Computational Fluid Finite Element Research Articles

FEM and CFD thermal modeling of an axial-flux induction machine with experimental validation

Axial-flux electrical machines are ideal candidates as in-wheel motors for electrical vehicles (EVs). Due to their characteristics of high power density and compact structure, thermal management is vital for them. Lowering the temperature of the stator windings can protect the insulation material from rapid degradation and reduce the extra copper losses by decreasing their electrical resistance. Contrary to the widely reported axial-flux permanent magnet synchronous machines, thermal modeling methods of axial-flux induction machines are rarely seen in previous literature. Hence, the present work aims at investigating their thermal response based on both the finite element method (FEM) and computational fluid dynamics (CFD) techniques. In addition, a test rig is built to validate the computed results of these two thermal models with the experimental measurement. The CFD conjugate heat transfer analysis is found to be more accurate than the FEM thermal analysis in predicting the temperature distribution of different components in the machine and the temperature rise of the airflow, with lower than 5 ∘C average errors deviating from the corresponding measured data at three rotation speeds. Additionally, the CFD simulation is able to capture the backflow occurring near the outlets of the casing that has been found during the experiments.

Design of a multi-direction piezoelectric and electromagnetic hybrid energy harvester used for ocean wave energy harvesting

Ocean waves contain a great deal of energy, and the collection and utilization of wave energy is of great significance for sustainable development. In this paper, a multi-direction piezoelectric and electromagnetic hybrid energy harvester (PEHEH) based on magnetic coupling is proposed that can collect low frequency vibration energy from multiple directions. The proposed PEHEH combines piezoelectricity and electromagnetism through magnetic coupling to collect energy in the same excitation. The mechanical model of the PEHEH is established, and finite element simulation software COMSOL and computational fluid dynamics are used to analyze and verify the feasibility and practicability of the PEHEH structure. An experimental platform is built to test the output performance of the PEHEH. The results show that the maximum energy generated by PEHEH is 19.4 mW when the magnetic distance is 16 mm and the excitation frequency is 9 Hz. The hybrid energy harvester can light 56 light emitting diodes, which verified the feasibility of practical application. Therefore, the proposed hybrid energy harvester can effectively collect low-frequency wave energy and has a broad application prospect as a power source for low-power electronic devices.

Computational and Experimental Study on Failure Mechanism of a GTD-111 First-Stage Blade of an Industrial Gas Turbine

This paper investigates the root cause of a recurring failure observed in the first-stage blades of an industrial gas turbine. The failure involves the loss of the trailing edge tip of the blades. The study employs a combination of metallographic analysis and computational simulations utilizing the finite element method and computational fluid dynamics. The metallographic analysis reveals significant degradation in the GTD-111 nickel-based superalloy within the region where the failure occurs. This degradation is characterized by the coarsening and coalescence of the gamma prime phase, which can be attributed to localized overheating. Additionally, the computational study enables the calculation of the trajectory, pressure, and temperature profiles of the hot gases, as well as the distribution of temperatures within the blade. These findings demonstrate that the cooling airflow is influenced by the hot gas flow, particularly in the vicinity of the fault location, owing to the orientation of the cooling ducts, which results in overheating in this area. Ultimately, the temperatures derived from the microstructural analysis using the Ostwald-ripening theory align remarkably well with the results obtained from the simulation, validating the accuracy of the computational model. By combining metallographic analysis and computational simulations, this study provides crucial insights into the failure mechanism of the first-stage blades.

Advancements and Applications of Rim-Driven Fans in Aerial Vehicles: A Comprehensive Review

As the aviation industry seeks sustainable propulsion solutions, innovative technologies have emerged, among which rim-driven fan (RDF) systems hold notable promise. This comprehensive review paper deeply investigates RDF technology, uncovering its principles, benefits, and transformative potential for aviation propulsion. Amid escalating concerns about greenhouse gas emissions, the aviation sector’s shift towards electric propulsion has gained impetus. RDF technology has emerged as a beacon of optimism, heralding the prospect of energy-efficient and eco-conscious air travel. Navigating the slower development pace of RDF technology for aerospace applications, this paper draws insights from analogous marine technologies and relevant literature. Merging these realms, this paper meticulously examines RDF systems, spotlighting their unique attributes, with particular emphasis on the rim-driven configuration and its fundamental design principles. This review delves into the progressive strides accomplished in RDF’s evolution, encompassing the spectrum from evolving electric motor variants to intricate design considerations, strategic noise and vibration management, innovative control methodologies, advancements in bearing technology, and the strategic integration of finite element analysis (FEA) and computational fluid dynamics (CFD) for comprehensive performance optimization. In the context of aviation’s electrification journey, the exploration of RDF technology marks a pivotal inflection point. This paper concludes by succinctly encapsulating pivotal insights, accentuating RDF technology’s central role in reshaping aviation’s propulsion paradigm. As the aviation sector charts a course towards sustainable progress, the lessons gleaned from RDF technology are poised to chart the trajectory of aviation’s environmental transformation.

Finite element analysis and computational fluid dynamic study of hybrid composite‐based offshore wind turbines

AbstractOffshore wind turbines are utilized for wind power harvesting through wind farms installed in bodies of water, normally at sea. The blades of the wind turbine resist the airflow and rotate and generate useful mechanical energy. Most of these wind blades are made of synthetic glass and carbon fibers. Synthetic fiber has higher mechanical strength but is non‐biodegradable in nature. The hybrid synthetic and natural composite materials overcome the non‐biodegradable issues to a certain extent and exhibit higher mechanical strength. In this prelude, the present work utilizes sisal, jute and rubber with epoxy‐based hybrid material used for wind blade manufacturing. The hybrid composite materials used in the present work have the volume fraction of synthetic fibers, natural fibers, and resin as 40 %, and 30 %, respectively. CATIA modelling software package is utilized to design the three‐dimensional model of the wind blade and is imported into the ANSYS Workbench. The structural, harmonic, and modal analyses are carried out, and the performance of the wind blades made of different hybrid composite materials is compared. Further, the computational fluid dynamic study is carried out to visualize the proposed composite offshore wind turbine's flow distribution. The results revealed that the proposed hybrid glass/jute/epoxy composite material yields better results and is more suited for offshore wind blade manufacturing.

How does the recurrence-related morphology characteristics of the Pcom aneurysms correlated with hemodynamics?

Posterior communicating artery (Pcom) aneurysm has unique morphological characteristics and a high recurrence risk after coil embolization. This study aimed to evaluate the relationship between the recurrence-related morphology characteristics and hemodynamics. A total of 20 patients with 22 Pcom aneurysms from 2019 to 2022 were retrospectively enrolled. The recurrence-related morphology parameters were measured. The hemodynamic parameters were simulated based on finite element analysis and computational fluid dynamics. The hemodynamic differences before and after treatment caused by different morphological features and the correlation between these parameters were analyzed. Significant greater postoperative inflow rate at the neck (Qinflow), relative Qinflow, inflow concentration index (ICI), and residual flow volume (RFV) were reported in the aneurysms with wide neck (>4 mm). Significant greater postoperative RFV were reported in the aneurysms with large size (>7 mm). Significant greater postoperative Qinflow, relative Qinflow, and ICI were reported in the aneurysms located on the larteral side of the curve. The bending angle of the internal carotid artery at the initiation of Pcom (αICA@PCOM) and neck diameter had moderate positive correlations with Qinflow, relative Qinflow, ICI, and RFV. The morphological factors, including aneurysm size, neck diameter, and αICA@PCOM, are correlated with the recurrence-inducing hemodynamic characteristics even after fully packing. This provides a theoretical basis for evaluating the risk of aneurysm recurrence and a reference for selecting a surgical plan.

Simultaneous optimization of stiffness, permeability, and surface area in metallic bone scaffolds

Metallic bone scaffolds fabricated by selective laser melting (SLM) have attracted significant attention in bone tissue engineering. Scaffolds based on triply periodic minimal surfaces (TPMS) are currently the subject of extensive investigation, making them a fitting benchmark for evaluating novel architectures. In this study, we introduced and assessed the viability of modified face-centered cubic (MFCC) scaffolds as an alternative to TPMS scaffolds. Two distinct categories of TPMS scaffolds, namely sheet TPMS and skeletal TPMS, were examined for comparative analysis. Employing finite element method (FEM) and computational fluid dynamics (CFD) analysis, we comprehensively evaluate the MFCC and TPMS scaffolds from structure, fluid flow, surface area, and surface curvature perspectives. Among the investigated porosities (75%, 80% and 85%), the MFCC scaffold category consistently exhibited dominant designs on the Pareto front, whereas the majority of TPMS scaffolds failed to achieve multiobjective optimality. MFCC scaffolds exhibited superior mechanical properties compared to skeletal TPMS scaffolds, while also demonstrating improved fluid flow characteristics in contrast to sheet TPMS scaffolds. Furthermore, MFCC scaffolds possessed a specific surface area that fell within the range observed in natural bone tissue, thereby bridging a crucial gap in the design space for optimizing bone scaffolds. The concave internal surfaces of MFCC scaffolds showed promising potential for enhancing bone cell growth. Selective laser melting (SLM) was employed to fabricate the designed scaffolds using stainless steel 316L. Subsequently, uniaxial compression tests were conducted on these scaffolds to validate the accuracy of the simulation results. This study provides valuable insights into multiobjective design and optimization of bone scaffolds, highlighting the significance of MFCC scaffolds as a valuable addition to the existing library of bone scaffold architectures.

Experimental Optimization Environment for Developing an Intracycle Pitch Control in Cross Flow Turbines

Cross-flow tidal turbines also known as vertical-axis turbines have not reached the efficiency as it is usual found for horizontal-axis turbines. This can be mainly accounted to the intensive development effort dedicated to the latter in the past 30 years in the area of wind energy. Less attention has been given to cross-flow turbines as they present mechanical cyclic loads that detriment their durability. Nevertheless, there is great potential for their employment in tidal energy exploitation as they are intrinsically independent from the flow direction and have a higher power output per area in farm installation. For this reason the research for cross-flow turbines have regain impulse.
 Among various approaches to improve their hydrodynamic characteristics found in the literature, the intracycle pitch control is one of the most promising one. It consists in actively pitching each blade as function of the azimuth angle.
 The present paper will introduce the overall experimental environment and methods for developing an optimal intracycle control for cross-flow turbines in tidal power generation. This is the main component of project OPTIDE at Otto-von-Guericke-University Magdeburg, Germany in cooperation with the LEGI at University Grenoble-Alpes, France and the University of Applied Sciences Magdeburg-Stendal.
 The experimental system consists of a turbine flume model equipped with a speed controlled generator. The three bladed turbine model has independent controlled pitch actuators embedded in each blade and a force sensing system in one of the blade holding arms. Local high-dynamic systems allow to control the speed of the generator and the pitch position as a function of the rotational angle of the runner i.e. pitch trajectory.
 A superimposed governing system which automates the experiment has been implemented. This allows to perform an optimization process with the experiment in the loop. Evolutionary algorithms are employed to solve the two objectives of the optimization: (1) Maximizing the efficiency by (2) minimizing the alternating structural loads on the runner. These kind of problems are usually solved with numerical simulations using finite element method (FEM) and computational fluid dynamics (CFD). However, this commonly comes with very high computational efforts and uncertainty. For this reason in our approach simulations are replaced by an experimental optimization technique.
 The optimization cycle implemented in the superimposed governing system chooses a set of individuals (pitch trajectories) for each generation on base of the genetic algorithm. Each pitch trajectory is performed sequentially while power output and loads are measured. This allows to evaluate each individual in about one minute. The best individuals are then the base for the offspring of the new generation. Cross-over from best performing parents and subsequent mutation ensure both, convergence and a thorough exploration of the entire design space.
 It is expected that this method will fast and reliably find the optimal pitch trajectories under various conditions. Selected cases will be analysed in detail by means of particle-image velocimetry (PIV) with synchronized force and torque measurements to research the underlying hydrodynamic mechanisms and the effects of the flow control performed by the pitching motion.

Effects of Volute Structure on Energy Performance and Rotor Operational Stability of Molten Salt Pumps

A double-volute molten salt pump with two outlet pipes is proposed based on the original pump model. A numerical approach coupling finite element analysis and computational fluid dynamics (CFD) is implemented to investigate the operational stability and energy performance of two molten salt centrifugal pumps for high-temperature molten salt. The entropy production of the single-volute and double-volute molten salt pumps is investigated. The effects of the volute structures on the mechanical behavior of the impeller and shaft are considered. According to the findings, the local entropy production in the molten salt pump is dominated by the local pulsating entropy production (Spro-T), with the double-volute scheme achieving reduced energy loss. A visualization of the flow field and the local entropy production rate (LEPR) distributions indicate that the LEPR is positively correlated with the complexity of the flow, and higher levels of turbulence intensity lead to greater LEPR. The double-volute scheme enhances the complexity of the flow in the impeller, resulting in an increase in the LEPR compared with the single-volute design. However, the LEPR in the whole double-volute molten salt pump is reduced compared with the single-volute design. It is discovered that the double-volute molten salt pump experiences a less radial hydraulic force. Although the double-volute design has a slightly higher maximum equivalent stress on the impeller than the single-volute scheme, the rotor deformation is significantly less. In general, the double-volute scheme reduces energy loss and ensures better structural stability.

Experimental and Numerical Study of Al2219 Powders Deposition on Al2219-T6 Substrate by Cold Spray: Effects of Spray Angle, Traverse Speed, and Standoff Distance.

Cold spray (CS) is an emerging technology for repairing and 3D additive manufacturing of a variety of metallic components using deformable metal powders. In CS deposition, gas type, gas pressure, gas temperature, and powder feed rate are the four key process parameters that have been intensively studied. Spray angle, spray gun traverse speed, and standoff distance (SoD) are the other three process parameters that have been less investigated but are also important, especially when depositing on uneven substrates or building up 3D freeform structures. Herein, the effects of spray angle, traverse speed, and SoD during CS deposition have been investigated holistically on a single material system (i.e., Al2219 powders on Al2219-T6 substrate). The coatings' mass gain, thickness, porosity, and residual stress have been characterized, and the results show that spray angle and traverse speed exercise much more effects than SoD in determining coatings' buildup. Finite element method (FEM) modeling and computational fluid dynamic (CFD) simulation have been carried out to understand the effects of these three parameters for implementing CS as repairing and additive manufacturing using aluminum-based alloy powders.

A REVIEW ON DESIGN OF CRUDE OIL PIPELINE WALL OPTIMIZATION DUE TO CORROSION AND HYDROGEN EMBRITTLEMENT

Crude oil pipeline infrastructures represent a high capital investment, and pipelines must be free from the risk of degradation due to corrosion and hydrogen embrittlement, which could cause environmental hazards and potential threats to human life. Pipeline integrity design, monitoring, and management become crucial, especially in subsea pipelines. Corrosion risk assessment is necessary to track pipeline reliability and life prediction effectively. The pipeline inspections cost a lot of money since the pipeline are hundreds of thousands of kilometres, and the maintenance process interrupts the production rates. Moreover, this cost will triple for the subsea pipeline as it requires special personal qualifications and tools, causing the oil and gas company to pay millions for frequent checks. It is proposed to utilize Finite Element Analysis (FEA) modelling technique and Computational Fluid Dynamics (CFD) to optimize the design and preventive maintenance prediction. Hence this paper aims to review the current work on this pipeline design problem, especially in the Tropical region, and discuss the factors that cause the deterioration of structural properties due to the presence of hydrogen within the crude oil.

An Iterative Two-Stage Multifidelity Optimization Algorithm for Computationally Expensive Problems

Engineering design optimization often involves use of numerical simulations to assess the performance of candidate designs. The simulations for computing high-fidelity (HF) performance estimates, such as finite element analysis or computational fluid dynamics, are typically computationally expensive. In some cases, it may also be possible to run an alternate or cheaper version of the simulation (through, e.g., use of a coarse mesh) to yield a low-fidelity (LF) performance estimate. Multi-fidelity optimization refers to the class of methods that aim to manage LF and HF evaluations efficiently to optimize computationally expensive problems within a limited computing budget. Among the prominent existing multi-fidelity approaches, some of them depend on a sufficiently dense a priori sampling; while others use unidirectional information exchange from LF to HF; both of which lead to a possibility of spending evaluation budget on unpromising search regions. This paper proposes an improved multi-fidelity approach using an iterative, two-stage scheme (MFITS). It uses the collective information from previously evaluated designs to determine a sampling neighbourhood for LF evaluations. These samples are in-turn used for building a co-kriging surrogate model that is then searched globally to identify a good candidate for HF evaluation. By restricting the LF sampling neighbourhood, the computational budget can be used more efficiently, as the search is focused on regions that have historically produced good quality solutions. Numerical experiments and benchmarking are conducted on two suites of test problems and two practical design optimization problems to demonstrate the efficacy of MFITS.

A Review of CFD Modeling of Erosion-induced Corrosion Formation in Water Jets Using FEA

A comprehensive review of all the related investigations carried on water jet cutting or AWJ (AWJ) cutting is performed. The experimental methods and results used on this subject were examined, defined and compared by the researchers. This research shows that further improvements are possible in the water jet cutting method. In order to reduce the high cost of the empirical technique and increase the time efficiency, it is important to perform computerized Finite Element Analysis (FEA) or Computational Fluid Dynamics (CFD) based AWJ processing. An attempt has been performed to systematically arranged the research investigations conducted on water jet cutting. The studies on the definition of the nozzle failure, calculate using CFD of water jet cutting or AWJ cutting processes, the studies on the parameters influencing water jet cutting are reviewed and the future work for the further improvement of water jet cutting process is highlighted.

Effectiveness of biomechanically stable pergola-like additively manufactured scaffold for extraskeletal vertical bone augmentation.

Objective: Extraskeletal vertical bone augmentation in oral implant surgery requires extraosseous regeneration beyond the anatomical contour of the alveolar bone. It is necessary to find a better technical/clinical solution to solve the dilemma of vertical bone augmentation. 3D-printed scaffolds are all oriented to general bone defect repair, but special bone augmentation design still needs improvement. Methods: This study aimed to develop a structural pergola-like scaffold to be loaded with stem cells from the apical papilla (SCAPs), bone morphogenetic protein 9 (BMP9) and vascular endothelial growth factor (VEGF) to verify its bone augmentation ability even under insufficient blood flow supply. Scaffold biomechanical and fluid flow optimization design by finite element analysis (FEA) and computational fluid dynamics (CFD) was performed on pergola-like additive-manufactured scaffolds with various porosity and pore size distributions. The scaffold geometrical configuration showing better biomechanical and fluid dynamics properties was chosen to co-culture for 2months in subcutaneously into nude mice, with different SCAPs, BMP9, and (or) VEGF combinations. Finally, the samples were removed for Micro-CT and histological analysis. Results: Micro-CT and histological analysis of the explanted scaffolds showed new bone formation in the "Scaffold + SCAPs + BMP9" and the "Scaffold + SCAPs + BMP9 + VEGF" groups where the VEGF addition did not significantly improve osteogenesis. No new bone formation was observed either for the "Blank Scaffold" and the "Scaffold + SCAPs + GFP" group. The results of this study indicate that BMP9 can effectively promote the osteogenic differentiation of SCAPs. Conclusion: The pergola-like scaffold can be used as an effective carrier and support device for new bone regeneration and mineralization in bone tissue engineering, and can play a crucial role in obtaining considerable vertical bone augmentation even under poor blood supply.

Aeroelastic analyses of functionally graded aluminium composite plates reinforced with graphene nanoplatelets under fluid-structural interaction

This study presents a comprehensive investigation on functionally graded (FG) graphene reinforced aluminium cantilever rectangular plates under aerodynamic loads. Two-way loosely coupled fluid structure interaction (FSI) is implemented by coupling finite element analysis (FEA) and computational fluid dynamics (CFD). FEA models are developed using FG graphene nanoplatelets (GPL) reinforced aluminium composite structures with different GPL distribution patterns. Fluid domain is modelled using finite volume method and FSI module is then used to connect FEA with the CFD code. The simulation results of FSI indicate that the maximum stress of the plate can be efficiently reduced with satisfactory aerodynamic performance after aeroelastic tailoring, depending on specific GPL distribution patterns. It is shown that in conjunction with aeroelastic tailoring technique, the composite plate can achieve optimized structural and aerodynamic performance. The present results of the FG graphene reinforced aluminium plates offer useful design guideline for their applications as the structural components in aeronautical fields.

Study on a Novel Hybrid Thermal Network of Homopolar Inductor Machine

The thermal analysis is necessary for the design and safe operation of the homopolar inductor machine (HIM) applied in the flywheel energy storage system (FESS). However, due to its unique three-dimensional (3-D) structure, the thermal analysis of HIM relies on the 3-D finite element analysis (FEA) or computational fluid dynamics (CFD), which is time-consuming and computationally inefficient. To facilitate the thermal analysis and design of HIM, a fast and accurate analytical model is essential. In this article, the novel 2-D and 3-D hybrid thermal networks combined with a coupled iterative analysis method are proposed to predict the temperature of HIM. First, the structure, operation principle, and material properties of HIM are illustrated. Second, the heat sources of HIM, including iron loss, rotor eddy current loss, rotor air friction loss, copper loss, and bearing loss, are fully analyzed and investigated. Third, the proposed hybrid thermal model (HTM) and coupled iterative analysis method are demonstrated and applied to predict its temperature. The proposed thermal model and analysis methods are explained in detail. The influences of different speeds and operation conditions on the temperature rise of HIM are analyzed based on the proposed thermal model and FEA. Finally, the temperature of an HIM prototype is tested, which proves the accuracy of FEA and the proposed method. The proposed HTM can quickly and accurately predict the temperature of HIM, which provides a new idea for the temperature prediction of this kind of machine.

Frequency dependency of dynamic force coefficients for hermetic squeeze film dampers utilizing fluid-bounding flexible structures

The following paper focuses on the dynamic behavior of hermetic squeeze film dampers (HSFD) that utilize fluid-bounding flexible members as a part of the support structure. More specifically, the current paper advances an engineering design modification to the existing HSFD concept, which is aimed at rendering the dynamic force coefficients frequency independent. The paper introduces analytical models, which are used to explain the frequency dependency of force coefficients observed in past experimental testing of HSFD. Furthermore, the insights gained from the analytical models are used to conceive a new frequency independent damper architecture. The analytical study leverages commercially available finite element analysis (FEA) and computational fluid dynamics (CFD) software to conduct several fluid-structure-interaction (FSI) simulations of various damper architectures. In addition to the FSI analysis a more computationally efficient reduced order model (ROM) was developed, coupling structural flexibility with the fluid dynamics in the damper. Ultimately, these design tools were used to identify critical design features and configurations needed for constant linear frequency independent force coefficients. The results show a damper configuration with minimal frequency dependency of the stiffness and damping coefficients when incorporating pass through channels in combination with accumulator volumes.

Considerations of Hull Structural Deformation on Hydrodynamic Performance of Sailing Yachts

_ The increasing availability of affordable finite element modeling software and computational fluid dynamics codes have given today’s sailing yacht designers tools that, in the past, were only available to designers of yachts competing in the most high-profile events. This paper provides a case study on the structural design of the International America’s Cup Class Yacht Stars & Stripes USA-34, which won the U.S. defender series, the Citizen Cup, leading up to the 29th America’s Cup competition in 1995. The authors have recently been able to publicly share this information, and feel that the problem-solving approach is of direct use to many of today’s designers. The design approach is twofold, the first being the use of Finite Element Analysis to minimize drag-inducing local deformations. Over 80 finite element models were analyzed with varying configurations, starting with an initial baseline structure based on the previous boat, USA-11. These structural improvements reduced local hull deflection from5 to 6 mm per meter on the previous design to less than 1 mm per meter on the USA-34 design. The second part of the design approach isolates the hydrodynamic effects of global bending under rig tension. Illustrative tank tests are provided to demonstrate how the global sagging of the hull, caused by rig tension, can often increase the resistance of a yacht (especially one built for racing). As part of a series of steps taken to mitigate the effect of rig tension, a novel design was developed, with soft patches and flexible structure to permit low-cost modification of the hull in the boatyard, giving approximately a 225mm increase in waterline length and 75 mm reduction in beam if needed—a modification that was made to USA-34 prior to winning the finals of the Citizen Cup, and at a cost of under $500. The reduction of drag-inducing local hull form deformations, and the development of the cost-saving hull modification concept, demonstrate how a creative designer can take advantage of the finite element modeling tools that are now widely available.

Evaluation of the behavior of coffee stored in cooled and natural environments Ednilton

The market value of coffee is strongly influenced by loss of quality, which makes storage one of the main steps in the entire production chain. The finite element method (FEM) and computational fluid dynamics (CFD) are numerical and computational techniques that facilitate the simulation of agricultural product storage systems. Computational modeling satisfactorily represents real experimentation, simplifies decision-making, and reduces costs. This study aimed to analyze mocha coffee storage for 6 months in a cooled environment with temperatures between 15 and 18 °C and in a natural environment. The water content, bulk density, specific heat, thermal conductivity, and thermal diffusivity were determined and colorimetry and sensory analysis were applied to compare initial and final samples of the product after storage. It was found that the water content and specific heat were the only properties that presented significant changes. Through sensory analysis, it was observed that the quality of the coffee was the same for both systems. A computational model was developed to simulate the heat transfer process during storage. The comparison of the simulation results with the experimental results for the temperature distribution in the grain mass showed overall mean relative errors of 2.34% for the natural environment and 5.74% for the cooled environment. Key words: Coffee; postharvest; storage.

Machine-Learning-Accelerated Simulations for the Design of Airbag Constrained by Obstacles at Rest.

Predicting airbag deployment geometries is an important task for airbag and vehicle designers to meet safety standards based on biomechanical injury risk functions. This prediction is also an extraordinarily complex problem given the number of disciplines and their interactions. State-of-the-art airbag deployment geometry simulations (including time history) entail large, computationally expensive numerical methods such as finite element analysis (FEA) and computational fluid dynamics (CFD), among others. This complexity results in exceptionally large simulation times, making thorough exploration of the design space prohibitive. This paper proposes new parametric simulation models which drastically accelerate airbag deployment geometry predictions while maintaining the accuracy of the airbag deployment geometry at reasonable levels; these models, called herein machine learning (ML)-accelerated models, blend physical system modes with data-driven techniques to accomplish fast predictions within a design space defined by airbag and impactor parameters. These ML-accelerated models are evaluated with virtual test cases of increasing complexity: from airbag deployments against a locked deformable obstacle to airbag deployments against free rigid obstacles; the dimension of the tested design spaces is up to six variables. ML training times are documented for completeness; thus, airbag design explorers or optimization engineers can assess the full budget for ML-accelerated approaches including training. In these test cases, the ML-accelerated simulation models run three orders of magnitude faster than the high-fidelity multi-physics methods, while accuracies are kept within reasonable levels within the design space.