In non-continuous stiffening, longitudinal stiffeners end within the panel, creating gaps before reaching transverse stiffeners or girder ends. This numerical parametric study examines a validated ...model subjected to uniform compression for ten imperfection patterns across 1080 geometric configurations, resulting in 10,800 GMNIAs. Findings refute the redundancy of imperfections due to eccentric loads and identify critical imperfection patterns. Stiffener stiffness minimally impacts ultimate loads. More stiffeners lower ultimate loads by restricting stress redistribution. Minimizing gap dimensions is recommended for optimal performance, indicating the need to update standards to include non-continuous stiffening.
•Positive half-sin shape imperfections are critical; full-sin shapes for long panels.•Smaller gaps yield higher loads; stiffener’s relative stiffness has low impact.•More stiffeners reduce load factor; fewer stiffeners improve stress redistribution.
Selective laser melting (SLM) produces a large amount of residual stress which limits its applicability. Despite the increasing number of studies to understand the relationship between the process ...parameters and the residual stress, the underlying complex mechanisms are yet to be understood. In this work, a 3D finite element model (FEM) is established to investigate the relationship between the process parameters and the residual stress during SLM. When the process parameters are in different ranges, the residual stress behavior is different. The complex relationship between the residual stress and the process parameters could be the reason for the contradictory parametric effects reported in the literature. The magnitude of the parametric effect on the residual stress is obtained. The influence of the scanning speed is stronger than that of the laser power, which is in turn stronger than that of the hatch spacing. These results can bring insights into the understanding of the residual stress during SLM.
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•The stress generation and evolution are investigated through the temperature and stress history during SLM.•The evolution of the stress can be divided into four areas. The residual stress is decided by the four stages.•When the process parameters are in different range, the residual stress behavior is different.•The magnitude of the parametric effect on the residual stress is scanning speed > laser power > hatch spacing.
Aluminum foam, carbon fiber reinforced plastics (CFRP) and foam-filled structures have been drawn growing attention for their outstanding lightweight and energy absorption capacity; therefore, ...crushing characteristics of a hybrid system involving these components would be of particular interest. In this study, quasi-static compression tests were carried out to experimentally investigate the crushing behaviors of foam-filled aluminum/CFRP hybrid tube subject to transverse loading condition. Based upon the experimental tests and numerical modeling, the interactive effects in between the aluminum foam filler and aluminum/CFRP hybrid tube was explored. It is found that the load carrying and energy absorption capacities of foam-filled hybrid tube were significantly improved in comparison with the summation of net foam filler and empty hybrid tube. The parametric study was carried out for exploring the effects of the aluminum foam density, aluminum tube thickness and ply number of CFRP tube on the crushing behaviors of foam-filled hybrid tube. It is found that both the total energy absorption (EA) of foam-filled hybrid tubes and the EA contributions of the aluminum foam (or aluminum tube, or CFRP tube) were enhanced with increase in density (or thickness, or ply number). The specific energy absorption (SEA) of foam-filled hybrid tubes increased from 3.45 J/g to 9.24 J/g with the foam density changed from 0.23 g cm−3 to 0.70 g cm−3; nevertheless, increase in aluminum tube thickness (or ply number of CFRP tube) has no evident influence on the SEA of foam-filled hybrid tubes. Finally, discrete design optimization was further performed to obtain the best possible foam-filled hybrid configuration for the transverse crushing characteristics. The optimum results showed that the SEA was largely improved by 213% in comparison with the baseline design.
•An innovative bolted connection with dual-slot hole was proposed.•Four full-scale specimens were tested and seismic behavior was obtained.•The FEM was validated using test data and different ...parameters were discussed.•A hysteresis model that compares well with the test curves was given.•Designs to improve the connection’s fast splicing and energy dissipation capacity were found.
Although a significant advantage for modular steel buildings (MSBs) is suitable for rapid construction, the unexpected installation error and initial defects of components in the construction site may lead to the failure of rapid assembly or even connection between modules. Aiming at the error sensitivity problem of module splicing, this paper proposes a new type of bolted connection with dual-slot hole and two kinds of connection strengthening methods, including diagonal brace strengthening and flange strengthening. To proceed, tests on four full-scale connections with cyclic loads were performed for seismic behavior. The test results presented the specimens’ failure mode, strength and stiffness properties, ductility, and energy dissipation capacity. Following that, the finite element model was validated against test data, and the influence of slot hole size and displacement effect was discussed. Finally, the hysteretic model was given. The results indicated that the proposed connection has reliable load-bearing, stable energy dissipation, and fast splicing capacity. The connection may be classified as semi-rigid type according to the stiffness feature for the structural behavior of MSBs. Both diagonal brace and flange strengthening can effectively improve the connections’ load-bearing capacity but weaken the energy dissipation capacity. The research results could serve as an effective reference for the inter-module bolted connection design of MSBs.
Radioisotope thermoelectric generators (RTGs) have been widely used as a promising power source for space mission, in which the Multi-Mission RTG (MMRTG) is the state of the art type. However, due to ...the scarcity of the 238Pu fuel and associated cost concerns, there exists an imperative need to increase the efficiency of RTGs. This requires intuitive, detailed and accurate system property predictions of the RTG system. In this work, a comprehensive finite element model of the MMRTG has been developed, by using a commercial software, COMSOL Multiphysics, including a full-size three-dimensional geometry model, temperature dependent materials and the thermoelectric and radiation heat transfer multiphysics fields involved. The calculation results agree well with reported experimental and simulated values. Through the obtained detailed temperature and voltage distribution, thermal and power properties of the MMRTG are characterized and the effects of non-uniform distributions of temperature and power generated in each TE couple are revealed. At last, the parametric analyses of operation conditions, thermal environment and key design factors are performed and several salient findings have been obtained. Through the analysis results, the design parameters and working mechanisms of the MMRTG are clarified, which can help the design and optimization of the future hundred-watt RTG.
•The comprehensive FEM method is first implemented in the MMRTG modeling and analysis.•The non-uniform distributions of temperature and power in TE modules are revealed.•Suitable load and sufficient thermal inventory ensure adequate power output.•The insensitivity of performance to ambient temperature expands MMRTG’s application.
Hierarchical honeycomb topology is one of the most promising bio-inspired ultralight materials with superior specific strength and stiffness. The existing investigations mainly focus on the ...hierarchical structures composed of conventional triangular or hexagonal unit cells; however, the influences of other types of polygonal unit cells and non-uniform wall thickness were less studied. This paper gives an insight into the out-of-plane crushing of vertex based hierarchical honeycombs with polygonal substructures and non-uniform wall thickness. The experimental results report that the deformation mode of hierarchical honeycomb varies from progressive folding to irregular folding at a relative density of 0.0386. With the increase of relative density, the failure mechanism changes from elastic wall bulking to plastic wall buckling. The theoretical solutions suggested that the wall thickness ratio affects the half wavelength and plateau crushing stress more considerably than the edge length ratio. Though the substructures with less edge number decrease the overall plateau crushing stress level of hierarchical honeycombs, they increase the maximum plateau crushing stress due to the raise of the wall thickness ratio achieved. The specific peak values of the maximum plateau crushing stress are increased by 27.7–51.8% compared to those of the uniform wall thickness hierarchical honeycombs.
Triggered by the pressing need to enhance the power conversion efficiency of photovoltaic systems, this work introduces a novel hybrid system that combines a concentrated photovoltaic cell (CPV) with ...a thermolytic pressure retarded osmosis heat engine (PRO). This innovative integration allows for the efficient recovery and conversion of waste heat from CPV into additional electricity, addressing the challenge of high-output dependence on lower operating temperatures. A detailed theoretical model of the system is developed to ultimately derive and analyze the mathematical expressions for key performance indicators. Numerical analysis confirms that the novel system achieves a maximum power density, energy efficiency, and exergy efficiency of 239.28 W m−2, 13.9 %, and 14.6 %, respectively, which are improved by 13.06 % over a sole concentrated photovoltaic cell. Comprehensive sensitivity analysis is conducted to obtain optimal selection criteria for crucial parameters including inlet concentration, concentration ratio, operating temperature, and diode ideality factor, which have a significant impact on overall performance. Comparative analysis shows that the CPV-PRO system outperforms existing CPV hybrids in terms of lower operational temperatures and enhanced economic viability, making it a superior choice for sustainable energy production.
•Proposing a novel CPV-driven thermolytic PRO heat engine.•Mathematical formulation of performance indicators for the coupled system.•Achieving energy and exergy efficiencies of 13.9 % and 14.6 %, respectively.•Realizing a 13.06 % efficiency improvement over the standalone CPV system.•Conducting in-depth sensitivity analysis of key performance parameters.
This study implements a comprehensive dynamic simulation using a moving-boundary method to characterize an organic Rankine cycle under assumption-free operating conditions. The novelty of the model ...lies in its unique methodology for determining the state vector variables and initial conditions of the system, particularly in integrating sub-models, notably the model of liquid receiver. Consequently, the implemented dynamic model accurately forecasts the system's performance, focusing solely on the boundary conditions. A comprehensive dynamic model is constructed, encompassing a wide range of scenarios and facilitating the interchangeability of models as required. One notable advantage of the model is its systematic approach, which begins each simulation by determining the system's initial conditions before conducting the dynamic model in parametric and dynamic studies. The capability and accuracy of model is confirmed through comparison with experimental data under various steady-state and dynamic conditions, while adhering to the main rules of mass and energy conservation. The prediction accuracy of the model is evaluated by mean absolute percent error. According to the results, the maximum deviations of simulation results mostly are less than 11 %.
•Using moving-boundary method to simulate an ORC under assumption-free conditions.•Using unique method for determining state vector variables and initial conditions.•Dynamic model precisely forecasts system performance, focusing on boundary conditions.•The maximum deviations between the simulation and experimental results are 11 %.•The simulation shows ORC's dynamic behavior when input conditions vary.
The performance of a PEMFC (Polymer Electrolyte Membrane Fuel Cell) is greatly influenced by the various operating variables like temperature, pressure, stoichiometry of reactants and humidity. The ...presented work deals with the experimental study of 30 cells low temperature PEM fuel cell stack employing Nafion®-212 membranes. Experimental results are discussed with polarization curves and compared with the steady state model results, developed in MATLAB. The model predicts increase PEMFC performance with increase in operating temperature, pressure and reactant humidity. The comparison shows good agreement between experimental and modeling results with deviations in the range of 7–15% only.
·Experimental evaluation of operating parameters' effect on fuel cell performance.·Steady state mathematical model development in MATLAB.·Model validation by comparison with experimental results.·Identification of optimum operating parameters.
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