One of the challenging issues in additive manufacturing (AM) oriented topology optimization is how to design structures that are self-supportive in a manufacture process without introducing ...additional supporting materials. In the present contribution, it is intended to resolve this problem under an explicit topology optimization framework where optimal structural topology can be found by optimizing a set of explicit geometry parameters. Two solution approaches established based on the Moving Morphable Components (MMC) and Moving Morphable Voids (MMV) frameworks, respectively, are proposed and some theoretical issues associated with AM oriented topology optimization are also analyzed. Numerical examples provided demonstrate the effectiveness of the proposed methods.
•New approaches for designing self-supporting structures are proposed.•Self-supporting structures can now be designed in a geometrically explicit way.•Numerical examples demonstrate the effectiveness of the approaches.
This paper presents a new method to fabricate 3D models on a robotic printing system equipped with multi-axis motion. Materials are accumulated inside the volume along curved tool-paths so that the ...need of supporting structures can be tremendously reduced - if not completely abandoned - on all models. Our strategy to tackle the challenge of tool-path planning for multi-axis 3D printing is to perform two successive decompositions, first volume-to-surfaces and then surfaces-to-curves. The volume-to-surfaces decomposition is achieved by optimizing a scalar field within the volume that represents the fabrication sequence. The field is constrained such that its iso-values represent curved layers that are supported from below, and present a convex surface affording for collision-free navigation of the printer head. After extracting all curved layers, the surfaces-to-curves decomposition covers them with tool-paths while taking into account constraints from the robotic printing system. Our method successfully generates tool-paths for 3D printing models with large overhangs and high-genus topology. We fabricated several challenging cases on our robotic platform to verify and demonstrate its capabilities.
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•A novel X-structured harvesting device is proposed for low frequency band.•It is an advantageous version compared to existing cantilever based harvesters.•It can achieve tunable ...harvesting bandwidth by adjusting key structural parameters.•It holds potentials for traffic-induced bridge vibration energy harvesting.
With a nonlinear X-shaped structure connected with piezoelectric harvesters through two types of special mounting configurations (horizontal and vertical cases), novel coupled vibration energy harvesting systems are purposely constructed and investigated for exploiting nonlinearity and structural coupling effect in vibration energy harvesting. Different from concentrating on a beam harvester itself in the literature (i.e. the beneficial nonlinearity comes from the beam itself), this study focuses on exploring the nonlinear benefits that the X-shaped structure could provide, together with structural coupling effect. The novelty lies in that the coupled X-structured harvesting systems have both the advantages of the existing simple cantilevered beam harvester (harvesting power only at around the natural frequency of the beam) and the spring-mass system supported beam harvester (harvesting energy only at around the natural frequency of the supporting spring-mass system). With the proposed X-structures, the effective operation bandwidth of traditional cantilever based harvesters can be greatly enlarged and also be extended to an ultralow frequency range. This is a very special feature of the proposed X-structure based harvesting systems compared with conventionally designed cantilevered harvesters or the spring-mass supported cantilevered harvesters. The proposed devices can be regarded as advantageous versions of the cantilever-based configurations for ultralow frequency range. In addition, the X-structured harvesters can achieve very tunable harvesting bandwidth (i.e. tuning the harvesting frequency of the first peak) by adjusting several structural parameters. The experiment tests demonstrate that the proposed harvesting devices hold potentials for traffic-induced bridge vibration energy harvesting, which can be used for powering the sensors for bridge health monitoring.
Two‐dimensional (2D) graphitic carbon nitride (g‐C3N4) nanosheets show brilliant application potential in numerous fields. Herein, a membrane with artificial nanopores and self‐supporting spacers was ...fabricated by assembly of 2D g‐C3N4 nanosheets in a stack with elaborate structures. In water purification the g‐C3N4 membrane shows a better separation performance than commercial membranes. The g‐C3N4 membrane has a water permeance of 29 L m−2 h−1 bar−1 and a rejection rate of 87 % for 3 nm molecules with a membrane thickness of 160 nm. The artificial nanopores in the g‐C3N4 nanosheets and the spacers between the partially exfoliated g‐C3N4 nanosheets provide nanochannels for water transport while bigger molecules are retained. The self‐supported nanochannels in the g‐C3N4 membrane are very stable and rigid enough to resist environmental challenges, such as changes to pH and pressure conditions. Permeation experiments and molecular dynamics simulations indicate that a novel nanofluidics phenomenon takes place, whereby water transport through the g‐C3N4 nanosheet membrane occurs with ultralow friction. The findings provide new understanding of fluidics in nanochannels and illuminate a fabrication method by which rigid nanochannels may be obtained for applications in complex or harsh environments.
A g‐C3N4 membrane assembled from two‐dimensional g‐C3N4 nanosheets demonstrates good chemical and mechanical stability, as well as ultralow water friction when applied in water purification. The nanosheets contain intrinsic (P1) and artificial (P2) nanopores, as well as self‐supporting spacers (S) formed by adhered unstripped fragments.
Ecosystem services (ES) have been broadly adopted as a conceptual framing for addressing human nature interactions and to illustrate the ways in which humans depend on ecosystems for sustained life ...and well-being. Additionally, ES are being increasingly included in urban planning and management as a way to create multi-functional landscapes able to meet the needs of expanding urban populations. However, while ES are generated and utilized within landscapes we still have limited understanding of the relationship between ES and spatial structure and dynamics. Here, we offer an expanded conceptualization of these relationships through the concept of service providing units (SPUs) as a way to plan and manage the structures and preconditions that are needed for, and in different ways influence, provisioning of ES. The SPU approach has two parts: the first deals with internal dimensions of the SPUs themselves, i.e. spatial and temporal scale and organizational level, and the second outlines how context and presence of external structures (e.g. built infrastructure or larger ecosystems) affect the performance of SPUs. In doing so, SPUs enable a more nuanced and comprehensive approach to managing and designing multi-functional landscapes and achieving multiple ES goals.
•Generation of ecosystem services is spatially explicit.•Contextual factors will influence the generation of ecosystem services.•A better understanding of service providing units is directly relevant to planning.•Our approach is especially well-suited to cities but can be applied in any landscape.
The external partitions of a building (walls, roof, etc.) in addition to their supporting functions must also ensure an internal microclimate suitable for comfortable human work, recreation and other ...activities. This article analyzes the thermal characteristics of the external walls of a residential house and thermographically examines the joints of the different structures of the building. Thermographical examination may be performed either passively or actively. In the former case, the object of the examination ir heated up to a given temperature, after which thermographical images of the object are taken and analyzed. In the latter case, thermographical analysis is made of the object in its naturally established thermal conditions. This article examines the thermal characteristics of the partition structures of a residential building. The values of the thermal properties of the materials are taken from the documentation provided by their manufacturers, and in their absence, the data of the technical building regulations is used. Calculated analytically: the wall of the western annex only meets the C energy class requirements, the insulation of the old part of the building raised the heat transfer coefficient of the partition to class A, the thermal characteristic of the eastern annex wall corresponds to the A + energy class. This thermographic examination showed that the facade covered by the fibrous cement siding absorbed less heat compared to the masonry facades. Based on theoretical calculations and the thermographic analysis, it is recommended to additionally insulate the western annex from the inside. If possible, it is also recommended to additionally insulate both facade joints with polyurethane foam and to seal them with waterproofing mastic to prevent the sunrays from reaching the foam.
•A HSLD stiffness vibration isolator with NSS and SLS is constructed.•The proposed NSS can be accurately described by quadratic polynomial.•The MT-IHBM is extended to capture multiple harmonics in ...vibration simultaneously.•The NSS can improve the isolation capacity of asymmetric supporting systems effectively.
In this paper, a high-static-low-dynamic stiffness (HSLDS) vibration isolator with a novel parabolic-cam-roller negative stiffness mechanism is proposed to study the effectiveness of negative stiffness on asymmetric spring supporting structures. Based on the physical model, the intrinsic geometrical nonlinearity of the isolator is analyzed and the differential equation of motion is derived by the generalized Lagrange's equation. Here, the multi-term incremental harmonic balance method (MT-IHBM) is employed and extended to capture both primary and subharmonic resonances in nonlinear response. By means of arc-length increment, the adaptability and reliability of this method are enhanced under strong nonlinear vibration. Vibration transmissibility and frequency response relationships of various frequency components are demonstrated in order to better explain the properties of asymmetry vibration. The analysis results indicate that the performance of the isolation system is affected by different parametric excitation. Under some parameters, the introduction of negative stiffness will cause obvious 1/2 subharmonic resonance. The existence of the bias term in response makes the peak and frequency of resonances shift vertically and horizontally, respectively. Due to the asymmetry, the proposed HSLDS isolator does not present quasi-zero stiffness at the static equilibrium position, but it has superior ability to suppress vibration. Meanwhile, comparisons show that adding negative stiffness mechanism can still significantly improve the vibration isolation performance when a supporting structure has the characteristic of asymmetric stiffness.
Precious metal catalysts are widely recognized for their excellent efficiency in OER and ORR, but high cost and stability limit further commercial expansion. Carbon-based catalysts with large ...specific surface area, although a potential alternative to noble metal catalysts in terms of price and performance, are notoriously weak in terms of corrosion resistance in extreme environments. Metal catalysts are able to solve the above problems and are gradually coming into the limelight, but the control of morphology is not as good as that of carbon-based catalysts. Therefore, in order to solve the above problems together, the development of bifunctional catalysts with high efficiency, stability, low cost and excellent morphology has become a bright research direction. In this study, a new catalyst consisting of phosphorus-doped self-supported nanostructured Ti4O7 and nickel-gallium alloy particles was investigated using an electrostatic spinning process. Most of the previous studies have simply prepared Ti4O7 nanofibers without in-depth investigation on how to better control their morphology. In contrast, this study presents a universal set of experimental parameters for the development of very fine Ti4O7 nanospinning. With the help of this set of parameters, we develop a novel Ti4O7/C composite substrate nanofiber catalyst with an average diameter less than 297 nm. Its excellent morphology and corrosion resistance make it an inexpensive bifunctional catalyst with great potential. Relevant OER performed in 1 M KOH electrolyte shows that the catalyst has a low Tafel slope (80.77 mV dec−1), a small overpotential (282 mV at 10 mA cm−2), and excellent stability (up to 5000 cycles). In a strongly alkaline environment, the catalyst outperforms commercially available RuO2 (299 mV and 105.79 mV dec−1). In addition, the catalyst demonstrates a half-wave potential of 0.86 V in 0.1 M KOH electrolyte, exhibiting excellent ORR performance. The maximum power density (161 mW cm−2) and energy density (813 mA h gZn−1) of the zinc-air battery assembled with this catalyst exceeds the performance of the air battery using the Pt/C catalyst with better stability. In summary, this study achieves significant methodological advances and develops a novel bifunctional catalyst, which is of interest to a wide range of researchers.
The first synthesis of a new low-cost catalyst, NiGa/Ti4O7@PCNFs, which is a new self-supporting bifunctional catalyst with exceptional performances in oxygen electrocatalysis and Zn-air batteries. Display omitted
•Parameters for the preparation of fine Ti4O7 nanofibers are proposed.•Novel catalyst NiGa/Ti4O7@PCNFs is prepared.•Cheap novel catalysts have better performance than precious metal catalysts.
In this work, a topology optimization approach is developed for additive manufacturing (AM) of 2D and 3D self-supporting structures. Three important issues, i.e., overhang angle control, avoidance of ...the so-called V-shaped areas and minimum length scale control are addressed. 2D solid polygon and 3D polyhedron features are introduced as basic design primitives that are capable of translations, deformations and intersections to drive topological changes of the structure. The overhang angle control is realized in a straightforward way only by imposing upper bounds to related design variables without introducing any nonlinear constraint. The V-shaped area is avoided by simply limiting the positions of solid features. Minimum length scale control is controlled by a robust formulation. Numerical examples in 2D and 3D demonstrate the effectiveness of the proposed approach for various build directions, critical overhang angles and minimum length scales considered in AM.
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