Fore End Research Articles

Причины повреждений корпусных конструкций в носовой оконечности судов

The operation of marine vessels, especially large-tonnage ones, is accompanied by the occurrence of serious damage to hull structures within bow in stormy conditions. A new mechanism to explain the catastrophic destruction of the side grillages of large-tonnage ships in the area of the bow is proposed. Simulation of the process of flow around the fore end when it is digged in a wave using SPH technology showed that when the flow speeds around the fore end occur when the vessel moves in developed waves, there is a sharp drop in pressure in certain areas of the bow end. This circumstance can lead to the occurrence of cavitation that is confirmed by modeling the process of flow around the fore end using ANSYS FLUENT software. During stall cavitation, a cavitation cavern of considerable size may arise, the collapse of which is accompanied by the occurrence of hydrodynamic loads that can destroy hull structures. A calculation method is proposed that allows one to estimate the magnitude of hydrodynamic loads acting on the ship’s hull during the collapse of a cavitation cavern. To prevent damage to the bow in storm conditions, a number of constructive measures have been proposed. One of the options for solving the problem is to install a deck fairing in the bow that eliminates the negative influence of structural cavitators in the traditional design when the bow is digged in the wave. It is also possible to install a compressed air supply system to those areas of the bow where vacuum occurs when a liquid flows around when digged in a wave.

Wake bi-modality: the effect of upstream boundary layer dynamics

The turbulent wake past a square-back Ahmed body in close proximity to the ground experiences random side-to-side switching between two asymmetric positions, a phenomenon known as bi-modality. It has been observed to be sensitive to the dynamics of the upstream boundary layers formed along the body surfaces. Close to the body fore end, these separate and reattach, with hairpin vortices emanating from the reattachment points and growing along the surfaces before breaking down upstream of the base. This study uses wall-resolved large eddy simulations to investigate the effect of using suction to suppress these upstream boundary layer separations on the wake bi-modality. It is seen that, in the unforced flow (in the absence of suction), the smaller top and side surface vortices resulting from breakdown interact as they convect downstream. Steady suction is confirmed to suppress the boundary layer separations on the different body surfaces. When the boundary layer separations on the two side (vertical) surfaces are suppressed, it is found that horizontal bi-modality is completely inhibited with weak vertical asymmetry preserved. The interaction of the small top/side surface vortices is interrupted, damping boundary layer fluctuations just upstream of the base. Applying suction on different combinations of side/top/bottom boundary layer separations is found to have different effects on the underbody flow and the wake vertical balance, with bi-modality suppression dependent on side surface suction. This confirms that bi-modality is triggered, at least in part, by boundary layer disturbances on the surfaces perpendicular to the switching direction.

Effect of bow hull form on the buckling strength assessment of the corner bracket connection

The aim of the paper is to study the influence on the structural strength assessment, in terms of fore end weight, in the conversion process from a conventional to an inverted bow hull of a platform supply vessel under bow flare impact loads. Linear and elastic buckling analyses of the corner bracket connection (deck beam with web frame) located in the fore body are obtained from modifications to its geometry and the inclusion of different stiffening methods. A series of numerical and experimental analyses are undertaken with the design and construction of a new auxiliary structure. The most effective combination (bracket geometry and stiffening method) is established and alternative geometries that optimize the local weight of the corner bracket are proposed by means of topology optimization, obtaining an innovative bracket geometry (omega bracket) that minimises weight while maintaining constant buckling strength. The results obtained establish useful and valuable design criteria that save material and weight to the ship's structure.

Hybrid Rocket Nozzle Erosion with Microaluminum-Added Fuel

Because of its relatively low cost and wide availability, carbon graphite is one of the most widely used ablative nozzle materials in hybrid rocket propulsion. The erosion characteristics of the nozzle material have paramount importance because it directly influences the performance. This is especially the case for upper-stage or in-space rocket motors operating with very long burn times. In this study, the effect of aluminum-added fuel on the graphite nozzle erosion is studied. In the experimental studies, a high regression rate paraffin-based fuel is loaded with micrometer-size aluminum powder for nozzle erosion reduction. In our approach, aluminum is added at high concentrations as a fuel ring in front of the main paraffin-based fuel which contains no aluminum. Based on the motor tests conducted with gaseous oxygen as an oxidizer, it is shown that aluminum addition decreased the nozzle erosion rate up to 45% and increased the nozzle erosion onset time by 1 to . The new method of introducing an energetic powder in a fuel ring positioned at the fore end of the motor offers an easy and scalable way of reducing the nozzle erosion and improving the performance of the rocket motor.

Experimental study on water entry of inclined circular cylinders with horizontal velocities

The complex impact cavities and motion behaviours of water entry by a multi-degree-of-freedom motion cylinder are investigated experimentally for different initial horizontal velocities and inclined angles. The cylinder is released above the free surface with controlled component velocities and inclined angles by a newly designed mechanism. A high-speed photography technique is employed to reveal the unique cavity flow phenomena that vary with horizontal velocity and inclined angle and to record the corresponding position of the cylinder in water. The cavity dynamics, including the initial jet, open cavity, surface seal, cavity break, break jet, side cavity and pinch-off, are investigated for different initial impact conditions. Moreover, the effects of horizontal velocity, inclined angle and angle of attack on the motion characteristics are studied. The experimental results demonstrate a special cavity flow phenomenon, a suction airchannel, that is due to the closure of the splash dome prior to the growth of the cavity volume. For cases of violent cavity break, a water wedge is formed as the break jet penetrates into the fore end cavity. The hydrodynamics of impact force, pressure drop and spin-induced lift acting on the descending cylinder cause obvious curvature in the trajectory. In particular, when the absolute value of the angle of attack is greater than 22°, a circuitous phenomenon is found, and the inclined angle decreases rapidly as the cylinder descends.

Effect of Material Mismatch on Static behavior of Flex Seal

A flex seal in a rocket nozzle provides required flexibility for smooth functioning of directional change of the rocket and acts as a pressure tight seal to prevent hot gases from the rocket motor. Flex seal consists of four different components, i) Elastomeric pads, ii) shims, iii) fore end ring and iv) aft end ring. Elastomeric pads are made of hyper elastic material like rubber to provide required flexibility in the system. Shims are made of either metals are composite materials to provides required stiffness to the flex seal. Fore end and Aft end rings are connected to the flex nozzle system and motor respectively. The objective of present work is to study the effect of mismatch in materials of shim and elastomeric pads. In the analysis, ground test conditions of flex seal system are simulated using 2D finite element models. From the analysis it is observed that there is no influence of the Poisson's ratio mismatch. Reduction in deflection and increase in stresses is observed with increase Young‘s modulus mismatch, which is varied by changing the Young‘s modulus of shims.

Design and Analysis of a Slanted Strapon Nose Cone (SSNC) of an Advanced Launch Vehicle

Launch vehicles are used to transport satellite or space craft into space. To minimize the aero acoustic and aerodynamic loads, the nose cones are slanted to an angle on free side and straight on the interference side in advanced launch vehicles. Objective of this paper is to design and analyze nose cone region of a typical launch vehicle using integrally stiffened panel concept, made of aluminium alloy material. The first part of the present work is to make the optimum design of a slanted SNC structure and the second is to verify the detailed design through finite element method. Linear static stress analysis, buckling analysis and free vibration analysis of the finalized design is carried out using finite element analysis software NISA. Aerodynamic pressure distribution over the surface is generated using computational fluid dynamic analysis code PARAS 3D. Static, dynamic and buckling analysis results are presented here. Optimum design based on the integrally stiffened panel construction is compared with the design by combination of stiffened skin with bulkheads and isogrid type of construction. 0 on the free side and straight on the interference side are selected based on various studies. The change in pressure rise on core will be more for slanted nose cone. But the zone of influence is more in regular nose cones. Appreciable weight savings are possible through the integral section design which also develops high resistance to buckling loads. This method improved performance through smoother exterior surfaces by reduction in number of attachments and non- buckling characteristics of skin. Design of structural components has to meet specific requirements which influence the complexity of its structure and the materials used in its construction. Aluminium, blended with small quantities of other metals is used on most types of aircraft because it is lightweight and strong. AA2014 aluminium alloy is an aluminium-based alloy often used in the aerospace industry.(1) It is easily machined in certain tempers, and among the strongest available aluminium alloys, as well as having high hardness. II. Slanted Strapon Nose Cone Configuration The non-dimensional parameters of the SSNC selected for the present study is described here. The base diameter D is selected as reference dimension for this configuration. Aft End (AE) ring is a cylindrical structure with inclined top surface and tangential to the conical section. Nose cone is a truncated cone with non-parallel top and bottom surfaces also tangential to the nose cap and AE ring at all interfacing location. SSNC having an overall height of 1.68D and fore end of the cone is covered by a spherical cap of radius 0.23D. The AE ring has a height of 0.25D at straight side and 0.36D on the other side due to the slanted configuration as shown in Fig. 1(a).

数値解析による踏切衝突事故の検証（鉄道車両の衝突安全性評価の研究）

A railway collision at a level crossing of the Hakodate line of JR Hokkaido occurred on January 29, 2010. The details of this accident can be obtained in the railway accident investigation report published by the Japan Transport Safety Board. Based on this railway accident investigation report, numerical simulations of the level crossing collision were conducted in order to investigate a correlation between the injury rate of passengers and the deceleration history during collision. New modeling methodologies and initial conditions derived from accident details were adopted and also in order to obtain accuracy of numerical simulations, analysis models of the cab end structure and the interface structure between cars in the train were validated by quasi-static compression tests. Since the numerical simulation shows good correlation in the deformations of the cab structure and a situation of scattered parts of the railway obstacle, this paper finally demonstrates the deceleration history of each car body of the relevant train set in the level crossing collision. In regards to the maximum value of the integration of the deceleration history: MID, it was found that 7.4m/s occurs at the leading car, which had the most injuries, and it appears that exceeding 4m/s results in increase of rate of injuries above 50%. Regarding injury parameters, values at forward facing seats are lower than the half of the criteria of FMVSS208 but values at the seat of the fore end of the cabin exceed the criteria. It is estimated that injury parameters at the seat of the fore end of the cabin are within the criteria if MID is kept under 6m/s.

Failure analysis of a vibration isolator used in launch vehicle applications

Vibration isolators are used in launch vehicles to protect sensitive electronic equipments from the rigors of flight structural vibrations during the lift-off and ascent phase. Failure of one such vibration isolator made of AISI 304 is reported in the present study after ground level testing has been completed. The vibration isolator had a crack of length approximately 42mm at the fore end corner. Detailed optical and scanning electron microscopy was conducted on the failed vibration isolator to understand the reasons for cracking. Finally, it was concluded that micro cracks formed during the deep drawing operation (due to large strains at the fore end corner) propagated during vibration testing resulting in the failure of the body of the vibration isolator.

An experimental study of machining characteristics and tool wear in the diamond wire sawing of granite

A diamond wire sawing process was developed for slicing granite in order to complement the disk sawing. Machining characteristics and tool wear during wire sawing of a granite material that consists of three major minerals, that is, quartz, feldspar and mica, were systematically investigated. The material removal mechanism involved in the sawing was explored. The scanning electron microscope examination of the sawn surfaces of the granite and the analysis of the force and temperature involved in the sawing process indicated that the material removal of the granite was dominated by brittle fracture. The typical cleaving and slipping behaviors of feldspar and mica associated with sawing resulted in unique morphologies on the sawn granite surfaces. The tool wear of the process was characterized by the nonuniform wear of diamond beads impregnated on the wire, with the fore end of the diamond beads experiencing greater wear than the rear part.

複合荷重下における船体梁の縦曲げ最終強度に関する研究

It is necessary to make clear the effect of torsional moment on the ultimate strength of the ships' hull girder for the accurate assessment of that of ultra large container ships with large deck openings. In the present study, the extension of the simplified method of progressive collapse analysis based on Smith’s method is attempted to the case of combined loading condition. Firstly, progressive collapse tests are carried out on 1/13-scale three-hold hull girder models referring to a Post-Panamax container ship. The models are fixed to the rigid wall at the aft end and a couple of forces are applied to the fore end so as to generate torsional and vertical bending moment simultaneously. The progressive collapse tests are conducted for the case of the various combinations of torsional and bending moment. The nonlinear finite element analyses by LS-DYNA are executed in accordance with the test conditions. From the test and calculation results, the progressive collapse behavior and the ultimate strength of hull girder models under combined loading are examined. The results will be a basis for the verification of a new simplified analysis method which will be presented in the forthcoming reports.

Theoretical and Simulative Study on Hydraulic Bridge of Water Hydraulic Servo Valve

An analysis has been conducted on the hydraulic bridge of the water hydraulic servo valve with annular clearance between sleeve and spool land as its first hydraulic resistance. Through some formula deductions, the simplified hydraulic bridge is drawn and the relationship between flapper displacement and differential pressure of spool ends, which is demonstrated by the subsequent simulation works, is extracted. By the CFD(computational fluid dynamics) simulation, firstly, the pressure distributions of the flapper face and the fore end face of the nozzle are obtained. Results show that the flapper has an annular area where the existing pressure is negative. Secondly, the relationship between flapper displacement and flow force acting on flapper is also acquired, which is much beneficial to the steady-state and dynamic analysis of the water hydraulic servo valve.

URANS and DES analysis for a Wigley hull at extreme drift angles

Vortical structures and associated instabilities for flows around the Wigley hull for a wide range of drift angles (10° ≤ α ≤ 60°) with free surface are identified and analyzed. Quantitative verification and validation are conducted on three systematically refined grids with comparison to the experimental data for α = 10°. Analysis of the flow pattern shows a strong correlation between the vortical structures and free-surface wave elevation. For α = 10° and 30°, the flows remain steady and vortices are generated at the keel and fore and aft perpendiculars of the hull. The strength and complexity of these vortices increase with increasing α. At α = 45°, flow becomes unsteady without any significant change in the main flow pattern. At α = 60°, a complex and unsteady flow field on the leeward side of the hull is formed with a large recirculation region from the aft to the fore end, which prevents the flow coming from below the keel from moving up and generating the keel vortices observed at lower drift angles. Karman-like and helical instabilities are analyzed. The effect of Froude number is more apparent for large than for small drift angles.

Use of a 3D compartment model for simplified full ship FE model. Part II: validation of the simplified FE model

This is Part II in a series of papers. Part I (J Mar Sci Technol 13:154–163) deals with an approach employed to construct a simplified FE model using a 3D compartment model available from the beginning of the ship design process. This paper begins by describing the limitations of an analytical approach based on shear warping beam theory for assessing torsional strength. Next, the structural parts of a container ship that have a negligible effect on hull girder bending strength and torsional strength are determined. This is verified by removing these parts from a conventional FE model and comparing the results obtained using this modified model with those yielded by the original model. The fore end part, the aft end part and the deck house are examined. Since these parts have complicated structures and relevant drawings for them are issued later than cargo structure drawings, modeling them exactly can result in a delay in the completion of the full ship FE model. This paper also verifies the validity of the simplified FE model built by applying the method proposed in Part I and comparing the results obtained with it with those given by a conventional full ship FE model. The stresses on hatch coaming top, the maximum diagonal elongations of the hatch coaming, and the maximum hatch corner movements are evaluated to check the validity of the simplified model.

Fishing lure with sound attraction

A fishing lure is disclosed having a body with two sections that move relative to one another. An aft section is connected via a shaft to a fore section and is slidable toward and away from the aft section along the shaft as the lure is pulled through the water. A contact post mounted on a rear end of the fore section or a fore end of the rear section impacts the other section as the lure is pulled through the water producing a clicking or popping sound which attracts fish.

荒天向波中における船首船橋船の安全運航の判断基準に関する研究 : 打ち込み水による船橋窓ガラスの破損

The wheel house front glass of a fore-bridge-ship was broken by the shipping of water in rough sea. This breakage of the front glass is incredible because the front glass was in 20(m) above the water surface. In order to analyze the reason of the accident and to avoid similar problems, we demonstrated a flow mechanism causing the strongly rising water flow to the wheelhouse, and then suggested a formula to estimate the rising flow velocity through water tank experiments (1) (2). In this paper, we study experimentally the characteristics of the crash impact water-pressure by using freely falling water mass, and then analyze the breakage condition of the wheelhouse front glass by comparing the above impact water-pressure with the maximum allowable pressure of the designed front glass. In addition a criterion for the breakage avoidance of a wheelhouse front glass is considered from the height of the shipping water level at the fore end over the bow deck. The results are summarized as follows : (1) The non-dimensional coefficient C_<pi> of the impact water-pressure was about 2.8 in the case of the crash angle φ being φ=90°. (2) The characteristics of C_<pi> for φ was able to describe as sin^<10> φ approximately. (3) The breakage of the front glass may occur under the condition that the shipping water level at the fore end reaches to about 2(m) over the bow deck. (4) The above water level would be a useful information for navigator to avoid the breakage of the front glass, because the information can be recognized easily.

Catheter type ultrasound probe

A catheter type ultrasound probe having an elongated flexible catheter and a controller for a rotational driver for the ultrasound transducer on the catheter member. The device includes a flexible sheathing tube closed at the fore end, a rotatable support member located in a tip end portion of the sheathing tube, an ultrasound transducer mounted on the rotatable support member and a flexible transmission shaft including at least a transmission coil having a series of intimately contacting helices. The flexible transmission shaft extends through the sheathing tube and is connected at the fore end to the rotatable support member. A rotational shaft is coupled to the other end of the flexible transmission shaft and is rotationally driven from the rotational driver on the controller. A pair of fore and rear stoppers located in the fore and rear end portions of the catheter retain the flexible transmission shaft in a tensioned state between predetermined head and tail end positions.

Bulk Carrier Safety

During the past ten years, more than 700 crewmen have died as a result of Bulk Carrier casualties. Following a rash of 25 Bulk Carrier losses in 1990 and 1991, The American Bureau of Shipping (ABS), The International Association of Classification Societies (IACS), and various other segments of the marine industry initiated measures in an attempt to correct this situation. During the next several years another 11 Bulk Carrier losses (resulting in the death of 174 crewmen), indicated that these measures, although improving the situation, did not go far enough to solve the problem. A close examination of the vessels involved indicated that the overwhelming majority of the bulk carriers were in excess of 15 years old. While inadequate maintenance and improper loading have been likely contributory factors, it is apparent that present BulkCarrier designs have not matched expectations as these vessels age. At ABS a study to investigate the response of the Bulk Carrier hull structure was undertaken in an attempt to understand the causes of the structural weaknesses which may have contributed to these losses. In applying a first principles approach of using representative and realistic dynamic loads, the critical areas, including hold frames and end brackets, corrugated transverse bulkheads, cross deck structures and fore end structures were studied. This study resulted in the development of a new complete, flexible, and integrated strength criteria for design and assessment of Bulk Carrier hull structures. The approach encompasses:the loading criteria,the strength criteria for minimum scantling requirements, andthe strength assessment procedures incorporating failure criteria dealing with material yielding, buckling/ultimate strength and fatigue. In this paper, an overview of this new strength standard is presented and the procedures to rectify problem areas unique to bulk carriers are discussed.

A spacecraft for the Earth observing system

The space segment of NASA's Earth observing system (EOS) includes three series of intermediate-sized spacecraft, plus two smaller spacecraft. The EOS-AM spacecraft is the first of the intermediate-sized spacecraft. EOS-AM accommodates sensors that measure cloud and aerosol radiative properties, and that provide data to study the water and energy cycles. Scheduled for launch in the late 1990s, the EOS-AM spacecraft is designed for a 5-year mission. The spacecraft will be launched from the Western Space and Missile Center (California) into a polar, Sun-synchronous, low-Earth orbit with a 16-day repeat cycle. In its flight configuration, the spacecraft is almost 20 ft long (including instruments mounted at the fore end of the spacecraft) and 6 ft wide (in its widest dimension), has a mass of about 13,000 Ibs and uses about 3000 W of electrical power. The spacecraft is compatible with the Atlas IIAS launch vehicle. EOS-AM has on-board storage for at least two orbits of science data. These data will be transmitted to the ground via the tracking and data relay satellite system (using data structures and protocols in compliance with the recommendations of the Consultative Committee for Space Data Systems). A direct downlink system to support distributed users will also be available.

Mouvements des mâchoires pharyngiennes pendant la prise de nourriture chez le Serranus scriba (Linné, 1758) (Pisces, Serranidae)

According to the morphology of its pharyngeal jaw apparatus, Serranus scriba can be considered as an intermediate type within the Acanthopterygians. The lower jaws are united only at their fore end. The upper pharyngeal jaws do not articulate with the skull base. Each of them consists of pharyngobranchials 2 and 3 (the latter being well developed), bearing a tooth plate, and of one posterior tooth plate, associated with two smaller tooth plates supported by epibranchials 2 and 3. The branchial musculature is of a generalized perciform type. Muscle activity generates variable cyclic movements of the pharyngeal jaws for transporting prey from the buccal cavity to the oesophagus, in cases where the prey is provided with a shell or a cuticle. Masticatory movements are not stereotyped as in more specialized fishes such as Labridae. Prey transport is more efficient when the upper and lower pharyngeal jaws retract together, either in complete synchrony or with a phase shift. This is often accompanied by downward movements of the upper jaws. The amplitude of movements of the components of the upper pharyngeal jaw may vary within one cycle. For instance, pharyngobranchial 2 could be drawn more forward, while pharyngobranchial 3 could be drawn more backward and the posterior tooth plate could move up and down independently. These movements can be induced passively by the interactions with the prey and (or) eventually by specific muscular activity as well. Stereotyped movements of other species probably allow them to meet only the requirements of a specialized diet. In contrast, the flexibility of this movement pattern allows S. scriba to explore a wider range of food types.