A geosim analysis of ship resistance decomposition and scale effects with the aid of CFD

Abstract

Historically, the prediction ship resistance has received its fair share of attention by the scientific community. Yet, a robust scaling law still lacks, leaving testing facilities to rely on experience-based approaches and large datasets accumulated from years of operation. Academia's concern regarding this has not led to an extrapolation procedure, capable of bearing scrutiny adequately. One way to circumvent what has become the bane of the study of ship resistance is to perform Reynolds averaged Navier-Stokes (RANS) simulations directly in full-scale. The rapid advent of such methods has meant that confidence levels in predictions achieved by RANS simulations are low. This paper explores and demonstrates scale effects on the constituent components of ship resistance by performing a geosim analysis using a Computational Fluid Dynamics approach. Emphasis is placed on challenging the assumptions imposed as part of the currently accepted ship resistance extrapolation procedure. Our results suggest that a high degree of uncertainty exists in the calculated full-scale resistance depending on the approach taken towards its evaluation. In particular, scale effects are demonstrated in wave resistance, while free surface effects are palpable in the frictional resistance.

Verification and Validation of CFD Based Form Factors as a Combined CFD/EFD Method

“…The previous CFD studies presented by Raven et al [42], Wang et al [25], Dogrul et al [26], Korkmaz et al [27], Terziev et al [24], Van et al [43], and Korkmaz et al [28] supported the existence of speed dependency for the form factors even though this should not be the case according to the hypothesis of Hughes [6]. Therefore, regardless of the choice of the CFD code, numerical methods, and settings, the choice of speed that the double body computations are performed for will have a significant impact on the CFD based form factors when the ITTC-57 model to ship correlation line is used.…”

“…As identified by the ITTC Specialist Committee on the Combined CFD/EFD Methods, if a part of the model testing or extrapolation procedure causes higher uncertainty than the numerical uncertainty and modeling errors of the CFD applications, the accuracy is expected to increase. In the 1978 ITTC Performance Prediction method [20], the form factor approach is identified as a major uncertainty source due to its determination method, i.e., the Prohaska Method [5], and the scale effects when the ITTC-57 model to ship correlation line is used [21][22][23][24][25][26][27][28]. The study performed by Wang et al [29] showed that when the Prohaska Method is replaced by CFD based form factors in the ITTC-78 Power Prediction Method, the sea trials correlated better for a ship.…”

Application of eddy-viscosity turbulence models to problems in ship hydrodynamics

“…With the exception of the two variants based on the SST model (k-ω SST, and k-ω γ), the closures predict a significantly higher skin friction than any friction line would suggest. This can be used to highlight the shortcomings of form factor and wave resistance extrapolation techniques, since a reliable frictional resistance is integral to the procedure (Terziev et al, 2019). Confidence in the predictions can be established due to their systematic predictions, as shown in Figure 11, in terms of their relative location on the plot.…”

“…The present study is motivated partially by the findings of Larsson et al, (2014), who observed a scatter in sinkage and trim predictions, as alluded to previously, and partially by recent work undertaken by the present authors. Sinkage and trim proved more difficult to simulate accurately than resistance in CFD (Terziev et al, 2019). In deep waters, the combined effect of sinkage and trim is known to be small on resistance and in some cases may even be neglected (Ponkratov, 2016).…”

Analisis Nilai Hambatan Total Dengan Perubahan Sarat Kapal Km. Kendhaga Nusantara 6

“…Semakin kecil nilai permukaan basah di kapal akan mempengaruhi hambatan kapal ketika beroperasi. Selain itu bentuk kapal dengan tipe catamaran dapat memudahkan kapal untuk mengeksplorasi dan mengurangi efek gelombang yang timbul dari kapal [12]. Dalam sebuah studi oleh Peng dengan judul "Wave pattern and resistance prediction for ships of full form" menunjukkan perubahan dalam modifikasi bentuk lambung kapal memberikan akibat pada hambatan total kapal dari bentuk gelombang laut yang ditimbulkan.…”