A generalised unsteady hybrid DES/BEM methodology applied to propeller-rudder flow simulation

A generalised hybrid viscous/inviscid flow model for the hydrodynamic analysis of marine propellers is presented. A Boundary Element Method (BEM) to predict propeller perturbation under inviscid-flow assumptions is combined with a Navier-Stokes solver to describe the viscous, turbulent flow with propeller effects recast as volume-force terms from BEM. In the present study, the viscous flow solution is based on a Detached Eddy Simulation (DES) model valid for unsteady flows. A numerical application is presented by considering a notional propeller-rudder assembly, and results from the hybrid DES/BEM solution are validated by comparisons with full DES. The validation study demonstrates the capability of the proposed hybrid viscous/inviscid flow model to describe transient propeller-induced flow perturbation and of propeller/rudder interaction in spite of the fact that the geometry of propeller blades is not resolved but described via a simple and fast volume force model

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF ASYMMETRICAL BEHAVIOUR OF RUDDER / PROPELLER FOR TWIN SCREW SHIPS

the present work addresses the asymmetrical functioning of rudder/propeller complex of twin screw/twin rudders ships. A series of free running model test results are analysed, with the aid of some simplified numerical calculations. this analysis allows to show the asymmetrical propeller loading during manoeuvres and the considerably different rudder functioning. A possible simplified model to include these effects in manoeuvring simulators is proposed and discussed, allowing to define the needs for future research activities to further improve the understanding of the different phenomena shown

Brain Plasticity in Charcot-Marie-Tooth Type 1A Patients? A Combined Structural and Diffusion MRI Study

Central nervous system involvement has been described in peripheral neuropathies, including different forms of Charcot-Marie-Tooth (CMT) disease. The aim of our study was to systematically investigate possible brain structural modifications in CMT1A patients, using volumetric MRI, and diffusion tensor imaging (DTI). In this prospective cross-sectional study, from May 2017 to May 2019, we acquired 3T MRI brain scans of genetically confirmed CMT1A patients and age- and sex-comparable healthy controls. Patients also underwent clinical and electrophysiological examinations assessing motor and sensory domains. Voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) analyses were performed using a non-parametric approach based on permutations, including age and sex (and total intracranial volume for VBM) as nuisance covariates. When between-group differences emerged at VBM or TBSS analyses, the first eigenvariate was extracted from the cluster and its age- and sex-adjusted standardized residuals tested for correlation with clinical and electrophysiological variables. Twenty CMT1A patients (34.5 ± 11.1 years; M/F:11/9) were enrolled, along with 20 healthy controls (30.1 ± 10.2 years; M/F:11/9). The VBM analysis revealed clusters of significantly increased GM volume in CMT1A patients compared to healthy controls, encompassing the bilateral cerebellar lobules III-VI and the left hippocampus (all ps = 0.04), with no differences in terms of DTI metrics at the TBSS analysis. A negative correlation (r = −0.502, p = 0.03) emerged between ulnar compound motor action potential and the z-scores corresponding to the right cerebellar cluster of augmented GM volume. Our data show evidence of structural reorganization in the brain of CMT1A patients, possibly reflecting neural plasticity mechanisms in response to peripheral nerve pathology and modulating the effect of axonal degeneration on functional impairment

Antibody response elicited by the SARS-CoV-2 vaccine booster in patients with multiple sclerosis: Who gains from it?

Background and purpose: Although two doses of COVID-19 vaccine elicited a protective humoral response in most persons with multiple sclerosis (pwMS), a significant group of them treated with immunosuppressive disease-modifying therapies (DMTs) showed less efficient responses. Methods: This prospective multicenter observational study evaluates differences in immune response after a third vaccine dose in pwMS. Results: Four hundred seventy-three pwMS were analyzed. Compared to untreated patients, there was a 50-fold decrease (95% confidence interval [CI] = 14.3–100.0, p < 0.001) in serum SARS-CoV-2 antibody levels in those on rituximab, a 20-fold decrease (95% CI = 8.3–50.0, p < 0.001) in those on ocrelizumab, and a 2.3-fold decrease (95% CI = 1.2–4.6, p = 0.015) in those on fingolimod. As compared to the antibody levels after the second vaccine dose, patients on the anti-CD20 drugs rituximab and ocrelizumab showed a 2.3-fold lower gain (95% CI = 1.4–3.8, p = 0.001), whereas those on fingolimod showed a 1.7-fold higher gain (95% CI = 1.1–2.7, p = 0.012), compared to patients treated with other DMTs. Conclusions: All pwMS increased their serum SARS-CoV-2 antibody levels after the third vaccine dose. The mean antibody values of patients treated with ocrelizumab/rituximab remained well below the empirical "protective threshold" for risk of infection identified in the CovaXiMS study (>659 binding antibody units/mL), whereas for patients treated with fingolimod this value was significantly closer to the cutoff

Association of Variants in the SPTLC1 Gene With Juvenile Amyotrophic Lateral Sclerosis

Importance: Juvenile amyotrophic lateral sclerosis (ALS) is a rare form of ALS characterized by age of symptom onset less than 25 years and a variable presentation.Objective: To identify the genetic variants associated with juvenile ALS.Design, Setting, and Participants: In this multicenter family-based genetic study, trio whole-exome sequencing was performed to identify the disease-associated gene in a case series of unrelated patients diagnosed with juvenile ALS and severe growth retardation. The patients and their family members were enrolled at academic hospitals and a government research facility between March 1, 2016, and March 13, 2020, and were observed until October 1, 2020. Whole-exome sequencing was also performed in a series of patients with juvenile ALS. A total of 66 patients with juvenile ALS and 6258 adult patients with ALS participated in the study. Patients were selected for the study based on their diagnosis, and all eligible participants were enrolled in the study. None of the participants had a family history of neurological disorders, suggesting de novo variants as the underlying genetic mechanism.Main Outcomes and Measures: De novo variants present only in the index case and not in unaffected family members.Results: Trio whole-exome sequencing was performed in 3 patients diagnosed with juvenile ALS and their parents. An additional 63 patients with juvenile ALS and 6258 adult patients with ALS were subsequently screened for variants in the SPTLC1 gene. De novo variants in SPTLC1 (p.Ala20Ser in 2 patients and p.Ser331Tyr in 1 patient) were identified in 3 unrelated patients diagnosed with juvenile ALS and failure to thrive. A fourth variant (p.Leu39del) was identified in a patient with juvenile ALS where parental DNA was unavailable. Variants in this gene have been previously shown to be associated with autosomal-dominant hereditary sensory autonomic neuropathy, type 1A, by disrupting an essential enzyme complex in the sphingolipid synthesis pathway.Conclusions and Relevance: These data broaden the phenotype associated with SPTLC1 and suggest that patients presenting with juvenile ALS should be screened for variants in this gene.</p

Aspects of twin screw ships semi-empirical maneuvering models

Simplified mathematical models based upon semi-empirical regression formulae describing forces and moments acting on the hull during manoeuvres are commonly used for the preliminary evaluation of ship steering capabilities. Many semi-empirical regressions have been developed, and are broadly adopted, for the manoeuvrability prediction of single screw slow/medium speed ships. Their application for the study of twin screw vessels (cruise ships, RoRo ferries, megayachts, naval vessels, for which dedicated regression formulae are scarce) manoeuvring capabilities could lead to misleading results. These ships are usually characterised by different hull forms and more complex stern configuration due to the presence of appendages like skegs, shaft lines and brackets, which can strongly affect manoeuvrability behaviour. In this work a novel procedure to properly account for the particular geometric and stern appendage characteristics of these kind of vessels is described. A thorough analysis has been performed on a ship model equipped with 13 different stern appendage configurations and new formulae have been developed in order to describe accurately their influence on ship manoeuvring behaviour

Experimental investigation of single blade loads by captive model tests in pure oblique flow. Part II: Propeller in-plane loads and preliminary comparison of single blade loads during transient phases

Off\u2013design and realistic operative conditions of the propulsion system have been progressively considered a frontier topic for the development of novel and successful design procedures. The availability of high accurate data on propeller performance, both experimental or numerical, is pivotal for the development of reliable tools and the enhancement of traditional ones. In this context, this paper continues the investigation described in (Ortolani et al., 2020), that was dedicated to analyze the single blade loads obtained by oblique towing tests and assess their consistency with those measured during the steady turning phase, reproduced by free running model tests. In this paper, the same analysis is broadened to two aspects. At first, the in\u2013plane forces and moments that are obtained by a conversion from the rotating frame of the measure to the fixed frame are discussed. These loads need quantification, because they are the primary cause of damages of the shafting structure, vibratory loads and also contribute to dynamic response of the ship. Then, the study is switched to the comparison of single blade loads during transient motions of the turning maneuvers, at weak and tight rudder angles, performed at the same reference speed as the captive model test. The analysis lays the basis for the enhancement of ship system (comprehensive) mathematical models, already used in ship design, to real\u2013time analysis of vibratory loads and emitted noise

Zig-zag maneuver simulation by CFD for a tanker like vessel

The zig-zag maneuver of a tanker like vessel has been simulated by means of the globally second order accurate finite volume solver χnavis. The aim is to stress the capability of the solver in predicting the yaw checking ability of a ship model characterized by a poor directional stability, an aspect that is usually exploited when performing zig-zag maneuvering. Numerical results have been compared to free running model tests. The effect of rudder rate and propeller modeling have been also investigated. The latter topic is crucial in order to draw the potentialities and further improvements of a simplified and computationally efficient propeller models

Free running prediction of a fully appended submarine: effects of stern plane configurations

In this paper numerical computations dedicated to the analysis of the maneuvering behavior of a fully appended submarine are presented. The work presented here is part of the CNR-INSEAN activities scheduled in the framework of a joint Italian and Norwegian MoDs project, with the partnership of MARINTEK, under the egida of the European Defence Agency. The aim of the project is to exploit the effect of cruciform and X rudder configuration on the turning qualities of the submarine in two operation conditions, namely open water and snorkeling depth. In this paper, the free running turning circle maneuver in open water condition is analyzed; predictions are achieved by an in-house CFD solver