• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.3
• /
• pp.419-425
• /
• 1988

It would be very useful if the dynamic response of a vehicle over rough ground could be predicted at the early design stage. This became more promising with the recent progress in computer hardware and software technologies. In this study, a model of a passenger car has been developed for the analysis of its dynamic response. This model can be easily used for the other passenger cars with little modification. This passenger car was modeled to be composed of lumped masses, rigid bodies, and the suspension systems with nonlinear properties. Even though a commercial dynamic simulation program, ADAMS, was used in this study, the developed model is valid for any other simulation program. Finally, the validity of the developed model and the analysis result was verified by an experiment.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.19 no.3
• /
• pp.20-28
• /
• 2015

Performance parameters of solid rocket motor with multi axis pintle nozzles were analyzed theoretically and modeled. For figuring out the governed variable of dynamic characteristics of system, dynamic analysis was done by using established model. To present characteristics of this system, the model should include not only internal ballistics of propulsion unit but also actuating system to move pintle. For solid rocket motor with multi axis pintle nozzles, not only performance of steady state but also dynamic characteristic of transient state is important design parameter to precise thrust control. Therefore, response time of open-loop system was analyzed by using established model and requirement about response time was satisfied by controlling pressure.

• Proceeding of EDISON Challenge
• /
• 2017.03a
• /
• pp.270-281
• /
• 2017

In this paper, a vibratory disturbance to the rotor system generated by gyroscopic precession through helicopter rotor is examined. Also, active vibration reduction method is designed and simulated by designing feedback controller. For this purpose, structural analysis is carried out using EDISON's geometric exact beam program which can analyze the rotor with the cantilever condition. And the aeroelastic analysis is performed by coupling it with the simple aerodynamic model. In order to obtain the real-time structural response, the EDISON program analysis results were modeled by nonlinear equations and the Newton-Raphson method was used for the trim analysis.

• Journal of the Society of Naval Architects of Korea
• /
• v.49 no.4
• /
• pp.287-295
• /
• 2012

Hydrodynamic performance of a movable submerged breakwater was analyzed using energy dissipation model. Based on two-dimensional boundary element method the equation of motion including a viscous dissipation term proportional to velocity squared was solved by Newton-Raphson method. Energy dissipation coefficients as well as reflection and transmission coefficients of a submerged flat plate were calculated with various plate lengths and thickness. Both real and imaginary components of body displacement and forces were used to solve the motion of breakwater accurately. The effect of the magnitude of dissipation coefficient on the body displacement was evaluated. The results from the potential theory with no dissipation term were found to be an overestimate in resonance frequency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.05a
• /
• pp.183-188
• /
• 2003

The present work was conducted to build a propulsion system for an airship. For this purpose, free shaft gas-turbine was modified to produce electrical power. he experiments were carried out to analyze the driving rotor condition at various power shaft loads. From this analysis, an appropriate damping device was required, and the changeable inertial moment from the fly-wheel was applied. Without the appropriate damping device, instability was found, and it was resulted as power loss. Also the amount of inertial moment was certified by the performance of dynamic transient effects from the engine test results. Knowledge gained from this research could benefit the propulsion and power conversion community by increasing the better understanding of shaft loads and inertial effects.

• Journal of the Society of Naval Architects of Korea
• /
• v.56 no.1
• /
• pp.11-22
• /
• 2019

In this paper, a Rankine source method is applied and validated to analyze the hydrodynamic response of a three-dimensional floating structure in the frequency domain. The boundary value problems for radiation and diffraction problem are solved by using a desingularized indirect boundary integral equation method (DIBIEM). The DIBIEM is simpler and faster than conventional methods based on the numerical surface integration of Green's function because the singularities of Green's function are located outside of fluid regions. In case of floating structure with complex geometry, it is difficult to desingularize the singularities of Green's function consistently. Therefore a mixed approach is carried out in this study. The mixed approach is partially desingularized except singularities of the body. Wave drift loads are calculated by the middle-field formulation method that is mathematically simple and has fast convergence. In order to validate the accuracy of the developed program, various numerical simulations are carried out and these results are analyzed and compared with previously published calculations and experiments.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.16 no.1
• /
• pp.33-42
• /
• 2003

This paper deals with the FEM analysis of nonlinear sloshing of incompressible, invicid and irrotational flow in two dimensional rectangular tank. We use laplace equation based on potential theory as governing equation. For large amplitude sloshing motion, kinematic and dynamic free surface conditions derived from Bernoulli equation are applied. This problem is solved by FEM using 9-node elements. For the time integration and accurate velocity calculation, we introduce predictor-corrector time marching scheme and least square method. Also, numerical stability in tracking of free surface is obtained by direct calculation of free surface location to time variation. Numerical results of sloshing induced by harmonic excitations, while comparing with those of linear theory and references, prove the accuracy and stability. After verification of our program, we analyze sloshing response characteristics to the fluid height and the excitation amplitude.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.9
• /
• pp.925-932
• /
• 2014

If a rotor possesses a high gyroscopic coupling or the running speed is high, the dynamical changes in the rotor become prominent. When active magnetic bearings are used to support such rotors, it is necessary for the bearing controller to take these dynamical changes into consideration. Independent-axis controllers, which are the most commonly used, modulate the bearing force solely based on the sensor output of the same axis. However, this type of controller has difficulties in overcoming the dynamical changes. On the other hand, mixed-axis controllers transform the sensor output into components corresponding to the vibrational modes. A separate controller can then be designed for each vibrational mode. In this way, the controller can be designed based on the dynamics of the rotor. In this paper, we describe a design process for a mixed-axis controller that uses a detailed mathematical model of the system. The performance of the controller is evaluated based on the ISO sensitivity requirements and unbalance response, while considering the change in the system dynamics due to the running speed.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.26 no.1
• /
• pp.25-32
• /
• 2014

Offshore wind power structures are subject to coastal hydrodynamic loading such as wind and wave loads. A considerable number of turbines have been installed in Europe, but so far none in Korea. Interest in offshore wind energy is growing in Korea, and it is expected that projects will reach the design stage in the near future. This paper discusses the level of structural reliability implied by the design rules of ABS(2010, 2013) and IEC(2009). Metocean conditions in 4 Korean seas(Gunsan, HeMOSU 1, Mokpo, Jeju) were used in the calibrations to calculate the aerodynamic and hydrodynamic loads as well as the structural responses of the typical designs of offshore wind turbines. Due to the higher variability of the wind and wave climate in hurricane-prone areas, applying IEC strength design criteria in combination with Korea west sea conditions could result in a design with much lower reliability index than what is anticipated from a design in European waters. To achieve the same level of safety as those in European waters, application of ABS 100 year design standards are recommended. Level-1 reliability-based design suitable for the Korean sea state conditions should be introduced because the IEC standards does not consider the typhoon effects in depth and the ABS standards is a WSD design method. In addition, the design equation should be established based on the statistical characteristics of the wind and wave loads of the Korean sea areas.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.11
• /
• pp.1757-1763
• /
• 2010

Flywheel energy storage system (FESS) is defined as a high speed rotating flywheel system that can save surplus electric power. The FESS is proposed as an efficient energy storage system because it can accumulate a large amount of energy when it is operated at a high rotating speed and no mechanical problems are encountered. The FESS consists of a shaft, flywheel, motor/generator, bearings, and case. It is difficult to simulate rotor dynamics using common structure simulation programs because these programs are based on the 3D model and complex input rotating conditions. Therefore, in this paper, a program for the FESS based on the 2D FEM was developed. The 2D FEM can model easier than 3D, and it can present the multi-layer rotor with different material each other. Stiffness changing of the shaft caused by shrink fitting of the hub can be inputted to get clear solving results. The results obtained using the program were compared with those obtained using the common programs to determine any errors.