Pub Date : 1900-01-01DOI: 10.14744/seatific.2023.0003
Ismael A. S. Ehtiwesh
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Pub Date : 1900-01-01DOI: 10.14744/seatific.2021.0005
G. Trincas
The most significant goals of this paper are: (i) to provide additional insight on the influence of hull form parameters on seakeeping performance of typical Mediterranean fishing vessels; (ii) to develop efficient and reliable metamodels for fast and reliable evaluation of seakeeping performance in a multiattribute decision-making environment; (iii) to facilitate and speed up the selection of the design with the best possible seakeeping performance at conceptual design stage. To enhance the accuracy and applicability of predictions of seakeeping characteristics and to find out guidelines for design scope, new metamodels have been developed from an extended database of 57 cases, which comprehends the hull form geometrical data, heave (h), pitch (p) and vertical acceleration (av) rms values of both old 39 cases studied previously as well as new 18 cases of Mediterranean coastal fishing vessels previously analysed for resistance assessment. Main statistical parameters of the derived regression equations show a substantial improvement of statistical accuracy in h, p and av estimates, particularly when geometrical descriptors of forebody and afterbody hull form are included as independent variables. Statistical homogeneity of the N57 extended database was verified by cluster analysis of selected responses with classical hull form coefficients/parameters, and new descriptors data altogether taken as discriminant variables in two nucleus clustering analysis. Values of heave, pitch and vertical acceleration yielded by the metamodels have been compared to the ones determined by means of direct computations. Low residuals have confirmed reliability of the proposed prediction metamodels to determine since conceptual design stage seakeeping performance of fishing vessels with hull forms and main dimensions which could be included in the design space defined by the population forming the extended database.
{"title":"Metamodels for seakeeping assessment of fishing vessels","authors":"G. Trincas","doi":"10.14744/seatific.2021.0005","DOIUrl":"https://doi.org/10.14744/seatific.2021.0005","url":null,"abstract":"The most significant goals of this paper are: (i) to provide additional insight on the influence of hull form parameters on seakeeping performance of typical Mediterranean fishing vessels; (ii) to develop efficient and reliable metamodels for fast and reliable evaluation of seakeeping performance in a multiattribute decision-making environment; (iii) to facilitate and speed up the selection of the design with the best possible seakeeping performance at conceptual design stage. To enhance the accuracy and applicability of predictions of seakeeping characteristics and to find out guidelines for design scope, new metamodels have been developed from an extended database of 57 cases, which comprehends the hull form geometrical data, heave (h), pitch (p) and vertical acceleration (av) rms values of both old 39 cases studied previously as well as new 18 cases of Mediterranean coastal fishing vessels previously analysed for resistance assessment. Main statistical parameters of the derived regression equations show a substantial improvement of statistical accuracy in h, p and av estimates, particularly when geometrical descriptors of forebody and afterbody hull form are included as independent variables. Statistical homogeneity of the N57 extended database was verified by cluster analysis of selected responses with classical hull form coefficients/parameters, and new descriptors data altogether taken as discriminant variables in two nucleus clustering analysis. Values of heave, pitch and vertical acceleration yielded by the metamodels have been compared to the ones determined by means of direct computations. Low residuals have confirmed reliability of the proposed prediction metamodels to determine since conceptual design stage seakeeping performance of fishing vessels with hull forms and main dimensions which could be included in the design space defined by the population forming the extended database.","PeriodicalId":170561,"journal":{"name":"Seatific Engineering Research Journal","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124909430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.14744/seatific.2021.0002
F. Cakici
In this study, the hydrodynamic coefficients associated with heave motion are obtained by using unsteady Reynolds-averaged Navier-Stokes (URANS) approach. The well-known Wigley hull is selected for the calculations of uncoupled added mass and damping coefficients (A33, B33) in deep water. Numerical simulations are performed for six different oscillation frequencies at the Froude number 0.3. First, the 3D ship model is forced in the heave direction with certain frequencies and then the hydrodynamic coefficients are computed with the help of Fourier series expansion. Numerical results are compared with those obtained by the experiments and strip theory. The verification and validation study for the damping term is also performed by implementing the Grid Convergence Index (GCI) method.
{"title":"Computational prediction of hydrodynamic coefficients for heave motion","authors":"F. Cakici","doi":"10.14744/seatific.2021.0002","DOIUrl":"https://doi.org/10.14744/seatific.2021.0002","url":null,"abstract":"In this study, the hydrodynamic coefficients associated with heave motion are obtained by using unsteady Reynolds-averaged Navier-Stokes (URANS) approach. The well-known Wigley hull is selected for the calculations of uncoupled added mass and damping coefficients (A33, B33) in deep water. Numerical simulations are performed for six different oscillation frequencies at the Froude number 0.3. First, the 3D ship model is forced in the heave direction with certain frequencies and then the hydrodynamic coefficients are computed with the help of Fourier series expansion. Numerical results are compared with those obtained by the experiments and strip theory. The verification and validation study for the damping term is also performed by implementing the Grid Convergence Index (GCI) method.","PeriodicalId":170561,"journal":{"name":"Seatific Engineering Research Journal","volume":"71 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130756520","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 1900-01-01DOI: 10.14744/seatific.2021.0003
S. Bayraktar
In the present paper, two-dimensional unsteady flows over circular cross-section cylinders are analyzed numerically. The effects of placement of the cylinders are investigated for two different arrangements: tandem and side-by-side. Several turbulence models are tested, and it is found that Spalart-Allmaras turbulence model is the best among oneand two-equation turbulence models. The most appropriate time step, which is one of the important parameters in unsteady simulations, is found as 0.002 seconds. After successful validations, the cylinders are positioned as side-by-side and tandem. The effects of the arrangement on flow regime, drag coefficient, lift coefficient and Strouhal number are presented for various distances between the cylinders. It is found that the flow is almost steady without any vortex in the gap when cylinders are in tandem and the gap between them is low. In contrast, the interactions are strong in case of side-by-side arrangement at the lowest gap. When the gap increases, the flow is affected that results in change on the global parameters.
{"title":"Numerical investigation of flow over tandem and side-by-side cylinders","authors":"S. Bayraktar","doi":"10.14744/seatific.2021.0003","DOIUrl":"https://doi.org/10.14744/seatific.2021.0003","url":null,"abstract":"In the present paper, two-dimensional unsteady flows over circular cross-section cylinders are analyzed numerically. The effects of placement of the cylinders are investigated for two different arrangements: tandem and side-by-side. Several turbulence models are tested, and it is found that Spalart-Allmaras turbulence model is the best among oneand two-equation turbulence models. The most appropriate time step, which is one of the important parameters in unsteady simulations, is found as 0.002 seconds. After successful validations, the cylinders are positioned as side-by-side and tandem. The effects of the arrangement on flow regime, drag coefficient, lift coefficient and Strouhal number are presented for various distances between the cylinders. It is found that the flow is almost steady without any vortex in the gap when cylinders are in tandem and the gap between them is low. In contrast, the interactions are strong in case of side-by-side arrangement at the lowest gap. When the gap increases, the flow is affected that results in change on the global parameters.","PeriodicalId":170561,"journal":{"name":"Seatific Engineering Research Journal","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124679077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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