Flexural excitation in a standard torsional-resonant column device

1998 ◽  
Vol 35 (3) ◽  
pp. 478-490 ◽  
Author(s):  
Giovanni Cascante ◽  
Carlos Santamarina ◽  
Najwa Yassir
Keyword(s):  
Test Procedure ◽  
Shear Stiffness ◽  
Modal Testing ◽  
Resonant Column ◽  
Loss Mechanism ◽  
Flexural Mode ◽  
Local Flow ◽  
Near Surface ◽  
High Attenuation ◽  
Resonant Column Device

The excitation of specimens in multiple modes enhances the characterization of granular materials. The purpose of this paper is to present the equipment modification and test procedure and data reduction for flexural excitation in a standard torsional-resonant column device. Typical results for dry and wet sand specimens are also presented. A salient advantage of the modified device is that it permits testing shear stiffness (torsional excitation) and longitudinal stiffness (flexural excitation) at frequencies which are relevant to high-resolution seismics and near-surface studies (approx. 50-200 Hz). High attenuation in flexural mode is measured in saturated and partially saturated specimens; local flow is suspected as a prevailing loss mechanism. Velocity and damping ratios are complementary indicators of saturation conditions prevailing in the specimen.Key words: mechanical waves, resonant column, velocity, attenuation, sands, modal testing.

Shallow near-surface effects

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. T221-T231 ◽  
Author(s):  
Christine E. Krohn ◽  
Thomas J. Murray
Keyword(s):  
Time Delay ◽  
Velocity Gradient ◽  
P Wave ◽  
Unconsolidated Sediments ◽  
P Waves ◽  
Large Computer ◽  
Near Surface ◽  
S Waves ◽  
High Attenuation ◽  
Pulse Broadening

The top 6 m of the near surface has a surprisingly large effect on the behavior of P- and S-waves. For unconsolidated sediments, the P-wave velocity gradient and attenuation can be quite large. Computer modeling should include these properties to accurately reproduce seismic effects of the near surface. We have used reverse VSP data and computer simulations to demonstrate the following effects for upgoing P-waves. Near the surface, we have observed a large time delay, indicating low velocity ([Formula: see text]), and considerable pulse broadening, indicating high attenuation ([Formula: see text]). Consequently, shallowly buried geophones have greater high-frequency bandwidth compared with surface geophones. In addition, there is a large velocity gradient in the shallow near surface (factor of 10 in 5 m), resulting in the rotation of P-waves to the vertical with progressively smaller amplitudes recorded on horizontal phones. Finally, we have found little indication of a reflection or ghost from the surface, although downgoing reflections have been observed from interfaces within the near surface. In comparison, the following have been observed for upgoing S-waves: There is a small increase in the time delay or pulse broadening near the surface, indicating a smaller velocity gradient and less change in attenuation. In addition, the surface reflection coefficient is nearly one with a prominent surface ghost.

Case Study: Vibration analysis for the design of a high-speed generator for a turbo-electric hybrid vehicle

1998 ◽  
Vol 212 (4) ◽  
pp. 271-283 ◽  
Author(s):  
C Leontopoulos ◽  
D. A. Robb ◽  
C. B. Besant
Keyword(s):  
Power Output ◽  
High Speed ◽  
Test Procedure ◽  
Volume Ratio ◽  
Hybrid Vehicle ◽  
Modal Testing ◽  
Diesel Generator ◽  
Element Analysis ◽  
Turbo Generator ◽  
Adequate Understanding

The project relates to the design and development of a prototype high-speed turbo-generator as the thermal engine in a series hybrid vehicle. The substantial benefit of the turbo-generator against a diesel generator lies in the very high power-weight, power-volume ratio and renders itself particularly attractive for use in hybrid vehicle applications. However, to achieve a 50 kW power output, the turbo-generator has to have an operating speed of 60 000 r/min and thus important mechanical problems have to be solved. The core of this study addresses the requirement for an adequate understanding of rotor-dynamic behaviour by combining the results from both analytical and practical techniques. The assessment of modal testing, finite element analysis and vibration-condition monitoring, their feedback within the design-make-and-test procedure and the practical compromises and design constraints are presented and a design methodology is formulated. It is concluded that, under certain conditions, the prototype generator can be directly coupled to a small gas turbine, can operate safely and can produce the required power output.

scholarly journals Experimental Investigation of Dynamic Characteristics of Subsea Sand-Silt Mixtures

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Tugen Feng ◽  
Yu Tang ◽  
Qiyenan Wang ◽  
Jian Zhang ◽  
Jian Song
Keyword(s):  
Cement Content ◽  
Damping Ratio ◽  
Shear Stiffness ◽  
Confining Pressure ◽  
Dynamic Responses ◽  
Resonant Column ◽  
Dynamic Shear ◽  
Column Tests ◽  
Mixture Ratio ◽  
Curing Age

In this paper, extensive resonant column tests were conducted to investigate dynamic responses of subsea sand-silt mixtures. The effects of confining pressure, mixture ratio, curing age, and cement content were evaluated. For the test condition considered in this study, the measured damping ratio is the smallest when the ratio of subsea sand to silt is in a range of 1.5 to 2.0. Moreover, unsolidified subsea sand-silt mixed at a ratio of 1.5 has almost the same maximum shear stiffness as the pure sand. For solidified subsea sand-silt mixture, cement can significantly increase the dynamic shear stiffness when the curing age is less than 14 days. However, the increase of the maximum dynamic shear stiffness is negligible when the curing age is longer than 14 days. When the cement content is 2%, the damping ratio of the solidified mixtures is very close to that of the unsolidified mixture. When the cement content is higher than 4%, the damping ratio of the solidified mixtures reduces significantly. This is mainly due to hydration reactions occurring in the solidified mixtures.

Poroelastic Backus averaging for anisotropic layered fluid‐ and gas‐saturated sediments

Geophysics ◽  
1997 ◽  
Vol 62 (6) ◽  
pp. 1867-1878 ◽  
Author(s):  
Stephan Gelinsky ◽  
Sergei A. Shapiro
Keyword(s):  
Large Scale ◽  
Seismic Waves ◽  
Seismic Anisotropy ◽  
Shear Stiffness ◽  
Effective Medium ◽  
Ray Theory ◽  
Partial Saturation ◽  
Local Flow ◽  
Low Frequencies ◽  
Static Limit

A homogeneous anisotropic effective‐medium model for saturated thinly layered sediments is introduced. It is obtained by averaging over many layers with different poroelastic moduli and different saturating fluids. For a medium consisting of a stack of vertically fractured horizontal layers, this effective medium is orthorhombic. We derive the poroelastic constants that define such media in the long‐wavelength limit as well as the effective large‐scale permeability tensor. The permeability shows strong anisotropy for large porosity fluctuations. We observe pronounced effects that do not exist in purely elastic media. At very low frequencies, seismic waves cause interlayer flow of pore fluid across interfaces from more compliant into stiffer layers. For higher frequencies, the layers behave as if they are sealed, and no fluid flow occurs. The effective‐medium velocities of the quasi‐compressional waves are higher in the no‐flow than in the quasi‐static limit. Both are lower than the high‐frequency, i.e., ray‐theory limit. Partial saturation affects the anisotropy of wave propagation. In the no‐flow limit, gas that is accumulated primarily in the stiffer layers reduces the seismic anisotropy; gas that is trapped mainly in layers with a more compliant frame tends to increase the anisotropy. In the quasi‐static limit, local flow keeps the anisotropy constant independent of partial saturation effects. For dry rock, no‐flow and quasi‐static velocities are the same, and the anisotropy caused by layering is controlled only by fluctuations of the layer shear moduli. If the shear stiffness of all layers is the same and only the compressive stiffness or saturation varies, only the ray‐theory velocity exhibits anisotropy.

Small-strain stiffness of Zenoz kaolin in unsaturated conditions

2012 ◽  
Vol 49 (3) ◽  
pp. 311-322 ◽  
Author(s):  
Mahnoosh Biglari ◽  
Anna d’Onofrio ◽  
Claudio Mancuso ◽  
Mohammad Kazem Jafari ◽  
Ali Shafiee ◽  
...  
Keyword(s):  
Shear Stiffness ◽  
Stress Path ◽  
Small Strain ◽  
Complex Stress ◽  
Resonant Column ◽  
Wetting And Drying ◽  
Isotropic Compression ◽  
Remarkable Effect ◽  
Constant Suction

An experimental study has been carried out to investigate the effects of isotropic compression, wetting, and drying on the initial shear stiffness of Zenoz kaolin, an unsaturated lean clay, both in normally consolidated and overconsolidated conditions. The proposed study was conducted using fixed–free resonant column – torsional shear (RCTS). Specimens were compacted using the undercompaction technique. Initial shear stiffness was measured almost continuously along complex stress paths including (i) an initial equalization stage to a suction value of 0, 50, 150, and 300 kPa; (ii) an isotropic compression stage at constant suction, up to a net stress high enough to move the loading collapse line; (iii) an isotropic unloading stage at constant suction; (iv) a wetting and (or) drying path. The mentioned stress path allowed elimination or determination of the overconsolidation effect on the initial shear stiffness measured. The behavior observed is qualitatively similar to that of saturated soil, while wetting data clearly indicate that G0 depends significantly on volumetric behavior. In normally consolidated samples where wetting is accompanied by collapse, reduction in suction has no remarkable effect on G0. Conversely, in overconsolidated samples G0 reduces significantly as suction decreases.

The Effect of Joint Conditions on the Longitudinal and Flexural Wave Velocities of a Rock Mass

2006 ◽  
Vol 321-323 ◽  
pp. 306-309
Author(s):  
Min Su Cha ◽  
Young Jong Sim ◽  
Gye Chun Cho ◽  
Sung Won Lee
Keyword(s):  
Rock Mass ◽  
Jointed Rock ◽  
Intact Rock ◽  
Flexural Wave ◽  
Resonant Column ◽  
Near Surface ◽  
Wave Velocities ◽  
Jointed Rocks ◽  
Steel Base ◽  
Equivalent Continuum

The behavior of a jointed rock is different from that of an intact rock, and the characteristics of elastic wave propagation in a jointed rock are different from those of an intact rock. In this study, a rock resonant column testing device is designed to measure the longitudinal and flexural wave velocities of jointed rocks under different states of stress. A column of more than 12 rock discs is stacked on a steel base, which acts as a free-fixed system. This configuration ensures that waves propagate under an equivalent continuum condition, thereby rendering a constant and unique velocity. The effect of joint conditions on the wave velocities is investigated through rock resonant column testings. The results show that velocities are sensitive to the state of stress and increase nonlinearly with stress. The velocities are also affected by joint conditions such as roughness, spacing, and filling. The results are useful for rock mass classification based on near-surface geophysical characterization.

scholarly journals Numerical Flow Characterization around a Type 209 Submarine Using OpenFOAM

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 66
Author(s):  
Ruben J. Paredes ◽  
Maria T. Quintuña ◽  
Mijail Arias-Hidalgo ◽  
Raju Datla
Keyword(s):  
Free Surface ◽  
Flow Velocity ◽  
Surface Effect ◽  
Surface Condition ◽  
Flow Characteristics ◽  
Scaled Model ◽  
Local Flow ◽  
Near Surface ◽  
Vortical Structures ◽  
Operational Conditions

The safety of underwater operation depends on the accuracy of its speed logs which depends on the location of its probe and the calibration thoroughness. Thus, probes are placed in areas where the flow of water is smooth, continuous, without high velocity gradients, air bubbles, or vortical structures. In the present work, the flow around two different submarines is numerically described in deep-water and near-surface conditions to identify hull zones where probes could be installed. First, the numerical setup of a multiphase solver supplied with OpenFOAM v7 was verified and validated using the DARPA SUBOFF-5470 submarine at scaled model including the hull and sail configuration at H/D=5.4 and Fr=0.466. Later, the grid sensitivity of the resistance was assessed for the full-scale Type 209/1300 submarine at H/D=0.347 and Fr=0.194. Free-surface effect on resistance and flow characteristics was evaluated by comparing different operational conditions. Results shows that the bow and near free-surface regions should be avoided due to high flow velocity gradient, pressure fluctuations, and large turbulent vortical structures. Moreover, free-surface effect is stronger close to the bow nose. In conclusion, the probe could be installed in the acceleration region where the local flow velocity is 15% higher than the navigation speed at surface condition. A 4% correction factor should be applied to the probe readings to compensate free-surface effect.

Effective bending and shear stiffness of cross-laminated timber by modal testing: Method development and application

2020 ◽  
Vol 198 ◽  
pp. 108225
Author(s):  
Jianhui Zhou ◽  
Ying Hei Chui ◽  
Jan Niederwestberg ◽  
Meng Gong
Keyword(s):  
Method Development ◽  
Shear Stiffness ◽  
Modal Testing ◽  
Cross Laminated Timber ◽  
Testing Method

Small-strain stiffness of compacted silty sand using a proximitor-based suction-controlled resonant column device

2010 ◽  
pp. 683-688
Author(s):  
L Hoyos ◽  
E Suescún ◽  
J Pineda ◽  
A Puppala
Keyword(s):  
Small Strain ◽  
Silty Sand ◽  
Resonant Column ◽  
Small Strain Stiffness ◽  
Resonant Column Device

scholarly journals Incorporating Shear Stiffness into Post-Fire Debris Flow Triggering Models

2021 ◽  
Author(s):  
ROBB MOSS ◽  
Noah Lyman
Keyword(s):  
Debris Flow ◽  
Shear Failure ◽  
Shear Stiffness ◽  
Near Surface ◽  
Rainfall Events ◽  
Fire Debris ◽  
Improved Performance ◽  
Good Coverage ◽  
Type Response ◽  
Liquefaction Analysis

Abstract Current post-fire debris flow triggering models consider predictor variables accounting for; rainfall intensity, rainfall accumulation, area burned, burned intensity, geology, slope, and others. These models represent the physical process of debris flow initiation and subsequent shear failure by quantifying near-surface soil characteristics. By including shear wave velocity as a proxy for sediment shear stiffness, models can better inform the likelihood of particle dislocation, contractive or dilative volume changes, and downslope displacement that results from debris flows. This broadly available variable common to other hazard predictions, such as liquefaction analysis, provides good coverage in the watersheds of interest for debris flow predictions. A logistic regression is used to compare the new variable against currently used variables for predictive post-fire debris flow triggering models. We find that the new variable produces improved performance in prediction of triggering while capturing the physics of sediment failing in a shearing and flow-type response. Additional suggestions are presented for utilizing statistical cross-validation methods to advance prediction performance, and the utility of different variables for quick assessment of likelihood during eminent high intensity rainfall events.

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