Wave Resistance Research Articles

State primary standard of the unit of wave resistance in coaxial waveguides GET 75-2023

The issues of measuring the wave resistance and complex reflection and transmission coefficients of devices operating at ultrahigh frequencies in coaxial waveguides are considered. Measurements of these parameters are important in the development and production of communication and information transmission systems, radar and radio navigation systems. In order to ensure the uniformity of measurements, reproduction and transmission of wave resistance units and complex reflection and transmission coefficients to measuring instruments with coaxial connectors of type 1 mm in the frequency range 0.01–67 GHz, the state primary standard of the unit resistance in coaxial waveguides GET 75-2023 has been approved. It includes means of reproducing the unit of wave resistance, complex reflection coefficients, a comparator and comparison standards in a coaxial path with a cross section of 1.0/0.434 mm with a connector of type 1 mm. The expressions for calculating the parameters of coaxial waveguides with bimetallic conductors are refined. The technical characteristics and results of metrological studies of GET 75-2023 are presented. The results of the research confirmed the high accuracy of GET 75-2023, which has comparable metrological characteristics with the standards of national metrological institutes of other countries.

The study of float wave formation for the usage as heavy-duty catamaran bulbs

The large cargo catamaran ferries can increase speed freight transportation on inland waterways. However, an increase of vessel's speed entails the growth in the heights of ship waves when the ship, which in turn adversely affects both the hydrodynamic characteristics of the ship itself, enhances wave impacts on the catamaran bridge and the ecological state of water bodies. According some scientific articles one way to reduce wave resistance of large catamarans may be deployment а a float-bulb between it hulls. Ship's wave and wave resistance depend on the shape of the float-bulb, so it is advisable to study the parameters of the waves formed first on the bulb in free flow, and then together with the catamaran. In this paper presents analytical equations for the resistance of the "float-catamaran complex", as well as formulas that also allow one to calculate the main parameters of the float-bulb. The results of numerical simulation are presented for the three ellipsoid's length: 29,2m (Fr=0,414-0,691), 14,6m (Fr=0,585-0,978) and 7,3m (Fr=0,827-1,383), ball d=1,76m (Fr=1,685-2,816). The characteristics of the generated ship waves is determined. Conclusions about the feasibility of modifying the float-bulb shape for heavy catamarans is given.

Investigating Fuel Injection Strategies to Enhance Ship Energy Efficiency in Wave Conditions

Abstract The prediction of fuel consumption and resulting transportation costs is a crucial stage in ship design, particularly for conditions involving motion in waves. This study investigates the real-time fuel consumption of a container ship when sailing in waves. The overall ship performance is evaluated using a novel non-linear coupled hull-engine-propeller interaction model. A series of towing tank experiments for hull resistance in waves and propeller performance are conducted. The ship engine is mathematically modelled by a quasi-steady-state model equipped with a linear Proportional-Integrator (PI) governor. Various scenarios of shipping transportation are studied, and the resulting instantaneous fuel consumptions and their correlation to other dynamic particulars are demonstrated. Additionally, daily fuel consumption and fuel cost per voyage distance are presented. It is also shown that the controller can effectively adjust the fuel rate, resulting in minimum fuel consumption. The study concludes that there is no correlation between fuel consumption and the frequency of fuel rates. The present framework and mathematical model can also be employed for ship design and existing ships to predict the total required energy per voyage.

Built or Social environment? Effects of perceptions of neighborhood green spaces on resilience of residents to heat waves

Large cities in North China are at an increasing risk of heat waves. Several previous studies have emphasized the significance of heat wave resilience but they generally failed to sufficiently consider the social level and to explore the mechanisms involved. In the present study, we investigated heat wave resilience as a full-cycle process and elucidated the related factors at the level of environmental perception. We selected 60 neighborhoods that are vulnerable to high temperatures in the central urban area of Tianjin. Using a questionnaire (N = 734), we evaluated the residents' perceptions in terms of the built-environmental perception (BEP) and socio-environmental perception (SEP) of neighborhood green spaces, as well as assessing the resilience levels of residents in the three phases comprising heat wave preparation, resistance, and recovery. Structural equation models were constructed to identify the mechanisms that influenced resilience in each phase. The results demonstrated a significant and direct effect of SEP on heat wave preparation and on the resistance phase. In addition, both BEP and SEP were critical for the recovery of residents. Using multi-group analysis, we identified differences in the mechanisms that allowed residents to acquire heat wave resilience. Based on these findings, we suggest that green space planning and policies should focus on optimizing the built environment, but also on the roles of residents' social support networks because they are crucial for guaranteeing the sustainability of vulnerable groups and helping communities to cope with heat waves.

Dynamics of collapse of free-surface bubbles: effects of gravity and viscosity

The rupture of the thin film at the top of a bubble at a liquid–gas interface leads to an axisymmetric collapse of the bubble cavity. We present scaling laws for such a cavity collapse, established from experiments conducted with bubbles spanning a wide range of Bond ( ${10^{-3}< Bo\leq 1}$ ) and Ohnesorge numbers ( ${10^{-3}< Oh<10^{-1}}$ ), defined with the bubble radius $R$ . The cavity collapse is a capillary-driven process, with a dependency on viscosity and gravity, affecting respectively, precursory capillary waves on the cavity boundary and the static bubble shape. The collapse is characterised by the normal interface velocity ( $U_n$ ) and by the tangential wave propagation velocity of the kink ( $U_t$ ), defined by the intersection of the concave cavity boundary formed after the rupture of the thin film with the convex boundary of the bubble cavity. During the collapse, $U_t$ remains constant and is shown to be $U_t=4.5U_c{\mathcal {W}}_R$ , where $U_c$ is the capillary velocity and ${\mathcal {W}}_R(Oh,Bo)={(1-\sqrt {Oh {\mathscr {L}}} )^{-1/2}}$ is the wave resistance factor due to the precursory capillary waves, with $\mathscr {L}(Bo)$ being the path correction of the kink motion. The movement of the kink in the normal direction is part of the inward shrinkage of the whole cavity due to the sudden reduction of gas pressure inside the bubble cavity after the thin film rupture. This normal velocity is shown to scale as $U_c$ in the equatorial plane, while at the bottom of the cavity $\bar {U}_{nb}=U_c(Z_c/R)({\mathcal {W}_R}/ {\mathscr {L}})$ , where $Z_c(Bo)$ is the static cavity depth. The filling rate of the cavity, which remains a constant throughout the collapse, is shown to be entirely determined by the shrinking velocity and scales as ${Q_T\simeq 2{\rm \pi} R Z_c U_c}$ . From $Q_T$ we recover the jet velocity scaling, thereby relating the cavity collapse with the jet velocity scaling.

THE USE OF TWO FREQUENCY VARIABLES IN THE DISTRIBUTED CIRCUITS SYNTHESIS.

One of the approaches to the design of filters from segments of non-uniform lines is the use of NLs connected by a quadrupole between the generator and the load. In this case, the required characteristic of selectivity is achieved by changing the wave resistance of the line according to a certain law. However, the input op of the NL loaded with an active resistance cannot be purely reactive at real frequencies, so the reflection coefficient cannot be equal to unity at any of them. Therefore, it is fundamentally impossible to obtain a significant attenuation at least at one point outside the passband of the filter. Only by choosing a certain class of complex loads can significant attenuation be achieved outside the passband. Another principle of filter construction is based on the use of the simplest heterogeneous lines that perform the functions of resonators. The necessary selective characteristic of the filter is achieved by selecting the parameters of resonators and communication circuits. This method of building filters is more rational. In addition, in the process of synthesis, you can use ideas and techniques characteristic of circles from segments of uniform lines. It is shown that in the synthesis of distributed circuits based on transmission lines, complex functions of two frequency variables should be used, which allows the construction arbitrary circuit functions and fully cover the classes of physically realized transfer functions. A description of the elements "inductance" and "capacitance" in the class of functions of two complex frequency variables was obtained, which allows synthesizing circuits using the ideas and methods of Richards’s circuit theory.

Penetration mechanics of ceramic/metal functionally graded plates under ballistic impact: An experimental perspective

This paper deals with a comprehensive experimental analysis of the penetration mechanics and failure mechanisms of SiC/AA6061 functionally graded plates under ballistic impact. The external, cross-sectional, and high-speed photographic damage and failure assessments of the plates were performed. The novelty of this study is to investigate the ballistic impact behavior of a ceramic/metal functionally graded plate with different compositional gradients in a wide range of impact velocities considering below and above the ballistic limit and to reveal a detailed analysis of the damage and failure mechanisms of the plate. This can provide fundamental insights into the design of ceramic/metal functionally graded armor materials. The results indicate that the metal-dense gradient plate shows localized ductile failures as ductile perforation and plugging, whereas the ceramic-dense gradient plate exhibits brittle failures as comminution and conoidal fracture. Tailoring a relatively continuous compositional gradient instead of an abrupt variation, namely the linear gradient, provides tensile stress wave attenuation and resistance to crack growth and fracture.

Investigation of An Inverted Bow on Frigate Hull Resistance

This study discusses the inverted bow design on the combatant hull form. Changes in the shape of the stem angle and flare bow are used as analytical parameters to investigate the ship's performance. Ship resistance and motion will be predicted using the Computational Fluid Dynamics (CFD) approach using the Reynolds Averaged Navier Stokes (RANS) equation and the k-ε turbulence model. The volume of fluid (VOF) method is applied to simulate the change in the free surface between water and air using an overset mesh technique. The ship's movement is limited to sinkage and trim motions, so the movement's accuracy can be predicted. The results revealed that the inverted bow reduced the total resistance by 6.30%, whereas the trim and sinkage showed no significant changes. The breakdown of the reduction ratio showed that friction resistance components were reduced by 10.62%, wave resistance by 44.05%, and viscous-pressure resistance by 45.33%. This highlights the effectiveness of an inverted bow in optimizing wave and viscous pressure, enhancing overall ship performance.

Computer simulation of operation plant effective modes for water disinfection by electrical discharges in gas bubbles

Purpose. Determination by means of computer simulation of the most efficient modes of operation of the installation for water disinfection using discharges in gas bubbles, in which (modes) the amplitude of voltage pulses at the processing unit and on the layer of treated water is not less than the voltage amplitude immediately after the switching discharger. Methodology. To achieve this goal, we used computer simulation using Micro-Cap 10. We used two different electrical circuits that simulate the operation of the experimental setup in two different modes: in a mode with a restoring electrical strength of the discharge gap in the gas bubble between two adjacent voltage pulses on the discharge node and in the mode without restoring this dielectric strength. In computer simulation, we varied the following factors: the maximum simulation step, inductances, capacitances, active resistances, wave resistance of a long line, and the delay time for the operation of a spark gap simulating a discharge gap in a gas bubble. Results. Computer modeling has shown that in order to increase the voltage amplitude at the treatment unit and on the layer of treated water, it is necessary to reduce the load capacitance – the capacitance of the water layer in the treatment unit to 10 pF or less, to increase the active resistance of the water layer to 500 W or more. An important factor for increasing the voltage and electric field strength in the discharge unit and, consequently, for increasing the efficiency of treated water disinfection is the discharge delay time in gas bubbles. The most rational delay time for the operation of the arrester, which is the gap in the gas bubble inside the water, under the conditions considered by us is 4–5 ns. It is with this delay time that the amplitude of voltage pulses at the node of disinfecting water treatment and on the layer of treated water is maximum, all other things being equal. Furthermore, with such a delay time this amplitude of voltage pulses significantly exceeds the voltage amplitude directly after the main high-voltage discharger, switching energy from the high-voltage capacitive storage to the processing unit through a long line filled with water. Originality. Using computer simulation, we have shown the possibility of increasing the voltage at the discharge unit of the experimental setup by 35 % without increasing the voltage of the power source. This provides a higher efficiency of microbiological disinfection of water by nanosecond discharges in gas bubbles and lower specific energy consumption. Practical value. The obtained results of computer simulation confirm the prospect of industrial application of installations using nanosecond discharges for disinfection and purification of wastewater, swimming pools and post-treatment of tap water.

A numerical study of added resistance performance and hydrodynamics of KCS hull in oblique regular waves and estimation of resistance in short-crested irregular waves through spectral method

Research on multidirectional waves is increasing as studies on added resistance advance. In this study, the added resistance of the multidirectional regular waves of the KCS hull was estimated by numerical analysis. The direction of the grid was changed according to the heading angle to consider waves in multiple directions. In addition, the method in which the entire domain moved along the movement of the hull was used without using the overset method to minimize the numerical errors. The added resistance and motion RAOs for each angle and the flow characteristics were compared to support the results. For fluid dynamics, time-averaged stern dynamics pressure, boundary layer, and nominal wake for each heading angle were compared, and differences compared to calm water were also reviewed. Based on the bow quartering sea condition analysis results, the added resistance in long-crested and short-crested irregular wave conditions was estimated using the spectral method. The JONSWAP spectrum was used as the target wave spectrum, and the cos-power type was considered the directional spreading function.

Study on the design method of an automatic outrigger layout control system for variable outrigger layout trimaran

During the navigation of a trimaran, its wave resistance is influenced by both sailing speed and outrigger layout. In the case of a variable outrigger layout trimaran, due to the adjustability of its outrigger layout according to different speeds, its wave resistance will be lower than that of traditional trimarans. In this paper, an automatic outrigger layout control system is figured out for a variable outrigger layout trimaran. The system can control and regulate the position of outriggers according to the traveling speed in order to reduce the wave resistance during navigation. The slender ship theory based resistance calculation program is applied as the solver in this system to evaluate the wave resistance of the trimaran and further determine the optimal outrigger layout under a specific speed. In order to improve the calculation accuracy, NURBS (Non-Uniform Rational B-Splines) method is introduced to modeling the hull surface. Model tests for trimaran with 6 different outrigger layouts are conducted to obtain the resistance of the trimaran in order to validate the numerical method. The steepest descent method is applied to solve the problem of searching the outrigger layout with minimum wave resistance efficiently. On this basis, an open-loop control system for trimaran outrigger layout is designed based on PID (Proportional Integral Derivative) algorithm with the control objective derived by the solver. Finally, a outrigger layout adjustment simulation (when speed changes from Fr=0.4 to Fr=0.35) is conducted on the experimental trimaran model. By comparing the resistance results obtained by numerical method utilized in this paper to the results obtained by CFD (Computational Fluid Dynamics) simulations, the effectiveness of the proposed system is validated.

HR Quality and Work Stress on Employee Performance in Potential Management Mangrove Forest Tourism

This study aims to determine the effect of the quality of human resources and work stress on employee performance, in this case, it is the Farmer's group Greening Forward Together with the new Dusun X Paluh Mangrove Village Rawa Market Village. Mangrove Forest is a tourist attraction in Langkat Regency which has a unique, mangrove forest that plays a role in regional life that can withstand seawater abrasion and wave resistance. Mangrove forests are also used for the income of local residents to meet their needs and as a place for the development of certain marine life and flora and fauna. One of the fauna found in mangrove forests is baronang fish. Baronang fish is one of the fish that is a mascot mangrove tourist attraction in Pasar Rawa Village. The source of data used in this study is primary data. Data collection method using a questionnaire. The results of the analysis in this study show that work stress has a significant effect on work productivity and workload affects work productivity. Keywords: Mangrove Forest, Potential, Human Resources

Practical ship afterbody optimization by multifidelity techniques

ABSTRACT This paper discusses multifidelity methods for CFD-based optimization of ship afterbody designs; aimed at a fast application to a variety of practical cases. Surrogate-based global optimization is used, using a multi-objective genetic algorithm. The surrogates are derived by combining few high-fidelity computations, by free-surface RANS codes, with many low-fidelity computations. For rather slender vessels for which the wave resistance variations over the design space are dominant, a free-surface potential flow code is found very effective as a low-fidelity solver, permitting a large reduction of the number of RANS computations and the associated cost. Examples are shown for model 5415 and a fast displacement vessel. For cases with variation in both viscous and wave resistance, an alternative method is used combining coarse and fine-grid RANS computations; the coarse-grid ones being about 20 times cheaper. Application of this coarse/fine grid multifidelity optimization to a containership and a motor yacht shows its effectivity.

Мodel of diffraction of electromagnetic waves on explosive objects

A model of electromagnetic wave diffraction on an explosive object without metal structural substances is proposed. The properties of the materials of the most common anti-personnel mines were analyzed and it was established that their shell is dielectric, and explosive substances are divided into two groups depending on their dipole moment. In particular, the explosive substances such as hexogen, pentaerythritol tetranitrate, and mercury fulminate with zero dipole moment and according to their electromagnetic properties, they belong to ideal dielectrics. The explosives trinitrotoluene, tetryl, lead trinitroresorcinate, and lead azide should be considered as low-loss dielectrics. An electrodynamic model was built to calculate the reflection coefficients and the passage of electromagnetic plane waves of the microwave range through the multilayer structure of an explosive object. To determine the equivalent wave resistance of the multilayer structure of an explosive object, the use of the theory of long lines is proposed. It is established that for microwave radiation, the layers of the case of explosive objects made of dielectric substances can be neglected due to their small thickness. The modeling results show that most anti-personnel mines have a low reflection coefficient, which makes them difficult to detect, but at the same time increases the amount of energy that can pass deep into the body of the explosive substance. It has been shown that explosive objects with dipole explosive substances are capable of absorbing electromagnetic radiation energy. The obtained results allow us to qualitatively assess the susceptibility of explosive substances to their remote detonation by irradiation with powerful pulses of electromagnetic radiation in the microwave range.

Изучение принципов построения широкополосной колебательной СВЧ системы на примере резонатора Фабри-Перо

In telecommunications and radar systems of the centimeter and millimeter wave ranges, span klystrons are widely used as medium and high power amplifiers. The use of high-quality resonators makes it possible to realize high efficiency and amplification factors. However, typical designs of 2 - 4 resonator klystrons have a bandwidth of 0.1 - 0.5 % due to the need to use resonators with a high Q – factor. The well-known method of expanding the amplified frequency band in the centimeter range up to 7 – 12 % and in the millimeter range up to 1 - 2 % consists in tuning the frequency of the intermediate klystron resonators by several percent of the central amplification frequency. But in this case, it is required to use 10 - 12 resonators. The authors of the work discovered that when a millimeter range electromagnetic wave is reflected from an electrodynamics system in the form of a metal film on the surface of a semiconductor layer, the input resistance phase-frequency characteristic of this system consists of a chain of frequency intervals with turnings from a positive phase-frequency characteristic to a negative one and vice versa. The possibility of constructing a phase shifter with a negative phase frequency response based on this phenomenon is demonstrated and its application for expanding the resonant frequency band is considered on the example of the Fabry - Perot interferometer model. This resonator contains a phase shifter in the form of a semiconductor layer F with a thickness DF, a conductivity σF, a relative dielectric eF and a magnetic mF permeability. The outer surface of the layer F contains a metal mirror, and the inner surface is adjacent to the layer W. The layer W which has the thickness of DW, eW, mW forms the internal space of the resonator. The external environment I with mI and eI. adjoins the layer W. A plane electromagnetic wave propagates in I media so that it excites the resonator at a wavelength of l0. The use of a phase shifter makes it possible to increase the resonant wavelength band Δl/l0 by 2 - 4 times and with an electromagnetic field amplification coefficient |G(l)| in the W layer by 10 - 20 times (the value of Dl/l0 corresponds to 0.707 max |G(l0)|). An increase of σF leads to an amplitude-frequency characteristic transforming of the field gain function G(l0) from two maxima to one maximum form with a transition through a flat top. In this case max |G(l0)| decreases and Dl/l0 increases. For the case, when the function |G(l)| has a flat top, an increase in the wave resistance ρW of the layer W with a corresponding decrease in sF and optimal values of DW leads to an increase in |G(l0)|. When this occurs, Dl/l0 becomes lower.

Motion of a submerged body under a free surface and an ice cover in finite water depth conditions

In this study, we consider the motion of a submerged body near the free surface of a liquid and a liquid covered with an ice cover in finite water depth conditions. The influence of water depth on the nature of motion of a submerged body has been experimentally and theoretically analysed. The experiments were performed in an ice tank. The use of a cable towing system allowed the researchers to measure the magnitude of the relative vertical displacement of the submerged body resulting from the action of the lift force. The influence of ice cover on the relationship between the vertical displacement, trim angle, criterion for ice breaking, and speed of movement of the submerged body model was established. For theoretical research, the ice cover was modelled by a viscoelastic floating plate, and the submarine was modelled by a source–sinks system in a fluid flow. The influence of water depth, the presence of an ice cover, changes in the submergence depth, and the speed of movement of the submerged body on the wave resistance, lift force, and trimming moment were analysed. Theoretical results are supported by experimental data.

Force impact of a flow of an infinitely deep liquid on a source under ice cover

A characteristic natural factor of the polar regions of the World Ocean and freezing sea areas is the presence of ice cover. The floating ice cover, which determines the dynamic interaction between the ocean and the atmosphere, affects the dynamics of not only the sea surface, but also subsurface waters, while both the ice cover and the entire mass of liquid beneath it participate in the general vertical movement. It is assumed that the ice cover is continuous, that is, its horizontal scales exceed the lengths of the excited waves and, under fairly natural conditions, is modeled by a thin elastic plate, the deformations of which are small and the plate is physically linear. The problem of calculating the force impact of a flow of an infinitely deep homogeneous liquid on a localized source under the ice cover is solved. The problem is solved for the two-dimensional case. Integral representation of the solution for wave drag and lift is obtained, which arise due to the presence of an ice cover and act on the source. The results of calculations of the force action acting on a localized source, simulating a blunt semi-infinite body of finite width, and a dipole, simulating a cylinder, are presented for various values of the oncoming flow velocity and their immersion depth. Numerical calculations show that as the depth of the source immersion increases, the force effect of the fluid flow, which occurs due to the presence of an ice cover, decreases. The dependences of the wave resistance and lift force on the velocity of the incoming fluid flow demonstrate a qualitatively different behavior. The obtained results with different values of the physical parameters included in them make it possible to evaluate the characteristics of ice cover disturbances and its impact on various sources of natural and anthropogenic disturbances observed in real marine conditions.

An efficient method for unsteady hydrofoil simulations, based on Non-Linear Dynamic Lifting Line theory

This paper presents a Non-linear Dynamic Lifting Line (NDLL)-based method for analysing hydrofoil vessels in waves. The method is validated, and its utility is demonstrated in a case study.The NDLL accounts for dynamic and 3D effects through a panellized wake and allows the evaluation of the pressure distribution on hydrofoils. Improved models are presented for wake deformation, wake composition, hydrofoil interaction, and the viscous core of vortex wake models. Furthermore, an efficient way of accounting for Green function terms through a matrix interpolation method is presented.Validation is performed by comparison with aerodynamic and hydrodynamic experiments and new 3D RANS simulations. The RANS simulations focus on geometries and operating conditions deemed representative of hydrofoiling fast ferries. Predictions of steady and dynamic lift, drag, wake velocities and cavitation inception are evaluated, and results correspond well with the benchmark data.A simulator framework is introduced, which integrates the hydrodynamic model with kinetics, kinematics, and control system models. This enables analyses of free-running vessels under active control, including assessments of resistance, motions, and the hydrofoil pressure distribution.The case study constitutes a qualitative verification of the simulator and flight control tuning methods, and reveals the possibility of negative added resistance in waves.

Robust optimal ship hulls based on Michell's wave resistance

We seek the hull of a ship with a given volume which minimizes the water resistance with uncertainties on the cruising speed. The water resistance is based on Michell's wave resistance functional, and the speed is a random variable whose probability distribution is known. We first handle the case where the support of the hull is given and then we also optimize this support for a given area. In each case, an optimal hull is shown to exist. The numerical simulations are costly so we adapt to our problem Newton's method for shape optimization. The Dirichlet energy is used as a test case. The numerical results for the robust optimal hull are compared with the case where the cruising speed is known.

A Numerical Study on the Performance of the 66k DWT Bulk Carrier in Regular and Irregular Waves

Accurate resistance performance evaluation is essential to predict the minimum propulsion horsepower required for ships in real sea. Therefore, in this paper, the added resistance performance of K-Supramax in various wave conditions was calculated using CFD (Computational Fluid Dynamics). First, to compare the resistance performance according to the DOF (Degree of Freedom), the added resistance performance in the head regular wave was investigated and compared with the experiment. The 2DOF and 6DOF results in the head regular wave had no significant differences. Second, to compare the resistance performance among various wave conditions, the effect of the heading angle was analyzed by comparing resistance and motion RAOs (Response Amplitude Operators) in bow quartering sea conditions using 6DOF. The added resistance showed the highest value near the resonance frequency of 170°. As the heading angle increased, the added resistance tended to decrease, regardless of the wavelength ratio. Also, the added resistance performance in irregular waves was investigated with reference to the adverse conditions. The spectral method, which linearly superimposes regular wave results, and the added resistance generated during irregular waves directly through CFD were compared. The resistance in irregular waves increased by approximately 92% for the spectral method and by approximately 72% for the direct irregular wave calculation compared to the resistance in calm water. In addition, the PSD (Power Spectral Density) of resistance and the distribution of motion RAOs obtained from direct irregular wave calculations were investigated.