High speed vessels of semi-displacement type are often equipped with appendages such as trim tabs, stern flaps and wedges to control the trim angle and improve the resistance performance. However, dynamic instability can be occurred if dimensions of those appendages are not suitable for the hull. So it is important to predict effects of appendages on the running attitudes of a vessel and choose proper dimensions of appendages at initial design stage. There are many researchers that calculate running attitudes of high speed vessels in calm water and in waves. Especially, steady states of prismatic planning hulls were theoretically predicted in some previous researches. In this paper, running attitudes of a semi-displacement vessel are predicted by theoretical methods, and model tests are carried out to verify theoretical calculations. Present calculations are based on previous formulas for prismatic planning hulls and developed to be applied to semi-displacement round bilge vessels. High speed model tests for the vessel with various trim tabs are performed in Seoul National University towing tank. Vertical motions in calm water are measured at various Froude numbers, and those are compared with calculation, results.Running attitudes of semi-displacement vessels are significantly changed at high speed and thus have an effect on resistance performance and stability of the vessel. There have been many theoretical approaches about the prediction of running attitudes of high-speed vessels in calm water. Most of them proposed theoretical formulations for the prismatic hard-chine planing hull. In this paper, running attitudes of a semi-displacement round bilge vessel are theoretically predicted and verified by high-speed model tests. Previous calculation methods for hard-chine planing vessels are extended to be applied to semi-displacement round bilge vessels. Force and moment components acting on the vessel are estimated in the present iteration program. Hydrodynamic forces are calculated by 'added mass planing theory', and near-transom correction function is modified to be suitable to a semi-displacement vessel. Next, 'plate pressure distribution method' is proposed as a new hydrodynamic force calculation method. Theoretical pressure model of the 2-dimensional flat plate is distributed on the instantaneous waterplane corresponding to the attitude of the vessel, and hydrodynamic force and moment are estimated by integration of those pressures. Calculations by two methods show good agreements with experimental results.The Effect of Appendages on the Course Keeping Ability of a Semi-DisplacementRound Bilge Ship0推荐请求原文传递导出分享到|It has been often reported that water-jet propelled high speed vessels lost the course keeping ability in seaway. In this study, model tests were performed to measure the running attitude and to check the course keeping ability of a high speed vessel. The ship may lose the course keeping ability at high speed, the variation of running attitudes such as bow drop and heel are closely related to the dynamic instability. So model tests were carried out to improve running attitudes by changing the position of longitudinal center of gravity and by using appendages at the bow and the stern of a model. The position of lateral center of pressure moved toward stern and the course keeping ability was improved by modifying the transom wedge angleDYNAMIC BEHA VIOR OF SEMI-DISPLACEMENT AND PLANNING VESSELS IN CALM WATER AND WA VES0推荐请求原文传递导出分享到|Main topics are dynamic instabilities, slamming and global wave-induced response of semidisplacement and planning vessels. Spinout and porpoising are discussed in detail. A nonlinear porpoising analysis shows that initial instabilities can lead to steady-state heave and pitch oscillations. A 2D+t nonlinear method is applied in the analysis of porpoising and wave-induced motions and accelerations of a planning vessel in head sea. The lack of correctly predicting the 3D flow at the transom stern influences, in particular, pitch accelerations. However, a fully 3D method can also lead to numerical difficulties in describing nonlinear wave effects on high-speed vessel. The latter occurred with a recently developed computer code in predicting second-order springing excitation in incident bichromatic waves. Wetdeck slamming is given special attention.THE RESISTANCE AND TRIM OF SEMI-DISPLACEMENT,DOUBLE-CHINE, TRANSOM-STERN HULL SERIES0推荐请求原文传递导出分享到|A new systematic series with a focus on the resistance and seakeeping characteristics, as well as the hull simplicity, was developed in the NTUA. The Series is primarily intended to be used for large high-speed vessels operating at speeds corresponding to F_N=0.5 to 0.9. Series main parameters and their ranges are the following: L/B=4.3-7.5, (M)=6.2-10.0, B/T=3.2-6.2, C_B=0.34-0.54, and LCB= -(12.4-14.6)%L. Regression analysis is used to establish a predictive technique and a mathematical representation of resistance and trim is provided. C_R and τ are chosen to be dependent variables, while L/B, (M), B/T and F_N are the independent ones. The mathematical models are suitable for implementation in software and can replace the "manual" power prediction calculations for the NTUA series.THE RESISTANCE AND TRIM OF SEMI-DISPLACEMENT, DOUBLE-CHINE, TRANSOM-STERN HULL SERIES0推荐请求原文传递导出分享到|A new systematic series with a focus on the resistance and seakeeping characteristics, as well as the hull simplicity, was developed in the NTUA. The Series is primarily intended to be used for large high-speed vessels operating at speeds corresponding to F_N=0.5 to 0.9. Series main parameters and their ranges are the following: L/B=4.3-7.5, (M)=6.2-10.0, B/T=3.2-6.2, C_B=0.34-0.54, and LCB=-(12.4-14.6)%L. Regression analysis is used to establish a predictive technique and a mathematical representation of resistance and trim is provided. C_R and τ are chosen to be dependent variables, while L/B, (M), B/T and F_N are the independent ones. The mathematical models are suitable for implementation in software and can replace the "manual" power prediction calculations for the NTUA series.Experimental and CFD Study of Wave Resistance of High-Speed Round Bilge Catamaran Hull Forms0推荐请求原文传递导出分享到|Although catamaran configuration has been around for a longtime, it is only in the recent past that such hull forms have seen unprecedented growth in the high-speed ferry industry. One of the design challenges faced by naval architects is accurate prediction of the hydrodynamic characteristics of such vessels primarily in the areas of resistance, propulsion and seakeeping. Even though considerable amount of research has been carried out in this area, there remains a degree of uncertainty in the prediction of calm water resistance of catamaran hull forms. This research attempts to examine the calm water wave resistance characteristics of a series of round bilge transom stern, semi-displacement slender catamaran hull forms based on computational fluid dynamics (CFD) modeling. While maintaining the same center of buoyancy and displacement, the influence of hull shape has been examined, specifically the effects of demi-hull spacing in the speed range corresponding to Froude numbers of 0.2 to 1.0. The results of CFD analysis have been compared with experimental towing tank results of NPL series, which closely resemble the systematic series developed here. The results obtained show considerable promise and development of an industry standard regression equation based on the data obtained from CFD analysis, model experiments and full-scale ship trials, can be seen as achievable.HIGH-SPEED MILITARY SEALIFT A RE-EXAMINATION OF OPTIONS0推荐请求原文传递导出分享到|Following the Gulf War, a focus for the US Military has been the transportation of military hardware from its home base or fort to the battle zone or foxhole in the most expedient way possible. One option was to re-examine the feasibility of higher speed military sealift that can take advantage of the significant recent trends occurring with high-speed commercial vessels. This paper serves to examine this possibility by studying emerging hullform technologies that could have both commercial viability and military feasibility for the future. The goal was to achieve asignificant reduction (from 15 days) for the time to transit a distance of up to 8700 nm from the Continental United States (CONUS) to the theater of operations, at a cost which is competitive with prepositioning and other options. New hullform concepts assessed included slender monohulls, semi-displacement monohulls, wave-piercing catamarans, semi-SWATH, and SES. For each hullform, parametric variations of the ship dimensions and performance capabilities were examined to determine optimum and feasible configurations. To assess their significance for the military sealift mission, outer envelopes of payload versus range and speed were developed to define what was scientifically possible to achieve by these ships. Envelopes were defined for ships having system technologies that would be available in the near-term and also in ten years from now. For their significance in commercial use, the ships were then assessed on a commercial Trans-Atlantic route. Here, their economic viability serving the "middle" market was determined for which fast-ship projects are now emerging. Then, the cost effectiveness of these ships in the desired (Trans-Pacific) Army sealift scenario was assessed. The study was conducted using unique ship design concept-exploration software that has been under developed for more than 20 years. Development of this software has focused on the use of physics-based algorithms to enhance the abilSIMULATION OF A FAST CATAMARAN'S MANOEUVRING MOTION BASED ON A 6-DOF REGRESSION MODEL0推荐请求原文传递导出分享到|Some observations of the manoeuvring motion of fast displacement catamarans indicated that dynamic changes in the ship's attitude in vertical planes (sinkage, trim and heel) observed during high-speed manoeuvring can have effect on the horizontal plane hydrodynamic forces and on the dynamic properties of these vessels. However, merely all catamaran manoeuvring simulations carried out so far were based on simplified 3DOF mathematical models. In the present study, used were regression models for all 6 components of the hull forces with account for the influence of the attitude alteration effects previously developed on the basis of Computerized Planar Motion Carriage captive-model tests. Basing on these regressions, a relatively complete 6DOF manoeuvring mathematical model was developed for a particular river-going catamaranequipped with steered water-jets. Certain components of the hydrodynamic force, which could not be determined from the captive-model tests, were estimated by means of the slender-body theory, the cross-flow drag concept and other semi-empiric approaches. Standard manoeuvres were simulated using both the 6DOF and 3DOF mathematical models. The results were compared with the available full-scale data and this comparison indicated that the 6DOF modelling becomes really more adequate at higher speed.。