The Effect of Pitch Moment of Inertia in Body Axes on the Performance or a Yacht in Waves

1997 ◽  
Author(s):  
C. J. Sutcliffe ◽  
A. Millward
Keyword(s):  
Water Channel ◽  
Moment Of Inertia ◽  
Superior Performance ◽  
Correct Prediction ◽  
Damping Force ◽  
Head Waves ◽  
Pitch Moment ◽  
Experimental Project ◽  
Heave Motion ◽  
Phase Angles

Observation of full size yachts sailing upwind in a seaway has shown that, because of the presence of the sails, the yacht is constrained to move in body axes (parallel to the mast) rather than in earth axes (normal to the water). It is thought that this is due to the effect of the sails in the air and the keel and other appendages in the water providing a large damping force which resists any motion normal to the mast line. An experimental project has been carried out therefore to investigate the effect of this change in motion axes on the forces and motions induced by the seaway. The experiments were carried out on a model of an IACC class hull in regular head waves for a range of wave heights in both earth and body axes using a recirculating water channel. The magnitudes and phase angles of resistance, side force, pitch, heave and heel moment were measured. Comparisons between the results of the present work and previous experimentation, with motion in earth axes, showed similar trends. However the results from the experiments using motion in body axes showed marked changes in the measured motion and resistance characteristics when compared to the earth axes data. It is thought that this difference could well affect the order of merit when comparing the performance of two hulls and it was concluded therefore that the change to measurement in body axes is important for the correct prediction of the performance of a yacht in a seaway. The effect of the pitch moment of inertia on the motion and forces on the model was then studied, first using motion in earth axes and subsequently using motion in body axes. In general it was found that in both earth and body axes there was a strong cross coupling between the pitching motion and the heave motion and that a low gyradius resulted in smaller motions and a reduced added resistance; however the effect of any change in pitch moment of inertia was more significant in body axes. The results showed that a yacht optimised for low pitch moment of inertia would have superior performance in comparison with a yacht which has a high inertia under identical wave conditions.

Center Body Burner for Sequential Combustion: Superior Performance at Lower Emissions

2021 ◽  
Author(s):  
A. Ciani ◽  
J. P. Wood ◽  
M. Maurer ◽  
B. Bunkute ◽  
D. Pennell ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Laser Doppler Anemometry ◽  
Fluid Dynamic ◽  
Mixture Fraction ◽  
Nox Reduction ◽  
Water Channel ◽  
Superior Performance ◽  
Fuel Flexibility ◽  
Air Mixing ◽  
Center Body

Abstract Modern gas turbines call for an ultra-high firing temperature and fuel flexibility while keeping emissions at very low levels. Sequential combustion has demonstrated its advantages toward such ambitious targets. A sequential combustion system, as deployed in the GT26 and GT36 engines, consists of two burners in series, the first one optimized to provide the optimum boundary condition for the second one, the sequential burner. This is the key component for the achievement of the required combustor performance dictated by F and H class engines, including versatile and robust operation with hydrogen-based fuels. This paper describes the key development considerations used to establish a new sequential burner surpassing state-of-the-art hardware in terms of emission reduction, fuel flexibility and load flexibility. A novel multi-point injector geometry was deployed based on combustion and fluid dynamic considerations to maximize fuel / air mixing quality at minimum pressure loss. Water channel experiments complemented by CFD describe the evolution of the fuel / air mixture fraction through the mixing section and combustion chamber to enable operation with major NOx reduction. Furthermore, Laser Doppler Anemometry and Laser Induced Fluorescence were used to best characterize the interaction between hot-air and fuel and the fuel / air mixing in the most critical regions of the system. To complete the overview of the key development steps, mechanical integrity and manufacturing considerations based on additive manufacturing are also presented. The outcome of 1D, CFD and fluid dynamic experimental findings were then validated through full-scale, full-pressure combustion tests. These demonstrate the novel Center Body Burner is enabling operation at lower emissions, both at part load and full load conditions. Furthermore, the validation of the burner was also extended to hydrogen-based fuels with a variety of hydrogen / natural gas blends.

Semi-Active Control of Civil Structures With a One-Step-Ahead Prediction of the Seismic Response

2009 ◽  
Author(s):  
Kazuhiko Hiramoto ◽  
Taichi Matsuoka ◽  
Katsuaki Sunakoda ◽  
Akira Fukukita ◽  
Issei Yamazaki
Keyword(s):  
Seismic Response ◽  
Active Control ◽  
Passive Control ◽  
Inertial Force ◽  
Damping Coefficient ◽  
Superior Performance ◽  
Damping Force ◽  
Civil Structures ◽  
One Step ◽  
Command Signal

We propose a semi-active control of civil structures based on a one-step-ahead prediction of the seismic response. The vibration control device (VCD), which has been developed by authors, generates two types of resistance forces, i.e., a damping force proportional to the relative velocity and an inertial force proportional to the relative acceleration between two stories. The damping coefficient of the VCD can be changed with a command signal to an electric circuit connected to the VCD. In the present paper the command signal for changing the damping coefficient of each VCD is assumed to take two values, i.e., the command to take the maximum or minimum damping coefficient. The optimal command signal is selected from all candidates of command signals so that the Euclidean norm of the one-step-ahead predicted seismic response is minimized. As an example a semi-active control of a fifteen-story building with three VCDs is considered. The simulation results show that the proposed semi-active control achieves superior performance on vibration suppression compared with a passive control case where the damping coefficient of each VCD is fixed at its maximum value.

scholarly journals Energetically optimal running requires torques about the centre of mass

2012 ◽  
Vol 9 (73) ◽  
pp. 2011-2015 ◽  
Author(s):  
James R. Usherwood ◽  
Tatjana Y. Hubel
Keyword(s):  
Large Body ◽  
The Body ◽  
Moment Of Inertia ◽  
Mechanical Work ◽  
Vertical Force ◽  
Centre Of Mass ◽  
Pitch Moment ◽  
Tail Structure ◽  
Reaction Forces ◽  
Long Head

Bipedal animals experience ground reaction forces (GRFs) that pass close to the centre of mass (CoM) throughout stance, first decelerating the body, then re-accelerating it during the second half of stance. This results in fluctuations in kinetic energy, requiring mechanical work from the muscles. However, here we show analytically that, in extreme cases (with a very large body pitch moment of inertia), continuous alignment of the GRF through the CoM requires greater mechanical work than a maintained vertical force; we show numerically that GRFs passing between CoM and vertical throughout stance are energetically favourable under realistic conditions; and demonstrate that the magnitude, if not the precise form, of actual CoM-torque profiles in running is broadly consistent with simple mechanical work minimization for humans with appropriate pitch moment of inertia. While the potential energetic savings of CoM-torque support strategies are small (a few per cent) over the range of human running, their importance increases dramatically at high speeds and stance angles. Fast, compliant runners or hoppers would benefit considerably from GRFs more vertical than the zero-CoM-torque strategy, especially with bodies of high pitch moment of inertia—suggesting a novel advantage to kangaroos of their peculiar long-head/long-tail structure.

SUPERIOR SEAWORTHINESS OF A RESONANCE-FREE FAST OCEANGOING SWATH

2021 ◽  
Vol 156 (A4) ◽  
Author(s):  
M Yoshida ◽  
H Kihara ◽  
H Iwashita ◽  
M Kanda ◽  
T Kinoshita
Keyword(s):  
High Speed ◽  
Time Lag ◽  
Ship Motions ◽  
Speed Reduction ◽  
Small Water ◽  
Motion Responses ◽  
Head Waves ◽  
Unsteady Characteristics ◽  
Hull Forms ◽  
Heave Motion

The speed reduction, additional resistance or slamming caused by the large amplitude ship motions, should be completely restricted for a large fast oceangoing ship because of the strict time-punctuality and the high value of the cargo. A “Resonance-Free SWATH (RFS)”, which has negative restoring moments due to the extremely small water plane area, is introduced to minimize the motion responses. A motion control system using small fins is necessary for the RFS, which has no stability during high speed cruising. Theoretical estimations and experiments to search for the optimum values of PD control gains have been performed. Unsteady characteristics of fin-generated lift such as the time lag and the interaction among the fins and lower hulls have been measured and they are taken into account in the motion equations. Then, experiments using the RFS model with controlling fins have been carried out to validate the theoretical estimation for the motion responses of the RFS in waves. The theoretical and experimental results agree well with each other. The motion responses of the RFS in regular and irregular head waves are compared with those of other hull forms, such as a mono-hull, an ordinary SWATH and a trimaran. The clear advantage of the RFS regarding the seaworthiness has been found. In summary, the heave motion response of the RFS is reduced to 1/60 and the pitch motion becomes1/8, compared with those of the existing mono-hull ship.

Numerical Simulation of Surface Ship Motion in Regular Head Waves

2018 ◽  
Author(s):  
Lixiang Guo ◽  
Peng Wei ◽  
Zhiguo Zhang ◽  
Yue Sun ◽  
Jiawei Yu
Keyword(s):  
Numerical Simulation ◽  
Free Surface ◽  
Pitch Angle ◽  
Degrees Of Freedom ◽  
Wave Length ◽  
Surface Ship ◽  
Dynamic Overset Grids ◽  
Head Waves ◽  
Heave Motion ◽  
Regular Head Waves

The motion of surface ship in wave environments is fully three-dimensional unsteady motion and includes complex coupling with hydrodynamic force and dynamic motion of the rigid body. This paper presents simulations of the KCS model with motions involve pitch and heave in regular head waves. Computations were performed with an in-house viscous CFD code to solve RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations and dynamic overset grids designed for ship hydrodynamics. RANS equations are solved by finite difference method and PISO arithmetic. Level-set method is used to simulate the free surface flow. The simulation geometry includes KCS hull and rudder under three conditions with three wave length and wave height combinations and two velocities (Fr = 0.26 and 0.33). Total resistance coefficient CT, heave motion z and pitch angle θ have been compared between CFD and EFD. Comparisons show that pitch and heave are much better predicted than the resistance. In the first section, simulations considered only 2 degrees of freedom (heave and pitch), for the second section, numerical simulation added the rolling motion to study the KCS in regular head waves. The second simulation cases were carried out with the same velocity and wave length and amplitude combination as the first cases. Comparisons of heave and pitch motion between 2DOF simulations and 3DOF simulations were presented in this paper. Results show the difference of heave motion z and pitch angle θ between the 2DOF and 3DOF-simulasions. In both cases the free surface were studied as an example of the flow generated by the ship pitching and heaving.

Experimental Research on the Influences of Wave Height on Towing of 4-Bucket Foundation Platform

2011 ◽  
Vol 243-249 ◽  
pp. 4723-4727
Author(s):  
Cong Huan Le ◽  
Hong Yan Ding ◽  
Guo Hai Dong ◽  
Pu Yang Zhang
Keyword(s):  
Wave Height ◽  
Experimental Research ◽  
Water Pressure ◽  
Roll Motion ◽  
Regular Waves ◽  
Bucket Foundation ◽  
Head Waves ◽  
The Stability ◽  
Heave Motion ◽  
Better Than

Internal air pressure and water pressure of the buckets foundation, acceleration and dragging force of the 4-bucket foundation platform were determined to analyze the influences of wave height on towing when 4-Bucket foundation platform is towing in conditions of a certain towing velocity, mooring point position and draught in different regular waves based on the model test. Comparing platform towing in following and head waves, the heave motion of the latter is more strenuous than that of the former; the stability and seakeeping of the former is better than those of the latter. Roll motion, pitch motion and heave motion appear aggravate phenomenon with the increase of wave height.

scholarly journals Modeling and Analysis of a SiC Microstructure-Based Capacitive Micro-Accelerometer

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6222
Author(s):  
Xiang Tian ◽  
Wei Sheng ◽  
Zhanshe Guo ◽  
Weiwei Xing ◽  
Runze Tang
Keyword(s):  
Low Frequency ◽  
Superior Performance ◽  
Viscous Damping ◽  
Damping Force ◽  
Modeling And Analysis ◽  
Time Frequency ◽  
Capacitive Accelerometer ◽  
Silicon Devices ◽  
Main Components ◽  
Inertial Measurements

In this study, a comb-type capacitive accelerometer based on a silicon carbide (SiC) microstructure is presented and investigated by the finite element method (FEM). It has the advantages of low weight, small volume, and low cross-coupling. Compared with silicon(111) accelerometers with the same structure, it has a higher natural frequency. When the accelerometer vibrates, its resistive force consists of two main components: a viscous damping and an elastic damping force. It was found that viscous damping dominates at low frequency, and elastic damping dominates at high frequency. The second-order linear system of the accelerometer was analyzed in the time-frequency domain, and its dynamic characteristics were best when the gap between the capacitive plates was 1.23 μm. The range of this accelerometer was 0–100 g, which is 1.64 times that of a silicon(111) accelerometer with the same structure. In addition, the accelerometer could work normally at temperatures of up to 1200 °C, which is much higher than the working temperatures of silicon devices. Therefore, the proposed accelerometer showed superior performance compared to conventional silicon-based sensors for inertial measurements.

Heave Motion Performance of Multiple Wave Energy Converters Arrayed in a Water Channel Resonator

2020 ◽  
Author(s):  
Jeongrok Kim ◽  
Il-Hyoung Cho
Keyword(s):  
Wave Energy ◽  
Water Channel ◽  
Standing Waves ◽  
Low Density ◽  
Energy Extraction ◽  
Multiple Wave ◽  
Wave Energy Converters ◽  
Internal Fluid ◽  
Heave Motion ◽  
Energy Converters

Abstract The performance of multiple wave energy converters (WECs) arranged in a Y-shaped water channel resonator (WCR) for amplifying the wave energy with low density was investigated. The WCR consists of a long channel and waveguide installed at the entrance. If the period of the incident wave coincides with the natural period of the fluid in the WCR, then resonance occurs, and the internal fluid is greatly amplified in the form of standing waves. The WECs were positioned at the anti-nodes of standing waves formed in the WCR to maximize energy extraction. We dealt with the heave motion, time-averaged power, and capture width ratio (CWR) of WECs, which are composed of a heaving cylinder and a linear generator. For this purpose, we used the boundary element method and WAMIT commercial code. In parallel, systematic model tests were conducted at the 2D wave tank in Jeju National University to validate the numerical solution. Both results were in good agreement. WECs with a short draft are efficient in energy extraction compared with WECs with a long draft. Numerical and experimental results reveal that the WECs arranged in a WCR have higher efficiency over a wide band of periods than a single WEC without a WCR. Therefore, the wave energy with low density can be amplified by the resonance of the internal fluid in the WCR.

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