Eccentric Mass Research Articles

Adaptive feedforward vibration compensation control strategy of bearingless induction motor

In order to solve the unbalanced vibration problem of bearingless induction motor caused by the rotor mass eccentricity, an adaptive feedforward vibration compensation control strategy is researched. Firstly, the inverse dynamic decoupling control me

An experiment evaluating how the tiny mass eccentricities in spin-stabilized projectiles affect the position of impact points

This study investigates and quantifies some possible sources affecting the position of impact points of small caliber spin-stabilized projectiles (such as 12.7 mm bullets). A comparative experiment utilizing the control variable method was designed to figure out the influence of tiny eccentric centroids on the projectiles. The study critically analyzes data obtained from characteristic parameter measurements and precision trials. It also combines Sobol’s algorithm with an artificial intelligence algorithm—Adaptive Neuro-Fuzzy Inference Systems (ANFIS) – in order to conduct global sensitivity analysis and determine which parameters were most influential. The results indicate that the impact points of projectiles with an entry angle of 0° deflected to the left to that of projectiles with an entry angle of 90°. The difference of the mean coordinates of impact points was about 12.61 cm at a target range of 200 m. Variance analysis indicated that the entry angle – i.e. the initial position of mass eccentricity – had a notable influence. After global sensitivity analysis, the significance of the effect of mass eccentricity was confirmed again and the most influential factors were determined to be the axial moment and transverse moment of inertia (IzzIyy), the mass of a projectile (m), the distance between nose and center of mass along the symmetry axis for a projectile (Lm), and the eccentric distance of the centroid (Lr). The results imply that the control scheme by means of modifying mass center (moving mass or mass eccentricity) is promising for designing small-caliber spin-stabilized projectiles.

Research on Modal Analysis of Rotor Shaft System of Hydro-generator

In this paper, the influence degree of eccentricity distance and guide bearing stiffness change on the vibration characteristics of the unit under the condition of rotor mass misalignment is discussed respectively, and the modal characteristics of the unit are studied for the problem of generator mass eccentricity. First of all, the guide bearing is parameterized, the whole axle system modeling is calculated by FEM modal analysis method, the results of the analysis obtain the first 10th order critical frequency and vibration mode analysis results, further determine the danger point of displacement deformation concentration. Comparing the vibration type, critical frequency and center vibration trajectory of the guide bearing under different constraint conditions, the characteristics of the unit vibration caused by the rotor quality is: the axis tile gap is gradually enlarged due to the eccentric rotation of the rotor of the unit, and the vibration characteristics of the main frequency in the unit vibration signal are unchanged. The results are confirmed by field inspection data.

Langerhans cell histiocytosis of the shoulder girdle, pelvis and extremities: a review of radiographic and MRI features in 85 cases.

To describe the radiographic and MRI features of histologically proven Langerhans cell histiocytosis (LCH) of the bone. A retrospective review of the radiographic and MRI features of 85 histologically proven cases of skeletal LCH over a 12-year period. Clinical data recorded included age, gender and location. Radiographic features evaluated included Lodwick grading, cortical/periosteal response and matrix mineralisation. MRI features assessed included lesion size and T1-weighted signal intensity (T1W SI), nature of margin, hypointense rim, enhancement pattern, bone marrow and soft tissue oedema, soft tissue mass, fluid-fluid levels, the penumbra sign and the budding and bulging signs. The study included 85 patients, 54 males and 31 females with mean age of 13years (range 1-76years). The femur was the commonest bone involved (38.8%), followed by the scapula (9.4%), clavicle (8.2%), ilium (8.2%) and ischium (8.2%). The mean maximal lesion size was 40mm (range 16-85mm). The commonest radiographic appearance was of a lytic lesion with no appreciable sclerotic rim, an intact expanded cortex and either absent or laminated periosteal response. MRI demonstrated a hypointense rim (41.5%), the budding (31.7%) and bulging (36.6%) signs, eccentric extra-osseous mass (42.7%), prominent bone marrow (95.3%) and soft tissue oedema (84.1%). Rarer features included haemorrhage (2.4%), the penumbra sign (3.5%) and fluid-fluid levels (2.4%). Thirteen of 25 post-contrast studies showed peripheral/rim enhancement with central necrosis. LCH classically presents as a moderately aggressive lytic bone lesion on radiography, with prominent reactive bone and soft tissue oedema being a characteristic feature on MRI.

Torsion control in structures isolated with the triple friction pendulum system

A parametric study was carried out to investigate the torsional response of structures isolated with the Triple Friction Pendulum (TFP) system with building properties such as uncoupled torsional to lateral frequency ratio, Ωs, building slenderness, and mass and stiffness eccentricities. A simplified model of a parametric multistory structure and a small deformation model of the TFP, but with the ability to capture uplift, were used to perform parametric 3D non-linear dynamic analyses. The input ground motions were 20 Chilean records selected using a conditional mean spectrum. Response history results showed that uplift in the devices occurs in structures with large mass eccentricity, and in some extreme cases, normal force values in the TFPs may be as large as 6 times the nominal average gravitational load in each isolator. Torsional envelope response results also show that mass eccentric systems may undergo larger normalized edge amplification factors relative to stiffness eccentric systems, with values 2.5 and 1.8, respectively, and that torsional balance cannot be achieved naturally. Although rotations are small in magnitude due to seismic isolation, displacement values in resisting planes of the superstructure equidistant from the geometric center of the plan will be different. Moreover, structures with large Ωs present correlation values between response histories of torsion and translation measured at the geometric center of the plan near one, as well as values above zero for different Ωs and plan eccentricity, which implies no torsional control in the weak sense. It is concluded that parameter Ωs strongly influences the torsional amplification values computed herein.

Electromagnetic transients and gravitational waves from white dwarf disruptions by stellar black holes in triple systems

ABSTRACT Mergers of binaries comprising compact objects can give rise to explosive transient events, heralding the birth of exotic objects that cannot be formed through single-star evolution. Using a large number of direct N-body simulations, we explore the possibility that a white dwarf (WD) is dynamically driven to tidal disruption by a stellar-mass black hole (BH) as a consequence of the joint effects of gravitational wave (GW) emission and Lidov–Kozai oscillations imposed by the tidal field of an outer tertiary companion orbiting the inner BH–WD binary. We explore the sensitivity of our results to the distributions of natal kick velocities imparted to the BH and WD upon formation, adiabatic mass loss, semimajor axes and eccentricities of the triples, and stellar-mass ratios. We find rates of WD–tidal disruption events (TDEs) in the range 1.2 × 10−3 − 1.4 Gpc−3 yr−1 for z ≤ 0.1, rarer than stellar TDEs in triples by a factor of ∼3–30. The uncertainty in the TDE rates may be greatly reduced in the future using GW observations of Galactic binaries and triples with LISA. WD–TDEs may give rise to high-energy X-ray or gamma-ray transients of duration similar to long gamma-ray bursts but lacking the signatures of a core-collapse supernova, while being accompanied by a supernova-like optical transient that lasts for only days. WD–BH and WD–NS binaries will also emit GWs in the LISA band before the TDE. The discovery and identification of triple-induced WD–TDE events by future time domain surveys and/or GWs could enable the study of the demographics of BHs in nearby galaxies.

Vibration analysis of mass nanosensors with considering the axial-flexural coupling based on the two-phase local/nonlocal elasticity

The influences of considering coupled axial-flexural vibrations on efficiency of cantilever mass nanosensors, modeled by Rayleigh and Timoshenko beam theories, are investigated in the frame work of a paradox-free nonlocal theory, i.e. two-phase local/nonlocal elasticity. However, the effects of axial-flexural coupling due to eccentricity of attached mass have been ignored in previous studies on mass nanosensors. Governing equations, boundary conditions, and corresponding compatibility conditions are derived by means of Hamilton’s principle and differential law of two-phase elasticity. Next, The Generalized Differential Quadrature Method (GDQM) as well as Generalized Integral Quadrature Method (GIQM) are utilized to attain the discretized two-phase formulation and coupled vibration characteristics of mass nanosensor. Several analogical studies are performed in detail to confirm the credibility of the present formulation and results. Comparisons between the uncoupled and coupled vibrations disclose that there are significant errors in obtaining the natural frequencies of corresponding mass value when the axial and transverse vibrations are considered separately. Therefore, the coupling of axial-lateral displacements resulted from the added mass eccentricity must be considered. This work can be a useful step forward to examine the coupling effects on vibration behavior of mass nanosensors, and it can be helpful to design the nanosensors with higher accuracy.

Peak seismic response of a symmetric base-isolated steel building: near vs. far fault excitations and varying incident angle

Since the peak seismic response of a base-isolated building strongly depends on the characteristics of the imposed seismic ground motion, the behavior of a base-isolated building under different seismic ground motions is studied, in order to better assess their effects on its peak seismic response. Specifically, the behavior of a typical steel building is examined as base-isolated with elastomeric bearings, while the effect of near-fault ground motions is studied by imposing 7 pairs of near- and 7 pairs of far-fault seismic records, from the same 7 earthquake events, to the building, under 3 different loading combinations, through three-dimensional (3D) nonlinear dynamic analyses, conducted with SAP2000. The results indicate that near-fault seismic components are more likely to increase the building\'s peak seismic response than the corresponding far-fault components. Furthermore, the direction of the imposed earthquake excitations is also varied by rotating the imposed pairs of seismic records from 0° to 360°,with respect to the major construction axes. It is observed that the peak seismic responses along the critical incident angles, which in general differ from the major horizontal construction axes of the building, are significantly higher. Moreover, the influence of 5% and 10% accidental mass eccentricities is also studied, revealing that when considering accidental mass eccentricities the peak relative displacements of the base isolated building at the isolation level are substantially increased, while the peak floor accelerations and interstory drifts of its superstructure are only slightly affected.

Fractional-order modeling and nonlinear dynamic analyses of the rotor-bearing-seal system

Abstract Unexpected vibrations induced by sealing and bearing faults in the rotor-bearing-seal system seriously affect the health and reliability of the rotating machinery. Here, to study the vibration performances more accurately, the sealing force model is extended from a very narrow integer-order scope to a flexible fractional-order scope, and a novel fractional-order mathematical model of the rotor-bearing-seal system is established from the view of engineering applications by using the finite element method. As a pioneering work, the effect of the fractional order of sealing on the journal and rotor are analyzed under different rotational speeds. Besides, the dynamic characteristics of the rotor-bearing-seal system with the changing rotational speed, mass eccentricity of rotor, sealing clearance and sealing pressure drop at a specific fractional order of sealing are also studied in detail. Then some stability discussions of the system are presented, which is synchronous with some special frequency characteristics. Finally, the methods and results can efficiently provide a theoretical reference for the design and operation of the rotor-bearing-seal system and be applied to forecasting and diagnosing vibration faults of them.

Effect of ground motion directionality on the seismic response of base isolated buildings pounding against adjacent structures

Seismic isolation is considered an effective design approach in averting structural and non-structural damage under severe seismic excitations. However, considerable relative displacements at the isolation level during a strong ground motion may lead to structural collisions with the surrounding moat wall and neighboring structures. Such pounding incidences, which may have detrimental consequences on the anticipated seismic behavior and performance of base isolated structures, are investigated in the presented research work. A computational methodology with the ability to capture impact forces is employed, in order to spatially examine potential structural impact with adjacent structures. Specifically, nonlinear time-history analyses of base isolated buildings, pounding with nearby conventionally fixed-supported buildings and/or the surrounding moat walls are carried out in order to examine the conditions that lead to pounding and quantify the effect of certain critical parameters on the corresponding peak seismic response. Specifically, the directionality of the imposed seismic excitations with respect to the primary construction axes of the simulated base isolated buildings is considered as an influencing parameter. The effect of other parameters, such as the clearance between the base isolated building and adjacent structures, the structural characteristics of the neighboring structures and the inclusion of accidental torsion for the seismically isolated structures in terms of mass eccentricities, is also investigated.

Effect of Eccentric Mass Distribution on the Motion of Spherical Particles in Shear Flows

Abstract A particle-resolved direct numerical simulation is performed on the motion of spherical particles with an eccentric internal mass distribution in lateral linear shear flow, which is oriented in the vertical direction and sheared in a horizontal direction. We examine the effect of mass eccentricity on the two-way interactions of particles with both laminar and turbulent shear flows. A spherical shell/hollow particle with an inner spherical core is focused on as a typical example of mass eccentric particles. The Navier–Stokes equations and the Newton–Euler equations are solved for the fluid phase and the particles, respectively. An immersed boundary method is adopted to represent the shell particle. The Newton–Euler equations are solved using the body-fixed coordinate system and four quaternion parameters, considering the deviation of the center of mass from the center of the spherical shell particle. Simulations are performed at a relatively low particle volume fraction of 0.4%. In turbulent flows, the Taylor-microscale Reynolds number reached about 49 at the end of the simulations. Numerical results show that shear-induced particle rotation is suppressed by the torque due to gravity. It is found that the lateral migration of mass eccentric particles becomes less vigorous in both laminar and turbulent flows since the effect of the Magnus lift force is also weakened for mass eccentric particles. It is also found that the evolution of fluid kinetic energy is significantly affected by the mass eccentricity of particles in laminar flows.

Formulae for the frequency equations of beam-column systemcarrying a fluid storage tank

In this work, a mathematical model of beam-column system carrying a double eccentric end mass system is investigated, and solved analytically based on the exact solution analysis. The model considers the case in which the double eccentric end mass is a rigid storage tank containing fluid. Both Timoshenko and Bernoulli-Euler beam bending theories are considered. Equation of motion, general solution and boundary conditions for the present system model are developed and presented in dimensional and non-dimensional format. Several important non-dimensional design parameters are introduced. Symbolic and/or explicit formulae of the frequency and mode shape equations are formulated. To the authors knowledge, the present reduced closed form symbolic and explicit frequency equations have not appeared in literature. For different applications, the results are validated using commercial finite element package, namely ANSYS. The beam-column system investigated in this paper is significant for many engineering applications, especially, in mechanical and structural systems.

Sommerfeld Effect and Unbalanced Response Analysis in Single Disk Rotor System with Eccentric Mass Considering Induction Motor Model

Sommerfeld Effect and Unbalanced Response Analysis in Single Disk Rotor System with Eccentric Mass Considering Induction Motor Model

The influence of the vertical cantledge mass on the vibratory drum vibrations during the material compaction

The road roller vibratory drum is considered as a three-mass vibration system consisting of the eccentric weight mass m1, vibratory drum mass m2, additional mass m3, which is transmitted to the vibratory drum axis through the roller frame. Differential equations of vertical vibrations were formulated, they were solved, analytical expressions were obtained of the amplitude A1 of the vibrator drum vertical vibrations and of the amplitude A2 of the additional mass m3 vibrations, rigidly connected with the road roller frame. The dependences of the vertical vibration amplitudes A1 and A2 on the vibration frequency, mass ratio (m1 + m2) and m3, stiffness factors and viscous friction factors of the soil and rubber-metal shock absorbers have been established. The additional mass m3 is considered as an additional shock absorber that protects the roller frame from vibration. The differential equation of the additional mass m3 vertical vibrations has been obtained, which are excited by the harmonic inertia force. The analytical dependence conclusion for the determination of the dynamic factor Kd as the ratio of the dynamic and static vibration amplitudes of the additional mass m3 of the vibratory drum have been specified. The specified dependence of the driving force transfer factor K determination on mass m3 to the roller frame has been obtained. The diagrams of the dependence of Kd and K factors on the frequency ratio of forced and natural vibrations of the mass m3 are constructed.

Design of Eccentric Mass-Type Vibration-Damping Electric Actuator Control System for Non-Fixed-Wing Aircraft

The main spiral blade of non-fixed wing aircraft will produce periodic vibration force when rotating, which will not only reduce the service life of airborne equipment, but also greatly affect the working state of pilots. Due to the narrow damping band of passive damping device, it is difficult to meet the vibration reduction requirements of modern aircraft. Therefore, this article proposes an eccentric mass block type electrical control system based on active vibration control Force actuator system and a prototype is developed. In this article, the output force model of eccentric wheel type anti vibration actuator, the periodic fluctuating load model of motor side, the linearization model of gear clearance and the dynamic model of the whole electric actuator are established. Secondly, according to the system stability control requirements, the controller parameters of the electric actuator are designed. The maximum value of the gear clearance dimension is introduced into the control system to correct the controller parameters, and provide theoretical design basis for the actuator gear clearance size. Finally, the sensitivity function from the disturbance side to the control error side is calculated. The effectiveness of the parameters and the robustness of the control system are verified by the sensitivity $H_{\infty }$ control theory. The results show that the prototype has good dynamic and steady-state performance and meets the vibration control requirements of the main spiral blade of the non-fixed wing aircraft.

Inward bound: the incredible journey of massive black holes as they pair and merge – I. The effect of mass ratio in flattened rotating galactic nuclei

ABSTRACT Understanding how supermassive black holes (SMBHs) pair and merge helps to inform predictions of off-centre, dual, and binary active galactic nuclei (AGNs), and provides key insights into how SMBHs grow and co-evolve with their galaxy hosts. As the loudest known gravitational wave source, binary SMBH mergers also hold centrestage for the Laser Interferometer Space Antenna (LISA), a joint ESA/NASA gravitational wave observatory set to launch in 2034. Here, we continue our work to characterize SMBH binary formation and evolution through increasingly more realistic high-resolution direct N-body simulations, focusing on the effect of SMBH mass ratio, orientation, and eccentricity within a rotating and flattened stellar host. During the dynamical friction phase, we found a prolonged orbital decay for retrograde SMBHs and swift pairing time-scales for prograde SMBHs compared to their counterparts in non-rotating models, an effect that becomes more pronounced for smaller mass ratios Msec/Mprim = q. During this pairing phase, the eccentricity dramatically increases for retrograde configurations, but as the binary forms, the orbital plane flips so that it is almost perfectly prograde, which stifles the rapid eccentricity growth. In prograde configurations, SMBH binaries form and remain at comparatively low eccentricities. As in our prior work, we note that the centre of mass of a prograde SMBH binary itself settles into an orbit about the centre of the galaxy. Since even the initially retrograde binaries flip their orbital plane, we expect few binaries in rotating systems to reside at rest in the dynamic centre of the host galaxy, though this effect becomes smaller as q decreases.

A study on the effects of torsional component of ground motions on seismic response of low‐ and mid‐rise buildings

SummaryThe torsional component of ground motion is a potential factor to excite the torsional response of buildings during earthquake, which is not explicitly considered in seismic design codes. Building codes have proposed accidental eccentricity to consider the effect of torsional component and other unpredicted factors, which may contribute to torsion in buildings. This study investigated the effects of torsional component on the buildings' responses and the adequacy of the accidental eccentricity. For this purpose, the torsional component of some selected ground motions was generated using single‐station procedure. Subsequently, 5, 10, and 15‐story buildings with different ratios of rotational to translational frequencies were analyzed; first, by translational components only, and second, by simultaneous application of translational and torsional components. Also, the role of mass eccentricity in the effects of torsional component was studied. Furthermore, all models were reanalyzed by applying the 5% accidental eccentricity, and the effects of torsional component and accidental eccentricity were compared accordingly. Results indicated that torsional component has significant impact on the buildings' responses and can increase the displacement and drift ratio up to 36% and 41%, respectively. However, the 5% accidental eccentricity is not sufficient to take account the torsional component effects, and leads to unreliable responses.

Reliability-Based Seismic Assessment of Multi-Story Box System Buildings under the Accidental Torsion

ABSTRACT Performance analysis of reinforced concrete (RC) buildings during past earthquakes has shown that irregular distribution of mass, stiffness, and strength may cause severe damage in structural elements. Accidental torsion, one of the most common reasons of damage and failure under the strong ground motions, is a complex phenomenon in which several variables are involved. The box-type structural system is considerably sensitive to torsion due to shear wall arrangement and that the torsional mode which governs structural response. Thus, understanding and evaluating accidental torsion is a fundamental step in seismic reliability evaluation of this structural system in comparison with other common structures. Therefore, in this study, seismic sensitivity of the box-type structural system is evaluated for various configurations of mass, stiffness, and strength centers. Several analyses, such as eigen-value, push-over, nonlinear time history, and seismic reliability analysis are performed using artificial records to predict structural characteristics and probabilities of failure. The results show that the mass eccentricity has a greater effect on the seismic response in comparison with the strength and stiffness eccentricities. The most critical condition occurs when the mass and stiffness centers are shifted in the same direction, so the story drift under the design and maximum credible earthquakes are 2.45 and 2.26 times the symmetrical model drift, respectively. Furthermore, it is shown that this box-type structural system demonstrates acceptable seismic reliability under the accidental torsion since the main elements of lateral bearing system remain in an immediate occupancy performance level under the design earthquake.

Dynamic behaviour of a 13-story reinforced concrete building under ambient vibration, forced vibration, and earthquake excitation

This paper presents a unique study of dynamic behaviour of a full-scale 13-story reinforced concrete building under forced vibration, ambient vibration, and distal earthquake-induced excitation. Initially, an eccentric mass shaker located on the upper floor of the building was used to excite the building while instrumented with eight accelerometers. Then, ambient vibrations induced by traffic and wind were recorded over a period of two weeks, utilizing over 40 tri-axial accelerometers. During the sampling period, the building was excited by a M6.5 earthquake and high-quality vibration data sets were recorded. Modal parameters of the building were identified with a range of frequency and time domain system identification (SI) methods, and the influence of excitation force characteristics on performance of various techniques was also investigated. A finite element model of the building was developed using SAP2000 to compare modal properties to the identified counterparts from experiments. Results showed a strong correlation between modal parameters identified by different SI methods, and all techniques provided accurate estimation of modal parameters when used with output-only data. Modal parameters determined from ambient vibrations were comparable to their forced vibration counterparts, providing evidence that ambient vibration testing can be as effective as forced vibration testing in determining modal parameters for similar size structures. The near stationary vibration data can produce accurate estimation of modal parameters. However, further study is required to facilitate application of output-only SI techniques with non-stationary data. There was a good match between peak displacement amplitudes obtained by the numerical model and those experimentally measured at different excitation frequencies. This match demonstrated the accuracy of the finite element model to predict realistic dynamic behaviour of the building under various harmonic excitation forces.

Modelling of shaft unbalance: Modelling a multi discs rotor using K-Nearest Neighbor and Decision Tree Algorithms

Multi discs rotors are widely used in the industry. Shaft unbalance in multi-discs’ rotors is the main failure origin that leads to global failures in rotary systems. Unbalance parameters that must be detected in the shaft are focused on this study. Unbalance parameters are eccentric mass value, eccentric radius, and disc number which are presenting an unbalance location. The main aim of the current paper is to identify unbalance parameters of a rotating shaft having multi-discs by artificial intelligent methods namely KNN and Decision Tree Algorithm. For both algorithms, data derived from a fabricated test rig consists of a shaft in which four discs are mounted on that. The results show that the KNN presents more accuracy in estimating of unbalance parameters compared to the Decision Tree in terms of unbalance locating.