Large Static Loads Research Articles

A Shoulder Injury Criterion for the EuroSID-2re Applicable in a Large Loading Condition Spectrum of the Military Domain.

The EuroSID-2re (ES-2re) is an Anthropometric Test Device (ATD) from the automotive domain designed for lateral impact. Since the 2000's, it has also been used by NATO armies to assess the risk of injury to armored vehicles occupants submitted to an Improvised Explosive Device (IED) attack. The resulting loading conditions from an explosion can vary a lot in term of impact velocity and duration. They range from high velocity impacts (~28 m/s), characterized by a short duration (~10 ms) corresponding to cases where the panel deforms under an explosion, to low velocity impacts (~4 m/s), ch aracterized by a long duration (~50 ms) similar to the automotive domain. The goal of the study is to develop a shoulder injury criterion for the EuroSID- 2re that is relevant over the whole loading conditions spectrum of the military domain. For that purpose, thirty-three laboratory ES-2re tests are conducted to replicate four PMHS shoulder impactor test series from the literature. Each test series corresponds to a different loading condition in term of impact velocity and duration: [28 m/s, 3 ms], [14 m/s, 9 ms], [7 m/s, 30 ms], [4 m/s, 50 ms]. The injury result (AIS 2015 scale) of each PMHS test is paired with the shoulder sensor force response signal of the corresponding ES-2re test, resulting in a sample of 75 paired-data. The proposed injury criterion resulting from the sample analysis is the straightened peak force Fs, which is an estimate of the peak of the external force applied to the shoulder. This criterion combines two metrics from the response signal of the shoulder force sensor Y-axis of the ES-2re ATD: the initial slope (S) and the peak (Fmax). The threshold value for a given injury risk depends on the duration of the impact: it is higher for the shorter duration. Thus, a third metric should be extracted from the ES-2re shoulder load cell: the duration of the force T. The present study proposes three force-duration threshold curves Fs=f(T) for low, medium, and high risks of shoulder AI2+ injury.

Key Stratum Structure and Support Working Resistance of Longwall Face with Large Mining Height in the Shallow Coal Seams, China

The fully mechanized mining with large mining height is the main method for high yield and efficient coal mining in China. The key stratum structure (KSS) is the basis of revealing the mechanism of roof weighting and determination of support working resistance of the longwall face with large mining height (LFLMH) in the shallow coal seam. The height of the caving zone at LFLMH is large, the thick immediate roof forms the “short cantilever beam” structure commonly, and the hinge layer of the overlying key stratum will move upward to the higher position. The “high position oblique step voussoir beam” structure of single‐key stratum (SKS) and “oblique step voussoir beam and voussoir beam” structure of double‐key stratum (DKS) in the shallow coal seam were proposed with physical simulation and Universal Distinct Element Code (UDEC). The analysis of the KSS and numerical simulation reveals the mechanism of strong roof weighting at the SKS longwall face and large‐small alternate periodic weighting at the DKS longwall. It is concluded that the large static load caused by the “equivalent immediate roof (EIR)” is the basic load, and the instability load of the KSS is the additional dynamic load of support. Besides, the calculation methods of the reasonable support working resistance at LFLMH were obtained and verified with engineering applications.

A dynamically controllable evaporative cooling system for thermal management of transient heat loads

Evaporation of thin liquid films has the potential to sustain significantly high heat fluxes. This cooling mechanism has been studied extensively to create devices capable of handling large static heat loads for electronic cooling. However, significant and sudden variations in the heat loads can result in the dryout of the thin film, which can jeopardize the performance of the cooling system causing irreversible damage to the electronic component. Hence, a mechanism capable of controlling the performance of evaporative cooling is necessary. This study presents a unique strategy that combines a novel evaporator with a vapor compression cycle, whose performance can be varied to address the transient heat loads. The evaporator is designed to take advantage of simultaneously-occurring multiple modes of heat transfer to dissipate large heat fluxes. This study presents a device and system-level analysis to quantify the effect of different system operating conditions that control the overall cooling performance and efficiency.

Holey graphene modified LiFePO4 hollow microsphere as an efficient binary sulfur host for high-performance lithium-sulfur batteries

Among various kinds of rising electrochemical energy storage systems, lithium-sulfur batteries (LSBs) are considered as one of the most promising candidates because of their high theoretical energy density and low material cost. However, the poor electronic conductivity and “shuttle effect” as well as large volume change during charge and discharge process of sulfur-based cathodes hinder their further practical applications. Here, LiFePO4 (LFP) hollow microspheres are compounded with holey graphene (HG) through an electrostatic attraction strategy coupled with high temperature treatment, and denoted as HG/LFP binary host, in which, LFP microspheres with relatively high redox potential play the key roles for chemically adsorption of soluble lithium polysulfide intermediates (LiPSs) and facilitating the transition process between long-chain LiPSs and short-chain Li2S2/Li2S, and thus effectively suppressing the “shuttle effect” during charge and discharge process. Moreover, the HG component could guarantee a good electronic conductivity and fast mass transport of the sulfur cathode, which further improves the kinetic process for electrochemical reactions. Therefore, HG/LFP/S cathode composite exhibits high specific capacity, outstanding rate performance and cycling stability under large sulfur loading condition (4.3 and 8.4 ​mg ​cm-2), which presents a great potential for practical application in LSBs cathodes.

Influence of pivot design on nonlinear dynamic analysis of vertical and horizontal rotors in tilting pad journal bearings

Abstract The influence of pivot design on nonlinear dynamic characteristics is investigated for vertical and horizontal rotors. Rocker-back pivot and ball-socket pivot designs are studied. A mathematical model is presented considering Hertzian contact theory for pivot stiffness calculation. Differential diameter effects are also discussed. The pivot design effects on the journal orbits, fluid film thickness and pressure are provided and analyzed. It is shown that pivot design can significantly alter the orbit, render an angular shift, and result in a decrease of film thickness and an increase of film pressure. Further, pivot design effects are sensitive to pivot load from both large unbalance and static load. When differential diameter is below 100 μm, its corresponding effects on journal orbits are significant.

Effect of strain rate on transient local strain variations in articular cartilage

The non-homogeneous, anisotropic material properties, and triphasic nature of articular cartilage enables diarthrodial joints to withstand large and complex physiological loading conditions. To develop biomaterials that provide similar functional properties as those found in articular cartilage, it is vital to have knowledge of the strain distributions in cartilage for a large range of loading conditions. Applied stress vs. strain properties of articular cartilage have been measured primarily for static conditions, but the dynamic properties are thought to be more relevant for joint function and cartilage biosynthesis. Furthermore, the dynamic stress-strain properties are expected to vary significantly from those obtained for static, steady-state conditions. Here, we present a method for the determination of axial strain fields throughout the depth of articular cartilage for static loading conditions and dynamic conditions performed at different loading rates. For the conditions tested here, the strain distributions throughout the cartilage depth were more uniform for the dynamic than the static loading conditions, and more uniform for high compared to low strain rates.

DEVELOPMENT OF INNOVATIVE BRAKE SYSTEM FOR ROLLING STOCK

In this paper is shown the importance of introducing innovative products in railway industry, especially when it comes to products from which depends the railway traffic safety, like the brake systems. These brake systems have the essential function of decelerating and stoping of rolling stock. Because the brake systems are a subject of large static and dynamic loads in external conditions, the development of this type of system is a long and complex process. In this paper is shown one part of innovative brake system development by using computer simulation.

The viscoelastic response of soft material: A theoretical and experimental study based on barreling deformation

The viscoelastic properties of polydimethylsiloxane (PDMS) measured are demonstrated by the uniaxial indentation test. Based on the barreling deformation, the viscoelastic models are established and the factors influencing the viscoelastic properties are discussed. These results indicate that the deformation response is greatly associated with load conditions and the PDMS materials exhibited more elastic properties at large load conditions as compared to small load conditions. It was reasonable to use the stress at the middle-section zone to investigate the viscoelastic behavior of the soft materials. The number and type of these elements in viscoelastic models affected the soft materials characteristics. These results would be helpful to further understand the viscoelastic properties and characterization of soft tissues.

Investigating the high frequency fatigue failure mechanisms of mono and multilayer PVD coatings by the cyclic impact tests

Serrated chips are produced at high frequency in the high-speed machining, which often induce a severe failure of the coated cutting tools. In such case, the high frequency fatigue properties of coatings are pivotal. A monolayer TiAlSiN coating and multilayer TiAlN/TiSiN nano-coating were deposited on the ISO P30 cemented carbide substrate. The cyclic impact tests with high frequency were performed with a developed impact tester, which could generate different oscillation amplitudes by using the ultrasonic actuator. The surface response and fatigue fracture of coatings were analyzed by the measurement of dynamic forces and investigation of SEM images. Besides, the sequential load-indentation tests were performed on these two coatings. These tests would be used as baseline reference for comparison purposes with the ones determined under cyclic loading conditions. The fatigue fracture processes of coatings in the high frequency cyclic impact tests were analyzed, and the crack propagation in the cross-sections of coatings were observed by using focused ion beam (FIB) machine to slot cut the impact imprints. It showed that the interfacial delamination of coating/substrate system was more susceptible to the high frequency cyclic impact tests. Furthermore, the multilayer TiAlN/TiSiN nano-coating exhibited higher cyclic impact resistance at low impact loading conditions, but worse cyclic impact resistance at large impact loading conditions compared to the monolayer TiAlSiN coating.

New design for inertial piezoelectric motors

We have designed, implemented, and tested a novel inertial piezoelectric motor (IPM) that is the first IPM to have controllable total friction force, which means that it sticks with large total friction forces and slips with severely reduced total friction forces. This allows the IPM to work with greater robustness and produce a larger output force at a lower threshold voltage while also providing higher rigidity. This is a new IPM design that means that the total friction force can be dramatically reduced or even canceled where necessary by pushing the clamping points at the ends of a piezoelectric tube that contains the sliding shaft inside it in the opposite directions during piezoelectric deformation. Therefore, when the shaft is propelled forward by another exterior piezoelectric tube, the inner piezoelectric tube can deform to reduce the total friction force acting on the shaft instantly and cause more effective stepping movement of the shaft. While our new IPM requires the addition of another piezoelectric tube, which leads to an increase in volume of 120% when compared with traditional IPMs, the average step size has increased by more than 400% and the threshold voltage has decreased by more than 50 V. The improvement in performance is far more significant than the increase in volume. This enhanced performance will allow the proposed IPM to work under large load conditions where a simple and powerful piezoelectric motor is needed.

Numerical Analysis of the Mixture Formation in a Two-Stroke Wall-Guided LPG DI Engine for Extended-Range Electric Vehicle

The use of automotive LPG characteristics which are easy to evaporate vaporization and carry. The paper presents a design of extended-range electric vehicle for wall-guided two stroke LPG engine with direct injection combustion system. Based on the modified vehicle LPG spray model, a database describing the characteristics of vehicle LPG fuel was built and imported into the CFD software. And the accuracy of the model is verified by the Schlieren experimental results. The concentration and velocity field of the mixture in the cylinder under different load conditions are numerically analyzed. The analyzed result indicated that the start injection time θ = 60°–70°CA BTDC under part load condition, the plug electrode near the gathering of a richer mixture is easy to be fired at spark ignition time, the obvious formation of mixture in cylinder is formed and the overall air-fuel ratio is above 40: 1. The start-transition working condition and large load conditions in the piston moves upward before closing the exhaust port to start injection LPG. The optimized LPG injection start time θ ensures that the fresh gas is locked in the cylinder when the exhaust port is closed (63°CA ABDC). In the ignition time of the spark plug, an ideal homogeneous mixture in the cylinder is realized.

A Flow Starvation Model for Tilting Pad Journal Bearings and Evaluation of Frequency Response Functions: A Contribution Toward Understanding the Onset of Low Frequency Shaft Motions

Direct lubrication tilting pad journal bearings (TPJBs) require less oil flow, reduce power consumption, and offer cooler pad temperatures for operation at high surface speeds. Although apparently free of hydrodynamic instability, the literature shows that direct lubrication TPJBs exhibit unexpected shaft vibrations with a broadband low frequency range, albeit small in amplitude. Published industrial practice demonstrates the inlet lubrication type, a reduced supply flow rate causing film starvation, and the bearing discharge conditions (evacuated or end sealed) affect the onset, gravity, and persistency of the subsynchronous vibration (SSV) hash motions. The paper presents a physical model to predict the performance of TPJBs with flow conditions ranging from over flooded to extreme starvation. Lubricant starvation occurs first on an unloaded pad, thus producing a (beneficial) reduction in drag power. As the supplied flowrate decreases further, fluid starvation moves toward the loaded pads and affects the film temperature and power loss, increases the journal eccentricity, and modifies the dynamic force coefficients of each tilting pad and thus the whole bearing. For a point mass rotor supported on a TPJB, the analysis produces eigenvalues and frequency response functions (FRFs) from three physical models for lateral rotor displacements: one with frequency reduced (4 × 4) bearing stiffness (K) and damping (C) coefficients and another with constant K–C–M (inertia) coefficients over a frequency range. The third model keeps the degrees of freedom (DOF) (tilting) of each pad and incorporates the full matrices of force coefficients including fluid inertia. Predictions of rotordynamic performance follow for two TPJBs: one bearing with load between pads (LBP) configuration, and the other with a load on a pad (LOP) configuration. For both examples, under increasingly poor lubricant flow conditions, the damping ratio for the rotor-bearing low frequency (SSV) modes decreases, thus producing an increase in the amplitude of the FRFs. For the LOP bearing, a large static load produces a significant asymmetry in the force coefficients; the rotor bearing has a small stiffness and damping for shaft displacements in the direction orthogonal to the load. A reduction in lubricant flow only exacerbates the phenomenon; starvation reaches the loaded pad to eventually cause the onset of low frequency (SSV) instability. The bearing analyzed showed similar behavior in a test bench. The predictions thus show a direct correlation between lubricant flow starvation and the onset of SSV.

Development of a Multiaction Hybrid Damper for Passive Energy Dissipation

A multiaction hybrid damper (MHD) is designed to have independent hysteretic characteristics under small and large loading conditions, and its control performance for building structures excited by wind or earthquake load is verified. The MHD is composed of steel elements, two friction pads, and two lead rubber bearings (LRBs). Because the friction pads and the LRBs are in series connection, only the LRBs deform before the friction pad slippage occurs. After the friction slippage, the damper deformation concentrates on the friction pads. The initial stiffness and hysteresis are dependent on the properties of the LRB, and the maximum force is determined by the friction pad. Accordingly, the load‐deformation behaviors before/after the friction slippage can be independently designed to show optimal performance for a building structure subject to wind and earthquake loads. The cyclic loading tests of a full scale MHD were conducted to evaluate the multiaction behaviors and energy dissipation capacity of the MHD. The control performance of the MHD damper is analytically investigated by using a 20‐story steel structure subject to wind loads and a 15‐story RC structure excited by earthquake loads. The MHD damper showed good performance for reducing both the linear wind‐induced and nonlinear earthquake‐induced responses.

Closed-Form Solution of Large Deflected Cantilever Beam a gainst Follower Loading Using Complex Analysis

The literature reveals that the non-conservative deflection of an elastic cantilever beam caused by applying follower tip loading was investigated and solved by various numerical methods like: Runge Kutta, iterative shooting, finite element, finite difference, direct iterative and non-iterative numerical methods. This is due to the fact that the Euler–Bernoulli nonlinear differential equation governing the problem contains the “slope at the free end”, this slope however needs special numerical treatment. On the other hand, some of these methods fail to find numerical solutions for extremely large loading conditions. Hence, this paper is aimed to obtain a closed-form solution for solving the large deflection of a cantilever beam opposed to a concentrated point follower load at its free end. This closed-form solution when compared with other conventional numerical approaches is characterized by simplicity, stability and straightforwardness in getting the beam deflection and slopes even for extremely large loading conditions. The closed-form solution is obtained by applying complex analysis along with elliptic-integral approach. Very good results were obtained when the elastica of the beam compared with that of various numerical methods which are used in analyzing similar problem.

Design and installation of subsea cable, pipeline and umbilical crossing interfaces

Abstract Deterioration of subsea cable, pipeline and umbilical crossings often occur due to relative movement between the crossing members. Any crossing design should aim to achieve a sound, fit for purpose solution that will be maintenance free over the crossing life. Due to the increased density of subsea fields, crossing instances need to be increasingly accommodated. Current subsea design codes are not explicit in the criteria for subsea crossings, beyond recommending pipeline separation distances. The work within this paper describes two case studies in the novel use of articulated padding applied to the crossing member, using the crossed pipeline as a support and then using the articulated padding resting on traditional grout-bag supports. The results highlight the ability of the articulated padding to provide the required separation on subsea crossings without the need for extra support design. It is also shown that the articulated padding can be used on grout-bag shoulder supports to allow full subsea crossing separation for crossing lays that will undergo large environmental loading conditions, and hence relative motion. The results presented also provide a basis for the development of future industry standards incorporating articulated padding designs.

Influence of Guide Vane Setting in Pump Mode on Performance Characteristics of a Pump-Turbine

Performance characteristics in pump mode of pump-turbines are vital for the safe and effective operation of pumped storage power plants. They are resultant of Euler head (power input) and hydraulic losses (power dissipation). In this paper, 3-D steady simulations were performed under 13mm, 19mm and 25mm guide vane openings (GVOs). Three groups of operating points under the three GVOs were chosen based on experimental validation to investigate the influence of guide vane setting on flow patterns upstream and downstream. Analysed results show that, the guide vane setting will obviously change the flow pattern downstream, which in turn influences the flow upstream. It shows a strong effect on hydraulic losses in guide and stay vanes. In addition, at the large part load conditions, the change of GVO will increase the relative flow angle at the runner outlet. As a consequence, it decreases the Euler head. However, at other operating conditions, it only has a little influence on Euler head. Flow patterns in pump mode are very dependent on the GVO and discharge.

A large-scale test of reinforced soil railway embankment with soilbag facing under dynamic loading

Geosynthetic reinforced soil retaining walls can be employed as railway embankments to carry large static and dynamic train loads, but very few studies can be found in the literature that investigate their dynamic behavior under simulated wheel loading. A large-scale dynamic test on a reinforced soil railway embankment was therefore carried out. The model embankment was 1.65 meter high and designed to have a soilbag facing. It was reinforced with HDPE geogrid layers at a vertical spacing of 0.3 m and a length of 2 m. The dynamic test consisted of 1.2 million cycles of harmonic dynamic loading with three different load levels and four different exciting frequencies. Before the dynamic loading test, a static test was also carried out to understand the general behavior of the embankment behavior. The study indicated the importance of loading frequency on the dynamic response of reinforced soil railway embankment. It also showed that toe resistance played a significant role in the dynamic behavior of the embankment. Some limitations of the test were also discussed.

반복하중을 받는 수동형 다중거동 복합 감쇠장치의 실험적 구조성능 평가

In this study, a multi-action hybrid damper (MHD) showing independent hysteretic characteristics for small and large loading conditions is presented. The MHD is composed of steel elements, two friction pads, and two lead-rubber bearings. Since the friction pads and the lead-rubber bearings are in series connection, only the lead rubber bearing deforms according to the excitation loads before the friction pad slippage occurs, and after the friction slippage, anymore deformation of the lead-rubber bearing does not occur and energy dissipation and damper deformation concentrates on the friction pad. Initial stiffness and hysteresis for small load such as wind for low-rise building is governed by the lead rubber bearing and yielding or friction load for the larger load such as earthquake is determined by the friction pad. Accordingly, the load-deformation behaviors before/after the friction slippage can be independently designed to show good performance for a building structure subject to wind and earthquake loads. The multi-action behavior and energy dissipation capacity of the MHD were evaluated by conducting the cyclic loading tests using a full scale MHD. The test results indicate that the MHD shows the expected hysteretic behavior and stable energy dissipation performance.

Influence of guide vane setting in pump mode on performance characteristics of a pump-turbine

Performance characteristics in pump mode of pump-turbines are vital for the safe and effective operation of pumped storage power plants. They are resultant of Euler head (power input) and hydraulic losses (power dissipation). In this paper, 3-D steady simulations were performed under 13mm, 19mm and 25mm guide vane openings (GVOs). Three groups of operating points under the three GVOs were chosen based on experimental validation to investigate the influence of guide vane setting on flow patterns upstream and downstream. Analysed results show that, the guide vane setting will obviously change the flow pattern downstream, which in turn influences the flow upstream. It shows a strong effect on hydraulic losses in guide and stay vanes. In addition, at the large part load conditions, the change of GVO will increase the relative flow angle at the runner outlet. As a consequence, it decreases the Euler head. However, at other operating conditions, it only has a little influence on Euler head. Flow patterns in pump mode are very dependent on the GVO and discharge.

The effect of beam inclination on the performance of a passive vibration isolator using buckled beams

Passive vibration isolators are desired to have both high static stiffness to support large static load and low local stiffness to reduce the displacement transmissibility at frequencies greater than resonance. Utilization of a vertical buckled beam as a spring component is one way to realize such a stiffness characteristic since it exhibits a smaller ratio of local stiffness to static stiffness than that of a linear spring. This paper investigates the behaviour of a vibration isolator using inclined beams as well as vertical ones and examines the effect of beam inclination for the purpose of improving the isolation performance. The experimental system investigated has an isolated mass which is supported by a combination of two types of beams: buckled beams and constraining beams. The buckled beams can be inclined from the vertical by attachment devices, and the constraining beams are employed to prevent off-axis motion of the isolated mass. The results demonstrate that the inclination of the buckled beams reduces the resonance frequency and improves the displacement transmissibility at frequencies greater than resonance.