Vertical Motion Responses Research Articles

Impacts of the North Atlantic biases on the upper troposphere/lower stratosphere over the extratropical North Pacific

The winter upper troposphere/lower stratosphere temperature/vertical motion response over the extratropical North Pacific induced by North Atlantic changes is not well understood. Here, using robust diagnostic calculations conducted in a fully coupled high-resolution climate model, we correct the North Atlantic ocean circulation biases and show that during wintertime, the North Atlantic cold surface temperature biases lead to a warmer upper troposphere/lower stratosphere over the extratropical North Pacific. In the upper troposphere/lower stratosphere over the extratropical North Pacific, this winter warming temperature response is linked to the vertical motion response through a simple leading order thermodynamic relationship between changes in the horizontal advection and adiabatic heating. The upper troposphere/lower stratosphere vertical motion response, which is also associated with the North Atlantic induced Walker circulation response over the tropical North Pacific, can provide a rough estimation of the upper troposphere/lower stratosphere warming response over the extratropical North Pacific.

Model Experimental Study on a T-Foil Control Method with Anti-Vertical Motion Optimization of the Mono Hull

T-foils with active control systems can adjust their attack angle according to the movement of the ship in real time, providing higher lift force and improving the seakeeping performance of a ship. The optimization of the control signal and that of the control method have an important influence on the effect of active T-foils. In this paper, the control method of the T-foil’s swinging angle is established and optimized on the basis of model testing in order to increase the effect of the T-foil. First, the governing equation is introduced by establishing the proportional relationship between the angular motion of the hull and the lift moment of the T-foil. On the basis of the model of the T-foil’s lift force, the governing equation of the T-foil’s swinging angle is deduced and simplified using the test results of the ship model with a passive T-foil and without a T-foil. Then, the active T-foil control system is established by comparing the effects of T-foils with different control signals. Finally, the efficacies of the passive and active T-foil are reported and discussed. It is found that the pitch angular velocity is a more appropriate signal than the pitch angle and pitch angular acceleration. T-foils with pitch angular velocity control can decrease the vertical motion response in the resonance region of a ship’s encounter frequency by more than about 20% compared to the case of the bare ship model, while also increasing the anti-bow acceleration effect by more than 15% compared to the case of passive control. The results obtained by model testing have a certain guiding significance for specific engineering practices.

Notes on a compressible extended Burgers model of rheology

SUMMARY Constitutive theory for viscoelasticity has broad application to solid mantle or ice deformations driven by tides, surface mass variations, and post-seismic flow. Geophysical models using higher order viscoelasticity can better accommodate geodetic observations than lower-order theory, typically provided by tensor versions of Maxwell, 4-parameter Burgers or standard linear (Zener) rheology. We derive, for the first time, a mathematical description of a compressible version of the extended Burgers material (EBM) model paradigm which has a distribution function of relaxation spectra. The latter model is often used for parametrizing high temperature background transient responses in the rock physics and mechanics laboratory setting and have demonstrated application to low frequency seismic wave attenuation. A new generalization of this practical anelastic model is presented and applied to the glacial isostatic adjustment momentum equations, thus providing useful guidance for generating initial-value boundary problem-solving software for quite general coding strategies. The solutions for the vertical motion response to a suddenly imposed surface load reveal a short-term transience of substantial amplitude.

Numerical prediction of ship motion and slamming load characteristics in cross wave

When waves from two weather systems converge at a certain sea area, cross waves can be produced. It is important to have a better understanding of the motion characteristics of ship in cross sea to ensure its navigation safety. In this paper, the motion responses of a S175 container ship hull in cross sea is first analyzed based on CFD technique using RANS method. VOF method is used to model and capture the free surface and overset grid technique is adopted to simulate ship motions in waves. Verifications on ship motion by the numerical method have been conducted for time step- and grid-independent studies. According to the motion results by numerical simulation, typical conditions are chosen for further investigation of slamming pressure on bow area and green water on deck. It is found that vertical motion responses of ship induced by cross waves can be quite large and the ship experienced obvious roll–pitch-coupled motion. Severe bow slamming and green water under cross sea state are also observed. The bow flare slamming pressure on the baseline can be quite large in symmetric cross wave. Asymmetrical slamming impacts occurred when the ship sails in an asymmetric cross wave field.

Influence of an Integral Heave Plate on the Dynamic Response of Floating Offshore Wind Turbine Under Operational and Storm Conditions

The hydrodynamic performance of the floating foundation for offshore wind turbines is essential to its stability and energy harvesting. A semi-submersible platform with an integral heave plate is proposed in order to reduce the vertical motion responses. In this study, we compare the heave, pitch, and roll free decay motions of the new platform with a WindFloat-type platform based on Reynolds-Averaged Navier-Stokes simulations. The differences of the linear and quadratic damping properties between these platforms are revealed. Then, a FAST (Fatigue, Aerodynamics, Structures, and Turbulence) model with the consideration of fluid viscosity effects is set up to investigate the performance of the new platform under storm and operational conditions. The time-domain responses, motion spectra, and the mooring-tension statistics of these two platforms are evaluated. It is found that the integral heave plate can increase the viscous hydrodynamic damping, significantly decrease the heave and pitch motion responses, and increase the safety of the mooring cables, especially for the storm condition.

CFD Investigation into The Effect of Heave Plate on Vertical Motion Responses of a Floating Jetty

CFD Investigation into The Effect of Heave Plate on Vertical Motion Responses of a Floating Jetty

Numerical Study on Change of Added Resistance due to Incident Waves in Finite Water Depth

AbstractIn this study, the effect of water depth on vertical motion responses and added resistance of ships in waves was numerically examined. The applied numerical method corresponded to the time ...

A comprehensive study on the seakeeping performance of high speed hybrid ships by 2.5D theoretical calculation and different scaled model experiments

In this paper, seakeeping performance of vessels is comparatively investigated by means of improved 2.5D theoretical calculation, small-scale model towing tank test and large-scale free running model sea trial. This study also provides a scheme of ship vertical motion stabilization technique by using Semi-Submerged Bow (SSB) appendages. Firstly, an improved strip theory based 2.5D theoretical seakeeping algorithm, which considers the viscous flow effects attributed to bow appendages, is developed to estimate ship vertical motion responses in regular waves. Short-term predictions are also made on the basis of spectral analysis theory to predict ship motion responses in irregular waves. Then corresponding small-scale models are made and tested in a laboratory towing tank for both regular and irregular wave conditions to confirm the numerical results. The tank testing results between different ship schemes are also compared to experimentally investigate the effects of SSB and fin on hull vertical motion stabilization. Furthermore, large-scale model sea trials are conducted in coastal waves for a final validation of the ship seakeeping performance in short-crested sea waves. Finally, comparisons of the results by different testing approaches are systematically made and analyzed.

Numerical studies on non-linearity of added resistance and ship motions of KVLCC2 in short and long waves

In this study, numerical simulations for the prediction of added resistance for KVLCC2 with varying wave steepness are performed using a Computational Fluid Dynamics (CFD) method and a 3-D linear potential method, and then the non-linearities of added resistance and ship motions are investigated in regular short and long waves. Firstly, grid convergence tests in short and long waves are carried out to establish an optimal mesh system for CFD simulations. Secondly, numerical simulations are performed to predict ship added resistance and vertical motion responses in short and long waves and the results are verified using the available experimental data. Finally, the non-linearities of added resistance and ship motions with unsteady wave patterns in the time domain are investigated with the increase in wave steepness in both short and long waves. The present systematic study demonstrates that the numerical results have a reasonable agreement with the experimental data and emphasizes the non-linearity in the prediction of the added resistance and the ship motions with the increasing wave steepness in short and long waves.

A combined first- and second-order theory for the deckwetness prediction of sandglass-type floating body in irregular head waves

Deckwetness is one of the most important problems for seakeeping performance. With regard to the conventional ship-type Floating Production, Storage, and Offloading Units (FPSOs), the deckwetness depends on the relative vertical motion which is dominated usually by the first-order wave frequency loads. However, it can not apply to the deckwetness prediction of the sandglass-type FPSO since the influence of second-order slowly varying loads is remarkable. In this paper, a combined first- and second-order theory accounting for the first-order wave loads and nonlinear second-order slowly varying loads, is established to predict the deckwetness occurrence. By using the second-order Volterra series model, the relative vertical motion between the bow and incident wave surface can be described as a stationary non-Gaussian process. Then general formulas are derived for the prediction of the deckwetness occurrence for the sandglass-type floating body, based on the mathematical characteristics of the relative vertical motion process. As an application, the theory presented is discussed with reference to the deckwetness prediction of the sandglass-type floating model. Therein, a time domain analysis is employed to get the relative vertical motion response whereby the above formulas can be efficiently calculated. The influence factors including the length of the time simulation and the randomness of the wave phase are examined. Next, the convergence of the results is investigated with the increase of the order of non-Gaussian terms included in the formulas. By comparing with the experimental data, the reasonability and validity of the proposed method are proved.

The influence of orographic Rossby and gravity waves on rainfall

Orography is known to influence winter precipitation in Asia and the Indo‐Pacific Ocean by mechanically forcing winds, but the dynamics involved in the precipitation response are incompletely understood. This study investigates how two types of orographically forced oscillatory motions alter time‐mean winds and precipitation. The quasi‐geostrophic omega equation is used together with previous ideas of ‘downward control’ to develop a simple theory of the spatial distribution and amplitude of the vertical motion response to orographically forced stationary Rossby waves and gravity wave drag in a precipitating atmosphere. This theory is then used to understand the response of the boreal winter atmosphere to realistic Asian orography in a global numerical model that includes representations of moist processes and unresolved gravity wave drag. We isolate the effects of the orographically forced stationary Rossby wave and the gravity wave drag by incremental addition of wave sources in this model. The peak precipitation response to the forced Rossby wave is about a factor of three larger than that of the gravity wave drag, but the wave drag response has a distinct spatial structure that dominates in some regions. Both the Rossby wave and the gravity wave drag perturb precipitation in areas distant from orography, producing shifts in the equatorial intertropical convergence zone, an increase in precipitation over southern Asia, and drying in much of northern Asia.

Experimental analysis of an air cavity concept applied on a ship hull to improve the hull resistance

At the forefront of ship design is the desire to reduce a ship׳s resistance, thus being the most effective way to reduce operating costs and fulfil the international criteria for reduction in CO2 emissions. Frictional drag is always proportional to the wetted surface of the vessel and typically accounts for more than 60% of the required propulsive power to overcome; hence the desire to reduce the wetted surface area is an active research interest. An initial full-scale sea trail on a vessel by introducing air as a lubricating medium has indicated 5–20% propulsive energy savings (DK-GROUP, 2010).Following the report of the fundamental tests with the air cavity concept applied on a flat plate, which was conducted in the Emerson Cavitation Tunnel of Newcastle University (Slyozkin et al., 2014), this paper explores the same concept only this time applied on an existing container ship model to investigate whether it benefits in frictional drag reduction, whilst producing a net energy saving. The middle section of this 2.2m ship model was modified to accommodate a 0.43×0.09m2 air cavity in the bottom of the hull and then various model scale tests have been conducted in the towing tank of Newcastle University. The model experiments produced results ranging from 4% to 16% gross drag reduction. Upon applying scaling factors, it is estimated from the experimental results that around 22% gross energy could be saved in a full-scale application with just a 5% reduction in the wetted surface area.Further complementary model tests were also conducted to explore the effect of the air cavity on the stability of the model and on the vertical motion responses in a regular head and following wave. While the cavity did not affect the vessel stability the motion response behaviour seemed to be affected non-linearly by the effect of the air cavity.

Experimental and numerical study of the vertical motions of a bulk carrier and a Ro–Ro ship in extreme waves

This paper investigates the experimental and numerical vertical motion responses of a bulk carrier and a Roll-on/Roll-off ship in extreme seas. The experimental data were obtained from seakeeping tests with scaled models in head waves at two Froude numbers. The wave traces were predefined, corresponding to wave records measured during storms in the North Sea. These wave records are particularly interesting because each of them include one abnormal wave. The ship models, which are similar in length but different in their geometry, were tested in the same predefined wave conditions to investigate the influence of the hull geometry on the extreme vertical ship responses. Conclusions are derived by comparing directly the measured responses from the two models. Experimental data are also used as benchmark to validate the predictions by a partially nonlinear time domain seakeeping numerical model. The numerical model code is then used to generalize the comparative analysis between the two ships.

선박의 파랑 중 부가저항에 대한 실험과 수치계산의 비교 연구

This paper considers experimental and numerical studies on added resistance in waves. As the numerical methods, three different methods, strip method, Rankine panel method and Cartesian-grid method, are applied. The computational results of vertical motion response and added resistance are compared with the experimental data of Series 60(<TEX>$C_B=0.8$</TEX>) hull, S175 containership and KVLCC2 hull. To investigate the influence of above-still water hull form, a Rankine panel method is extended to two nonlinear methods: weakly-nonlinear and weak-scatterer approaches. As nonlinear computational models, three ships are considered: original KVLCC2 hull, 'Ax-bow' and 'Leadge-bow' hulls. Two of the three models are modified hull forms of original KVLCC2 hull, aiming the reduction of added resistance. The nonlinear computational results are compared with linear results, and the improvement of computational result is discussed. As experimental approach, a series of towing-tank experiment for ship motions and added resistance on the three models (original KVLCC2 hull, 'Ax-bow' and 'Leadge-bow') are carried out. For the original KVLCC2 hull, uncertainty analysis in the measurement of vertical motion response and added resistance is performed in three waves conditions: <TEX>${\lambda}/L=0.5$</TEX>, 1.1, 2.0. From the experimental results, the effects of hull form on added resistance are discussed.

The Effect of Moist Convection on the Tropospheric Response to Tropical and Subtropical Zonally Asymmetric Torques

Abstract Tropospheric winds can be altered by vertical transfers of momentum due to orographic gravity waves and convection. Previous work showed that, in dry models, such zonally asymmetric torques produce a pattern of tropical ascent that is well described by linear dynamics, together with meridional shifts of the midlatitude jet. Here a series of idealized models is used to understand the effects of moisture on the tropospheric response to tropical and subtropical zonally asymmetric, upper-tropospheric torques. The vertical motion response to a torque is shown to be amplified by the reduction in effective static stability that occurs in moist convecting atmospheres. This amplification occurs only in precipitating regions, and the magnitude of subsidence in nonprecipitating regions saturates when clear-sky radiative cooling balances induced adiabatic warming. For basic states in which precipitation is concentrated in an intertropical convergence zone (ITCZ), most of the vertical motion response is thus confined within the basic-state ITCZ, even when the torque is remote from the ITCZ. Tropical and subtropical torques perturb the extratropical baroclinic eddy field and the convectively coupled equatorial wave field. Resulting changes in momentum flux convergence by transient eddies induce secondary meridional overturning circulations that modify the zonal-mean response to a torque. The net effect allows tropical torques to merge a double ITCZ into a single equatorial ITCZ. The response of tropical transient eddies is highly sensitive to the representation of convection, so the zonal-mean response to a torque is similarly sensitive, even when the torque is located in the subtropics.

Uma revisão: contribuições dos modos de gravidade e de Kelvin para a resposta do movimento vertical

In earlier papers of a series of real data integrations of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM) with tropical heat anomalies display regions of pronounced subsidence and drying located several thousand kilometers westward poleward of the heating for cases of tropical Atlantic heating and tropical east Pacific heating. This highly predictable sinking response is established within the first five days of these integrations. The normal-modes of a set of nonlinear primitive equations for an atmosphere: Adiabatic, hydrostatic, incompressible, dry, without friction and viscosity are linearized about a basic state at rest and used to partition model response into gravity-inertia and Rossby modes. The emphasis of this review is given upon the contributions of the gravity and Kelvin modes for the vertical motion response.

정면 규칙파 중 활주형 고속선의 운동 응답에 대한 실험적 연구

The running attitude of a high-speed planing craft may change significantly depending on its speed in seaway. Other variables that may influence its running attitude are its weight, center of gravity, sea conditions, and so on. In this paper, planing craft model tests were carried out with respect to above variables in SNU towing tank, and vertical motion responses of a planing craft in regular head waves were analyzed. The experimental results in regular waves were compared with those in calm water, and compared with the theoretical estimations. Finally, the effects of running speeds of a planing craft on its motion amplitudes are confirmed.

Contribuições do segundo e do terceiro modos internos de gravidade para a resposta do movimento vertical

In earlier papers of a series of real data integrations of the National Center for Atmospheric Research Community Climate Model with tropical heat anomalies display regions of pronounced subsidence and drying located several thousand kilometers westward poleward of the heating for cases of tropical Atlantic heating and tropical east Pacific heating. This highly predictable sinking response is established within the first five days of these integrations. The normal-modes of a set of adiabatic primitive equations linearized about a basic state at rest are used to partition model response into gravity-inertia and Rossby modes. The most important contribution for the vertical motion response comes from the gravity modes added for all vertical modes. The principal emphasis is given upon the contributions of the second and third internal vertical modes (with equivalent depths on the order of a fews hundred meters) for the vertical motion response

Control of vortex shedding-induced effects in a sectional bridge model by spanwise perturbation method

An experimental study was conducted to determine the effectiveness of the spanwise sinusoidal perturbation method (SPPM) in controlling vortex-induced vibrations (VIV) in a plate girder bridge section model. The geometric parameters of the plate girder section model were selected to give the maximum VIV response. A SPPM module was attached to both the leading and trailing edges of the section model. Two different SPPM configurations with two different wavelengths and the same amplitude were utilized. Vertical motion responses, surface pressure measurements, as well as hotwire measurements in the wake of the section model were taken. The results revealed that the SPPM with the higher wave steepness distinctively suppressed the VIV responses. The behavior of the model with the SPPM is remarkably different with a fixed section model. Generally, a reduction in the fluctuating surface pressure components is observed, indicating an increase in the degree of steadiness of the flow around the model with either of the two SPPM configurations. However, no qualitative difference could be observed between the effects of the low and high wave steepness configurations. Moreover, wake measurements did not show any distinctive effect for either configuration when compared to the base case.

The Dynamical Basis of Regional Vertical Motion Fields Surrounding Localized Tropical Heating

A series of real-data integrations of the National Center for Atmospheric Research Community Climate Model with tropical heat anomalies display regions of pronounced subsidence and drying surrounding the anomaly. The present emphasis is upon subsidence and drying centers located several thousand kilometers westward and poleward of the heating. These features are repeatedly found in several different series of medium to extended range forecast experiments, including cases of tropical Atlantic heating and tropical east Pacific heating. This highly predictable sinking response is established within the first five days of these integrations. The normal modes of a set of primitive equations linearized about a resting basic state are used to partition model response into gravity-inertia and Rossby modes. The results show that most of the vertical motion response can be explained by gravity-mode contributions. The sensitivity of the response is examined through a series of numerical experiments with a simple global forecast model. These integrations suggest that the subsiding response surrounding the heated region is somewhat sensitive to the ambient circulation. In particular, the extratropical response tends to be greatest in the winter hemisphere, and it is relatively less sensitive to the precise location of the tropical heating than to the nature of the zonally averaged background flow. Further experimentation suggests that the peak subsidence response is almost linear in the heating amplitude. These experiments also demonstrate that a significant portion of the early response occurs independently of any fluctuations of the vorticity field and therefore is not merely a secondary circulation associated with extratropical Rossby wave responses. The latter response is relatively more sensitive to the presence of longitudinal vorticity gradients, and the dynamical interpretation is then less clear.