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ABSTRACT: The displacement and the stress of marine gate valves were analyzed by FEM to investigate the possibility of design improvement such as weight reduction. As a result, it was clarified that the proper ribs on the body can reduce the displacement as much as 60 %, and redesigning the shape of the bonnet flange also leads to reduce the displacement. The body weight could also be reduced about 10 % by changing its thickness on the basis of safety factor 8. 1 INTRODUCTION New standard rules for many marine devices have been proposed recently by ISO (International Organization for Standardization). The Japanese government and manufacturers of marine valves also have coped with the new trend, and consideration should soon be given to the standardization of the valves to be applied to ISO rule. There are some problems to be solved, however, before marine valves are properly designed according to the new proposed standard instead of current rule ) called as JIS (Japanese Industrial Standards) Because one of the differences between JIS-type valves and ISO-type valves is the flange distance. In case of the valve of nominal pressure 10 kgf/cm and nominal diameter 200 mm, the distance of JIS-type valve is 320 mm and that of ISO-type valve is 292 mm. If the distance of JIS-type valves is changed in accordance with ISO rule, the valve body must be made longer in the vertical line so that the pipe flange touches the bonnet flange. The stretched valve body might make their stiffness weak. Up to now, a few reports 2)3) concerning analysis of the valves have been published. And marine valves have been designed based on the plate theory4)-&) and it is hoped that the valves are made basing on a suitable design.
ABSTRACT: The discrete element method has been applied successfully to the elastic analysis of a wide variety of highly non-linear problems in structures under conditions of gross deformations. For certain types of frame it has been found possible to program this method of second-order analysis and account satisfactorily for large deformations so that one can produce solutions satisfying equilibrium and compatibility almost anywhere in the load-deformation field. The method was first applied by the author to suspension cables and inflatable dams which are structures for which a linearelastic analysis is inappropriate if not meaningless. It was later extended to deal with flexurally stiff elements and it subsequently provided some interesting insights into the nature of equilibrium bifurcation states for symmetrically loaded arches, rings and portal frames. The problem with the method is that it is difficult to generalise it so that the one program will handle a wide range of structural forms as is the case with frame stiffness programs and finite element packages. Thus far, the discrete element method has been successful in applications to frames forming a single closed loop such as beams and beam-columns, rings, arches and portal frames. The paper concludes with a description of attempts to extend the method to multi-storey and multi-bay frameworks. INTRODUCTION The forms of structure devised by designers have often been determined by the available analytical methods. But the various methods of structural analysis have been difficult to classify. One can think of the material behaviour and refer to plastic as compared with elastic methods. Alternatively one may consider the nature of the deformations occurring in the structure under real or ultimate loading conditions. The deformations may be small, finite or large. Some structures may be very stiff and deform very little under normal conditions.
ABSTRACT: Load carrying capacity of a tubular member with a circumferential through-thickness crack is investigated. A series of pure bending tests is carried out. Based on the experimental results. a generation phase analysis is performed with the finite element method. in which both material and geometrical non-linearities are taken into account. Application phase analyses are also performed employing the J-integral and the Crack Opening Angle (COA) as parameters which rule the initiation and the continuation of a crack growth respectively. It has been found that a higher ultimate strength may be attained with higher critical values of J-Integral and COA and the decrease in load carrying capacity is strongly affected by the critical value of COA. INTRODUCTION Many types of offshore structures have been built and in service to get seabed resources such as petroleum and natural gas. However, the connections of tubular members sometimes experience a fatigue damage due to small welding defects, large strain concentrations and cyclic wave loads. The denting damages caused by supply boat collisions or object fallings from a platform deck may also act as a crack initiator because of the large strain concentration at the bottom of the dent. In general, a material with sufficient ductility is used for legs and bracing members in offshore structures and the initiation of a crack does not lead to the immediate breaking of the cracked member. However, a crack usually grows under cyclic wave loads, and a plastic collapse or an abrupt breaking of a cracked member may occur when the structure is exposed to severe sea condition. The collapse of a cracked member may further cause that of other intact members because of the redistribution of internal forces, which may finally lead to an overall collapse of the structure.
- Well Completion > Hydraulic Fracturing (0.47)
- Well Drilling (0.34)
ABSTRACT: Presented is the numerical method algorithm of jacket type offshore stationary platforms dynamic calculation for the effect of two-dimensional random waves of finite, heights described by different spectra. Numerical research of single- and multilegged structures of different pliability with various diameters supports station and dynamic reactions under the action of random waves are cited. It is shown that structures dynamic reactions do not practically depend on wave spectrum type; probability of exceeding functions reactions mainly depending on wave load velocity and inertial components relation, structure pliability and its length along wave ray. INTRODUCTION Nowadays known are analytic methods of dynamic offshore structure calculation for random wave effect based on linear spectral wave theory and wave load linearization /1 2/. The limited use of these methods results in impossibility to define correctly distribution (probability of exceeding) functions of structures reactions. Well-defined theoretical solutions of offshore structures dynamic calculations for random wave of finite height are absent. This is explained by the difficulty of considering such factors as wave load non-linearity, wetted height variation of structure supports in time and space, structure length. To overcome these difficulties method of dynamic numerical calculation of deep water stationary jacket-type platforms under the action of two-dimensional random waves of finite height was developed. In wave load calculation the real three dimensional structure is replaced by a system of vertical supports of different diameters ("package of supports"), the wave load of which is equal to that of real structure. In dynamic calculation the structure design scheme is considered as linear damping system of single approximable leg rigidly fixed to the bottom. Distributed along the leg mass m is assumed constant and is equal to the sum of distributed mass of platform structure and added water mass.
ABSTRACT: Numerical study on near wake flows of a flat plate in three lands of oncoming flow is made using discrete vortex model and some improved techniques. For steady oncoming flow, the gross and detailed features are calculated and discussed. For harmonic oscillatory oncoming flow the different wake flow patterns are obtained for KC=2, 4 and 10. Our results for low KC numbers present a new wake flow pattern describing a new mode of vortex shedding, pairing and moving. The calculated drag and inertia force coefficients are closer to experimental data from U- tube than the previous results of vortex simulation. For in- line combined oncoming flow the vortex lock- In and dynamic characteristics are Simulated and compare well with experiments. INTRODUCTION The discrete vortex simulation of flow over a plate in Uniform oncoming flow has been well studied and reviewed by many Investigators. In the simulation the vorticity creation technique has been a major concern which has been provided by MVP (Sarpkaya, 1975), MFP (Klya et ai, 1977), and other approach (Chein et ai, 1988). The gross features of the flow field such as the vortex shedding frequency, the drag coefficients and the vorticity shedding rate predicted in their studies are In fair agreement with experimental measurements. The discrete vortex calculations of the detailed features of the near wake, such as the velocity profiles, the turbulent intensities and Reynolds stress were also performed by Klya et al (1982) and Chein et al (1988), and some predictions are compared With experimental data. Concerning the near wake flows of a flat plate In unsteady oncoming flows, Graham (1979,1985) and other investigators have applied different vortex models to study the near wake flow of the plate in harmonic oscillatory flows.
ABSTRACT: In this study estimation of extreme sea level from observational data is attempted. Type III asymptotic distribution is employed to achieve that purpose. Application of type III asymptotic distribution to the data requires the determination of distribution parameters. A nonlinear regression method, a skewness method, a maximum likelihood method, and a multinomial discretization method are used to evaluate the parameters. Ochi proposed modified type III asymptotic distribution based on the nonlinear multiple regression method. In the present study the authors applied that scheme to the above mentioned 4 methods. The results show good agreements with the observed data. 1. Introduction Extreme values from observational data are the information of special importance in several areas of engineering applications. In the field of ocean engineering, wave height is main factor to be considered for various design purposes. This paper discusses the methods of statistical estimation of extreme significant wave height which may be encountered for a certain return period. Gumbel(1958) had classified the asymptotic distributions of the extremes as the type I, II, and III asymptotic forms. Ochi(1986) has shown that the type I distribution may yield an increasingly overestimation of the extreme value with increasing variate values. In this study Type III asymptotic distribution is intensively applied to observational data. Estimation methods of distribution parameters must be follow up subjects in extreme value theory. These are the maximum likelihood method, the skewness method, and the nonlinear regression method. In this study, the multinomial discretization method is newly employed in the field of extreme sea level estimation. The calculations using these methods do not give satisfactory results. Ochi(1986) proposed a newly developed modified type III asymptotic extreme value distribution which yields an excellent fit over the entire variate range of the cumulative distribution.
ABSTRACT: This paper analyzes the results of the theoritical studies of the spirally re1nforced compos1te mater1als oota1ned by using a new model of calculation of the behavior of the material unter two types of conditions:auxiliary layer and inner part of the structural element are Isotropic. auxiliary and inner part of layer is orthotropic the element is transversally isotropic. The paper gives on est1mat1on of the influence of the layer properties on the compos1te" s state of strain as well as the calculation of carbon reinforced epoxy-bended plastic conducted for the case of planar state of stress by specially developed computer programme. The requirements to be satisfied by the composite materials have to correspond to the types of the pasts of constructions for Which they are produced. It 1S not rear that such requirements demand new types of composites for Which theoretical and experimental studies would have to be conducted in order to obtain materials with optimal caracteristiques. This paper considers the influence of auxiliary layer composite materials created on the basis of spirally wound reinforcing filling agents. Elementary structural unit of spirally reinforced material is obtained by disposition on the surface of the main reinforcing filling agent an intermediate layer formed of fibrous filaments. dimensions of winding, and characteristics of which differ from those of the main filling argent. Microstructural studies of the composite have assessed as in works [8.9] that the disposition of structural units in material is hexgonal and the main reinforcing filling agent (zone 2.,) is an infinite cylinder of a circular cross section the generating line of which is perpendicular to the plane xOy the lntermediate layer (zone 1) has a form of a void cylinder and a matrix (zone 2) represents an lsotropic body.
Seasonal Variability Of Physical-Mechanical Characteristics Of Sea Ice
Gavrilo, V.P. (Arctic and Antarctic Research Institute) | Lebedev, G.A. (Arctic and Antarctic Research Institute) | Fedotov, V.I. (Arctic and Antarctic Research Institute) | Cherepanov, N.V. (Arctic and Antarctic Research Institute)
ABSTRACT: A numerical analysis of seasonal variability of the Young" s modulus E and ice flexural strength 6f is given on the basis of theoretical and experimental data, obtained in recent years. The calculations are made for 6 sea ice age gradations:10-30cm, 70-120 cm, 120-200 cm, 200-300 cm and > 300 cm. The effect of volumetric ice porosity (concentrations of salt inclusions) on seasonal variability of the Young" s modulus is shown and a comparison of calculated and experimental data is given. The data of seasonal variations of 6j calculated according to different methods is presented. INTRODUCTION On the basis of these dependences one can in principal estimate seasonal variability of physical ice values, characterizing its behavior under load, including for example, the ice cover bearing capacity. Taking into account the increasing demands of engineering activity (which is connected with the organization of transportation under winter conditions and exploration of hydrocarbon resources in the Arctic shelf area, etc) we believe it is necessary on the basis of generalized data of theoretical and experimental studies of ice physical- mechanical properties, which have been collected in recent years to make a numerical analysis (and if there are sufficient observation series, a probabilistic analysis) of seasonal variability of some sea ice characteristics. Also it is desirable to condict the analysis in conjunction with the ice types (or its age gradations) in accordance with some commonly used ice classification and/or WMO Sea Ice Nomenclature so as after that to make a probabilistic estimation of ice physical-mechanical properties in specific areas, issuing corresponding maps. THE YOUNG" S MODULUS EXPERIMENTAL AND CALCULATED DATA To estimate seasonal variability of the Young" s modulus, let us use experimental and calculated data, characterizing particular dependences of this elasticity characteristics on both internal parameters and ice properties and external conditions.
- Asia (0.68)
- North America > Canada (0.46)
- Europe > Russia (0.28)
ABSTRACT: An efficient method for computation of responses of cable - ROV system as a result of forces from waves and current and/or thrust of ROV is presented. Analyses are performed for the model consisting of series of links connected to each other by ball-and-socket joint representing the tethered cable and ROV, subjected to gravity and buoyancy and drag forces induced by the relative motion of the cable with wave and current. For the analysis, a computer program is developed. The program is capable of solving dynamic behavior of a nonlinear, three-dimensional, finite segment model of a submerged multi-component cable with ROV. Two different integration algorithms, i.e., Houbolt method and Newmark method are incorporated respectively, with the lumped mass method originally developed by Walton and Polachek in 1959 in the program. The time histories of dynamic tension and/or behavior of a tether cable under hydrodynamic loading, tension excitations caused by surface vessel and the thrust of ROV system are easily predicted. The present Finite Difference scheme is believed to have practical application potentials for engineers since the procedure is concise and computing time is relatively small comparing with Finite Element Method approach. For typical - ROV systems, the two methods are employed for the dynamic analysis and the results are compared. Also several examples are presented to show the reliable performance of the scheme with the comparison of experiments with relatively good agreement. INTRODUCTION ROV is the new technology equipment being made to replace manned systems, both manned submersibles and divers. Principal task of ROV is to freely travel and steadily approach to an object in aqua-space and transmit video information of it to water surface by using tether cable, since electro-magnetic wave cannot be utilized in water, although it is very powerful means on land and the aero-apace.
ABSTRACT: This work deals with the types of nonlinearities of the sea bed ground, those arising in offshore pile activities. The iteration methods of nonlinear ground computer calculation were proposed. The modification of Murzenko" s model (1966) was given with the account of plastic strenthening-disstrenthening and. dilatation. This nonlinear-elastic approach is an effective one in solving the problems when offshore platforms" and port facilities" design takes large pile displacements into an account. The results of calculations of test experiments showed a satisfactory convergence. INTRODUCTION Steel tube pile foundations are widely used for port hydro technical construction and for shelf platform erections for oil-gas extraction. The piles accept considerable horizontal loads from its upper part exerted by waves and ice. Calculation and pile foundation design techniques are highly requires because of the high costs and reliability of offshore structures. Lengthy piles and complex variable geological conditions give rise to a set of nonlinear factors affecting "the pile-ground" system interaction. It" s very important to take into account the pile disconnection and its sliding along the ground, pile spatial work along with formations of diverse stress states, pile group effect, in the ground. The paper presented describes the techniques of ground rigidity calculations required for pile evaluation accounting physical and geometrical nonlinearities. The techniques developed afford to combine the calculations of "the upper structure - pile group - ground". NONLINEAR ELASTIC APPROACH FOR MEDIA WITH LARGE DEFORMATION At large pile displacements an immence deformation is developing in the ground, and the hypothesis accepted small deformations becomes untrue. Here it is used the non-linearelastic approach based on nonlinear dependence between stresses and strains taken to be common in all points in the ground rook. Elastic and non-elastic deformations are not divided and empiric "stress - elastic-plastic deformation" relationship is used.