Comparative Numerical Study Research Articles

A Comparative Numerical Study of Effectiveness of Cold Aisle Containment in Data Centers by Varying Rack Porosity Using Computational Fluid Dynamics

Depending on specific needs and workloads, several racks with varied component densities may be used in a data center. As server density increases, porosity decreases, and the opposite is also true. A frequently used method called cold aisle containment separates hot air and cold air flows in data center settings to improve cooling effectiveness. In this paper, the performance of a data center is investigated using computational fluid dynamics, and the influence of porosity on cold aisle containment is evaluated using well-established non-dimensional performance parameters. The value of RTI without containment increased with an increase in porosity and a maximum RTI of 217 was found with a porosity of 0.75. Regardless of the rack number and porosity, containment provides the optimal RTI values. The results indicate that the SHI and RHI values for rack 1 for all porosities, without confinement, are outside of the permissible range and at higher porosities containment has no significant effects on SHI and RHI. RCILO values for racks 2, 3, and 4, with or without containment, fall within the 80-85% range, indicating temperatures below 13°C. RCIHI value is 1 for all cases considered indicating no rack is out of the recommended temperature of 25°C.

Shipment lead time hedging and coordination in prefabricated construction supply chain

This paper aims to coordinate a shipment lead time hedging (SLTH) problem between a building contractor and a logistics provider in the prefabricated construction supply chain (PCSC). In the PCSC, untimely (early or late) delivery of prefabs can lead to project time and cost overruns. To mitigate this challenge, the building contractor requires the logistics provider to reduce the shipping time variability, which is termed the SLTH strategy. While this benefits the building contractor, it also puts more investment and operational pressures on the logistics provider. To solve this conflict, we introduce a coordination mechanism which involves two terms: an SLTH level related cost term is charged by the logistics provider to the building contractor, and a constant transfer term is adopted to fairly allocate the system surplus. Three decentralized models are investigated: i.e., two Stackelberg game models with alternative decision-making sequences and an equal power model. Further comparative analysis and numerical studies reveal that our proposed coordination mechanism increases the SLTH level and ensures a win–win situation. Moreover, some interesting managerial implications are derived.

Numerical Simulation of Rapid Heat Storage in Plate-Fin Phase Change Heat Exchanger

Rapid phase change heat storage has significant application value in high-power density thermal management systems. This paper presents a comparative numerical simulation study of the rapid heat storage and release dynamics of two types of finned plate heat exchangers with different fin shapes. The study reveals that, under the same fin thickness and volume fraction, the contact surface area of triangular fins is 1.6 times that of rectangular fins, but the heat storage rate of triangular fin heat exchangers is 2 times that of rectangular fin heat exchangers. Due to the small characteristic scale and high material viscosity of the heat exchanger, the natural convection velocity of the liquid phase during the heat storage process is low, and its influence on enhancing the heat storage rate is weak.

Exponential Synchronization of Markovian Jump Neural Networks Based on Asynchronous Delayed-Feedback Controller With Uncertain Hidden Information.

Due to the complex network environment, the feedback information cannot be timely received by the controller. This article proposes a method on the exponential synchronization for the Markovian jump neural networks, which is achieved by designing a new asynchronous delayed-feedback controller, with its feedback delay taken into account. The quantized relationship between the exponential synchronization and the feedback delay is derived from a new designed Lyapunov functional, to acquire delay boundaries. With the help of a hidden-Markov process, the designed controller shows asynchrony, which allows controller modes to run free. In particular, the detection probability is assumed to be bounded known, marking a breakthrough over existing results. Moreover, the proposed method proves to be applicable in both synchronous and asynchronous cases. By using the proposed method, the computation freedom of the controller gain matrix can be substantially augmented. Further, comparative numerical studies are implemented to validate the effectiveness and superiority of the proposed method.

Comparative numerical study of floor heating systems using parallel and spiral coil

This article presents a comparative numerical study aimed at determining the optimal pipe layout solution for the heating benches of traditional steam baths, with the goal of ensuring an optimal temperature distribution for customer comfort. This layout incorporates insulation on the lower side to direct most of the emitted heat upwards. The temperature distribution across the floor surface varies depending on the configuration of the buried pipes. Calculations were performed using the CFD software "COMSOL Multiphysics" to investigate the thermal behavior of an underfloor heating system. The results were used to discuss certain critical parameters that require control for the proper operation of the system. These parameters include the flow velocity inside the pipes, inlet temperatures, and pipe configuration. A new parameter designed to measure the thermal homogeneity of the floor was introduced and evaluated. In general, the findings demonstrated that the modulated spiral configuration is the best solution, minimizing pressure losses while ensuring optimal thermal homogenization across the entire floor surface.

Towards the use of natural thermal insulation on the exterior of vertical building walls in desert regions: A case study in the city of Bechar, Algeria

The use of natural-based exterior thermal insulation systems constitutes a significant challenge for achieving energy efficiency of construction. The purpose of this article is to propose new exterior thermal insulation solutions based on natural materials such as wood wool, cellulose wadding, expanded cork, hemp fiber, and sheep’s wool, in order to minimize energy consumption, address durability concerns, maintain thermal comfort, and promote the use of natural materials in thermal insulation system designs. The methodology followed consists of presenting a comparative numerical study of different exterior insulation techniques (ETI) using a dynamic thermal simulator for desert regions. The study evaluated ETI systems for vertical walls attached to a concrete block wall, including one EPS system with coating (wet process) and six systems with cladding (dry process). The results show that applying exterior insulation to walls using the two cladding systems based on hemp fiber and sheep wool resulted in a total reduction in building energy consumption of 42.21% and 42.81%, respectively. These results confirm the effectiveness of natural materials in improving the energy performance of buildings, particularly the system based on sheep wool.

A Comparative Numerical Study of Thermo-Mechanical Behavior among Various IMC Joints under Thermal Cycling Condition

A Comparative Numerical Study of Thermo-Mechanical Behavior among Various IMC Joints under Thermal Cycling Condition

A Comparative Numerical Analysis of Cold Plates for Thermal Management of Chips With Hotspots

Abstract Thermal and hydraulic performances of seven water-cooled minichannel cold plates with different internal structures are compared using numerical analysis. Recent increasing demands for high-performance computing have led to serious challenges in the thermal management of electronic devices. In addition to dangerous on-chip temperatures, heterogeneous integration and local regions of elevated temperatures (hotspots) lead to nonuniform chip-level temperature distributions. As a result, the lifespan and reliability of electronic devices are adversely impacted. Due to the limitation of the air-cooled heat sinks, several new methods, such as liquid-cooled microchannel cold plates are developed to remedy these challenges. The objective of this work is to provide a comparative numerical study of the effectiveness of different minichannel cold plate internal structures in the thermal management of a chip with a nonuniform power map and a hotspot. Cold plate thermal resistance, on-chip temperature uniformity, and pump power were the metrics used for this comparison. For four coolant inlet flow rates within the laminar regime, it is seen that increasing the inlet flowrate enhances the thermal resistance of all cold plate designs while creating less uniformity in chip-level temperature distribution relative to the conventional straight microchannels. Concentrating pin fins on the hotspot showed a 7.2% reduction in thermal resistance, despite increasing temperature nonuniformity by about 7.6%. However, it is observed that hotspot-focused pin fins are more effective in lowering the chip's maximum temperature. Obtaining lower chip-level nonuniformity may be possible by modifying the inlet and outlet conditions of the cold plates.

Comparative study by simulation betweentwo structures CdS/CZTS and ZnS/CZTS via SCAPS-1D software

This comparative numerical simulation study investigates the electrical characteristics of two heterojunction thin-film solar cells based on Kësterites Copper Zinc Tin Sulfide. The study compared two solar cells with different structures, Zinc Oxide ZnO/Cadmium Sulfide CdS/Kësterites CZTS/Molybdenum Mo and Zinc Oxide ZnO/Zinc Sulfide ZnS/Kësterites CZTS/Molybdenum Mo, to determine which is more efficient in achieving maximum photovoltaic efficiency. The results showed that the ZnO/ZnS/CZTS/Mo solar cell is the better option, outperforming the CdS/CZTS/Mo solar cell in terms of short-circuit current density Jsc, open-circuit voltage Voc, form factor FF, and photovoltaic efficiency η. The study also investigated the effect of doping and layer thickness of CZTS and ZnS on photovoltaic parameters. The optimized ZnS/CZTS solar cell achieved an efficiency of 16.29% for ZnS and CZTS layer thicknesses of 0.02µm and 4μm, respectively, and doping concentrations of 1018 and 1016cm-3 , respectively. Overall, this study provides valuable insights for designing more efficient solar cells and optimizing their photovoltaic efficiency using Kësterites CZTS, CdS, and ZnS materials.

Energy based techno-economic and environmental feasibility study on PV/T and PV/T heat pump system with phase change material-a numerical comparative study.

A sustainable, affordable, and eco-friendly solution has been proposed to address water heating, electricity generation, space cooling, and photovoltaic (PV) cooling requirements in scorching climates. The photovoltaic thermal system (PV/T) and the direct expansion PV/T heat pump (PV/T DXHP) were numerically studied using MATLAB. A butterfly serpentine flow collector (BSFC) and phase change material (PCM) were assimilated in the PV system and MATLAB model was developed to evaluate the economic and enviroeconomic performance of the PV/T water system (PV/T-W), PV/T PCM water system (PV/T PCM-W), the PV/T DXHP system, and the PV/T PCM heat pump system (PV/T-PCM-DXHP). In this study, annual energy production, socioeconomic factors, enviro-economic indicators, and environmental characteristics are assessed and compared. Also, an economic, environmental, and enviro-economic analysis was conducted to assess the commercial viability of the suggested system. The PV/T PCM-DXHP demonstrated the highest electrical performance of 53.69%, which is comparatively higher than the other three configurations. The discounted levelized cost of energy (DLCOE) and payback period (DPP) of the PV/T PCM-DXHP were ₹2.87 per kW-h and 3-4years, respectively, resulting in a total savings of ₹67,7403 over its lifetime. Furthermore, installing this system mitigated 280.72 tonnes of CO2 emissions and saved the mitigation cost by ₹329,700 throughout its operational lifecycle.

A Comparative Numerical Study of Lithium-Ion Batteries with Air-Cooling Systems towards Thermal Safety

Given the growing demand for increased energy capacity and power density in battery systems, ensuring thermal safety in lithium-ion batteries has become a significant challenge for the coming decade. Effective thermal management plays a crucial role in battery design optimization. Air-cooling temperatures in vehicles often vary from ambient due to internal ventilation, with external air potentially overheating due to vehicle malfunctions. This article highlights the efficiency of lateral side air cooling in battery packs, suggesting a need for further exploration beyond traditional front side methods. In this study, we examine the impact of three different temperature levels and two distinct air-cooling directions on the performance of an air-cooling system. Our results reveal that the air-cooling direction has a more pronounced influence compared with the air-cooling temperature. By employing an optimal air-cooling direction and ambient air-cooling temperature, it is possible to achieve a temperature reduction of approximately 5 K in the battery, which otherwise requires a 10 K decrease in the air-cooling temperature to achieve a similar effect. Therefore, we propose an empirical formula for air-cooling efficiency under various conditions, aiming to provide valuable insights into the factors affecting air-cooling systems for industrial applications toward enhancing the fire safety of battery energy storage systems.

An Electromagnetic Load Identification Method Based on the Polynomial Structure Selection Technique

Electromagnetic loads can effectively monitor motor health and improve motor design. Considering the weak correlation of the modal shape and Chebyshev orthogonal polynomial in the space-time independent electromagnetic load identification method, a proposed method combining the polynomial structure selection technique together with limited measured displacement responses is presented, in which an error reduction ratio is used to pick out the significant mode shape matrix and the Chebyshev orthogonal polynomial. The time-history function of the electromagnetic load is reconstructed by combining the significant mode shape matrix and the identified concentrated load through modal transformation, and the corresponding spatial distribution function is fitted by the significant Chebyshev orthogonal polynomial. Eventually, a comparative numerical study considering the selection of significant components and measurement noise is carried out to prove the effectiveness of the presented method.

Comparative Numerical Study of Conventional and Hydraulic Wells Turbine for Ocean-Wave Energy Conversion

The Wells turbine is an ocean wave energy converter that has been implemented in several countries around the world. The hysteresis phenomenon, which causes a torque reduction when the rotor acquires air flow acceleration, is one of the Wells turbine's drawbacks. One enhancement strategy is converting the conventional Wells turbine, which operates in air, into a hydraulic Wells turbine, which operates in ocean water. This method aims to obtain a higher density of working fluid, which can increase the momentum acting on the Wells turbine blades. This research compared the performance and hysteresis phenomenon of conventional and hydraulic Wells turbines. A CFD method based on Reynolds Averaged Navier-Stokes (RANS) and k-ω SST turbulence model is used in this study. Under transient conditions, 3D modeling with periodic boundaries is applied to model the hysteresis phenomenon. This study demonstrated that the hydraulic Wells turbine outperforms the conventional Wells turbine. According to the simulation result, the hydraulic turbine achieves a significant improvement in maximum torque, approximately 124% of the conventional air turbine torque. The concept of immersing the Wells turbine in ocean water improves its efficiency as well. Furthermore, unlike the conventional one, the hydraulic Wells turbine does not exhibit hysteresis.

Comparative numerical and experimental studies of the tensile strengths of concrete incorporating recycled and natural aggregates

The aim of this study is to carry out a comparative numerical and experimental analysis of the tensile strengths of concrete. To do this, a physical and mechanical characterization of the aggregates was carried out, followed by the formulation of current concretes. Tensile strength characterization tests and a theoretical numerical study according to BAEL 91 revised 99 and Eurocode 2 of the concrete samples were carried out. The analysis of tensile strengths shows that at 7 days of age the average tensile strengths calculated according to Eurocode 2 are higher than those experimental and BAEL 91 revised 99. At 28 days of age, the experimental results are higher than the theoretical results obtained, except for the average tensile strengths of BR2 (2.25 MPa) and BC1 (2.23 MPa) of Eurocode 2, which are slightly higher than those obtained experimentally (BR2=2.08 MPa ; BC1=2.09 MPa). Furthermore, the relationship established between the theoretical and experimental results shows at 7 days of age that the average tensile strengths according to BAEL 91 revised 99 are closer to those experimental with respectively a correlation coefficient and the standard error equal to 0.502 and 0.1687. At 28 days of age those of Eurocode 2 are closer to the experimental values with respectively a correlation coefficient and the standard error equal to 0.9206 and 0.0813. From these analyses, it can be seen that Eurocode 2 provides a better prediction of the mechanical tensile behaviour of concrete based on recycled and/or natural aggregates.

Discrimination of leucine and isoleucine via fragmentation by electromagnetic field.

We conduct comparative numerical studies of the effects of electric dipole field and electromagnetic radiation field on the amino acids leucine and isoleucine. Since they are structural isomers, distinguishing them by mass is a non-trivial task, while determination of protein structure can be crucial on many occasions. We emphasize the influence of the magnetic field of radiation by utilizing a modified basis sets with correction coefficients to the [Formula: see text] and [Formula: see text] orbitals following the Anisotropic Gaussian Type Orbitals method. Studying the electric potential of the isomers in dipole electric or electromagnetic fields proves that the different layout of leucine vs isoleucine is the main reason why some fragments could not be formed during chemical bond cleavage. Comparison of the chemical structure of the fragments created due to the decomposition of the isomers in the dipole electric or electromagnetic fields shows that their decomposition products are different. These findings can be used also for discrimination between the two isoleucine conformers, for which the cleavage starts at different values of the dipole electric field strength, as well as the products of the decomposition reaction are not identical. Our numerical calculations of the fragmentation outcomes, taking into account the magnetic field effects, can serve as a guidance for discrimination between the isomers/conformers. We applied the Becke's three-parameter hybrid functional approach with non-local correlation by Lee, Yang, and Parr ([Formula: see text]), together with the [Formula: see text] basis set as it is implemented in the GAUSSIAN09 quantum chemistry package in order to obtain the most stable conformers of leucine and isoleucine. We used the options provided by GAUSSIAN09 to add finite external field in order to perform the calculations of leucine and isoleucine in the electric dipole and electromagnetic fields. The Anisotropic Gaussian Type Orbitals method was used to obtain the correction coefficients which modify the original [Formula: see text] basis set in order to account for the effects of magnetic field of radiation. Results were visualized and the electrical potentials analyzed by the Molden visualization program.

Numerical study on flow and heat transfer in a novel symmetric sinusoidal wavy microchannel heat sink with rectangular rib prisms

To enhance thermal and overall performances, a novel microchannel heat sink (SSW-RP) was devised by integrating symmetric sinusoidal wavy sidewalls with rectangular rib prisms within the channels. A numerical comparative study was conducted to explore heat transfer mechanism in channels by investigating the flow and heat transfer characteristics of SSW-RP in comparison with those of smooth straight microchannel (MC), smooth straight microchannel with rectangular rib prisms (MC-RP), and symmetric sinusoidal wavy microchannel (SSW). The results show that the addition of rib prisms makes the fluid flow into wave peaks, reducing and even eliminating vortices from wave peaks of the symmetric sinusoidal wavy microchannel, thus significantly improving heat transfer performance. The new design SSW-RP had the highest relative Nusselt number, which reaches 4.16 at Re = 800. Further, the hydrothermal performance sensitivity of SSW-RP to the relative width (α) and length (β) of rib prisms is studied, and the best overall performance factor of SSW-RP finally can be achieved up to 1.88 at α = 0.35, β = 0.4 and Re = 800.

A comparative numerical study of three similar passive solar stills: Single slope, V-type, and greenhouse

In this paper, three solar stills with similar geometries are numerically investigated for analysis and comparison. The solar stills include single slope, V-type, and greenhouse stills. Steady-state laminar flow numerical simulations with different water surface temperatures and cover glass temperatures are performed. Simulation results were confirmed with data from analytical and experimental models to ensure reliability. The results showed that the V-type still has a higher number of recirculation zones than that of single slope and greenhouse stills. These vortex regions are small, but the velocity magnitude is no less than the other two stills. This difference makes the freshwater yield and convection heat transfer coefficient of V-type still the largest. Daily freshwater productions of single slope, V-type, and greenhouse stills are 0.592, 0.673, and 0.623 kg/m2, respectively. Productivity at 15 PM is 2.5 times higher than the hours from noon to 14 PM. The natural convection heat transfer coefficient seemed to be unvaried with the temperature difference but changed strongly with the still geometry.

Comparative numerical study to simulate masonry with bed joint reinforced repointing

Bed joint reinforced repointing is a retrofitting technique for unreinforced masonry structures that is commonly applied in the Netherlands to repair settlement-induced damage. Using this technique, the bed joints of masonry walls are reinforced with steel rebars that are embedded in a high strength repair mortar. Due to the increase of induced seismic events in the northern part of the Netherlands, an experimental study was carried out at Delft University of Technology to investigate the performance of this retrofitting technique for combined settlement and seismic loading. This paper aims to simulate the experimental results, with a focus on the comparison of different finite element modelling approaches for studying both un-strengthened and strengthened full-scale tested walls. To that end, three different models are investigated – comprising both macro (continuum) and simplified and detailed micro (brick-to-brick) modelling approaches. The bricks and mortar joints are modelled as one homogenous continuum in the macro model, whereas in the two brick-to-brick models these structural components are modelled separately, with the detailed model including interface elements to simulate the brick–mortar bonds. Nonlinear pushover analyses are subsequently carried out using all three modelling approaches, for both monotonic and cyclic loading cases. Based on these analyses, the detailed brick-to-brick model was found unsuitable to simulate the strengthened wall because cracks in the model mainly occur in the form of opening of the brick–mortar bond interfaces, while smeared cracking in the plane stress elements of the mortar joints is very limited. Similarly, the continuum damage model was found to be inaccurate when pre-existing damage in the experiment needed to be taken into account. The continuum damage model also showed lower axial stresses in the rebars, compared with the simplified brick-to-brick model, as the former does not allow for the direct assignment of material properties for the high strength repair mortar in the strengthened joints.

Different effects of interfacial properties on the tensile and compressive damage mechanisms of 3D woven composites: Multiscale damage model and numerical comparative study

A multiscale damage model is proposed based on a micro-mesoscale bridging model and a multiscale kinking model, which can predict the damage development processes of 3D woven composites (3DWCs) under different loading conditions using only few material parameters. At the microscale, the various mesoscopic damage modes of yarns, including tensile fiber breakage, compressive fiber kinking and transverse inter-fiber crack, can be simply divided into matrix- and fiber-dominated damage. Using this multiscale damage model, a numerical comparative study is conducted to investigate the effect of interfacial properties on the mechanical performances and damage mechanism of 3DWCs. The numerical results indicate that the interfacial properties exhibit different effects on the tensile and compressive strengths and damage mechanisms of 3DWCs. The interaction of different damage modes controls the overall trend of the tensile strength of 3DWCs. There is an optimum point for the tensile strength of 3DWCs at different interfacial fracture toughness. Beyond the optimum point, the tensile strength of 3DWCs is negatively correlated with interfacial properties. Unlike the tensile loading case, the better the interfacial properties, the later fiber kinking occurs, resulting in higher compressive strength of 3DWCs.

Condition-based maintenance optimisation for multi-component systems using mean residual life

This paper aims to propose a Novel Condition-based maintenance (CBM) decision aid model for optimising the maintenance of complex multi-component systems. As the degradation level of each component is assumed to be independent and stochastic, it follows a specific probability distribution determined from historical data of experimental observations and inspection. The main objective is to optimise the total cost for providing maintenance actions and reducing the excess of spare parts usage. The decision support model consists of determining measurements on components with the aim of estimating the instant of time of removing predictively one or a group of components before they fail. The measurement model includes the mean residual lifetime (MRL) and some extensions developed for this purpose. For demonstrating the pertinency of the proposed model, we use a preventive maintenance strategy for one-component systems and a grouping/opportunistic maintenance for multi-component systems. Besides, a numerical comparative study performing these measurements is carried out using several examples and a case study from Electric energy distribution systems. The solution is illustrated as a decision-making optimal model for optimising the maintenance operations’ costs and the total number of spare parts. The numerical results and the comparison show the efficiency of the proposed approach.