Internal Dissipation Research Articles

Full-scale analysis of smart fluid-filled barrier technology: Numerical and experimental study of fixture configurations

Roadside barriers are often deployed to prevent vehicles from colliding with roadside obstacles or hazards and from leaving the road surface. These barriers primarily take the form of guardrails or crash cushions and are designed to absorb energy through severe plastic deformation. Due to the severity of these types of collisions, the energy-absorbing mechanisms can fail resulting in the barrier becoming a hazard. To address this issue, a (US Patented) multi-chambered, smart fluid-filled barrier technology (SFFBT) was proposed as a potential replacement for such roadside barriers. This new patented technology utilizes fluid transport between the internal chambers and viscous dissipation as an additional energy-absorbing mechanism to help reduce the effects the severe deformation imparts on the colliding vehicle and its occupants. Numerical models were developed in ABAQUS dynamic explicit environment, and full-scale experimental testing was conducted at the Midwest Roadside Safety Facility of the University of Nebraska—Lincoln. Three barrier configurations were considered for this study with two different fluid levels resulting in six unique test samples. The three test configurations were (a) free-standing, (b) abutted against a rigid backstop, and (c) anchored. Fluid levels chosen were 25% and 33% filled volume. The results show that the proposed designs and fluid addition provided an increase in energy absorption while decreasing overall deformation stroke by up to 5%. Additionally, kinetic energy reduction increased by 15% with a nearly 140% increase in fluid energy dissipation. The best-performing configurations were the rigid backstop cases, followed by anchored and free-standing configurations. The effects of varying anchoring schemes provide additional performance evaluations for maximizing the energy-absorbing performance of the SFFBT system for use as an impact attenuator.

Radiation and energetics of M2 internal tides in the Okhotsk Sea

Tidal mixing around the Kuril Island Chain (KIC) significantly modulates the transport of Okhotsk Sea Mode Water into the Pacific Ocean and, hence, the formation of North Pacific Intermediate Water. Although previous studies have revealed the dominant role of trapped K1 internal tides in driving mixing, the energetic M2 internal tides that have been observed by altimetry are not sufficiently clarified. In this study, we investigated the generation, radiation, and dissipation of semidiurnal M2 internal tides in the Okhotsk Sea using a high-resolution model. The results showed that KIC is the main generation site for M2 internal tides, with an integrated energy conversion of 2.07 GW. The generated M2 internal tides propagated over a long distance into the Okhotsk Sea and Northern Pacific Ocean and exhibited asymmetry on the two sides of the KIC. In addition, the generation of M2 internal tides on the Kashevarov Bank in the northwestern Okhotsk Sea made a minor contribution. Although the integrated dissipation of the M2 internal tides at KIC was lower than that of the K1 internal tides, the M2 internal tidal energy dissipation rates exceeded 10−8 W/kg near the topography. More importantly, energy dissipation in the far field was dominated by radiating M2 internal tides, which induced higher diapycnal diffusivity than K1 internal tides. These results revealed the important role of M2 internal tides in driving mixing at KIC and surrounding regions, which was previously overlooked.

Analytical and numerical determination of the forming load in the Chain-die forming process

Recently there has been a growing demand for Advanced High-Strength Steel (AHSS) in the automotive sector because it can offer similar strength and crash resistance at a lower mass. However, conventional manufacturing is having trouble processing AHSS, and many technical issues such as substantial residual strains and unpredictable springback arose during the process. Thus, a new forming technique Chain-die forming was developed to address this situation. Past research has shown the advantage of the Chain-die forming method. However, systematic research and more case studies should be done to further explore the feasibility of the Chain-die forming in industrial practice. In this work, two fast estimation of the forming load methods are proposed. The first method estimates the forming load experienced by the forming device by superimposing the duplicated load curve extracted from a two-dimensional stamping simulation. The second method is an analytical model considering the stretching and bending behaviour of the sheet metal during forming. It is established using the internal deformation energy and the geometric relationship of the toolings and forming devices. Furthermore, this analytical model is based on equating the external work to the internal dissipation of the energy to estimate the forming load. The estimated results have been verified with the experimental data and show good agreement. The findings of this study can be implemented in the future development of Chain-die forming to improve the efficiency of the design and optimisation process.

SABIC earns UL Verified for STAMAX™ 30YH570, offers bio-based NORYL, presents new data on low internal dissipation in ELCRES™ dielectric films and sets record with Genbeta racecar

On August 22, SABIC's STAMAX™ 30YH570 resin has earned the UL Verified Mark from Underwriters Laboratories. This 30 percent glass fiber-reinforced copolymer resin, a featured product offered under the company's BLUEHERO™ electrification initiative, reportedly is the first polymer used in electric vehicle (EV) battery systems to receive UL Verification for marketing claims of thermal and mechanical performance. UL Verification, reportedly based on an objective, scientific assessment by a respected third party, should give customers high confidence in the flame delay performance of this product.

Seismic Stability Limit Analysis of Unsaturated Soil Slopes Reinforced by Frame Beam Anchor Plates

The frame beam anchor plate (FBAP) reinforced slope has been popularized and applied in some fill slope projects. Nevertheless, the existing design method ignores the influence of earthquake action and the suction effect of unsaturated soils. The stability of unsaturated soil slopes reinforced with FBAPs under an earthquake is analyzed based on the upper bound theorem of limit analysis and pseudo-dynamic method to solve the above problems. The influence of the suction effect on the effective weight and strength of unsaturated soils under one-dimensional steady seepage conditions was considered in the derivation of the energy balance equation. A simplified method based on the volume integral of the rotating body is used to calculate the external work rate. Two possible failure modes of anchorage structures are considered when solving internal energy dissipation. Results show that the influence of suction and seepage conditions on slope stability decreases with the increasing soil pore size distribution parameter n and saturated hydraulic conductivity ks. Also, the stability of the slopes is significantly improved with the increase of total rows of anchor plates. Likewise, the stability of slopes decreases with the increase in the horizontal seismic coefficient kh and amplification coefficient fa.

The effect of swelling on vocal fold kinematics and dynamics.

Swelling in the vocal folds is caused by the local accumulation of fluid, and has been implicated as a phase in the development of phonotraumatic vocal hyperfunction and related structural pathologies, such as vocal fold nodules. It has been posited that small degrees of swelling may be protective, but large amounts may lead to a vicious cycle wherein the engorged folds lead to conditions that promote further swelling, leading to pathologies. As a first effort to explore the mechanics of vocal fold swelling and its potential role in the etiology of voice disorders, this study employs a finite-element model with swelling confined to the superficial lamina propria, which changes the volume, mass, and stiffness of the cover layer. The impacts of swelling on a number of vocal fold kinematic and damage measures, including von Mises stress, internal viscous dissipation, and collision pressure, are presented. Swelling has small but consistent effects on voice outputs, including a reduction in fundamental frequency with increasing swelling (10Hz at 30% swelling). Average von Mises stress decreases slightly for small degrees of swelling but increases at large magnitudes, consistent with expectations for a vicious cycle. Both viscous dissipation and collision pressure consistently increase with the magnitude of swelling. This first effort at modeling the impact of swelling on vocal fold kinematics, kinetics, and damage measures highlights the complexity with which phonotrauma can influence performance metrics. Further identification and exploration of salient candidate measures of damage and refined studies coupling swelling with local phonotrauma are expected to shed further light on the etiological pathways of phonotraumatic vocal hyperfunction.

Momentum transfer on impact damping by liquid crystalline elastomers

The effect of elastomeric damping pads, softening the collision of hard objects, is investigated comparing the reference silicone elastomer and the polydomain nematic liquid crystalline elastomer, which has a far superior internal dissipation mechanism. We specifically focus not just on the energy dissipation, but also on the momentum conservation and transfer during the collision, because the latter determines the force exerted on the target and/or the impactor—and it is the force that does the damage during the short time of an impact, while the energy might be dissipated on a much longer time scale. To better assess the momentum transfer, we compare the collision with a very heavy object and the collision with a comparable mass, when some of the impact momentum is retained in the target receding away from the collision. We also propose a method to estimate the optimal thickness of an elastomer damping pad for minimising the energy in impactor rebound. It has been found that thicker pads introduce a large elastic rebound and the optimal thickness is therefore the thinnest possible pad that does not suffer from mechanical failure. We find good agreement between our estimate of the minimal thickness of the elastomer before the puncture through occurs and the experimental observations.

Thermal analysis of boundary layer nanofluid flow over the movable plate with internal heat generation, radiation, and viscous dissipation

This study examines the convective flow of a constant, laminar, and incompressible viscous fluid over a plate that moves by the assumption of nanoparticles, such as Al and Cu. In the governing equations, we considered three major effects of heat transfers: radiation, internal heat generation, and viscous dissipation factor. Either we used “similarity transformations” we converted momentum and temperature PDE “Partial Differential Equations” to nonlinear ODE “Ordinary Differential Equations.” Those governing equations were resolved by a new and effective semi-analytic approach named the Akbari-Ganji method (AGM). Comparison of the problem-solving outcomes by the methods used with the outcomes of the previous search exhibits good agreement. When the suction parameter values are increased velocity of the nanofluid is augmented, but temperature reduces with a rising of the suction parameter in both nanofluids. Increasing the λ “slip term of velocity “cause rising values of the velocity term compared with the temperature gradient, which decreases strongly. Also, the temperature and velocity variations are between −0.5 and 1.5.

Seismic Bearing Capacity Solution for Strip Footings in Unsaturated Soils with Modified Pseudo-Dynamic Approach

In engineering mathematics, the unsaturated nature of soil has a significant impact on the seismic bearing capacity solution. However, it has generally been neglected in the published literature to date. Based on the kinematic approach of limit analysis, the present study proposes a method for calculating the bearing capacity of shallow strip footings located in unsaturated soils, taking four common types of soils as examples. The modified pseudo-dynamic (MPD) approach is used to calculate the seismic forces varying with time and space, and the layerwise summation method is used to derive the power generated by the seismic forces. In the calculation of internal energy dissipation, this paper introduces the effective stress based on the suction stress to derive the cohesion expression at different depths. The analytical formula of bearing capacity is obtained by the principle of virtual work, and its value is optimized by the Sequential Quadratic Programming (SQP) algorithm. In order to verify the validity of the proposed method, the present results are compared with the solutions published so far and a good agreement is obtained. Finally, a parametric study is performed to investigate the influence of different types of parameters on the bearing capacity.

Large-scale impacts of small-scale ocean topography

While large-scale seafloor features (e.g. continental slopes, mid-ocean ridges) help shape the broad patterns of ocean circulation, small-scale rough topography (e.g. seamounts, abyssal hills) can also impact the large-scale dynamics in two significant ways. First, they impact the momentum budget through flow steering, flow blocking and drag force, non-local momentum transfer via the generation of radiating internal waves and momentum dissipation by topographically induced turbulence. Second, they impact the density budget. Turbulence induced by flow–topography interactions facilitates ocean overturning circulation by upwelling dense, deep waters which form in polar oceans and sink to the abyss. Rough topography and its associated dynamics are of subgrid scale in Earth systems models (ESMs) and need parameterization for the foreseeable future. A parameterization of the intertwined impacts of flow–topography interactions on momentum and density budgets is currently non-existent, although its importance is well established. Radko (J. Fluid Mech., vol. 961, 2023, A24) provides a novel analytical model for representing the impact of rough seafloor on larger-scale flows, spanning slow to fast flow-speed regimes in homogeneous and multilayer models. The proposed ‘closure’ is in remarkable agreement with high-resolution numerical simulations and provides a crucial step forward in parameterizing the impact of rough topography in coarse-resolution ocean models. Extending the model to the full Navier–Stokes equations, linking it to the density budget and considering more realistic ocean topography are three critical future steps towards implementing Radko's theory in operational ESMs.

Analytical Investigation of Surface Temperatures for Different Sized CubeSats at Varying Low Earth Orbits

Abstract Thermal management is a challenging engineering problem for CubeSats due to the limited available volumes restricting the thermal control applications. Therefore, performing thermal modeling and analyses of these small satellites is very crucial for applying proper thermal control measures to maintain safe operating conditions in space. Despite the growing interest in this field, there are still a limited number of studies investigating the thermal behavior of CubeSats. In this paper, surface temperature profiles of 1U, 2U, 3U, 5U, 6U, and 12U sized CubeSats are simulated for varying low earth orbits. The effects of altitudes changing from 400 km to 2000 km and the beta angles changing from 0 to 75 deg are analytically investigated. Not only the coatings with different absorptance and emissivity values but also different amounts of internal heat dissipations are examined to reveal their impact on the thermal balance of satellites. Results demonstrate surface temperatures are highly dependent on those variables. The amount of heat absorbed by satellite panels is affected by the different sizes of CubeSats, different coating properties of panels, and different orbital configurations. The outcomes of this research may be beneficial especially in the early design phase for designing small satellites and selecting proper orbital configurations.

Research on Upper Bound Limit Stability Analysis of Multi-Step High Steep Slope

In order to explore the stability of multi-step high steep slope, this paper considers layer distribution of soil and builds a slope failure mechanism which meets requirements of velocity separation based on plastic mechanics principles, then derives the calculation method of external force power and internal energy dissipation power in failure area using numerical analysis theory, and proposes a loop algorithm for slope stability analysis combining upper bound limit analysis theorem and strength reduction principle. At the same time, in order to enhance the applicability of the upper bound limit analysis method, this paper develops a slope stability calculation system of upper bound limit analysis combined with computer programming technology and evaluates the accuracy of the calculation system through slope engineering practice in open-pit mine. The results show that stability factor by calculation system of upper bound limit analysis is an upper limit solution compared with limit equilibrium method, but the error rate of two methods is less than 5%, which indicates that the slope stability calculation system established in this paper has high accuracy in stability analysis of multi-step high steep slope in the practice of open-pit mine. On the other hand, the most dangerous sliding surface searched by upper bound limit analysis can fully solve velocity problems of multi-step high steep slope failure, so it has stronger reference values in engineering practice.

A New Kinematical Admissible Translational–Rotational Failure Mechanism Coupling with the Complex Variable Method for Stability Analyses of Saturated Shallow Square Tunnels

Tunnels are commonly constructed in water-bearing zones, which necessitates stability analyses of saturated tunnels based on the upper bound of the plastic theory. Previous kinematical approaches have the following drawbacks: (1) using an empirical approach to estimate pore-water pressure distributions; (2) using failure mechanisms that are not rigorously kinematically admissible. To overcome these shortcomings, we proposed a rigorously kinematically admissible translational–rotational failure mechanism for an underwater shallow square tunnel where velocity discontinuity surfaces were derived. Then, the pore-water pressure field surrounding the tunnel under the boundary of constant water pressure is analytically generated based on the complex variable method and imported into the kinematically admissible velocity field. Work rates performed by external forces and the internal dissipation rate are numerically computed to formulate the power balance equation, followed by a mixed optimization algorithm to capture the critical states of the surrounding soils of tunnels. The outcomes of pore-water pressure distributions, safety factors, and failure mechanisms are in tandem with those given by the numerical simulation but show higher computational efficiency than the numerical simulation. In the end, we highlight the advantages of the proposed model over the empirical approach, where soil properties and water table elevation effects are analyzed.

A grounded inerter-based oscillating TMD for suppressing harmonic and random vibrations

Inspired by the lightweight passive vibration control technology, in this work a new anti-vibration device is proposed to significatively improve the protection for stationary mechanical structures subjected to different kinds of vibratory loads. Such a device is herein termed as the grounded inerter-based two-degree-of-freedom tuned mass damper (GI-TDOF-TMD) composed by a grounded inerter and TDOF-TMD with rotational and translational motions, which controls the primary structure's dominant modal shape by using the synergistic dynamic effects of both devices. In order to fairly evaluate the GI-TDOF-TMD's vibration mitigation effectiveness with respect to other devices, the damped and undamped primary structure's nondimensional compliance and mobility transfer functions are firstly computed from a generalized mathematical model that considers four types of random and harmonic excitation inputs which are the following: force general case, base acceleration excitation, base displacement input and inertial force generated by the unbalance in rotary machinery. For harmonically excited mechanical systems, the H∞ performance measure is applied to minimize the maximum resonant peaks of the displacement and velocity dimensionless frequency response functions (FRFs). As the Extended Fixed-Points Technique (EFPT) is analogous to the H∞ criterion, quasi-optimal solutions are firstly computed to perfectly calibrate the FRF's invariant points. After performing this, the evolution of the FRF's control invariant frequencies revealed that GI-TDOF-TMD performs well at low inertance values. Therefore, the GI-TDOF-TMD's maximum control performance is obtained when the inerter's inertial force is the same as that yielded by the TMD's physical mass. In view of such a dynamic behavior, the GI-TDOF-TMD approximately provides 40% and 17% improvements when compared with respect to the classic dynamic vibration absorber (DVA) and TMD-inerter (TMDI), respectively. Then, the GI-TDOF-TMD's power dissipation capability is demonstrated by applying the H2 norm approach to the randomly excited damped mechanical structures. Additionally, it is also revealed through the stochastic energy balance that the GI-TDOF-TMD's internal power dissipation effectiveness is directly reflected on the minimization of the primary structure's kinetic energy. Moreover, for random inputs, the proposed device can broaden the effective operating bandwidth in approximately 45% and 19% when compared to the classic DVA and TMDI, respectively. Therefore, the GI-TDOF-TMD works better than the TMDI in terms of structural displacement and velocity response mitigation, which can be useful in civil engineering applications.

Body Heat Powered Wirelessly Wearable System for Real‐time Physiological and Biochemical Monitoring

AbstractThrough harvesting energy from the environment or human body, self‐power wearable electronics have an opportunity to break through the limitations of battery supply and achieving long‐term continuous operation. Here, a wireless wearable monitoring system driven entirely by body heat is implemented. Based on the principle of maximizing heat utilization, while optimizing internal resistance and heat dissipation, the stretchable TEG improves the power density of previous similar devices from only a few microwatts per square centimeter to tens and makes it possible to continuously drive wireless wearable electronic systems. Furthermore, ceaseless self‐power energy gives wearable electronics unparalleled continuous working ability, which can realize the tracking and monitoring of biochemical and physiological indicators at different time scale. A practical system demonstrates the ability to real‐time monitor heart rate, sweat ingredient and body motion at a high sampling rate. This study marks an important advance of self‐powered wearable electronics for wirelessly real‐time healthy monitoring.

Coarse-grained numerical simulation for compressible fluid–particle two-phase flows

Compressible fluid–particle two-phase flows broadly exist in engineering problems, and the Eulerian–Lagrangian method is a popular branch of simulation studies. Usually, the coarse-grained strategy is adopted to reduce computational costs, and the coarse-grained criterion becomes critical for maintaining accuracy. In this study, a coarse-grained criterion was proposed for simulating compressible particulate two-phase flows by considering similarity invariants and regime transition behaviors. Based on our developed computation framework, in which the particle phase is solved using the discrete element method, a series of benchmark cases, including shock impacting granular column, shock impacting granular layer, and shock impacting granular ring cases, were considered to investigate the validity of the proposed criterion. It was proven that the stiffness coefficient should be scaled to the parcel size to maintain the invariance of the spreading velocity of the particle stress wave and the restitution coefficient should be reduced to help recover the internal energy dissipation inside the parcels. Furthermore, to describe more accurately the regime transition behaviors, which are common phenomena in compressible particulate two-phase flows, an adaptive interpolation operator was introduced to adjust the influencing range of the Lagrangian parcels dynamically.

Study on upper bound limit analysis of horizontal layers slope stability based on optimization method

Slope stability is an important problem in the field of geotechnical engineering. In order to widen the application range of upper bound limit analysis in engineering practice, this paper analyzes layered distribution characteristics of slope soil and establishes horizontal layers slope failure mechanism which satisfies the separation of velocity, then proposes calculation method for external force power and internal energy dissipation power using discrete algorithm. On this basic, this paper prepares cycle flow of slope stability analysis by upper bound limit principle and strength reduction principle, and develops stability analysis system by computer programming technology. Taking typical mine excavation slope as engineering background and calculates stability coefficient corresponding to different slope angles and evaluate analysis results accuracy by combining with limit equilibrium method. The results show that the stability coefficient error rate of two methods is between 3 and 5%, which can satisfy requirements of engineering practice. Moreover, stability coefficient obtained by upper bound limit analysis is an upper limit solution, and calculation errors are easy to eliminate, so it has certain applicability in slope engineering practice.

Crashworthiness Study of a Newly Developed Civil Aircraft Fuselage Section with Auxiliary Fuel Tank Reinforced with Composite Foam

Over the past two decades, aircraft crashworthiness has seen major developments, mainly with modern computing systems and commercial finite element (FE) codes. The structure and the material have been designed to absorb more kinetic energy to ensure enough safety during a controlled crash condition. However, the fuselage section with an onboard auxiliary fuel tank requires special arrangements, since the inclined strut system with an efficient energy absorber is difficult to install under the cabin floor due to the space occupied by the fuel tank. To solve this shortcoming, a PVC composite foam along with an aluminum plate is introduced beneath the fuel tank to improve the crashworthiness metrics of the fuselage. Drop tests for both the conventional design and the proposed model are investigated by adopting the nonlinear explicit dynamics code Ansys Autodyn, with an impact velocity of 9.14 m/s. It was found that the kinetic energy absorption of the original fuselage section can be improved by 3.54% by reinforcing the foam and the plate. Moreover, they contribute to 20% of total internal energy dissipation. Numerical outcomes also suggest that the cabin floor surface experiences a 41% lower maximum stress, in addition to the mitigation of the maximum peak acceleration responses of the cabin floor at different measured locations from 6% to 36%.

A geotechnical seismic isolation system based on marine sand cushion for attenuating ground shock effect: Experimental investigation

In this paper, an experimental study is introduced on the feasibility of applying a geotechnical seismic isolation system based on marine sand cushion (GSI-MSC) to resist explosion-induced ground shocks. The isolation system is characterised by low cost, easy availability, and slippage limitations, and it is particularly suitable in the protection of engineering structures during emergencies. Laboratory experiments on a steel tank structure were performed using a self-developed explosion shock and vibration simulation platform. The attenuation effects of the isolation system on ground motion, superstructural vibration and structural deformation were analysed. The results showed that GSI-MSC can reduce the intensity of ground shock, decrease the amplification effect of structural vibration, and weaken structural deformation. The attenuation effects were significantly enhanced with an increase in sand cushion thickness. The isolation mechanism was revealed from the perspective of spectrum analysis. The decreased lateral stiffness and reduced damping ratio improved the soft layer effect and internal energy dissipation of the sand cushion. This in turn led the GSI-MSC to exhibit a better harmonic attenuation effect over a wider range of high frequencies, beginning at a lower threshold. After isolation, the principal frequency of the ground motion decreased while the amplitude of high-frequency harmonics decreased, resulting in the weakening of the superstructural dynamic response. This indicated that the isolation system has a more stable attenuation effect on the low-period structures.

Linear viscoelastic response of the vertex model with internal and external dissipation: Normal modes analysis

We use the normal mode formalism to study the shear rheology of the vertex model for epithelial tissue mechanics in the overdamped linear response regime. We consider systems with external (e.g., cell-substrate) and internal (e.g., cell-cell) dissipation mechanisms, and derive expressions for stresses on cells due to mechanical and dissipative forces. The semi-analytical method developed here is, however, general and can be directly applied to study the linear response of a broad class of soft matter systems with internal and external dissipation. It involves normal mode decomposition to calculate linear loss and storage moduli of the system. Specifically, displacements along each normal mode produce stresses due to elastic deformation and internal dissipation, which are in force balance with loads due to external dissipation. Each normal mode responds with a characteristic relaxation timescale, and its rheological behavior can be described as a combination of a standard linear solid element due to elastic stresses and a Jeffreys model element due to the internal dissipative stresses. The total response of the system is then fully determined by connecting in parallel all the viscoelastic elements corresponding to individual normal modes. This allows full characterization of the potentially complex linear rheological response of the system at all driving frequencies and identification of collective excitations. We show that internal and external dissipation mechanisms lead to qualitatively different rheological behaviors due to the presence or absence of Jeffreys elements, which is particularly pronounced at high driving frequencies. Our findings, therefore, underscore the importance of microscopic dissipation mechanisms in understanding the rheological behavior of soft materials and tissues, in particular.