Bar Mode Research Articles

Triaxial braided sandwich composite guide bar potentially used in high-speed warp knitting machine

Integrated manufacturing technology was applied to fabricate a 3-D triaxial braided sandwich composite (TBSC) guide bar based on a real geometric shape. The axial compression, three-point bending, and vibration performance of bar specimens were investigated. Frequencies and vibration modes of the TBSC bar at free and constraint conditions were obtained by the numerical model, and the parametric analysis of different braiding angles was carried out. Effectiveness of the full-scale model was verified by vibration experiments. It is found that the frequency of TBSC and steel guide bar were close at the order 1 and 2; but when the order was higher than 2, the TBSC frequency was significantly improved. For the steel bar, axial periodic torsion and cross-section distortion were found at the orders 4, 5, 6, and 8; While for the TBSC structure, transverse bending was the main vibration deformation. Under a constrained state, the bending deformation was either localized at one end or in the middle of the bar, less than 1/3 length of the whole bar. The effect of braiding angle was significant on the deformation morphology. The increase of braiding angle had a negative effect on the frequency at the order 1 to 6. But such tendency changed at higher orders from 7 to 14. The frequency of [+15/0/-15]3 and [+75/0/-75]3 TBSC bars were much lower than that of [+30/0/-30]3 and [+45/0/-45]3 counterparts. If the maximum deformed displacement is considered, the [+45/0/-45]3 configuration will be the best choice, especially for vibration resistance at high frequency.

Genesis of morpho-kinematic lopsidedness in minor merger of galaxies

ABSTRACT An m = 1 lopsided asymmetry is common in disc galaxies. Here, we investigate the excitation of an m = 1 lopsidedness in host galaxies during minor mergers while choosing a set of 1:10 merger models (with varying orbital configurations, morphology of the host galaxy) from the GalMer galaxy merger library. We show that a minor merger triggers a prominent m = 1 lopsidedness in stars of the host galaxy. The strength of the m = 1 lopsidedness undergoes a transient amplification phase after each pericenter passage of the satellite, in concordance with past findings of exciting an m = 1 lopsidedness by tidal encounters. However, once the merger happens, and the post-merger remnant readjusts itself, the lopsidedness disappears in short time-scale (∼ 500 − 850 ${{\rm Myr}}$). Furthermore, a delayed merger can drive a prolonged (∼2 ${\rm Gyr}$) lopsidedness in the host galaxy. We demonstrate that the m = 1 lopsidedness rotates with a well-defined pattern speed which is much slower than the m = 2 bar pattern speed, and is retrograde with respect to the bar. This gives rise to a dynamical scenario where the Inner Lindblad resonance of the m = 1 lopsidedness falls in between the corotation and the Outer Lindblad resonance of the m = 2 bar mode. A kinematic lopsidedness also arises in the host galaxy; the resulting temporal variation closely follows that of the density lopsidedness. The minor merger also triggers a transient off-centred stellar disc-dark matter halo configuration due to the tidal encounter with the satellite.

Energy dissipation in reinforced concrete members before or after yielding

AbstractModels for the pre‐ and post‐yield energy dissipation in reinforced concrete (RC) members are developed using a database of about 1200 tests with over 18,000 load cycles. Before yielding, the equivalent viscous damping ratio exceeds 5%, especially if the member is initially uncracked. It can be considered by using either a dedicated pre‐yield hysteretic model with parameters established in the paper or global viscous damping and special provisions against double counting of energy dissipation. The post‐yield model can be combined with various post‐yield hysteretic laws. It accounts for the member's type, shear‐span‐to‐depth ratio and likely failure mode, the continuity, ratio, and surface characteristics of longitudinal bars, and for FRP wrapping, if any. Alternatively, it recognizes only four member types but accounts also for the transverse steel ratio and the normal stress due to the axial load.

In-plane selective excitation of arbitrary vibration modes using thickness-shear (d 15) piezoelectric transducers

Experimental modal analysis is of great importance for the dynamic characterization of structures. Existing methods typically employ out-of-plane forces for excitation and measure the acceleration or strain for modal analysis. However, these methods encountered difficulties in some cases. In this work, we proposed an in-plane excitation method based on thickness-shear (d 15) piezoelectric transducers. Through the combination of distributed d 15 PZT strips, arbitrary vibration modes can be selectively excited in a wide frequency range. Both simulations and experiments were conducted and the results validated the proposed method. Specifically, bending, torsional, and longitudinal vibration modes of a rectangular bar were selectively excited. Torsional modes of a shaft were excited without the aid of brackets and bending modes of a circular plate were excited with actuators placed at nodal lines. Furthermore, the electromechanical impedance of the PZT-structure system was measured from which the natural frequency and quality factor were directly extracted. Due to its simplicity and flexibility, the proposed vibration excitation method is expected to be widely used in near future.

High piezoelectricity after field cooling AC poling in temperature stable ternary single crystals manufactured by continuous-feeding Bridgman method

After field cooling (FC) alternating current poling (ACP), we investigated the dielectric and piezoelectric properties of [001]pc-oriented 0.24Pb(In1/2Nb1/2)O3 (PIN)-0.46Pb(Mg1/3Nb2/3)O3 (PMN)-0.30PbTiO3 (PT) (PIMN-0.30PT) single crystals (SCs), which were manufactured by continuous-feeding Bridgman (CF BM) within morphotropic phase boundary (MPB) region. By ACP with 4 kVrms/cm from 100 to 70 °C, the PIMN-0.30PT SC attained high dielectric permittivity (ε33T/ε0) of 8330, piezoelectric coefficient (d33) of 2750 pC/N, bar mode electromechanical coupling factor k33 of 0.96 with higher phase change temperature (Tpc) of 103 °C, and high Curie temperature (TC) of 180 °C. These values are the highest ever reported as PIMN-xPT SC system with Tpc > 100 °C. The enhancement of these properties is attributed to the induced low symmetry multi-phase supported by phase analysis. This work indicates that FC ACP is a smart and promising method to enhance piezoelectric properties of relaxor-PT ferroelectric SCs including PIMN-xPT, and provides a route to a wide range of piezoelectric device applications.

Statistically-informed deep learning for gravitational wave parameter estimation

We introduce deep learning models to estimate the masses of the binary components of black hole mergers, , and three astrophysical properties of the post-merger compact remnant, namely, the final spin, , and the frequency and damping time of the ringdown oscillations of the fundamental bar mode, . Our neural networks combine a modified WaveNet architecture with contrastive learning and normalizing flow. We validate these models against a Gaussian conjugate prior family whose posterior distribution is described by a closed analytical expression. Upon confirming that our models produce statistically consistent results, we used them to estimate the astrophysical parameters of five binary black holes: GW150914, GW170104, GW170814, GW190521 and GW190630. We use PyCBC Inference to directly compare traditional Bayesian methodologies for parameter estimation with our deep learning based posterior distributions. Our results show that our neural network models predict posterior distributions that encode physical correlations, and that our data-driven median results and 90% confidence intervals are similar to those produced with gravitational wave Bayesian analyses. This methodology requires a single V100 NVIDIA GPU to produce median values and posterior distributions within two milliseconds for each event. This neural network, and a tutorial for its use, are available at the Data and Learning Hub for Science.

Compression behavior of GFRP bars under elevated In-Service temperatures

The use of glass fiber-reinforced polymer (GFRP) bars is becoming accepted as internal longitudinal reinforcement in concrete members subject to compressive load. In building and construction, GFRP reinforcement is subject to elevated in-service temperatures that might soften the polymer matrix and affect the mechanical properties of the reinforcement. That notwithstanding, information on the compressive behavior of GFRP bars under elevated in-service temperatures is limited. This study investigated the effects of elevated in-service temperatures ranging from 23℃ to 140℃ and different slenderness ratios (Lu/db) of 4, 8, and 16 on the compressive behavior of GFRP bars. The test results show that the failure mode of GFRP bars changed from fiber-dominant to matrix-dominant with increased temperature. Similarly, the increase in Lu/db ratio changed the failure from shear-crushing to buckling-splitting failure. Furthermore, the GFRP bars retained most of their compressive strength when exposed to temperatures of up to 60℃, but significantly decreased thereafter. The compressive strength retention of the GFRP bars at 140℃ was around 20% regardless of the Lu/db ratio. Based on these results, prediction equations were derived to reliably describe the compressive behavior of GFRP bars and to appropriately determine the minimum concrete cover needed to effectively design GFRP-reinforced concrete members under compression exposed to elevated in-service temperatures.

Tuning of bending and torsional modes of bars used in mallet percussion instruments.

The present paper proposes a generic design-optimization procedure for the concomitant tuning of bending and torsional modes of bars used in mallet percussion instruments. The undercut model uses a series of discontinuous cuts aimed to facilitate the manufacturing process. Compared to one-dimensional beam models, the use of three-dimensional (3-D) finite element modeling not only allows for the calculation of torsional modes but also provides an increased accuracy in the prediction of modal frequencies, an important aspect when dealing with the demanding tuning tolerances required in a musical context. A global optimization problem is formulated and solved using a surrogate function algorithm, which enables fast computations even with the expensive function evaluations associated with 3-D finite element models. Modal identification of experimental bars demonstrates the potential of the proposed procedure, leading to bars with demanding tuning ratios (six target frequencies) at absolute tuning deviations typically below 15 cents. Measurements of the radiated sound from the experimental bars illustrate the benefits of the improved designs compared to those without torsional tuning. The proposed framework, aside from dealing with the comprehensive tuning of percussive musical bars, also accounts for important practical considerations regarding efficient optimization, modeling accuracy, and manufacturing complexity.

Spiral instabilities: little interaction with a live halo

ABSTRACT In order to address the question of whether spiral disturbances in galaxy discs are gravitationally coupled to the halo, we conduct simulations of idealized models of disc galaxies. We compare growth rates of spiral instabilities in identical mass models in which the halo is held rigid or is represented by particles drawn from an equilibrium distribution function. We examine cases of radial and azimuthal bias in the halo velocity ellipsoid in one of our models, and an isotropic velocity distribution in both. We find at most marginal evidence for an enhanced growth rate of spiral modes caused by a halo supporting response. We also find evidence for very mild dynamical friction between the spiral disturbance and the halo. We offer an explanation to account for the different behaviour between spiral modes and bar modes, since earlier work had found that bar instabilities became significantly more vigorous when a responsive halo was substituted for an equivalent rigid mass distribution. The barely significant differences found here justify the usual simplifying approximation of a rigid halo made in studies of spiral instabilities in galaxies.

A novel method for effecting flexible guided wave propagation in elliptical vibration cutting

As a key part of elliptical vibration cutting (EVC) technology, a two-dimensional ultrasonic elliptical vibration cutting (UEVC) device has become a prevalent area of importance and research interest. This paper dissects through the conventional structural design and creatively proposes the UEVC device with flexible guided wave propagation. The device resolves the problems of poor coupling efficiency of two-way excitation signal, complex structure design, non-orthogonal, and the difficulty in controlling the ellipse trajectories of the tool tip. It has been confirmed that a flexible guided wave exhibits an effective unidirectional propagation and lateral load decoupling ability via establishing its system dynamic response and frequency impedance characteristics. Here, we explain the coupling mechanism of the two-way flexible guided wave in the UEVC device. Results suggested that the experimental measurement of the impedance for the cutting device and the individual transducer shows that the cutting device with the transducer and the tool bar connected by the flexible guided wave has a lower impedance increase ratio compared to the individual transducer, and hardly influence the tool bar mode of the cutting device. At the same time, the tool tip trajectory of the cutting device having a phase difference of 90° showed a satisfactory “elliptical” shape, while the microstructure processed by the tool tip ellipse trajectory with a phase difference of 60° reached a burr-free state. Theoretical and experimental findings reveal that the flexible guided waves exhibit excellent weak coupling characteristics in the non-transmitting direction. This is convenient to the independent, orthogonal and stable propagation of signals in the two directions. Based on flexible guided wave propagation technology, our findings provide theoretical foundation and application value for the design of a two-dimensional UEVC device.

Three-dimensional tuning of idiophone bar modes via finite element analysis.

The timbre of marimba and other idiophone bars can sometimes be polluted by untuned torsional modes, leading to substandard instruments or rejected materials. Makers have complained of problems with these untuned modes over a specific range of notes. Marimba, vibraphone, and similar idiophone bars are tuned by carving one side of the bar to bring up to three flexural modes into harmonic relationships. Torsional and other mode types are commonly left untuned. The relative frequency of these untuned modes with respect to the fundamental mode will vary along the keyboard. This paper investigates tuning both torsional and flexural modes simultaneously. This tuning is achieved using sophisticated carved geometries, and without employing concentrated masses or additional materials. Bars are modeled using three-dimensional finite elements. Geometry is defined by a large number of input parameters. Algorithms are implemented to identify bar modes automatically, eliminating the need for human intervention. Tuning is performed via a Newton-Raphson approach using the Moore-Penrose generalized matrix inverse to solve systems of tuning equations. This method is found to be effective at finding satisfactory bar geometries in proximity to initial conditions. Numerous example marimba and vibraphone bar models are provided, representing both typical and atypical modal tuning ratios.

Simulation Analysis and Experimental Study on the Working State of Sinking Headframe in the Large Underground Shaft

Based on the newly developed sinking headframe for the deep and large shaft, the finite element model of the full-scale headframe was established by using SAP2000. Through the calculation, the theoretical stress of the headframe at sinking depths of 40 m, 143 m, 223 m, 518 m, 762 m, 1000 m, 1250 m, and 1503 m was obtained and then compared with the field measured stress. The results show that with the increase of shaft sinking depth, the theoretical stress of finite element simulation and the field measured stress of each member of the sheave wheel platform and the headframe increase linearly, and for the maximum member stress in the upper, middle, and lower layers of the headframe, the numerical simulation value is greater than the field measured value and less than the designed steel strength. In other words, under normal working conditions, headframe members are in the elastic stress stage and meet the design requirements, and instability failure of headframe members will not occur. The end-restraint mode of the supporting bars has a great influence on the force of the top member. The reasonable selection of the restraint mode in the simulation is the key to the accuracy of the calculation results. The simulation results well reflect the actual stress of the headframe and provide a reliable guarantee for the follow-up work of the project.

Simulation of mallet percussion instruments by a coupled modal vibroacoustic finite element model.

A three-dimensional coupled vibroacoustic finite element model for physics-based simulations of the sound generation by mallet percussion instruments in the time domain is discussed in the present paper. The mechanical model takes the orthotropic material properties of the wooden sound bars and the nonlinear nature of the interaction force between the mallet head and the sound bar into account while the acoustical model considers radiation into an unbounded domain. A direct coupling of the sound bars, acoustical cavity resonators, and the excitation by a mallet is considered with exploiting the modal basis to reduce the number of degrees of freedom of the system. Both the mechanical and acoustical models are validated by comparing them to measurements performed on an Orff xylophone. A case study shows the capabilities of the coupled model, including the analysis of the energy balance, the effect of tuning the resonator, and the excitation of the torsional modes of the sound bar.

Investigation on nonlinear dynamics and active control of boring bar chatter

This article deals with identification of nonlinear dynamics and active control of boring bar chatter. A control system with unidirectional actuation is proposed, which consists of an accelerometer sensor that monitors the cutting tool vibrations as well as an electrodynamic shaker that exerts a controllable force to a boring bar in the radial direction. The forward path model for actuator–boring bar assembly is identified using the fundamental concepts of system identification. A novel parameter-varying transfer function is suggested to model the nonlinear dynamics of forward path, which originally stems from the cutting tool structure. The proposed model describes the variations of system’s output response with respect to frequency and amplitude of input excitation. The identified dynamic model is then utilized for model-based controller tuning. The chatter control system utilizes a Direct Velocity Feedback (DVF) controller, and the optimal control gain is computed based upon the disturbance rejection criterion. It is confirmed that the performance of optimally tuned DVF controller does not depend on variations of forward path dynamics. The practical performance of optimal controller is experimentally verified by conducting impact tests as well as cutting tests on Aluminum alloy 6063-T6. According to the obtained results, the dynamic stiffness of active cutting tool is significantly improved by 20-fold. Moreover, chatter is perfectly attenuated around the fundamental mode of boring bar. The DVF controller efficiently attenuates the vibrations by 70 dB. Finally, the viability of using an active cutting tool with embedded electromagnetic damper is studied for industrial applications.

Experimental Investigation of the Mechanical Behaviour of Wall\u2013Beam\u2013Strut Joints for Prefabricated Underground Construction

Prefabricated construction is becoming increasingly prevalent, however, it is rarely applied in underground constructions, except for tunnel linings, due to the difficulties that arise in jointing various prefabricated components in underground conditions. To solve the vertical location problem of embedded mechanical couplers during the construction of wall–beam–strut joints for a prefabricated metro station, a new connection using welded steel plates is proposed. In this paper, four full-scale specimens of wall–beam–strut joints connected using welded steel plates and mechanical couplers were experimentally tested under monotonic and low-reversed cyclic loading conditions. The testing results were analysed in terms of the ultimate bearing capacity, failure mode, hysteresis, skeleton curve, stiffness degradation, energy dissipation and strain of the reinforcement bars. Notably, the two kinds of joints had similar ultimate bearing capacities and failure modes, but the crack distributions on the tops of the waler beams were different. For the specimens with the welded steel plate connection, tensile horizontal cracks first appeared on the top surface of the beam, where the welded steel plate was located, and then coalesced gradually; however, this cracking pattern was not observed during the experimental test of the specimens connected with the mechanical couplers. Furthermore, it was determined that the energy dissipation and ductility of the welded steel plate connection were better than those of the mechanical coupler connected joint, because the steel plate could redistribute the internal force in the joint and increase the stiffness. It was concluded that the proposed welded steel plate connection could be more favourable than the mechanical coupler connection in the construction of a prefabricated metro station in Guangzhou. Moreover, the results obtained from these experiments could provide guidelines for the corresponding connections employed in underground-prefabricated structures.

Visualization of soil deformation shape in longitudinal vibration mode of elastic bar coupled with soil

Visualization of soil deformation shape in longitudinal vibration mode of elastic bar coupled with soil

Reliability and Validity of Using the Push Band v2.0 to Measure Repetition Velocity in Free-Weight and Smith Machine Exercises.

Hughes, LJ, Peiffer, JJ, and Scott, BR. Reliability and validity of using the Push Band v2.0 to measure repetition velocity in free-weight and Smith machine exercises. J Strength Cond Res XX(X): 000-000, 2019-The purpose of this study was to investigate the test-retest reliability and concurrent validity of using the Push Band device 2.0 (PUSH) to quantify repetition velocity across 4 common resistance training exercises performed using free-weight and Smith machine training modalities. Twenty well-trained men (age: 25.1 ± 2.9 years, height: 182.4 ± 6.0 cm, body mass: 77.9 ± 12.0 kg, training age: 5.2 ± 1.4 years) visited the laboratory on 6 occasions (3 free-weight and 3 Smith machine sessions). Baseline strength assessments were conducted in the first session with each modality for squat, bench press, overhead press, and prone row exercises. The subsequent sessions featured repetitions performed with 30, 60, and 90% 1-repetition maximum. During these sessions, velocity was measured simultaneously using a validated linear position transducer (LPT; considered the criterion for this study) and 2 PUSH devices, one in body mode (PUSHBODY) and the other bar mode (PUSHBAR). Test-retest reliability was examined using the intraclass correlation coefficient (ICC) and coefficient of variation (CV). The LPT demonstrated slightly greater reliability (ICC = 0.80-0.98, CV = 0.4-5.1%) than the PUSHBODY (ICC = 0.65-0.95, CV = 0.8-6.9%) and PUSHBAR (ICC = 0.50-0.93, CV = 0.7-7.1%) devices. Near-perfect correlations existed between velocity measured using LPT and PUSH devices (r = 0.96-0.99). No significant differences existed between mean velocity measures obtained using LPT and either PUSH device. The PUSH device can be used in either bar or body mode to obtain reliable and valid repetition velocity measures across a range of loads and exercises performed using either free weights or a Smith machine.

Analytical model for the prediction of the tensile behaviour of corroded steel bars

An analytical model was developed to predict the tensile behaviour of a corroded steel bar. The model was established based on cross sectional analysis and was validated using experimental data for slotted steel bars and electrochemically corroded steel bars. The model was further used to predict the tensile behaviour of a corroded steel bar. The corrosion mode of the steel bar was supposed to be pitting corrosion and the distribution of the corroded section was supposed to follow a lognormal distribution. A power law between the parameters of the lognormal distribution and the average corrosion rate of the steel bar was used to predict the statistical distribution of the cross section area of a corroded steel bar. Based on these assumptions, the yield strength, ultimate strength and ductility of a corroded steel bar were predicted with different corrosion rates. The predicted behaviours are compared to collected experimental results from various sources. It is found that the numerical results of yield strength and ultimate strength agree well with the collected experimental results. The model slightly underestimates the ductility of the corroded steel bars. The result of the model would be helpful for the prediction of the tensile behaviour of reinforced concrete member subjected to chloride induced corrosion.

Anchorage behaviour of headed bars as connection system for precast reinforced concrete structural components

Precast reinforced concrete (RC) structural joint is a critical region which demands appropriate connection system for adequate shear transfer. Prevalent dowel bars connection for precast components is prone to damage during the seismic motion. This paper proposes an innovative modified dowel bar connection, termed as headed bars, wherein the reinforcement bars are attached to the steel head anchor through welding and embedded into the concrete. To investigate the anchorage behaviour of headed bars, pull-out tests were conducted on a total of 144 specimens, which were differentiated on the parameters of head profile i.e., plain, grooved, ribbed and without head (representing dowel bar); varying length of the head and varying embedment depth into the concrete. The anchorage behaviour of headed bars was studied from the standpoint of failure mode, bond capacity and slip of bar. Dowel bars demonstrated pull-out failure with low bond capacity, whereas headed bars exhibited slip of bar and concrete failure along with higher bond capacity. Based on the experimental results, geometrical specifications for headed bars are recommended. A numerical analysis was carried out to evaluate the efficacy of headed bars as a connection system, where precast RC wall and columns connected using headed bars of proposed geometry were subjected to displacement controlled lateral loading and compared with the structural performance of connection using conventional dowel bars. Numerical analysis exhibited superior performance of precast RC wall-columns connected through headed bars in comparison to the dowel bar connection.

Excitation of guided wave modes in arbitrary cross-section structures by applied surface tractions

To assure the integrity and safety of truss structures, much work has been done for inspection in bars using ultrasonic guided waves methods. Guided waves have been widely used for Non-Destructive Testing (NDT) and Structural Health Monitoring (SHM) because of their long propagation distance and reliable responses. Though good for assessment of guided wave in the regular section structures such as cylinders, pipes and rails, the excitation of guided wave modes in irregular bars lack further research due to the arbitrary cross-section. This paper presents the excitation and propagation of guided waves in arbitrary cross-section structures by coupling the normal mode expansion (NME) method with the semi-analytical finite element (SAFE) method. Then, a Tee-bar example of finite element (FE) simulations is performed to validate the proposed SAFE-NME method. Moreover, the validated method is used to develop a double mode inspection strategy for multi-damages identification, showing the potential for NDT & SHM applications.