Main Source Of Energy Dissipation Research Articles

Impact of impeller blade count on inlet flow pattern and energy characteristics in a mixed-flow pump

Mixed-flow pumps, which amalgamate centrifugal and axial-flow attributes, play a pivotal role in various sectors due to their high efficiency and versatility. This paper, utilizing numerical simulation and experimental validation, addresses the critical role of impeller blade count in mixed-flow pump performance. It investigates the effect of the number of impeller blades on the energy dissipation mechanism and inlet flow pattern of a mixed-flow pump. The results reveal that dynamic and static interference effects, along with the separation vortex due to flow separation, are the main sources of energy dissipation in the pump. Under part-load and part-overload conditions, the increase in the number of blades contributes to the improvement of the flow pattern and performance but may induce more intense rotating stall effects under part-load conditions. In overload conditions, the increase in the number of blades significantly amplifies the volume of the inlet vortex structure, consequently deteriorating the inlet conditions of the impeller. This study provides valuable insights for the design and optimization of mixed-flow pumps.

On the seismic response of rack structures affected by pinching

The nonlinear static and dynamic behavior of rack structures affected by joint pinching are studied using a simplified single-degree-of-freedom system. Since the joints of steel rack structures play a crucial role in the capacity design methodology, as they are the main source of energy dissipation, their behavior is widely studied in the literature, highlighting their reduced hysteresis loop. However, no systematic study investigates and associates these characteristics with a possible increase in displacement demand. Using a single-degree-of-freedom system focuses attention on the type of cyclic behavior and allows a comparison of linear and nonlinear responses, the latter evaluated using both elastic-plastic and pinching laws. At prescribed ductility, the elastic-plastic and pinching responses can be compared with the prescriptions of Italian and European building codes. This simplified method was also applied to case studies of experimental pushover tests on racks found in the literature. Results showed that neglecting the joint pinching behavior for a rack structure can lead to an underestimation of the displacement demand in the case of the application of the nonlinear static seismic analysis method and hence to the overestimation of the q-factor for the application of linear seismic analysis methods.

Compressive Behavior, Microstructural Properties, and Freeze-Thaw Behavior of Tailing Recycled Aggregate Concrete with Waste Polypropylene Fiber Addition.

To improve the high brittleness of recycled aggregate concrete containing iron ore tailings (TRAC), the feasibility of adding polypropylene fiber (PPF) to TRAC was studied by performing a compression stress–strain curve test, scanning electron microscope characterization, and a freeze–thaw cycle test. The results indicated that PPF had a beneficial impact on reducing the brittleness of TRAC. With the increase in PPF content, the peak strain increased, the elastic modulus decreased, and the peak stress and energy absorption capacity increased at first and then decreased. Furthermore, the microstructure investigation revealed that the interface friction between the PPF, aggregate, and cement matrix was the main source of energy dissipation. When the load acted on the concrete, the stress was dispersed to the fiber monofilaments, thus effectively enhancing the peak stress and peak strain of concrete and suppressing the generation and development of cracks in the concrete. In terms of freeze–thaw resistance, adding a small amount of PPF could reduce the negative effects of the freeze–thaw process on the cement matrix. On the premise of ensuring strength, the waste utilization should be as high as possible. Therefore, it was suggested that the content of PPF in fiber-reinforced tailings recycled aggregate concrete (TRAC-PP) should be 0.6%.

CFD Based Non-Dimensional Characterization of Energy Dissipation Due to Verticle Slosh

We present the CFD based non-dimensional characterization of violent slosh induced energy dissipation due a tank under vertical excitation. Experimentally validated CFD is used for this purpose as an ideally suited and versatile tool. It is thus first demonstrated that a weakly compressible VoF based CFD scheme is capable of computing violent slosh induced energy dissipation with high accuracy. The resulting CFD based energy analysis further informs that the main source of energy dissipation during violent slosh is due liquid impact. Next, a functional relationship characterising slosh induced energy dissipation is formulated in terms of fluid physics based non-dimensional numbers. These comprised contact angle and liquid–gas density ratio as well as Reynolds, Weber and Froude numbers. The Froude number is found the most significant in characterising verticle violent slosh induced energy dissipation (in the absence of significant phase change). The validated CFD is consequently employed to develop scaling laws (curve fits) which quantify energy dissipation as a function of the most important fluid physics non-dimensional numbers. These newly developed scaling laws show for the first time that slosh induced energy dissipation may be expressed as a quadratic function of Froude number and as a linear function of liquid–gas density ratio. Based on the aforementioned it is postulated that violent slosh induced energy dissipation may be expressed as a linear function of tank kinetic energy. The article is concluded by demonstrating the practical use of the novel CFD derived non-dimensional scaling laws to infer slosh induced energy dissipation for ideal experiments (with exact fluid physics similarity to the full scale Aircraft) from (non-ideal) slosh experiments.

Friction-induced traveling wave coupling in tuned bladed-disks

Flutter is a major constraint on modern turbomachines; as the designs move toward more slender, thinner, and loaded blades, they become more prone to experience high cycle fatigue problems. Dry friction, present at the root attachment for cantilever configurations, is one of the main sources of energy dissipation. It saturates the flutter vibration amplitude growth, producing a limit cycle oscillation whose amplitude depends on the balance between the energy injected and dissipated by the system. Both phenomena, flutter and friction, typically produce a small correction of the purely elastic response of the structure. A large number of elastic cycles is required to notice their effect, which appears as a slow modulation of the oscillation amplitude. Furthermore, even longer time scales appear when multiple traveling waves are aerodynamically unstable and exhibit similar growth rates. All these slow scales make the system time integration very stiff and CPU expensive, bringing some doubts about whether the final solutions are properly converged. In order to avoid these uncertainties, a numerical continuation procedure is applied to analyze the solutions that set in, their traveling wave content, their bifurcations and their stability. The system is modeled using an asymptotic reduced order model and the continuation results are validated against direct time integrations. New final states with multiple traveling wave content are found and analyzed. These solutions have not been obtained before for the case of microslip friction at the blade attachment; only solutions consisting of a single traveling wave have been reported in previous works.

Thermoelastic Damping in Fully Clamped Circular Plate Resonators Based on Nonlocal Thermoelasticity

Thermoelastic damping (TED) is the main source of energy dissipation in resonators. The modelling of TED is of great importance for the design of micro-electro-mechanical systems (MEMS) and the improvement of quality factor. Most of the previous TED models are based on classical continuum mechanics and Fourier heat conductive model. However, small-scale effects are widely found for structures at nano and sub-micron level and the classical theories cannot describe their size-dependent behaviors. Based on the nonlocal elasticity theory and the nonlocal heat conductive model, the thermoelastic coupled governing equations of a circular plate with out-of-plane vibration under the influence of nonlocal effect are derived in this paper. The influences of nonlocal thermoelasticity on TED in circular plates are discussed by numerical examples under different boundary conditions, frequencies, thicknesses and modes.

Finite element analysis of the seismic shake‐table response of a rocking podium structure

AbstractRocking podium structures consist of rocking columns supporting a platform to achieve kinematic seismic isolation of the superstructure above. This article presents detailed finite element (FE) analysis modeling and results of the benchmark rocking podium structure that was tested as part of a blind prediction contest organized by the Pacific Earthquake Engineering Research center (PEER) at UC Berkeley, the University of Bristol, and ETH Zurich in 2019. Details of the FE modeling approach, as well as a discussion on key results and findings of this study are outlined herein. It was found that the FE model of the rocking podium structure was not sensitive to the element type, mesh layout or maximum time step, while the choice of contact algorithm influences the stability of the predicted rocking behavior. Modeling of the friction interactions between the rocking interfaces also had a nontrivial influence on the dynamic rocking response as it represented the main source of energy dissipation in the system. Further, instead of assuming an arbitrary value for inherent damping which was deemed to be very low for such a structure, explicit modeling of the frictional dissipation mechanism at the column‐to‐podium interface was preferred in this study.

Numerical investigation of the recent Chenhecun landslide (Gansu, China) using the discrete element method

Loess–mudstone landslides are widely distributed in Northwest China. However, the deformation features and kinematic processes of these landslides are still not well understood. The Chenhecun landslide occurred on June 10, 2016, near Chenhe village, Dongxiang County, China. Based on detailed field surveys, Google Earth images, and borehole investigations, a geological profile of the landslide was constructed. Using the two-dimensional discrete element software MatDEM, this work analyses the deformation behaviours and kinetic characteristics of the landslide. In the dynamic analysis, the landslide failure process, velocity, displacement, heat generation, and energy conversion are taken into account. During the whole simulated landslide process, the sliding mass at the rear and bottom edges exhibits lower mobility than at the front and upper edges. The kinetic energy of the landslide dominates in the acceleration stage, and friction is the main source of energy dissipation during the entirety of the landslide movement. A band-like high-heat zone is formed near the sliding belt, and this zone expands forward with sliding. The gravitational potential energy is mainly converted into heat, kinetic energy, and elastic potential energy. In addition, the simulated geometry and accumulation characteristics from the MatDEM are in good agreement with the topographic features of the landslide. This work could provide an important reference for understanding the motion of similar geological hazards in the area.

Quality factor of circular microdiaphragm with surface effects in contact with liquids

This paper reports an investigation of the influences of surface effects and residual stress on the quality factor of a circular microdiaphragm in contact with liquids on one side. Acoustic radiation, as the main source of energy dissipation, can decrease the quality factor of a circular microdiaphragm. An approximate solution for the natural frequency can be obtained based on the Rayleigh–Ritz energy method. The results show that the influence of surface effects on the quality factor is obvious, in particular for thinner microdiaphragms. A stiffened surface decreases the quality factor, while a softened surface increases it. Furthermore, the quality factor increases with increases in the normalized tension parameter k for both stiffened and softened surfaces. If k is greater than 30, the influence of the surface effects on the quality factor must be considered. The results can provide effective guidance for the determination of dimensions and selection of material parameters in designing microdiaphragm resonant sensors.

Highly toughened PA6 using residue of plasticized PVB film via two-step reactive melt blending

For sustainable development and environmental protection, residue of plasticized poly(vinyl butyral) film (r-PVB) was reactive mixed with maleated poly(ethylene-1-octene) (POE-g-MA) to obtain masterbatch in a torque rheometer, which was then melt extruded with polyamide 6 (PA6). The existence of POE-g-MA could efficiently modulate the phase morphology and performance of incompatible PA6/r-PVB blends due to its reactivity with PA6 and r-PVB. Moreover, increasing the POE-g-MA content could significantly enhance the interfacial adhesion among the components and was a favor to the formation of “multicore” structure (POE-g-MA encapsulated by r-PVB) in the ternary blends, which were two key issues to obtain high impact toughness. In particular, the maximum impact strength of the obtained super-toughened PA6 blends was about 137.5 kJ/m2, 24 times higher than that of neat PA6. The appearance of massive shear yielding strips in matrix and large deformation of the dispersed phase were the main source of energy dissipation under the impact loading. This work provides a feasible, low-cost but very effective strategy to fabricate super-toughened PA materials.

Mechanical modelling of exposed column base plate joints under cyclic loads

ABSTRACT Dealing with steel Moment Resisting Frames (MRFs) the current European seismic design rules suggest, in case of severe earthquakes, to enforce the formation of plastic zones in members or joints. When joints are the main source of energy dissipation, a thorough knowledge of their inelastic behaviour is needed. This is the reason why, in past years, many efforts have been devoted to the study of the static and seismic response of connections. However, as well known, traditionally, the main efforts of the scientific community have been devoted to beam-to-column joints, neglecting the seismic behaviour of column bases which, indeed, count a significantly lower number of experimental and numerical investigations. Within this framework, in this paper, in order to provide a contribution towards a better understanding of the seismic response of base plate joints, the possibility to model their rotational cyclic behaviour by means of the so-called component method is examined. This approach in case of load reversals requires the development of the following steps: i) identification of the main sources of deformability, resistance and energy dissipation; ii) characterization of the single components; iii) model assembly. Therefore, starting from previous studies concerning the monotonic and cyclic behaviour of the single components, a mechanical model able to predict the cyclic response of exposed base plate connections is proposed. The model is validated against cyclic tests on exposed base-plate joints presented in this work or taken from technical literature. The comparisons show a satisfactory accuracy of the developed model.

An Alternative System for Eccentrically Braced Frames Resisting Lateral Loads

Eccentrically braced steel frames are structures used to resist lateral loads as they combine the ductility that is characteristic of moment frames and the stiffness associated with braced frames. Damper devices can be used as the main source of energy dissipation and have become more popular lately for the lateral control of structures. Control devices generally reduce damage by increasing structural safety, serviceability and preventing the building from collapse during vibration. This study focused on improving the performance of the structures with a proposed damping system, which has more advantages than eccentrically braced frames (EBFs). It can accommodate many architectural features and make construction and complementarity in the structures easier. The purpose of this study is to evaluate the performance of the structure with the proposed damping system and its construction in the building.

Nanojunction Effects on Water Flow in Carbon Nanotubes

We report on the results of extensive molecular dynamics simulation of water imbibition in carbon nanotubes (CNTs), connected together by converging or diverging nanojunctions in various configurations. The goal of the study is to understand the effect of the nanojunctions on the interface motion, as well as the differences between what we study and water imbibition in microchannels. While the dynamics of water uptake in the entrance CNT is the same as that of imbibition in straight CNTs, with the main source of energy dissipation being the friction at the entrance, water uptake in the exit CNT is more complex due to significant energy loss in the nanojunctions. We derive an approximate but accurate expression for the pressure drop in the nanojunction. A remarkable difference between dynamic wetting of nano- and microjunctions is that, whereas water absorption time in the latter depends only on the ratios of the radii and of the lengths of the channels, the same is not true about the former, which is shown to be strongly dependent upon the size of each segment of the nanojunction. Interface pinning-depinning also occurs at the convex edges.

New Insights into the Dynamics and Energetics of Phage T4 Injection Machineray using a Continuum Model

Bacteriophage T4, from the family Myoviridae, is one of the most common tailed viruses that infects E.coli. Phage T4 is composed of three major protein structures; 1) a large capsid containing the viral genome, 2) a contractile tail structure connected to the capsid which generates the driving force to pierce the host membrane and conveys DNA from the capsid to the host, and 3) a baseplate equipped with fibers that recognize and bind to the host. The contractile tail consists of a rigid tail tube surrounded by an elastic six-helical-stranded sheath. During injection, the sheath undergoes a large conformational transition from a high-energy extended state to a low-energy contracted state, thereby releasing energy needed for the tail tube to penetrate the host. While the atomic structure of phage T4 is largely known, the dynamics of the injection process is not, including time scale and energetics of injection. To fill that gap, we propose a dynamic model of the entire phage T4 to simulate the dynamics of the injection process. The simulation follows in two stages; first, we employ molecular dynamic (MD) simulations to calculate the elastic stiffness constants and internal friction of the sheath strands. Second, we employ those material properties in a continuum model of the entire virus. The continuum model treats the tail sheath as a six-interacting elastic helical strands that are coupled to a massive cylinder representing the capsid and to a rigid rod representing the tail tube. The resulting model predicts that the driving energy of injection process is about 5500kT, the time scale of sheath contraction is on the order of milliseconds, and the internal friction of sheath strands is a main source of energy dissipation during sheath contraction.

Smart Energy Dissipation

The use of outriggers in tall buildings is a common practice to reduce response under dynamic loading. Viscous dampers have been implemented between the outrigger and the perimeter columns, to reduce vibrations without increasing the stiffness of the structure. This damped outrigger concept has been implemented for reducing vibrations produced by strong winds. However, its behaviour under strong earthquakes has been not yet properly investigated. Strong earthquakes introduce larger amount of energy into the building’s structure, compared to moderate earthquakes or strong winds. In tall buildings, such seismic energy is dissipated by several mechanisms including bending deformation of the core, friction between structural and nonstructural components, and eventually, damage. This research focuses on the capability of tall buildings equipped with damped outriggers to undergo large deformations without damage. In other words, when the ground motion increases due to strong earthquakes, the dampers can be assumed to be the main source of energy dissipation whilst the host structure displays an elastic behaviour. These investigations are based on the assessment of both the energy demands due to large-earthquake induced motion and the energy capacity of the system, i.e. the energy capacity of the main components, namely core, outriggers, perimeter columns and dampers. The objective of this research is to determine if the energy dissipated by hysteresis can be fully replaced by energy dissipated through the action of passive dampers. This research is based on finite element (FE) models developed in Diana-FEA software. These analytical models consider the use of nonlinear settings throughout almost the whole FE model. The numerical investigations on passive damped outriggers are based on master Matlab scripts, which run combined parametric analysis within Diana.

Modeling wave attenuation by salt marshes in Jamaica Bay, New York, using a new rapid wave model

AbstractUsing a new rapid‐computation wave model, improved and validated in the present study, we quantify the value of salt marshes in Jamaica Bay—a highly urbanized estuary located in New York City—as natural buffers against storm waves. We augment the MDO phase‐averaged wave model by incorporating a vegetation‐drag‐induced energy dissipation term into its wave energy balance equation. We adopt an empirical formula from literature to determine the vegetation drag coefficient as a function of environmental conditions. Model evaluation using data from laboratory‐scale experiments show that the improved MDO model accurately captures wave height attenuation due to submerged and emergent vegetation. We apply the validated model to Jamaica Bay to quantify the influence of coastal‐scale salt marshes on storm waves. It is found that the impact of marsh islands is largest for storms with lower flood levels, due to wave breaking on the marsh island substrate. However, the role of the actual marsh plants, Spartina alterniflora, grows larger for storms with higher flood levels, when wave breaking does not occur and the vegetative drag becomes the main source of energy dissipation. For the latter case, seasonality of marsh height is important; at its maximum height in early fall, S. alterniflora causes twice the reduction as when it is at a shorter height in early summer. The model results also indicate that the vegetation drag coefficient varies 1 order of magnitude in the study area, and suggest exercising extra caution in using a constant drag coefficient in coastal wetlands.

Vibration transmission and energy dissipation through the gear-shaft-bearing-housing system subjected to impulse force on gear

Abstract In this work, an eight-degree-of-freedom (DOF) dynamic model of the gear-shaft-bearing-housing system is established and the vertical vibration transmission and energy dissipation characteristics through the multiple transmitting interfaces under the impulse force due to gear fault are studied. The elastic deformations at the interfaces between gear and shaft, inner race and outer race, outer race and housing are formulated by the corresponding contact stiffness. The housing compliance is also included. A half-sine impulse force with two characteristic parameters as amplitude and time duration, which are associated with the defect type and size, is employed to represent the effect of gear fault on the system dynamics. The acceleration responses for different transmitting components as gear, inner race, outer race and housing are calculated for different impulse time duration, different impulse force amplitudes and shaft rotating speeds. The vibration transmission and energy dissipation through the multiple interfaces are characterized by the defined vibration transmission ratio and energy dissipation ratio. Obvious attenuation in acceleration magnitude is observed between the transmitting components from gear to housing. The maximum attenuation occurs at the transmission from inner race to outer race, while the minimum is between the outer race and the housing. The time duration of the impulse force determines the resonance and also the vibration transmission characteristics of the system. The energy dissipation increases nonlinearly with the amplitude of the applied impulse force. Results also suggest that the interface between inner race and outer race, and the interface between gear and shaft dissipated about 60% and 40% of the total energy, are the main sources of energy dissipation in the system. However, the shaft rotating speed has limited effect on the vertical impulse vibration amplitude, vibration transmission and energy dissipation. Experimental validation is performed, which supports the characteristics obtained from numerical results.

Simulating dynamic processes and hypermobility mechanisms of the Wenjiagou rock avalanche triggered by the 2008 Wenchuan earthquake using discrete element modelling

The discrete element method is well suited for simulating the cracks and subsequent large displacements of catastrophic landslides or rock avalanches, and is therefore a useful tool for analysing their complicated dynamic processes and hypermobility mechanisms. In this study, particle flow code was used to investigate the dynamic processes and hypermobility mechanisms of the Wenjiagou rock avalanche triggered by the 2008 Wenchuan earthquake. Characterization of the avalanche dynamics was achieved using a model comprising four stages: failure rupture, projectile motion, granular debris flow, and debris mass accumulation. The results show that collision on the valley floor was the main factor causing the fragmentation of the Wenjiagou rock avalanche. The upper and front edge of the landslide body were the most likely to move over a long distance. The results also show that friction was the main source of energy dissipation during the entirety of the avalanche movement. The high gravitational potential energy of the avalanche was the basis of the high mobility. In addition, because of their effects on energy dissipation, the low basal friction coefficient, favourable block movement, and topographical conditions played key roles in the rapid, long-runout Wenjiagou avalanche process.

Temperature-dependence of wetting properties of carbon nanotubes

We have carried out molecular dynamics simulations to study the spontaneous imbibition of water into a single-wall carbon nanotube (CNT) at various temperatures, ranging from 270 K to 370 K. The simulations indicate that by increasing the temperature, the rate of mass uptake improves as well. Considering the end-loss friction as the main source of energy dissipation and ignoring the inertial effect on the nano-scale transport, we derive a simple expression that relates the CNT’s wettability to the fluid viscosity and the rate of imbibition over the temperature range that we study. Our results also indicate that the increase in the wettability of the CNT, and the reduction in the viscosity of water at higher temperatures cause enhancement of water uptake into the nanotube. They also enable us to estimate the wetting transition temperature for TIP3P model of water in the CNTs.

Cyclic behaviour of beam-to-column joints with cast steel connectors

This paper presents a comprehensive study on steel beam-to-column joints equipped with weld-free cast steel connectors used as replaceable energy-dissipating components. The basic idea was to use the connectors as the main source of deformation and energy dissipation, and to realize rapid repair of the joints by simple replacement of theses connectors after earthquakes. The research commenced with tests on five full scale specimens, including one specimen with conventional welded T-stub connectors and four specimens with the innovative cast steel connectors. The specimens with cast steel connectors were shown to have good energy dissipation capacity with stable and plump hysteretic curves, and the equivalent viscous damping could achieve up to 37.5%. These joints were also shown to meet the classification criteria of semi-rigid joints in terms of stiffness, and the ductility, which was governed by fracture of energy dissipating elements, was found to be satisfactory. The presence of shear tab connection was found to increase the initial stiffness and ultimate strength of the joints, but the energy dissipation was not significantly improved. Importantly, the yielding regions and main source of energy dissipation were limited to the cast steel connectors, while the adjacent structural members remained in the elastic range, indicating minimal repair work in the aftermath of earthquakes. For a further understanding of the proposed joints, finite element models were established, and based on test and numerical observations, preliminary design recommendations, including those on cast steel connector detailing and normal component-based joint design strategies, were finally outlined.