Bottom Structures Research Articles

New Rotating Coanda-Type Intake for Sediment-Laden Flows

Tyrolean and Coanda types of water intake structures are the most widely preferred bottom intake structures used to divert water from channels and river systems for various purposes, such as energy production, irrigation, and domestic use. Estimation of withdrawal water and filtered sediment amounts are important to obtain maximum efficiency from an intake structure. The purpose of this study is to numerically analyze a newly patented rotating Coanda-type intake system to achieve the highest Water Capturing Efficiency and Sediment Release Efficiency. The newly patented system (patent no: TR2021011306B) presented here incorporates Coanda screens with variable void ratios, autonomously selected based on the sediment characteristics of the inflowing water. The process of selecting and positioning the appropriate screen is fully automated, requiring no human intervention. The system rotates under motor control to place the suitable screen at the operational point based on the specific requirements of the incoming sediment-laden flow.

Broadband and low-loss power splitter with polarization manipulation using subwavelength gratings

A broadband and low-loss power splitter with polarization manipulation using subwavelength gratings (SWGs) is proposed and analyzed, where SWGs are embedded in input taper/output inverse tapered waveguides in the bottom layer to form an SWG-based structure, and a silicon nitride layer is placed above the bottom layer to form a low-index guiding structure. In the bottom layer, the TE mode is cut off as the input strip waveguide is tapered down. In this way, the injected TE mode is evenly coupled to two adjacent output ports with high efficiency by the assistance of SWGs. By contrast, the input TM mode is well supported by the above silicon nitride layer and directly transmitted to the Through port, which is almost not influenced by the bottom structures. Consequently, both power splitting and polarization handling are achieved in the designed device simultaneously. Simulation results show that an extinction ratio (ER) of 32.63 dB (18.56 dB) and insertion loss (IL) of 0.16 dB (0.16 dB) for the TE (TM) mode are obtained at 1.55 µm. The bandwidth is up to 191 nm (1450–1641 nm) for the TE mode and 200 nm (1450–1650 nm) for the TM mode with an ER exceeding 15 dB and IL below 0.3 dB. Furthermore, fabrication tolerances and power distribution with polarization manipulation through the device are also presented.

Influence of bottom protection structures group on the hydraulic characteristics in sharp bends

Bottom protection (BP) is a commonly used engineering measure in river training. A 3D hydrodynamic numerical model is established to study the influence of the overall arrangements of BP structures on the hydraulic characteristics of the sharp bends. Under the action of the BP structures group, the maximum longitudinal flow velocity is closer to the water surface vertically and closer to the concave bank laterally compared with no BP. The high shear stress zones on the riverbed at the exit straight section of the bend do not occur. The so-called primary circulation after the apex of the bend gradually weakens and disappears. If the coverage rate of BP is increased to 1.5 times that of the sequential BP, the average longitudinal flow velocity near the bottom of BP decreases by 10% and the average bed shear stress at the outlet section of the bend decreases by 35%. In the staggered BP condition, the average bed shear stress at the outlet section of the bend is reduced by 23% compared with the sequential BP. Moreover, the results show that the protection effects of the dense BP and the staggered BP are better than that of sequential BP.

Excellent hydrophobicity and high mobility of condensate droplets on hierarchical nanostructured surfaces: Insights from MD simulations

Comprehending the fundamental physical mechanisms behind condensation and the formation of suspended droplets on hierarchical structured surfaces is of paramount importance in the design of anti-frosting surfaces. In this study, we characterize the nucleation, growth and dynamic wetting behaviors of condensate droplets on hierarchical nanostructured surfaces by molecular dynamics simulation, and reveal that hierarchical structures facilitate the rapid formation and high mobility of suspended droplet during condensation. The mechanism underlying the formation of suspended droplets on hierarchical surfaces is unveiled, which can be attributed to the spontaneous dewetting transition induced by confined growth of individual droplets. Additionally, the impact of solid fraction and secondary structure distribution on condensation and dynamic wetting is systematically discussed. The results indicate that an increase in solid fraction or the number of secondary structures enhances the stability of suspended droplets and improves the droplet mobility. In particular, the presence of bottom secondary structures on sidewalls plays a crucial role in the formation of suspended droplets on hierarchical surface. It is expected that the above findings could provide valuable guidance for optimizing the design of functionalized surfaces with anti-frosting and self-cleaning performance.

Effects of internal waves on bottom thermal structures and turbulent mixing in the Xisha Islands

Using velocity and high-resolution temperature mooring data from the fore-reef slope of Yongxing Island in the northwest South China Sea (water depth of 69 m), we examine the effects of internal waves on the temporal variations in temperature, bottom mixed layer (BML) and turbulent mixing. The diurnal tide is found to be the dominant tidal force and the baroclinic tide is highly active, which would account for the 11 d abnormal spring-neap cycle in the barotropic tidal current. During the ebb period (tidal elevation decreases), the bottom diurnal baroclinic current transports cold water upslope, resulting in a decrease in temperature, and vice versa during the flood period. The BML thickness Hbml widely varies around 1.5m, approximately 2% of the water depth. The bottom turbulent mixing is not so active, indicated by the bulk dissipation Eɛ of 10 mWm−2 and turbulent diffusivity κz of 2×10−4m2s−1. Both Hbml and Eɛ approximate a log-normal distribution, demonstrating strong intermittency. The high-frequency (ω) internal bores can increase Hbml by four times and enhance the turbulent mixing by one order, which should be responsible for the slow cascade of Hbml(∼ω−1.5) and Eɛ(∼ω−1.0). In the downslope phase, Hbml is about 30% thicker, and turbulent mixing is enhanced by 3 times stronger than those in the upslope phase. It is revealed that under the forcing of internal waves, turbulent mixing corresponds to a thick BML with Hbml∼〈κz〉0.25, and stratification (N) has a significantly negative correlation with the development of BML, Hbml∼〈N〉−1.8.

The influence of lateral pressure on ultimate strength of ship structure

ABSTRACT The lateral pressure influences the ultimate strength of double-bottom structure. In the midship section of bulk carrier, upward bottom local loads typically exceed downward loads, resulting in increased longitudinal thrust in the outer bottom plating and a reduction in the ultimate strength of the hull girder during hogging conditions. In the present research, the typical stiffened plate and double bottom structures of the Kamsarmax type bulk carrier are taken as the research objects. The nonlinear finite element method is considered to analyze the collapse behaviour of the stiffened plate and double-bottom structure under the longitudinal thrust/bending and lateral pressure, respectively. The influence of lateral pressure on buckling modes, stress distribution, collapse mode and ultimate strength is systematically demonstrated and analyzed. This research contributes significantly to the safety design of hull structures.

Design and analysis of a complementary structure-based high selectivity tri-band frequency selective surface

This work presents a novel tri-band bandpass frequency selective surface (FSS) that achieves high-order filtering responses in different frequency bands by means of a complementary structure. The proposed FSS is composed of three metal periodic arrays, which are separated by multilayer dielectric substrates. The gridded-double convoluted loop (G-DCL) structure, which is the middle layer structure, is a hybrid resonator that generates different resonant frequencies. The top and bottom layer structures are designed as complementary structures to the middle layer. To accurately describe the frequency responses, an equivalent circuit model (ECM) has been constructed over the entire band from 0 to 16 GHz. The results of the simulation indicate that the developed FSS can generate three pass-bands operating at 3.79 GHz, 8.34 GHz, and 12.52 GHz, respectively, and − 3 dB fractional bandwidths are 52.8%, 13.7%, and 19.7%. The transmission responses at the edges of each passband show a quick roll-off from the passband to the stopband, and there is significant out-of-band suppression between adjacent passbands. Moreover, the FSS maintains excellent angular and polarization stability within a 50° range. For verification, the tri-band FSS has been fabricated and tested. The experimental results match the simulation results, validating the accuracy of the FSS design.

Maximizing efficiency: Numerical modeling and optimization of 2-terminal perovskite/silicon tandem devices with different bottom cell structures

Two-terminal perovskite/silicon (Si) tandem solar cells have made significant progress in terms of efficiency and are considered suitable candidates for the next generation of photovoltaic devices. However, research on Si bottom cell optimization is limited, with optimization being conducted only within a specific structure reported as high efficiency. To present more general and higher efficiency possibilities, optimization is necessary not only for the perovskite and interlayer but also for each bottom Si solar cell structure. In this study, we proposed a numerical modeling approach for analyzing and optimizing the effects of optical and electrical properties in 2-terminal tandem structures. First, the properties for each layer were discussed to minimize optical loss using optical simulations, considering the recently reported high-efficiency 2-terminal perovskite/Si tandem system. After fixing the top perovskite and recombination layer using these properties, each bottom Si structure, which is divided into homojunction (PERC and TOPCon structure) and heterojunction (HIT structure), was electrically simulated. The characteristics of Si bottom cells were identified based on bulk properties (bulk lifetime and resistivity). Consequently, we proposed an improvement method and structure capable of achieving maximum possible efficiency of more than 30 % as a tandem device for each bottom cell structure.

Variations of single event transient induced by line edge roughness (LER) and temperature in FinFET

The impacts of line edge roughness (LER) and temperature effect on single event transient (SET) in Silicon-On-Insulator (SOI) FinFET at 14 nm technology node are studied. Based on the calibrated model of the rectangle FinFET, all of possible fin structures induced by LER in the vertical direction are proposed by considering the correlation between the line edges. When an energetic particle hits, due to the corporate effects of the gate control capability from the equivalent gate width and the current density from the cross section, thin fin shape represents more immunity to SET with the relative decrement in current peak, collected charge, deposited charge, pulse width and bipolar amplification coefficient by 23.78 %, 31.61 %, 19.16 %, 23.77 % and 15.40 %, respectively. However, the SET responses of big bottom and fat fin structures indicate that they are more sensitive to SET. Because of the driven current increase induced by the inversion of the temperature effect in FinFET, as the environment temperature increases, the SET responses of all of fin shapes decrease and their relative decrements are close. When the temperature increases from 258K to 398K, the average relative decrements in current peak, and collected charge are 24.22 %, 20.90 %, respectively.

Effect of Channel Shape on Performance of Printed Indium Gallium Zinc Oxide Thin-Film Transistors.

Printing technology will improve the complexity and material waste of traditional deposition and lithography processes in device fabrication. In particular, the printing process can effectively control the functional layer stacking and channel shape in thin-film transistor (TFT) devices. We prepared the patterning indium gallium zinc oxide (IGZO) semiconductor layer with Ga, In, and Zn molar ratios of 1:2:7 on Si/SiO2 substrates. And the patterning source and drain electrodes were printed on the surface of semiconductor layers to construct a TFT device with the top contact and bottom gate structures. To overcome the problem of uniform distribution of applied voltages between electrode centers and edges, we investigated whether the circular arc channel could improve the carrier regulation ability under the field effect in printed TFTs compared with a traditional structure of rectangular symmetry and a rectangular groove channel. The drain current value of the IGZO TFT with a circular arc channel pattern was significantly enhanced compared to that of a TFT with rectangular symmetric source/drain electrodes under the corresponding drain-source voltage and gate voltage. The field effect properties of the device were obviously improved by introducing the arc-shaped channel structure.

Modeling and interpretation of bistatic bottom reverberation in deep water near seamounts.

The received reverberation signal can be beamformed by utilizing a vertical array, generating a vertical-angle time record (VATR) that enables analysis of spatiotemporal distribution characteristics. Due to the influence of multipath propagation effects, deep-sea reverberation exhibits highly complex characteristics, especially in a seabed with significant depth variation. In a recent bistatic reverberation experiment with a vertical array receiver, peculiar bright stripes were observed in the VATR. These stripes are the result of scattering caused by large-scale bottom structures and are closely associated with seamounts. To accurately model and interpret these stripes, a bistatic reverberation model is initially established to reproduce the VATR. This model enables us to numerically simulate the spatiotemporal distribution of reverberation in the VATR, offering a qualitative explanation for these stripes. However, the model alone is incapable of predicting the specific stripe structure associated with a particular seamount. To address this limitation, an equation system is introduced to calculate the stripe parameters based on the seamount parameters. By analyzing and deducing the dependency of the stripes on the seamount, conclusions were drawn using the equation system. Ultimately, the presented model and equation system successfully reproduce and comprehensively explain the observed abnormal stripes from the experiment.

Invasive diatom, Cymbella janischii adhering on body surface of native aquatic beetles, Grouvellinus nitidus (Elmidae) and Ectopria opaca (Psephenidae) in Japan

AbstractCymbella janischii, an invasive species of diatom, has been broadening its geographical range in Japan since 2004, flourishing in substantial colonies in river beds. As thick and mucilaginous colonies of this diatom often cover large areas of river beds, this elicits concerns regarding the potential alteration of sedimentary bottom structures and resultant effects on the native ecosystems. The presence of the diatoms growing on the body surface of two aquatic beetles, Grouvellinus nitidus (Elmidae) and Ectopria opaca (Psephenidae) in a Japanese river was confirmed. This constitutes the inaugural documentation of invasive diatoms having a specific relationship with native aquatic insects at an individual level.

ANALYSIS OF AUTOMATIC CONTROL SYSTEMS OF A MULTIPURPOSE AUTONOMOUS UNMANNED UNDERWATER VEHICLE WITH COMPLEX MOTION DYNAMICS

The overview article is devoted to the analysis of control systems of autonomous unmanned underwater vehicles, which belong to robotic underwater complexes and are used to provide search and deep-sea emergency and rescue operations, survey of various underwater objects (main pipelines, bottom structures, ship hulls, etc.), conducting scientific oceanographic surveys research, monitoring of the marine environment. The work examines scientific literary sources, which provide the results of development and research of orientation, navigation and motion control systems of multi-purpose autonomous unmanned underwater vehicles with complex movement dynamics, in particular when performing missions in a limited space with movement along complex trajectories. Special attention is focused on such modes of movement of devices as trajectory tracking, path-following and way point tracking. An analysis of the means of navigation and control, which can be used to ensure different modes of movement, was carried out, as well as the directions of development of both the unmanned underwater vehicles themselves and their control systems were considered.
 In order to substantiate the development of a control system for a multi-purpose maneuverable mini-class autonomous vehicle, the main requirements are formulated. It is proposed to conduct a synthesis and research of the control system based on the simulation of the dynamics of the movement of the mini-vehicle for different modes of movement in terms of parameters and trajectories, to develop algorithms for the adaptive control of the vehicle, to improve the system orientation and navigation, built on the basis of MEMS sensors. An information model of the development process is proposed and substantiated, which specifies the sequence of determining important parameters and characteristics of the vehicle and performing important stages of synthesis and analysis of the control system.

P-type nickel oxide deposited by reactive hollow cathode gas flow sputtering for the potential usage in thin-film transistors

Thin Nickel Oxide film were deposited by reactive pulsed-direct current hollow cathode gas flow sputtering. This unique technique allows for sputtering magnetic target materials with very high rates without magnetron. Deposition was carried out from a nickel target at room temperature. The influence of process parameters on optical, electrical, and structural film properties are investigated. High deposition rates of 6 nm/s and 2 nm/s are achieved for both direct current and pulsed-direct current power supply. All films are highly resistive and show p-type conduction that is tunable with oxygen flow. The films exhibit optical band gap around 3,8 eV depending on process parameters like oxygen flow and pulsing parameter. Secondary electron microscopy shows pillar-like growth perpendicular to the surface, while grazing incidence X-ray diffraction reveals smaller, randomly oriented crystals. Electrical properties of the films were tested by Hall measurements, revealing mobilities in the range of 1 cm2Vs. The nano crystalline thin films were tested in staggered bottom gate Thin-Film Transistor structures for potential use as channel layer.

Dynamic response evaluation due to construction system modification of 155 m barge ship using finite element method

The application of lightweight sandwich material as a ship structure was an innovative breakthrough that provided an excellent strength-to-weight ratio. In the sandwich application process, the proposed structural design and scantling must be designed according to the equivalent strength requirement with low weight compared to the existing structure. The research aims to evaluate the dynamic response of different construction systems of barge ships due to applying various hybrid sandwich types in the deck, ship hull, and bottom structures using the current Lloyd’s Register standard. A total of three proposed construction systems: longitudinal, transverse and mixed framing systems, are investigated under different plate configurations, material types, and scantling sizes. The numerical-based finite element approach is used to evaluate dynamic properties of natural frequency and mode shape using free vibration analysis at low mode numbers. The finite element result from the dynamic characteristic and weight reduction estimation between the existing structure and the proposed construction systems under various plate configurations, material types, and scantling sizes is evaluated to determine the application of lightweight sandwich panels in the barge structure.

Thirty years of satellite derived bathymetry – The charting tool that hydrographers can no longer ignore

Thirty years after being introduced into national chart series, Satellite Derived Bathymetry (SDB) charts are still struggling to be recognised as valid navigation documents, capable of meeting the level of confidence required by the S-44 IHO standards for hydrographic surveys. The advent of new generation satellite constellations, such as Sentinel-2*, provide improved geolocation and, thanks to higher revisit frequency, an almost unlimited capacity to detect natural dangers visible from space within the limits of the sensing instruments. Thus, this negative vision of SDB must change. Written by Hydrographers, this article aims to provide a scientific background adapted to practical Hydrography; introduce the notion of “Perfect Image”, first mentioned at the International Hydrographic Remote Sensing workshop (Ottawa, September 2018); and rehabilitate older concepts such as Depth of Penetration (DOP), which make SDB an incomparable instrument to chart the World’s shallow waters (Fig. 1). Here, “incomparable” does not mean “perfect”, as there are limits to SDB capacity to detect and quantify bottom structures that will be detailed later. *The frequent mention of Sentinel-2 should not lead the reader to believe that the authors are focussing on this constellation. The intention is to show how satellite hydrography has evolved naturally from exploiting unique images to processing large collections that provide ever-improved information, the latest example happening to be Sentinel-2.

Numerical investigation and optimization of the geometric profiles of dimple bottom structure in frictional interaction pairs

Dimple texture forming in the interaction pairs is a wear reduction technique like lubrication. Dimple-texturing is an efficient and sustainable way of altering the surface topography to improve the tribological characteristics of interacting surfaces. In this work, sliding interaction pairs with circular dimples, three different dimple bottom structures, namely flat, V-shaped and U-shaped, are selected for numerical investigation using the Reynolds equation to enhance the hydrodynamic characteristics. The numerical design and investigation on the dimple area density (ρ), aspect ratio (λ), and flow velocity (V) is done using unblocked central-composite design (UCD) under response surface methodology (RSM) along with multi-objective gray relation analysis method for individual dimple bottom structures to minimize the coefficient of friction and increase the load bearing capacity in the interaction pairs. The flat bottom structure exhibits excellent load-bearing capacity and minimum coefficient of friction when compared to V-shaped and U-shaped bottom structures. Compared to flat bottom structure, the V-shaped and U-shaped bottom structures has 40.37% and 7.81% lesser load-bearing capacity, respectively, and 54.08% and 7.81% higher coefficient of friction, respectively. In a flat bottom structure, the flow velocity is identified as an effective variable factor to improve the outcome characteristics, followed by dimple area density and aspect ratio. The optimal dimple area density and aspect ratio values are observed in the range of 30–40% and 0.025 – 0.030, respectively. In addition, the optimal value of flow velocity is observed to be 2.5 m/s.

Comparative Analysis of Seakeeping of Offshore Photovoltaic Floating Unit

Background: In recent years, offshore photovoltaic (PV) power systems have become an emerging hot issue. For offshore PV, the marine environmental loads are more complex, especially wave loads will put higher demands on the mooring system, and a failure of the mooring system will cause great harm. In order to ensure the safe operation of the system, the floating unit should be designed for high seakeeping. Objective: In this paper, six common configurations of floating units are selected, and the six configurations are divided into two experimental groups, one of which includes floating units with different shapes of holes, and mainly discusses the effects of different shapes of holes on the seakeeping of floating units, and the other experimental group includes common configurations of catamarans and trimarans in ships, and mainly discusses the effects of different bottom structures on the seakeeping of floating units. And after determining the better configuration, further shape optimization is performed. Methods: The problem described in this paper cannot ignore the change of the solid deformation on the flow field boundary, when both interaction processes between the two phases need to be calculated. Therefore, this paper discusses a bi-directional fluid-solid coupling process. For the six float units, a bi-directional fluid-structure coupling calculation analysis was carried out with high seakeeping as the research objective, and the effects of different float unit configurations on the seakeeping performance of floats were discussed. Results: Ultimately, the trimaran configuration is considered to have better seakeeping performance than the remaining configurations among the six configurations. On this basis, the bottom structure of the trimaran configuration was further optimized, and the cross-sectional shape of the bottom structure with better seakeeping performance was obtained. Conclusion: The wave resistance of the trimaran configuration was calculated to be superior compared with other configurations. The cross-sectional shape of the bottom structure of the trimaran was further analyzed. It is concluded that the trimaran structure with a bottom structure cross-section whose bottom edge is at an angle of 0° with the horizontal plane has the best wave resistance. It provides some guidance for the design of similar marine structures with high seakeeping.

Structure Integrity Analysis Using Fluid–Structure Interaction at Hydropower Bottom Outlet Discharge

Dam reliability analysis is performed to determine the structural integrity of dams and, hence, to prevent dam failure. The Chenderoh Dam structure is divided into five parts: the left bank, right bank, spillway, intake section, and bottom outlet, with each element performing standalone functions to maintain the overall Dam’s continuous operation. This study presents a numerical reliability analysis of water dam reservoir banks using fluid–structure interaction (FSI) simulation of the bottom outlet structures operated at different discharge conditions. Three-dimensional computer-aided drawings were used to view the overall Chenderoh Dam. Next, a two-way fluid–structure interaction (FSI) model was developed to explore the influence of fluid flow and structural deformation on dam systems. The FSI modeling consists of Ansys Fluent and Ansys Structural modules to consider the boundary conditions separately. The reliability and performance of the reservoir bottom outlet structure was effectively simulated and recognised using FSI. The maximum stress on the bottom outlet section is 18.4 MPa, which is lower than the yield stress of mild steel of 370 MPa. Therefore, there will be no structural failure being observed on the bottom outlet section when the butterfly valve is fully closed. With a few exceptions, the FSI models projected that bottom outlet structures would be able to run under specified conditions without structural collapse or requiring interventions due to having lower stress than the material’s yield strength.

Primjena sendvič panel sustava na 155 m barži (teglenici): konfi guracija konstrukcijskog sustava, smanjenje težine i procjena dinamičkih karakteristika

The SPS application in ship structure is an innovative breakthrough that provides an excellent strength-to-weight ratio. SPS application for new construction is crucial to ensure the proposed design has better static and dynamic behavior than conventional design. The study aims to evaluate the weight savings and dynamic characteristics of different proposed framing systems of 155 m barge due to the application of various SPS types in the deck, ship hull, and bottom structures. A total of three proposed construction systems: longitudinal, transverse, and mixed framing systems, are investigated under different plate configurations, material types, and scantling sizes. In addition, the free vibration analysis is used to evaluate the influence of damage occurrence on the structural characteristics. Several damage parameters, including damage size, location, shape, and depth, are investigated using ABAQUS software. The promising result of weight saving indicates SPS application results in about 9-13%. Moreover, the debonding assessment reveals that eigenvalue decreases with increasing debonding size, where the damaging effect in higher modes is more substantial. The stiffness loss due to debonding causes a high local deformation in the debonded area. Moreover, interfacial debonding reduces eigenvalues significantly, particularly in localized debonding shapes. It can be found that several damage parameters, including damage size, location, depth, and shape, influence the eigenvalue shifts.