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With growing concern about global warming, alternatives to fossil fuels in internal combustion engines are searched. In this context, hydrogen is one of the most interesting fuels as it shows excellent combustion properties such as laminar flame speed and energy density. In this work a CFD methodology for 3D-CFD in-cylinder simulations of engine combustion is proposed and its predictive capabilities are validated against test-bench data from a direct injection spark-ignition (DISI) prototype. The original engine is a naturally aspirated, single cylinder compression ignition (Diesel fueled) unit. It is modified substituting the Diesel injector with a spark plug, adding two direct gas injectors, and lowering the compression ratio to run with hydrogen fuel. A 3D-CFD model is built, embedding in-house developed ignition and heat transfer models besides G-equation one for combustion. Three different lean-burn conditions are selected among the tested ones for the validation of the numerical framework. The investigated conditions are characterized by the same revving speed (3000 rpm) but different equivalence ratios (0.4, 0.6 and 0.8, respectively). A good agreement with the experimental dataset is observed, confirming the validity of the proposed CFD approach, and opening the possibility of further virtual optimizations of the engine.

In the field of bone tissue engineering, particular interest is devoted to the development of 3D cultures to study bone cell proliferation under conditions similar to in vivo ones, e.g. by artificially producing mechanical stresses promoting a biological response (mechanotransduction). Of particular relevance in this context are the effects generated by the flow shear stress, which governs the nutrients delivery rate to the growing cells and which can be controlled in perfusion reactors. However, the introduction of 3D scaffolds complicates the direct measurement of the generated shear stress on the adhered cells inside the matrix, thus jeopardizing the potential of using multi-dimensional matrices. In this study, an anisotropic hydroxyapatite-based set of scaffolds is considered as a 3D biomimetic support for bone cells deposition and growth. Measurements of sample-specific flow resistance are carried out using a perfusion system, accompanied by a visual characterization of the material structure. From the obtained results, a subset of three samples is reproduced using 3D-Computational Fluid Dynamics (CFD) techniques and the models are validated by virtually replicating the flow resistance measurement. Once a good agreement is found, the analysis of flow-induced shear stress on the inner B-HA structure is carried out based on simulation results. Finally, a statistical analysis leads to a simplified expression to correlate the flow resistance with the entity and extensions of wall shear stress inside the scaffold. The study applies CFD to overcome the limitations of experiments, allowing for an advancement in multi-dimensional cell cultures by elucidating the flow conditions in 3D reactors.

Fuel cells are considered a key technology to decarbonize the power generation sector, thanks to the absence of pollutants emissions related to the direct chemical-electric energy conversion, their high global efficiency, and the possibility for on-board electricity production, overcoming the storage limits of batteries. An example of the renewed interest towards fuel cells is the research in Proton Exchange Membrane Fuel Cell (PEMFC) in the automotive sector, as a candidate alternative to fossil fuels-fed internal combustion engines (ICEs). The complex interplay of electrochemical and physical phenomena concurring in PEMFC makes their understanding and optimization a challenging task. This is a field of active research thanks to the development of advanced CAE tools, e.g., 3D-CFD simulations of non-isothermal reactive flows, in which all the relevant physics is numerically solved, allowing to identify governing mechanisms as well as system bottlenecks. Among the multiple complex aspects, the material property characterization of PEMFC components is one of the major modelling challenges for modern CAE tools. This is usually provided as a set of boundary conditions for the numerical model, having a large impact on the simulated results which is often motivated by an oversimplification of materials characteristics. Examples of commonly overlooked aspects are direction-independent thermal/flow properties for fibrous materials, the neglection on the deformed (compressed) status, and the simplified contact approach. All of these might alter the key parameters (e.g., water management) and mislead designers’ conclusions on PEMFC optimization. In this paper three-dimensional CFD simulations are used to weight the impact of orthotropic diffusion layer properties on both flow distribution and heat transfer. In the first part, a simplified test case from literature is created and used to investigate the flow convection/diffusion balance in the gas diffusion layer considering the orthotropic permeability typical of pressed fibrous layers. Differences with respect to the still widely used isotropic permeability will be assessed, and implications on channel bypass and mass transport to the catalyst layer will be provided. In the second part, the analysis moves to the use of orthotropic thermal conductivity for the fibrous gas diffusion layers, which is another commonly discarded aspect despite being well documented in literature. A critical analysis of heat transfer routes between parts of different heat capacity (membrane, diffusion layers, solid plates) and thermal field for all the components will be assessed. Finally, thermal contact resistance between adjacent pressed materials will be applied. The altered thermal pathways for heat removal will be critically analyzed, as well as the differences in temperature distribution and their implication on electricity production and water management. This hierarchical flow/thermal analysis will provide guidelines for more accurate 3D-CFD models for a deeper understanding of flow and heat dynamics in PEMFC.

In the present paper, a comprehensive, wall-adapted zonal URANS/LES methodology is shown for the multidimensional simulation of modern direct-injection engines. This work is the latest update of a zonal hybrid turbulence modeling approach, specifically developed by the authors for a flexible description of in-cylinder turbulent flow features with an optimal balance between computational costs and accuracy. Compared to the previous developments, a specific near-wall treatment is added, in order to preserve full-URANS behavior in the first near-wall cells, having in mind typically available mesh resolution in this part of the fluid domain. The updated methodology is applied to the multi-cycle simulation of a reference single-cylinder optical engine, which features a twin-cam, overhead-valve pent-roof cylinder head, and is representative of the current generation of spark-ignited direct-injection thermal power units. Results based on phase-specific flow field statistics and synthetic quality indices demonstrate the consistency and effectiveness of the proposed methodology, which is then qualified as a suitable candidate for affordable scale-resolving analyses of cycle to cycle variability (CCV) phenomena in direct-injection engines.

Purpose to evaluate the impact of bi- and 3-dimensional preoperative aortic morphological features and their immediate postoperative variations on the outcome of abdominal aortic aneurysms (AAA) treated by endovascular exclusion with standard devices (EVAR). Materials and Methods Double centre retrospective analysis of prospectively collected registry data of EVAR patients. For all patients, preoperative and 30-day computed tomographic angiography images (CTA) were reviewed. Preoperative maximum AAA diameter >59 mm and volume >159 cm 3 , and any 30-day postoperative increasing at CTA, were considered as potentially influencing the outcome. The outcome measures were: primary technical success; 30-day, 1-year, and mean follow-up reintervention, all-cause and AAA-related mortality rates, and also endoleak-related reinterventions. Results Three hundred and thrity-three patients were enrolled. Mean preoperative and 30-day AAA diameter and volume were 50.4 mm ± 11.8 vs. 49.1 mm ± 12.1, and 112.9 cm3 ± 79.5 vs. 112.1 cm3 ± 80.5, respectively. Primary technical success was achieved in all cases. At 34.9 months follow-up, cumulative reintervention rate was 12.0%, mortality rates 7.2%, without AAA-related deaths. Endoleak-related reintervention rate was 7.5%. At uni- and multi-variate analysis, preoperative AAA diameter >59 mm, and AAA volume >159 cm 3 were significantly associated to reintervention (P = 0.012; P = 0.002), and reintervention and death (P = 0.002; P = 0.001) during follow-up. Additionally, any increase in postoperative AAA diameter or volume was significantly associated with reintervention (P = 0.001, P = 0.001) and reintervention and death (P = 0.006, P = 0.001). Endoleak-related reintervention were also significantly associated with all of the analysed morphological parameters (P = 0.019, P = 0.005, P = 0.005, and P = 0.002, respectively). Conclusions Patients with larger baseline AAA size and volume as well as unfavourable early remodelling of the sac are associated to worse long-term EVAR outcome.

This study investigates the biological effects on a 3D scaffold based on hydroxyapatite cultured with MC3T3 osteoblasts in response to flow-induced shear stress (FSS). The scaffold adopted here (B-HA) derives from the biomorphic transformation of natural wood and its peculiar channel geometry mimics the porous structure of the bone. From the point of view of fluid dynamics, B-HA can be considered a network of micro-channels, intrinsically offering the advantages of a microfluidic system. This work, for the first time, offers a description of the fluid dynamic properties of the B-HA scaffold, which are strongly connected to its morphology. These features are necessary to determine the FSS ranges to be applied during in vitro studies to get physiologically relevant conditions. The selected ranges of FSS promoted the elongation of the attached cells along the flow direction and early osteogenic cell differentiation. These data confirmed the ability of B-HA to promote the differentiation process along osteogenic lineage. Hence, such a bioactive and naturally derived scaffold can be considered as a promising tool for bone regeneration applications.

A zonal hybridization of the RNG [Formula: see text]-[Formula: see text] URANS model is proposed for the simulation of turbulent flows in internal combustion engines. The hybrid formulation is able to act as URANS, DES or LES in different zones of the computational domain, which are explicitly set by the user. The resulting model has been implemented in a commercial computational fluid dynamics code and the LES branch of the modified RNG [Formula: see text]-[Formula: see text] closure has been initially calibrated on a standard homogeneous turbulence box case. Subsequently, the full zonal formulation has been tested on a fixed intake valve geometry, including comparisons with third-party experimental data. The core of the work is represented by a multi-cycle analysis of the TCC-III experimental engine configuration, which has been compared with the experiments and with prior full-LES computational studies. The applicability of the hybrid turbulence model to internal combustion engine flows is demonstrated, and PIV-like flow statistics quantitatively validate the model performance. This study shows a pioneering application of zonal hybrid models in engine-relevant simulation campaigns, emphasizing the relevance of hybrid models for turbulent engine flows.

Gasoline replacement with alternative non-fossil fuels compatible with existing units is widely promoted around the world to reduce the dependency on oil-based products by adopting domestic renewable sources. In this context, the possibility to obtain bio-alcohols from non-edible residues of food and plants is particularly attractive for gasoline replacement in SI (Spark Ignition) engines. Such bio-fuels are characterized by higher laminar flame speed (LFS) and octane rating, resulting in improved thermal efficiency and reduced regulated emissions. Low-carbon alcohols (e.g. ethanol) are disadvantageous as gasoline replacement due to poor energy density and high corrosive action on distribution pipelines, whereas high-carbon ones (e.g. n-butanol) are particularly promising candidates thanks to the physical properties and the energy density closer to those of gasoline. High latent heat of vaporization and low saturation pressure are the most relevant weaknesses of n-butanol related to gasoline replacement in DISI (Direct Injection SI) power units. On equal injection pressure and phasing, the slow evaporation rate of n-butanol leads to poor mixture preparation and larger fuel deposits. In particular, this is emphasized by low charge and wall temperatures during part load operation, reducing combustion efficiency and promoting the formation of pollutant particles. Split injection is a promising strategy to improve charge preparation contemporary reducing fuel deposits and improving mixture homogeneity, mostly for low-evaporating fuels. In the present work different split injection strategies are tested in an optically accessible SI engine fueled with n-butanol and simulated through CFD with the aim of identifying trends and understanding the root causes behind measured behaviors. CFD simulations help in understanding changes in charge stratification using different injection strategies, allowing to explain both combustion behavior and soot formation tendency from the analysis of fuel distribution. Mixture quality in the spark region and the presence of very rich mixture pockets in the combustion chamber are identified as the most critical aspects that should be optimized when changing the injection strategy; this in turn contributes to avoid slow burn rates or excessive soot production during operation with low evaporating fuels such as n-butanol. A strong correlation between diffusive flames and rich mixture pockets is found in terms of both location and intensity, proving the first order role of fuel deposits formation and mixture homogenization on both combustion development and soot formation.

Experimental techniques like particle image velocimetry provide a powerful technical support for the analysis of the spatial and temporal evolution of the flow field in internal combustion engines. Such techniques can be used to investigate both ensemble-averaged flow structures and their cyclic variations. These last are among the major causes of cycle-to-cycle variability of the engine processes (mixture formation, combustion, heat transfer, emission formation), the reduction of which has become a paradigm recently in engine development. Proper orthogonal decomposition has been largely used in conjunction with particle image velocimetry to analyze flow field characteristics. Several methods involving proper orthogonal decomposition have been proposed in the recent years to analyze engine cycle-to-cycle variability. In this work, phase-invariant proper orthogonal decomposition analysis, conditional averaging and triple and quadruple proper orthogonal decomposition methods are first introduced and applied to a large database of particle image velocimetry data from a well-known research engine. Results are discussed with particular emphasis on the capability of the methods to perform both quantitative and qualitative evaluations on cycle-to-cycle variability. Second, a new quadruple proper orthogonal decomposition methodology is proposed and compared to those available in the literature. All the methods are found to be helpful to identify the turbulent structures responsible for cycle-to-cycle variability. They can be equally applied to both experimental and numerical datasets to analyze turbulent fields in detail and to make comparisons.

Background Aim of this study was to evaluate peri-procedural incidence of new diffusion-weighted-magnetic-resonance-imaging (DWMRI) brain lesions in CAS patients treated by carotid mesh stent (CGuard™) or closed-cell stent (Wallstent™). Methods Consecutive patients with asymptomatic carotid stenosis ≥ 70% were submitted to preoperative DW-MRI scan, to exclude the presence of preoperative silent cerebral lesions. Patients were randomized to CGuard or Wallstent. DWMRI was performed immediately after the intervention and at 72-hour postoperatively. Moreover, pre and postoperative Mini-Mental-State-Examination Test (MMSE) and a Montreal-Cognitive-Assessment (MoCA) test were conducted, and S100β and NSE neurobiomarkers were measured at 5-time points (preoperatively, 2, 12, 24, and 48 h postoperatively). Results From January 2015 to October 2016, sixty-one consecutive eligible patients were submitted to preoperative DWMRI scan. Three patients were excluded because of preoperative silent cerebral lesions. In 29 CGuard patients, 1 developed a minor stroke and 8 silent new lesions were observed in the 72 h-DWMRI (31%): 4 lesions were ipsilateral, and 4 lesions were contra or bilateral. In 29 Wallstent patients, 7 clinically-silent new lesions were found in the 72 h-DWMRI (24.1%; p = 0.38). In 4 cases lesions were ipsilateral and in 3 cases contra or bilateral. S100B values doubled at 48 h in 24 patients, and among them 12 presented new DWMRI lesions. 48-h S100B increase was significantly related to 72-h DWMRI lesions (p = 0.012). Conclusions In our experience both stents showed an acceptable rate of subclinical neurological events with no significant differences at 72-hour DWMRI between groups. Bilateral/contralateral lesions suggest that periprocedural neurological damage may have extra-carotid sources.

Turbulent jet ignition is seen as one of the most promising strategies to achieve stable lean-burn operation in modern spark-ignition engines thanks to its ability to promote rapid combustion. A nearly stoichiometric mixture is ignited in a small-volume pre-chamber, following which multiple hot turbulent jets are discharged in the main chamber to initiate combustion. In the present work, a detailed computational investigation on the turbulent combustion regime of premixed rich propane/air mixture in a quiescent divided chamber vessel is carried out, to study the characteristics of the jet flame without the uncertainties in mixing and turbulent conditions typical of real-engine operations. In particular, the paper investigates the dependency of flame propagation on nozzle diameter (4, 6, 8, 12 and 14 mm) and pre-chamber/main-chamber volume ratio (10% and 20%); CFD results are compared to the experimental outcomes. Results show that the combustion regime in the quiescent pre-chamber follows a well-stirred reaction mode, rendering the limitation in using conventional flamelet combustion models. Furthermore, due to the very high turbulence levels generated by the outflowing reacting jets, also the main chamber combustion develops in a well-stirred reactor type, confirming the need for a kinetics-based approach to combustion modelling. However, the picture is complicated by thickened flamelet conditions possibly being verified for some geometrical variations (nozzle diameter and pre-chamber volume). The results show a general good alignment with the experimental data in terms of both jet phasing and combustion duration, offering a renewed guideline for combustion simulations under quiescent and low Damköhler number conditions.

In recent years, internal combustion engine (ICE) downsizing coupled with turbocharging was considered the most effective path to improve engine efficiency at low load, without penalizing rated power/torque performance at full load. On the other side, issues related to knocking combustion and excessive exhaust gas temperatures obliged adopting countermeasures that highly affect the efficiency, such as fuel enrichment and delayed combustion. Powertrain electrification allows operating the ICE mostly at medium/high loads, shifting design needs and constraints towards targeting high efficiency under those operating conditions. Conversely, engine efficiency at low loads becomes a less important issue. In this track, the aim of this work is the investigation of the potential of the oversizing of a small Variable Valve ActuationSpark Ignition gasoline engine towards efficiency increase and tailpipe emission reduction. To enhance the potential improvements of such an approach, a lean combustion concept is adopted, where the flame speed propagation is supported by doping gasoline with the addition of a percentage of hydrogen (10% by mass). The analysis is carried out by a 1D simulation tool, widely validated for the base engine supplied with pure gasoline and under stoichiometric/rich combustion. The combustion and knock models are here extended to handle the flame speed and auto-ignition characteristics of gasoline/H2 blends. The comparison between the base gasoline engine and the oversized gasoline/H2 variant highlights significant efficiency advantages at full load operations, which are due to the possibility to remove fuel enrichment and combustion delays. Exceptfor unburned hydrocarbons, pollutants and CO2 emissionsare reducedthanks to the synergic effects of H2addition and ultra-lean mixtures. A certain penalization of efficiency arises at very low loads, where engine oversizingdegrades the combustion process.

Polymeric Exchange Membrane Fuel Cells (PEMFC) are promising power propulsion systems for the decarbonization of the transportation sector. Despite being a well-known method for the direct production of electric current from the reactants chemical energy, one of the major limitations to their large-scale industrial development are fluid dynamics and mass transport aspects, crucially limiting the electrochemistry rate under critical conditions. This is especially verified in PEMFC with serpentine-type gas distributors, for which such areas are identified in proximity of the gas channel bends where the dominant mechanism for species transport shifts from a convection-enhanced to a diffusion-limited one. An engineering method to enhance the convective transport in such deficient areas is the use of gas distributors with tapered channels, effectively forcing the flow in diffusive media and improving the reactants delivery rate and products removal. A numerical analysis is presented on a limited domain representing a section of a serpentine gas distributor. A multi-dimensional CFD study is carried out comparing conventional-type and tapered channel distributors, evaluating the combined effect of pressure losses, catalyst layers utilization, flow regime in anisotropic diffusion media and convection/diffusion balance via a non-dimensional analysis. The study covers various inlet Reynolds numbers and in-plane permeability of porous materials for two diffusion media thicknesses, with the aim to extend the generality of the study. Conclusions based on the simulation results outline channel tapering as a very effective way to improve the power density of PEMFC, although an energetic cost/benefit analysis indicates a reduced cell efficiency.

The large-scale adoption of fuel cells system for sustainable power generation will require the combined use of both multidimensional models and of dedicated testing techniques, in order to evolve the current technology beyond its present status. This requires an unprecedented understanding of concurrent and interacting fluid dynamics, material and electrochemical processes. In this review article, Polymer Electrolyte Membrane Fuel Cells (PEMFC) are analysed. In the first part, the most common approaches for multi-phase/multi-physics modelling are presented in their governing equations, inherent limitations and accurate materials characterisation for diffusion layers, membrane and catalyst layers. This provides a thorough overview of key aspects to be included in multidimensional CFD models. In the second part, advanced diagnostic techniques are surveyed, indicating testing practices to accurately characterise the cell operation. These can be used to validate models, complementing the conventional observation of the current–voltage curve with key operating parameters, thus defining a joint modelling/testing environment. The two sections complement each other in portraying a unified framework of interrelated physical/chemical processes, laying the foundation of a robust and complete understanding of PEMFC. This is needed to advance the current technology and to consciously use the ever-growing availability of computational resources in the next future.

Large-eddy simulation has been increasingly applied to internal combustion engine flows because of their improved potential to capture the spatial and temporal evolution of turbulent flow structures compared with Reynolds-averaged Navier Stokes simulation. Furthermore, large-eddy simulation is universally recognized as capable of simulating highly unsteady and random phenomena, which drive cycle-to-cycle variability and cycle-resolved events such as knocks and misfires. To identify large-scale structure fluctuations, many methods have been proposed in the literature. This article describes the application of several analysis methods for the comparison between different datasets (experimental or numerical) and the identification of large-structure fluctuations. The reference engine is the well-known TCC-III single-cylinder optical unit from the University of Michigan and GM Global R&D center; the analyses were carried out under motored engine conditions. A deep analysis of in-cylinder gas dynamics and flow structure evolution was performed by comparing the experimental results (particle image velocimetry of the velocity fields) with a dataset of consecutive large-eddy simulation cycles on four different cutting planes at engine-relevant crank angle positions. Phase-dependent proper orthogonal decomposition was used to obtain further conclusions regarding the accuracy of the simulation results and to apply conditional averaging methods. A two-point correlation and an analysis of the tumble center are proposed. Finally, conclusions are drawn to be used as guidelines in future large-eddy simulation analyses of internal combustion engines.

A zonal hybrid unsteady Reynolds-averaged Navier–Stokes/large eddy simulation (URANS-LES) Zonal detached-eddy simulation (ZDES) model is applied to internal combustion engine (ICE) simulation and comparisons of predicted flow morphology and variability are carried out against on the transparent combustion chamber (TCC-III) particle image velocimetry (PIV) data set for motored conditions. To this aim, a previously developed model derived from a standard seamless-detached eddy simulation (DES) formulation is adopted for two different grid resolutions. In particular, two zonalization choices are evaluated based on previous single-grid results, in order to assess the model outcomes based on the joint turbulence treatment/grid density: the seamless-DES mode is applied (1) only to the cylinder (TCC-Z1) and (2) to the cylinder and intake port (TCC-Z2). Multi-cycle simulations (50 samples) are carried out and the results are compared to experimental data in terms of PIV images using multiple quality indices on multiple planes ( Y = 0 and X = 0). Finally, comparison of predicted mean flow fields is extended to standard URANS mode. Results show that the use of a cylinder-only seamless-DES treatment on a relatively coarse grid results in a quantitative agreement between simulated and measured (PIV) flow fields, both in terms of average morphology and flow variability, whereas the extension of the DES mode to the intake port does not introduce relevant variations. Quality indicators seem to be moderately sensitive to the grid resolution, thus confirming the adaptive potential of a ZDES–like model and promoting the use of DES–type turbulence modelling even on relatively low-resolution grids. The analysis of average fields compared to URANS simulations highlights the benefit for both grids of a scale-resolving ZDES modelling when the same underlying turbulence model ( k-ε RNG) is used. This study reinforces the recommendation in the use of hybrid URANS-LES models to simulate ICE flows. The adopted ZDES formulation based on the two-equation k-ε RNG model shows that high-quality results can be obtained even on engineering-grade grids, both in terms of average and cycle-to-cycle variation. The numerical results obtained using the two grids with variable resolution are consistent, and this further promotes a wider adoption of this class of models to simulate engine flows in industrial applications.

Computational fluid dynamics has become a fundamental tool for the design and development of internal combustion engines. The meshing strategy plays a central role in the computational efficiency, in the management of the moving components of the engine and in the accuracy of results. The overset mesh approach, usually referred to also as chimera grid or composite grid, was rarely applied to the simulation of internal combustion engines, mainly because of the difficulty in adapting the technique to the specific complexities of internal combustion engine flows. The article demonstrates the feasibility and the effectiveness of the overset mesh technique application to internal combustion engines, thanks to a purposely designed meshing approach. In particular, the technique is used to analyze the cycle-to-cycle variability of internal combustion engine flows using large eddy simulation. Fifty large eddy simulation cycles are performed on the well-known TCC-III engine in motored condition. Results are analyzed in terms of tumble center trajectory and using proper orthogonal decomposition to objectively characterize the spatial and temporal evolution of turbulent flow field in internal combustion engines. In particular, an original decomposition method previously applied by the authors to the TCC-III measured flow fields is here extended to computational fluid dynamics results.

Background The objective of the study was to report immediate and midterm results of an unselected population of patients treated for abdominal aortic aneurysms (AAAs) by endovascular aneurysm repair (EVAR) using the Ovation stent graft. Methods A double-center retrospective study was conducted on a prospectively collected database between 2012 and 2015. One hundred fifty-six elective patients were included. The outcome measures considered for analysis were primary technical success, 30-day and midterm reinterventions, and all-cause and AAA-related mortality rates. The presence of an aortic neck ≤10 mm, and of a noncylindrical aortic neck, as well as a narrowed aortic bifurcation was defined as an aortic bifurcation average diameter (AB average ) ≤ 18 mm or an AB area ≤ 20 mm 2 , and an external iliac artery diameter ≤5 mm was considered as independent factors potentially influencing the outcome. Results Male patients totaled 128 (82.1%), and mean age was 74.83 ± 6.76 years (range: 56–91). Mean aortic diameter was 57.15 ± 8.77 mm, mean diameter at inferior renal artery level + 13 was 24.44 ± 3.31 mm, and mean aortic neck length was 18.77 ± 8.45 mm. Fifty-four patients (34.6%) had an aortic neck ≤10 mm, and cylindrical aortic neck shape was present in 34 patients (21.8%). Regarding the aortic bifurcation (AB), 31 patients (19.9%) presented AB average ≤ 18 mm, and 35 (22.4%) an AB area ≤ 20 mm 2 . Technical success was achieved in all cases. At 30-day follow-up, 2 type I endoleaks (1.3%) were detected. One patient was successfully treated endovascularly by proximal aortic cuff implantation, while the other patient refused further treatment. Three-month unscheduled computed tomographic angiography shows endoleak resolution and complete aneurysm seal. One patient suffered from a limb graft occlusion, managed by medical treatment. At a mean follow-up time of 20.4 ± 8.8 (1–60) months, 6 reinterventions were reported, including 2 embolizations for type II endoleak and 4 for iliac and femoral vessel occlusive disease. Log-rank test on preoperative anatomical features showed no significant differences in terms of freedom from reinterventions, and P values were 0.653 for aortic neck length ≤10 mm, 0.309 for noncylindrical aortic neck length shape, 0.520 for AB average ≤ 18 mm, 0.604 for AB area ≤ 20 mm 2 , and 0.421 for external iliac artery diameter ≤5 mm. Conclusions Our initial experience suggests that in an unselected patient population undergoing AAA repair, EVAR by Ovation stent graft can be performed safely with satisfactory immediate and midterm outcomes.

The aim of the present study was to evaluate the impact of the aortic bifurcation (AB) morphological characteristics, analyzed on computed tomography angiography (CTA), on outcomes of patients with abdominal aortic aneurysms (AAAs), treated by endovascular aneurysm repair (EVAR) in a single-center experience. A retrospective analysis was conducted using a prospectively collected database. Morphological features considered as potentially impacting outcomes were maximum AB diameter (ABmax), minimum diameter (ABmin), mean diameter (ABaverage), AB area (ABarea), and AB calcification (ABcalcification) and thrombosis (ABthrombosis). Outcome measures were perioperative, 30-day, and midterm AAA-related reinterventions and all-cause mortalities. Investigators reviewed 306 preoperative CTA scans. Maximum aortic diameter was 51.4 ± 12.4 mm (range 40–110), and mean ABmax was 24.2 ± 8.8 mm (range 10–60), ABmin 17.0 ± 5.4 mm (range 4–40), ABaverage 20.6 ± 6.5 mm (range 9–47.5), and ABarea 35.2 ± 24.2 mm2 (range 6–176). ABcalcification ≥ 50% was present in 63 patients (20.6%), and ABthrombosis ≥ 50% in 102 patients (33.3%). Technical success was obtained in all cases, without perioperative reintervention or death. At 30-day follow-up, the reintervention rate was 3.3%, and mortality rate was 1.3%. At a mean follow-up period of 35 ± 28.6 (range, 1–72) months, reintervention and mortality rates were 6.5 and 4.9%, respectively. None of the analyzed thresholds were predictive of adverse outcomes. At multivariate analysis, association of a narrowed AB with severe calcification of the distal aorta showed a significant differences in terms of reinterventions (p = 0.009). Our limited experience seems to reveal that a cutoff of ≤ 20 mm for AB diameter, as in current guidelines, is ineffective in predicting outcomes after EVAR.

To disentangle genetic and environmental influences on the development of femoral plaques using a population of adult twins. To evaluate the potential role of shared genetic and environmental factors in the co-occurrence of femoral and carotid plaques. The sample included 566 twins belonging to 164 monozygotic (MZ) and 119 dizygotic (DZ) twin pairs, who underwent peripheral arterial assessment by B-mode ultrasound in different centers. The variance in femoral plaques onset was due to genetic factors and the remaining 50% was explained by common (15%) and unique (35%) environmental factors. Findings on sidedness and number of femoral plaques indicated that also these traits were mainly under genetic control. No effect of common environment was found on plaques composition, and variability of this trait was explained by genetics (64%) and unique environment (36%). Covariation between the liabilities to carotid and femoral plaques was mainly attributed to shared genes (77%), with the remaining 23% explained by individual-specific environmental factors shared by the two districts. Inter-individual differences in plaque onset as well as in their number, sidedness and composition are mainly genetic in origin. The results on the cooccurrence of carotid and femoral plaque underline the genetic role in atherogenesis.

Engine knock is one of the most limiting factors for modern Spark-Ignition (SI) engines to achieve high efficiency targets. The stochastic nature of knock in SI units hinders the predictive capability of RANS knock models, which are based on ensemble averaged quantities.To this aim, a knock model grounded in statistics was recently developed in the RANS formalism. The model is able to infer a presumed log-normal distribution of knocking cycles from a single RANS simulation by means of transport equations for variances and turbulence-derived probability density functions (PDFs) for physical quantities. As a main advantage, the model is able to estimate the earliest knock severity experienced when moving the operating condition into the knocking regime.In this paper, improvements are introduced in the model, which is then applied to simulate the knock signature of a single-cylinder 400cm3 direct-injection SI unit with optical access; the engine is operated with two spark timings, under knock-safe and knocking conditions respectively. The statistical prediction of knock resulting from the presented knock model is compared to the experimental evidence for both investigated conditions.The agreement between the predicted and the measured knock distributions validates the proposed knock model. Finally, limitations and some unprecedented possibilities given by the model are critically discussed, with particular emphasis on the meaning of RANS knock prediction.

The increasing limitations in engine emissions and fuel consumption have led researchers to the need to accurately predict combustion and related events in gasoline engines. In particular, knock is one of the most limiting factors for modern SI units, severely hindering thermal efficiency improvements. Modern CFD simulations are becoming an affordable instrument to support experimental practice from the early design to the detailed calibration stage. To this aim, combustion and knock models in RANS formalism provide good time-to-solution trade-off allowing to simulate mean flame front propagation and flame brush geometry, as well as "ensemble average" knock tendency in end-gases. Still, the level of confidence in the use of CFD tools strongly relies on the possibility to validate models and methodologies against experimental measurements. In the paper, two sets of cycle-resolved flame visualizations are available from a single-cylinder 400 cm3 direct-injection spark-ignition (DISI) unit with optical access. The engine is operated at two spark timings, ranging from knock-safe to light-knock conditions. On this basis, a numerical analysis is carried out to reproduce flame kernel growth and propagation using the well-known ECFM-3Z combustion model for all the operating conditions. CFD results are compared in terms of enflamed volume and flame morphology against cycle averaged experimental data. In addition, average knock is simulated by means of the in-house built UniMORE Knock Model [1] in terms of knock onset location and phasing. The agreement between predicted and measured position of the flame front and knock inception location for the two different operating conditions confirms the validity of the adopted models and proves their predictive capability for engine design and optimization.

This paper provides the analysis of a fast iterative method for finding sparse solutions to underdetermined linear systems. It is based on a fixed-point iteration scheme which combines nonconvex Lipschitzian-type mappings with canonical orthogonal projectors. The former are aimed at uniformly enhancing the sparsity level by shrinkage effects, the latter are used to project back onto the space of feasible solutions. The iterative process is driven by an increasing sequence of a scalar parameter that mainly contributes to approach the sparsest solutions. It is shown that the minima are locally asymptotically stable for a specific smooth 0-norm. Furthermore, it is shown that the points yielded by this iterative strategy are related to the optimal solutions measured in terms of a suitable smooth 1-norm. Numerical simulations on phase transition show that the performances of the proposed technique overcome those yielded by well known methods for sparse recovery.

Hybrid URANS/LES turbulence modeling is rapidly emerging as a valuable complement to standard LES for full-engine multi-cycle simulation. Among the available approaches, zonal hybrids are potentially attractive due to the possibility of clearly identify URANS and LES zones, eventually introducing further zone types with dynamically switching behavior. The present work aims at evaluating the impact of different zonal configurations on the simulated flow statistics using the well-assessed TCC-III experimental engine setup. More specifically, different methods (URANS, LES or seamless DES) are applied inside the cylinder volume, as well as into the intake/exhaust ports and plenums. For each of the five tested configurations, in-cylinder flow features are compared against the reference TCC-III experimental measurements, in terms of velocity field statistics and quality indices. In addition, a detailed analysis using Proper Orthogonal Decomposition (POD) is carried out to quantitatively compare the results from experiments and simulation sets. The study outcomes are used as a starting point for discussing the applicability of zonal hybrid turbulence modeling to realistic engine geometries, critically analyze the model assumptions (e.g. the domain zonal decomposition) and provide guidelines for general application of such method.

In 1885, Osler described the infected peripheral aneurysms, resulting from endocarditis embolism for the first time. Over the years, many authors have reported different classification and pathophysiological mechanisms of infected aortic aneurysms. Those conditions are rare and aneurysms involving visceral arteries even more so.

Pollutant regulations and fuel consumption concerns are the driving guidelines for increased thermal efficiency and specific power in current internal combustion engines. The achievement of such challenging tasks in Spark Ignition units is often limited by the onset of knock, which hinders the possibility to operate the engine with the optimal combustion phasing. The sporadic occurrence of individual knocking events is related to cycle-to-cycle variability of turbulent combustion. This is avoidable by only accepting a safety margin from its earliest onset. On one side, the stochastic nature of knock and turbulence-related combustion variability would indicate Large-Eddy Simulation (LES) as the most appropriate technique for CFD analyses. Nevertheless, Large-Eddy Simulation remains a very time- and CPU-demanding approach, hardly integrated in the industrial timeframe for the design exploration and development of new units. Therefore, Reynolds Averaged Navier Stokes (RANS) models representing the average flow are chosen to limit CPU and development times, though they suffer from the intrinsic inability to account for cycle-dependent phenomena (e.g. knock). This is particularly critical at knock-borderline conditions, where far-from-average knocking events may occur. A previously developed statistical RANS-PDF knock model partly overcomes this limitation using equations for mixture fraction and enthalpy variance, ultimately reconstructing log-normal distributions of knock intensity. This allows RANS simulations to be directly compared to the usual statistical knock analysis at the test-bench. In this paper all the mentioned modelling techniques (LES, RANS and RANS-PDF) are applied to simulate combustion and knock in a currently made turbocharged GDI engine under knock-safe, knock-limited and light-knocking conditions. The study relevance lays in the critical comparison of the results. The full potential of the statistical RANS-PDF model for engine development is highlighted on a coherent basis. The possibility to preserve the RANS formalism while enriching the results with knock statistical description is a relevant advancement in the virtual design of high-efficiency engines.

The scientific literature focusing on the numerical simulation of fuel sprays is rich in atomization and secondary break-up models. However, it is well known that the predictive capability of even the most diffused models is affected by the combination of injection parameters and operating conditions, especially backpressure. In this paper, an alternative atomization strategy is proposed for the 3D-Computational Fluid Dynamics (CFD) simulation of Gasoline Direct Injection (GDI) sprays, aiming at extending simulation predictive capabilities over a wider range of operating conditions. In particular, attention is focused on the effects of back pressure, which has a remarkable impact on both the morphology and the sizing of GDI sprays. 3D-CFD Lagrangian simulations of two different multi-hole injectors are presented. The first injector is a 5-hole GDI prototype unit operated at ambient conditions. The second one is the well-known Spray G, characterized by a higher back pressure (up to 0.6 MPa). Numerical results are compared against experiments in terms of liquid penetration and Phase Doppler Anemometry (PDA) data of droplet sizing/velocity and imaging. CFD results are demonstrated to be highly sensitive to spray vessel pressure, mainly because of the atomization strategy. The proposed alternative approach proves to strongly reduce such dependency. Moreover, in order to further validate the alternative primary break-up strategy adopted for the initialization of the droplets, an internal nozzle flow simulation is carried out on the Spray G injector, able to provide information on the characteristic diameter of the liquid column exiting from the nozzle.

The need for Internal Combustion Engines (ICEs) to face near-future challenges of higher efficiency and reduced emissions is leading to a renewed interest towards lean-combustion. Several operational issues are associated to lean combustion, such as an abrupt increase of combustion cycle-by-cycle variability (CCV), leading to unbearable levels of Indicated Mean Effective Pressure (IMEP) variation and to misfiring cycles. Significant potential in the wide-scale establishment of lean combustion might come from Large Eddy Simulation (LES), which is able to elucidate the relationships between local physical processes (e.g. velocity magnitude, Air to Fuel Ratio (AFR), etc.) and early combustion progress (e.g. 1%) in unprecedented manners. To this aim, an improved ignition model for LES is proposed in the paper. Two premixed propane-air lean strategies are selected from the wide TCC-III database. A lean-stable ( λ = 1.10 , also named lean) and lean-unstable ( λ = 1.43 , also named ultra-lean) conditions are simulated, highlighting the model capability to well reproduce the sudden rise in CCV for increased mixture dilution. Explanations are given for the observed behaviour and a hierarchical quest for CCV dominant factors is presented. Finally, the different role of local flow field is highlighted for the two cases, and the comparison of optical acquisitions of OH* emission against simulated flame iso-surface up to 1% burn duration reinforce the simulation fidelity. The study shows the investigation possibilities of innovative combustion strategies given by advanced LES simulations. The understanding of turbulent combustion dynamics and the knowledge of the related lean-burn instabilities are key enabler for the exploration of new efficient lean-burn operations.

We compared intima–media thickness (IMT) and the prevalence of plaques in the common carotid artery (CCA) and common femoral artery (CFA) in apparently healthy participants. This multicenter study included 322 participants (59.9% female; age 20-78 years, mean 52.1 ± 15.3 years) who underwent Echo-color Doppler examination of the CCA and CFA bilaterally. Prevalence and composition of plaque were recorded. A significant ( P < .01) difference between mean CCA-IMT and mean CFA-IMT was detected (0.70 vs 0.73 mm). Plaque prevalence was significantly higher in the CFA compared to the CCA (40.7% vs 30.4%). Atherosclerotic plaques were found in both CFA and CCA in 46% of the cases, solely in CFA in 38%, and in CCA alone in 17%. The observed difference in plaque prevalence was even greater when only fibrolipid isolated plaques were considered (CFA 39.4% vs CCA 22.1%). In a healthy general population, atherosclerotic plaques were present in the CFA but not in the CCA in over one-third of the cases. Further studies must confirm whether ultrasonography of the CFA might be introduced in the screening protocols for cardiovascular risk assessment.