Bottom Loads Research Articles

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.

Effect of Ultra-Lightweight High-Ductility Cementitious Composite in Steel–Concrete–Steel (SCS) Plate to Mitigate Ship Slamming Loads

Bottom slamming loads cause considerable local damage to a ship’s body and reduce the ship’s structural performance against harsh sea waves. Although extensive studies have worked on stiffening elements to compensate for local damage due to slamming loads, few studies have concentrated on the ship’s body itself while using new generations of composite plates. Accordingly, a numerical study is conducted to determine the effect of using ultra-lightweight high-ductility cementitious composite in steel–concrete–steel (SCS) composite plate to mitigate bottom slamming loads. A large-scale model of the ship using SCS composite plates is modelled in Abaqus software, and fluid–solid (FSI) interaction is precisely modelled using the Coupled Eulerian–Lagrangian (CEL) method. The results show that using the CEL method with a large-scale 3D model precisely simulates FSI by providing a 6.5% deviation from the experimental result. Moreover, using an SCS plate when considering ultra-lightweight high-ductility cementitious composite results in a considerable reduction (around 95%) in the maximum strain of the ship body and, accordingly, reduces local damage so that, although about 22% of the strain of the outer layer is transferred to the inner part of the ship body containing only steel plate, almost 0% stress transfer is observed for the SCS-based ship’s structure.

A Bayesian analysis for the quantification of strength model uncertainty factor of ship structures in ultimate limit state

The assessment of ship structural reliability involves the quantification of hull girder ultimate bending capacity. Traditionally, Smith’s method is employed for the probabilistic modeling of capacity. The modeling uncertainty associated with Smith’s method is considered by an independent multiplicative random variable Xr. As real-scale data from hull collapses are not available, the quantification of Xr is usually based on the combination of engineering judgment with more objective information, such as non-linear finite element analysis (NLFEA). In this paper, we propose a Bayesian analysis for the determination of Xr. Specifically, we use Bayesian statistical inference to estimate the parameters that characterize the probabilistic model of Xr based on expert judgment and a limited number of high-fidelity NLFEA data. We demonstrate the applicability of the method on container ships, for which two typical load scenarios are considered: (i) pure hogging moment and (ii) combined hogging moment with local bottom loads. For each load scenario, the corresponding Xr is determined. For cases where specific information from a target ship is available, a classical Bayesian updating scheme is proposed to adjust the distribution of Xr based on the individual ship’s structural characteristics. We present a numerical demonstration for the case of the MOL Comfort at the time of the accident. Finally, the impact of the proposed Xr on the failure probability estimate of a 4,400 TEU and a 9,400 TEU container ship is investigated. We show that using the proposed Xr the estimate of the uncertainty in Smith’s model prediction in pure hogging condition is considerably reduced. In addition, we demonstrate that the action of bottom local loads, which considerably decreases the hull girder ultimate strength and the reliability level of container ships in hogging, can be captured by the proposed Xr without any intervention in the conventional Smith method.

Three-dimensional semi-analytical solutions of arbitrary functionally graded piezoelectric doubly curved shell panel under thermo-electric load

In this article, a methodological approach for the three-dimensional (3D) static behavior of functionally graded (FG) thermo-electro-elastic doubly curved shells subjected to a thermal and electrical load is presented. A coupling procedure based on the state space, a multilayered Runge-Kutta and transfer matrix methods is elaborated for numerical solution of the 3D thermo-electro-elastic governing equations. In the thickness direction, recursive relationships using a propagator matrix are elaborated allowing to handle arbitrary functionally graded effects. A global transfer matrix is formulated permitting to investigate the effects of various types of bottom and top surface temperature loads and heat flux. Some benchmark tests are presented to validate the presented approach and to analyze the influence of the material-property gradient index, the curvature radius ratio, the span-to-thickness ratio, the temperature, normal heat flux, and the electric voltage on the mechanic, electric, and thermal variables of doubly curved shells.

Numerical Analysis of Flow-Induced Vibration of Deep-Hole Plane Steel Gate in Partial Opening Operation

Hydraulic steel gates are the core adjustment mechanism for water conservancy projects, the safety of which is related to the safety of the entire water conservancy project. In this study, the issue of flow-induced vibration under the influence of pulsing water pressure when the deep-hole plane steel gate construction is partially opened is investigated using a numerical calculation approach of CFD–CSD coupling. The time-history pulsating pressure loads of each part are first determined by tracking the upstream, bottom, and downstream pulsating water pressure loads under partially open operation conditions of the gate. The impact of the water in front of the gate on the natural vibration mode and frequency of the gate is then investigated based on the analysis of the dry/wet modes of the gate structure. Additionally, the hydrodynamic load is applied to the finite element model of the gate structure while taking into account the fluid–structure coupling effect, and the results of the gate flow-induced vibration response are obtained. Three typical local opening relative openings are chosen, with the operating state of the design water head (Hs = 70 m) of a deep-hole plane steel gate as an example. According to the analysis’s findings, the gate’s natural vibration frequency is greatly lowered under the influence of the water in front of it, and its amplitude increases by 50%. The pressure value pressing on the gate changes dynamically as it is partially opened and discharged. The maximum dynamic displacement value and the maximum dynamic stress value of the gate both appear in the middle and lower part of the gate under the condition of partial opening, and both occur when the relative opening is e/H = 0.125. The maximum displacement value is 3.43 mm, and the maximum stress value is 161 MPa. The maximum dynamic displacement and dynamic stress of each gate component steadily decrease with an increase in the relative openness. The gate dynamic response analysis approach described in this research can serve as a guide for hydraulic engineering design.

Loads and response on flexible conical and cylindrical fish cages: A numerical and experimental study based on full-scale values

This paper presents drag forces from uniform water current on two flexible net cage designs, commonly used in Norwegian fish farming, obtained through model-scale testing and numerical simulations. The primary focus is on the comparison between model tests and numerical simulations and performance of the numerical model for the different net cage designs. The two designs were a cage with a cylindrical main section with straight walls and conical bottom with a sinker tube weight system and a cage where both the main section and bottom has a conical shape. The latter cage has a central weight instead of a sinker tube. The effect of the governing parameters was explored by varying the design and loads of the weighting system. Both physical tests and numerical simulations revealed increased drag forces and reduced ability for deformation when increasing the load from the weighting system. Lower weight system load or weight system designs that allow for more deformation decrease the loads on the net cage. Although it was not a focus in the present work, fish welfare is dependent on sufficient available volume in the net cage, meaning that large reductions in volume to reduce drag forces at high current velocities may be undesirable. Comparisons between model scale tests and numerical simulations reveal good agreements for the highest weight system loads tested. Decreasing the weight system loads decrease the accuracy of the numerical simulations. This may be caused by larger deformations of the net cage when the bottom loads are reduced resulting in a larger number of net panels with small angles of attack relative to the incident current. Predictions of forces for low angles of attack may be less accurate than for larger angles of attack while there is a possibility of increased flow velocity reduction (wake effect) and flow deflection. The cages were tested and simulated for flow velocities up to 1.25 m/s (full scale value). Measurements of the flow velocity in the middle of the net cages revealed a higher velocity reduction than predicted with theory, with the exception of the highest velocity.

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads, Part 2: An extension of Smith's method

This paper is the second of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. The nonlinear finite element analysis in Part 1 has shown that local bending deformation of a double bottom due to bottom lateral loads significantly decreases the ultimate hogging strength of container ships. In this Part 2, extending Smith's method for pure bending collapse analysis of a ship's hull girder, a simplified method of progressive collapse analysis of ultimate hogging strength of container ships considering bottom local loads is developed. The double bottom is idealized as a plane grillage and the rest part of the cross section as a prismatic beam. An average stress-average strain relationship of plate/stiffened plate elements employed in Smith's method is transformed into an average stress-average plastic strain relationship, and implemented in the conventional beam finite element as a pseudo strain hardening/softening behaviors. The extended Smith's method is validated through a comparison with nonlinear finite element analysis.

О нагрузках на днище сухого дока судостроительного комплекса «Звезда» при постройке ледокола «Лидер»

О нагрузках на днище сухого дока судостроительного комплекса «Звезда» при постройке ледокола «Лидер»

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads part 1: Nonlinear finite element analysis

This paper is the first of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. In the midship part of container ships, upward bottom local loads are usually larger than the downward ones. This leads to the increase of biaxial compression in the outer bottom plating and the reduction of the ultimate hull girder strength in the hogging condition. In this Part 1, the collapse behavior and ultimate strength of container ships under combined hogging moment and bottom local loads are analyzed using nonlinear finite element method. Buckling collapse behavior of bottom stiffened panels during the progressive collapse of a hull girder is closely investigated. It has been found that major factors of the reduction of ultimate hogging strength due to bottom local loads are (1) the increase of the longitudinal compression in the outer bottom and (2) the reduction of the effectiveness of the inner bottom, which is on the tension side of local bending of the double bottom. The obtained results will be utilized in the Part 2 paper to develop a simplified method of progressive collapse analysis of container ships under combined hogging moment and bottom local loads.

Decadal effects of solid industrial wastes on the coastal environment: Gulf of Gabes (Tunisia, Southern Mediterranean Sea) as an example

The present work examines the different types of solid effluents dumped in the coastal environment from Gabes phosphate fertilizer plants, describes their coastal repartition and assesses their long-term environmental impacts. Scanning Electron Microscopy analysis of collected beach sediment samples showed that these wastes consist of phosphogypsum, fluorapatite (phosphate ore grains), smokey quartz, calcite, fluorite, calcite-Mg, apatite, pyrite, albite, sphalerite-Cd-U, fluorosilicates, sulfur dross and spent catalysts. Using fluorapatite as a mineralogical marker of the coastal spatial distribution of industrial wastes, solid effluents were found to carry bottom and/or suspended loads with a coastal transport limited at Essorrag Wadi, ∼10 km south from the industrial emissary. Phosphogypsum which is the main solid effluent was found to be completely dissolved in the seawater. The main decadal consequences of solid effluents on the coast were found to be the following: local disappearance of Posidonia oceanica seagrass, formation of an azoic benthic zone between Gabes and Ghannouche ports, gradual fattening of the beach, shoreline advancement, formation of a belt of coastal dunes, mouth clogging of coastal streams and formation of coastal lakes.

Studies on strength properties of a separable drilling milling tool

A drilling tool is the most important and highly loaded element of a drill rod which determines the efficiency of blast hole drilling. To improve the design of separable drilling tools (SDT), it is required to have complete information on the loads acting on bit elements. The stress-strain state of a separable cutting rotary bit (DRDF-244.5-2) was studied in ANSYS using finite-element modeling technology. Calculations were performed under maximum drilling machine and borehole bottom loads which were unevenly distributed. The article presents distribution results for fields of equivalent stresses occurring in the bit body, rotation axes and tooth-disk mills with double-row carbide cutting structures. The performance of bits under various operating conditions is analyzed.

Dynamic modeling and vibration suppression for an offshore wind turbine with a tuned mass damper in floating platform

The worldwide demand for renewable energy is increasing rapidly. Wind energy appears as a good solution to copy with the energy shortage situation. In recent years, offshore wind energy has become an attractive option due to the increasing development of the multitudinous offshore wind turbines. Because of the unstable vibration for the barge-type offshore wind turbine in various maritime conditions, an ameliorative method incorporating a tuned mass damper (TMD) in offshore wind turbine platform is proposed to demonstrate the improvement of the structural dynamic performance in this investigation. The Lagrange's equations are applied to establish a limited degree-of-freedom (DOF) mathematical model for the barge-type offshore wind turbine. The objective function is defined as the suppression rate of the standard deviation for the tower top deflection due to the fact that the tower top deflection is essential to the tower bottom fatigue loads, then frequency tuning method and genetic algorithm (GA) are employed respectively to obtain the globally optimum TMD design parameters using this objective function. Numerical simulations based on FAST have been carried out in typical load cases in order to evaluate the effect of the passive control system. The need to prevent the platform mass increasing obviously has become apparent due to the installation of a heavy TMD in the barge-type platform. In this case, partial ballast is substituted for the equal mass of the tuned mass damper, and then the vibration mitigation is simulated in five typical load cases. The results show that the passive control can improve the dynamic responses of the barge-type wind turbine by placing a TMD in the floating platform. Through replacing partial ballast with a uniform mass of the tuned mass damper, a significant reduction of the dynamic response is also observed in simulation results for the barge-type floating structure.

Vertical Axis Wind Turbine Design Load Cases Investigation and Comparison with Horizontal Axis Wind Turbine

The paper studies the applicability of the IEC 61400-1 ed.3, 2005 International Standard of wind turbine minimum design requirements in the case of an onshore Darrieus VAWT and compares the results of basic Design Load Cases (DLCs) with those of a 3-bladed HAWT. The study is based on aeroelastic computations using the HAWC2 aero-servo-elastic code A 2-bladed 5 MW VAWT rotor is used based on a modified version of the DeepWind rotor For the HAWT simulations the NREL 3-bladed 5 MW reference wind turbine model is utilized Various DLCs are examined including normal power production, emergency shut down and parked situations, from cut-in to cut-out and extreme wind conditions. The ultimate and 1 Hz equivalent fatigue loads of the blade root and turbine base bottom are extracted and compared in order to give an insight of the load levels between the two concepts. According to the analysis the IEC 61400-1 ed.3 can be used to a large extent with proper interpretation of the DLCs and choice of parameters such as the hub-height. In addition, the design drivers for the VAWT appear to differ from the ones of the HAWT. Normal operation results in the highest tower bottom and blade root loads for the VAWT, where parked under storm situation (DLC 6.2) and extreme operating gust (DLC 2.3) are more severe for the HAWT. Turbine base bottom and blade root edgewise fatigue loads are much higher for the VAWT compared to the HAWT. The interpretation and simulation of DLC 6.2 for the VAWT lead to blade instabilities, while extreme wind shear and extreme wind direction change are not critical in terms of loading of the VAWT structure. Finally, the extreme operating gust wind condition simulations revealed that the emerging loads depend on the combination of the rotor orientation and the time stamp that the frontal passage of gust goes through the rotor plane.

船底局部荷重を考慮したコンテナ船の縦曲げ最終強度解析に関する研究

This paper is the first of two companion papers dealing with ultimate longitudinal strength analysis of a container ship considering local loads effects. The purpose of this paper is to clarify the effect of bottom local loads on the longitudinal bending collapse behavior of a large container ship. An important problem is a bending deformation of the double bottom due to upward bottom local loads that may reduce the hull girder ultimate strength.

Low Velocity Penetration Mechanical Behaviors of Aluminum Foam Sandwich Plates at Elevated Temperature

This paper presents the low-velocity impact tests on the sandwich plates with aluminum foam core and aluminum skins at elevated temperatures. A furnace, attached to an Instron Dynatup 9250 HV drop hammer system, was designed to accomplish the penetration tests at temperatures up to 500°C. In order to process the experimental data accurately, the numerical vibration analysis was conducted to determine the threshold frequencies of the fast Fourier transform (FFT) filter for the original impact data. The experimental results showed that the failure modes of the sandwich, peak load and absorbed energy varied obviously with temperatures. Furthermore, the results showed that the failure modes of the top skin and metal foam core showed minor changes with respect to temperatures. Whereas the failure mode of the bottom skin and peak loads changed significantly with respect to temperatures. Also, the absorbed energy revealed a three-stage variation with the change of temperature.

4E1 円管内積層ガラスビーズのタッピングによる底面荷重変化に関する研究([GS]機械材料・材料加工)

4E1 円管内積層ガラスビーズのタッピングによる底面荷重変化に関する研究([GS]機械材料・材料加工)

Mechanical Response of Unbraced Wood Composite I-Joist to Walking Loads

Lateral buckling of unbraced wood composite I-joists is a form of instability that causes the joist to deflect laterally and rotate. This instability may be a cause of worker falls and should be explored to understand the range of loading and out-of-plane motion required to cause lateral buckling. While walking on unbraced joists is uncommon on construction sites, understanding the movement of unbraced joists is needed to model more commonly observed partially braced joists. This paper investigated the load and out-of-plane movement of several unbraced wood composite I-joists subjected to human walking loads. Vertical load at the ends of the joist, top and bottom horizontal loads at one end of the joist, as well as lateral deflection and rotation at the midspan and quarter-span were measured while participants traversed the joist. Lateral buckling of joists was observed due to walking loads. Total vertical load measured was similar to participant weight, while horizontal loads ranged from 9.6 to 13.7% of participant weight. Differences were observed in I-joist behavior between different lengths and manufacturers studied. Load, lateral deflection, and rotation of the joist increased as participant weight increased. Vertical load at each end, lateral deflection, and rotation were positively correlated with participant weight. A set of curves demonstrating the lateral deflection and rotation for different joists as a function of participant weight was developed.

Numerical prediction of slamming loads

It is important to include the contribution of the slamming-induced response in the structural design of large vessels with a significant bow flare. At the same time it is a challenge to develop rational tools to determine the slamming-induced loads and the prediction of their occurrence. Today it is normal practice to apply a standard sea-keeping procedure to determine the relative velocity distribution between the water surface and the hull and then to estimate the bottom slamming loads and the bow-flare slamming loads based on two-dimensional formulations similarly to water-entry problems. The pressure distribution as well as the total force is then determined by integration over a pseudo-three-dimensional presentation of the hull geometry. In this paper the evaluation of the slamming load is taken one step further by performing direct three-dimensional, fully non-linear numerical calculations in a realistic wave environment. Both the global and the local slamming loads are assessed numerically using a finite-volume formulation with the free surface captured by a volume-of-fluid technique. This numerical procedure is justified by comprehensive validation studies where numerically evaluated slamming pressures are compared with experimentally measured results. To obtain an insight into the three-dimensional flow effects the next step is to apply the validated numerical procedure to evaluate and compare the accuracy and performance of the traditionally used two-dimensional formulations by a comparison with three-dimensional numerical formulations for a fine-form Panamax container ship bow hitting a flat water surface at a constant trim angle. Finally, the slamming evaluation is carried out on the basis of a three-dimensional case study of the same container ship sailing in a head sea at half the service speed in a critical wave episode which is defined conditional on a given extreme response level of the hull girder bending moment.

Distortional buckling of overhanging monorails

Abstract This paper is concerned with the elastic lateral-distortional (LD) buckling of overhanging steel monorail I-beams and its influence on their design strengths. Distortion of a slender web reduces the elastic buckling resistance of an intermediate length beam below its flexural-torsional (FT) resistance. A finite element computer program was used to study the elastic LD buckling of overhanging monorails with bottom flange loads at the free ends. The ratio M L D / M F T of the elastic LD to FT buckling moments decreased significantly as the flange width-to-thickness ratio b f / t f decreased, but varied only slightly with the web depth-to-thickness ratio b w / t w . The value of M L D varied almost linearly with the ratio of the supported span to the overhang length, and the effect of top flange torsional restraint at the exterior support on M L D was similar to that on M F T . Distortion effects were very small when there was no torsional restraint, but they increased significantly with the torsional restraint stiffness. The full plastic moment was often reached before M L D , especially for low values of b f / t f and high values of the torsion parameter K . Conservative approximations were developed for predicting the elastic LD buckling moments for ranges of sections, slendernesses, span ratios, and torsional restraint stiffnesses. A method of designing overhanging steel monorails against LD buckling was proposed and its use demonstrated by a worked example.

Lateral–distortional buckling of monorails

This paper is concerned with the elastic lateral–distortional (LD) buckling of single span steel monorail I-beams and its influence on their design strengths. The distortion of a slender web reduces the elastic buckling resistance of an intermediate length beam below its flexural–torsional (FT) resistance. A finite element computer program was used to study the elastic LD buckling of single span beams. The LD to FT buckling moment ratios were generally higher for simply supported beams with bottom flange central concentrated loads than for uniform bending, and lower for shear centre concentrated loads. For beams with bottom flange loading and unrestrained bottom flanges, there were very significant reductions in these ratios, but they increased when rigid web stiffeners or top flange torsional restraints were provided at the supports. For beams with bottom flange loading and unrestrained bottom flanges, the reductions in the elastic buckling resistance were greater for beams with stocky flanges than for slender flanges. Approximations were found for estimating the reduced resistances which were generally of high accuracy or conservative, and for estimating the increased resistances caused by elastic and rigid top flange end torsional restraints. A method of designing steel beams against LD buckling was proposed and its use demonstrated by a worked example.