Freeform Geometries Research Articles

Aerodynamic Design Optimization of a Transonic Strut-Braced-Wing Regional Aircraft

The aerodynamic design and fuel burn performance of a Mach-0.78 strut-braced-wing regional jet is investigated through aerodynamic shape optimization based on the Reynolds-averaged Navier–Stokes equations. Conceptual-level multidisciplinary design optimization is first performed to size the strut-braced-wing aircraft for a design mission similar to the Embraer E190-E2, with a design range of 3100 nmi at a maximum capacity of 104 passengers, and a maximum payload of 30,200 lb. For direct performance comparisons, a conventional tube-and-wing regional jet is also sized and optimized based on the same reference aircraft. Gradient-based aerodynamic shape optimization is then performed on wing–body–tail models of each aircraft, with the objective of drag minimization at cruise over a 500 nmi nominal mission. Design variables include twist and section shape degrees of freedom, which are realized through a free-form and axial deformation geometry control system, whereas nonlinear constraints include constant lift, zero pitching moment, minimum wing volume, and minimum maximum thickness-to-chord ratios. Results indicate that the optimizer is capable of mitigating shock formation, boundary-layer separation, and other flow interference effects from each wing design, including those within the wing–strut junction of the strut-braced wing. With year 2020 technology levels, the strut-braced-wing regional jet offers a 12.9% improvement in cruise lift-to-drag ratio over an Embraer E190-E2-like conventional tube-and-wing aircraft, which translates to a 7.6% reduction in block fuel for the nominal mission.

Investigating the feasibility of using carbon fiber tapes as reinforcement for 3D concrete printing

AbstractThe main advantages of textiles as concrete reinforcement are high corrosion resistance, allowing for thin concrete covers, high drapability, and high strength. Due to these advantages, textiles are particularly suitable as reinforcement for 3D printed concrete, where thin elements and freeform geometries are possible. In this article, a new type of textile reinforcement for the integration into 3D concrete printing is investigated: unidirectional carbon fiber tapes. Carbon fiber tapes are made from carbon fiber rovings by spreading. Three carbon fiber tapes are produced and used as reinforcement in concrete specimens subjected to four‐point bending tests. The results show that for a spreading factor of 2.2 (areal weight 136 g/m2), the flexural strength of the beams is increased by 125% compared to reference beams reinforced with unspread rovings. Further increase of the spreading factor does not increase flexural strength further as the failure mode changes from rupture to spalling.

3D weaving with curved ribbons

Basket weaving is a traditional craft for creating curved surfaces as an interwoven array of thin, flexible, and initially straight ribbons. The three-dimensional shape of a woven structure emerges through a complex interplay of the elastic bending behavior of the ribbons and the contact forces at their crossings. Curvature can be injected by carefully placing topological singularities in the otherwise regular weaving pattern. However, shape control through topology is highly non-trivial and inherently discrete, which severely limits the range of attainable woven geometries. Here, we demonstrate how to construct arbitrary smooth free-form surface geometries by weaving carefully optimized curved ribbons. We present an optimization-based approach to solving the inverse design problem for such woven structures. Our algorithm computes the ribbons' planar geometry such that their interwoven assembly closely approximates a given target design surface in equilibrium. We systematically validate our approach through a series of physical prototypes to show a broad range of new woven geometries that is not achievable by existing methods. We anticipate our computational approach to significantly enhance the capabilities for the design of new woven structures. Facilitated by modern digital fabrication technology, we see potential applications in material science, bio- and mechanical engineering, art, design, and architecture.

Controlled Turning Process for the Production of Friction-Reduced Cylinder Liners with a Defined Free-Form Geometry

Controlled Turning Process for the Production of Friction-Reduced Cylinder Liners with a Defined Free-Form Geometry

Soft Twisting Pneumatic Actuators Enabled by Freeform Surface Design

Twisting motion plays an important role in kinematics of soft robots. However, current twisting actuators usually suffer from complex mechanical design with multiple materials and undesired coupling with bending and stretching motions. In this letter, we propose a new class of soft twisting pneumatic actuators that purely rely on the freeform chamber geometry to achieve large bi-directional twisting rotations. The freeform chamber surface integrates geometric flexibility in the cross section, lateral profile, and axial chirality, which are parameterized as design variables. We develop a finite element analysis model and investigate the effect of the geometry parameters on the actuators' mechanical behavior. The actuator naturally undergoes combined twisting and axial motions, and achieves a bi-directional twisting rotation of 116.7 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , blocking torque of 0.81 N · m, and energy density of 1907 J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , well in line with the theoretical prediction. When it is constrained from axial motions, the actuator delivers pure twisting motion, achieving a bi-directional twisting rotation of 72.5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , blocking torque of 0.56 N· m, and energy density of 925 J/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . This letter represents an important step toward leveraging the full potential of the freeform geometry design to create novel compact soft-bodied actuators and robots.

An innovative Fast Layer-wise Simulation of Temperature distribution using a Chessboard Strategy (FALS TECHS) in the powder-bed fusion process

The thermal evolution of a printed part plays a crucial role in the ultimate quality of components that are produced using powder-bed fusion (PBF) processes. Temperature distribution throughout an exposure-layer can be employed as a significant proxy to optimize the process parameters and explore the effects of different scan strategies on the thermal evolution of the fabrication process. Nevertheless, previous works have not provided any technique to simulate the temperature distribution throughout a layer with freeform complex geometry and in actual size. This conspicuous lack is predominantly due to the high computational cost of existing simulation techniques. This paper introduces a Fast Layer-wise Simulation of Temperature distribution using a Chessboard Strategy” or “FALS TECHS” in the PBF process. This innovative technique simulates the temperature distribution throughout the layers of a freeform shape using actual dimensions in a fraction of computational time achieved by previously reported methods. The developed capability assists designers in the modification of scanning strategies according to the geometry of the exposure-layer to achieve a uniform temperature distribution, thus, reducing the residual stress throughout the printed layer. Furthermore, the technique helps to optimize the process parameters of the scanning strategy. We investigated the accuracy of the methodology by comparing simulation results with experimental thermal images. The results show a close correspondence between the two.

Free-form geometries in contemporary architecture – dimensional rules of Folded, Blob and Formlessness architecture

The style of Free-form Geometry (FFG) has emerged in contemporary architecture within the last three decades around the world through the progress of digital design tools and the development of constructive materials. FFG is considered as the hard efforts of several contemporary architects to release their products from familiar restrictions to discover new and unfamiliar styles under the perspective of innovation. Many contemporary architects seek to recognize their forms and facilitate dealing with according to specific dimensional rules. The main research problem is the lack of knowledge, in the field of architecture, in previous literature about the formation processes in achieving FFG in contemporary architecture as a response to the new requirements that make architecture more flexible in the final expression and breaking away from regularity. Thus, this paper aims to establish a theoretical framework to determine dimensional rules as formation techniques and utilize them as tools in designing processes, to finally benefit to attain several free-form geometries in architecture now and in the future. The research results confirm the importance of dimensional rules in the designing processes as an effective contribution to achieving FFGs in contemporary architecture.

Free-form broadband flat lenses for visible imaging

The resolution of a conventional lens is governed by its numerical aperture (NA) while its light-concentration ability is governed by its f-number (f/#), both of which are dependent on the diameter and focal length of the lens. Hence, these properties for a conventional lens are inherently coupled. Here, we show that by utilizing the principle of free-form broadband diffractive optical elements (BDOEs), we can create ultra-flat optical elements that are able to concentrate incoming light over a fixed aperture to different sized focal spots engineered in the shape of a square. Hence, we are able to decouple the NA and f/# of a lens by being able to independently control the size of the input aperture and the resolution of these devices. Specifically, we designed, fabricated, and characterized three BDOE lenses operating in the visible band (450nm–750nm), each having f/# of 11.25, but with NAs of 0.00075, 0.0067, and 0.054, respectively. We further use simulations to emphasize that such decoupling is possible even at much higher NAs. Experiments confirm achromatic focusing and broadband imaging. One of the lenses exhibited a depth-of-focus almost 2 orders of magnitude larger than the diffraction limit. Such BDOE lenses can eliminate the need for anti-aliasing filters and could also be very useful in focal-plane arrays with large pixel sizes, where light collection efficiency needs to be maintained. Furthermore, by abandoning rotational symmetry, one can achieve free-form geometries in the focal spot, such as a square that can more closely match the geometry of the sensor pixel.

New mechanistic model to predict machining time for milling free form geometries using 4-axis milling

Predicting the required time to machine a component is very important for planning the production of a factory. However, in milling of free form parts, commercial CAM software are not able to estimate the time precisely. This is because the CAM does not consider individual machine limitations. This work presents a mechanistic method developed to estimate more accurate the time to mill a free form geometry using any 4-axis milling machine. The maximum error observed on experimental validation of the method was less than 6%, 200 times more accurate than commercial CAM.

Process behavior charts used to check the consistency of CT instruments

Digital manufacturing is one of the enabling methodologies associated with the concept of flexible mass customization, which has been boosted by the recent advances in Additive Manufacturing (AM) technologies, from which complex freeform geometries, internal and reentrant features can be reproduced based on the CAD model. From the standpoint of coordinate metrology, AM calls for a measurement technology capable of acquiring high data density of these complex structures. Computed Tomography (CT) is the technology of choice to holistically measure them and respond to the needs of mass customization. However, due to the complexity of the CT measurement chain, the numerous influence factors, and their difficult quantification, the measurement uncertainty evaluation remains an issue yet to be resolved. In this regard, one topic that has received attention is the determination of the geometric errors of the CT instrument, which cause errors to dimensional measurements. Using an imaging method to quantify the geometric errors, process behavior charts are detailed and used to check the consistency of the CT measurement process with regard to the geometric errors. The utilization of process behavior charts is the major contribution of this work since they allow us to operate the measurement process up to its full potential, and to evaluate the actual effectiveness of the imaging method to quantify the errors.

Oral Soluble Films: Attributes of the Polymeric Material and Critical Process Parameters for Designing Good Quality Films

Background::Soluble films prepared using polymeric matrices have gained prominence in drug delivery because of its multifarious merits. They are emerging as a momentous technology for designing precision medicines using printing technology, wherein the drugs, proteins/peptides and hormones in printing ink solution can be printed on placebo films targeted for specific age group dosage administration. Advances made in 3D printing technology in biomanufacturing for sophisticated tailor-made scaffolds of bone and tissue have further given impetus to digitally-controlled depositing of materials to create freeform geometries in the field of dosage form development.Objective:The patent expiry of a significant number of existing chemical entities is an encouraging factor for the possible market potential of these films as a novel drug delivery system through the oral route, topical route and ocular route. Most prominent amongst them is the oral route simply because of its substantial advantages over other pre-existing oral dosage forms.Method:Oral soluble films can be tailored for both local action in the buccal cavity as well as for systemic action to other parts of the body by direct absorption into the systemic circulation through the buccal mucosa. Depending upon the material attributes of its polymeric components, they can be targeted for buccal, sublingual, ocular or topical administration and can also be loaded inside hard gelatin capsule shells for administration into the gastrointestinal tract. Polymeric oral film technology has been exploited to address gaps in varied therapeutic segments including pain and inflammation management to provide instant relief, anti-emesis following chemotherapy, central nervous system disorders due to ease of administration to the caregivers and patient compliance, cardiovascular diseases due to faster onset of action, cancer therapy with enhanced safety and efficacy due to direct systemic absorption bypassing the first pass metabolism effect.Conclusion:This review summarizes the research works done to address gaps in varied therapeutic areas with an emphasis on critical material attributes of its polymeric components and the critical process parameters to be considered for manufacturing robust good quality medicinal films.

A 3D concrete printing prefabrication platform for bespoke columns

Recent developments in computational design and digital fabrication with concrete enable the realization of freeform geometries that optimize material use. 3D Concrete extrusion Printing (3DCP) is presently one of the most utilized digital fabrication methods with concrete. The expected advantages of 3DCP result from shaping concrete without formwork and from placing material only where functionally required. Although these advantages were pointed out more than 20 years ago, it is difficult to find competitive examples and their usage in real buildings. Consequently, the nonspecific character of the process acts as a shortcoming by opening up extensive possibilities without a clear direction. This paper proposes an automated 3DCP prefabrication platform for customized columns. The process-specific parameters are, therefore, fine-tuned for high-quality products with diverse forms and textures. Additionally, this paper proposes an evaluation method for geometric complexity and identifies the types of column typologies that may benefit from a 3DCP prefabrication platform.

Design of freeform geometries in a MEMS accelerometer with a mechanical motion preamplifier based on a genetic algorithm

This paper describes a novel, semiautomated design methodology based on a genetic algorithm (GA) using freeform geometries for microelectromechanical systems (MEMS) devices. The proposed method can design MEMS devices comprising freeform geometries and optimize such MEMS devices to provide high sensitivity, large bandwidth, and large fabrication tolerances. The proposed method does not require much computation time or memory. The use of freeform geometries allows more degrees of freedom in the design process, improving the diversity and performance of MEMS devices. A MEMS accelerometer comprising a mechanical motion amplifier is presented to demonstrate the effectiveness of the design approach. Experimental results show an improvement in the product of sensitivity and bandwidth by 100% and a sensitivity improvement by 141% compared to the case of a device designed with conventional orthogonal shapes. Furthermore, excellent immunities to fabrication tolerance and parameter mismatch are achieved.

3D Printing Low-Stiffness Silicone Within a Curable Support Matrix.

Embedded 3D printing processes involve extruding ink within a support matrix that supports the ink throughout printing and curing. In once class of embedded 3D printing, which we refer to as "removable embedded 3D printing," curable inks are printed, cured, then removed from the uncured support matrix. Removable embedded 3D printing is advantageous because low-viscosity inks can be patterned in freeform geometries which may not be feasible to create via casting and other printing processes. When printing solid-infill geometries, however, uncured support matrix becomes trapped within the prints, which may be undesirable. This study builds on previous work by formulating a support matrix for removable embedded 3D printing that cures when mixed with the printed silicone ink to solve the problem of trapped, uncured support matrix within solid-infill prints. Printed specimens are shown to have a nearly isotropic elastic modulus in directions perpendicular and parallel to the printed layers, and a decreased modulus and increased elongation at break compared to specimens cast from the ink. The rheological properties of the support matrix are reported. The capabilities of the printer and support matrix are demonstrated by printing a variety of geometries from four UV and addition-cure silicone inks. Shapes printed with these inks range by nearly two orders of magnitude in stiffness and have failure strains between approximately 50 and 250%, suggesting a wide range of potential applications for this printing process.

Measurement of complex freeform additively manufactured parts by structured light and photogrammetry

Abstract Additively manufactured parts are fabricated by generating complex shapes, allowing almost infinite freedom of design. Such parts present significant measurement challenges related to the accessibility and the quality of the measurement results, due to the presence of hollow features, and freeform geometries. Optical measuring instruments are being increasingly applied for complex form measurement, because, compared to contact measurements, they feature higher speeds, higher point densities and often better capabilities to access recessed regions. In this paper, a novel set of indicators is presented that can be used to investigate the performance of measurement solutions based on high-density point-based sampling when applied to form measurement of complex parts. The indicators address surface coverage, sampling density and measurement error as a function of local geometric properties. The indicators are applied to an example comparative analysis involving structured light scanning and photogrammetry measurements of a complex freeform additively manufactured automotive part.

A Calculation Method for Interconnected Timber Elements Using Wood-Wood Connections

Wood-wood connections, widely used in the past, have been progressively replaced by steel fasteners in timber constructions. Currently, they can be manufactured and implemented more efficiently thanks to digital fabrication techniques. In addition, with the emergence of new timber plate engineered products, digitally produced wood-wood connections have been developed with a strong focus on complex free-form geometries. The gained knowledge through research and building implementations have pushed the development of more standardized structural elements. As a result, this work presents a new concept of building components using through tenon connections based on the idea of transportable flat-packs directly delivered and assembled on site. The main objective of this research is to develop a convenient calculation model for practice that can capture the semi-rigid behavior of the connections and predict the effective bending stiffness of such structural elements. A case study is used as a reference with three large-scale slabs of a 8.1 m span. Bending and vibration tests are performed to study the mechanical behavior and assess the proposed calculation method. The results show the high influence of the semi-rigid behavior of connections on the bending properties and, therefore, on the serviceability limit state. The model is in good agreement with the test results, and further improvements can be made regarding the local behavior of the connection. This study demonstrates the feasibility of the proposed construction system and the applicability of the developed calculation model to design practice.

X-ray CT and image analysis methodology for local roughness characterization in cooling channels made by metal additive manufacturing

The increasingly complex shapes and geometries being produced using additive manufacturing necessitate new characterization techniques that can address the corresponding challenges. Standard techniques for roughness and texture measurements are inept at characterizing the internal surfaces in freeform geometries. Hence, this work presents a new methodology for extracting and quantitatively characterizing the roughness on internal surfaces. The methodology links X-ray CT with complete roughness characterization of channels manufactured by laser powder bed fusion through a novel image analysis approach of X-ray CT data. Global and local orientation parameters are defined to enable a full 360° description of the roughness inside additively manufactured channels. X-ray CT data is analyzed to generate 3D deviation data – based on which multiple local roughness profiles are extracted and analyzed in accordance with the ISO 4287:1997 standard. To demonstrate the proposed methodology, seven circular 17-4 PH stainless steel channels produced at different inclinations and with a diameter of 2 mm are investigated as a case study. Qualitative and quantitative characterization of the roughness is obtained through the use of the proposed methodology. A strong dependence of the local roughness on the corresponding α and β orientations is found. A simple regression model is subsequently extracted from the calculated roughness values and allows prediction of Ra-values in the channels for the ranges between 0° ≤ α ≤ 90° and 80° ≤ β ≤ 280°. In addition to decreasing the effective hydraulic diameter of a cooling channel, the surface roughness also influences the local Nusselt number, which is quantified using the extracted regression model.

Investigation of the influence of surface waviness of aluminium on the burnishing quality of a combined process

Burnishing is an effective chipless finishing process for improving workpiece properties such as: hardness, vibration resistance and surface quality. Recently, the process has been increasingly applied to prismatic workpieces and free-form geometries. Before burnishing can be carried out, a milling process created the shape of the workpiece, especially for free-form surfaces. The application of different milling tools does not only produce different roughnesses, it also creates waviness which can influence the burnishing process. This publication focuses on the relationship between roughness and waviness of the milling process on the following burnishing of ductile workpiece materials. The presented work also considers the different machining directions and tool movements of this process combination. Within the evaluation the interdependence between milling and burnishing parameters are examined and the remaining frequency components of the two processes on the generated surface are compared.

Electrical properties of 3D printed graphite cellular lattice structures with triply periodic minimal surface architectures

Selective laser sintering (SLS) provides a way to fabricate 3D graphite parts, and allows the fabrication of complex free-form geometry that could not have been achieved using traditional manufacturing techniques. This study investigates the manufacturability and electrical properties of SLS produced graphite cellular lattice structures, which are designed by the mathematically-known triply periodic minimal surfaces (TPMS). TPMS are a class of non-self-intersecting surfaces created by local surface area minimization principle, which can provide advanced or multifunctional performance for a range of applications. Here, the effective electrical conductivity of three well-know TPMS architectures (Gyriod, IWP and Diamond) of different unit cell sizes is investigated experimentally and numerically [using finite element analysis (FEA)]. The results show that the structure made by SLS has a good geometric agreement with the original design models. When the volume fraction is constant, the structure with more unit cells exhibits better electrical properties. Moreover, the structure based on Gyriod shows the best electrical performance and after impregnation and high-temperature carbonization, the electrical conductivity of the sample can reach 317 S cm−1.

Efficient generation strategy for hierarchical porous scaffolds with freeform external geometries

The external geometry design and manipulation of internal porosity distribution according to the actual application demands are the main challenges of scaffold generation; moreover, computational efficiency is a key factor that should be considered. This paper proposes efficient generation strategies for constructing internal porous architectures by using triply periodic minimal surfaces (TPMSs) and external freeform shapes through T-spline surfaces. After discretizing the geometries as slicing contours, TPMSs can be efficiently extracted using the intersection-interpolation method in 2D space, and then be offset as infill areas of sheet solids. Based on the proposed fractal sheet TPMSs, hierarchical scaffolds are further generated using the refined constrained Delaunay triangulation method to construct multiscale pores. The porosity features can be conveniently controlled in 2D space according to the actual computed tomography images. Eventually, the resulting infill areas can be directly fabricated as scaffolds by additive manufacturing technology. Several experimental instances validate the effectiveness and efficiency of the proposed strategies.