Abstract: Accurate evaluation of the cerebral aneurysm rupture risk is currently a challenge. Indeed, an accurate prediction is crucial for optimising clinical surveillance and treatment decisions. This study aims to evaluate rupture risk by analysing hemodynamic and morphological factors that would influence aneurysm growth and rupture. A computational fluid dynamics approach was employed to simulate blood flow dynamics with aneurysm geometry obtained through angiography. The blood was modelled as a non-Newtonian, incompressible, turbulent fluid, using velocity profiles derived from transcranial Doppler ultrasound as the inflow condition. The outcomes of this investigation yield significant insights into the interior of the aneurysm, specifically regarding pressure distributions and wall shear stress. These were evaluated in conjunction with the characteristics of the aneurysm shape.

Keywords: Cerebral aneurysm | CFD | rupture

Abstract: In the field of structural engineering, the optimization process is crucial for ensuring both the efficiency and safety of designed structures. The persistent search for solutions that maximize structural performance while minimizing costs presents a fascinating and complex challenge. In this context, this paper aims to analyze and compare three different Nature-inspired optimization algorithms that are derived from theory of biological evolution, swarm intelligence, and chemical and physical processes. Specifically, the study aims to provide a comprehensive overview of the performance and characteristics of Genetic Algorithms, the Firefly Algorithm, and the Group Search Optimizer Algorithm in the context of structural optimization within the ANSYS APDL environment.

Keywords: ANSYS | finite element method | meta-heuristic algorithms | Structural optimization

Abstract: The increasing interest in foiling sailing yachts, recently driven by the American’s Cup, led to a wider application even in small boats such as dinghies or windsurfing. Foiling seems to be recent but since the early twenty-century years, hydrofoils has been experimented in Italy. This paper shows the complete foil design process starting from classical wing design based on theoretical consideration and illustrating the importance of modern simulation environments in design processes. Commercial CFD code Ansys Fluent® has been used and the results have been compared with those obtained through ad hoc developed vortice lattex method software, showing a substantial agreement with RANS simulation and theoretical calculation in front of incredible time reduction for simulation process that would allow a numerical planform optimization in a reasonable time.

Keywords: CFD | Foiling | Yacht design

Abstract: In the Medical Reverse Engineering (MRE) field, the manipulation of computed tomography (CT) scans from patients is complex, especially regarding the development of 3D anatomical models of patients’ anatomy. This complexity depends on the variability of human anatomy, thus involving several challenges in the fabrication of custom biomedical devices. Low back pain is a worldwide widespread disease, whose cause is still unknown today. Indeed, a comprehensive understanding of spinal biomechanics is the goal that needs to be achieved for the evolution of surgical therapies and the design of useful devices for pathologies. Hence, Finite Element (FE) modelling of the lumbar spine is an important tool, useful for understanding the spinal physiological and pathological conditions. However, the obstacle of complex geometries is of extreme relevance. The aim of this paper is to support the existing literature to provide new models that can be used in FE modelling of the spine. Therefore, a novel model of the lumbar spine L4-5 with simplified intervertebral disc geometry was created and then the following model was validated using experimental data obtained from the literature about the long-term loading.

Keywords: Biomechanics | Intervertebral disc | Lumbar spine | Medical Reverse Engineering

Abstract: The use of osseointegrated implants as a solution for amputation treatment, providing a stable connection between the stump and prosthetic limb, is expanding its application to different anatomical districts. A particular focus is put on upper limb amputations, where socket-suspended systems often lead to high abandonment rates of prostheses and osseointegrated implants can enhance prosthetic-limb use, and improve bone perception and range of motion, leading to a better quality of life. This study aims to evaluate the effect of bone-implant interference and implant length of a straight implant, on the primary stability of a humerus CAD model through finite element analysis. The results suggest that a compromise can be made between interference and length to accommodate varying bone morphology and stump length. Additionally, the study results may suggest re-evaluating the prescribed weight limits for transhumeral implants based on their actual load-bearing capacity.

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Abstract: Total ankle arthroplasty (TAA) is a common surgical intervention for end-stage ankle arthritis. This study investigates the impact of polyethylene insert size on TAA stability. Dynamic finite element modeling incorporating anatomically accurate talus and tibia components, along with varying insert sizes, was utilized. Kinematic data acquired through dynamic radiostereometric analysis have been used as input in the FE model. Results showed that a congruent ankle prosthetic implant (all components of size 2) involves in a greater stability but also in concentrate contact pressures. This aspects could lead to a better proprioception of the patient but also to a faster insert wear over time. This underscores the importance of personalized insert sizing in TAA surgery, guided by patient-specific factors. Advanced imaging and computational tools facilitate precise preoperative planning and intraoperative decision-making. Optimal insert selection is crucial for improving long-term TAA outcomes.

Keywords: Contact pressure | FE model | RSA dynamic | TAA stability | Total ankle arthroplasty

Abstract: As is widely recognized, advancements in new design and rapid prototyping techniques such as CAD modeling and 3D printing are pioneering individualized medicine, facilitating the implementation of new methodologies for creating customized orthoses. The aim of this paper is to develop a new automatic technique for producing personalized orthoses in a straightforward manner, eliminating the necessity for doctors to collaborate directly with technicians. A novel design method for creating customized wrist orthoses has been implemented, notably featuring a generative algorithm for the parametric modeling of the orthosis. To assess the efficacy of the developed algorithm, a case study was conducted involving the design and rapid prototyping of a wrist orthosis using Fused Deposition Modeling (FDM) technology. Subsequently, the developed algorithm was tested by clinicians and patients. The results obtained indicate that the implemented algorithm is user-friendly and could potentially enable non-expert users to design customized orthoses. These results introduce innovative elements of originality within the CAD modeling, offering promising solutions to the challenges associated with the design and production of customized orthoses. Future developments could consist of a better investigation regarding the parameters that influence the accuracy of the scanning and of the printing processes.

Keywords: additive manufacturing | CAD | generative design | reverse engineering | wrist orthosis

Abstract: The present paper is devoted to the proposal of appropriate numerical modelling able to provide a suitable description of the mechanical behavior of a composite geopolymer. Reference is made to a natural sisal-fiber-reinforced geopolymer. The study is based on the results of appropriate experimental investigations for compressive, flexural and splitting loadings, taking into account different weight percentages of fibers to evidence their role in the mechanical behavior. The main objective of the paper is to calibrate the microplane constitutive model, available in ANSYS software version 18.1, where the numerical analyses are performed. Therefore, the present study is structured in two different steps. Firstly, the mechanical behavior of geopolymers reinforced with sisal fibers is experimentally investigated, and subsequently, the gathered test data are interpreted and utilized to calibrate the relevant constitutive model to be used in the numerical stage. The obtained results are compared with experimental data, yielding good correlations. The paper’s results supply the parameters required to obtain an affordable numerical model of the reinforced geopolymer for different percentages of fibers to be adopted for material design with assigned mechanical properties.

Keywords: experimental tests | geopolymer composites | microplane model | numerical simulations | sisal fiber

Abstract: The process of designing a sail can be a challenging task because of the difficulties in predicting the real aerodynamic performance. This is especially true in the case of downwind sails, where the evaluation of the real shapes and aerodynamic forces can be very complex because of turbulent and detached flows and the high-deformable behavior of structures. Of course, numerical methods are very useful and reliable tools to investigate sail performances, and their use, also as a result of the exponential growth of computational resources at a very low cost, is spreading more and more, even in not highly competitive fields. This paper presents a new methodology to support sail designers in evaluating and optimizing downwind sail performance and manufacturing. A new weakly coupled fluid–structure interaction (FSI) procedure has been developed to study downwind sails. The proposed method is parametric and automated and allows for investigating multiple kinds of sails under different sailing conditions. The study of a gennaker of a small sailing yacht is presented as a case study. Based on the numerical results obtained, an analytical formulation for calculating the sail corner loads has been also proposed. The novel proposed methodology could represent a promising approach to allow for the widespread and effective use of numerical methods in the design and manufacturing of yacht sails.

Keywords: Computational fluid dynamics | Finite element method | FSI | Gennaker | Sail design | Sail loads

Abstract: The spreading of high computational resources at very low costs led, over the years, to develop new numerical approaches to simulate the fluid surrounding a sail and to investigate the fluid–structure interaction. Most methods have concentrated on upwind sails, due to the difficulty of implementing downwind sailing configurations that present, usually, the problem of massive flow separation and large displacements of the sail under wind load. For these reasons, the problem of simulating the fluid–structure interaction (FSI) on downwind sails is still subject of intensive investigation. In this paper, a new weak coupled procedure between a RANS solver and a FEM one has been implemented to study the FSI problem in downwind sailing configurations. The proposed approach is based on the progressive increasing of the wind velocity until reaching the design speed. In this way, the structural load is also applied progressively, therefore, overcoming typical convergence difficulties due to the non-linearity of the problem. Simulations have been performed on an all-purpose fractional gennaker. The new proposed method has been also compared with a classic weak FSI approach. Comparable results have been obtained in terms of flying shape of the gennaker and fluid-dynamic loads. The most significant characteristic of the proposed procedure is the easiness to find a solution in a very robust way without convergence problem, and also the capability to reduce the simulation time with regard to the computational cost.

Keywords: Computational fluid dynamics | Finite element method | Fluid–structure interaction | Gennaker | Interactive sail design | Mainsail

Abstract: Aim of this paper is presented a new methodology to study how different geometric parameters affect the performance of a hydraulic actuator. Preliminarily, the real working conditions of a hydraulic machine have been simulated by means of a CFD module. After, to test the reliability of the simulations, the obtained numerical results have been compared with the experimental data of a real prototype. This comparison demonstrates a good level of agreement between numerical and experimental results. Different simulations have been setup by modifying the actuator geometry and evaluating the efficiency of every analysed configuration. The results of this study give useful guidelines for the choice of the best geometry depending on the working conditions of the actuator.

Keywords: CAD model | CFD | Experimental analysis | Hydraulic actuator | Numerical simulation

Abstract: The use of glass fiber reinforced polymer materials (GFRP) has increased in recent years for structural engineering. The intrinsic non isotropic nature of GFRP materials together with many manufacturing characteristics encourages the extensive investigation of the real constitutive behaviour. Among the full-field contactless techniques electronic speckle-pattern interferometry (ESPI) plays an important role as a result of its capability to produce real-time fringe patterns on objects with optically rough surfaces, with a displacement sensitivity close to the light wavelength. The aim of this paper is to experimentally analyze the bending behaviour of GFRP specimens. This goal is achieved first by applying ESPI, handled by a phase-stepping technique, to obtain the experimental four-point flexural response of GFRP prismatic specimens with their longitudinal axis aligned with the pultrusion direction as well as with the orthogonal one. All the analysis are carried out by means of an in-plane set-up configuration and the images obtained are filtered by an appropriate developed iterative filter. The second step is to numerically reproduce the experimental behaviour by suitably setting the constitutive material model in an appropriate finite element code. The results obtained confirm that the GFRP material tested does not behave in an isotropic way and possesses a different Young's modulus in tension and compression.

Keywords: Displacement field | Glass fiber reinforced polymer materials | Pultruded material | Speckle interferometry

Abstract: In the present paper some experimental analyses of Dacron© 360 woven with and without surface treatment are presented to evaluate the effect of this treatment on the constitutive behaviour. This woven, widely adopted in sail manufacturing, is obtained by weaving polyethylene terephthalate (PET) yarn and it shows some peculiar features due to the manufacturing process. The experimental tensile tests, clearly show the orthotropy behaviour of the material. The effect of the treatment results in a stiffer behaviour especially along the warp and bias direction and in an increment of ultimate strength in all directions.

Keywords: Dacron | Mechanical behavior | Surface finish | Woven

Abstract: In this paper, the displacement field induced by the split-sleeve cold expansion of holes was measured using both digital image correlation (DIC) and digital speckle pattern interferometry (DSPI) techniques. Thus, the experimental results, which were evaluated on the inlet surface of a 6082-T6 aluminium plate, were compared with those from theoretical prediction. DIC provided accurate measurements up to the elastic-plastic boundary, whereas the DSPI technique highlighted the changes of displacement in the elastic domain. Prediction of the displacement based on the existing analytical model agreed with the experimental results achieved with both techniques. Possible explanations for the differences are discussed.

Keywords: cold expansion of holes | digital image correlation | digital speckle pattern interferometry | displacement measurement

Abstract: This paper presents the results of an extended method of measurement on a tyre for an off-road vehicle 175/82 R16, inserting Prescale paper at the contact with the ground. The experimental analysis of the pressures is carried out, in a cross-sectional direction, in five zones corresponding to the middle of the single dowels that constitute the tread. The results are analysed by means of suitable software so as to refer easily to the value of the pressure. The obtained results are critically analysed and the results are compared with those obtained by the formulae of Rowland and MacLaurin, and by the nominal pressure at the ground, concluding that the expression of MMP for vehicles on wheels is simply to consider a pointer of the performances, in comparison with other vehicles or wheels, rather than a real prediction of the pressure on the ground. Furthermore, a good agreement is found between the tyre deflection calculated and measured experimentally.

Keywords: Behaviour of the tyre | MMP | NGP | Prescale paper

Abstract: The propagation of an interface crack subjected to mixed mode I/II was investigated for two 2024-T351 aluminum thin layers joined by means of DP760 epoxy adhesive produced by 3M©. On the basis of beam theory, an analytical expression for computing the energy release rate is presented for the mixed-mode end loaded split (MMELS) test. The analytical strain energy release rate was compared by finite element (FE) analysis using the virtual crack closure technique (VCCT). Several fatigue crack growth tests were carried out in a plane bending machine to compare the experimental energy release rates to those of the analytical and FE solutions. Experimental results showed the relationship between the delamination modality and initial crack length rather than the applied load. The crack growth behavior showed stable crack growth followed by rapid propagation at the interface with the adhesive layer.

Keywords: Adhesive joint | Crack growth | Interface crack | MMELS specimen | Virtual crack closure technique

Abstract: This paper describes an approach to the keel design of a sailing yacht. The related software, which is fully automatic, leads to the optimal shape by modifying the surface used to define the keel planform. B-spline curves and surfaces have been used due to their ability in following complex shapes. The algorithm integrates ad hoc implemented original software with computational fluid dynamics (CFD) commercial ones. The optimisation procedure uses genetic algorithms (GAs) and a gradient-based optimiser for the refinement of the solution. A careful CAD and CFD modelling leads to a stable and efficient generalised method, which has been applied to the design of the centreboard of the 5o5 international class racing dinghy.

Keywords: CFD | Design optimisation | GAs | Sailing yacht

Abstract: A numerical procedure, which combines two hybrid finite element formulations, was developed to analyse the stress intensity factors in cracked perforated plates with a periodic distribution of holes and square representative volume elements. The accuracy of the method in predicting the stress intensity factor was verified by a comparison with experimental measurements, carried out by a photoelasticity method, and by commercial finite element software. Several simulations were executed by varying both the crack length and the hole diameters, and the effects of the holes on the stress intensity factor are illustrated. The method shows high accuracy and efficiency, as small differences were observed when compared with the traditional finite element method, notwithstanding a strong reduction in degrees of freedom and mesh complexity.

Keywords: Hybrid finite element | Perforated plate | Photoelasticity | Stress intensity factor

Abstract: In the paper the results of a wide range of experiments on friction stir welding (FSW) of aluminium alloys are reported. In particular, the AA6082-T6 butt joints fatigue resistance was investigated by varying the most relevant process parameters. In addition, a revolutionary pitch was utilized in order to investigate the effects of the tool rotating speed and the tool feed rate. Observations of the fracture insurgence were developed for different levels of applied load.

Keywords: Aluminium alloys | Fatigue resistance | Friction stir welding

Abstract: This paper deals with the influence of matrix cracks on the failure mode of bimaterial systems and composite materials. In order to investigate such an influence, the stress field near a crack embedded into the more yielding material and propagating perpendicularly to the interface, has been analyzed by using systematic numerical simulations. Such analysis has shown that the crack propagation give rises to transversal stresses that can damage the reinforcing materials when this has low modulus, as glass fibers, or low transversal strength, such as carbon fibers. Moreover, the longitudinal stress concentration can damage the reinforcing material only if this has high stiffness, as in the case of aramid and carbon fibers. Also, the numerical results have permitted to implement simple formulas that allows the user an accurate evaluation of the SIF as well as to predict possible debonding or fiber splitting phenomena. Finally, the SIFs evaluated numerically have been corroborated by experimental tests carried out by using an efficient procedure based on RGB digital photoelasticity.

Keywords: Bimaterial systems | Boundary element method | Fracture mechanics | Photoelasticity | Stress intensity factor