Increase In External Load Research Articles

Dynamic analysis of the suspended composite pipelines conveying pulsating fluid

The problems of oscillations of a viscoelastic pipeline conveying fluid flow are considered in the paper. Mathematical models of these problems are constructed in a one-dimensional statement. The motion of a pipeline completely filled with a flowing fluid is studied. The transverse oscillations of a pipeline interact with the pipe walls, changing the nature of system oscillations. It is assumed that a pulsating fluid flows in the pipeline. Though the effect of flowing fluid on the pipe motion is considered in the paper, the effect of the pipe on fluid flow is not taken into account here. The mathematical model of the problem is described by the systems of partial integro-differential equations (IDE) with corresponding initial and boundary conditions. Partial IDE obtained using the Bubnov-Galerkin method under considered boundary conditions are reduced to solving ordinary IDE systems with constant coefficients relative to time function. The integration of systems of equations obtained on the basis of a polynomial approximation of deflections was carried out numerically. Based on this method, the algorithms are developed for numerically solving one-dimensional problems of oscillation and stability of viscoelastic pipes conveying fluid flow. It was found that an increase in internal pressure parameter leads to a decrease in critical flow rate. It was shown that an increase in the singularity parameter and the rigidity parameter of continuous layer of a base leads to an increase in critical flow rate. It was revealed that an increase in transverse stationary external load leads to an increase in the amplitude of pipe oscillations.

Experimental Investigation on the Dynamic Modulus Properties of Methane Hydrate Sediment Samples

Studying the strength and deformation properties of sediments containing gas hydrates is one of the key problems during the process of hydrate resource exploitation. In this paper, considering the effects of temperatures (−5, −3, −1 °C), confining pressures (0.5, 1, 2 MPa) and porosities (40%, 80%) on the dynamic modulus characteristics of sediments containing methane hydrates, several dynamic loading experiments were conducted. The results show that the sediment structure was more easily destroyed under a larger amplitude of dynamic loading. According to the dynamic stress–strain curves, the skeleton curves of the sediment samples were obtained, and it was shown that the deformation behaved with elastic characteristics in the initial stage, and then plastic deformation increased gradually and played a leading role with the increase in external loading. The maximum dynamic elastic modulus of sediments was reduced under the conditions of higher temperature and porosity, and effectively enhanced under higher confining pressure. Finally, on the basis of the Hardin–Drnevich equivalent model, and considering the influences of temperatures and confining pressures on model parameters, a viscoelastic constitutive model applied to analyze the dynamic modulus characteristics of sediments containing methane hydrate was established. The comparison showed that these calculated values of sediments’ dynamic elastic modulus accorded quite well with the experimental values.

Stress transfer of single yarn drawing in soft fabric studied by micro Raman spectroscopy

The load transfer behavior of the Kevlar 49 soft fabric commonly used for bulletproof clothing in yarn drawing test was investigated by micro-Raman spectroscopy. The linear relationship between Raman shift and axial stress of single yarn was established. The axial stresses of warp yarn in soft fabric with and without preload condition were obtained by Raman measurement under tension, and they conform to the theoretical prediction using a yarn-drawing model with interface debonding. The experimental results show that the drawing load is transferred along the yarn from the beginning to the end. In the process of straightening the yarn, the interfacial friction shear stress caused by the yarn relative sliding remains almost constant, and the length of straightened yarn becomes longer as the external load increases. The preload plays a role in inhibiting the straightening of the yarn, which is helpful for the load transfer in the sliding friction section.

Relation between damage processes of reinforced concrete under uniaxial compression and electric response to pulsed mechanical impact

The main regularities of the relation between the actual destruction of reinforced concrete samples under uniaxial compression and the characteristics of fracture mechanics and indirect physical parameters are investigated in this work. Studies of samples with different types of reinforcement and different strength of concrete are carried out. Destruction stages of reinforced concrete under uniaxial compression are established and the corresponding diagnostic criteria of evaluation are proposed. The evaluation procedure is based on measuring the electric response to a weak mechanical impact. Measurements of the electric response are carried out periodically during a gradual increase of external load. Analysis of signals in the time and frequency domain is the basis of the algorithm used for evaluating the degradation processes of reinforced concrete under uniaxial compression.

Application tests of a new-type LNG rapid gasification unit

Liquefied natural gas (LNG) is stored under low temperature and high pressure. It has to be gasified before it is used. Therefore, LNG gasification unit is essential and it is vital to the high-efficiency utilization of LNG. In this paper, a new-type LNG rapid gasification unit was developed. Adopted in this unit are some innovative technologies authorized with the national patent of invention, such as the umbrella-shape gas flow circle unit, the flue gas circulation system and the water feeding system, which help to guarantee its operation safety and increase its operation efficiency. After it was justified in lab test, the unit for industrial application was designed and manufactured and then tested to verify its design rationality. The results show that the new-type LNG rapid gasification unit meets the design requirements in the aspect of efficiency, exhaust gas loss, radiation loss and fuel gas consumption rate; at a load of 1800–2200 m3/h, its efficiency is over 95%; at a load of 1976.0 m3/h which is close to the design value of 2000 m3/h, its efficiency is 96.34% or even up to 2800 m3/h. This new-type LNG rapid gasification unit is adaptable to a large range of loads and can adapt to the rapid increase of external load. Its fuel gas consumption rate is only 1.5%, which is in the range of energy conservation. It presents the advantages of high heating efficiency, rapid startup, high gasification rate, compact structure, small land occupation and invulnerability to the environment, therefore, it is applicable to the middle and small independent regions which cannot be connected to the natural gas supply pipeline networks due to various reasons.

Influence of external load on the frictional characteristics of rotary model using a molecular dynamics approach

Based on the swash plate–slipper in water hydraulic axial piston pump, a rotary model is built using the molecular dynamics approach to study the frictional characteristics in the perspective of atoms. The model consists of a diamond rotator and a copper substrate and the diamond rotator rotates around the cooper substrate at different external loads. The frictional force is calculated by summing all the atomic forces of diamond rotator along the opposite direction of linear velocity and the real contact area is defined by the number of atoms that interact chemically across the contact interface. Influences of external load on the frictional force and coefficient of friction are analyzed. The simulation results show that the total atomic force varies with rotary cycle according to the sine law with a periodic cycle of 2π in the rotary model. However, the frictional force is basically not a periodic signal. It fluctuates around the average frictional force which is linearly dependent on the real contact area. Besides, it is demonstrated that the coefficient of friction decreases with the increase of external load, which is due to the nonlinear increase of real contact area. As a result, the present work will have an important impact on the fundamental understanding of the wear mechanism of rotary model.

Creep behaviors of methane hydrate coexisting with ice

A series of creep tests were carried out in order to clarify the creep behaviors of methane hydrate coexisting with ice, which may exist in the ice-bearing permafrost. Measurements on synthetic methane hydrate-ice specimens indicate that (1) higher external load will increase the initial strain and the axial strain during the whole creep test. And the creep strain rate will increase with the increase of external load; (2) the initial strain, axial strains and creep strain rate of the specimens under certain external load increase with the decrease of confining pressure; (3) temperature drop leads to the decrease of initial strain and axial strains of the specimens under certain external load. And the creep strain rate firstly increases and then decreases with the increase of temperature, due to the refreezing of dissociated water from methane hydrate; (4) the specimens run to the secondary creep stage earlier when they endure lower external load, higher confining pressure and lower temperature; (5) the specimens under higher confining pressure and lower temperature show higher failure strength.

Failure analysis of directional crossing pipeline and design of a protective device

Abstract Failure analysis of crossing pipelines in the operation process after the completion of construction was investigated. Dent and collapse are the common failure modes of crossing pipelines in bad geological strata. The deformation processes of dent behaviour and collapse behaviour of crossing pipelines were simulated. The results show that high stress distribution extends along the axial and circumferential directions under the boulder load, and the maximum equivalent plastic strain appears at the centre of the dent. The collapse process of the crossing pipeline can be divided into six phases. The cross-section changes from an oval shape to a “gourd” shape and then to an “8” shape as the external load increases. Before buckling appears, the decrease in the cross-section area of the crossing pipeline is small. However, the cross-section area increases as the surrounding soil pressure increases after buckling appears. When the cross-section shape reaches the “8”, the decrease in the cross-section area reaches a maximum value of 88.1%. To reduce the failure probability and improve the service life of the crossing pipeline, a protective device was designed for preventing damage. For the protective device, the dent rate of the protective pipeline decreases as the annulus pressure increases under the action of boulders. However, the dent rate of the crossing pipeline increases as the annulus pressure increases. Under the same stratum movement, the deformation of the crossing pipeline with the protective device is smaller than without the protective device. Therefore, the protective device can effectively protect the crossing pipeline and prevent a collapse accident. The protective device can be effectively used on any parts of the crossing pipeline in different locations due to its simple structure and convenient installation in bad geological strata.

A numerical study of macro-mesoscopic mechanical properties of gangue backfill under biaxial compression

Based on the Particle Flow Code (PFC2D) program, we set up gangue backfill models with different gangue contents and bond strength, and studied the stress–strain behaviours, the pattern of shear band and force chains, motion and fragmentation of particles under biaxial compression. The results show that when the bond strength or contents of gangue are high, the peak strength is high and the phenomena of post-peak softening and fluctuation are obvious. When gangue contents are low, the shape of the shear band is symmetrical and most strong force chains transfer in soil particles. With an increase in gangue content, the shape of the shear band becomes irregular and the majority of strong force chains turn to transfer in gangue particles gradually, most of which distribute along the axial direction. When the gangue content is higher than 50%, the interconnectivity of strong force chains decreases gradually; at the same time, the strong force chains become tilted and the stability of the system tends to decrease. With an increase in external loading, the coordination numbers of the system increase at first and then decrease and the main pattern of force chains changes into columnar from annular. However, after the forming of the advantageous shear band, the force chains external to the shear band maintain their columnar shape while the inner ones bend obviously. As a result, annular force chains form.

Sliding of a wavy indentor on a viscoelastic layer surface in the case of adhesion

The contact problem of constant velocity sliding of the doubly periodic wavy surface of a rigid indentor along a viscoelastic layer on a rigid foundation is considered with the adhesive attraction between the surfaces taken into account. A method is proposed for calculating the configuration of the contact regions and adhesive interaction regions, the pressure distribution on the contact surface, and the deformation component of the friction force for various values of the viscosity, adhesion, velocity, and microgeometry parameters of the surface. We study how these parameters affect the merging of contact spots and the transition from discrete to saturated contact as the external load increases.

Field tests and finite element modeling of a Prestressed Concrete Pipe pile-composite foundation

The Prestressed Concrete Pipe (PCP) pile-composite foundation was initially employed in the foundation of a culvert in the ancient Yellow River of China. To analyze the reinforcement effect of the foundation, a composite foundation composed of PCP piles was investigated with field tests and numerical simulations. A static load test was conducted to investigate the stress and deformation of the PCP pile-composite foundation, and a finite element model under three-dimensional (3D) axisymmetric conditions was developed to simulate the stress and deformation of the foundation. The Finite Element (FE) model used a nonlinear constitutive model for the soil, cushion and pile-soil interface. The results of the numerical simulations correspond with the load sharing, stress and displacement results of the static load test and indicate that the soil stress is primarily compressive. The cushion reduces the difference in settlement between the middle region and the side region of the bearing plate and increases the bearing capacity of the PCP pile-composite foundation. The stress of the pile significantly varies in the upper 1 m. The pile-soil load-sharing ratio increases with an increase in external load. This paper is expected to be useful for scientific research and efficient applications of PCP pilecomposite foundations.

An experimental study of the dynamic behavior of a 2 kW proton exchange membrane fuel cell stack under various loading conditions

The dynamic behavior of the PEM (proton exchange membrane) fuel cell stack has great effect on the safety and effective operation of its applications. In this paper, a self-designed bulb-array is used to simulate the various loading conditions and study the dynamic behavior of a 2 kW PEM fuel cell stack. An evaluation index, including oscillation rate, pressure variation and dynamic resistance factor, is used to analyze the transient response of the PEM fuel cell stack. It is observed that the stack current increases about 8.6%, and the Oscillation rate decreases more rapidly after activation. In the step-up load stage, the oscillation rate and the dynamic resistance decrease more rapidly as the external load increases. Due to the periodic anodic purge process, a periodic voltage fluctuation can be seen. In addition, when the stack works in the open-loop state (working without the external load), the transient response of the stack current is significantly affected by the hydrogen humidity and the charge double-layer.

Control of Wind-Induced Vibration of Transmission Tower-Line System by Using a Spring Pendulum

The high-voltage power transmission tower-line system, which is a high flexible structure, is very susceptible to the wind-induced vibrations. This paper proposes the utilization of the internal resonance feature of the spring pendulum to reduce the wind-induced vibration of a transmission tower. The kinetic expression of the spring pendulum system is obtained through Lagrangian equation. The condition of the internal resonance is verified to beλ = 2, in whichλis the ratio of the spring mode frequency over the pendulum mode frequency. A 55 m tower in the Liaoning province is established in SAP2000 to numerically verify the effectiveness of the proposed device. The spring pendulum is modeled using Link element. The wind speed history is generated based on Kaimal spectrum using harmonic superposition method. Results show that, (1) compared with the suspended mass pendulum, the spring pendulum absorbs more energy and reduces the oscillation more effectively and (2) the vibration control performance of the proposed spring pendulum improves as the external wind load increases.

Large-scale tests of pile-supported earth platform with and without geogrid

In recent years, concrete piles, such as cast-in-place piles and precast concrete piles, have been increasingly used to support superstructures and embankments when they are constructed on soft soils. On the top of pile head elevation, a certain thick granular cushion including geosynthetic reinforcement is usually installed to transfer more external load onto the piles through soil arching effect and membrane effect. This technique involving the use of rigid piles, gravel cushion and geosynthetics is usually referred to as geosynthetic-reinforced and pile-supported earth platform. This paper presents two well-instrumented large-scale tests of pile-supported earth platform with and without geogrid reinforcement. The performance of the pile-supported platform with geogrid and its load transfer behavior were investigated and compared with those for the test without geogrid. The validation of the EBGEO (2010) calculation was performed based on the test results. The test results indicate that under lower applied load, the loads carried by the piles in the test with geogrid were close to those in the test without goegrid, while with an increase in external load the loads carried by piles in the test with geogrid increased faster than those in the test without geogrid. The negative skin friction for the test with geogrid was smaller than that for the test without geogrid. Based on the contours of earth pressures on foundation base the maximum earth pressures were distributed along the edge of central cap in the test with geogrid. The minimum earth pressures were on midway subsoil between two caps in both tests. Based on the test results, the efficacy for the test with geogrid was 2.5% greater than that for the test without geogrid at the end of loading. The efficacies predicted by the EBGEO (2010) calculation agreed well with the measured efficacies.

Is muscle coordination affected by loading condition in ballistic movements?

This study aimed to investigate the effect of loading on lower limb muscle coordination involved during ballistic squat jumps. Twenty athletes performed ballistic squat jumps on a force platform. Vertical force, velocity, power and electromyographic (EMG) activity of lower limb muscles were recorded during the push-off phase and compared between seven loading conditions (0–60% of the concentric-only maximal repetition). The increase in external load increased vertical force (from 1962 N to 2559 N; P=0.0001), while movement velocity decreased (from 2.5 to 1.6ms−1; P=0.0001). EMG activity of tibialis anterior first peaked at 5% of the push-off phase, followed by gluteus maximus (35%), vastus lateralis and soleus (45%), rectus femoris (55%), gastrocnemius lateralis (65%) and semitendinosus (75%). This sequence of activation (P=0.67) and the amplitude of muscle activity (P=0.41) of each muscle were not affected by loading condition. However, a main effect of muscle was observed on these parameters (peak value: P<0.001; peak occurrence: P=0.02) illustrating the specific role of each muscle during the push-off phase. Our findings suggest that muscle coordination is not influenced by external load during a ballistic squat jump.

착지 시 외부 무게 부하에 따른 남성과 여성의 하지 관절 각속도, 모멘트, 에너지 흡수에 미치는 영향

This study aimed to analyze the effects of external load between male and female on angular velocity, moment, and absorbed energy of the lower-extremity joints during drop landing. The study subjects were 9 male(<TEX>$mass=70.82{\pm}4.64kg$</TEX>, <TEX>$height=1.71{\pm}0.04m$</TEX>, <TEX>$age=24.5{\pm}1.84years$</TEX>), 9 female(<TEX>$mass=50.14{\pm}4.09kg$</TEX>, <TEX>$height=1.61{\pm}0.03m$</TEX>, <TEX>$age=23.6{\pm}2.62years$</TEX>), without any serious musculoskeletal, coordination, balance, or joint/ligament problems for 1 year before the study. The angular velocity, flexion/extension and abduction/adduction moments, and absorbed energy of the lower-extremity joints were compared between the men and women during drop landing under 4 different conditions of external load(0%, 8%, 16%, and 24%) by using two-way repeated ANOVA(p < .05). The women landed with a greater peak angular velocity of the ankle joint, greater peak inversion moment, and lower peak hip-extension moment than the men did, under all 4 conditions. Additionally, the landing characteristics of the women were distinct from those of the men; the women showed a greater peak knee-adduction moment and greater absorbed energy of the knee joint. These differences indicate that anterior cruciate ligament(ACL) strain was greater in the women than in the men and therefore, women may be at a higher potential risk for noncontact injuries of the ACL with an increase in external load.

Feasibility of pile-shell foundations with prestressed soil beds

Interaction between a large-scale model of a combined pile-shell foundation with a clayey soil bed is examined under field conditions. The influence exerted on the change in the stress-strain state of the soil bed by prestressing of the soil after pressing of the under-shell space and an increase in external load is described

Power output in vertical jumps: does optimum loading depend on activity profiles?

The previously proposed maximum dynamic output hypothesis (MDO: i.e. the optimum load for maximizing the power output during jumping is one's own body) was tested on individuals of various activity profiles. Forty males (10 strength-trained athletes, 10 speed-trained athletes, 10 physically active non-athletes, and 10 sedentary individuals) performed different vertical jumps on a force plate while a pulley system was used to either reduce or increase the subject's body weight by 10-30 %. As expected, an increase in external loading resulted in a significant increase (p < 0.001) in force output and a concomitant decrease of peak jumping velocity in all groups of participants. The main finding, however, was that all groups revealed the maximum peak and mean power output at approximately the subjects' own body weight although their weight represented prominently different percentage of their maximum dynamic strength. While a significant (p < 0.05), albeit moderate, 'group × load' interaction in one jump was observed for the peak power output, the individual optimum load for maximizing the power output number did not differ among the groups. Although apparently further research on various types of movements is needed, the present results provide, so far, the strongest support of the MDO hypothesis.

Mechanisms Underlying the Reduced Performance Measures from Using Equipment with a Counterbalance Weight System

Bench press throws are commonly used in the assessment of upper-body power and are often performed on a Smith machine that uses a counterbalance weight to reduce the net load on the barbell. The use of a counterbalanced Smith machine was recently shown to reduce performance measures, but the mechanisms for this reduction have not been established. The purpose of this study was to determine the underlying physiological and biomechanical causes of the reduced performance measures found when using a counterbalanced Smith machine. Twenty-four men (mean ± SE: age, 23 ± 1 years; weight, 91.0 ± 3.5 kg; height, 178.9 ± 1.2 cm) performed Smith machine bench press throws at 30% of 1-repetition maximum under 4 conditions: (a) rebound movement and counterbalance, (b) rebound movement and no counterbalance, (c) concentric-only movement and counterbalance, and (d) concentric-only movement and no counterbalance. Peak power, peak force, and peak concentric and eccentric velocities were measured using a linear accelerometer, and peak ground reaction force was measured using a force plate. The counterbalance condition produced significantly (p < 0.05) lower peak accelerometer-based force (-21.2 and -17.0% for rebound and concentric-only bench press throws, respectively) but increased peak ground reaction force (5.3 and 3.2%). The discrepancy between changes in peak accelerometer-based force and peak ground reaction force suggests that an increase in net external load occurred during the movement. For performance testing of explosive movements, the use of a counterbalance system results in an underestimation of performance capability, likely because of an increase in the net external load during the concentric phase. Therefore, a counterbalance system should not be used for explosive movement performance testing.

Analysis of Sinking Mechanism and Finite Element for Static Pile in Collapsed Loess Region

The static pile sinking calculation model has been established based on cavity expansion theory and the elastic-plastic analytical solution has been solved. This model can truly reflect the static pile sinking mechanism in collapsed loess region, providing a theoretical basis for the analysis and design of static pile. A finite element model has been set up to simulate the entire pile sinking process. The results show that due to relatively large pile rigidity and strength compared with the soil, under instantaneous load, the surrounding soil will produce a large deformation, which is mainly caused by pile friction diffusion. When the external load increases, the interaction between stress and pile-soil gradually increases; when reaching the proportion of limited load, both of them are close to constant, accordingly, the growth slows down and tend to be stable; when the external load is greater than the proportional limit load, the phenomenon of mutation occurs. Finally, after comparison, the finite element calculation results match well with the test results. Through analysis and engineering practice, static pile is found to have a good prospect in collapsed loess region. Some useful conclusion can be used as references for similar projects in these areas.