Incorporating steps into a hull reduces the wetted surface, promoting improved hydrodynamic lift and reduced resistance at high speeds, provided that the step is designed appropriately. Traditional hydrodynamics studies rely on scaled model testing in towing tanks, but numerical tools offer a more efficient alternative. This study focused on investigating the hydrodynamic performance of stepped hulls by modifying the parent hull of the Naples Systematic Series (C1). The Computational Fluid Dynamics (CFD) code SIEMENS PLM STAR CCM+ version 2302 was used for simulations, including four different beam Froude numbers ($F{r}_B$ = 1.13, 2.22, 2.56, and 2.96) and a total of 15 hull configurations with single and double steps. By employing a three-dimensional computational analysis of multiphase flow using Dynamic Fluid–Body Interaction (DFBI) and overset mesh, various performance parameters such as resistance coefficient, dimensionless wetted surface, sinkage, and dynamic trim were analyzed. The accuracy of the CFD results was confirmed through comparison with experimental data and grid uncertainty assessment. The study demonstrated that placing a single step near the transom decreased trim and increased resistance and wetted surface. Conversely, positioning a step in the forward section reduced the trim angle at lower step heights but increased trim at higher step heights in single-stepped hulls. The application of these findings contributes to the design optimization of stepped hulls for enhanced performance in high-speed maritime applications.

Objectives: To determine the effectiveness of mechanical traction in supine versus prone lying position for lumbosacral radiculopathy. Methods: A quasi experimental trial was conducted from April to September 2020 among sixty patients of chronic lumbosacral radiculopathy at Ibn-e-Siena Hospital, Multan. Participants were divided into two groups. Group-A (Supine) participants received lumbar traction in supine lying along with conventional treatment. Group-B (Prone) underwent the same treatment except the lumbar traction being applied in prone lying position. Participants were evaluated twice: at pre- treatment (week 0) and at the post treatment (week 2). Oswestry Disability Index and Numeric Pain Rating Scale were used as outcome measure. Data was analyzed on SPSS 23. Results: The mean (±S.D) age of the patients was 39±5.7 vs. 40±5.3 years in supine vs. prone group respectively. Mean ODI score was 25.2±6.13 vs. 26.0±6.26 at the start of treatment in supine vs. prone position respectively while it was 19.45±7.12 vs. 11.05±4.40 at end of treatment in supine vs. prone position respectively. Mean NPRS score was 7.73±1.23 vs. 7.67±0.96 at start of treatment in supine vs. prone position respectively while it was 4.63±0.89 vs. 3.13±0.90 at the end of treatment in supine vs. prone position respectively. Conclusion: Lumbar traction in prone lying position is more effective than lumbar traction in supine lying position for the treatment of chronic lumbosacral radiculopathy. doi: https://doi.org/10.12669/pjms.37.5.4200 How to cite this:Khan RR, Riaz S, Rashid S, Sulman M. Effectiveness of mechanical traction in supine versus prone lying position for lumbosacral radiculopathy. Pak J Med Sci. 2021;37(5):1451-1455. doi: https://doi.org/10.12669/pjms.37.5.4200 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In high-speed crafts, whisker spray increases viscous resistance by enlarging the wetted surface near the stagnation line. Spray rails (SRs) mitigate this issue by redirecting water flow, reducing the wetted surface, and lowering overall resistance. This study investigates the effect of SRs on the hydrodynamic performance of the C1 hull of Naples Systematic Series (NSS), focusing on the systematic variations in size, number, and placement. Numerical simulations, validated with towing tank results, were conducted using STAR CCM+ 2306. Mesh independence analysis was also performed to optimize computational efficiency. Key findings highlight the critical role of SR design in performance optimization. Wider SRs (e.g., three per side, 0.96% LWL) reduced resistance by up to 8.5% at high speeds (${Fr}_{\nabla }=$ 3.26), but slightly increased the resistance at lower speeds (~2%) due to a larger wetted surface. Narrower SRs (e.g., three per side, 0.48% LWL) achieved resistance reductions of up to 4.6%, while configurations with multiple SRs (e.g., three per side, 0.72% LWL) outperformed single-rail designs by reducing resistance up to 4%. Placement near the chine proved more effective than near the keel, offering a 4% additional reduction in resistance. Additionally, SRs generated lift, raising the hull, and reducing immersion. The study underscores the importance of optimizing SR size, number, and placement to enhance hydrodynamic efficiency, particularly for high-speed operations.

This paper presents a computational method for determining the planar static equilibrium of a tether cable subjected to a uniform current and constant-velocity vehicle motion, to support design analysis and ensure the safe operation of tether management system (TMS)–remote-operated vehicle (ROV) systems. The tether cable was modeled as an inextensible, torsion-free element subjected to distributed loads, including its effective self-weight and hydrodynamic forces. The governing equations were formulated as a boundary-value problem in which the positions of both cable endpoints were prescribed. The hydrodynamic forces were evaluated using computational fluid dynamics (CFD) simulations conducted over a range of current velocities, cable diameters, and inflow angles from 0° to 90°. The CFD results were synthesized and parameterized as drag and lift coefficients that depend on the local cable inclination angle and were subsequently approximated with polynomial models to enable efficient evaluation during the static analysis. The resulting nonlinear boundary-value problem was solved using a Newton iterative method. The proposed approach enabled rapid predictions of the cable geometry and tension distribution, providing an effective tool for static analysis and operational planning of ROV systems under steady-current conditions and constant-velocity vehicle motion.