Effects Of Ship Motion Research Articles

Evaluation of added resistance of kvlcc2 in short waves

The added resistance of KVLCC2 in short and regular head waves has been studied theoretically and experimentally. Model tests are performed to determine how well the asymptotic formula (Faltinsen et al. 1980) predicts the typical level of added resistance in short waves. Because the asymptotic formula neglects the effects of ship motions, it is combined with theoretical methods to calculate the added resistance in long waves using an R function to predict the added resistance in the intermediate wavelength region where both ship motions and wave reflection are important. A unique feature of this experiment is that the ship model is divided into three segments to explore the added resistance distribution with respect to hull segment. This paper discusses the sensitivity of experimental results to the quality of the incident regular head waves. Moreover, a novel procedure for analyzing added resistance is described. Finally, the experimentally determined added resistance of KVLCC2 is compared with theoretical results. It is shown that the added resistance from the combined theoretical methods agrees well with experimental results in both the intermediate and short wave regions. The use of hull segments shows that added resistance is concentrated primarily at the bow.

Effects of ship motions on laminar flow in tubes

The thermal–hydraulics of barge-mounted floating nuclear desalination plants is the incentive for this study. Laminar flow in tubes in heaving motion is modeled. The friction factor and heat transfer coefficient are obtained. All the equations of laminar flow in steady state are applicable for heeling motion. The effect of ship motions on the laminar developing region is also analyzed. The ship motions can weaken the boundary layer in the laminar developing region and strengthen the laminar frictional resistance. The effect of ship motions on the instability of laminar flow is also investigated. The ship motions do not affect the instability point, but they can shorten the distance between the instability point and the transition point, and cause the transition from laminar flow to turbulent flow to occur earlier.

Effect of ship motion on spinal loading during manual lifting

This study investigated the effects of ship motion on peak spinal loading during lifting. All measurements were done on a ship at sea. In 1-min trials, which were repeated over a wide range of sailing conditions, subjects lifted an 18 kg box five times. Ship motion, whole body kinematics, ground reaction forces and electromyography were measured and the effect of ship motion on peak spinal moments and compression forces was investigated. To investigate whether people time their lifts in order to reduce the effect of ship motion on back loading, trials were performed at a free and at a constrained (lifting every 10s) work pace. With increase of the (local) vertical ship acceleration, increased moments and compression forces were found. Furthermore, lifting at a free work pace did not result in smaller effects of ship motion on spinal moments and compression forces than working at a constrained work pace.

Study on coupling effects of ship motion and sloshing

This study considers the coupling effects of ship motion and sloshing. The linear ship motion is solved using an impulse-response-function (IRF) method, while the nonlinear sloshing flow is simulated using a finite-difference method. The IRF method requires the frequency-domain solution prior to conversion to time domain, but the computational effort is much less than that of direct time-domain approaches. The developed scheme is verified by comparing the motion RAOs between the frequency-domain solution and the solution obtained by the IRF method. Furthermore, a soft-spring concept and linear roll damping are implemented to predict more realistic motions of surge, sway, yaw, and roll. For the simulation of sloshing flow in liquid tanks, a physics-based numerical approach adopted by Kim [2001. Numerical simulation of sloshing flows with impact load. Applied Ocean Research 23, 53–62] and Kim et al. [2004. Numerical study on slosh-induced impact pressures on three-dimensional prismatic tanks. Applied Ocean Research 26, 213–226] is applied. In particular, the present method focuses on the simulation of the global motion of sloshing flow, ignoring some local phenomena. The sloshing-induced forces and moments are added to wave-excitation forces and moments, and then the corresponding body motion is obtained. The developed schemes are applied for two problems: the sway motion of a box-type barge with rectangular tanks and the roll motion of a modified S175 hull with rectangular anti-rolling tank. Motion RAOs are compared with existing results, showing fair agreement. It is found that the nonlinearity of sloshing flow is very important in coupling analysis. Due to the nonlinearity of sloshing flow, ship motion shows a strong sensitivity to wave slope.

Modeling Helicopter Blade Sailing: Dynamic Formulation in the Planar Case

As part of a research project aimed at simulating rotor dynamic response during shipboard rotor startup and shutdown operations, a dynamic model of the ship–helicopter–rotor system that is appropriate for use in predicting rotor elastic response was developed. This planar model consists of a series of rigid bodies connected by rotational stiffness and damping elements that allow motion in the flapwise direction. The rotors were partitioned into an arbitrary number of rigid beam segments having the inertial and geometrical properties of a typical rotor. Helicopter suspension flexibility and damping were also modeled, although the helicopter was otherwise considered as a rigid body. Lagrange’s equation was used to derive the governing dynamic equations for the helicopter–rotor model. The effect of ship motion on blade deflection was also considered. The ship motion supplied as input to the model included representative frigate flight deck motion in three dimensions corresponding to an actual sea spectrum, ship particulars and ship operating conditions. This paper is intended to detail the dynamic approach adopted for this blade sailing study, and its conceptual validation in the planar case. The methodologies that have been developed lend themselves to easy expansion into three dimensions, and into torsion and lead/lag modeling. The amount of blade motion induced by ship motion on nonrotating helicopter blades is included. Although aerodynamic loads are a major contributor to blade sailing, this paper focuses on the dynamics aspect of the problem, and thus does not include aerodynamic effects.

EFFECT OF SHIP MOTION ON LOW BACK MOMENTS DURING MANUAL LIFTING

INTRODUCTION Performing heavy work (such as lifting) on a ship is associated with a high prevalence of musculoskeletal problems [1,2]. Lifting results in high low back loading [3], thereby affecting low back pain risk. Ship motion may have an additional effect on low back loading during lifting [4]. Depending on the timing of a lifting movement, ship motion can either increase (for example when a ship accelerates upwards) or decrease (for example when a ship accelerates downwards) low back loading. The aim of the present study was to find out to what extent ship motion affects the peak low back moment at the L5S1 joint during manual lifting on a ship at sea. Furthermore, it was investigated whether people are able to time their lifting movements in such a way that the effect of ship motion reduces peak low back moments.

Modeling Ship Motion Effects on Human Performance for Real Time Simulation

Modeling the effects of ship motions on human task performance is an emerging technology, and implementing these models in real time distributed simulation for virtual naval platforms is a new discipline. The environmental, ship and computer technologies embodied in the virtual naval platform concept are summarized. The types and severity of human performance problems related to ship motions are reviewed and task performance issues are discussed. Requirements for modeling fatigue, motion sickness, biodynamic problems and task performance are discussed, and existing models are described. Recommendations are made for developing new performance models and for enhancing existing models.

Effects of ship motions on natural circulation of deep sea research reactor DRX

DRX is a very small integral type PWR (750 kW t) for a scientific deep-sea research bathyscaph. The core having a small amount of steam is cooled by natural circulation and pressurized by self-pressurization. During operation of the bathyscaph in a deep sea or near the water surface, a ship inclination or ship motions will affect the reactor behavior. This paper describes the effect of a heeling or a heaving on the thermal hydraulic behavior of reactor system, which is analyzed by retran-02/grav improved so to simulate the effect of ship motions. The dynamics has a feature of nuclear power-natural circulation flow coupling under the condition of external forces. The analysis shows that ship inclination induces the core flow to decrease but reactor power recovers to the initial level without help of the reactor automatic control system. The heaving makes the core flow and the reactor power oscillate in phase with heaving, which are different from a density wave oscillation. Oscillation amplitudes of the flow and the power have peaks at the heaving period of 5 s. The peaks are due to resonance of the natural circulation flow and the heaving. An effective measure to suppress this oscillations due to heaving is to pressurize the primary loop by filling non-condensable gas. The density wave oscillation occurs when the reactor power increases over the rated power, and the boundary of its occurrence is analytically revealed. Under the condition of both density wave oscillation and heaving, the system shows to oscillate with the overlapped effect.

Effects of Motion at Sea on Crew Performance: A Survey

Current efforts to minimize ship crews now more than ever require all persons on board to be fully functional and capable of conducting their prescribed duties and responsibilities. However, inherent in the nature of any maritime profession, ships and, therefore, people are exposed to a multitude of motions as a result of weather and sea conditions. Coincident with these motions are a host of physiological, biomechanical, and psychological responses that can quickly reduce even the best efforts of the crew to a fraction of their utility when performed on a stable platform. Ship motions limit a crew's ability to perform essential command, control, and communications functions, navigation tasks, maintenance responsibilities, and even the preparation of food. Additionally, and more importantly, emergency situations may become more threatening in a situation where only a portion of the crew is able to respond effectively. This survey is intended to provide a working knowledge of effects of ship motions on crew performance, fatigue, and motivation. This information can then be used to improve ship and equipment design, and lead to enhanced vessel effectiveness and performance and, more importantly, to enhanced safety of the individuals on board. As ship design evolves and crew sizes decrease, greateremphasis must be placed upon the human factor input in order to ensure safety and efficiency during both routine and emergency operations.

The Design Of Visual Landing Aids For Shipborne Helicopter Operations

ABSTRACTAny aircraft approach to landing that takes place over featureless terrain presents operational difficulties to pilots due to the absence of those ground‐derived textural cues that normally enable them to assess the flight path of the aircraft. Night, low visibility, crosswind and ship motion effects are factors that further increase the task difficulty for ship‐borne operations. Visual aids such as a Glide Slope Indicator are of vital importance in these circumstances.Currently the trend in helicopter operations from ships is toward more flights taking place in high sea states and low visibility. This reinforces the need for the full stabilization of precision guidance aids and requires the use of high intensity lighting. To support operations in high sea states it is necessary for the visual aids to function at pitch and roll angles greater than those defined for safe landings.A Stabilized Glide Slope Indicator and a fully Stabilized Horizon Bar together with ship outline lighting significantly enhance the cues that a pilot can derive from the ship. By using green luminescent panels for these latter aids a system is created that is effective in precipitation and is compatible with the use of Night Vision Goggles (NVG). These aids enhance safety and operational limits.

Optimal takeoff performance of a vectored thrust aircraft

AbstractThe optimal takeoff performance of a vectored thrust V/Stol aircraft is analysed by a nonlinear programming method based on a sequential unconstrained minimisation technique. The study is focused on ship operations which involve VTO and ski-jump STO launches. Once the optimal ramp geometry is determined, minimum-fuel and minimum-time problems are solved. The optimal control sequences are evaluated and the effects of ship motion and atmospheric winds are discussed. A microburst encounter following an STO launch is also dealt with in terms of aircraft survival.

ON THE DEVELOPMENT OF SEAKEEPING CRITERIA

In order to determine the effects of ship motion on operational performance, quantitative seakeeping criteria are required. In this paper, it is proposed that seakeeping criteria should be presented in terms of limits on the incidence of whatever degrading event is determined to curtail the operation of interest, rather than limits on the underlying ship motions. For personnel operating on deck, the degrading events of most interest are the onset of loss-of-balance incidents, termed motion-induced interruptions, due to tipping or sliding. For unsecured helicopter operations, the most important degrading event is the helicopter sliding. The authors present a frequency-domain method of predicting the incidence of personnel or of equipment sliding which includes the forces due to roll, pitch, longitudinal, lateral and vertical accelerations, and also the effects of non-zero mean heel angles. They then present a method for predicting the incidence of personnel experiencing motion-induced interruptions due to loss of balance which includes the above forces and also the effects of steady and unsteady winds. In order to work in the frequency-domain, all of the forces are linearised and we consider only the linear turbulent wind force, and neglect the nonlinear term. Two main applications of the methods are anticipated. The first application is to design. The seakeeping criteria presented here are closely linked with the physical phenomena that are causing performance to be degraded, and are equally applicable to all ship types. The second application is to active operational guidance systems which provide real time information to the operators of naval vessels on the effects of changes in speed or heading on operations. Developing criteria in terms of the degrading events of most interest to the operator should result in an immediate improvement in the quality of the guidance.

On the Development of Seakeeping Criteria

ABSTRACTIn order to determine the effects of ship motion on operational performance, quantitative seakeeping criteria are required. In this paper, we propose that seakeeping criteria should be presented in terms of limits on the incidence of whatever degrading event is determined to curtail the operation of interest, rather than limits on the underlying ship motions. For personnel operating on deck, the degrading events of most interest are the onset of loss‐of‐balance incidents, termed motion‐induced interruptions, due to tipping or sliding. For unsecured helicopter operations, the most important degrading event is the helicopter sliding.We present a frequency‐domain method of predicting the incidence of personnel or of equipment sliding which includes the forces due to roll, pitch, longitudinal, lateral and vertical accelerations, and also the effects of non‐zero mean heel angles. We then present a method for predicting the incidence of personnel experiencing motion‐induced interruptions due to loss of balance which includes the above forces and also the effects of steady and unsteady winds. In order to work in the frequency‐domain, all of the forces are linearized and we consider only the linear turbulent wind force, and neglect the nonlinear term.Two main applications of the method are anticipated. The first application is to design. The seakeeping criteria presented here are closely linked with the physical phenomena that are causing performance to be degraded, and are equally applicable to all ship types. The second application is to active operational guidance systems which provide real time information to the operators of naval vessels on the effects of changes in speed or heading on operations. Developing criteria in terms of the degrading events of most interest to the operator should result in an immediate improvement in the quality of the guidance.

Thermal-hydraulic behavior of a marine reactor during oscillations

The effect of ship motion, such as heaving and rolling, on the thermal-hydraulic behavior of marine reactors was investigated. The COBRA-IV-I CODE was modified to analyse the thermal-hydraulic performance on the critical heat flux under oscillating acceleration conditions. The critical heat flux in the code was verified experimentally using freon as a comparison. The Critical Heat Flux Ratio (CHFR) at the hottest channel of the PWR subchannel was analysed using the same code. A system code RETRAN-02/MOD2-GRAV was developed by improving RETRAN-02/MOD2 to simulate the thermal hydraulic transient under ship motion. It was verified by comparison using the experimental results of both two-phase natural circulation flow under heaving motion and single-phase natural circulation flow at an inclined attitude. The code was used to analyse reactor plant behavior in the nuclear ship Mutsu. Natural circulation flow during rolling motion was investigated experimentally. The characteristics of loop flow and core flow rates were clarified. The core flow rate correlated well with the Reynolds number of rolling motion.

Motion‐Induced Interruptions as Ship Operability Criteria

ABSTRACTAn important goal of operability research is the development of quantitative seakeeping criteria to permit the effects of ship motions on operations to be assessed. This paper examines the problem of developing seakeeping criteria for deck operations. The lateral force estimator is generalized to permit frequency‐domain computation of the incidence of personnel losing balance in the presence of non‐zero vertical acceleration.The inadequacy of roll‐angle based seakeeping criteria for deck operations is shown. Other possible criteria for deck operations are discussed, and it is concluded that a limit on the number of motion‐induced interruptions during deck operations is most suitable, since it is platform‐independent, and may now be computed in the frequency‐domain.

Problems of defining criteria for protecting crew from ship motion effects

The single‐frequency model of motion sickness incidence (MSI) developed by H. F. O'Hanlon and M. E. McCauley [Aerospace Med. 45, 366–369 (1974)] does not reliably predict MSI in complex oscillation typical of ship motion, as was shown by systematic measurements of MSI during combined heave motions [J. C. Guignard and M. E. McCauley, Aviat. Space Environ. Mede. 53, 554–563 (1982)]. Clinical and physiological observations (complemented by inertial measurements of head motion) during dynamically simulated 48‐h rough‐sea deployments of a projected 2000‐ton surface effect ship provided further insight into the phenomenon of seasickness. Sixteen of 19 fit young naval volunteers discontinued testing, because of severe motion sickness; and all experienced symptoms. Severe motion sickness caused abandonment of psychomotor task performance; but two subjects consistently resistant to sickness performed their tasks throughout the experiment (although experiencing some nausea and exhibiting post‐run postural instability). Ataxia, and symptomatic motion sickness in some cases, persisted for several hours after motion. Habituation to motion severe enough to provoke continuing vomiting did not occur in these simulations, although there was indirect evidence of some transfer of habituation from prior single‐frequency motion exposure. We recommend that motion effects be studied systematically in relation to the physical parameters of provocative motion. [Work of Naval Aerospace Medical Research Laboratory Detachment ♯ 1 (now Naval Biodynamics Laboratory), New Orleans; supported by Office of Naval Research. Views not necessarily those of the Department of the Navy. Archival data in letter report to ONR (1980) and Paper ♯9 to NATO/DRG Seminar, Toronto (1983).]

Dynamic response of a wingsail mast to unsteady aerodynamic loads including ship motion effects

An analytical procedure for determining the dynamic response of a wingsail mast is discussed. The method uses lifting strip theory to calculate the unsteady aerodynamic lifts and moments acting on a wingsail mounted on a rolling ship. The procedure is implemented on a microcomputer to make it accessible to engineers. The procedure is appropriate for the preliminary structural design of wingsail masts. Sample calculations on a wingsail based on a design for the retrofit of a chemical tanker are discussed. The results of the example indicate that the unsteady aerodynamic loads may be of the same magnitude as the steady aerodynamic loads under certain conditions.

HUMAN FACTORS ENGINEERING PRINCIPLES FOR MINIMIZING ADVERSE SHIP MOTION EFFECTS: THEORY AND PRACTICE

ABSTRACTAs part of a wider seakeeping program conducted by the David Taylor Naval Ship Research and Development Center, two mission‐critical workstations were evaluated for the United States Coast Guard (USCG). These workstations (the communications support center and the communications center) have been specifically identified by the USCG as having exceptional seasickness problems. Five potentially applicable human factors engineering (HFE) approaches to enhance seakeeping through prevention and mitigation of adverse ship motion effects, especially seasickness, were recognized and are discussed in this report in the light of observations made aboard the ship. These are: (1) locate critical stations near ship's effective center of rotation; (2) minimize head movements; (3) align operator stations with a principal axis of the ship's hull; (4) avoid combining provocative sources; and (5) provide an external visual frame of reference at stations where seasickness may seriously impair mission effectiveness. This report relates how the application of relatively simple HFE principles (ideally at the early ship design and arrangement stage) may reduce seasickness and other adverse ship motion effects and so enhance seakeeping.

Concurrent underwater acoustic wave front fluctuations at two frequencies over a 75‐nmi path

An experiment was performed to investigate the fluctuations in wave front shape of signals transmitted over a distance of about 75 nmi from a ship‐suspended sound source to a bottomed set of receivers. An experimental set of eight receivers, spanning a distance of about 2300 ft in both the downslope and cross‐slope directions, was laid on a 26° slope southwest of Bermuda at about 5000‐ft depth. Pulses of 200‐ and 400‐Hz signals were transmitted alternately from the projector, by the second‐order RSR mode; these were recorded on an oscillograph, and delays in arrival time at each receiver were measured. Plane wave fronts were fitted to the delay data, and the azimuth and elevation angles for the wave fronts were calculated. The effect of ship motion and stationary effects were removed from the raw delays. Plane wave front fits to the adjusted data were made, and deviations from these wave fronts were found for each receiver. The wave fronts are characterized by two actions: (1) gross wave front rocking and tilting, and (2) crinkling of the wave front (short‐scale effects, a dimension smaller than the maximum receiver spacing).

Motion compensation system for ocean profiling

The vertical profiles of ocean temperature and salinity measured with instruments lowered by cable from surface ships can be seriously affected by the nonuniform drop rate caused by ship motion. This paper describes a motion compensation system developed for conductivity, temperature, and depth profilers that significantly reduces the effect of ship motion on profiler drop rates, thereby enhancing the measurement capabilities of vertical profilers.