robot SCalf. The energy model including the mechanical power and heat rate is established, which can be used to obtained the energy consumption of the robot. Compared with a cubic spline interpolation reference trajectory, a foot trajectory based on Fourier series is studied to reduce the joints energy consumption, and the parameters of the foot trajectory are acquired by the Pattern Search method. The effectiveness of the energy efficient trajectory is verified by simulations and verified on the robot prototype.

This paper presents a numerical investigation of ignition and combustion stabilization of a novel design of a solid-fuel ramjet (SFRJ) motor with and without swirl flow. The proposed design includes two solid fuels, retaining the simple design of the classic SFRJ. Numerical simulations of unsteady, turbulent, reactive, and swirling flow coupled with solid-fuel pyrolysis have been performed using an in-house CFD solver. Experiments on SFRJ were conducted via a connected-pipe test facility to validate the developed code. Furthermore, the code was validated for chemical reactions, heat diffusion, and swirl flow by using benchmark test cases of shock-induced, semi-infinite plate, and dump combustor with swirl flow, respectively. Then, the proposed and classic designs were simulated for the same inflow conditions and configurations, and the results were analyzed and discussed. It is found that the mixing degree, reactant residence time, mass flux, ignition delay time, and regression rate im... [more]

Aerodynamics of the Darrieus wind turbine is an extremely complex issue requiring the use of very advanced numerical methods. Additional structural components of this device, such as, for example, a rotating shaft disturb the flow through the rotor significantly impairing its aerodynamic characteristics. The main purpose of the presented research is to validate the commonly-used unsteady Reynolds averaged Navier−Stokes (URANS) approach with the shear stress transport (SST) k-ω turbulence model based on the particle image velocimetry (PIV) studies of a two-bladed rotor operating at the moderate tip speed ratio of 4.5. In the present numerical studies, a two-dimensional turbine rotor with a diameter of 1 m was considered. The following parameters were evaluated: instantaneous velocity fields; velocity profiles in the rotor shadow and aerodynamic blade loads. The obtained numerical results are comparable with the reference experimental results taken from the literature. The second purpose... [more]

To address the problem of the supply−demand imbalance caused by network transmission losses in integrated power and heating systems (IPHS), this paper presents an optimal economic dispatch strategy to minimize system operation cost and realize coordination and optimization between power and heat. Firstly, an innovative economic dispatch model considering transmission losses is developed, where both power and heat transmission losses models are established with good precision together. In addition, the coordination equation is derived from the formulated nonlinear, multi-constrained coupling optimization problem, where the coordination relationship of units’ outputs is clearly analyzed in an analytic way. Then, a double- λ -iteration algorithm is proposed, which can not only effectively solve the nonlinear coupling optimization problem but also decrease computation burden with faster convergence rate. Finally, simulations performed on five case studies illustrate the satisfying perf... [more]

Harmonic stability of double-fed induction generators (DFIGs) now has become a significant topic because of its harmful impact on power quality issues of the system. Since the double pulse width modulation (PWM) converter is one of the main harmonic sources in DFIGs, it may cause harmonic instability with increasing harmonic contents. Thus, the modeling and stability analyses of PWM converters in DFIGs are essential steps to assess the harmonic stability of DFIGs. Aiming at dual PWM converters, which include the grid side converter (GSC) and the rotor side converter (RSC), this paper divides converters into two parts: circuit modules and control modules. Closed-loop input impedance models of each module are then derived by means of transfer functions. Hence, the stability of the system can be readily predicted through Nyquist diagrams. The contributions of parameters to the system’s harmonic stability are also identified. Finally, time-domain simulations are conducted in a real-time di... [more]

It is well accepted that faults have significant impacts on the safe production of underground coal mines; however, the fault-slip mechanism during longwall mining through a fault still needs to be investigated. In this study, the distribution of microseismicity events during panel mining through a fault is analyzed, and 3-dimensional fast Lagrangian analysis of continua was used to study the mining stress distribution and fault-slip behavior under the two different mining directions, i.e., mining the panel through the fault from the footwall, or mining the panel through the fault from the hanging wall. The research shows that when the panel is mined through the fault from the footwall, the shear displacement of the fault is significantly greater than those created by mining the panel through the fault from the hanging wall. Under the two mining directions, the variation behaviors of the normal stress and shear stress on the fault are quite different, and fault-slips mainly occur in fa... [more]

This study aims to investigate the influence of the current direction on the energy production of a tidal turbines array. It is based on a three-dimensional (3D) numerical simulation of the flow where the turbines are represented with actuator disks. The case study consists of modelling the energy extraction of a small array of turbines (staggered and aligned layouts) placed in the Raz Blanchard (Alderney Race, France). The simulations are performed with hydrodynamic data (current magnitude and direction) representative of a mean tide, with several resistance forces and ambient turbulence intensities. The influence of the current direction on the energy production is highlighted by comparing the simulations forced with the real current direction with those in which the angle of incidence between the incoming flow and the turbine’s axis is “switched off” (bi-directional flow). When the flow is aligned with the turbines’ axis (misalignment “switched off”), the staggered layout produces m... [more]

Of the cost centres that combine to result in Levelised Cost of Energy (LCOE), O&M costs play a significant part. Several developers have calculated component costs, demonstrating how they can become commercially competitive with other forms of renewable energy. However, there are uncertainties relating to the O&M figures that can only be reduced through lessons learned at sea. This work presents an O&M model calibrated with data from real sea experience of a wave energy device deployed at the Biscay Marine energy Platform (BiMEP): the OPERA O&M Model. Two additional case studies, utilising two other O&M calculation methodologies, are presented for comparison with the OPERA O&M Model. The second case study assumes the inexistence of an O&M model, utilising a Simplified Approach. The third case study applies DTOcean’s (a design tool for ocean energy arrays) O&M module. The results illustrate the potential advantages of utilising real sea data for the calibration and development of an O&... [more]

In this study, a type-2 fuzzy chance-constrained fractional integrated programming (T2FCFP) approach is developed for the planning of sustainable management in an electric power system (EPS) under complex uncertainties. Through simultaneously coupling mixed-integer linear programming (MILP), chance-constrained stochastic programming (CCSP), and type-2 fuzzy mathematical programming (T2FMP) techniques into a fractional programming (FP) framework, T2FCFP can tackle dual objective problems of uncertain parameters with both type-2 fuzzy characteristics and stochastic effectively and enhance the robustness of the obtained decisions. T2FCFP has been applied to a case study of a typical electric power system planning to demonstrate these advantages, where issues of clean energy utilization, air-pollutant emissions mitigation, mix ratio of renewable energy power generation in the entire energy supply, and the displacement efficiency of electricity generation technologies by renewable energy ar... [more]

Despite the international trend of actively utilizing BIM in the field of energy simulation, it is difficult to actively utilize BIM in domestic certification-related practice. As a result, the work process is not integrated and the work efficiency is reduced, such as the occurrence of redundant tasks. In this paper, the integrated process based on the BIM geometry information automated extraction module was presented and its effectiveness was reviewed and verified through self-developed automation module and uniformity and error-causing analysis. The construction of an integrated process through automatic configuration information extraction has the advantages of reducing the workload, enabling additional tasks through module function expansion, sharing information through the web, and ease of service manufacture. In addition, an experiment comparing the data of automatic and manual calculations with three subjects confirmed that automatic calculation database through automation modul... [more]

With the compact circuit layout and small size, hydraulic manifolds sometimes cause high pressure loss. The purpose of this paper is to investigate the pressure loss under different circumstances with various geometry features and present solutions to reduce pressure loss. The pressure loss performance is evaluated by both experimental and numerical methods. Verified by the experiments, the numerical simulations are qualified to depict the correct trend of the pressure drop. After the basic analysis of traditional passages, three novel forms are proposed, which are very hard to be manufactured by a common method. Furthermore, the geometrical features are selected optimally by means of full factorial experiments to balance the pressure loss and space requirement. Moreover, taking advantage of 3D printing, it is possible to build the passages in novel forms which are beyond the capacity of conventional manufacturing. Results show that the pressure loss can be reduced considerably by adop... [more]

The Swiss energy strategy aims at increasing electricity generation from solar power by 2050, to fulfil Switzerland’s commitments in the Paris Agreement. However, the market of single- and two-family houses is characterized by low return rates for excess power injected to the grid, and the installation of rooftop solar photovoltaic (PV) is sensitive to financial incentives. We assess the drivers influencing the diffusion of rooftop solar PV systems until 2050, by employing an agent-based model. An agent is a single- or two-family house, and its decision to invest depends on the economic profitability of the investment, the agent’s income, environmental benefits (injunctive social norm), awareness and knowledge about the solar PV technology, and the impact of the social network (descriptive social norm). The model includes a synthetic population of agents, statistically equivalent to the true population. We also investigate the impact of different support policies, technology learning r... [more]

The limitation of nitrogen oxides emissions is nowadays a challenge in several engineering fields. Recent European regulations have reduced the maximum NOx emissions and therefore forced the glass production sector to develop emission reduction strategies. Two different systems have been developed within the framework of the European LIFE project and are currently applied to glass regenerative furnaces: the Waste Gas Recirculation (WGR) and the Hybrid Air Staging (HyAS). The above systems are primary NOx reduction strategies because they both operate to control the combustion evolution. Both WGR and HyAS systems have been conceived with the extensive use of Computational Fluid Dynamics (CFD) models: design strategies for both systems have been developed based on the use of CFD and are currently under use by glass furnace designers. In the present work, the CFD procedures routinely used for the design of the above systems are described. The systems effectiveness, due to the harsh condit... [more]

The present paper introduces an iterative methodology to progressively reduce building simulation model complexity with the aim of identifying potential trade-offs between computational requirements (i.e., model complexity) and energy estimation accuracy. Different levels of model complexity are analysed, from commercial building energy simulation tools to low order calibrated thermal networks models. Experimental data from a residential building in Germany were collected and used to validate two detailed white-box models and a simplified white-box model. The validation process was performed in terms of internal temperature profiles and building thermal energy demand predictions. Synthetic profiles were generated from the validated models and used for calibrating high order models. A reduction (trimming) procedure was applied to reduce the model complexity using an energy performance criterion prior to model trimming. The proposed methodology has the advantage of keeping the physical s... [more]

The ability to model fluid flow and heat transfer in process equipment (e.g., shell-and-tube heat exchangers) is often critical. What is more, many different geometric variants may need to be evaluated during the design process. Although this can be done using detailed computational fluid dynamics (CFD) models, the time needed to evaluate a single variant can easily reach tens of hours on powerful computing hardware. Simplified CFD models providing solutions in much shorter time frames may, therefore, be employed instead. Still, even these models can prove to be too slow or not robust enough when used in optimization algorithms. Effort is thus devoted to further improving their performance by applying the symmetric successive overrelaxation (SSOR) preconditioning technique in which, in contrast to, e.g., incomplete lower−upper factorization (ILU), the respective preconditioning matrix can always be constructed. Because the efficacy of SSOR is influenced by the selection of forward and... [more]

Operating rooms are stringent controlled environments. All influential factors, in particular, airborne particles, must be within the limits established by regulations. Therefore, energy efficiency stays in the background, prioritizing safety and comfort in surgical areas. However, the potential of improvement in energy savings without compromising this safety is broad. This work presents a new procedure, based on calibrated simulations, that allows the identification of potential energy savings in an operating room, complying with current airborne particle standards. Dynamic energy and airborne particle models are developed and then simulated in TRNSYS and calibrated with GenOpt. The methodology is validated through experimental contrast with a real operating room of a hospital in Spain. A calibrated model with around 2% of error is achieved. The procedure determines the variation in particle concentration according to the flow rate of ventilation supplied and the occupancy of the ope... [more]

In several industrial sectors, induction machines are being replaced with permanent magnet based alternatives, owing to the potential for higher power density and efficiency. However, high-speed applications feature a wide flux-weakening region, where advanced induction machines could bring benefits in terms of system-level optimization. This paper gives an overview the technological challenges for high-speed drives with induction machines, materials, simulations and future challenges for the power electronics in these applications. The target application is a high-speed induction machine for a naval turbocharging system. The comparison with permanent magnet synchronous machines will demonstrate how the extended flux weakening operation effectively allows for a weight reduction of the overall system.

To predict the thrust of magnetoplasmadynamic thrusters (MPDTs), a modified electromechanical model was proposed and a comparison with experimental results is presented in this paper. The motion of propellant in the thruster was divided into two portions: the axial motion which was accelerated by the interaction of current and induced self-field, and the swirling motion which was accelerated by the interaction of current and applied magnetic field. The electromechanical model was in good agreement with the experimental data, and the fitting degrees of the model were greater than 0.93. Furthermore, the influence of parameters on the performance of MPDT were investigated by utilizing the electromechanical model. The results indicate that the thrust performance of the thruster improved with the increase of discharge current, anode radius, applied magnetic field strength, and the decrease of mass flow rate. However, the large anode radius and low mass flow rate readily led to the failure o... [more]

Over the years, numerous investigations have established the gerotor fundamentals. This work aims to provide a complete review of the literature from the last decade, focusing on the articles published in the past five years on gerotor technology in hydraulic machines. The report gives a catalogue of guidelines based on the trochoidal-envelope definition, a background analysis, the worldwide distribution of articles in each continent and country and the most frequently used keywords in the field. The paper identifies state-of-the-art research, and reports on current mainstream ideas. From the historical background, this literature review reports the current approaches in gerotor pumps (geometry and performance approaches, modeling and numerical simulations), orbital motors and new concepts. The report will serve as a guide and a directory for novel engineers working with gerotor technology in hydraulic machines. Another intention of this paper is to disseminate the works of the researc... [more]