Complicated Geometry Research Articles

Investigations of Suction Recirculation in Primary Sodium Pump of Future Indian Fast Breeder Reactors

The design of the next generation of fast breeder reactors has commenced, with the main targets being enhanced safety and improved economy. Nuclear heat generated in the fuel subassembly of fast reactors is removed by circulating sodium through the core using centrifugal pumps. The primary sodium pumps (PSPs) used are large-capacity pumps, and the design of these pumps is different from that of traditional pumps. Though many works have been reported for the performance prediction of centrifugal pumps, most of these works have been carried out in a decoupled way, and only a few works have been reported where the pump is modeled with all the associated geometric structures. Centrifugal pumps are prone to a phenomenon called suction recirculation, which occurs when pumps are operated significantly below the best efficiency point. This suction recirculation has a strong potential to damage the impeller. Correlations given in the literature for the prediction of the onset of recirculation cannot be used for complicated inlet geometries, and three-dimensional computation fluid dynamics (CFD) investigations are most suited for such applications. Many devices have been reported in the literature to reduce the intensity of (or to suppress) suction recirculation. Webs provided in the suction plenum will modify the velocity distribution at the impeller inlet and also can influence suction recirculation. In this work, the centrifugal pump used for primary sodium pumping for fast reactor applications is simulated using CFD techniques in an integrated way. The frozen rotor approach is used to simulate the impeller-diffuser hydraulics. The effect of flow hydraulics in the suction plenum, flow distribution in the standpipe–pump gap, and flow conditions in the pool on the performance characteristics of PSPs are simulated. The flow rate for the onset of suction recirculation is predicted and compared with correlations available in the literature. Simulations are carried out to study the effect of webs on suction recirculation. The effects of the number of webs and the web geometry are also studied.

A novel prefabricated auxetic honeycomb meta-structure based on mortise and tenon principle

Existing auxetic honeycomb meta-structures are generally integrated structures with complicated microstructural geometry which hence should be fabricated by costly additive manufacturing (AM) technology. The high cost and low production efficiency of AM technology is still the main bottleneck restricting the engineering applications of such kind of structures. In this work, a prefabricated auxetic honeycomb meta-structure with modularized components was proposed based on mortise and tenon (M&R) principle originated in ancient China. The modularized components of the prefabricated auxetic honeycomb are all tubular structures which can be easily fabricated by traditional manufacturing with low cost and high technical maturity. The mechanical properties of the proposed meta-structure were then detailed investigated numerically under quasi-static and dynamic loading conditions. The referenced integrated auxetic honeycomb meta-structure was also considered as a benchmark for comparison. Results show that the proposed prefabricated design exhibits lower strength and stiffness compared with its integrated counterpart, owing to the introduction of more flexibility. Consequently, the proposed design processes a much more stable stress plateau stage with a larger deformation range and effectively reduces the reactive force of the protected structure. The present work paves a novel avenue to design protective meta-structures with low-cost and high performance.

A semi-analytical approach for two-dimensional frictional contact of anisotropic magneto-electro-elastic solids

In this work, we present a semi-analytical modeling approach for solving the frictional contact of two-dimensional anisotropic magneto-electro-elastic (MEE) solids. The method is established in a broad framework in which the contact body is made of generally anisotropic MEE materials, the punch head can be arbitrary, and the punch can be subjected to generalized loading conditions including mechanical forces and electric and magnetic charges. An analytical solution of generalized distributed load along the half-plane surface is derived and utilized to formulate the semi-analytical equations governing the relation between the generalized displacements and tractions. Based upon the semi-analytical equations, the semi-analytical model in which the influence matrices can be calculated explicitly and its effectiveness is established. An iterative procedure is then used for determining the contact region, contact status, generalized surface deformation and the distribution of contact tractions, as well as the punch’s indentation depth and electric and magnetic potentials. The present approach is verified by comparing its numerical results with those obtained by the existing analytical solutions and boundary element method. The influences of different factors, such as punch profile, mechanical load, electric and magnetic charges, friction coefficient and material properties, are also analyzed. The capability of this method to handle complicated geometry, such as rough surfaces, is finally discussed, showing the potential performance of the developed method for practical engineering applications.

3D study of the vibrational behaviour of lithic flint blades

Stone Age sites are well known to often contain many lithic flint blades and flakes, which may provide important information about early European Stone Age cultures and their environment. Understanding the mechanical behaviour of lithic flint blades represents an important problem for scientists in general and archaeologists in particular. In this study, the structural behaviour of lithic flint blades is studied. Ten specimens with different geometric shapes (tilted, curved, with bumping surfaces) were studied and tested. Their natural frequencies, damping ratios, and mode shapes (that is how the specimen deforms under any external excitation) are estimated using two models: an analytical model that accounts for the specimen's curvature and a 3D Finite Element (FE) method. Advanced experimental methods, including ultrasound techniques, were used to measure the mechanical properties of the specimens. The experimental set-up was built around a laser vibrometer that measured the specimen's displacement. The model predictions were compared with the experimental data to validate their effectiveness. A good agreement is observed between the models and the real data. It is particularly observed that despite their complicated geometries, the specimens still follow a structured pattern in their dynamic response. The presented study supports the use of acoustic methods as an effective tool to characterize and detect submerged prehistoric materials. This work contributes to the dynamic characterization of submerged Stone Age materials.

Effective Ti-6Al-4V Powder Recycling in LPBF Additive Manufacturing Considering Powder History

Laser powder bed fusion (LPBF) is an outstanding additive manufacturing (AM) technology that can enable both complicated geometries and desired mechanical properties in high-value components. However, the process reliability and cost have been the obstacles to the extensive industrial adoptions of LPBF. This work aims to develop a powder recycling procedure to reduce production cost and minimize process uncertainties due to powder degradation. We used a recycle index (R) to reuse Ti-6Al-4V powder through 10 production cycles. Using this recycle index is more reasonable than simply replying on recycle numbers as it incorporates the powder usage history. A recycling procedure with simple virgin powder top-up can effectively mitigate powder degradation and maintain stable powder properties, chemical compositions, and tensile properties. The experimental finding points to a sustainable recycling strategy of Ti alloy powders with minimal material waste and without noticeable detriment to observed mechanical performance through LPBF production cycles.

Vehicular Connectivity on Complex Trajectories: Roadway-Geometry Aware ISAC Beam-Tracking

In this paper, we propose sensing-assisted beamforming designs for vehicles on arbitrarily shaped roads by relying on integrated sensing and communication (ISAC) signalling. Specifically, we aim to address the limitations of conventional ISAC beam-tracking schemes that do not apply to complex road geometries. To improve the tracking accuracy and communication quality of service (QoS) in vehicle to infrastructure (V2I) networks, it is essential to model the complicated roadway geometry. To that end, we impose the curvilinear coordinate system (CCS) in an interacting multiple model extended Kalman filter (IMM-EKF) framework. By doing so, both the position and the motion of the vehicle on a complicated road can be explicitly modeled and precisely tracked attributing to the benefits from the CCS. Furthermore, an optimization problem is formulated to maximize the array gain by dynamically adjusting the array size and thereby controlling the beamwidth, which takes the performance loss caused by beam misalignment into account. Numerical simulations demonstrate that the roadway geometry-aware ISAC beamforming approach outperforms the communication-only-based and ISAC kinematic-only-based technique in tracking performance. Moreover, the effectiveness of the dynamic beamwidth design is also verified by our numerical results.

Seismic imaging of the Northern Andean subduction zone from teleseismic tomography: a torn and fragmented Nazca slab

SUMMARY The Nazca-South America subduction zone in Ecuador is characterized by a complicated along-strike geometry as the slab transitions from flat slab subduction in the south, with the Peruvian flat slab, to what has been characterized as ‘normal’ dipping subduction beneath central Ecuador. Plate convergence additionally changes south to north as the trench takes on a convex shape. Highly heterogeneous bathymetry at the trench, including the aseismic oceanic Carnegie Ridge (CR), and sparse intermediate-depth seismicity has led many to speculate about the behaviour of the downgoing plate at depth. In this study, we present a finite-frequency teleseismic P-wave tomography model of the northern Andes beneath Ecuador and Colombia from 90 to 1200 km depth. Our model builds on prior tomography models in South America by adding relative traveltime residuals recorded at stations in Ecuador. The complete data set is comprised of 114 096 relative traveltime residuals from 1133 stations across South America, with the added data serving to refine the morphology of the Nazca slab in the mantle beneath the northern Andes. Our tomography model shows a Nazca slab with a fragmented along-strike geometry and the first teleseismic images of several proposed slab tears in this region. At the northern edge of the Peruvian flat slab in southern Ecuador, we image a shallow tear at 95–200 km depth that appears to connect mantle flow from beneath the flat slab to the Ecuadorian Arc. Beneath central Ecuador at the latitudes of the CR, the Nazca slab is continuous into the lower mantle. Beneath southern Colombia, the Malpelo Tear breaks the Nazca slab below ∼200 km depth.

CFD-validated pore network modeling of packed beds of non-spherical particle

In this work, the hydrodynamics inside packed beds of particles with different shapes are investigated: spherical, cylindrical, and cubical particles. The cylindrical and cubical geometries contain sharp ridges, which give rise to complicated pore geometries. In this study, Pore Network Modeling (PNM) validated with the Particle-Resolved Computational Fluid Dynamics (PR-CFD) simulations of packed beds with these non-spherical particles will be reported. The results show that the PNM predicts the same average flow behavior and pore pressure variations as PR-CFD. However, the PNM prediction of the pressure values is less accurate at the pore level compared to the PR-CFD for the cubical particles.

Fresh prepreg multilayer scrap reuse

Fresh prepreg multilayer scrap reuse To address waste generated during production, a processing route for uncurde material is developed in MC4. Multilayer fresh prepreg scrap is processed to obtain new intermediate products that can be used to manufacture new parts. Developing dedicated valorisation processes for each composite scrap is essential to exploit their potential and avoid decreasing the remaining performances during processing or increasing costs. In the case of multilayer fresh prepreg scrap, it is typical of the aeronautical field in which automated lay-up technologies such as automatic fibre placement or automated tape laying create a flat stack with a tailored laminate. This laminate is then cut by ultrasonic equipment. Despite being high-quality, the leftovers remaining are discarded because of the complexity of finding a suitable application for these cutoffs and the complicated geometry of laminate parts. It must also be considered that this kind of scrap is often designed to keep a predominant orientation, presenting a higher amount of fibre.

How different is the magnetic field at the core–crust interface from that at the neutron star surface? The range allowed in magnetoelastic equilibrium

ABSTRACT This study was focused on the investigation of a magnetic field penetrating from the core of a neutron star to its surface. The range of possible field configurations in the intermediate solid crust is less limited owing to the elastic force acting on the force balance. When the Lorentz force is excessively strong, the magnetoelastic equilibrium does not hold, and thus, the magnetic field becomes constrained. By numerically solving for the magnetoelastic equilibrium in a thin crust, the range of the magnetic field at the core–crust interface was determined, while assuming the exterior to be fixed as a dipole in vacuum. The results revealed that the toroidal component should be smaller than the poloidal component at the core–crust interface for the surface dipole, B0 > 2.1 × 1014 G. Consequently, a strong toroidal field, for example, B ∼ 1016 G, as suggested by free precession of magnetars should be confined to a deep interior core and should be reduced to B ∼ 1014 G at the bottom of the crust. The findings of this study provide insights into the interior field structure of magnetars. Further investigations on more complicated geometries with higher multipoles and exterior magnetosphere are necessary.

Modification of 316L steel powders with bronze using high energy ball milling for use as a binder component in PBF-LB/M printing of diamond-metal matrix composites

For the processing of diamond-metal matrix composites, the powder bed fusion using a laser for metals (PBF-LB/M), represents a new promising method for the additive manufacturing of diamond tools for concrete and rock machining, even with more complicated geometries. Previous research activities show a strong tendency for cracking and delamination during the construction process of the samples. This behavior is caused by thermal residual stresses associated with the embedded diamonds. To control these negative effects on the process side, the volume energy density is reduced accordingly, which, however, led to increased pore formation. This publication deals with an approach on the material side to modify a 316L stainless steel base powder with an addition of 20 wt% bronze via a high energy ball milling (HEBM) process in such a way that a homogeneous solid solution phase is created. A significantly increasing of the melting interval and a decreasing of both solidus and liquidus temperature was observed, which can reduce pore formation in the PBF-LB/M-process. In addition, XRD-diffractometry and SEM/EDS-analysis showed that the homogeneous solid solution phase of this alloyed powder segregates again into Fe- and Cu-rich phases when heated up to the melting point.

Framework for sustainable building design and construction using off-cut wood

Irregularly shaped wood created as waste from construction is considered challenging to reuse because of its complicated geometry and a lack of well-defined design methods. Here, we propose a sustainable building design and construction framework as a systematic methodology for upcycling irregular off-cut wood into new components. This framework consists of repeatable steps, as follows: a. material reclamation system: 3D scanning is employed as the main technical method to record a material’s 3D information and material-specific parameters and create a database; b. structural generation and assessment system: material screening, voxel-based filling, and structure generation based on finite element analysis to employed to assess the generated results prior to construction to optimize the final structure. Using furniture, building components, and installations/buildings, we verify the use of this framework for material recycling and generative design and construction.

Performance assessment of carbon dots based nano cutting fluids in improving the machining characteristics of additively manufactured 316L stainless steel

The advantages of additive manufacturing (AM) over conventional manufacturing techniques, such as the ability to build parts with complicated geometry, have led to a rise in its applications in recent years. However, the mechanical and tribological qualities of an additively manufactured (AMed) parts are distinct from those of a conventionally made components because of the layer-by-layer nature of AM process. However, there is a need to machine these complex geometries of AMed components to achieve the desired final dimension and surface finish. Therefore, this study investigates the impact of four environmental regimes (dry, flood, MQL, and N-MQL) on the metal cutting of AMed 316L stainless steel specimen, with a focus on the efficacy of N-MQL lubrication containing rice bran oil + carbon dots (CDs) particles. Responses measured include cutting temperature, surface roughness (Ra), tool wear, microstructure, and micro-hardness. Outcomes show that N-MQL outperforms other cutting regimes, offering enhanced machining performance and surface quality, making it a crucial choice for AMed specimens.

A smoothed assumed enhanced strain method for frictional contact with constant strain elements

This paper presents a finite element framework for imposing frictional contact conditions on embedded fracture faces, implemented by the constant-strain assumed enhanced strain (AES) method, where penalty method is used to impose both non-penetration constraint and Coulomb's law of friction. The proposed constant-strain AES method for modeling embedded frictional contact can be cast into an integration algorithm similar to those used in the classical plasticity theory, where displacement jump is calculated from the local traction equilibrium at Gauss point, so the method does not introduce any additional global degrees of freedom. Moreover, constant-strain elements are often desirable in practice because they can be easily created automatically for large-scale engineering applications with complicated geometries. As encountered in other enriched finite element methods for frictional contact, the problem of normal contact pressure oscillations is also observed in the constant-strain AES method. Therefore, we developed a strain-smoothing procedure to effectively mitigate the oscillations. We investigated and verified the proposed AES framework through several numerical examples, and illustrated the capability of this method in solving challenging nonlinear frictional contact problems.

Deep Ocean Circulation Governs Sedimentary CaCO3 Accumulation in the Northeast Pacific Ocean

AbstractThe meridional overturning circulation influences the deep‐sea carbon reservoir, global carbon cycle, and climate change on century to millennium time scales. However, the influence of deep‐sea circulation on sedimentary carbonate accumulation and thus deep‐sea carbonate system in the North Pacific Ocean is difficult to quantify owing to the complicated geometry of deep ocean ventilation attributed to its topographic complexity. In this study, we reanalyzed the distribution patterns of sedimentary calcium carbonate contents (wtCaCO3%) in the deep Northeast Pacific in a quantitative manner. Our results in conjunction with data from the Northwest Pacific Ocean, suggest that the deep ocean circulation plays a critical role in elucidating the basin‐scale features of sedimentary CaCO3 distribution in the North Pacific Ocean, despite elevated non‐carbonate dilution exerted by detritus from active geological processes on the topographic structure. Moreover, enhanced carbonate dissolution in the Guatemala and Panama Basins, controlled by higher flow rates of deep currents, influences the depth‐profiles of sedimentary wtCaCO3% in that region. These findings suggest a novel avenue to reconstruct past changes in ocean circulation and carbon cycling in the Northeast Pacific Ocean based on the wtCaCO3% records in sediments.

Investigation of mode-I fracture behavior by essential work of fracture during the single-point incremental forming process

A promising technique for manufacturing low-thickness workpieces with complicated geometries is Incremental Sheet Forming (ISF). Due to its dieless process, ISF is a proper candidate for the production of workpieces at low rates or prototypes of the samples. The mechanical properties of the workpieces produced by ISF are a critical factor in determining their potential applications. Pyramid-shaped samples made of cold rolled steel (DC01) were produced using the single point incremental forming (SPIF) process in this study. To examine how the forming process affects mechanical properties, specimens were obtained from both raw and deformed surfaces. Subsequently, the specimens underwent tensile and fracture tests. The fracture toughness of the specimens was assessed using the essential work of fracture (EWF) technique. Through the use of incremental forming process, the tensile tests revealed a considerable improvement in both ultimate and yield tensile strength, with increases of 33.72% and 90.02%, respectively. However, the forming process led to a reduction of 86.64% in formability compared to the raw specimens. Fracture tests performed on the deformed specimens demonstrated a noteworthy reduction of 59.12% in the amount of energy needed for the initiation of crack growth, compared to the raw specimens. Additionally, we examined how the properties of deformed specimens are affected by the initial rolling direction of the sheets in this study. The study revealed that the mechanical properties and fracture characteristics of the material varied significantly along the transverse direction. The study utilized scanning electron microscopy (SEM) to analyze the fracture mechanisms and found that ductile fracture was the dominant mode of failure. The raw specimens demonstrated more ductile fractured surfaces, which corresponded to higher values of essential work of fracture (EWF).

In-situ X-ray computed tomography tensile tests and analysis of damage mechanism and mechanical properties in laser powder bed fused Invar 36 alloy

Laser powder bed fusion (LPBF) is a potential additive manufacturing process to manufacture Invar 36 alloy components with complicated geometry. Whereas it inevitably introduces specific microstructures and pore defects, which will further influence the mechanical properties. Hence, aiming at exploring the LPBF process-related microstructures and pore defects, and especially their influences on the damage mechanism and mechanical properties, Invar 36 alloy was manufactured by LPBF under designed different laser scanning speeds. The microstructure observations reveal that higher scanning speeds lead to equiaxed and short columnar grains with higher dislocation density, while lower scanning speeds result in elongated columnar grains with lower dislocation density. The pore defects analyzed by X-ray computed tomography (XCT) suggest that the high laser scanning speed gives rise to numerous lamellar and large lack-of-fusion (LOF) pores, and the excessively low laser scanning speed produces relatively small keyhole pores with high sphericity. Moreover, the in-situ XCT tensile tests were originally performed to evaluate the damage evolution and failure mechanism. Specifically, high laser scanning speed causes brittle fracture due to the rapid growth and coalescence of initial lamellar LOF pores along the scanning direction. Low laser scanning speed induces ductile fracture originating from unstable depressions in the surfaces, while metallurgical and keyhole pores have little impact on damage evolution. Eventually, the process-structure-property correlation is established. The presence of high volume fraction of lamellar LOF pores, resulting from high scanning speed, leads to inferior yield strength and ductility. Besides, specimens without LOF pores exhibit larger grain sizes and lower dislocation density at decreased scanning speeds, slightly reducing yield strength while slightly enhancing ductility. This understanding lays the foundation for widespread applications of LPBF-processed Invar 36 alloy.

Experimental Investigation of SPIF Process for Conical Frustum

In sheet metal industries, single point incremental forming (SPIF) is a popular technology for quick prototyping and small series manufacturing techniques. In producing specific components with complicated geometries, the technique has become known for its flexibility, effectiveness, and simplicity of usage. The objective of this research work is to carry out the numerical investigation of the SPIF process to study the effect of different parameters on the formability for truncated cone. Al 1060 grade of aluminium is used for this study which is commonly used for kitchenware, reflectors, electronic components etc; where strength is not a major concern. Three dimensional models were developed for different set of parameters using commercial finite element software ABAQUS 6.13 with Dynamic/Explicit solver using solid mechanics model. Taguchi analysis has been carried out to find the effect of parameters (Tool rotational speed, Feed, Step size, Tool diameter and Wall angle) on thickness reduction. Each parameter was varied for three levels and L9 orthogonal array was used. The ANOVA tool has been used to summarize the contribution of each variable. Results have been compared with reported experimental results for validation. The process modelling is concluded with a brief overview of approaches for improving part quality.

Impacts of proppant distribution on development of tight oil reservoirs with threshold pressure gradient

Field evidence indicates that proppant distribution and threshold pressure gradient have great impacts on well productivity. Aiming at the development of unconventional oil reservoirs in Triassic Chang-7 Unit, Ordos Basin of China, we presented an integrated workflow to investigate how (1) proppant placement in induced fracture and (2) non-linear flow in reservoir matrix would affect well productivity and fluid flow in the reservoir. Compared with our research before (Yue et al., 2020), here we extended this study into the development of multi-stage fractured horizontal wells (MFHWs) with large-scale complicated fracture geometry. The integrated workflow is based on the finite element method and consists of simulation models for proppant-laden fluid flow, fracture flow, and non-linear seepage flow, respectively. Simulation results indicate that the distribution of proppant inside the induced cracks significantly affects the productivity of the MFHW. When we assign an idealized proppant distribution instead of the real distribution, there will be an overestimation of 44.98% in daily oil rate and 30.63% in cumulative oil production after continuous development of 1000 days. Besides, threshold pressure gradient (TPG) also significantly affects the well performance in tight oil reservoirs. If we simply apply linear Darcy’s law to the reservoir matrix, the overall cumulative oil production can be overrated by 77% after 1000 days of development. In general, this research provides new insights into the development of tight oil reservoirs with TPG and meanwhile reveals the significance of proppant distribution and non-linear fluid flow in the production scenario design.

Learning Implicit Neural Representation for Satellite Object Mesh Reconstruction

Constructing a surface representation from the sparse point cloud of a satellite is an important task for satellite on-orbit services such as satellite docking and maintenance. In related studies on surface reconstruction from point clouds, implicit neural representations have gained popularity in learning-based 3D object reconstruction. When aiming for a satellite with a more complicated geometry and larger intra-class variance, existing implicit approaches cannot perform well. To solve the above contradictions and make effective use of implicit neural representations, we built a NASA3D dataset containing point clouds, watertight meshes, occupancy values, and corresponding points by using the 3D models on NASA’s official website. On the basis of NASA3D, we propose a novel network called GONet for a more detailed reconstruction of satellite grids. By designing an explicit-related implicit neural representation of the Grid Occupancy Field (GOF) and introducing it into GONet, we compensate for the lack of explicit supervision in existing point cloud surface reconstruction approaches. The GOF, together with the occupancy field (OF), serves as the supervised information for neural network learning. Learning the GOF strengthens GONet’s attention to the critical points of the surface extraction algorithm Marching Cubes; thus, it helps improve the reconstructed surface’s accuracy. In addition, GONet uses the same encoder and decoder as ConvONet but designs a novel Adaptive Feature Aggregation (AFA) module to achieve an adaptive fusion of planar and volume features. The insertion of AFA allows for the obtained implicit features to incorporate more geometric and volumetric information. Both visualization and quantitative experimental results demonstrate that our GONet could handle 3D satellite reconstruction work and outperform existing state-of-the-art methods by a significant margin. With a watertight mesh, our GONet achieves 5.507 CD-L1, 0.8821 F-score, and 68.86% IoU, which is equal to gains of 1.377, 0.0466, and 3.59% over the previous methods using NASA3D, respectively.