Concentrated Mass Model Research Articles

Seismic Response Effect on Base-Isolated Rigid Structures by Mass Eccentricity in Nuclear Plants

The purpose of this paper is to analyze the seismic response effect caused by the mass eccentricity of individual equipment when conducting base isolation for the improvement of the seismic performance of a nuclear power plant. Recent research has interpreted and confirmed through analysis and testing that base isolation for safety-related equipment in nuclear power plants is an efficient alternative to designing for excessive seismic loads. Depending on the equipment, unavoidable mass eccentricity can occur, which necessitates verification of the response impact caused by eccentricity. In this paper, we analyze the seismic response impact of equipment with mass eccentricity using small base isolators. To do so, sensitivity analysis of the seismic response due to mass eccentricity is conducted for a base-isolated concentrated mass model. Furthermore, three efficient mass eccentricity models suitable for testing are designed and manufactured. Simulation analyses using the finite element method (FEM) models are performed, followed by three-axis shake table tests to validate the seismic response impact of mass eccentricity. In conclusion, it is confirmed that applying small base isolators to equipment with mass eccentricity can affect seismic response impact to some extent when compared for a beyond-design-basis earthquake (BDBE).

Analysis of thermoacoustic phenomenon using concentrated mass model

In general acoustic analysis, temperature of the air is often assumed to be constant. However, in some cases, the relationship between sound waves and temperature cannot be ignored. For example, a temperature gradient in an acoustic tube can generate self-excited vibrations of the air. A temperature gradient can also be generated by the input of sound waves. Engines and refrigerators that apply these phenomena can use exhaust heat as a drive source, so that they are expected as thermoacoustic devices with little adverse effect on the environment. Thermoacoustic devices have been actively studied in recent years, and efficient analytical methods including non-linearity of sound waves are still required. In this study, we propose an analysis method of thermoacoustic phenomena using a concentrated mass model. This model consisted of masses, springs, and dampers, and efficiently analyses thermoacoustic phenomena as a vibration system. In addition, this model is suitable for non-linear analysis and coupled analysis with other vibrating bodies. In this paper, we formulated an acoustic tube with a temperature gradient using the proposed model and verified the validity of the model by numerical calculations.

Impact-meshing vibration characteristics of high-speed gear systems with Backlash

The meshing process includes high-speed impact between the teeth. The vibration and noise in the gear transmission become prominent owing to the backlash between gears. Currently, the concentrated mass model is primarily used to analyse the vibration and noise mechanism of gear transmission, and it is difficult to effectively explain high-speed gear collision. In this study, an improved impact vibration model was applied to the meshing state of a high-speed gear. The gear transmission was simplified as a collision vibration system with absolute and traversable boundaries, and the piecewise-smooth dynamics model of the gear system is established. A mapping dynamic analysis method was then used to describe the impact and meshing boundary of gears. The impact-meshing situation of the gear system was observed, and the vibration response of the system under different speeds and loads was analysed using numerical simulation. The results revealed that the main source of the gear vibration was the meshing frequency of a gear pair. The resonance generated by the modulation of the rotation and meshing is the main reason for the long-term impact-meshing phenomenon of the gear transmission system. The results of this study are of great significance as they reveal the vibration characteristics of a high-speed gear transmission system.

Effect of internal excitation induced by non-uniform contact of roller bearings on nonlinear vibration and stability of rotor system under combined loads

The misalignment of roller bearing rings will results in moment load, together with the unbalance and external loads, forming the combined dynamic loads. The complex combined load can cause non-uniform contact of rollers and rings, which reduces the bearing’s life and significantly affect the vibration of rotor systems. This paper mainly studies the roller bearing internal contact performances under combined loads and the influence of internal excitation on the nonlinear vibration of rotor systems. First, the “slices” method is used to establish the mechanical model of roller bearings, which considers the radial clearance and nonlinear Hertz contact. The obtained time-varying bearing nonlinear support reaction is introduced into the rotor concentrated mass model, and a roller bearing–rotor system dynamic model is proposed. Further, the system’s complex nonlinear vibrations, such as bifurcation and chaos, are analyzed by spectrum, orbits, bifurcation, and Poincare map. The roller bearing contact performances and stability under the influence of ring tilt angle, rotational speed, and unbalance, are analyzed by contact load statistical features. Finally, based on a rolling bearing–rotor test rig, the vibration experiment considering the combined load was performed, and the experiment results are compared with simulation results to verify the proposed model and conclusions.

Research on the natural frequencies of an integrated offshore wind turbine model considering blades

The offshore wind turbine (OWT) is a high-rise structure that is extremely sensitive to dynamic loads such as wind, waves, and earthquakes. Therefore, in order to avoid resonance, it is extremely important to accurately calculate the natural frequencies of the OWT at the design stage. The integrated finite element model of DTU (Technical University of Denmark) 10 MW OWT is established based on OpenSees finite element software. The correctness of the superstructure simplification method is confirmed by comparing it to the frequencies calculated by the wind turbine dynamic analysis software HAWC2 for the single-blade model and the fixed constraint model at the bottom of the tower. The frequencies and mode shapes calculated by the overall model are compared with those calculated by the fixed model at the mudline and the concentrated mass model at the top of the tower. Then, the parameters of the soil shear modulus G0, void ratio e, pile embedded length L, pile diameter D, water depth, and blade stiffness are analyzed using the lumped mass model and the blade model at the top of the tower, and some regular conclusions about the variation of natural frequency with the parameters are obtained. Finally, based on the blade model, the influence of short-term cyclic loading on the natural frequency for OWT monopiles in dense sand is studied. The results indicate that the pile-soil interaction has a significant impact on the natural frequencies, the blade has a higher influence on the second bending frequency of the OWT, and the front-after direction is more significantly impacted than the side-side direction. The short-term cyclic loading are unlikely to significantly affect natural frequency for OWT monopiles in dense sand.

Analysis of two-dimensional nonlinear sloshing in a rectangular tank by using a concentrated mass model

Major problems can occur when liquid sloshes in a tank, such as in liquid storage tanks during an earthquake, and this is an important engineering problem to address. To analyze this phenomenon, the finite-element method is generally used but involves many degrees of freedom when the tank is large. In this paper, a nonlinear numerical model with relatively few degrees of freedom is established for vertical and horizontal two-dimensional nonlinear sloshing in a rectangular tank excited horizontally. In addition, a method is proposed for reducing the number of degrees of freedom in the two-dimensional model. The natural frequencies, modes, and frequency responses are then compared among the concentrated mass model, theoretical calculations, and experimental results. Good agreement was achieved among them, thus demonstrating the validity of the model.

Audible sound analysis of parametric speaker by concentrated mass model (Steady-state response analysis for cylindrical acoustic space by substructure synthesis method)

Audible sound analysis of parametric speaker by concentrated mass model (Steady-state response analysis for cylindrical acoustic space by substructure synthesis method)

Modeling and design of a tuned liquid damper using triangular-bottom tank by a concentrated mass model

Rectangular flat-bottom liquid tanks known as tuned liquid dampers (TLDs) are often used as passive mechanical dampers. Sloped- and triangular-bottom TLDs have been reported to be more effective than flat-bottom TLDs, but optimum tuning and damping of sloped- and triangular-bottom TLDs have not yet been proposed, and nonlinear analysis of such TLDs has not been performed. This study aims to establish a practical analytical model for nonlinear sloshing in a triangular-bottom TLD and a method for designing a TLD using a triangular-bottom tank. We modify the concentrated mass model proposed in our previous paper to simulate nonlinear shallow water wave phenomena in a triangular-bottom tank. To confirm the validity of the modified model, its results are compared with the natural frequencies in a triangular-bottom tank obtained from FEM and experimental results for a triangular-bottom tank. All the model results agree well with the FEM and experimental results. Furthermore, optimum tuning and damping based on the concentrated mass model are derived in the case of a triangular-bottom TLD, and the physical reason why a triangular-bottom TLD is more effective than a flat-bottom TLD is investigated.

Parametric speaker analysis in acoustic space with impedance boundary by using concentrated mass model

Parametric speaker analysis in acoustic space with impedance boundary by using concentrated mass model

Analysis of a parametric speaker by using concentrated mass model

Analysis of a parametric speaker by using concentrated mass model

Two-dimensional Acoustic Analysis by Concentrated Mass Model

Two-dimensional Acoustic Analysis by Concentrated Mass Model

Analysis of self-excited thermoacoustic vibrations by using concentrated mass model

Analysis of self-excited thermoacoustic vibrations by using concentrated mass model

Wave Analysis of Parametric Array Loudspeaker by Concentrated Mass Model

Wave Analysis of Parametric Array Loudspeaker by Concentrated Mass Model

Analysis of acoustic tube with temperature gradient by concentrated mass model

Analysis of acoustic tube with temperature gradient by concentrated mass model

Couple analysis of vibro-acoustics by concentrated mass model

Couple analysis of vibro-acoustics by concentrated mass model

Nonlinear Torsional Vibration Analysis and Control of Semidirect Electromechanical Coupling Transmission System in Shearer

The nonlinear torsional vibration and instability oscillation caused by nonlinear damping in the shearer electromechanical coupling cutting transmission system in shearer driven by the permanent magnet synchronous motor (PMSM) is investigated in this paper. The electromechanical coupling transmission system in the shearer is equivalent to a concentrated mass model for the purpose of establishing the system dynamic model by the Lagrange–Maxwell equation. Then, the Routh–Hurwitz criterion is used to determine the torsional vibration critical point and stability region for the Hopf bifurcation for the cutting transmission system. According to the Routh–Hurwitz stability criterion, the Hopf bifurcation type and the effect of the supercritical Hopf bifurcation in the torsional vibration of the cutting transmission system are analyzed. Furthermore, based on the washout filter, the Hopf bifurcation controller is designed for suppressing the transmission system’s large vibration amplitude and unstable oscillation. In addition, the influences of the linear gain and nonlinear gain on the bifurcation point and the limit cycle amplitude are discussed. Finally, the numerical simulation results indicate the effectiveness of the designed controller. The research achievements can provide a theoretical basis for design or optimize the cutting transmission system of high‐reliability shearer driven by PMSM.

Analysis for Coupling Vibration between Sloshing and Elastic Vibration by Using Concentrated Mass Model

Analysis for Coupling Vibration between Sloshing and Elastic Vibration by Using Concentrated Mass Model

Active noise control for complicated space by concentrated mass model

Active noise control for complicated space by concentrated mass model

Effect of adding mass to rotor on in-plane squeal in automotive disc brake

This study experimentally examined disc brake-generated inplane squeal by looking at vibration modes. The in-plane squeal was determined to be closely related to both the out-of-plane squeal that has directionality caused by Coulomb friction and the in-plane squeal caused by dry friction. The characteristics of in-plane squeal were also analytically investigated using a concentrated mass model formed by connected massless beams, and the relationship between mass added to the rotor and squeal suppression was clarified.

Coupled analysis of two-dimensional acoustic and membrane vibration by concentrated mass model: Proposal of spurious mode elimination model

When using the finite element method for structural–acoustic coupled analysis, the mass and stiffness matrices are not symmetric because the acoustic space is described by sound pressure and the st...