Simulation Techniques for Design and Control of a Waste Heat Recovery System in Marine Natural Gas Propulsion Applications

Waste Heat Recovery (WHR) marine systems represent a valid solution for the ship energy eciency improvement, especially in Liquefied Natural Gas (LNG) propulsion applications. Compared to traditional diesel fuel oil, a better thermal power can be recovered from the exhaust gas produced by a LNG-fueled engine. Therefore, steam surplus production may be used to feed a turbogenerator in order to increase the ship electric energy availability without additional fuel consumption. However, a correct design procedure of the WHR steam plant is fundamental for proper feasibility analysis, and from this point of view, numerical simulation techniques can be a very powerful tool. In this work, the WHR steam plant modeling is presented paying attention to the simulation approach developed for the steam turbine and its governor dynamics. Starting from a nonlinear system representing the whole dynamic behavior, the turbogenerator model is linearized to carry out a proper synthesis analysis of the controller, in order to comply with specific performance requirements of the power grid. For the considered case study, simulation results confirm the validity of the developed approach, aimed to test the correct design of the whole system in proper working dynamic conditions

MARINE CYCLOIDAL PROPULSION MODELLING FOR DP APPLICATIONS

This paper presents the numerical modelling of a cycloidal propeller in freerunning conditions together with its possible applications. The model calibration is carried out by comparing simulation results with experimental data of an existing cycloidal unit. The achieved results support the main strength of the proposed simulation approach: propeller fluid dynamics is not calculated, avoiding demanding computations that would not allow an effective simulation of the whole propulsion plant. As a case study, the cycloidal propulsors model is used for the thruster allocation assessment of the Dynamic Positioning (DP) system of a surface vessel, originally equipped with traditional propellers. Then, the steady-state performance analysis of the DP system is carried out in terms of a comparison between the two distinct propulsion configurations

Motion Control for Autonomous Navigation in Blue and Narrow Waters Using Switched Controllers

Autonomous ships represent one of the new frontiers of technological innovation in marine engineering, which demand the development of innovative control systems to guarantee efficient and safe navigation of vessels. A convenient control system should be able to command the several actuators installed on board in different conditions\u2014for instance, during oceanic navigation, harbor approach, narrow channels, and crowed areas. Such tasks are accomplished by different switching controllers for high and low speed motion, which have to be orchestrated to ensure an effective maneuvering. An approach to the design of hierarchies of controllers for maneuvering and navigation of ships equipped with a standard propulsion configuration in both blue and narrow water is proposed. Different levels of control, from global to local, are defined and integrated to steer the vessel in such a way to increase the maneuvering capability in various scenarios

Rapid prototyping for enhanced dynamic positioning systems

The paper aims to show the design procedure for a Class-2 dynamic positioning system, from initial conceptualisation to factory assessment test. The approach involves the use of simulation-based design combined with hardware in the loop testing. This kind of approach involves a detailed knowledge of the investigated ship but gives significant well-known advantages. The main are: the reduction of the design duration, the optimisation of the system performance, the debug of the control logics before the installation onboard, the reduction of the sea trial costs. Finally, the result of this process is a product ready to be installed onboard. Moreover, over the years, the interest of the classification societies in simulation results for certifying such systems is increased. This study shows both the approach and the results of designing a dynamic positioning system for a Platform Supply Vessel. A custom simulation platform has been developed to have realistic feedbacks of the case-study ship. The DP controller structure, including regulator, force and thrust allocation; have been conceptualised, and then, after the porting procedure, the DP software has been downloaded in the real PCL. Several HIL tests have been carried out to fine-tune the controller parameters. The results show, under different environmental conditions, the respect of the design criteria

Role of nutrition and adherence to the mediterranean diet in the multidisciplinary approach of hidradenitis suppurativa: Evaluation of nutritional status and its association with severity of disease

Hidradenitis suppurativa (HS) is a chronic, inflammatory and debilitating skin disorder. The exacerbating factors of HS include nutrition and adiposity. We aimed to investigate the relationships between body composition and the adherence to the Mediterranean diet (MD) with the severity of HS in a sample of naive-treatment patients with HS. In this case⁻controlled, cross-sectional study, we enrolled 41 HS patients and 41 control subjects. Body composition was evaluated by a bioelectrical impedance analysis (BIA) phase-sensitive system. PREvención con DIeta MEDiterránea (PREDIMED) and the 7-day food records were used to evaluate the degree of adherence to the MD and dietary pattern, respectively. The clinical severity was assessed by using the Sartorius HS score. HS patients had a worse body composition, in particular lower phase angle (PhA) (p < 0.001), and a lower adherence to the MD than controls, in spite of no differences in energy intake between the two groups. The receiver operator characteristic (ROC) analysis showing a value of PhA of ≤ 5.7 and a PREDIMED score of ≤ 5.0 identified HS patients with the highest clinical severity of the disease. After adjusting for sex, age, body mass index (BMI), and total energy intake, the HS Sartorius score maintained negative correlations with PhA (p < 0.001), PREDIMED score, and n-3 polyunsaturated fatty acids (p = 0.005). The results of the multivariate analysis showed PhA and PREDIMED score were the major determinants of HS Sartorius score, explaining 82.0% and 30.4% of its variability, respectively (p < 0.001). Novel associations were demonstrated between PhA and the degree of adherence to the MD with the HS severity. PhA and PREDIMED score might represent possible markers of severity of HS in a clinical setting

Phase angle and Mediterranean diet in patients with acne: Two easy tools for assessing the clinical severity of disease

Acne is a chronic, inflammatory and debilitating skin disorder. Dietary factors and nutritional status are among the exacerbating factors of acne. Phase angle (PhA), a direct measure of Bioelectrical Impedance Analysis (BIA), represents an indicator of the chronic inflammatory state. The Mediterranean diet (MD) is a healthy dietary pattern that can exert anti-inflammatory effects in several inflammatory diseases. We aimed to investigate the difference in PhA and adherence to the MD and their associations with the severity of acne in a sample of naïve treatment patients with acne compared to control group

Association of Trimethylamine N-Oxide (TMAO) with the Clinical Severity of Hidradenitis Suppurativa (Acne Inversa)

: In this case-control, cross-sectional, observational study, we evaluated circulating trimethylamine n-oxide (TMAO) levels, a gut-derived metabolite associated with inflammation and cardiometabolic risk, in patients with hidradenitis suppurativa (HS), a highly disabling inflammatory skin disease associated with an elevated prevalence of comorbidities, especially cardiovascular and metabolic diseases. In this study, we enrolled 35 naive-treatment patients with HS and 35 controls, matched for sex, age, and body mass index (BMI). HS Sartorius score was 49.0 (33.0-75.0), while according to the Harley system 12 and 23 patients presented grade 1 and grade 2 severity, respectively. HS patients had a lower adherence to the Mediterranean diet (MD) (p = 0.002), lower phase angle (PhA) (p < 0.001), and higher circulating TMAO levels (p < 0.001) than the control group. HS patients with grade 2 rather than grade 1 of Harley grade severity showed a higher BMI (p = 0.007), waist circumference (p = 0.016), total energy intake (p = 0.005), and lower PhA (p < 0.001) and adherence to the MD (p = 0.003). Of interest, patients with Hurley grade 2 of severity exhibited higher circulating TMAO levels (p < 0.001) compared to grade 1. Circulating TMAO levels showed a positive correlation with HS Sartorius score even after adjustment for confounding covariates, including BMI, waist circumference, adherence to the MD, total energy intake, and PhA (r = 0.570, p = 0.001). Using a linear regression model, circulating TMAO levels and PhA were the main predictors of the clinical severity of HS

X-ray polarimetry reveals the magnetic field topology on sub-parsec scales in Tycho's supernova remnant

Supernova remnants are commonly considered to produce most of the Galactic cosmic rays via diffusive shock acceleration. However, many questions about the physical conditions at shock fronts, such as the magnetic-field morphology close to the particle acceleration sites, remain open. Here we report the detection of a localized polarization signal from some synchrotron X-ray emitting regions of Tycho's supernova remnant made by the Imaging X-ray Polarimetry Explorer. The derived polarization degree of the X-ray synchrotron emission is 9+/-2% averaged over the whole remnant, and 12+/-2% at the rim, higher than the 7-8% polarization value observed in the radio band. In the west region the polarization degree is 23+/-4%. The X-ray polarization degree in Tycho is higher than for Cassiopeia A, suggesting a more ordered magnetic-field or a larger maximum turbulence scale. The measured tangential polarization direction corresponds to a radial magnetic field, and is consistent with that observed in the radio band. These results are compatible with the expectation of turbulence produced by an anisotropic cascade of a radial magnetic-field near the shock, where we derive a magnetic-field amplification factor of 3.4+/-0.3. The fact that this value is significantly smaller than those expected from acceleration models is indicative of highly anisotropic magnetic-field turbulence, or that the emitting electrons either favor regions of lower turbulence, or accumulate close to where the magnetic-field orientation is preferentially radially oriented due to hydrodynamical instabilities.Comment: 31 pages, 7 figures, 3 tables. Accepted for publication in ApJ. Revised versio

Observations of 4U 1626-67 with the Imaging X-ray Polarimetry Explorer

We present measurements of the polarization of X-rays in the 2-8 keV band from the pulsar in the ultracompact low mass X-ray binary 4U1626-67 using data from the Imaging X-ray Polarimetry Explorer (IXPE). The 7.66 s pulsations were clearly detected throughout the IXPE observations as well as in the NICER soft X-ray observations, which we use as the basis for our timing analysis and to constrain the spectral shape over 0.4-10 keV energy band. Chandra HETGS high-resolution X-ray spectra were also obtained near the times of the IXPE observations for firm spectral modeling. We find an upper limit on the pulse-averaged linear polarization of <4% (at 95% confidence). Similarly, there was no significant detection of polarized flux in pulse phase intervals when subdividing the bandpass by energy. However, spectropolarimetric modeling over the full bandpass in pulse phase intervals provide a marginal detection of polarization of the power-law spectral component at the 4.8 +/- 2.3% level (90% confidence). We discuss the implications concerning the accretion geometry onto the pulsar, favoring two-component models of the pulsed emission.Comment: 19 pages, 7 figures, 7 tables; accepted for publication in the Astrophysical Journa

IXPE and XMM-Newton observations of the Soft Gamma Repeater SGR 1806-20

Recent observations with the Imaging X-ray Polarimetry Explorer (IXPE) of two anomalous X-ray pulsars provided evidence that X-ray emission from magnetar sources is strongly polarized. Here we report on the joint IXPE and XMM-Newton observations of the soft {\gamma}-repeater SGR 1806-20. The spectral and timing properties of SGR 1806-20 derived from XMM-Newton data are in broad agreement with previous measurements; however, we found the source at an all-time-low persistent flux level. No significant polarization was measured apart from the 4-5 keV energy range, where a probable detection with PD=31.6\pm 10.5% and PA=-17.6\pm 15 deg was obtained. The resulting polarization signal, together with the upper limits we derive at lower and higher energies 2-4 and 5-8 keV, respectively) is compatible with a picture in which thermal radiation from the condensed star surface is reprocessed by resonant Compton scattering in the magnetosphere, similar to what proposed for the bright magnetar 4U 0142+61.Comment: 11 pages, 3 figures, accepted for publication in Ap