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1.
TANGLi-qiang ZHENGGui CAIYan-hong 《船舶与海洋工程学报》2004,3(2):73-78
A mechanical model of visco-elastic material is established in order to investigate viscous effect in dynamic growing crack-tip field of mode Ⅱ. It is shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity, namely, (σε) ∝r^-1/(n-1). The asymptotic solutions of separatied variables of stress, stain and displacement in crack-tip field are obtained by asymptotic analysis, and the results of numerical value of stress and strain in crack-tip field are obtained by shooting method. Through numerical calculation, it is shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. By the asymptotic analysis to the crack-tip field, the fracture criterion of mode Ⅱ dynamic growing crack of visco-elastic materials is put forward from the point of view of strain. 相似文献
2.
为了研究船用工程复合材料的界面裂纹特性,建立了刚性-压力敏感粘弹塑性材料Ⅰ型准静态扩展裂纹的力学模型.在稳态扩展阶段,应力和应变具有相同的奇异量级,即(σ,ε)∝γ<'-1/(n-1)>.引入Airy应力函数,通过渐近分析得出了裂纹尖端应力和应变的分离变量形式的渐近解,并采用打靶法求得了裂纹尖端应力和应变的数值结果.数值计算结果表明,界而裂尖场主要受材料的泊松比和幂硬化指数的控制.通过对裂纹尖端场的渐近分析,从应变角度出发,提出了刚性一压力敏感性材料界面Ⅰ型准静态扩展裂纹的断裂判据. 相似文献
3.
TANG Li-qiang LIU Chang-hai and ZHENG Gui School of Civil Engineering Harbin Engineering University Harbin China 《船舶与海洋工程学报》2003,2(2):11-16
A mechanical model is established for mode Ⅱ interfacial crack static growing along an elastic-elastic power law creeping bimaterial interface. For frictional contact of boundary conditions on crack faces, asymptotic solutions of the stresses and strains of near tip-crack are got. It was shown that in stable creep growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, the stress and strain have the same singularity and there is not the oscillatory singularity the field. Through numerical calculation, it is shown that the frictional coefficient η notably influence the crack-tip field. 相似文献
4.
Self-propulsion computations using a speed controller and a discretized propeller with dynamic overset grids 总被引:2,自引:0,他引:2
Pablo M. Carrica Alejandro M. Castro Frederick Stern 《Journal of Marine Science and Technology》2010,15(4):316-330
A method that can be used to perform self-propulsion computations of surface ships is presented. The propeller is gridded
as an overset object with a rotational velocity that is imposed by a speed controller, which finds the self-propulsion point
when the ship reaches the target Froude number in a single transient computation. Dynamic overset grids are used to allow
different dynamic groups to move independently, including the hull and appendages, the propeller, and the background (where
the far-field boundary conditions are imposed). Predicted integral quantities include propeller rotational speed, propeller
forces, and ship’s attitude, along with the complete flow field. The fluid flow is solved by employing a single-phase level
set approach to model the free surface, along with a blended k−ω/k−ɛ based DES model for turbulence. Three ship hulls are evaluated: the single-propeller KVLCC1 tanker appended with a rudder,
the twin propeller fully appended surface combatant model DTMB 5613, and the KCS container ship without a rudder, and the
results are compared with experimental data obtained at the model scale. In the case of KCS, a more complete comparison with
propulsion data is performed. It is shown that direct computation of self-propelled ships is feasible, and though very resource
intensive, it provides a tool for obtaining vast flow detail. 相似文献
5.
This paper numerically investigates the influence of separation variation of the outriggers on the hydrodynamic performance of a high speed trimaran (HST) aiming at improving its applicability in diverse realistic disciplines. The present investigation was performed within the framework of the 2-D slender body method (SBM) by calculating the resistance of three symmetric trimaran series moving in a calm free surface of deep water. Each trimaran series comprises of 4681 configurations generated by considering 151 staggers (50%≤α≤+100%), and 31 separations (100%≤β≤400%) for 81 Froude numbers (0.20≤Fn≤1.0). In developing the three trimaran series, Wigley-st, AMECRC-09, and NPL-4a models were used separately for both the main and side hulls of each individual series models. A computer macro named Tri-PL was created using the Visual Basic for Applications. Tri-PL sequentially interfaced Maxsurf then Hullspeed to generate the models of the three trimaran series together with their detailed hydrostatic particulars, followed by their resistance components. The numerical results were partially validated against the available published numerical calculations and experimental results, to benchmark the Tri-PL macro and hence to rely on the analysis outcomes. A graph template was created within the framework of SigmaPlot to visualize the significant results of the Tri-PL properly. 相似文献
6.
Alexander B. Phillips Stephen R. Turnock Maaten Furlong 《Journal of Marine Science and Technology》2010,15(3):201-217
Manoeuvring underwater vehicles experience complex three-dimensional flow. Features include stagnation and boundary layer
separation along a convex surface. The resulting free vortex sheet rolls up to form a pair of streamwise body vortices. The
track and strength of the body vortex pair results in a nonlinear increase in lift as body incidence increases. Consequently,
accurate capture of the body vortex pair is essential if the flow field around a manoeuvring submarine and the resulting hydrodynamic
loading is to be correctly found. This work highlights the importance of both grid convergence and turbulence closure models
(TCMs) to the strength and path of the crossflow-induced body vortices experienced by the DOR submarine model at an incidence
angle of 15°. Five TCMs are considered; Spalart–Allmaras, k-ε, k-ω, shear stress transport, and the SSG Reynolds stress model. The SSG Reynolds stress model shows potential improvements in
predicting both the path and strength of the body vortex over standard one- and two-equation TCMs based on an eddy viscosity
approach. 相似文献
7.
Adopting an elastic-viscoplastic, the asymptotic problem of mode I propagating crack-tip field is investigated. Various asymptotic
solutions resulting from the analysis of crack growing programs are presented. The analysis results show that the quasistatically
growing crack solutions are the special case of the dynamic propagating solutions. Therefore these two asymptotic solutions
can be unified. 相似文献
8.
Lateral drift occurs due to the effects of wind forces, wave drifting forces, or both on ships sailing in actual seas. It
is important therefore to investigate the influence of lateral drift on seakeeping performance for improved ship operation.
The velocity potential was expanded as an asymptotic power series in terms of the lateral speed parameter, τ, defined as ω
e
V
0/g, where ω
e
is the frequency of wave encounter; V
0 denotes the lateral velocity, which is assumed to be sufficiently small; and g is the acceleration due to gravity. By combining this technique with the strip method, two sets of motion equations of all
the hydrodynamic force coefficients for ship seakeeping were derived. The first set is for ships without lateral drift and
is the same as the equations in the new strip method, and the second set is for the additional motions induced by lateral
drift. It was found that all ship motion modes except surge are coupled when a ship drifts laterally in waves. 相似文献
9.
0 INTRODUCTIONWeknowthatthemetalmaterialwillbegincreepwhenthetemperatureishigherthan 30 per centoftheirsmeltingpoint.Foraturbine,adieselengine,anaerospacestructureandothermotivepowermechanisms,thematerialsstillworkwhentheirtemperaturesovershootthecreepthresholdval ue.Thecreepdeformationwilloccuratnormaltem peratureforthepolymerstructures(e.g .plasticspipingelements) .Inthecaseofcreepingthefrac tureofthestructureoccursduetocreepfractureandcreepcrackgrowth.Thereforetheresearchonthecrackgro… 相似文献
10.
Based on a volume of fluid two-phase model imbedded in the general computational fluid dynamics code FLUENT6.3.26, the viscous flow with free surface around a model-scaled KRISO container ship (KCS) was first numerically simulated. Then with a rigid-lid-free-surface method, the underwater flow field was computed based on the mixture multiphase model to simulate the bubbly wake around the KCS hull. The realizable k-ε two-equation turbulence model and Reynolds stress model were used to analyze the effects of turbulence model on the ship bubbly wake. The air entrainment model, which is relative to the normal velocity gradient of the free surface, and the solving method were verified by the qualitatively reasonable computed results. 相似文献
11.
Yukinobu Nagata Koji Gotoh Masahiro Toyosada 《Journal of Marine Science and Technology》2009,14(1):104-114
Many accidents are caused by fatigue in welded built-up steel structures, and so it is important to estimate the fatigue lives
of such structures quantitatively for safety reasons. By assuming that fatigue cracks cannot grow without an accumulation
of alternating tensile/compressional plastic strain, one of the authors identified an improved effective stress intensity
factor range ΔK
RPG based on the re-tensile plastic zone generating (RPG) load, which represents the driving force for fatigue cracks, and suggested
that ΔK
RPG should be used as the parameter to describe fatigue crack growth behavior. The “FLARP” numerical simulation code in which
ΔK
RPG is implemented as the fatigue crack growth parameter, was developed in order to predict fatigue crack initiation and propagation
behavior. In this paper, it is demonstrated that FLARP gives accurate estimates for fatigue life by comparing the estimated
fatigue crack growth curves and S–N curves with the experimental results for in-plane gusset welded joints, which are used in many welded steel structures. Moreover,
the effect of induced bending moment due to the linear misalignment in the out of plane direction on the fatigue strength
of in-plane gusset welded joints is investigated through numerical simulations. 相似文献
12.
13.
We propose a new method to estimate the depth of a surface crack based on the measurement of crack opening deformation (COD)
by using strain gauges. Through finite-element (FE) analysis of several surface cracks with different crack depth, it was
found that the distribution of crack depth along the crack line can be approximated by multiplying a certain proportional
α to the distribution of COD per unit nominal strain (normalized COD). The strain gauges are cemented just on the crack line
and at a reference position, and the normalized CODs are measured under the impact load excited by hammer punching. The surface
crack depth is estimated from the normalized COD measurements by a numerical–experimental iteration method based on FE analysis.
The estimated distribution of the surface crack depth along the crack line shows good agreement with the shape of a real crack
depth. 相似文献
14.
Naoki Osawa Yasumitsu Tomita Kiyoshi Hashimoto 《Journal of Marine Science and Technology》2003,7(4):189-204
In order to accumulate knowledge about how material compositions and manufacturing methods affect fatigue strength, this
paper investigates the relationship between the swiftness of the changes in the macroscopic indices of the crack initiation
process and the hardening properties of a material. This is done by calculating the cyclic deformation behavior of a f.c.c.
single crystal. The relationship between the swiftness of the changes and the crystal geometries is also examined by calculating
the deformation behavior of a f.c.c. crystal with a high Schmid factor buried in a large crystal with a low Schmid factor.
In addition, a multiscale hardening rule based on forest theory is developed in order to examine the microscopic mechanisms
of fatigue slip band (persistent slip bands, PSBs) formation. The validity of the theories presented is examined by comparing
the changing nature of the measured and calculated hysteresis loop shapes of f.c.c. single crystals. Inhomogenous slip deformation
through the crystal is also investigated, and inferences are then drawn about the microscopic mechanisms of cyclic hardening
and PSB formation.
Received: August 5, 2002 / Accepted: December 18, 2002
Address correspondence to: N. Osawa (osawa@naoe.eng.osaka-u.ac.jp)
Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Nav Archit Jpn 1998;184:351–363, 1999;185:283–292
and 186:535–544, 2001;190:539–551) 相似文献
15.
Antonio Pinto-Heredero Tao Xing Frederick Stern 《Journal of Marine Science and Technology》2010,15(4):295-315
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. 相似文献
16.
Many experimental investigations have previously been performed and recently done on different shipbuilding structural steels
where the specimens size and crack depth/specimen width (a/W) were varied. A series of interesting results have been gained. It is worthwhile to have a review on the effect of a/W ratio on fracture toughness, and further theoretical analysis is necessary. In this paper, experimental work in elasticplastic
fracture mechanics (EPFM) was discussed. Tests had been carried out on 10 kinds of strength steels. Results showed that J
i
and δ1 values increased with decreasing a/W when a/W<0.3 for three-point bend specimens and that shallow crack specimens which have less constrained flow field give markedly
higher values of toughness than deeply notched specimens. However, for a/W>0.3, the toughness was found to be independent of a/W. Slip line field analysis shows that for shallow cracks, the hydrostatic stress is lower than that from standard deeply cracked
bend specimen which develops a high level of crack tip constraint, provides a lower bound estimate of toughness, and will
ensure an unduly conservative approach when applied to structure defects especially if initiation values of COD/J-integral are used. 相似文献
17.
Riccardo Broglia Stefano Zaghi Andrea Di Mascio 《Journal of Marine Science and Technology》2011,16(3):254-269
The simulations of the flow around a high-speed vessel in both catamaran and monohull configurations are carried out by the
numerical solution of the Reynold averaged Navier–Stokes (RANS) equations. The goal of the analysis is the investigation of
the interference phenomena between the two hulls, with focus on its dependence on the Reynolds number (Re). To this aim, numerical
simulations are carried out for values of Re ranging from 106 to 108 for two different values of the Froude number (Fr = 0.30, 0.45). Wave patterns, wave profiles, limiting streamlines, surface pressure and velocity fields are analyzed; comparison
is made between the catamaran and the monohull configurations. Dependence of the pressure and viscous resistance coefficients,
as well as of the interference factor, on the Reynolds number is investigated. Verification and validation for both resistance
coefficients and wave cuts is also performed. 相似文献
18.
针对焊接过程的二维有限元计算与实际情况存在一定差别的问题,使用三维热弹-塑性有限元法对不同焊接顺序下加筋板焊接过程进行了仿真,获得了加筋板焊接引起的温度场、位移场和应力场。结果表明:在4点约束条件下,加筋板横截面的变形为中垂变形,纵筋的变形为中拱变形,方案1横截面变形更小,方案2纵筋变形更小。焊接引起的加筋板残余应力主要表现为横向应力,其在近焊缝区为拉应力,达到材料屈服强度,远离焊缝区表现为压应力,达到0.2倍材料屈服强度。加强筋横向应力峰值出现在起弧端和收弧端,约为0.85倍材料屈服强度,纵向应力峰值出现在焊接起弧端,约为0.3倍材料屈服强度。在加筋板横截面位置,焊接顺序主要影响加强筋处的残余应力;在加强筋位置,焊接顺序主要影响纵向应力。每组焊缝同时同向焊接,且每根纵筋从左向右依次焊接的焊接方案产生更小的残余应力。 相似文献
19.
20.
Cheng-Yuan Chen 《Journal of Marine Science and Technology》2009,14(4):499-512
Experiments were carried out in a wave flume to examine the propagation of depression-type internal solitary waves (ISWs)
over a submerged triangular-shaped obstacle. We observed the distortion and breaking of the ISW depression in a two-layer
stratified fluid system as induced by the obstacle on the bottom. Physical factors, such as the amplitude of the wave, the
thickness of the two layers, and the height of the submerged obstacle were utilized in our analysis of the wave–obstacle interaction.
Wave breaking was determined in relation to input parameters arranged before the experimental runs. A classification scheme
based on the blockage parameter ζ was proposed. The various degrees of ISW-obstacle interaction were visually classified with three schematic forms (ζ < 0.55 for a weak encounter; 0.55 < ζ < 0.7 for a moderate encounter; and 0.7 < ζ for wave breaking). Furthermore, the reflection and transmission coefficients were utilized to explore the resultant influence
on changes in amplitude and energy of an ISW. The wave characteristics (e.g., amplitude-based wave reflection, energy-based
reflection, amplitude-based transmission, and energy-based transmission) during the wave–obstacle interaction showed an approximately
linear relation with the blockage parameter. Influenced by the submarine obstacle, the transmitted waves were found to always
consist of a leading pulse (solitary wave) followed by a dispersive wave train. Moreover, due to bottom friction the energy
budget of the leading pulse was reduced by a factor of at least 5% which could approach 50% in cases with strong breaking. 相似文献