Level Of Energy Dissipation Research Articles

Parametric Identification of Nondegrading Hysteresis in a Laterally and Torsionally Coupled Building Using an Unscented Kalman Filter

AbstractA parametric approach is proposed for identifying the inelastic response of individual elements, which provide resistance against lateral loads in torsionally coupled buildings. Depending on the severity of the ground shaking in each lateral direction and the amount of eccentricity, different lateral load resisting elements (LLREs) will experience different levels of permanent deformation and energy dissipation based on their location and orientation. The proposed method utilizes the well-known Bouc-Wen model for representing the hysteretic response of each LLRE. An unscented Kalman filtering approach is implemented for identifying the Bouc-Wen model parameters, and for direct estimation of the force-displacement loops experienced by each LLRE during damaging seismic events. The simulated response of a single-story building to ground motion is used for demonstrating the utility of the proposed method, which may also be applied to multistory frames in a straightforward fashion, if certain instrumen...

Relationships Between Surface Thermal Gradients and Disc Distortion During Stop-Braking with High Energy Dissipation

This paper focuses on the study of the relationships between brake disc surface temperatures and disc distortion for various high-energy stop-braking conditions. An original thermal metrology method combining an infrared camera and a fibre-optic two-colour pyrometer was used to record the spatial and temporal variation in disc surface temperature during braking. Disc distortion was investigated in situ by means of a high-frequency displacement sensor. In addition, an optical trigger kept track of disc revolutions and enabled the synchronization of the IR camera, two-colour pyrometer and displacement sensor measurements. This experimental set-up was successfully used to determine the surface temperature and investigate thermal localization and waviness distortion during braking. The results were correlated with each other in relation to the level of energy dissipation. It was shown that the highest temperature was reached in the hot spot regions at an early stage of stop-braking. By contrast, the greatest disc distortion appeared much later, during the last stage of stop-braking.

Energy dissipation in the non-propagating surface cracks in steel round bar at torsional vibration

In a result of experimental investigations of steel R2M cylindrical specimens with a surface transverse and slant crack at torsional vibrations it was revealed that the damping characteristic of the specimens is strongly dependent on the crack sizes and stress amplitude. The energy dissipation in the non-propagating transverse crack is caused mainly by the plastic area along the crack front and practically is not related to the friction between the crack faces. The level of energy dissipation in this crack is determined uniquely by the equivalent stress intensity factor.

Effects of loading patterns on seismic behavior of CHS KK-connections under out-of-plane bending

This paper deals with experimental investigations to study the seismic behavior of circular hollow section (CHS) KK-connections used in steel tubular structures. Cyclic out-of-plane bending (OPB) loading patterns were varied in testing two full-scale specimens in order to evaluate their effect on connection behavior. Test results indicated that the strength efficiency of these connections significantly depended on the loading patterns. CHS KK-connections under alternate opening and closing out-of-plane bending (AOCO) developed more satisfactory levels of ductility and energy dissipation than that under alternate clockwise aligned and counter-clockwise aligned out-of-plane bending (ACCO), although the final failure modes for both showed similar fracture initiated from the chord wall. This observation was further verified by the proposed simplified analytical model results. Finite element (FE) analyses were performed to simulate the experimental behavior and facilitate the interpretation of the important test observations. Additionally, it was found that the energy dissipation due to the ductile chord crack propagation could be utilized effectively to some extent for earthquake resistance.

TSUNAMI HAZARDS: FLOW RESISTANCE AND IMPACT MITIGATION BY COASTAL GREEN BELTS

In the aftermath of the Indian Ocean Tsunami, the protection offered by coastal vegetation became evident in many countries affected and the role of coastal green belts in mitigating tsunami impacts has now been clearly recognized. Coastal green belts also attract attention as an environmental friendly and cost effective measure of impact mitigation. In this research, attention was concentrated on expanding the preliminary experimental on the resistance offered by coastal vegetation to tsunami overland flow, to determine the energy dissipation characteristics in detail, and to assess the effectiveness of coastal green belts in tsunami impact mitigation. Detailed experimental studies were conducted in which the vegetation was represented by geometrically similar small scale models. The effectiveness of coastal green belts was assessed by the percentage energy reduction for various forms of vegetation. Reduction levels in the range up to 30 % were obtained in the experiments indicating the possibility of achieving significant levels of energy reduction of tsunami inundation by coastal green belts. The reliance of the level of inundation reduction on the level of energy dissipation was also investigated.

Biologically inspired crack delocalization in a high strain-rate environment

Biological materials possess unique and desirable energy-absorbing mechanisms and structural characteristics worthy of consideration by engineers. For example, high levels of energy dissipation at low strain rates via triggering of crack delocalization combined with interfacial hardening by platelet interlocking are observed in brittle materials such as nacre, the iridescent material in seashells. Such behaviours find no analogy in current engineering materials. The potential to mimic such toughening mechanisms on different length scales now exists, but the question concerning their suitability under dynamic loading conditions and whether these mechanisms retain their energy-absorbing potential is unclear. This paper investigates the kinematic behaviour of an 'engineered' nacre-like structure within a high strain-rate environment. A finite-element (FE) model was developed which incorporates the pertinent biological design features. A parametric study was carried out focusing on (i) the use of an overlapping discontinuous tile arrangement for crack delocalization and (ii) application of tile waviness (interfacial hardening) for improved post-damage behaviour. With respect to the material properties, the model allows the permutation and combination of a variety of different material datasets. The advantage of such a discontinuous material shows notable improvements in sustaining high strain-rate deformation relative to an equivalent continuous morphology. In the case of the continuous material, the shockwaves propagating through the material lead to localized failure while complex shockwave patterns are observed in the discontinuous flat tile arrangement, arising from platelet interlocking. The influence of the matrix properties on impact performance is investigated by varying the dominant material parameters. The results indicate a deceleration of the impactor velocity, thus delaying back face nodal displacement. A final series of FE models considered the identification of an optimized configuration as a function of tile waviness and matrix properties. In the combined model, the optimized configuration was capable of stopping the ballistic threat, thus indicating the potential for bioinspired toughened synthetic systems to defeat high strain-rate threats.

Coastal Flooding and Protection from Bio-Shields

In addition to the flooding associated with heavy rainfall, coastal flooding can also be caused by storm surges, tidal waves and tsunamis. The potential of such hazards to cause severe damages in coastal regions and the protection offered by bio shields—coral reefs, coastal sand dunes and vegetation was evident in the aftermath of the Indian Ocean Tsunami in 2004. In this investigation, attention was focussed on the mitigation of tsunami induced flooding by coastal vegetation and results of small scale physical model studies carried out to assess the energy dissipation characteristics of selected forms of vegetation and the reduction in the extent of inundation due to the presence of vegetation are presented. The results indicate significant levels of energy dissipation and reduction in the extent of inundation. A vegetation may be characterized by the type of plants, density (spacing), extent, pattern and location and the relative influence of these characteristics on energy dissipation and reduction of inundation are also presented.

Transiting exoplanets from theCoRoTspace mission

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V = 12.9 mag F6 dwarf star (M∗ = 1.27 ± 0.05 M⊙, R∗ = 1.37 ± 0.03 R⊙, Teff = 6440 ± 120 K), with an orbital period of P = 2.994329 ± 0.000011 days and semi-major axis a = 0.0436 ± 0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (vsini ⋆ = 40 ± 5 km s-1) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of Mp = 2.33 ± 0.34 MJup and radius Rp = 1.43 ± 0.03 RJup, the resulting mean density of CoRoT-11b (ρp = 0.99 ± 0.15 g/cm3) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior.

Shod landing provides enhanced energy dissipation at the knee joint relative to barefoot landing from different heights

Athletic shoes can directly provide shock absorption at the foot due to its cushioning properties, however it remains unclear how these shoes may affect the level of energy dissipation contributed by the knee joint. This study sought to investigate biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. Twelve healthy male recreational athletes were recruited and instructed to perform double-leg landing from 0.3-m and 0.6-m heights in barefoot and shod conditions. The shoe model tested was Brooks Maximus II. Markers were placed on the subjects based on the Plug-in Gait Marker Set. Force-plates and motion-capture system were used to capture ground reaction force (GRF) and kinematics data respectively. 2 × 2-ANOVA (barefoot/shod condition × landing height) was performed to examine differences in knee kinematics, kinetics and energetics between barefoot and shod conditions from different landing heights. Peak GRF was not significantly different (p = 0.732–0.824) between barefoot and shod conditions for both landing heights. Knee range-of-motion, flexion angular velocity, external knee flexion moment, and joint power and work were higher during shod landing (p < 0.001 to p = 0.007), compared to barefoot landing for both landing heights. No significant interactions (p = 0.073–0.933) were found between landing height and barefoot/shod condition for the tested parameters. While the increase in landing height can elevate knee energetics independent of barefoot/shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights.

Kinetic responses of Dunaliella in moving fluids

The objective of this work was to quantify the kinetic behavior of Dunaliella primolecta (D. primolecta) subjected to controlled fluid flow under laboratory conditions. In situ velocities of D. primolecta were quantified by micron-resolution particle image velocimetry and particle tracking velocimetry. Experiments were performed under a range of velocity gradients and corresponding energy dissipation levels at microscopic scales similar to the energy dissipation levels of natural aquatic ecosystems. An average swimming velocity of D. primolecta in a stagnant fluid was 41 microm/s without a preferential flow direction. In a moving fluid, the sample population velocities of D. primolecta follow a log-normal distribution. The variability of sample population velocities was maximal at the highest fluid flow velocity in the channel. Local fluid velocity gradients inhibited the accrual of D. primolecta by twofold 5 days after the initiation of the experiment in comparison to the non-moving fluid control experiment.

Dehydration rate and time of desiccation affect recovery of the lichenic algae Trebouxia erici: alternative and classical protective mechanisms

The mechanisms involved in desiccation tolerance of lichens and their photobionts are still poorly understood. To better understand these mechanisms we have studied dehydration rate and desiccation time in Trebouxia, the most abundant chlorophytic photobiont in lichen. Our findings indicate that the drying rate has a profound effect on the recovery of photosynthetic activity of algae after rehydration, greater than the effects of desiccation duration. The basal fluorescence (F'(o)) values in desiccated algae were significantly higher after rapid dehydration, than after slow dehydration, suggesting higher levels of light energy dissipation in slow-dried algae. Higher values of PSII electron transport were recovered after rehydration of slow-dried Trebouxia erici compared to rapid-dried algae. The main component of non-photochemical quenching after slow dehydration was energy dependent (q (E)), whereas after fast dehydration it was photoinhibition (q (I)). Although q (E) seems to play a role during desiccation recovery, no significant variations were detected in the xanthophyll cycle components. Desiccation did not affect PSI functionality. Classical antioxidant activities like superoxide dismutase or peroxidase decreased during desiccation and early recovery. Dehydrins were detected in the lichen-forming algae T. erici and were constitutively expressed. There is probably a minimal period required to develop strategies which will facilitate transition to the desiccated state in this algae. In this process, the xanthophyll cycle and classical antioxidant mechanisms play a very limited role, if any. However, our results indicate that there is an alternative mechanism of light energy dissipation during desiccation, where activation is dependent on a sufficiently slow dehydration rate.

Probability-based optimal design of friction-based seismic isolation devices

In earthquake engineering the design of seismic isolation devices plays an important role to ensure structural safety and integrity. Such devices on one hand must allow for a sufficiently high level of structural decoupling and energy dissipation in order to reduce structural damage, and on the other hand must provide enough stiffness in order to prevent excessive deformations or residual offsets. This leads to trade-off considerations which can be dealt with through an optimization process. In the present paper, the earthquake excitation is treated as a non-stationary random process. Therefore, the design of the isolation device is based on a suitable probabilistic characterization of the dynamic response, i.e. the first-passage probability of critical response levels. The required first-passage probabilities are computed using a novel efficient Monte Carlo based simulation technique called asymptotic sampling. The design space is covered by using a design of experiment based on Latin Hypercube sampling. Due to the inherent statistical error of Monte-Carlo based analysis it is useful to apply a response surface technique (smoothing) based on the Moving Least Squares method. The design optimization involves conflicting objectives which can be resolved by applying a Pareto-type optimization approach. The main contribution of this paper lies in the connection of high-dimensional Monte-Carlo-based reliability analysis with multi-objective design optimization using a response surface approach and its application to an earthquake engineering problem.

Background to seismic design provisions in CSA A23.3–04 for high-strength concrete

This paper presents the background experimental and analytical research that was carried out to develop the provisions for the seismic design of high-strength concrete structures in the 2004 Canadian standard CSA A23.3–04. It is noted that the 1994 Canadian standard CSA A23.3–94 limited the concrete compressive strength to 55 MPa for the seismic design of nominally ductile and ductile structures, while the 1995 New Zealand Standard limited the concrete compressive strength to 70 MPa. In contrast, the 2008 American Concrete Institute (ACI) code ACI 318M has no upper limit on concrete strength, even for the seismic design of ductile structural elements. This tremendous variation in these limits indicated that more experimental evidence was needed. This paper presents experimental results of reversed cyclic loading tests on large-scale structural components as well as simulated seismic loading tests of a frame structure constructed with high-strength concrete. The goal of this collaborative research program at the University of Sherbrooke and McGill University was to determine the seismic design and detailing requirements for high-strength concrete structures to achieve the desired level of ductility and energy dissipation. The experimental programs include full-scale testing of the following: columns subjected to a pure axial load (square and circular columns); columns subjected to flexure and axial loads; beam-column subassemblages (square and circular columns); coupling beams in coupled wall structures; shear walls and a two-storey, three-dimensional frame structure. The results of the responses of the high-strength concrete structural specimens are compared with the responses of companion specimens constructed with normal-strength concrete.

Effect of patterned nanoscale interfacial roughness on interfacial toughness: A finite element analysis

A finite element analysis was used to determine how patterned, nanoscale interfacial roughness could potentially increase the apparent interfacial toughness of brittle, thin-film material systems. The pattern analyzed was composed of parallel channels with either a rectangular-toothed or a rippled cross-section. Results are presented for a thin, linear elastic, bimaterial strip loaded by displacing the top edge relative to the bottom edge. The finite element calculations indicate that the interface does not unzip in a steady, continuous manner. Instead, the crack tip stalls as it tries to kink in a direction that is offset from its original path. The apparent interfacial toughness is found to depend on the intrinsic interfacial toughness, the ratio of real-to-nominal interfacial area, the extent of ligament, tooth-tip damage that occurs before crack propagation, strain energy locked in by persistent contact, and the level of energy dissipation associated with dynamic fracture.

Mechanical Energy Dissipation and Performance in Alpine Ski Racing

Supej et al. (2005) introduced a method of computing an alpine skier's instantaneous mechanical energy losses to his surroundings as a measure of turn quality. This energy dissipation represents the difference between the change in skier potential energy (EPOT) and the corresponding change in kinetic energy (EKIN). The turning phase of a turn cycle is associated with high levels of energy dissipation. It is thought that one factor differentiating fast and slow skiers may be the pattern of energy loss over a turn cycle. PURPOSE: To determine if fast and slow skiers differ with respect to the distribution of energy dissipation over the turn cycle. METHODS: Six members of the Norwegian men's Europa Cup team were analyzed while skiing through 2 complete turns during a slalom race simulation. Skier 3-D positions were determined using a DLT-based method with 4 panning cameras and calibration control points distributed near the course (Nachbauer et al., 1996). Skier EKIN and EPOT were determined knowing the center of mass velocity and altitude. Energy dissipation was then calculated for each 10% increment in the turn cycle knowing the changes in EKIN and EPOT (Energy dissipation = −(ΔEPOT + ΔEKIN)/m), where m is the skier's body mass. Based on performance time, skiers were divided into two groups, the 3 fastest (FAST) and 3 slowest (SLOW). The average energy dissipation for each 10% turn increment for each group was calculated. RESULTS: The group differences in energy dissipation for each increment varied systematically throughout the turn cycle. The greatest differences were found early in the turn, where FAST skiers had 0.84 J/kg greater dissipation (p=.507), and the later part of the turn phase, where SLOW skiers had 1.24 J/kg greater dissipation (p=.053). The shift of distributions of energy dissipation from early for fast skiers to later for slow skiers was apparent across multiple increments in time, however none were statistically different due to low power associated with the small sample size of elite skiers. CONCLUSIONS: Faster skiers tend to dissipate energy earlier, and slower skiers later in the slalom turn cycle. Although these differences are not statistically significant, they may be practically significant.

Characterization of two friction interfaces for use in seismic damper applications

This paper describes an experimental research program on the friction interface characteristics for a new type of friction damper for use in seismic building applications. Two friction interface types (leaded-bronze against stainless steel and leaded-bronze against alloy cast steel) are subjected to a series of triangular and sinusoidal displacement loading waveforms. The test parameters include the loading frequency, displacement amplitude, number of cycles, and normal force applied on the friction interface. The experiments show that the dampers can provide predictable and consistent levels of energy dissipation that is largely independent of excitation displacement, frequency, and velocity for the ranges expected to occur during an earthquake. The results are used to determine the coefficient of friction for the dampers and to verify an analytical model for friction-damped precast concrete frame buildings.

Seismic Design of Friction-Damped Precast Concrete Frame Structures

This paper presents the seismic design of unbonded posttensioned precast concrete frame structures that use friction dampers for supplemental energy dissipation. A procedure is described to determine the friction damper slip forces and posttensioning steel areas needed to satisfy prescribed design lateral strength and energy dissipation requirements for a trial frame with given geometry, beam and column member dimensions, and selected damper distribution. The proposed design procedure assumes that the lateral strength requirements for the frame have been obtained from a linear elastic analysis of the structure under equivalent lateral forces. Nonlinear reversed-cyclic analyses of friction-damped precast concrete beam-column subassemblies and multistory frame structures under lateral loads are conducted to critically evaluate the design procedure and to identify areas where improvement may be needed. The analytical results show that friction-damped precast frames can be designed to achieve significant energy dissipation levels while maintaining a large level of self-centering capability due to the posttensioning force.

Dynamic analysis of slip damping in clamped layered beams with non-uniform pressure distribution at the interface

Slip damping is a mechanism exploited for dissipating noise and vibration energy in aerodynamic and machine structures. Such slip in layered structures can be simulated by applying pressure to hold the members together at the interface. However, while most analyses of the mechanism assume an environment of uniform pressure at the interface, experiments to date have confirmed that this is rarely the case. There have been recent attempts to relax the restriction of uniform interface pressure to allow for more realistic pressure profiles that are encountered in practice. However, such works have mostly been limited to static loading for which it has been established that the interfacial pressure gradient does play a dominant role in modulating the level of energy dissipation. This paper is an attempt to extend such analyses to account for cases of realistic dynamic loading that drive such structural vibration in the first instance. In particular, it is shown that under dynamic loads, frequency variation more than non-uniformity in the interface pressure can have significant effect on both the energy dissipation and the logarithmic damping decrement associated with the mechanism of slip damping in such layered structures.

Steel beam–column connection using copper-based shape memory alloy dampers

This study presents the details of an experimental investigation on a prototype partially restrained connection using copper-based shape memory alloy (SMA) bars. The proposed configuration consists of an end-plate connection between a rectangular hollow structural steel beam and a wide flange steel column, where four CuAlBe ( ϕ = 3 mm ) bars, in austenitic phase, are used to prestress the end-plate to the column flange. A physical model of the connection was tested by applying a controlled cyclic displacement history at the tip of the beam with two different characteristic frequencies of 0.25 and 1 Hz. Potentiometers and load cells were used to measure strains and stresses in the bars and the displacement and load applied at the beam tip. Similar bars, with the same thermal treatment, had been previously tested in cyclic tension at several nominal strains and frequencies, showing superelastic behavior for deformations up to 2.3% strain. In static tensile tests, the fracture strain was approximately 8%, with a transgranular fracture mechanism. The equivalent damping ratio for the single bar test increases for larger strains, being 6% for a 2.3% strain. The beam–column connection also exhibited superelastic behavior, a moderate level of energy dissipation, and no strength degradation after being subjected to several cycles up to 3% drift. Finally, a set of numerical simulations are conducted to compare the performance of a rigid steel frame and a partially restrained frame with SMA connections using a three-story benchmark structure.

Energy dissipation estimates in oscillating grid setup: LDV and PIV measurements

The dissipation of turbulent kinetic energy has been increasingly used as a scaling parameter to integrate microbiological accrual and metabolic rates with fluid-flow motion in natural and engineered aquatic ecosystems. The estimation of turbulent kinetic energy under field conditions and the generation of energy dissi- pation rates under controlled laboratory conditions with microbiological organisms are necessities required to integrate environmental/ecological laboratory protocols with a moving fluid in the environment. Turbulent fluid-flow conditions were gen- erated in an oscillating grid setup, and turbulence variables were quantified using laser-Doppler velocimetry (LDV) and particle image velocimetry (PIV) measuring techniques. The rate of dissipation of the turbulent kinetic energy in the setup ranged from 10 −9 to 10 −4 m 2 /s 3 and was similar to the levels of energy dissipation commonly