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Numerical modelling of non-fullerene organic solar cell with high dielectric constant ITIC-OE acceptor
摘要： The low dielectric constant of organic semiconductors has been a limiting factor in the organic photovoltaics. Non-Fullerene Acceptor Bulk Heterojunction (NFA-BHJ) organic solar cells with high dielectric constant acceptors have been gaining a lot of attention. No simulation work has been done on NFA-BHJ organic solar cell with a high dielectric constant acceptor so far to study the influence of various material parameters on the device performance. In this work, a comprehensive device modelling of the conventional structure of NFA-BHJ with poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c]dithiophene-4,8-dione)] (PBDB-T)as the polymer donor and (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetraki(4-hexylphenyl)-dithieno [2,3-d:2,3-d]-s-indaceno [1,2-b:5,6-b]dithiophene)) with Oligo-Ethylene side chain (ITIC-OE) as the non-fullerene acceptor is performed. We did a detailed analysis on the impact of technological parameters on the cell performance and optimized the device characteristics to produce improved efficiency. Numerical simulation is done using SCAPS 1-D program and the validity of simulated output has been verified by comparing with the measurements from reported literature. Optimization of the device parameters produced an improved device performance with an open circuit voltage of 0.9562 V, short circuit current density of mA/cm2, Fill factor of 69.75 % and a power conversion efficiency of 11%. The results are encouraging to develop NFA-BHJ organic solar cells with high dielectric constant acceptors in the near future.
关键词： numerical modelling,Non-Fullerene Acceptor Bulk Heterojunction,high dielectric constant,ITIC-OE acceptor,organic solar cells
更新于2025-09-23 15:19:57
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Applicability of small-signal laser and fiber models for passive optical networks operating at the 1550??nm window
摘要： Small-signal techniques are a useful engineering tool to estimate system performance, though small-signal models need to be tested against the large-signal from which they are derived. We show that combined small-signal models for lasers and optical fiber are valid for passive optical networks employing directly modulated semiconductor lasers, provided that the modulation extinction ratios are < 4 dB and the transmission distances < 25 km. For larger extinction ratios and longer transmission distances, large-signal approaches are needed in order to investigate system capabilities. The small-signal models break down due to the increasing adiabatic chirp in semiconductor lasers with increasing modulation current. We estimate how the small-signal models can estimate for the performance of 10 Gbit/s signal from directly modulated lasers. We verify the equivalence of the small-signal and large-signal regimes and we develop a quality metric to identify the range of fiber lengths and signal extinction ratios over which the small-regime remains valid.
关键词： Frequency,Modulation,Passive Optical Networks,Semiconductor lasers,Phase,Fiber dispersion,Numerical modelling
更新于2025-09-23 15:19:57
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Investigation of spectrally-dependent phonon relaxation mechanism in Yb:YAG gain media and its consequences for thin disk laser performance
摘要： Nonlinear phonon relaxation in Yb:YAG gain media has previously been investigated, and a hypothesis correlating photo-induced free electrons and heat generation in crystals pumped at a wavelength of 940 nm was established (Brandt et al 2011 Appl. Phys. B 102 765–8). Later, we demonstrated efficient suppression of nonlinear phonon relaxation by zero-phonon line (ZPL) pumping of Yb:YAG (969 nm). However, no hypothesis has yet been tested that correlates the heat load and the free electrons in Yb:YAG media. We investigate, both theoretically and experimentally, the behaviour of an Yb:YAG slab pumped by a high-power laser diode at a conventional broadband line (absorption maximum at 941 nm) and a ZPL (absorption maximum at 969 nm), and we compare the generated photocurrent, temperature, and absorbed pump power for those two pump wavelengths. Although the hypothesis established by Brandt et al (2011 Appl. Phys. B 102 765–8) was not confirmed, and the measured photocurrent was identical for the two pump wavelengths, our measurement contributes to the knowledge of the inner processes in Yb:YAG active media. In the following steps we characterized an Yb:YAG thin disk laser, measured the spectrally-resolved absorption and disk surface temperature, and optimised our predictive model of thin disk behaviour. All the experimental and theoretical results are reported.
关键词： numerical modelling,thin disk,thermal effects,Yb:YAG,photocurrent
更新于2025-09-16 10:30:52
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Numerical modelling and experimental validation of thermal history of titanium alloys in laser beam melting
摘要： During selective laser melting processes parts will heat up with each layer depending on the geometry and surrounding powder material. This leads to process boundary conditions that are not certainly defined and can induce unstable melt pool sizes. These will have an influence on surface roughness and dimensional accuracy. One way to deal with this is an individual adaptation of process parameters, but without knowing the exact thermal boundary conditions in each layer one will not be able to adapt the parameters properly. In this paper a model for prediction of the macroscopic temperature history is presented and experimentally calibrated. A sample with characteristic features like overhanging’s was designed. These samples were produced by selective laser melting and simultaneously monitored by an infrared camera to calibrate the boundary conditions of a numerical model. This lays the foundation for part individual adaption of process parameters to improve the quality of SLM parts.
关键词： Experimental Validation,Numerical Modelling,Titanium Alloys,SLM
更新于2025-09-12 10:27:22
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[IEEE 2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO) - Manama, Bahrain (2019.4.15-2019.4.17)] 2019 8th International Conference on Modeling Simulation and Applied Optimization (ICMSAO) - Thermal Analysis in Laser Surface Alloying of Ti6Al4V with TiC
摘要： Laser Surface Alloying employs high laser power density to melt alloying material and a portion of the underlying substrate to form an alloyed layer over substrate. As melting temperature of Ti alloys is very high, it poses difficulty in alloying using conventional methods. Titanium alloys are vulnerable to induced thermal stresses at high temperature. In this study thermal analysis of laser surface alloyed Ti6Al4V with TiC at different laser power and laser spot diameter is modelled. Melt pool depth and developed thermal stresses at different process parameters are predicted. Subsequently, model is verified with published experimental results. It is observed that developed model is adequate in predicting pool depth with 6.43% error. The von-Mises stress is observed to be lower than the yield strength of the material, indicating less possibility of thermally induced cracks.
关键词： Thermal stress,Numerical modelling,Pool depth,Laser surface alloying,Thermal analysis
更新于2025-09-12 10:27:22
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Numerical study of a two pass shell and tube latent heat energy storage system
摘要： The thermal behaviour of PCM in different configuration of heat exchangers is analysed for the purpose of design and optimisation of a latent heat thermal energy storage unit. Numerical modelling in conjunction with scale analyses provides a cost effective means to examine the performance of different configurations of latent heat storage systems. The main objective of this work is to scale down an experimental set up to a numerical model which can represent the thermal behaviour of the system with reasonable computational time. A U-tube element from a shell and tube thermal storage experimental set up was used as the model for a numerical study, using FLUENT. The predicted results of the temperature profiles in the PCM domain are in agreement with the measured data. Moreover, the heat transfer fluid outlet temperature and duration of the phase change processes are consistent with experimental results. Using the experimental initial temperature at each point in comparison to using an average initial temperature from all points can improve the predicted temperature profiles. Furthermore, three different mushy zone constants; namely 105, 107, 108 were used to examine the impact on the rate of melting. It was found that the constant 107 provides a closer solution to the experimental results. Results of this study show that the small scale model can represent the lab scale set up, providing more detail about the thermal behaviour of the PCM which is difficult to capture by measurement. The model can also be used for further examination of a high temperature PCM within the same set up for a CSP application.
关键词： FLUENT,shell and tube,numerical modelling,PCM,latent heat thermal energy storage
更新于2025-09-10 09:29:36
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[IEEE 2018 20th International Conference on Transparent Optical Networks (ICTON) - Bucharest (2018.7.1-2018.7.5)] 2018 20th International Conference on Transparent Optical Networks (ICTON) - Time Domain Modeling of Multimode Selenide-Chalcogenide Glass Fiber Based Mid Infrared Spontaneous Emission Sources
摘要： We develop time domain models of selenide-chalcogenide glass fiber based MIR spontaneous emission sources. The modeling parameters used are derived from experimentally obtained data. The models are based on the rate equations’ approach to simulate the distribution of ions between the relevant energy levels. The optical power distribution within the fiber is calculated by solving a set of partial differential equations using specially developed finite difference schemes that allow for a direct inclusion of the step discontinuities appearing at the fiber facets. The results obtained allow for a thorough analysis of luminescence from lanthanide ion doped chalcogenide fibers.
关键词： mid infrared photonics,chalcogenide glass fibers,numerical modelling
更新于2025-09-10 09:29:36
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Solar plant with short diffuser concept: Further improvement of numerical model by included influence of guide vane topology on shape and stability of gravitational vortex
摘要： An alternative renewable energy concept, i.e. the concept of a solar power plant with short diffuser (SPD), was numerically investigated by more advanced computational fluid dynamics (CFD) model. Developed model is characterized by a more sophisticated and streamlined guide vane topology. The main novelty of this work is conducted optimization of the guide vane topology, for a specific novel application related to the alternative renewable energy concept (SPD). Optimization involved determining the required guide vane topology using minimal number of geometry influencing parameters. The objective was to result in vortex genesis and stabilization with respect to the desired circumferential velocity and to minimize the required pressure potential that is necessary for stable operation of the SDP plant. Provided numerical investigation was necessary, and for sure a step forward towards consideration of the experimental plant (which will assume introduction of the turbines). It needs to be taken into account that we deal with complex flow structure that requires gradual numerical investigation, in order to be able to get detail insight in the various influences and processes that can strongly affect SPD operating parameters. The guide vane topology was altered to develop an SPD capable of establishing and maintaining a stable gravitational vortex in pressure ranges which resemble atmospheric vortex phenomena (feasible for development of a compact system, and with maximal velocities in chimney throat regions below 20 m s?1). The study outlines nine cases, each representing the altered guide vane design, where the best case is determined and compared with the available experimental data from other research groups. The comparison indicates that the numerical model, although quite simple, is accurate and robust in predicting the distribution of local velocity and pressure profiles and fit for implementation on wind turbines in order to determine the influence of the installed turbines on the vortex shape and stability in a future study. An important finding is that the swirl ratio can be manipulated by altering the guide vane shape, and it is independent of the Reynolds number (which will be important during the design phase since it can be used as a control strategy for vortex genesis and as a prevention of unintentional genesis regarding additional multiple vortices). The gained numerical results revealed specific operating conditions that will ensure a safer environment around the SPD and that will enable a carbon free electricity production.
关键词： Solar power plant,Numerical modelling,Carbon-free electricity production,Thermodynamics,Vortices,Solar energy
更新于2025-09-04 15:30:14
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Applicability of Effective Medium Approximations to Modelling of Mesocrystal Optical Properties
摘要： Rigorous superposition T-matrix method is used to compute light interaction with mesocrystalline structures. The results are used to validate the applicability of effective medium theories for computing the effective optical constants of mesocrystal structures composed of optically isotropic materials. It is demonstrated that the Maxwell-Garnett theory can fit the rigorous simulation results with an average accuracy of 2%. The thus obtained refractive indexes can be used with any electromagnetic simulation software to represent the response of mesocrystals composed of optically small primary particles arranged into a cubic type lattice structures.
关键词： Mie scattering,numerical modelling,particles,mesocrystals,T-matrix,Maxwell-Garnett,light scattering,effective medium theory
更新于2025-09-04 15:30:14