• Advances in concrete construction
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• v.15 no.5
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• pp.303-312
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• 2023

The present study investigates the effects of Cattaneo-Christov thermal effects of stagnation point in Walters-B nanofluid flow through lubrication of power-law fluid by taking the slip at the interfacial condition. For the solution, the governing partial differential equation is transformed into a series of non-linear ordinary differential equations. With the help of hybrid homotopy analysis method; that consists of both the homotopy analysis and shooting method these equations can be solved. The influence of different involved constraints on quantities of interest are sketched and discussed. The viscoelastic parameter, slip parameters on velocity component and temperature are analyzed. The velocity varies by increase in viscoelastic parameter in the presence of slip parameter. The slip on the surface has major effect and mask the effect of stagnation point for whole slip condition and throughout the surface velocity remained same. Matched the present solution with previously published data and observed good agreement. It can be seen that the slip effects dominates the effects of free stream and for the large values of viscoelastic parameter the temperature as well as the concentration profile both decreases.

• Advances in nano research
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• v.16 no.5
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• pp.473-487
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• 2024

The current study employs the nonlocal Timoshenko beam (NTB) theory and von-Kármán's geometric nonlinearity to develop a non-classic beam model for evaluating the nonlinear free vibration of bi-directional functionally-graded (BFG) nanobeams. In order to avoid the stretching-bending coupling in the equations of motion, the problem is formulated based on the physical middle surface. The governing equations of motion and the relevant boundary conditions have been determined using Hamilton's principle, followed by discretization using the differential quadrature method (DQM). To determine the frequencies of nonlinear vibrations in the BFG nanobeams, a direct iterative algorithm is used for solving the discretized underlying equations. The model verification is conducted by making a comparison between the obtained results and benchmark results reported in prior studies. In the present work, the effects of amplitude ratio, nanobeam length, material distribution, nonlocality, and boundary conditions are examined on the nonlinear frequency of BFG nanobeams through a parametric study. As a main result, it is observed that the nonlinear vibration frequencies are greater than the linear vibration frequencies for the same amplitude of the nonlinear oscillator. The study finds that the difference between the dimensionless linear frequency and the nonlinear frequency is smaller for CC nanobeams compared to SS nanobeams, particularly within the α range of 0 to 1.5, where the impact of geometric nonlinearity on CC nanobeams can be disregarded. Furthermore, the nonlinear frequency ratio exhibits an increasing trend as the parameter µ is incremented, with a diminishing dependency on nanobeam length (L). Additionally, it is established that as the nanobeam length increases, a critical point is reached at which a sharp rise in the nonlinear frequency ratio occurs, particularly within the nanobeam length range of 10 nm to 30 nm. These findings collectively contribute to a comprehensive understanding of the nonlinear vibration behavior of BFG nanobeams in relation to various parameters.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.6
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• pp.587-594
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• 2009

In the paper the effect of a stern-plate attached to a ship was taken into account. The relationship between the trim angle of a ship and the wave-resistance coefficient induced by the a stern-plate was studied using the potential flow analysis method. Numerical algorithm was described using the panel method and the vortex lattice method(VLM) to simulate the flow phenomena around a ship. The non-linearity of the free surface boundary conditions were considered using the iterative method and the IGE-GMRES(Incomplete Gaussian Elimination-The Generalized Minimal RESidual) algorithm was adopted to solve the linear equation at each iterative step. Numerical calculations were carried out to investigate the validity of the adopted algorithm using KCS(KRISO 3600 TEU Container) hull. Possible cases for attachment of the plate were checked. The results showed that the numerical algorithm could be physically appropriate.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6B
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• pp.643-651
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• 2008

In the present paper, turbulent open-channel flows over longitudinal bedforms are numerically simulated. The Reynolds- averaged Navier-Stokes equations in curvilinear coordinates are solved with the non-linear $k-{\varepsilon}$ model by Speziale( 1987). First, the developed model is applied to rectangular open channel flows for purposes of model validation and parameter sensitivity studies. It is found that the parameters $C_D$ and $C_E$ are important to the intensity of secondary currents and the level of turbulent anisotropy, respectively. It is found that the non-linear $k-{\varepsilon}$ model can hardly reproduce the turbulence anisotropy near the free surface. However, the overall pattern of the secondary currents by the present model is seen to coincide with measured data. Then, numerical simulations of turbulent flows over longitudinal bedforms are performed, and the simulated results are compared with the experimental data in the literature. The simulated secondary currents clearly show upflows and downflows over the ridges and troughs, respectively. The numerical results of secondary currents, streamwise mean velocity, and turbulence structures compare favorably with the measured data. However, it is observed that the secondary currents towards the troughs were significantly weak compared with the measured data.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.400-408
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• 2003

A study on the progressive inelastic deformation behavior of the 316 L stainless steel cylindrical structure with plate-to-shell junction under moving temperature front was carried out by structural test and analysis. The structural test intends to simulate the thermal ratcheting behavior occurring at the reactor baffle of the liquid metal reactor as free surface of hot sodium pool moves up and down under plant transients. The thermal ratchet load that heats the specimen up to 550$^{\circ}C$ was applied repeatedly and residual deformation was measured. The thermal ratcheting test was carried out with two types of cylindrical structures, one with plate to-shell junction and the other without the junction to investigate the effects of the geometric discontinuities on the global ratcheting deformation. The temperature distributions of the test specimens were measured and were used for the ratcheting analysis. The ratchet deformations were analyzed with the constitutive equation of the non-linear combined hardening model. The analysis results were in good agreement with those of the structural tests.

• Proceedings of the KSRS Conference
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• v.2
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• pp.934-937
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• 2006

In the northeastern South China Sea (SCS), fast westward moving (about 2.9 m/s) non-linear internal waves (NLIWs) are emanated nearly daily from the Luzon Strait. Their propagation speed is faster than NLIWs previously observed in the deep water of world oceans, their amplitude of 140 m or more is the largest free propagating NLIWs so far observed in the deep ocean. These NLIWs energized the top 1500 m of the water column, heaving it up and down in 20 min. Their associated energy density and energy flux are the largest observed to date. During 2005 and 2006 experiment, they were found west of the HengChun Ridge (HCR) that links Luzon and Taiwan Islands. This coincides with founding in satellite images, no NLIW front was found east of HCR. But, the turbulent environment east of HCR may prohibit surface signature of NLIWs that were emanated from sills between Batan Islands. The relative contribution of the two ridges on NLIW in Luzon Strait is still under study.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.58-63
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• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.173-178
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• 2004

The estimation of springing responses for recent ships are carried out and application to a ship design are described. To this aim, springing effects on hull girder were re-evaluated including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder by the superposition method. The strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level and added asymptotic interpolation along the high frequency range. Several applications to the existing ships were carried out. They are Bishop and Price's container ship, S-175 container ship, large container, VLCC and ore carrier. One of them is compared with ship measurement result while another with that of model test. Comparison between analytical solution and numerical one for homogeneous beam type artificial ship shows good agreement. It is found that most springing energy came from high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega^{-3}\;instead\;of\;\omega^{-4}\;or\;\omega^{-5}$ for springing calculation.

• Ocean Systems Engineering
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• v.7 no.4
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• pp.435-460
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• 2017

The main objective of this study is to investigate the turning and zig-zag maneuvering performance of the well-known naval surface combatant DTMB (David Taylor Model Basin) 5415 hull with URANS (Unsteady Reynolds-averaged Navier-Stokes) method. Numerical simulations of static drift tests have been performed by a commercial RANS solver based on a finite volume method (FVM) in an unsteady manner. The fluid flow is considered as 3-D, incompressible and fully turbulent. Hydrodynamic analyses have been carried out for a fixed Froude number 0.28. During the analyses, the free surface effects have been taken into account using VOF (Volume of Fluid) method and the hull is considered as fixed. First, the code has been validated with the available experimental data in literature. After validation, static drift, static rudder and drift and rudder tests have been simulated. The forces and moments acting on the hull have been computed with URANS approach. Numerical results have been applied to determine the hydrodynamic maneuvering coefficients, such as, velocity terms and rudder terms. The acceleration, angular velocity and cross-coupled terms have been taken from the available experimental data. A computer program has been developed to apply a fast maneuvering simulation technique. Abkowitz's non-linear mathematical model has been used to calculate the forces and moment acting on the hull during the maneuvering motion. Euler method on the other hand has been applied to solve the simultaneous differential equations. Turning and zig-zag maneuvering simulations have been carried out and the maneuvering characteristics have been determined and the numerical simulation results have been compared with the available data in literature. In addition, viscous effects have been investigated using Eulerian approach for several static drift cases.

• Journal of Chest Surgery
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• v.28 no.6
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• pp.571-578
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• 1995

Rastelli operation in which right ventricle[RV and pulmonary artery[PA is connected with an artificial graft is effective in increasing the pulmonary blood flow in certain types of congenital heart disease but, in many, it requires a reoperation because of the relative stenosis of graft that develops as the patients become old. The purpose of this study is to evaluate the various factors which many influence the long term outcome of such patients following a Rastelli operation. A total of 47 patients underwent a Rastelli operation during a 15 year period between November, 1978 and October 1993. The mean follow-up period is 76.1 51.3 months.1 Among the 47 patients, a valved conduit was used in 30[63.8% , and non-valved conduit in 17[36.2% patients. In the 8 patients[17.0% who died postoperatively, a valved conduit was used in 5 [16.6% and a non-valved conduit in 3[17.6% . There was no statistical difference in mortality between the 2 groups. There was a good linear correlation between the body surface area[X and the conduit size[Y [Y=3.86X + 14.6, R=0.55, P=0.01 .2 Ten patients underwent replacement of the conduit during the follow-up period. The type of conduit used and the frequency of subsequent replacement were as follows: Ionescu-Shiley, valved-33.3%, Carpentier-Edwards, valved-30.8%, Hancock, valved-80% and non-valved conduit-9.1%. The median period free of reoperation was 110 months for the valved and 79 months for the non-valved group, there being no statistical difference between the 2 groups. 3 The patients who did not require reoperation are all doing well [New York Heart Association Functional Classification: Class I . Pressure gradient between the RV and the PA was 20 mmHg in 10 randomly selected patients who did not require reoperation and 92 9 mmHg in 10 patients who did require reoperation.4 In the 10 patients who underwent a conduit replacement procedure.5 Among patients undergoing reoperation, 2 died from endocarditis.The remaining 8 patients are doing well without limitation in physical activity at a mean follow-up period of 32.7 33.9 months [range 2 to 89 months . 6 At 5, 7, and 10 years, the reoperation-free rates among all patients were 96%, 91% and 29% and the survival rates were 82%, 82% and 71%. In conclusion, Rastelli operation is an effective procedure in ameliorating symptoms in a select group of patients with congenital heart disease. Because of the inherent nature of relative graft stenosis and degeneration, a long-term follow-up is required under the proper selection of the graft material.