Non-uniform Rational Basis Spline Research Articles

Hands-free printed door opener to limit the spread of Coronavirus: Design through topology optimization

Recently, the necessity of reducing the probability of spread of viruses has fostered the creativity of engineers to develop tools that would allow actions of every-day life to be executed differently. Moreover, the maturity of the Fused Filament Fabrication (FFF) technology and the associated low costs has allowed creative solutions to be produced and used in real-life applications. A distinctive example is represented by the common action of opening a door. Since hands are a typical vector of contamination for viruses such as Coronavirus, hands-free devices aim at making use of the existing structure and kinematic to complete the same action in a different fashion. Typically, the mechanical and manufacturing requirements of these devices include a suitable stiffness-to-mass ratio, a reduced printing time as well as the minimization of supports which need to be removed in a post-printing phase. To tackle all these requirements a dedicated topology optimization (TO) method can be used since the preliminary design phase. Several design requirements of different nature can be included in the problem formulation: mechanical ones, like mass and stiffness, and manufacturing ones, like drawing direction or minimum member size. In this paper, a feasibility study on a hands-free 3D printed door opener has been carried out by means of the Solid Isotropic Material with Penalization (SIMP) method for TO and its CAD-compatible variant, i.e., the SIMP approach reformulated in the framework of non-uniform rational basis spline hyper-surfaces. The aim of the study is to identify optimal solutions to be adapted to a real-case scenario wherein different loading cases and manufacturing constraints are evaluated. Different optimal solutions are obtained, reconstructed to be compatible with CAD environment and the optimized geometry numerically assessed. Finally, the optimal solutions are also evaluated with respect to indicators such as printing time, total filament mass and mass of the supports required by the printing process.

Development of scalable lymphatic system in the 4D XCAT phantom: Application to quantitative evaluation of lymphoma PET segmentations.

Digital anthropomorphic phantoms, such as the 4D extended cardiac-torso (XCAT) phantom, are actively used to develop, optimize, and evaluate a variety of imaging applications, allowing for realistic patient modeling and knowledge of ground truth. The XCAT phantom defines the activity and attenuation for a simulated patient, which includes a complete set of organs, muscle, bone, and soft tissue, while also accounting for cardiac and respiratory motion. However, the XCAT phantom does not currently include the lymphatic system, critical for evaluating medical imaging tasks such as sentinel node detection, node density measurement, and radiation dosimetry. In this study, we aimed to develop a scalable lymphatic system in the XCAT phantom, to facilitate improved research of the lymphatic system in medical imaging. Using this scalable lymphatic system, we modeled the lymph node conglomerate pathology that is characteristically observed in primary mediastinal B-cell lymphoma (PMBCL). As an extended application, we evaluated positron emission tomography (PET) image quantification of metabolic tumor volume (MTV) and total lesion glycolysis (TLG) of these simulated lymphomas, though the phantoms may be applied to other imaging modalities and study design paradigms (e.g., image quality, detection). A template model for the lymphatic system was developed based on anatomical data from the Visible Human Project of the National Library of Medicine. The segmented nodes and vessels were fit with non-uniform rational basis spline surfaces, and multichannel large deformation diffeomorphic metric mapping was used to propagate the template to different XCAT anatomies. To model conglomerates observed in PMBCL, lymph nodes were enlarged, converged within the mediastinum, and tracer concentration was increased. We used the phantoms as inputs to a PET simulation tool, which generated images using ordered subsets expectation maximization reconstruction with 2-8mm Gaussian filters. Fixed thresholding (FT) and gradient segmentation were used to determine MTV and TLG. Percent bias (%Bias) and coefficient of variation (COV) were computed as measures of accuracy and precision, respectively, for each MTV and TLG measurement. Using the methodology described above, we introduced a scalable lymphatic system in the XCAT phantom, which allows for the radioactivity and attenuation ground truth to be generated in 116±2.5s using a 2.3GHz processor. Within the Rhinoceros interface, lymph node anatomy and function were modified to create a cohort of 10 phantoms with lymph node conglomerates. Using the lymphoma phantoms to evaluate PET quantification of MTV, mean %Bias values were -9.3%, -41.3%, and 20.9%, while COV values were 4.08%, 7.6%, and 3.4% using 25% FT, 40% FT, and gradient segmentations, respectively. Comparatively for TLG, mean %Bias values were -27.4%, -45.8%, and -16.0%, while COV values were 1.9%, 5.7%, and 1.4%, for the 25% FT, 40% FT, and gradient segmentations, respectively. In this work, we upgraded the XCAT phantom to include a lymphatic system, comprised of a network of 276 scalable lymph nodes and corresponding vessels. As an application, we created a cohort of phantoms with lymph node conglomerates to evaluate lymphoma quantification in PET imaging, which highlights an important application of this work.

NURBS Surface-Altering Optimization for Identifying Critical Slip Surfaces in 3D Slopes

The evaluation of slope stability of a three-dimensional slope requires identifying the critical slip surface with the minimum factor of safety, which is a complex optimization problem. Failure to identify the critical slip surface can lead to unconservative conclusions about the stability of a slope. This paper proposes a novel 3D surface-altering optimization method, which iteratively alters the geometry of a 3D slip surface to find the critical slip surface representing the minimum factor of safety in a slope. The geometry of the slip surface is defined via nonuniform rational basis spline (NURBS) curves formed over a plan grid of control points. The proposed method includes a series of five subroutines that apply various forms of transformations to the control points. These subroutines include minimization problems, which determine the optimal transformation parameters for minimizing the obtained factor of safety of the resulting slip surfaces. Given that any geometrically defined slip surface can be approximated using an equivalent series of NURBS control points, the proposed method can be used in efforts to further reduce the global factor of safety first obtained via conventional search methods, such as those involving spherical or ellipsoidal slip surfaces. To demonstrate its effectiveness, the proposed method was applied to further optimize the critical ellipsoidal slip surfaces reported in some numerical examples. Comparing the results with those limited to ellipsoidal slip surfaces, the proposed method was consistently able to identify slip surfaces with significantly lower factors of safety. The postaltered slip surfaces also matched closely with finite element shear strength reduction results. As such, the proposed method is effective in searching for critical slip surfaces and can be used as a final step in the critical surface searching routine.

Integrated shape and size optimization of curved tetra-chiral and anti-tetra-chiral auxetics using isogeometric analysis

Taking advantage of the powerful design potentials of isogeometric analysis, an integrated shape and size optimization framework for designing tetra chiral and anti-chiral auxetics is proposed to be capable of obtaining excellent designs without complicated implementation efforts. The framework utilizes a non-uniform rational basis spline (NURBS) based parametrization method that describes the chiral and anti-chiral structures with a small number of size and shape parameters. With this effective framework, systematic design studies considering both plane strain and stress conditions are performed to provide bounding graphs for the best achievable auxeticities under different stiffness requirements. Designs with tunable effective properties are also provided to demonstrate the capabilities of the proposed framework. The potential for electronic-skin applications is illustrated.

BDDC Deluxe Algorithms for Two-Dimensional H($curl$) Isogeometric Analysis

Isogeometric analysis has been introduced as an alternative to finite elements to simplify the integration of computer-aided design and the discretization of variational problems of continuum mechanics. In contrast to finite elements, the basis functions of isogeometric analysis, B-splines and nonuniform rational basis splines, are typically not nodal which makes the interface between subdomains fat with several layers of knots and which creates new issues in the design and analysis of iterative solvers based on domain decomposition methods. The resulting systems of algebraic equations also tend to be much more ill-conditioned than those derived from finite elements. The deluxe variant of adaptive balancing domain decomposition by constraints algorithms have proven successful, and in this study, it is applied to two-dimensional problems formulated in H($curl$). Numerical results show very good performance even for high degrees of the underlying B-splines, and fast convergence has been found for $p \leq 7$ using no more than $2(p^2+p-1)$ global (primal) variables per subdomain, where $p$ is the degree of the B-splines. All our results are focused on the most difficult case with the maximum degree of continuity of the B-splines.

Data-driven conservation actions of heritage places curated with HBIM

Digital surveying tools provide a highly accurate geometric representation of cultural heritage sites in the form of point cloud data. With the recent advances in interoperability between point cloud data and Building Information Modelling (BIM), digital heritage researchers have introduced the Heritage/Historic Information Modelling (HBIM) notion to the field. As heritage data require safeguarding strategies to ensure their sustainability, the process is closely tied to conservation actions in the architectural conservation field. Focusing on the intersection of the ongoing trends in HBIM research and the global needs for heritage conservation actions, this paper tackles methodological pipelines for the data-driven management of archaeological heritage places. It illustrates how HBIM discourse could be beneficial for easing value-based decision-making in the conservation process. It introduces digital data-driven conservation actions by implementing a novel methodology for ancient building remains in Erythrae archaeological site (Turkey). The research ranges from a) surveying the in-situ remains and surrounding stones of the Heroon remains with digital photogrammetry and terrestrial laser scanning to b) designing a database system for building archaeology. The workflow offers high geometric fidelity and management of non-geometric heritage data by testing out the suitability and feasibility for the study of material culture and the physical assessment of archaeological building remains. This methodology is a fully data-enriched NURBS-based (non-uniform rational basis spline) three-dimensional (3D) model—which is integrated and operational in the BIM environment— for the holistic conservation process. Using a state-of-the-art digital heritage approach can be applied from raw data (initial stages) to decision-making about an archaeological heritage site (final stages). In conclusion, the paper offers a method for data-driven conservation actions, and given its methodological framework, it lends itself particularly well to HBIM-related solutions for building archaeology.

Influence of Three-Dimensional Visual Reconstruction Technology Combined with Virtual Surgical Planning of CTA Images on Precise Resection of Liver Cancer in Hepatobiliary Surgery.

Hepatobiliary malignancies, such as hepatocellular carcinoma (HCC) and biliary tract cancers, namely, gallbladder carcinoma and cholangiocarcinoma, are linked to a high rate of morbidity and mortality, depending on the phase of the disease. The intricate hepatobiliary anatomy and the need for accurate peroperative management, especially in patients with advanced liver disease, make these tumors difficult to treat. Surgical resection is a notable therapy for hepatobiliary cancers. Unnecessary or excessive liver excision influences patient rehabilitation, normal liver function, and postoperative complications. Hepatobiliary operations must therefore include accurate liver removal. The present advancements in imaging technology are aimed at improving the diagnostic efficacy of liver injury even more. Three-dimensional visual reconstruction is becoming more important in the diagnosis as well as treatment of a variety of disorders. In this paper, we proposed a novel three-dimensional visual reconstruction technology using enhanced nonuniform rational basis spline (ENURBS) combined with virtual surgical planning of Computed Tomography Angiography (CTA) images for precise liver cancer resection. The purpose of this project is to rebuild 2D CTA scan images of liver cancer into a 3D reconstructed model for efficient visualization and diagnosis of liver cancer and to prepare an effective preoperative surgical plan for precise liver excision based on a 3D recreated liver model. This method's performance is compared to that of 2D planning in terms of accuracy and time taken to complete the plan. It is concluded that our proposed technique outperforms the planning technique based on 2D images.

Static analysis of anisotropic doubly-curved shells with arbitrary geometry and variable thickness resting on a Winkler-Pasternak support and subjected to general loads

Laminated doubly-curved shells constituted by innovative materials have become a standard application in several engineering fields. However, this requires a proper formulation of such structures, since several very complex issues affecting such applications must be kept in mind, among all, the curvature effect and the coupling issues between two adjacent layers. In the present work a generalized formulation based on Higher Order Theories is proposed for the linear static analysis of curved structures with completely anisotropic materials in each layer of the lamination scheme. The shell model is described according to the Equivalent Single Layer approach and a mapping procedure based on a Non-Uniform Rational Basis Spline (NURBS) description of the shell edges is applied for the geometric description. Different thickness variations have been considered in the analyses. The fundamental equations of the static problem are derived from the minimum potential energy principle directly in the strong form and the effect of the Winkler-Pasternak support has been accounted for. The external surface load has been applied in each principal direction and arbitrary actions have been enforced to the external edges of the structure. The proposed approach has been validated with respect to the outcomes of some 3D Finite Element models and very good agreement is found between such simulations. Shells characterized by very complex shapes have been accounted for and accurate results have been found with a reduced number of degrees of freedom.

An investigation on adaptive sculpting for the thin-walled surface parts using on-machine measurement

PurposeComplex and exquisite patterns are sculpted on the surface to beautify the parts. Due to the thin-walled nature, the blank of the part is often deformed by the forming and clamping processes, disabling the nominal numerical control (NC) sculpting programs. To address this problem, a fast adaptive sculpting method of the complex surface is proposed.Design/methodology/approachThe geometry of the blank surface is measured using on-machine measurement (OMM). The real blank surface is reconstructed using the non-uniform rational basis spline (NURBS) method. The angle-based flattening (ABF) algorithm is used to flatten the reconstructed blank surface. The dense points are extracted from the pattern on the image using the OpenCV library. Then, the dense points are quickly located on the complex surfaces to generate the tool paths.FindingsBy flattening the reconstructed surface and creating the mapping between the contour points and the planar mesh triangular patches, the tool paths can be regenerated to keep the contour of the pattern on the deformed thin-walled surface.Originality/valueThe proposed method can adjust the tool paths according to the deformation of the thin-walled part. The consistency of sculpting patterns is improved.

On the structural stiffness maximisation of anisotropic continua under inhomogeneous Neumann–Dirichlet boundary conditions

This work discusses three aspects of topology optimisation (TO) problems dealing with structural stiffness maximisation of anisotropic continua under mixed inhomogeneous Neumann–Dirichlet boundary conditions (BCs). Firstly, the total potential energy (TPE) is introduced as intuitive measure of the structural stiffness, instead of the work of applied forces and displacements (WAFD). Secondly, it is proven that the WAFD under mixed BCs is not a self-adjoint functional, while the one related to the TPE is always a self-adjoint functional, regardless of the BCs nature. Thirdly, the influence of the anisotropy, of the applied BCs and of the design requirement on the volume fraction on the optimised topology is investigated: depending on these features, the optimal solutions of the two problem formulations, i.e., minimisation of the functional involving the TPE or minimisation of the WAFD subject to a constraint on the volume fraction, can coincide. The problem is formulated in the context of a special density-based TO approach wherein a Non-Uniform Rational Basis Spline (NURBS) hyper-surface is used to represent the topological descriptor, i.e., the pseudo-density field. The properties of NURBS entities are exploited to derive the gradient of the physical responses involved in the problem formulation and to easily satisfy the minimum length scale requirement (related to manufacturing needs). The differences between TPE-based and WAFD-based formulations and the effectiveness of the proposed method are shown on 2D and 3D problems.

A Geomatics Approach in Scan to FEM Process Applied to Cultural Heritage Structure: The Case Study of the “Colossus of Barletta”

Artistic, architectural and Cultural Heritage (CH) structures are often exposed to a high risk of damage caused by seismic events, natural disasters and more by negligence and poor state of preservation and conservation; the use of a series of technologies, based on digital acquisition and high-level data processing, allows the realisation of a three-dimensional model of high detail. In order to preserve structures of particular historical and architectural value, it is necessary to assess their structural stability. In addition, many structures, such as statues, have rather complex geometries. Therefore, it is necessary to identify a methodology able to transform the point cloud generated through a geomatics approach into a model suitable for FEM (Finite Element Analysis) analysis. This process, known as Scan to FEM, is addressed in this paper. The paper shows the case study of the “Colossus of Barletta”, a bronze statue dating back to the 5th century A.D. located in the city of Barletta, Italy. To analyse this structure, a suitable methodology has been developed which is based on the optimisation of the surface model of the structure; in this way, it is possible to obtain an efficient transformation from a digital photogrammetric model with complex geometry into a model suitable for structural finite element analysis. The digital photogrammetry technique was applied for the survey of the structure, which allowed us to obtain a very high-resolution dense point cloud and a geometrically accurate three-dimensional mesh model, i.e., in a TIN (Triangulated Irregular Network) model. Subsequently, the TIN was transformed into a quad mesh model (identifying a suitable reduction value) and finally into NURBS (Non-Uniform Rational Basis-Splines) to be optimised and imported into a finite element calculation software. This geomatics approach has validated an efficient Scan to FEM process; in fact, thanks to this methodology, it is possible to elaborate three-dimensional models with complex geometry and draw a series of considerations related to structural behaviour or specific restoration interventions.

Sensitivity analysis and design optimization of 3T rotating thermoelastic structures using IGBEM

<abstract> <p>In this study, the isogeometric boundary element method (IGBEM) based on non-uniform rational basis spline (NURBS) is used to perform shape design sensitivity and optimization of rotating three-temperature (3T) thermoelastic structures. During the optimization process, the shape design sensitivity within the IGBEM formulation was derived to include precise geometries and greater continuities. It was found through the application of the IGBEM that the shape design velocity has a significant effect on accuracy of the obtained shape design sensitivity. As a result, the developed shape design sensitivity analysis (SDSA) technique based on the considered IGBEM formulation outperforms the computational solution based on the traditional SDSA method. The isogeometric shape sensitivity and optimal design for a complicated three-temperature thermoelastic problem in rotating structures are investigated. The impact of rotation on the thermal stress sensitivity, optimal three-temperature, optimal displacement and optimal three temperature thermal stress distributions are established. It is shown that the SDSA derived using IGBEM is efficient and applicable for most three-temperature thermoelastic optimization problems.</p> </abstract>

Analysis of a Preliminary Design Approach for Conformal Lattice Structures

An important issue when designing conformal lattice structures is the geometric modeling and prediction of mechanical properties. This paper presents suitable methods for obtaining optimized conformal lattice structures and validating them without the need for high computational power and time, enabling the designer to have quick feedback in the first design phases. A wireframe modeling method based on non-uniform rational basis spline (NURBS) free-form deformation (FFD) that allows conforming a regular lattice structure inside a design space is presented. Next, a previously proposed size optimization method is adopted for optimizing the cross-sections of lattice structures. Finally, two different commercial finite element software are involved for the validation of the results, based on Euler–Bernoulli and Timoshenko beam theories. The findings highlight the adaptability of the NURBS-FFD modeling approach and the reliability of the size optimization method, especially in stretching-dominated cell topologies and load conditions. At the same time, the limitation of the structural beam analysis when dealing with thick beams is noted. Moreover, the behavior of different kinds of lattices was investigated.

Two-scale topology optimisation of cellular materials under mixed boundary conditions

This work proposes a theoretical/numerical framework for the topology optimisation of anisotropic architected cellular materials at different scales. In particular, the topological variable (i.e., the pseudo-density field) is defined at both the scale of the representative volume element (i.e., the unit cell) of the material and at the macroscopic scale of the structure. The two-scale topology optimisation problem is formulated in the most general sense, i.e., by considering non-zero Neumann-Dirichlet boundary conditions. The proposed method is based on: (a) non-uniform rational basis spline hyper-surfaces to represent the topological variable at each scale, (b) the solid isotropic material with penalisation approach, (c) a general numerical homogenisation scheme based on the strain energy to establish the link between scales. The proposed formulation exploits the properties of non-uniform rational basis spline entities to determine the relationships occurring among the topological variables defined at different scales to correctly state the optimisation problem and to satisfy the hypotheses at the basis of the homogenisation method. In particular, scale separation (a necessary condition to be met in order to apply the homogenisation method) and manufacturing requirements are implicitly ensured by introducing minimum length scale constraints on the topological variables defined at both macroscopic scale and unit cell scale, respectively. Furthermore, the sensitivity of the optimised topology (at each scale) to the applied boundary conditions and to the elastic symmetry group of the representative volume element is investigated by founding new and original results. The effectiveness of the approach is tested on 2D and 3D benchmark problems taken from the literature.

Flexible multibody impact simulations based on the isogeometric analysis approach

Usually detailed impact simulations are based on isoparametric finite element models. For the inclusion in multibody dynamics simulation, e.g., in the framework of the floating frame of reference, a previous model reduction is necessary. A precise representation of the geometry is essential for modeling the dynamics of the impact. However, isoparametric finite elements involve the discretization of the geometry. This work tests isogeometric analysis (IGA) models as an alternative approach in the context of impact simulations in flexible multibody systems. Therefore, the adaption of the flexible multibody system procedure to include IGA models is detailed. The use of nonuniform rational basis splines (NURBS) allows the exact representation of the geometry. The degrees of freedom of the flexible body are afterwards reduced to save computation time in the multibody simulation. To capture precise deformations and stresses in the area of contact as well as elastodynamic effects, a large number of global shape functions is required. As test examples, the impact of an elastic sphere on a rigid surface and the impact of a long elastic rod are simulated and compared to reference solutions.

Multi-constraint and multi-objective optimization of free-form reticulated shells using improved optimization algorithm

This paper proposes a novel multi-constraint and multi-objective optimization method to improve the integrated performance of a free-form surface reticulated shell. A geometric model was established using a non-uniform rational basis spline (NURBS) technology and bidirectional parameter line bisecting method. The height of the control points and section size of the rods were taken as optimization variables. The strain energy, economic index, and geometric integrated index were taken as optimization objectives. The sensitivity-NSGA-III hybrid multi-objective optimization algorithm (SH-NSGA-III) is developed. The SH-NSGA-III algorithm has significantly better efficiency than the NSGA-III, MOEA/D, and SPEA2 algorithms. The concept of constrained non-dominant sorting was introduced into the hybrid algorithm to process the constraints in a multi-constraint and multi-objective optimization problem. Meanwhile, an integrated multi-attribute decision-making method was used to select the optimal solution based on the Pareto optimal solution set. The multi-constraint and multi-objective optimization of a free-form surface reticulated shell was performed using the proposed method. The results demonstrated that the Pareto optimal solution set could effectively satisfy the constraints. The strain energy, economic index, and geometric integrated index were reduced by 61.4%, 36.8%, and 19.5%, respectively, and the geometric indexes were reduced by 22%, 11.5%, 20.8%, and 18.4%.

Thermal design of graded architected cellular materials through a CAD-compatible topology optimisation method

Architected cellular materials (ACMs) with a periodic micro-structure are often employed in high-performance components obtained through additive manufacturing (AM) technologies due to their high specific strength and stiffness. ACMs are also used in thermal applications, where their high surface-to-mass ratio can be conveniently exploited to enhance heat transfer. In this work, a numerical approach to predict the effective thermal conductivity (ETC) of ACMs obtained by AM is proposed. The model is based on a general numerical homogenisation scheme and an explicit description of the representative volume element (RVE) of the ACM. Numerical analyses have been conducted on 31 RVEs geometries: results show that the macroscopic ETC of ACMs strongly depends on the relative density and the geometrical features of the RVE. Moreover, starting from the database of RVEs geometries, seven configurations are chosen to design graded ACMs through a computer-aided design-compatible topology optimisation method based on non-uniform rational basis spline hyper-surfaces to represent the pseudo-density field, and on the well-known solid isotropic material with penalisation (SIMP) approach. In particular, the penalisation law used in the SIMP method is replaced by a physically-based penalisation scheme obtained by interpolating the results of the homogenisation for each RVE topology and a suitable post-processing phase is developed to recover the distribution of the graded ACM over the structure from the results of the optimisation process. The effectiveness of the proposed approach is shown on 2D and 3D benchmark problems taken from the literature.

Deep-learning-based isogeometric inverse design for tetra-chiral auxetics

Auxetic materials with the counter-intuitive effect of negative Poisson’s ratio (NPR) have potentials for diverse applications. Typical shape optimization designs of auxetic structures involve complicated sensitivity analysis and a time-consuming iterative process, which is not beneficial for designing functionally-graded structures where the auxetics at different locations need to be inversely designed. To improve the efficiency of the inverse design and simplify the sensitivity analysis, we propose a deep-learning-based inverse shape design approach for tetra-chiral auxetics. First, a non-uniform rational basis spline (NURBS)-based parameterization of tetra-chiral structures is developed to create design samples and computational homogenization based on isogeometric analysis is used in these samples to generate a database consisting of mechanical properties and geometric parameters. Then, the database is utilized to train deep neural networks (DNN) to generate a surrogate model that represents the effective mechanical properties as a function of geometric parameters. Finally, the surrogate model is directly used in the inverse design framework where sensitivity analysis can be calculated analytically. Numerical examples with verifications are presented to demonstrate the efficiency and accuracy of the proposed design methodology.

Establishment of a finite element model based on craniofacial soft tissue thickness measurements and stress analysis of medical goggles

In this study, an accurate finite element (FE) stress analysis of head-mounted products for Chinese users was performed. Using craniofacial computed tomography scans of 280 Chinese individuals, the total soft tissue thickness and thickness of the fat and muscle layers for 41 landmarks were measured. The data were used to construct FE head models (FEH). An FE stress test was conducted to analyse the wearing of medical goggles using two FE models based on one-layer (FEH 1) and three-layer (FEH 3) soft tissue material parameters. When compared with the experimental results, the modelling results for FEH 3 were more realistic than those for FEH 1. Wearing medical goggles led to stress concentration over five landmark areas, A: upper medial forehead, B: temporal, C: zygion, D: infraorbital fossa and E: rhinion, of which B, C and D caused the most discomfort during long-term goggle wear. Practitioner summary: A precise FE head model can reflect the complex contact pressure of a head-related product. Two FE models based on one- and three-layer soft tissue material parameters were established and tested separately with medical goggles. The model can be used to improve the comfort of head-related products. Abbreviations: FE: finite element; FEH: FE head models; FEH 1: FE models based on one-layer; FEH 3: FE models based on three-layer; VR: virtual reality; AR: augmented reality; 3D: three-dimensional; WSU: Wayne State University; WSUBIM: Wayne State University Brain Injury Model; CT: computed tomography; MRI: magnetic resonance imaging; CFSTT: craniofacial soft tissue thickness; FSR: force sensing resistor; NURBS: non-uniform rational basis spline; SPSS: statistical product and service solutions; STL: stereolithography; STP: standard for the exchange of product model data; BDF: glyph bitmap distribution format; EEG: electroencephalogram

Retraced memories - virtual reconstruction of an architectural landmark

<p class="VARAbstract">This paper addresses the challenge of digitally reconstructing ruined architectural sites and retracing their history, in order to virtually recompose their geometrical, stylistic and material integrity. To this end, the research team analyzed the ruins of the church of Santa Maria de Monasterio Albo, located in the ancient village of Misterbianco (Sicily) and destroyed (together with the entire hamlet) by the 1669 eruption of Mount Etna. In the last years, some excavation campaigns brought the church to the light, unveiling the remains of the main portal and six altars, which are one of the most remarkable examples of Mannerist art in eastern Sicily. This research aimed to three-dimensional (3D) reconstruct both the altars and the portal, ideally reviving their original 17<sup>th</sup> century configuration. This goal was achieved through an in-depth archival research (documents dating back to the years between 1300 and 1666 were consulted), an analysis of Classic and Renaissance treatises, and two integrated digital survey campaigns (laser scans and photogrammetry). The outcome is represented by the 3D models of the seven artifacts, which include surviving parts reconstructed as photogrammetric meshes, several fragments were placed in their likely early location through a virtual anastylosis, and NURBS (Non Uniform Rational Basis-Splines) surfaces (recreating the no longer existing elements). The latter were 3D modelled based on the treatises (which provided information on the correct proportioning) or in analogy with other coeval similar artifacts. Overall, the digital reconstruction was based on the ethical principles of transparency of the intervention, recognition of non-original additions and distinction between evidence and hypothesis, according to the London Charter and the Seville Principles. The experimentation provides a valid support for possible interventions in the real world and is the starting point to develop a digital archive of the site, which would make the different accuracy levels the reconstruction explicit.</p><p><strong>Highlights:</strong></p><ul><li><p>3D virtual reconstruction is effective to visualize and bring back to life ruined architectural artefacts.</p></li><li><p>Information about the artefacts original appearance was harvested through digital survey campaigns, archival documents, and comparisons with iconographic sources and coeval buildings.</p></li><li><p>The 3D reconstruction follows ethical principles of transparency and combines photogrammetric meshes (partly relocated through a virtual anastylosis) and NURBS surfaces.</p></li></ul>