ABSTRACTThe present paper introduces a novel temporal acceleration strategy for computationally efficient prediction of residual stresses and deformations in wire arc additive manufacturing (WAAM) ...components. It employs a semi-analytical approach, dividing temperature into the analytical and the complementary fields. The analytical field is obtained by a closed-form solution, and the complementary field is employed to solve the boundary conditions. A temporal acceleration factor for the heating period is applied. Meanwhile, the diffusion time in the analytical field is manipulated to guarantee accurate temperature prediction. Validation via WAAM experiments, including both a thin-wall structure and a practical engineering component with characteristic dimensions on the order of metres, indicates that the predicted stresses is 50 MPa lower than the experimental values. Moreover, the discrepancy of between the predicted deformations and the experimental measurements is less than 10%, demonstrating reasonable accuracy can be achieved with attractive computational efficiency.
In additive manufacturing of metallic materials, an accurate description of the thermal histories of the built part is important for further analysis of the distortions and residual stresses, which ...is a big issue for additively manufactured metal products. In the present paper, a computationally volumetric heat source model based on a semianalytical thermal modeling approach is proposed. The proposed model is applied to model the thermal response during a selective laser melting (SLM) process. The interaction between the laser and the material is described using a moving volumetric heat source. High computational efficiency can be achieved with considerable accuracy. Several case studies are conducted to examine the accuracy of the proposed model. By comparing with the experimentally measured melt-pool dimensions, it is found that the error between the predictions obtained by the proposed model and the experimental results can be controlled to less than 10%. High computational efficiency can also be achieved for the proposed model. It is shown that for simulating the thermal process of scanning a single layer with the dimension of 2 mm × 2 mm, the calculation can be finished in around 110 s.
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•Two circular-based models with cylindrical and spherical internal pore structures were designed.•The porosity, surface area to volume ratio (Sp/Vt), compression/shear modulus, stress ...distribution, torsional rigidity, and hydraulic permeability of two types of unit cells were comprehensively explored.•The precisely fabricated 3D printed scaffolds of poly(propylene fumarate) (PPF) supplied an excellent platform to systematically compare the simulative and experimental results.•The present method can be extended to efficiently predict the mechanical properties and fluid permeability of other porous structures and their both in vitro and in vivo performance.
Tissue engineering scaffolds have been used for curing bone defects. Poly(propylene fumarate) (PPF) is promising in bone tissue engineering. The ideal scaffolds should have high porosity and sufficient mechanical properties. In this comparative study, two models with cylindrical and spherical pore structures have been designed in the Abaqus software based on the pore opening size (L) to strut length (D) ratio (L/D). Structural analyses including compression, shear, and torsion simulation were performed using finite element analysis (FEA). Compression experiments on the PPF scaffolds fabricated using projection micro-stereolithography (PμSL) were conducted with digital image correlation (DIC). Fluid simulation was further performed to investigate the fluid permeability of the scaffolds. The porosity and surface area (Sp) to volume (Vt) ratio (Sp/Vt) are found to be generally larger in the spherical pore unit cells than in the cylindrical ones. At the same L/D or porosity, the cylindrical pore unit cells have higher compression/shear modulus with better stress distribution, higher torsional rigidity, and higher hydraulic permeability than the spherical ones. This research provides guidance to the design of bone tissue engineering scaffolds as the bulk properties and fluid permeability of the scaffolds could be adjusted by using different pore structures with varied microstructure parameters.
High-salvage perishable products have the characteristics of a short life cycle and high residual value. To extract the maximum value of this kind of product, a closed-loop supply chain network model ...based on the product life cycle is constructed under various uncertainties. This model incorporates various assumptions such as multiple products, multiple periods, timeliness of recycling, and four-echelon supply chain including manufacturers, wholesalers, recycling centers, and consumer markets. Where the recovery cost and the reuse rate are denoted by interval numbers, the demand and the capacity are denoted by stochastic and fuzzy numbers respectively. A Two-step interactive method based on fuzzy flexible programming is used to handle the uncertainties. The optimum solutions in the harsh environment and favorable environment are obtained by a numerical example, and the results show the proposed method is more accurate in grey degree and more robust in site selection than the interval chance-constraint mixed-integer nonlinear programming method. Besides, we demonstrate the relationships between the sensitivity coefficients and the profits. i.e., the higher the probability of stockout in the secondary market, the harsher the external environment is, the stockout will get increasing, and the corresponding expected profit will get lower; inversely, the higher the degree of satisfaction in the e-commerce market, the more favorable the external environment is, the stockout will get decreasing, and the corresponding expected profit will get higher. Furthermore, the numerical simulation also shows that the price of recycled products fluctuates with the increase of the probability of no stockout, where the price fluctuation in the secondary market and the e-commerce market are fundamentally the same, while the price of parts fluctuates least. Finally, according to the results of the sensitivity analysis, some managerial insights are given in the conclusion.
Geothermal energy is a type of renewable energy that has rich reserves, is clean, environmentally friendly and has been widely used in the heating industry. The single-well closed-loop geothermal ...system is a technology with the characteristics of “taking heat without taking water” and is mainly used for geothermal energy heating. Although the heating requirements in the cold region of Northeast China are urgent, the traditional heating mode not only has high economic costs but also causes serious damage to the environment. Therefore, it is of important practical significance to change the heating structure and develop and utilize geothermal energy for heating according to local conditions. In this study, the actual operating single-well geothermal system in the Songyuan area of Jilin Province is used as a case study, and a numerical model is established based on the T2WELL simulation program. The flow production temperature and heat extraction response law of the single-well system in the M1 and M2 wells are contrasted and analyzed under the three key factors of geothermal gradient and injection temperature and flow rate. Based on the simulation results, an optimized development and utilization plan for the M1 and M2 wells is proposed. These results provide a theoretical reference and heating potential evaluation for the promotion of single-well geothermal systems in Northeast China. Taking the geothermal gradient of 4.2 ° C/hm as an example, after 30 years of operation, the heat extraction of the M1 well is 406 kW, and that of the M2 well is 589 kW. Compared with the M1 well, although the M2 well has higher heat extraction, the radial variation in reservoir temperature is more than 50 m under long-term operation, which is not conducive to long-term development and utilization.
We developed an improved depth of extreme point (DEXP) method, characterized as an effective and rapid imaging method that can estimate the depth and distribution of a source quickly. Its main ...purpose is to solve various challenges. The automatic calculation aspect of the traditional method is often limited; namely, there is a problem with achieving automatic and reliable processing when the observed surface presents undulating topography, and this problem cannot be ignored. Therefore, we propose the addition of the constant method and the hypothetical observed surface method to achieve improvements in the traditional method. Firstly, we test the improved method on the synthetic models to demonstrate its notable advantage: the achievement of a fully automatic calculation without requiring any other additional information such as structural index (SI) values and threshold values. Meanwhile, we also demonstrate its ability and reliability to handle undulating topography with acceptable accuracy for imaging results. Furthermore, we verify the robustness of the improved method by applying it to real gravity data from the potash salt deposit in the Sakhon Nakhon basin, Laos. In this case, the improved DEXP method effectively identified the location of the potash deposit. Moreover, combined with the optimal edge detection method, gravity prospecting for potash salt deposits exhibited significant advantages.
The permeability of reservoirs is a key factor affecting the exploitation and utilization of geothermal resources. This test used a core flow meter and other advanced experimental devices to ...investigate the evolution of the permeability characteristics of loose sandstone samples (with a diameter of 25 mm and a length of 50 mm) in the Zijiao Town area under various temperatures, confining pressures, injection rates, and cyclic loading and unloading conditions. The results show that (1) as the temperature increases, the overall trend of rock permeability decreases, which is mainly related to the thermal expansion of rock particles. In addition, the higher the temperature, the greater the gravel outflow. (2) The critical pressure for pore closure in the unconsolidated sandstone in the region is approximately 15 MPa. (3) The permeability change of loose sandstone under low injection rate conditions is relatively small and can be neglected. However, there is reason to believe that under high-flow injection conditions, the permeability of this type of rock mass will undergo significant changes. (4) Under the condition of loading and unloading, the permeability ratio curve of the unloading stage at three temperatures is almost a straight line. The higher the temperature, the smaller the slope, and the permeability at 20 °C with the highest recovery degree is only about 50% of the initial one.
► We evaluated the antioxidant activities of crude extract and its derived soluble fractions from the flower of Sophora viciifolia in five different test systems. ► Correlation analysis suggested ...that the flavonoids might be the major contributors for the high antioxidant activity. ► We obtained 11 compounds and evaluated the antioxidant capacities of compounds 3–7. ► We determined the contents of compound 3 and 4, and 3 might play an important role for the antioxidant activity of this flower.
The antioxidant activities of crude extract and its derived soluble fractions from the flower of Sophora viciifolia were evaluated in five different test systems (DPPH, ABTS, FRAP, reducing power and inhibition of lipid peroxidant models) for the first time. The ethylacetate soluble fraction exhibited the highest antioxidant effect. Correlation analysis suggested that the flavonoids might be the major contributors for the high antioxidant activity of this flower. In addition, 11 compounds were isolated from this flower, and the antioxidant capacities of 5 flavonoids were evaluated by DPPH assay. Compound 3 (luteolin) had a significant DPPH radical-scavenging activity, and was also present at the highest concentration (5.56mg/gdrysample), implying an important role of 3 for the antioxidant activity of this flower. The study suggests that the flower of S. viciifolia can provide valuable functional ingredients and can be used for the prevention of diseases related to various oxidant by-products of human metabolism.
The seismic performance of prefabricated reinforced concrete shear walls is a key point in the safety of the whole assembly structure under earthquake actions. In this study, six specimens of ...reinforced concrete shear walls were assembled with a cast-in-place vertical joint with a straight, L, or convex shape. The specimens were tested using a low cyclic loading test under an axial compression ratio of 0.2 or 0.3. The stress process, failure pattern, and hysteretic curve of each specimen were measured. Combined with a numerical analysis using the finite element method, the variations in the bearing capacity, stiffness degradation, ductility, and energy dissipation capacity of the tested specimens were analyzed. Results showed that all specimens failed in a shear pattern without an obvious failure phenomenon along the vertical joint. The hysteresis curves exhibited an obvious pinch phenomenon and good deformation ability. The seismic behavior decreased in sequence for the shear walls assembled with a cast-in-place vertical joint with a straight, L, or convex shape, while a higher axial compression ratio improved the bearing capacity of the shear walls. The shear wall with an L-shaped vertical joint had similar seismic behavior to that with a straight vertical joint, but the shear wall with a convex vertical joint exhibited a decrease of 8.5% and 10.9% in bearing capacity, 18.2% and 1.2% in ductility, and 13.1% and 20.6% in energy dissipation, respectively, under an axial compression ratio of 0.2 and 0.3. The bearing mechanisms of shear walls with different vertical joints are explained with the numerical analysis of the stress vector maps of concrete and the stress cloud maps of reinforcements at different stress levels.
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