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Wave overtopping occurring in offshore wind renewable energy structures such as tension leg platforms (TLPs) or semi-submersible platforms is a phenomenon that is worth studying and preventing in order to extend the remaining useful life of the corresponding facilities. The behaviour of this phenomenon has been extensively reported for linear coastal defences like seawalls. However, no referenced study has treated the case of cylindrical structures typical of these applications to a similar extent. The aim of the present study is to define an empirical expression that portrays the relative overtopping rate over a vertical cylinder including a variety of bull-nose type mitigation structures to reduce the overtopping rate in the same fashion as for the linear structures characteristic of shoreline defences. Hydrodynamic interaction was studied by means of an experimentally validated numerical model applied to a non-impulsive regular wave regime and the results were compared with the case of a plain cylinder to evaluate the expected improvement in the overtopping performance. Four different types of parapets were added to the crest of the base cylinder, with different parapet height and horizontal extension, to see the influence of the geometry on the mitigation efficiency. Computational results confirmed the effectivity of the proposed solution in the overtopping reduction, though the singularity of each parapet geometry did not lead to an outstanding difference between the analysed options. Consequently, the resulting overtopping decrease in all the proposed geometries could be modelled by a unique specific Weibull-type function of the relative freeboard, which governed the phenomenon, showing a net reduction in comparison with the cylinder without the geometric modifications. In addition, the relationship between the reduced relative overtopping rate and the mean flow thickness over the vertical cylinder crest was studied as an alternative methodology to assess the potential damage caused by overtopping in real structures without complex volumetric measurements. The collection of computational results was fitted to a useful function, allowing for the definition of the overtopping discharge once the mean flow thickness was known.

Submarine hulls are pressure vessels for which excellent structural integrity under underwater pressure loads is essential. The use of light-weight materials contributes to reduced fuel consumption, improved speed, and increased payload while strength properties are retained. The focus of this paper is on the collapse behavior of a filament-wound cylindrical structure that serves as the main hull of a submarine subject to hydrostatic pressure loads. This paper presents a computational modelling approach for the prediction of the collapse behavior mechanism using a commercial finite element (FE) solver. The collapse strength obtained from the numerical model corresponded closely to available experimental data. The composite and aluminum material models were compared and the effects of stacking angle and thickness portion in the ply sequence on collapse strength were investigated. The advantages and disadvantages of available design codes (i.e., American Society of Mechanical Engineers (ASME) BPVC-X and National Aeronautics and Space Administration (NASA) SP-8007) were reviewed by direct comparison with numerical results. It is concluded that the application of effective engineering constants for the prediction of the collapse pressure of submarine hulls may be feasible.

In the present study, we experimentally investigate water surface deformation due to the impact of rounded cylindrical projectiles with different aspect ratios (1.0–8.0). The subsequent jet and splash formation is closely related to the dynamics of an underwater cavity. To control the cavity formation, two kinds of surface conditions (smooth and rough) are applied to the front parts of the projectiles, and two impact speeds are considered. The Froude, Reynolds and Weber numbers are in the ranges of 32–90, $5\\times 10^{4}{-}8.4\\times 10^{4}$ and 1700–5000, respectively. When the front is smooth, the water film rises up along the body surface immediately after impact, and the temporal variation of its height is analytically estimated. The film converges at the rear pole to create an apex jet at lower aspect ratios and simply rises up and falls with the body at higher aspect ratios. The jets could be further distinguished as thin and thick jets, whose breakdown is found to be a function of the viscous force and surface tension, i.e. the Ohnesorge number. On the other hand, when the front is rough, the water film cannot rise up along the body surface, and instead early separation occurs to make the splash above a free surface. The splash size is quantified to assess the effects of the aspect ratio and impact speed. Upon splash formation, a cavity is created under the free surface, which emanates from the nose of the projectile. As the body sinks, the cavity pinch-off occurs due to the imbalance between the hydrostatic pressure and air pressure inside the cavity. At higher aspect ratios, cavity pinch-off occurs on the side wall of the projectile and leaves a portion of the cavity bubble on it. When the surface is smooth, no underwater cavity forms. Finally, we compare the hydrodynamic force acting on the sinking bodies with and without cavity formation, based on the underwater trajectory of each projectile. It is found that the underwater cavity reduces the drag force on the sinking body when it fully encapsulates the body; however, if the air bubbles are partially attached to the body after pinch-off, they tend to detach irregularly or impose additional drag on the body.

In practical engineering structures, complex low-frequency vibrations are often encountered. However, most reported elastic metamaterials are designed for high-frequency ranges or rely on substantial additional mass to control low-frequency vibrations, making them difficult to apply in real-world engineering scenarios. To address this limitation, we propose a homogeneous locally resonance metamaterial with tunable low-frequency bandgaps. This design overcomes the challenges associated with conventional local resonators, which are often large and heavy, making them impractical for engineering applications. By integrating resonator structures composed of elastic chiral spiral beams and mass blocks onto the supporting structure, we achieve low-frequency vibration control within limited spaces, broadband absorption with gradient parameter units, and vibration control under different curvatures. The effectiveness of the proposed design is validated through comparative computational methods, dispersion curve calculations, frequency response simulations, and experimental tests. This study proposes a novel LRM structure with a full bandgap from 96.9 to 124 Hz. The transmittance is negative in most of the band gap range, which has been verified through numerical and experimental results. This approach effectively meets the complex low-frequency vibration control requirements of various curved structures in engineering applications, providing a viable solution for low-frequency vibration control of structures such as flat and cylindrical shells.

An impulsively starting motion of two cylindrical bodies floating on a free liquid surface is considered. The shape of the cross-section of each body and the distance between them are arbitrary. The integral hodograph method is advanced to derive the complex velocity potential defined in a rectangular parameter region in terms of the elliptic quasi-doubly periodic Jacobi theta functions. A system of singular integral equations in the velocity magnitude on the free surface and in the slope of the wetted part of each body is derived using the kinematic boundary condition, which is then solved numerically. The velocity field, the pressure impulse on the bodies and the added mass coefficients of each body immediately after the impact are determined in a wide range of distances between the bodies and for cross-sectional shapes such as the flat plate and half-circle.

During its Grand Finale, the Cassini spacecraft collected crucial gravity data, revealing Saturn's low‐degree gravity harmonics and large‐scale zonal winds extending about 8,000 km deep. However, determining the high‐degree gravity field, essential for understanding small‐scale atmospheric dynamics, is challenging due to the limited spatial coverage of Cassini's periapses. To overcome this limitation, we employed Slepian functions, orthogonal within a bounded domain, to represent Saturn's localized high‐degree gravity field. Focusing on latitudes from 32°S to 32°N, we estimated Slepian coefficients that represent short‐scale latitudinal gravity variations. The reconstructed wind profile that explains low‐degree harmonics can also reproduce these high‐degree variations, assuming Saturn's atmosphere is, to first order, in thermal wind balance. Our findings suggest that small‐scale winds may extend to depths between 7,000 km and 9,000 km, providing strong evidence that Saturn's zonal flows are oriented along coaxial cylinders, rotating at different angular velocities. Plain Language Summary We explore Saturn's small‐scale atmospheric dynamics by analyzing data from the final phase of the Cassini mission. As the spacecraft flew between Saturn's rings and upper atmosphere, it collected detailed gravity measurements that provided important insights into the planet's winds and their depths. While Saturn's large‐scale winds are well understood, the patterns of small‐scale winds remain less clear. Using a new mathematical technique, we focused on specific regions of Saturn's gravity field covered by Cassini's data. This approach allowed us to detect rapid gravity variations influenced by small‐scale winds. Our findings suggest that these small‐scale winds may extend to depths comparable to the large‐scale winds, reaching between 7,000 and 9,000 km below Saturn's visible surface. This confirms that the deep winds inside Saturn have cylindrical structures. The study highlights the complexity of Saturn's atmospheric dynamics and the significant role of small‐scale wind patterns in shaping the planet's gravity field. These insights pave the way for future research on the atmospheric dynamics of gas giants, enhancing our understanding of their internal processes. Key Points Cassini's Grand Finale radio science data revealed Saturn's high‐degree gravity field from low‐to mid‐latitudes Saturn's small‐scale winds extend to depths comparable to those of large‐scale winds, between 7,000 km and 9,000 km Slepian functions improve retrieval of local high‐degree gravity fields from data with limited coverage, compared to spherical harmonics

Structures with slender cylindrical geometries, such as subsea power cables are critical components of infrastructure systems. These structures are prone to bending deformation under load, which can ultimately cause structural failure. In this study, distributed optical fibre sensors are used to monitor the bending deformation in slender cylindrical structures. Brillouin optical time-domain reflectometry-based strain sensing was used to experimentally study three-point bending and approximately constant curvature bending of a 6 m long circular hollow section (CHS). Optical fibres were attached to the outer surface of the CHS in two different configurations: parallel to the longitudinal axis and helically wound around the CHS. Strain responses due to changing magnitudes of deformation and changing orientation of the optical fibre around the circumference of the CHS were studied. A finite element model was employed to simulate and interpret the observed strain responses. A strain response inverse analysis was conducted using the strain data obtained from the experimental study to reconstruct the deformed shapes of the CHS. Both the longitudinally aligned and helically wound fibres showed distinct strain profiles that differentiate the three-point bending and constant curvature bending behaviours. The results revealed the ability of optical fibre sensing to evaluate the type; magnitude; and orientation of the bending deformations. This fundamental understanding supports the design of sensing systems for critical cylindrical infrastructure.

Two-dimensional (2-D) quadrant analysis is generally used for investigating flow and sediment dynamics around a rigid structure in open channel flows. Given that particle distribution around rigid obstacles is not spatially uniform and changes in time, while vortices evolve to become three-dimensional (3-D) structures, 2-D quadrant analysis might be unsuitable to completely determine the sediment transport. Hence, 3-D quadrant and 3-D octant analyses should be considered, using the 3-D instantaneous velocity data and relative 3-D bursting process to define sediment transport surrounding the submerged square and circular cylinders. The turbulent kinetic energy (TKE), transition probabilities, occurrence probabilities, stress fraction and angles of inclination of 3-D bursting events are considered to quantify the coherent structures surrounding the cylinders and their interaction with bed particles. Experiments were conducted at the Hydraulics and Water Resources Engineering Laboratory, School of Infrastructure, Indian Institute of Technology, Bhubaneswar, Odisha, India, and velocity data were recorded at different cross-sections around the submerged cylinders using an acoustic Doppler velocimeter. Results show that the TKE is greater for internal ejection, external ejection, and internal sweep, external sweep in the upstream of the circular and square cylindrical structures. On the other part, the TKE is significant for internal ejection, external ejection, and internal sweep, external sweep in the downstream of the aligned square cylindrical structures, which justifies the highest scour depth that occurred upstream of the circular and square cylindrical structures and downstream of the aligned square cylindrical structure. The transition probability of the bursting events was determined using the Markov process from the measured velocity data to investigate the consecutive occurrence of bursting events. Further, the importance of sweeps and ejections on sediment erosion surrounding the cylinders within the scour hole at various stages of its development was investigated via 3-D quadrant analysis of the bursting occurrences. The outcomes show that external sweep and internal ejection events are active mechanisms for bed particle transport surrounding the cylinder. The maximum transition probability values are found around aligned cylindrical structures in comparison with the circular and square cylindrical structures in the transverse direction. This depicts the formation of a trailing vortex on both sides of the aligned square cylindrical object. The results reveal that the effect of inclination angles with respect to the water flow is greater for internal ejection and external sweep from upstream to downstream within the scour hole surrounding the cylindrical structures at various phases of development as horseshoe vortices and downflow develop upstream of the cylindrical structures while trailing vortices and wake vortices form at the top and downstream of the cylindrical structures. Internal and external ejection have a higher stress fraction than an internal and external sweep for square cylinders with alignment angles of 0°, 20° and circular cylinders over underdeveloped and developed scoured beds, respectively. With the higher percentage of fractional contributions for internal sweeps, the external sweep is predicted close to the cylindrical objects in comparison with the internal ejection and external ejection events because of the formation and warping of the horseshoe vortex close to the cylindrical objects, suggesting a significant probability of 3-D bursting occurrences with sediment movement near the cylindrical structures.

In internal parasitism, the respiration strategy within the host's body is as essential as evading attack from the host's immune system. Tachinid flies are parasitoids of terrestrial arthropods, mostly insects, during their larval stage. To obtain oxygen while living in the host body, they build a cylindrical structure known as the respiratory funnel at the aperture opened by the tachinid larva on the host integument or trachea. These funnels can be divided morphologically into sheath and cone types. Previous research on sheath-type funnels revealed that they are derived from the encapsulating substance produced by the host's immune system. In contrast, the cone-type funnels cover part of the body of the larval tachinid and may be constructed independently from the host immune system. To determine the mechanisms of cone-type funnel formation, histological observations were carried out on Gymnosoma rotundatum (L.) (Diptera: Tachinidae), which possesses this type of funnel. The respiratory funnel of G. rotundatum was found to be derived from the tube-shaped faeces wrapped with the peritrophic membrane and excreted by the fly larva, not from host tissue or haemocytes. Additionally, secretory glands putatively involved in the funnel formation were discovered around the larval anal plate of G. rotundatum . A comparison of funnel types within Tachinidae revealed that Phasiinae and Dexiinae have cone-type funnels, which may be created by the same mechanism as in G. rotundatum . These new findings suggest that funnel formation that does not use the host immune system is relevant to tachinid phylogeny.

There are various hotspots in the Atlantic Ocean, which are underlain by mantle plumes that likely cross the mantle and originate at the core‐mantle boundary. We use teleseismic core‐diffracted shear waves to look for an Ultra‐Low Velocity Zone (ULVZ) at the potential base of central Atlantic mantle plumes. Our data set shows delayed postcursory phases after the core‐diffracted shear waves. The observed patterns are consistent in frequency dependence, delay time, and scatter pattern with those caused by mega‐ULVZs previously modeled elsewhere. Synthetic modeling of a cylindrical structure on the core‐mantle boundary below St. Helena provides a good fit to the data. The preferred model is 600 km across and 20 km high, centered at approximately 15° South, 15° West, and with a 30% S‐wave velocity reduction. Significant uncertainties and trade‐offs do remain to these parameters, but a large ULVZ is needed to explain the data. The location is west of St. Helena and south of Ascension. Helium and neon isotopic systematics observed in samples from this region could point to a less‐outgassed mantle component mixed in with the dominant signature of recycled material. These observations could be explained by a contribution from the Large Low Shear Velocity Province (LLSVP). Tungsten isotopic measurements would be needed to understand whether a contribution from the mega‐ULVZ is also required at St. Helena or Ascension. Plain Language Summary Nearly 3,000 km beneath the Atlantic to the West of the island of St. Helena, on the boundary between Earth's metal core and rocky mantle, we have discovered a new area where seismic waves diffracting along that boundary travel significantly slower than expected. This area is called an ultra‐low velocity zone. In this study, we use seismic waves which propagate along the core‐mantle boundary. The waves that interact with the ultra‐low velocity zone are scattered and become severely delayed. Using the observations, we have constrained the ultra‐low velocity zone to a broadly cylindrical structure, 600 km across, 20 km high and centered at 15° South, 15° West. The material inside is reduced by 30% in seismic shear wave velocity compared to outside. We confirmed this model by computing and comparing synthetic waveforms for a range of different ultra‐low velocity zone models. This ULVZ location is right beside or just inside a much larger region of low velocity, dubbed the African Large Low Shear‐Velocity Province (LLSVP). The observed ultra‐low velocity zone could be the base of the upwelling or mantle plume rising through the mantle and causing the hotspots of St. Helena and/or Ascension at the surface. Key Points Observation of significant Sdiff postcursors sampling the CMB beneath the Atlantic Modeling of postcursors reveals a previously unknown mega‐ULVZ situated on the CMB to the West of St. Helena Further measurements of St. Helena and Ascension samples are needed to identify a potential ULVZ‐associated geochemical signature