英语原文共 8 页
APPROXIMATING THE ADDED RESISTANCE COEFFICIENT FORA BULK CARRIER SAILING IN HEAD SEA CONDITIONS BASEDON ITS GEOMETRICAL PARAMETERS AND SPEED
Tomasz Cepowski, Prof.
Maritime University of Szczecin, Poland
ABSTRACT：The article presents the mathematical function to calculate the added wave resistance transfer function for bulk carriers. Based on this function, the statistical mean added wave resistance generated by an irregular head wave with arbitrary statistical parameters can be forecasted. The input parameters are: waterplane area, waterplane coefficient,ship speed, and frequency of the regular wave. The model has been developed based on the theory of artificial neural networks. The presented function can be used in design analyses, and for planning shipping routes in situations when basic geometrical parameters of the hull are only available and not the full technical documentation. The article presents sample cases of use of this function to calculate the added wave resistance transfer function and the statistical mean added wave resistance..Another presented application refers to waterplane coefficient optimisation taking into account the added wave resistance at the stage of preliminary bulk carrier design.
Keywords: bulk carrier; resistance; added wave resistance; added resistance coefficient; regular wave; irregular wave; ship designing; preliminary design stage; artificial neural networks; approximation; forecasting; speed; waterplane area; waterplane coefficient, sample case, task, designing.
Assumptions concerning the design of a floating objectdesigned for arbitrary purposes usually include two basicgroups of requirements, which are :
bull; economic requirements,
bull; technical requirements.
Meeting the first group of requirements usually means realisation of ship function at minimal financial costs of building and maintenance of the object, while meeting the other group is equivalent to objectrsquo;s ability to keep afloat and possess other technical features which will secure safety of the performed operations. To meet the above requirements, aso-called design goal and design constraints are formulated.
For bulk carriers, the design goals are mainly the result of the transport study. Basic design goals for the bulk carrier refer to：
1. mass of the cargo to be transported,
2. operating speed of the ship, shipping route, and the distance between transhipment ports.
Reaching the assumed operating speed by the bulk carrierdepends, among other factors, on operating parameters andconditions of the propulsion system, the efficiency of thepropulsion system and hull, and the total hull resistance.
Among other components, the total hull resistance includes
the added wave resistance, which:
bull; is connected with ship navigation in storm waves,
bull; can contribute to about 30-50% of total ship resistance,
bull; leads to remarkable drop of operating speed,
bull; depends on, among other factors, hull dimensions andshape.
That is why forecasting the added wave resistance of the ship is a considerable challenge for ship designers, due to economic aspects of selection of ship propulsion parametersand assessment of fuel consumption and time of voyage, as well because of the need to improve energy efficiency of ship operation.
Forecasting the added wave resistance is also an important element of various shipping route planning systems. When the detailed data on ship resistance-propulsion characteristics taking into account the added wave resistance and hull geometry are missing, these characteristics are to be forecasted using simplified methods.
预测增加的波浪阻力也是各种航线规划系统的重要元素。当考虑到增加的波阻和船体几何形状的船舶阻力 - 推进特性的详细数据缺失时，这些特征将使用简化的方法进行预测。
（1）THE ADDED WAVE RESISTANCE
Accounting methods used to assess the added wave resistance are limited to resistance calculations for the head wave. These methods base on the assumption that the added resistance has the nature of wave resistance and does not depend on the calm water resistance. The mean added wave resistance is calculated using the function which initially describes the resistance contribution from a regular (sine)wave, R AW (omega;E ). Then, applying the superposition principle to the spectral distribution of the irregular wave (given by function Szeta;zeta; (omega;E)), the increase of the statistical mean resistanceRw in irregular (statistical) wave is calculated as：
Rw – statistical mean wave resistance increase,
RAW – added resistance from the regular wave,
omega;E – encounter frequency of the harmonic wave,
zeta;a – amplitude of the regular wave,
Szeta;zeta; – wave energy spectrum density function.