Cushion Systems Research Articles

Evaluating the Use of Predicted Cushion Curves for Comparing the Performance of Some Sustainable Cushion Systems

ABSTRACTThis paper studies the cushion performance of a range of sustainable cushion systems and applies two methods to estimate cushion curves from limited cushion test data. The methods employed were previously developed to allow for (1) the conversion of cushion curves representing a material's performance for a given drop height and sample thickness to alternative (non‐measured) drop heights and sample thicknesses and (2) generating a complete cushion curve for a given thickness and drop height from a single acceleration (shock) measurement. The results include those generated for medium‐density polyethylene (MDP) closed‐cell foam for benchmarking of the materials and to aid in validating the approach. The results indicate that predicting cushion curves from single shock measurements is generally accurate for polymeric materials (MDP closed‐sell foam and HDPE inflated bag) but much less so for organic materials (sugarcane bagasse and perforated cardboard). Finally, all alternative cushioning materials and systems evaluated are shown to only be effective for very low static stresses. This finding demonstrates that much higher volumes are required when using the alternative materials to achieve the same cushioning effectiveness as MPD foam.

Modeling and analysis for landing airbag–lunar soil interaction using a CPU–GPU-based FMBD-DEM computational framework

To investigate the landing performance of airbag cushion systems on the discrete lunar soil, this study proposes a novel modeling approach that couples multi-physics fields, including the flexible multibody systems (FMBS), the granular systems, and the gas effects. In this model, the GPU parallelism technique is utilized to address challenges arising from the large number of particles and complex contact detection involving large deformation and overall motions, and an efficient contact implementation between finite elements and particles is introduced. Additionally, contact modeling between airbags is realized using master–slave techniques. Then, a modified conventional serial staggered procedure is employed to couple flexible multibody dynamics (FMBD) and discrete element method (DEM) modules. Finally, a series of numerical examples is presented to validate the proposed dynamic model. The validated model successfully simulates the interaction between landing airbags and lunar soil. Subsequent parametric analysis contributes to the design optimization of the landing system. Moreover, discussions regarding computational efficiency illustrate that the proposed CPU–GPU-based FMBD-DEM is advantageous in engineering scenarios involving flexible components and large-scale granular systems.

Three Industrial Cases of Sheet Metal Forming Simulations with Elastic Dies

Previous research and experience points to many advantages if sheet metal forming is simulated with elastic dies. Some areas that are enabled by simulations with elastic dies are virtual spotting, improved digital twins, and improved production support. A promising method was selected from the literature, and after important modifications it is deemed to be fast and robust for simulating industrial sized dies. The method consists of meshing die solids with a coarse mesh to represent the structural behaviour of the die. The forming surfaces are then represented by a fine shell mesh connected to the solid mesh by tied contacts with an offset. With additional modifications to reduce solver time this yields a robust and flexible way of modelling sheet metal forming with elastic dies. There is an increase in preprocessing and simulation time compared to using rigid tools, but industrial dies can now be modeled within an hour and solved within a working day. It is also easy to update the model by replacing separate parts such as die solids or forming surfaces. One of the main criteria in favor of the selected approach is the realistic modeling of blankholder and cushion systems. In this paper simulations of three industrial cases are demonstrated: one case of virtual die spotting and two cases of production support. The three cases demonstrate the importance and potential of using elastic dies during virtual die tryout, production support, and for cases like digital twins and production control.

Design and characterization of an OPV-ETFE multi-layer semi-transparent glazing

Architectural glazing has several advantages in terms of aesthetics and user well-being perspectives. However, they can have large impacts on heating and cooling demands and artificial lighting requirements. Ethylene tetrafluoroethylene (ETFE) cushion systems present adequate insulating and transparency characteristics, and, combined with organic photovoltaic (OPV) modules, become a glazing element leading towards energy efficient buildings. The present manuscript reports on a detailed optical, thermal and electrical analysis of a 3-layer ETFE/ OPV cushion that helps the design of these glazing-type systems by providing a better understanding of their performance. Spectrophotometric optical measurements up to 50μm allow proper estimations of an individual layer radiative behavior. As a matter of fact, these measurements feed the radiative and thermal models that aim at determining the behavior of the organic photovoltaic module as a function of its position in the cushion. Based on the organic photovoltaic module spectral response, electrical power production is estimated. Results reveal that the best configuration is the one placing the organic photovoltaic module in the outer layer, since it represents the case where the OPV module performs better due to the higher incident irradiance and the low dependency on temperature of the generated power.

Application of EPS geofoam in rockfall galleries: Insights from large-scale experiments and FDEM simulations

Expanded polystyrene (EPS) geofoam presents a promising application in the protection of galleries against rockfall. This paper focuses on experimental and numerical studies that aim to more effectively characterise the impact kinematics between single-block rockfalls and galleries with homogeneous sand and EPS, as well as the EPS–sand composite cushion system. The compression, tensile, and shear properties of EPS are firstly recognised with mathematical descriptions. Then, large-scale experiments considering the rock block mass and velocity help illustrate the general features of impact processes, and quantify the structural dynamic responses as well as the energy dissipation of the cushioning. Finally, the combined finite and discrete element method (FDEM) is first adopted to simulate the combined failure modes of EPS subjected to impact. The numerical model is well verified and exhibits great predictability in the contribution of different materials in the composite cushion system to energy dissipation. The results demonstrate the effective impact resistance of the EPS-sand cushioning. Additionally, they engender an extended methodology for analysing more EPS-based composite cushion systems applied in rockfall galleries.

Energy Savings Analysis for Operation of Steam Cushion System for Sensible Thermal Energy Storages

The paper presents an analytical discussion of how to improve the energy efficiency of the steam cushion system operation for a Thermal Energy Storage (TES) tank. The EU’s green deal 2050 target policy requires an increase in the energy efficiency of energy production and use, as well as an increase in the share of renewable energy in the overall energy production balance. The use of energy-efficient TES is considered as one of the most important technologies to achieve the objectives of this EU policy. The analyses presented in the paper of energy-efficient operation of steam cushion (SC) systems were carried out by using operational data received from three District Heating Systems (DHSs) that supply heat and electricity to one of the largest cities in Poland and are equipped with the TES systems. These three analyzed TESs differ in capacities from 12,800 to 30,400 m3, tank diameters from 21 to 30 m and shell height from 37 to 48.2 m. The main purpose of using a steam cushion system in the TES tank is to protect the water stored in it against the absorption of oxygen from the surrounding atmospheric air through the surge chamber and safety valves located on the roof of the tank. The technical solutions presented here for the upper orifice for charging and discharging hot water into/from the tank and the suction pipe for circulating water allow to us achieve significant energy savings in the steam cushion systems. Both the upper orifice and the end of suction pipe are movable through the use of pontoons. Thanks to the use of this technical solution, a stable insulating water layer is created above the upper orifice in the upper part of the TES tank, where convective and turbulent transport of heat from the steam cushion space to the hot water stored in the tank is significantly limited. Ultimately, this reduces the heat flux by approximately 90% when compared to the classic technical solutions of steam cushion systems in TES tanks, i.e., for the upper orifice and circulation water pipe. The simplified analysis presented in the paper and comparison of its results with experimental data for heat flow from the steam cushion space to hot water stored in the upper part of the TES tank fully confirms the usefulness of the heat-flow models used.

Motion and Force Control of Servo Die Cushion System using Bilateral Control

Servo die cushion systems perform position control for pre-acceleration function to reduce the impact force between slider and cushion, and force control of the blank holder to avoid fracture and wrinkling. This paper applies bilateral control to perform position and force control with a hybrid switching strategy for smoothly switching between the pre-acceleration and blank holder force control. Implementation on a test rig verifies the proposed method.

Experimental, analytical, and numerical investigation of multi-chambered fluid-filled barrier for highway crash attenuators

Guardrail end terminals and roadside crash cushions are common technologies deployed to absorb and redirect the energy of a colliding vehicle. The purpose of these devices is to reduce damage to structures and vehicles while limiting the effects these collisions have on motorists. The primary mode of energy absorption of these structures is through physical deformation. This physical deformation can often create hazardous scenarios for vehicle occupants. This paper shows the study of a new (patent pending) crash attenuator composed of a multi-chambered, fluid-filled barrier. Kinetic energy of the colliding vehicle is transferred to the fluid and through the internal structure. As fluid moves through the structure, energy is dissipated through viscous friction; therefore, reducing the peak forces experienced by the vehicle and its occupants and reducing damage to the structure and the vehicle. Experiments were conducted using a mechanical ram to impact a dual-chambered cylindrical plastic container partially filled with water. The impact event was recorded using a high-speed camera and the acceleration impulse was measured using an accelerometer attached to the ram. The results of this study show that the addition of interior chambers and fluid decreased the reaction forces by nearly 50% and a two-fold increase in energy absorbing efficiency as compared to an empty structure. Analytical and numerical approaches were used to assess the energy dissipation due to plastic deformation of the structure. The addition of fluid and internal chamber reduced the plastic deformation of the sample by 9.1% as compared to the empty structure. This confirms the ability of the present structure to maintain low reaction forces while reducing damage to the structure and in turn increasing barrier lifetime. The present barrier technology can potentially replace existing guardrail end terminal and crash cushion systems and due to its small footprint, can be utilized in areas where traditional systems cannot be deployed due to space constraints.

A novel steel damping system for rockfall protection galleries

A new steel damping device is proposed to achieve an effective solution for rockfall protection galleries. The system consists of an assembly of cold-formed steel crash boxes, namely Collapsible Tubular Element (CTE), with a transversal section and a length designed to assure, under axial loads, a compressive plastic deformation (folding) without the need of any guide means. Assembled in groups to create a modular cushion, the system reduces the deceleration and the derived impact force due to an impacting block mass during a rockfall event. The influence of both the system module configuration (number of CTEs, presence of restraining cables) and the boulder parameters (mass, angle, and velocity at the impact) is investigated, and a Dynamic Finite Element analyses, along with a full-scale experimental test, have been carried out to evaluate the system performances. The obtained results indicate how the proposed system mitigates the dynamic amplification of the forces transmitted from the impact point to the roof slab, with a mean value of the impact force increased by only 2% within the damping cushion, showing, if compared with the mainly adopted damping cushion systems, a drastic reduction of both impact force and dead load on the gallery's roof. Finally, due to its dimensional stability, the proposed damping device is not affected by compaction over time and by the consequent increase of the impact force.

Application of the Stress-Energy Method to Evaluate Enclosed Air Cushion Systems

Cushion curves are used to ensure cushions used by packaging systems are adequately designed to protect products from shocks experienced during transport. However, no commercially available curves exist for enclosed air cushion systems despite its wide use as a cushioning material. In general, there are two types of enclosed air systems, individual bubble and continuous bubble. This paper summarizes the theory and recent work applying the stress-energy method and different curve fit models to these type systems to generate cushion curves. This paper also compares stress-energy predicted deceleration values to actual ASTM D4168 deceleration values as a method of determining whether the stress-energy method is a viable alternative for generating curves for these cushion systems. Results indicate the stress-energy method can be used to successfully generate cushions curves for enclosed air cushion systems. The following stress-energy equations were produced from this research. The stress-energy equation for the Individual Bubble cushion system was y = 3.0611e 0.435x . The stress-energy equation for the Continuous Bubble cushion system was y = 1.9133e 0.4782x . These equations are designed to predict cushion performance of these cushion systems. Predicted deceleration values were within ± 10% of the actual average deceleration indicating that the model is appropriate for applications where these cushion systems are employed.

Application of the Stress-Energy Method to Evaluate Enclosed Air Cushion Systems

Application of the Stress-Energy Method to Evaluate Enclosed Air Cushion Systems

Beneficiary feedback effects on alpine cushion benefactors become more negative with increasing cover of graminoids and in dry conditions

Summary In facilitative interactions, the beneficiary feedback effect (BFE) has been defined as the effect of beneficiary species (facilitated species) on their benefactor. BFEs have been shown to be dependent on environmental conditions and the composition of the beneficiary community. In alpine cushion systems, BFEs are more negative with more abundant, diverse and phylogenetically aggregated communities of beneficiary species. We tested the hypothesis that the functional composition of the beneficiary communities correlates with the direction and strength of BFE received by alpine cushion benefactors and specifically that a more negative BFE would occur with increasing density of graminoids and a more positive BFE would occur with increasing density of forbs and legumes. Additionally, we predicted that the negative BFE of graminoids would increase with increasing summer aridity. We used a data base of alpine cushion communities from 30 sites throughout the world to assess the overall relationship between the composition of beneficiary communities and the total flower density of cushion benefactors, and its variation with increasing drought. Additionally, in order to assess more precisely the role of the functional composition of the beneficiary communities on BFE in a very dry site with cushion benefactors exhibiting contrasting functional compositions of beneficiary communities, we also designed a field study in the Qilian Shan mountain range (China). At this site with a highly continental climate, we compared the number of flowers and fruits of different phenotypes of the alpine cushion species Thylacospermum caespitosum hosting numerous graminoids, numerous forbs or very few beneficiary species. In the intercontinental study, we found a negative relationship between graminoids and cushion benefactor flower density but no effect of other functional groups. The negative BFE of graminoids increased with increasing summer drought. In the dry Qilian Shan range, we found both a negative effect of graminoids on total flower density and a positive effect of forbs on flower density and fruit set. Our study indicates that the context dependence of BFE may be partially explained by the composition of beneficiary communities and in particular the negative effect of graminoids.

Computer Simulation of Electro-pneumatic Drives for Vertical Motion Mobile Robots

This work is devoted to computer simulation of electro-pneumatic drives for vertical motion mobile robots. These robots are equipped with suction pads to move on walls and ceiling. An output highlights a conflict between the main requirements to such robot drives: simultaneous ensuring of high speed and smoothness of movement of robots with a considerable mass of moved objects. The low efficiency of traditional cushion systems of cylinders is shown in development of such kind of robots. New structure of electro-pneumatic drive for applications with considerable inertia load is developed. This structure represents mechatronic system and consists from the set of on-off valves and computer control device that operates the valves and reaches the optimum motion control of the object with required smoothness. This could be achieved due to the multistep braking in the end of stroke. The paper also represents the mathematical model of developed drive with description of throttle elements, friction forces and details of computer control systems. Mathematical model realized in computer program allows to simulate processes of movement of electro-pneumatic drives.The results of computer modeling show that developed structure and multistep computer control allows to develop effective electro-pneumatic drives for high-quality and high-speed control of massive objects in the part of vertical motion mobile robots. Developed program represents effective analysis instrument, so it can be used in the process of design engineering.

Cost-Benefit Analysis of Crash Cushion Systems

Crash cushions vary in geometry and cost. In this study, crash cushions were categorized in three different categories: redirecting with repair costs greater than $1,000 (RGM), redirecting with repair costs less than $1,000 (RLM), and nonredirecting sacrificial (NRS). Typically, RGM systems are less expensive initially, but life-cycle costs are high. RLM systems typically reciprocate this trend. NRS crash cushions (e.g., sand barrels) are generally less expensive but require total replacement after a crash has occurred, which may be impractical at high-traffic volume locations. Due to limited funding, there is often a need to identify the most cost-effective crash cushion category for highway scenarios with different roadway, traffic, and roadside characteristics. This study was commissioned to determine benefit-cost ratios for each crash cushion category in a wide range of roadway and roadside characteristics using the probability-based encroachment tool, Roadside Safety Analysis Program. Only RGM and RLM systems were cost-effective for freeways and divided rural arterials, but all three categories competed against the unprotected condition on undivided rural arterials and local roads.

Contaminant Trasportation of Cd<sup>2+</sup> in the Cushion System of the Municipal Waste Landfill

The cushion systems with low leakage performance are usually utilized in the municipal solid waste landfills to prevent the contaminants of the leachate from polluting the groundwater and soil beneath the landfill. Even there are the rigorous demands in related specifications in China and other countries all over the world for the design of the cushion system in the landfill. Pollution of the groundwater and the soil beneath the landfill still occurred in a large number of rubbish landfills because of the seepage. To investigate the seepage rate of the Cd2+ in the cushion systems, the minimum requirements for the design of the cushion systems are summarized according to the provisions of China and US. Comparative studies using 1-dimensional migration model are performed to investigate the seepage performance of the cushion systems consisting of geomembrance (GM) and compacted clay layer (CCL) sastifying the related minimum design demands. It could be concluded that the cushion system designed according to the minimum demands of China provide better anti-leakage performance, while that of US perform the lower. Finally, some advices for the releavent design standards are suggested according to the analyses.

Characteristic verification and parameter optimization of airbags cushion system for airborne vehicle

The major methods to investigate the airbags cushion system are experimental method, thermodynamic method and finite element method (FEM). Airbags cushion systems are very complicated and very difficult to be investigated thoroughly by such methods. For experimental method, it is nearly impossible to completely analyze and optimize the cushion characteristics of airbags of airborne vehicle because of charge issue, safety concern and time constraint. Thermodynamic method fails to take the non-linear effects of large airbag deformation and varied contact conditions into consideration. For finite element method, the FE model is usually complicated and the calculation takes tens of hours of CPU time. As a result, the optimization of the design based on a nonlinear model is very difficult by traditional iterative approach method. In this paper, a model based on FEM and control volume method is proposed to simulate landing cushion process of airborne vehicle with airbags cushion system in order to analyze and optimize the parameters in airbags cushion system. At first, the performance of airbags cushion system model is verified experimentally. In airdrop test, accelerometers are fixed in 4 test points distributed over engine mount, top, bottom and side armor plate of hull to obtain acceleration curves with time. The simulation results are obtained under the same conditions of the airdrop test and the simulation results agree very well with the experimental results, which indicate the established model is valid for further optimization. To optimize the parameters of airbags, equivalent response model based on Latin Hypercube DOE and radial basis function is employed instead of the complex finite element model. Then the optimal results based on equivalent response model are obtained using simulated annealing algorithm. After optimization, the maximal acceleration of airborne vehicle landing reduces 19.83%, while the energy absorption by airbags increases 7.85%. The performance of the airbags cushion system thus is largely improved through optimization, which indicates the proposed method has the capability of solving the parameter optimization problem of airbags cushion system for airborne vehicle.

Analysis of cushion systems for impact protection design of bridges against overheight vehicle collision

Based on several theoretical models of elastic and elastic–plastic impact as well as energy method, a systematic methodology for design analysis of cushion structures for impact protection of bridges against overheight vehicle collision is presented with consideration of the shear-off effect of projectiles and the nonlinear crushing behavior of sandwich cores. Three design criteria based on contact force, deflection, and energy are proposed, and the theoretical models for elastic, elastic–plastic, and after-densification impact including the shear-off effect of projectile are developed to improve the analysis and design of cushion structures against overheight vehicle impact. Realistic analysis of cushion structures is resulted from the above models, and it can be applied to design of cushion structures for the sake of bridge protection from overheight vehicle collision.

Centrifuge scaling laws for guided free fall events including rockfalls

Concrete protection galleries are generally used in mountainous regions to protect the local infrastructure and lifelines against potential impacts from rock boulders. These can be protected further by carefully designed cushion systems, most of which rely on granular geomaterials. Rockfall impact energies can reach magnitudes of the order of millions of Joules, requiring understanding of the combined energy absorption mechanisms at high energy levels for improved design of the gallery and cushion. These prototype high-energy ranges can be achieved at the laboratory scale with the help of a geotechnical centrifuge. The model is rotated under high g levels, thereby increasing the unit weight of the material. Prototype energy levels can be represented in a small scale model with consideration of appropriate scaling laws, and although free fall events in a centrifuge experience components of the Coriolis acceleration, projectiles (boulders) will move out of the centripetal gravity field when losing contact with the rotational field. A guiding tube is used in this case to keep the boulder in the acceleration field (ng) in order to achieve sufficient input energy levels to represent existing design criteria. The change in the g-level during the fall of the boulder in the centrifuge, due to the change in the radius, has to be taken into account for determination of the impact energy. In this case, direct application of traditional scaling laws for centrifuge modelling is invalid. This paper focuses on the determination of the change in the g field with time during the fall of the boulder to estimate the g level at the time of impact and this value is used in the calculation of the prototype energy levels. A summary of the performance of various cushion materials is given.

Prediction of Cushion Curves for Closed Cell Polyethylene-Based Foams. Part II: Experimental

In this paper the compressive impact behaviour of a collection of low density polyethylene (LDPE) and polyethylene-co-vinyl acetate (EVA) based foams with different densities, during purely compressive impacts, has been studied. The experimental cushion curves for these materials were compared with several theoretical models. The results have shown that the simplest models, adiabatic and isothermal, are able to fit the experimental data and to predict qualitatively the evolution of the minima in the cushion curves as a function of foam thickness and falling height. In addition, it has been shown that the impact behaviour of closed cell polyethylene based foams deteriorates after compressive creepperiods. This fact should be considered in the design of real cushion systems.

Optimal Programming of Multi-point Cushion Systems for Sheet Metal Forming

Numerical optimization technique coupled with finite element analysis of the stamping/sheet hydroforming process was developed to predict four possible modes for application of blank holder force (BHF) in multiple-point cushion systems, namely a) BHF constant in space/location and time/stroke, b) BHF variable in time/stroke and constant in space/location, c) BHF variable in space/location and constant in time/stroke and d) BHF variable in space/location and time/stroke. The BHF was predicted by (a) minimizing the risk of failure by tearing (thinning) in the formed part and (b) avoiding wrinkling. The developed technique was applied to predict the BHF to form a) an automotive part (liftgate-inner) from AA6111-T4 aluminum alloy, b) an asymmetric part from aluminum alloy AA5083-H32 by sheet hydroforming process with die (SHF-D) and c) a round cup by sheet hydroforming with punch (SHF-P). Experimental results showed that the FEM based optimization methodology can reduce trial and error effort and is able to predict the blank holder force necessary to form the parts without fracture and wrinkling in the investigated stamping and sheet hydroforming operations.