D Savitsky

Bio: D Savitsky is an academic researcher. The author has contributed to research in topics: Seakeeping & Transom. The author has an hindex of 1, co-authored 1 publications receiving 169 citations.

Procedures for hydrodynamic evaluation of planing hulls in smooth and rough water

Abstract: Recent Davidson Laboratory basic studies of planing hull hydrodynamics have produced a wealth of technology which is not generally available to the small boat design profession. Included are studies related to the pre-planning resistance of transom stern hulls; the effectiveness of trim control flaps; the effect of bottom warp on planing efficiency; the influence of re-entrant transom forms; and the seakeeping of planing hulls. The present paper consolidates these results in a form suitable for design purposes and illustrates their application in predicting planing performance in smooth and rough water.

Toward free-surface modeling of planing vessels: simulation of the Fridsma hull using ALE-VMS

Abstract: In this paper we focus on a class of applications involving surface vessels moving at high speeds, or "planing". We introduce a Fridsma planing hull benchmark problem, and simulate it using the finite-element-based ALE-VMS (Bazilevs et al. in Math Models Methods Appl Sci 2012; Takizawa et al. in Arch Comput Methods Eng 19: 171---225, 2012) approach. The major reasons for selecting this problem is the relative simplicity of the hull geometry and the existence of high-quality experimental data used for the purposes of validation. The ALE-VMS approach is formulated in the context of the Mixed Interface-Tracking/Interface-Capturing Technique (MITICT) (Tezduyar in Arch Comput Methods Eng 8:83---130, 2001; Akin et al. in Comput Fluids 36:2---11, 2007; Cruchaga et al. in Int J Numer Methods Fluids 54:1021---1031, 2007), where the level set technique is used for capturing the air---water interface, and the Arbitrary Lagrangian Eulerian (ALE) method is employed to track the interface between the fluid and structure. In this work, the planing hull structure is treated as a six-degree-of-freedom rigid object. The computational results obtained for the Fridsma hull, which include convergence of the trim angle and drag under mesh refinement, match well with the experimental data.

Surface wave contours associated with the forebody wake of stepped planing hulls

Abstract: Results of an extensive series of model tests that define the longitudinal surface wake profiles aft of prismatic hulls having deadrise angles of 10 o, 20 o and 30 o are presented. Empirical equations are developed that quantitatively define these profiles and are in a form that can be easily applied by designers of stepped planing hulls. These equations are applicable for an expected range of variations in trim angle, speed coefficient, and loading coefficient typical for these hulls. A brief introduction to the concept and to the hydrodynamic advantages of stepped planing hulls is presented to orient the reader as to the importance of wake data in their design. Examples are presented that illustrate the application of these wake data for stepped planing hulls with wetted forebody chine to achieve maximum hydrodynamic lift/drag ratios. Finally experimental results are presented that illustrate the potential resistance penalty associated with the operation of chines dry forebodies where the stagnation line crosses the step.

VISIR-I: small vessels – least-time nautical routes using wave forecasts

Abstract: . A new numerical model for the on-demand computation of optimal ship routes based on sea-state forecasts has been developed. The model, named VISIR (discoVerIng Safe and effIcient Routes) is designed to support decision-makers when planning a marine voyage. The first version of the system, VISIR-I, considers medium and small motor vessels with lengths of up to a few tens of metres and a displacement hull. The model is comprised of three components: a route optimization algorithm, a mechanical model of the ship, and a processor of the environmental fields. The optimization algorithm is based on a graph-search method with time-dependent edge weights. The algorithm is also able to compute a voluntary ship speed reduction. The ship model accounts for calm water and added wave resistance by making use of just the principal particulars of the vessel as input parameters. It also checks the optimal route for parametric roll, pure loss of stability, and surfriding/broaching-to hazard conditions. The processor of the environmental fields employs significant wave height, wave spectrum peak period, and wave direction forecast fields as input. The topological issues of coastal navigation (islands, peninsulas, narrow passages) are addressed. Examples of VISIR-I routes in the Mediterranean Sea are provided. The optimal route may be longer in terms of miles sailed and yet it is faster and safer than the geodetic route between the same departure and arrival locations. Time savings up to 2.7 % and route lengthening up to 3.2 % are found for the case studies analysed. However, there is no upper bound for the magnitude of the changes of such route metrics, which especially in case of extreme sea states can be much greater. Route diversions result from the safety constraints and the fact that the algorithm takes into account the full temporal evolution and spatial variability of the environmental fields.

Progress in the Analysis and Design of Marine Structures : Proceedings of the 6th International Conference on Marine Structures (MARSTRUCT 2017), May 8-10, 2017, Lisbon, Portugal

Abstract: The investigation of wetdeck slamming phenomenon is a challenging Fluid-Structure Interaction (FSI) problem for both experimental and numerical analysis, requiring detailed design and structural assessment of the physical model. The focus of this paper is to document the design approach and the testing effort devoted to provide a reliable and well identified physical model before the towingtank tests were carried out for giving key insights into the wetdeck load and responses as well as an FSI validation dataset for numerical solvers. Thus, one of the main objectives is reducing the uncertainty linked to the modeling of the multi-hull structure by performing a series of both static and dynamic characterization tests on the as built catamaran model. The insight gained from this test campaign will be used to update the structural models coupled within the FSI solvers to increase the accuracy of the predicted hydrodynamic loading. Among FSI problems still receiving positive attention in ship and offshore engineering, the accurate prediction of complex loading and responses on multi-hull vessels is particularly demanding, since it involves two-way coupling of the deck structure with the flow impinging on it. Currently, there is a gap in available experimental FSI data related to this problem that can be used for numerical solver validation. Current FSI data sets are severely limited by the uncertainties associated with the experimental setups. Furthermore, though segmented model tests have become more feasible and popular for monohulls, not many experimental campaigns (Hermundstad et al. 1995, Kyyro & Hakala 1997, Cheng, F. 1997) exist for segmented catamarans that provide both global and local loads and hull responses. The only systematic investigation on elastically scaled catamarans was carried out by Lavroff et al. (2007, 2013). Dessi et al. (2016) have already illustrated the preliminary experimental results on an elastically scaled model of a SWATH aimed to accurately depict the wave loading and structural response from seakeeping tests. In the present paper the focus is instead on the structural tests performed for the physical model qualification with an extended account of the dry and wet vibration mode identification of the entire catamaran.