A Numerical Method to Fit the Need of a Straightforward Characterization of Viscoelastic Materials for Marine Applications

In the field of green shipping the reduction of acoustic noise partially transmitted into water and the need of guarantee high comfort levels are important aspects in the view to agree with the UN 2030 Agenda in respect to life below water and good health and well-being. Both these aspects imply actions to increase absorption and dissipation of vibrational energy radiated towards the hull. To accomplish this effect, viscoelastic materials (VEM) characterized by high levels of damping are commonly used on board ships. In the last times, new strict requirements led to the development of Isocyanate free VEM, so the necessity of a provisional method to investigate in an efficient way new VEM is required. Experimental tests are essential in order to obtain performance indicators (non-standard procedure) or material physical characteristics (Oberst’s beam test, ASTM E756 – 05). The implementation of the usual experimental setup could result rather complicated and it needs a high degree of accuracy, so in the last times finite element methods (FEM) has been increasingly used. Knowing VEM physics parameters allows numerical simulation in both the provisional and the optimization phase to be accurate and reliable. In this paper, an experimental-numerical method is proposed, with the aim of overtake the issues linked to the small-scale traditional cantilever beam test and paving the way to the selection of the most appropriate shape of the specimen. The innovation proposed through this method lies in the evaluation of the VEM complex modulus based on a reverse engineering approach, in which the loss factor estimation, contrarily from the traditional methods, is free from peak sharpness dependence. The proposed procedure is validated by comparison with the traditional metho

A combined CFD-FEM approach to evaluate acoustic performances of an integrated scrubber-silencer for marine applications

In recent years, green shipping becomes one of the fundamental challenges for the marine industry: the limits imposed on ship emissions by IMO (International Maritime Organization) are increasingly stringent, especially in terms of SOx (sulfur oxides). The installation on board of scrubbers has proved to be a helpful solution to SOx abetment, in particular for the ships already in navigation: it allows to respect the limits imposed by the IMO even with the use of HFOs (Heavy Fuel Oils), so without the need to carry out a complete refitting of the propulsion system. However, such systems, usually installed in the funnels, have large dimensions. The integration between components is the best method to optimize the spaces, facilitating the installation of the scrubbers on board. The present work investigates a combined CFD-FEM (Computational Fluid Dynamics-Finite Element Method) methodology to evaluate the acoustic performances of a model-scale scrubber. Some papers in the literature consider the acoustic properties of SCRs (Selective Catalytic Reduction systems) for marine applications, while a thorough study on scrubbers' performances is missing. Independent CFD or FEM calculations may evaluate the acoustic properties of the scrubber. However, the combined methodology reduces the computational burden by about 90% compared to the CFD modelling. Moreover, it gives the advantage of considering the influence of flow on acoustic properties, which is impossible for a fully FEM approac

Integration and optimization of the after-treatments systems to reduce the acoustic footprint of the ships

Exhaust Gas Cleaning Systems (EGCS) such as scrubbers are mandatory and extensively used to abate SOx in exhaust gases when high sulphur content fuel oil is employed in the marine engine in order to comply with international ship emission regulations, both in new and existing ships. Currently, about 13% of bulker, container, and tanker ships have a scrubber installed, despite the fact that their installation on board is challenging due to their large dimensions to be fitted into the funnel and the complexity of the system, since the exhaust line must control both the chemical and acoustic emissions. In the presented work a combined FEM, CFD simulations and GA optimization methodology aimed at the integration of the abatement system, while optimizing the acoustic properties, is developed. The methodology is first assessed on an industrially-relevant scenario that involves the use of a Genset mock-up equipped with a reference Diesel Oxidation Catalyst (DOC) and a scrubber for the abatement of both NOx and SOx, showing that acoustic performances of the DOC are reliably modelled by the FEM-CFD methodology, which has a significantly reduced computational cost as compared to conventional CFD modelling of acoustic properties. The GA optimization is carried out to improve the DOC acoustic properties showing that it is possible to confer the silencing effect to the after-treatment systems, thus eliminating the traditional silencers from the exhaust line. This leads to a compact exhaust line that integrates the EGCS while maintaining efficient both the chemical pollution abatement capability, and silencing effects to guarantee full compliance (i.e., acoustic and chemical) with the international regulations

Design procedure for the development of new floating floors to improve comfort on ships

The paper presents a procedure developed for designing new floating floors for marine applications. The procedure aims at the improvement of the capability of a new floating floor to isolate structure borne noise. After an introduction to the theoretical background on which this procedure is built, the authors present the results obtained applying the developed procedure to a case study. The procedure includes numerical Finite Element simulations and experimental tests. The simulations aim at the optimization of the resilient material used to decouple the upper floor from the structures. The optimized configurations are then built and tested in laboratory. These tests allow the researchers to identify the floating floor resonances and to evaluate their effect on the Transmission Loss levels. The results of the research activity show the effectiveness of the developed procedure and highlight the importance of the experimental tests to validate the outcomes of the simulations

Numerical study on the influence of porous baffle interface and mesh typology on the silencer flow analysis

The study of the internal component geometries (i.e. perforated elements) is relevant for the acoustic performance optimisation of a silencer. During the design phase, the evaluation of the properties of a silencer is performed by numerical analysis. In the literature, there is a lack of general guidelines and comparisons among different modelling strategies. So, in this study, the influence of grid type (i.e. trimmed vs tetrahedral) on the numerical prediction of the flow inside a reactive silencer is analysed. Moreover, using a porous baffle interface to model the perforated pipe is investigated, searching for a faster and easier way to model perforated elements. The simulations are carried out with the commercial CFD software STAR-CCM+. The comparison of the obtained axial velocity with a literature case study assesses the numerical model reliability. The analysis highlights that velocity and pressure predicted with both the mesh typologies does not significantly differ, but the trimmed mesh allows to save cells number, reducing the computational cost. Instead, obtain a reliable flow description using the porous baffle interface is strictly correlated to the settings of the resistance coefficient. This assumption does not provide accurate results for the analysed perforated pipe. On the other hand, using a simplified model allows to easily perform a comparison between different muffler geometries, as the holes have not to be drowned and meshed after each modification

Green shipping-multifunctional marine scrubbers for emission control : silencing effect

Scrubber systems abate the sulphur oxide emissions of engines when cheap fuel oils that are high in sulphur content are employed as combustibles. However, the ships with these voluminous devices installed on board is space demanding. This work analyses the feasibility of incorporating the acoustic abatement of the exhaust gas noise functionality into the scrubber design to provide a combined scrubber–silencer system. For this purpose, a finite element analysis is performed on a simple expansion chamber, which is assessed using both analytical and experimental data. The transmission loss is the acoustic parameter chosen in this work. The numerical model depicts a good correlation with the transmission loss measured on a model scale scrubber. Finally, scrubber geometry modifications alter the transmission loss, changing and/or enhancing its featuring. These abilities indicate the feasibility to confer to scrubber silencing effects

Highly integrated workflows for exploring cardiovascular conditions: Exemplars of precision medicine in Alzheimer's disease and aortic dissection

For precision medicine to be implemented through the lens of in silico technology, it is imperative that biophysical research workflows offer insight into treatments that are specific to a particular illness and to a particular subject. The boundaries of precision medicine can be extended using multiscale, biophysics-centred workflows that consider the fundamental underpinnings of the constituents of cells and tissues and their dynamic environments. Utilising numerical techniques that can capture the broad spectrum of biological flows within complex, deformable and permeable organs and tissues is of paramount importance when considering the core prerequisites of any state-of-the-art precision medicine pipeline. In this work, a succinct breakdown of two precision medicine pipelines developed within two Virtual Physiological Human (VPH) projects are given. The first workflow is targeted on the trajectory of Alzheimer's Disease, and caters for novel hypothesis testing through a multicompartmental poroelastic model which is integrated with a high throughput imaging workflow and subject-specific blood flow variability model. The second workflow gives rise to the patient specific exploration of Aortic Dissections via a multi-scale and compliant model, harnessing imaging, computational fluid-dynamics (CFD) and dynamic boundary conditions. Results relating to the first workflow include some core outputs of the multiporoelastic modelling framework, and the representation of peri-arterial swelling and peri-venous drainage solution fields. The latter solution fields were statistically analysed for a cohort of thirty-five subjects (stratified with respect to disease status, gender and activity level). The second workflow allowed for a better understanding of complex aortic dissection cases utilising both a rigid-wall model informed by minimal and clinically common datasets as well as a moving-wall model informed by rich datasets

GW250114: Testing Hawking’s area law and the Kerr nature of black holes

The gravitational-wave signal GW250114 was observed by the two LIGO detectors with a network matched-filter signal-to-noise ratio of 80. The signal was emitted by the coalescence of two black holes with near-equal masses m1 ¼ 33.6þ1.2 −0.8M⊙ and m2 ¼ 32.2þ0.8 −1.3M⊙, and small spins χ1;2 ≤ 0.26 (90% credibility) and negligible eccentricity e ≤ 0.03. Postmerger data excluding the peak region are consistent with the dominant quadrupolar ðl ¼ jmj ¼ 2Þ mode of a Kerr black hole and its first overtone. We constrain the modes’ frequencies to 30% of the Kerr spectrum, providing a test of the remnant’s Kerr nature. We also examine Hawking’s area law, also known as the second law of black hole mechanics, which states that the total area of the black hole event horizons cannot decrease with time. A range of analyses that exclude up to five of the strongest merger cycles confirm that the remnant area is larger than the sum of the initial areas to high credibility

GW241011 and GW241110: exploring binary formation and fundamental physics with asymmetric, high-spin black hole coalescences

We report the observation of gravitational waves from two binary black hole coalescences during the fourth observing run of the LIGO–Virgo–KAGRA detector network, GW241011 and GW241110. The sources of these two signals are characterized by rapid and precisely measured primary spins, nonnegligible spin–orbit misalignment, and unequal mass ratios between their constituent black holes. These properties are characteristic of binaries in which the more massive object was itself formed from a previous binary black hole merger and suggest that the sources of GW241011 and GW241110 may have formed in dense stellar environments in which repeated mergers can take place. As the third-loudest gravitational-wave event published to date, with a median network signal-to-noise ratio of 36.0, GW241011 furthermore yields stringent constraints on the Kerr nature of black holes, the multipolar structure of gravitational-wave generation, and the existence of ultralight bosons within the mass range 10−13–10−12 eV

GW231123: a binary black hole merger with total mass 190–265 M⊙

On 2023 November 23, the two LIGO observatories both detected GW231123, a gravitational-wave signal consistent with the merger of two black holes with masses 137+23-18 M⊙ and 101+22-50 M⊙ (90% credible intervals), at a luminosity distance of 0.7–4.1 Gpc, a redshift of 0.40+0.27-0.25, and with a network signal-to-noise ratio of ∼20.7. Both black holes exhibit high spins— 0.90+0.10-0.19 and 0.80+0.20-0.52, respectively. A massive black hole remnant is supported by an independent ringdown analysis. Some properties of GW231123 are subject to large systematic uncertainties, as indicated by differences in the inferred parameters between signal models. The primary black hole lies within or above the theorized mass gap where black holes between 60–130 M⊙ should be rare, due to pair-instability mechanisms, while the secondary spans the gap. The observation of GW231123 therefore suggests the formation of black holes from channels beyond standard stellar collapse and that intermediate-mass black holes of mass ∼200 M⊙ form through gravitational-wave-driven mergers