Behavior of Magneto-Rheological Fluids Subject to Impact and Shock Loading

Investigations on the design of controllable magneto-rheological (MR) fluid devices have focused heavily on low velocity and frequency applications. The extensive work in this area has led to a good understanding of MR fluid properties at low velocities and frequencies. However, the issues concerning MR fluid behavior in impact and shock applications are relatively unknown. To investigate MR fluid properties in this regime, a drop-tower was developed to subject MR fluid dampers to impulsive loads. The drop-tower design uses a guided drop-mass, which is released from variable heights to achieve different impact energies. The nominal drop-mass is 55 lb and additional weight may be added to reach a maximum of 500 lb. The nominal drop-mass of 55 lb was used throughout this study. Five drop-heights were investigated, 12, 24, 48, 72 and 96 inches, corresponding to impact velocities of 86, 127, 182, 224 and 260 in/s. Two fundamental MR damper configurations were tested, a single-stage, double-ended piston and a two-stage, mono-tube with nitrogen accumulator. Both dampers operate in the valve flow mode and contain MRF-128 TD fluid from Lord Corporation. The results indicate that the two damper configurations exhibit different force-displacement characteristics during impulsive loading. For the single-stage, double-ended damper, the peak force occurs close to the beginning of the impact. Conversely, the two-stage, mono-tube damper does not reach the peak force until after the nitrogen accumulator bottoms out. To verify this behavior, a theoretical model of the accumulator is derived and compared to the experimental data. The results also show that for a given impact velocity, the peak force does not depend on the current supplied to the damper. Since increasing the supply current causes an increase in the apparent yield stress, it was anticipated that the peak force would depend on the supply current as well. This disagreement is hypothesized to be the result of the fluid inertia preventing the fluid from accelerating fast enough to accommodate the rapid piston displacement. Thus, the peak force is primarily attributed to fluid compression, rather than the resistance to flow associated with the fluid passing through the magnetic field. It is important to note that this study is in its early stages and only preliminary conclusions are presented. Follow up publications will include additional results and modeling, and attempt to relate device design and MR fluid properties to dynamic behavior.

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Springs® Design Optimized By Seawater Quality. Laboratory Pilot Tests

10.4043/31184-ms ◽

2021 ◽

Author(s):

Pierre Pedenaud ◽

Marianna Rondon ◽

Nicolas Lesage ◽

Eric Tournis ◽

Riccardo Giolo ◽

...

Keyword(s):

Water Quality ◽

Operating Conditions ◽

Single Stage ◽

Plant Performance ◽

Future Application ◽

Feed Water ◽

Nanofiltration Membranes ◽

Two Stage ◽

Seawater Quality ◽

The Impact

Abstract A new seawater laboratory pilot has been installed in order to evaluate the impact of the seawater quality on the performance of nanofiltration membranes and filters. The test program implemented was designed to produce the data required to optimize the design and operating parameters of a subsea sulfate removal plant, particularly with respect to the technology developed by Total, Saipem and Veolia, co-owners of the development. The equipment qualification plan is approaching completion with the development of subsea barrier-fluidless pumps, all-electric control systems, high-cycling valves operated by electric actuators and subsea water analyzers. This presented pilot laboratory study completes this plan. Nanofiltration membranes are commonly used to remove the sulfates found in seawater before the water is injected into wells. The principal advantages of relocating this equipment from topside to subsea are better reservoir sweep control, a substantial subsea water injection network reduction and savings on space and weight on the topsides deck. The move to subsea offers the opportunity to simplify the process due to improved deep water quality. This was previously demonstrated through a subsea test campaign. This new pilot study provides data both on the performance of a plant operating with different feed water quality and on the success of operating changes to further optimize the plant performance. The pilot has been installed at the Palavas-les-Flots site in France. Raw water collected from the basin was mixed with ultra-filtered water in order to calibrate the feed water quality. The pilot includes a two stage nanofiltration configuration and single stage nanofiltration unit. The two stage configuration was used to produce data for operation across an array of feed water quality and plant operating conditions. The single stage unit was used to produce data on membrane fouling over a long operating duration. Results from these tests and discussion on how this data relates to subsea plant performance shall be presented. This innovative approach enables a wide range of subsea water quality to be simulated and tested against different process configurations of the subsea unit. Indeed, for each industrial subsea application, the raw seawater quality is dependent on both the region and the depth of the seawater inlet. With this experimental data acquisition campaign and understanding of the seawater quality at inlet, the system design can be tailor-made for each future application case.

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One Stage and Two Stage Vibration Isolators as Applied to High Speed Textile Spindles to Achieve Noise Reduction

Journal of Mechanical Design ◽

10.1115/1.3453890 ◽

1978 ◽

Vol 100 (1) ◽

pp. 33-40 ◽

Cited By ~ 1

Author(s):

L. W. Foster

Keyword(s):

Low Noise ◽

Single Stage ◽

Sound Power ◽

Octave Band ◽

Noise Levels ◽

Two Stage ◽

Noise And Vibration ◽

Vibration Isolators ◽

One Stage ◽

The Impact

The operation of ring spinning frames in textile mills can create spinning room noise levels of 90 to 95 dBA. The spindle bobbin mechanisms (generally 300 to 400 per machine) which are operated at spindle speeds of 6,000 to 14,000 rpm are major sources of noise in this type of machinery. The rotating unbalance force in the spindle-bobbin mechanism creates high frequency vibrations in the spindle blade and in the spindle bolster which contains the bearings on which the blade rotates. The vibrations generated by the spindle bobbin mechanism and the bearings are transmitted through the spindle bolster to the rail structure of the spinning frame where they cause sand energy to be radiated. This paper describes the use of two types of elastomeric vibration isolators located between the spindle bolster and the rail to achieve reductions of vibration and noise levels associated with the spindle-bobbin-rail subsystem of spinning frames. The two types of elastomeric isolators employed are: (1) a single-stage isolator where a bonded elastomeric mounting of annular design is placed between the bolster and the rail, and (2) a two-stage isolator which incorporates an annular intermediate mass element between two annular elastomeric sections that provide the interfaces to the spindle and to the rail. The two stage isolator is a novel design for rotating spindle type applications and employs the classical two stage isolator principle to achieve greater attenuation of vibrations. While it has been known for some time that single stage elastomeric isolators provide an effective means of reducing vibrations and noise in textile spinning and twisting machines, recent emphasis on reducing machine noise levels has motivated increased effort to better describe and apply elastomeric isolators. The two-stage isolator concept has been employed in an attempt to achieve higher operating speeds and, therefore, higher productivity while keeping noise levels within acceptable limits. In order to demonstrate the degrees of noise and vibration reductions that can be attained using the two types of isolators in comparison with the non-isolated or hard-mounted spindle, tests were performed using a single oil base type spinning spindle with a full bobbin. The spindle-bobbin mechanism was mounted to a representative rail by the three mounting methods described previously and operated at speeds of 11,000 rpm and 14,000 rpm in a reverberation room. Octave band sound power level measurements and one-tenth octave band sound pressure measurements were made to compare the performance of the mounting methods. These measurements were made using six microphones at different locations and sampling their output signals at a high rate over an extended interval of time. One-tenth octave horizontal and vertical rail acceleration responses were obtained concurrently with the noise responses. These noise and vibration responses are presented and discussed in the paper. The results show that the elastomeric isolators provide significant reductions in rail vibration response levels in the spindle bearing vibration frequency range of 500 to 2000 Hz. The corresponding overall sound power levels for the two operating speeds when using one stage isolators were 8 to 18 dBA below the hard-mounted spindle condition. When using the two-stage isolator, the overall sound power levels for the two operating speeds were 9 and 20 dBA below the hard mounted spindle condition. The results demonstrate the importance of properly designing the mounting to tune the system for low noise responses while minimizing the impact on other operatonal criteria such as spindle static deflection and dynamic motion. A discussion of the isolator design parameter trade-offs is presented along with comments regarding the limitations of the testing and the constraints involved in predicting the noise level reduction to be expected for a whole spinning frame.

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Impact Resistance of Functionally Layered Two-Stage Fibrous Concrete

Fibers ◽

10.3390/fib9120088 ◽

2021 ◽

Vol 9 (12) ◽

pp. 88

Author(s):

Gunasekaran Murali ◽

Nandhu Prasad ◽

Sergey Klyuev ◽

Roman Fediuk ◽

Sallal R. Abid ◽

...

Keyword(s):

Impact Test ◽

Impact Resistance ◽

Injection Technique ◽

Two Stage ◽

Polypropylene Fibres ◽

Drop Mass ◽

Fibrous Concrete ◽

Definition Of ◽

Protective Structures ◽

The Impact

The impact resistance of functionally layered two-stage fibrous concrete (FLTSFC) prepared using the cement grout injection technique was examined in this study. The impact resistance of turtle shells served as the inspiration for the development of FLTSFC. Steel and polypropylene fibres are used in more significant quantities than usual in the outer layers of FLTSFC, resulting in significantly improved impact resistance. An experiment was carried out simultaneously to assess the efficacy of one-layered and two-layered concrete to assess the effectiveness of three-layered FLTSFC. When performing the drop-mass test ACI 544, a modified version of the impact test was suggested to reduce the scattered results. Instead of a solid cylindrical specimen with no notch, a line-notched specimen was used instead. This improvement allows for the pre-definition of a fracture route and the reduction of the scattering of results. The testing criteria used in the experiments were impact numbers associated to first crack and failure, mode of failure, and ductility index. The coefficient of variation of the ACI impact test was lowered due to the proposed change, indicating that the scattering of results was substantially reduced. This research contributes to the idea of developing enhanced, more impact-resistant fibre composites for use in possible protective structures in the future.

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The anaerobic treatment of a ligno-cellulosic substrate offering little natural pH buffering capacity

Water Science & Technology ◽

10.2166/wst.1998.0574 ◽

1998 ◽

Vol 38 (4-5) ◽

pp. 29-35 ◽

Cited By ~ 17

Author(s):

C. J. Banks ◽

P. N. Humphreys

Keyword(s):

Ph Control ◽

Anaerobic Treatment ◽

Buffering Capacity ◽

Single Stage ◽

Stable Operation ◽

Reactor Performance ◽

Two Stage ◽

Ph Buffering ◽

Stage System ◽

The Stability

The stability and operational performance of single stage digestion with and without liquor recycle and two stage digestion were assessed using a mixture of paper and wood as the digestion substrate. Attempts to maintain stable digestion in both single stage reactors were unsuccessful due to the inherently low natural buffering capacity exhibited; this resulted in a rapid souring of the reactor due to unbuffered volatile fatty acid (VFA) accumulation. The use of lime to control pH was unsatisfactory due to interference with the carbonate/bicarbonate equilibrium resulting in wide oscillations in the control parameter. The two stage system overcame the pH stability problems allowing stable operation for a period of 200 days without any requirement for pH control; this was attributed to the rapid flushing of VFA from the first stage reactor into the second stage, where efficient conversion to methane was established. Reactor performance was judged to be satisfactory with the breakdown of 53% of influent volatile solids. It was concluded that the reactor configuration of the two stage system offers the potential for the treatment of cellulosic wastes with a sub-optimal carbon to nitrogen ratio for conventional digestion.

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Robust Inferences from a Before-and-After Study with Multiple Unaffected Control Groups

Journal of Causal Inference ◽

10.1515/jci-2012-0010 ◽

2013 ◽

Vol 1 (2) ◽

pp. 209-234 ◽

Cited By ~ 1

Author(s):

Pengyuan Wang ◽

Mikhail Traskin ◽

Dylan S. Small

Keyword(s):

Sensitivity Analysis ◽

Control Groups ◽

Two Stage ◽

Time Effects ◽

Unaffected Control ◽

Group Time ◽

Before And After ◽

Group Variation ◽

The Impact ◽

Before And After Study

AbstractThe before-and-after study with multiple unaffected control groups is widely applied to study treatment effects. The current methods usually assume that the control groups’ differences between the before and after periods, i.e. the group time effects, follow a normal distribution. However, there is usually no strong a priori evidence for the normality assumption, and there are not enough control groups to check the assumption. We propose to use a flexible skew-t distribution family to model group time effects, and consider a range of plausible skew-t distributions. Based on the skew-t distribution assumption, we propose a robust-t method to guarantee nominal significance level under a wide range of skew-t distributions, and hence make the inference robust to misspecification of the distribution of group time effects. We also propose a two-stage approach, which has lower power compared to the robust-t method, but provides an opportunity to conduct sensitivity analysis. Hence, the overall method of analysis is to use the robust-t method to test for the overall hypothesized range of shapes of group variation; if the test fails to reject, use the two-stage method to conduct a sensitivity analysis to see if there is a subset of group variation parameters for which we can be confident that there is a treatment effect. We apply the proposed methods to two datasets. One dataset is from the Current Population Survey (CPS) to study the impact of the Mariel Boatlift on Miami unemployment rates between 1979 and 1982.The other dataset contains the student enrollment and grade repeating data in West Germany in the 1960s with which we study the impact of the short school year in 1966–1967 on grade repeating rates.

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Numerical assessment on the performance of variable area single- and two-stage ejectors: A comparative study

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

10.1177/09544089211033129 ◽

2021 ◽

pp. 095440892110331

Author(s):

Anil Kumar ◽

Virendra Kumar ◽

PMV Subbarao ◽

Surendra K Yadav ◽

Gaurav Singhal

Keyword(s):

Change Theory ◽

Single Stage ◽

Two Stage ◽

Entrainment Ratio ◽

Ansys Fluent ◽

One Dimensional ◽

Flow Parameters ◽

Constant Rate ◽

Numerical Assessment ◽

The One

The two-stage ejector has been suggested to replace the single-stage ejector geometrical configuration better to utilize the discharge flow’s redundant momentum to induce secondary flow. In this study, the one-dimensional gas dynamic constant rate of momentum change theory has been utilized to model a two-stage ejector along with a single-stage ejector. The proposed theory has been utilized in the computation of geometry and flow parameters of both the ejectors. The commercial computational fluid dynamics tool ANSYS-Fluent 14.0 has been utilized to predict performance and visualize the flow. The performance in terms of entrainment ratio has been compared under on- design and off-design conditions. The result shows that the two-stage ejector configuration has improved (≈57%) entrainment capacity than the single-stage ejector under the on-design condition.

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A Two-Stage Joint Model for Nonlinear Longitudinal Response and a Time-to-Event with Application in Transplantation Studies

Journal of Probability and Statistics ◽

10.1155/2012/194194 ◽

2012 ◽

Vol 2012 ◽

pp. 1-18 ◽

Cited By ~ 6

Author(s):

Magdalena Murawska ◽

Dimitris Rizopoulos ◽

Emmanuel Lesaffre

Keyword(s):

Empirical Bayes ◽

Cox Model ◽

Data Sets ◽

Two Stage ◽

Nonlinear Mixed Effects Model ◽

Resistance Evolution ◽

Longitudinal Response ◽

Longitudinal Measurements ◽

Subject Specific ◽

The Impact

In transplantation studies, often longitudinal measurements are collected for important markers prior to the actual transplantation. Using only the last available measurement as a baseline covariate in a survival model for the time to graft failure discards the whole longitudinal evolution. We propose a two-stage approach to handle this type of data sets using all available information. At the first stage, we summarize the longitudinal information with nonlinear mixed-effects model, and at the second stage, we include the Empirical Bayes estimates of the subject-specific parameters as predictors in the Cox model for the time to allograft failure. To take into account that the estimated subject-specific parameters are included in the model, we use a Monte Carlo approach and sample from the posterior distribution of the random effects given the observed data. Our proposal is exemplified on a study of the impact of renal resistance evolution on the graft survival.

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A Novel Design of Landing Gear Oleo Strut Damper Using MR Fluid for Aircraft and UAV’s

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.225.275 ◽

2012 ◽

Vol 225 ◽

pp. 275-280

Author(s):

Chandra B. Asthana ◽

Rama B. Bhat

Keyword(s):

Shock Absorber ◽

Fluid Viscosity ◽

Simulation Approach ◽

Body Frame ◽

Mr Fluid ◽

Orifice Area ◽

Aerial Vehicle ◽

Impact Kinetic Energy ◽

The Impact ◽

Novel Design

Most landing gears used in aircraft employ very efficient oleo-pneumatic dampers to absorb and dissipate the impact kinetic energy of the aircraft body frame. A single-acting shock absorber is most commonly used in the oleo strut that has a metering pin extending through the orifice, which can vary the orifice area upon compression and extension of the strut. This variation is adjusted by shaping the metering pin so that the strut load is fairly constant under dynamic loading. In this paper, it is proposed to further change the damping coefficient as a function of time in order to achieve a semi-active control of the aircraft vibrations during landing by using Magnetorheological (MR) fluid in the Oleo. With the metering pin designed for a nominal flight condition, further variation in the fluid viscosity would help achieve the optimal performance in off-nominal flight conditions. A simulation approach is employed to show the effect of different profiles for viscosity variation in the MR fluid. The utility of such a damper can be very well exploited to include different criteria such as the landing distance after touchdown. This type of system can be used also in Unmanned Aerial Vehicle (UAV) application where the focus of design may be to accomplish the task without the consideration of passenger comfort.

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