scholarly journals Ships Added Mass Effect on a Flexible Mooring Dolphin in Berthing Manoeuvre

2021 ◽  
Vol 9 (2) ◽  
pp. 108
Author(s):  
Aleksander Grm
Keyword(s):  
Mass Effect ◽  
Added Mass ◽  
Hydrodynamic Effect ◽  
Theory Approach ◽  
Additional Mass ◽  
Strip Theory ◽  
Rocking Motion ◽  
The Mathematical Model ◽  
Surrounding Fluid ◽  
Zero Frequency

This paper deals with the hydrodynamic effect of the ship on a flexible dolphin during a mooring manoeuvre. The hydrodynamic effect refers to the change in momentum of the surrounding fluid, which is defined by the concept of added mass. The main reason for the present study is to answer the question, “What is the effect of the added mass compared to the mass of the ship during the mooring procedure for a particular type of ship?” Measured angular frequencies of dolphin oscillations showed that the mathematical model can be approximated by the zero frequency limit. This simplifies the problem to some extent. The mooring is a pure rocking motion, and the 3D study is approximated by the strip theory approach. Moreover, the calculations were performed with conformal mapping using conformal Lewis mapping for the hull geometry. The fluid flow is assumed to be non-viscous, non-rotating and incompressible. The results showed that the additional mass effect must be taken into account when calculating the flexible dolphin loads.

Fluid Added Mass Effect in the Modal Response of a Pump-Turbine Impeller

2009 ◽  
Author(s):  
Eduard Egusquiza ◽  
Carme Valero ◽  
Quanwei Liang ◽  
Miguel Coussirat ◽  
Ulrich Seidel
Keyword(s):  
Natural Frequencies ◽  
Experimental Tests ◽  
Mass Effect ◽  
Added Mass ◽  
Mode Shapes ◽  
Pump Turbine ◽  
Modal Response ◽  
Surrounding Fluid ◽  
Turbine Impeller ◽  
Good Agreement

In this paper, the reduction in the natural frequencies of a pump-turbine impeller prototype when submerged in water has been investigated. The impeller, with a diameter of 2.870m belongs to a pump-turbine unit with a power of around 100MW. To analyze the influence of the added mass, both experimental tests and numerical simulations have been carried out. The experiment has been performed in air and in water. From the frequency response functions the modal characteristics such as natural frequencies and mode shapes have been obtained. A numerical simulation using FEM (Finite Elements Model) was done using the same boundary conditions as in the experiment (impeller in air and surrounded by a mass of water). The modal behaviour has also been calculated. The numerical results were compared with the available experimental results. The comparison shows a good agreement in the natural frequency values both in air and in water. The reduction in frequency due to the added mass effect of surrounding fluid has been calculated. The physics of this phenomenon due to the fluid structure interaction has been investigated from the analysis of the mode-shapes.

scholarly journals Effects of Time-Varying Fluid on Dynamical Characteristics of Cantilever Beams: Numerical Simulations and Experimental Measurements

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
Mingyu Shao ◽  
Chicheng Ma ◽  
Shuaizhao Hu ◽  
Chuansong Sun ◽  
Dong Jing
Keyword(s):  
Numerical Simulations ◽  
Beam Theory ◽  
Mass Effect ◽  
Added Mass ◽  
Experimental Measurements ◽  
Time Varying ◽  
Cantilever Beams ◽  
Dynamical Characteristics ◽  
The Mathematical Model ◽  
Euler Bernoulli Beam

In order to obtain the effects of time-varying fluid on dynamical characteristics of cantilever beams, this paper gives a comprehensive study of cantilever beams vibrating in a fluid with variable depth. The mathematical model of the cantilever beams in time-varying fluid is derived by combining Euler–Bernoulli beam theory and velocity potential theory, and the influence of the time-varying fluid is discussed. Then, a two-way fluid-structure interaction (FSI) numerical simulation procedure is proposed to calculate the transient responses of the beam. The validity and accuracy are verified according to the comparison among theoretical analysis, numerical simulations, and experimental measurements. Results show that, besides the added mass effect, a damping-like term is also induced due to the motion of the fluid, which is proportional to the moving velocity of the fluid. Both the added mass and the added damping increase with the increment of the width of the beam. The surrounding fluid near the free end affects the beam more significantly. As a negative damping is caused while the fluid decreases, resulting in a much slower decay of the time responses. Therefore, the added damping should not be neglected in the analysis of the FSI problems with time-varying fluid.

Hydrodynamically coupled oscillators

2011 ◽  
Vol 677 ◽  
pp. 589-606 ◽  
Author(s):  
R. TIRON ◽  
E. KANSO ◽  
P. K. NEWTON
Keyword(s):  
Angular Momentum ◽  
Simple Model ◽  
Coupled Oscillators ◽  
Normal Modes ◽  
Mass Effect ◽  
Added Mass ◽  
Momentum Exchange ◽  
Ring Configuration ◽  
Curved Paths ◽  
Surrounding Fluid

A submerged spring–mass ring is analysed as a simple model for the way in which an underwater swimmer couples its body deformations to the surrounding fluid in order to accomplish locomotion. We adopt an inviscid, incompressible, irrotational assumption for the surrounding fluid and analyse the coupling response to various modes of excitation of the ring configuration. Due to the added mass effect, the surrounding fluid provides an environment which effectively couples the ‘normal modes’ of oscillation of the ring, leading to nonlinear trajectories if the ring is free to accelerate based on the effective forces the oscillations induce. Through a series of examples, we demonstrate various features that the model supports, including the locomotion on curved paths as a result of energy and angular momentum exchange with the surrounding fluid.

scholarly journals ON THE HYDRODYNAMIC FORCES OF TWIN-HULL VESSELS

1970 ◽  
Vol 1 (12) ◽  
pp. 103
Author(s):  
Shen Wang
Keyword(s):  
Oscillation Frequency ◽  
Three Dimensional ◽  
Vertical Motion ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Theory Approach ◽  
Damping Coefficients ◽  
Damping Characteristics ◽  
Spacing Ratio ◽  
Strip Theory

The added mass and damping coefficients for semi- and fully submerged twin cylinders in vertical motion are determined as functions of the oscillation frequency, the cylinder spacing ratio, and the cylinder submergence ratio It has been found that resonance may occur in particular combinations of cylinder spacing and oscillation frequency at which the hydrodynamic mertial and damping characteristics deviate from the trend curves for the case of a single cylinder Justification of using the two-dimensional results to calculate motions of three dimensional twin-hull vessels is discussed It is suggested that, by means of strip theory approach, these results can be used to estimate the hydrodynamic forces for catamaran type vessels in pitch and heave motions.

An Investigation to Added Mass Force on the Wing of Insect Inspired from a Rigid Sphere Model

2012 ◽  
Vol 476-478 ◽  
pp. 2485-2488
Author(s):  
Mei Jun Hu ◽  
Xing Yao Yan ◽  
Jin Yao Yan
Keyword(s):  
Insect Flight ◽  
Aerodynamic Force ◽  
Mass Effect ◽  
Added Mass ◽  
Rigid Sphere ◽  
Force Model ◽  
Mass Force ◽  
Real Time Control ◽  
Wing Model ◽  
Force Peak

There is a force peak at the beginning of each stroke during the insect flight, this force peak contributes a lot to the total aerodynamic force. To build a man made insect inspired man-made micro aero vehicle, this force need to be considered in the aero force model, and this model should as simple as possible in order to be used in feedback real-time control. Here we presented a simplified model to take the medium added mass effect of the wing into account. Simulated results show a high force peak at the beginning of each stroke and are quite similar to the measured forces on the physical wing model which were carried out by Dickinson et.al.

scholarly journals CALCULATION OF A JET ENGINE IN A COMPLEX PLANE USING A ONE-DIMENSIONAL SOLUTION OF THE NAVIER-STOKES EQUATION

2021 ◽  
Vol 7 (1(37)) ◽  
pp. 9-22
Author(s):  
E.G. Yakubovsky
Keyword(s):  
Speed Of Sound ◽  
Added Mass ◽  
Navier Stokes ◽  
Speed Of Light ◽  
Attached Mass ◽  
Additional Mass ◽  
Navier Stokes Equation ◽  
Dimensional Solution ◽  
Jet Engine ◽  
One Dimensional

This article proposes an algorithm to describe the motion of a body in the atmosphere using the added mass. Attached mass is the property of a medium to form additional mass, as I assume with a relativistic denominator at the speed of sound instead of the speed of light. Newton’s second law for added mass assumes two terms with the same speed, one is relativistic at the speed of light, and the other is attached mass with a relativistic denominator at the speed of sound. The use of a relativistic denominator with the speed of sound is a new idea that allows, according to well-known formulas with added mass, which is valid at low speeds of a body, to describe

scholarly journals Structural seismic characteristics assessment of LMFR fuel assembly hexagonal wrapper over operational temperature range

2019 ◽  
Vol 34 (4) ◽  
pp. 313-324
Author(s):  
M. Khizer ◽  
Zhang Yong ◽  
Yang Guowei ◽  
Wu Qingsheng ◽  
Wu Yican
Keyword(s):  
Fuel Assembly ◽  
Fast Reactor ◽  
Natural Frequencies ◽  
Mass Effect ◽  
Added Mass ◽  
Reactor Fuel ◽  
Temperature Range ◽  
Fast Reactor Fuel ◽  
Lead Bismuth Eutectic ◽  
Reactor Fuel Assembly

In this study, the structural integrity of liquid metal fast reactor fuel assembly has been established for different parameters considering the optimum fuel design. Analytical calculation of added mass effect due to lead bismuth eutectic and verification through previously presented theories, has been established. The integrity of the hexagonal wrapper of fuel assembly has been guaranteed over the entire operating temperature range. Effect of temperature on the density of lead bismuth eutectic, the subsequent change in added mass of lead bismuth eutectic, the effect on natural frequencies and effect on stresses on wrapper, has been studied in detail. A simple empirical relationship is presented for estimation of added mass effect for lead bismuth eutectic type fast reactors for any desired temperature. An approach for assessment of fast reactor fuel assembly performance has been outlined and calculated results are presented. Nuclear seismic rules require that systems and components which are important to safety, shall be capable of bearing earthquake effects and their integrity and functionality should be guaranteed. Mode shapes, natural frequencies, stresses on wrapper and seismic aspect has also been considered using ANSYS. Modal analysis has been compared in vacuum and lead bismuth eutectic using the calculated added mass.

scholarly journals Analysis on the lateral vibration of drill string by mass effect of drilling fluid

2019 ◽  
Vol 10 (2) ◽  
pp. 363-371 ◽  
Author(s):  
Chunxu Yang ◽  
Ruihe Wang ◽  
Laiju Han ◽  
Qilong Xue
Keyword(s):  
Drilling Fluid ◽  
Dynamic Pressure ◽  
Mass Effect ◽  
Drill String ◽  
Natural Vibration Frequency ◽  
Lateral Vibration ◽  
Test Results ◽  
Additional Mass ◽  
Mass Coefficient ◽  
Fluid Environment

Abstract. It is well known that the influence of the internal and external drilling fluid on the lateral vibration characteristics of drillstring cannot be ignored. In this paper, experiment apparatus for simulating drillstring vibration was established. Hammering method is used to measure drillstring lateral natural vibration frequency when the internal and external drilling fluid is considered. The test results show that the drilling fluid can decrease the natural frequency of the drillstring. Based on the simulation model, considering the influence of the internal and external drilling fluid, an external drilling fluid additional mass coefficient is derived considering the dynamic pressure effect caused by external drilling fluid. Additional mass coefficient can get the result with high precision, which can meet the needs of the project. the simulation results are in good agreement with the test results, and the error is within 2 %. This work provides a useful attempt and lays the foundation for the dynamics of the drill string in the drilling fluid environment.

Tacking in the Wind Tunnel

2009 ◽  
Author(s):  
Frederik C. Gerhardt ◽  
David Le Pelley ◽  
Richard G. J. Flay ◽  
Peter Richards
Keyword(s):  
Wind Tunnel ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Added Mass ◽  
Mass Moment ◽  
Strip Theory ◽  
Dynamic Velocity ◽  
Order Of Magnitude ◽  
Velocity Prediction ◽  
Unsteady Effects

In recent years a number of Dynamic Velocity Prediction Programs (DVPPs), which allow studying the behaviour of a yacht while tacking, have been developed. The aerodynamic models used in DVPPs usually suffer from a lack of available data on the behaviour of the sail forces at very low apparent wind angles where the sails are flogging. In this paper measured aerodynamic force and moment coefficients for apparent wind angles between 0° and 30° are presented. Tests were carried out in the University of Auckland’s Twisted Flow Wind Tunnel in a quasi-steady manner for stepwise changes of the apparent wind angle. Test results for different tacking scenarios (genoa flogging or backed) are presented and discussed and it is found that a backed headsail does not necessarily produce more drag than a flogging headsail but increases the beneficial yawing moment significantly. The quasisteady approach used in the wind tunnel tests does not account for unsteady effects like the aerodynamic inertia in roll due to the “added mass” of the sails. In the second part of paper the added mass moment of inertia of a mainsail is estimated by “strip theory” and found to be significant. Using expressions from the literature the order of magnitude of three-dimensional effects neglected in strip theory is then assessed. To further quantify the added inertia experiments with a mainsail model were carried out. Results from those tests are presented at the end of the paper and indicate that the added inertia is about 76 % of what strip theory predicts.

Natural Frequency Shift in a Centrifugal Compressor Impeller for High-Density Gas Applications

2011 ◽  
Author(s):  
Yohei Magara ◽  
Kazuyuki Yamaguchi ◽  
Haruo Miura ◽  
Naohiko Takahashi ◽  
Mitsuhiro Narita
Keyword(s):  
Centrifugal Compressor ◽  
Natural Frequencies ◽  
Mass Density ◽  
Mass Effect ◽  
Added Mass ◽  
High Density ◽  
Experimental Results ◽  
Centrifugal Compressors ◽  
Resonance Frequencies ◽  
Discharge Gas

In designing an impeller for centrifugal compressors, it is important to predict the natural frequencies accurately in order to avoid resonance caused by pressure fluctuations due to rotorstator interaction. However, the natural frequencies of an impeller change under high-density fluid conditions. The natural frequencies of pump impellers are lower in water than in air because of the added mass effect of water, and in high-pressure compressors the mass density of the discharge gas can be about one-third that of water. So to predict the natural frequencies of centrifugal compressor impellers, the influence of the gas must be considered. We previously found in the non-rotating case that some natural frequencies of an impeller decreased under high-density gas conditions but others increased and that the increase of natural frequencies is caused by fluid-structure interaction, not only the added mass effect but also effect of the stiffness of the gas. In order to develop a method for predicting natural frequencies of centrifugal compressor impellers for high-density gas applications, this paper presents experimental results obtained using a variable-speed centrifugal compressor with vaned diffusers. The maximum mass density of its discharge gas is approximately 300 kg/m3. The vibration stress on an impeller when the compressor was speeding up or slowing down was measured by strain gages, and the natural frequencies were determined by resonance frequencies. The results indicate that for high-density centrifugal compressors, some natural frequencies of an impeller increased in high-density gas. To predict this behavior, we developed a calculation method based on the theoretical analysis of a rotating disc. Its predictions are in good agreement with experimental results.

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