Time-domain solution for transient dynamic response of a large-diameter thin-walled pipe pile

The propagation of stress waves in a large-diameter pipe pile for low strain dynamic testing cannot be explained properly by traditional 1D wave theories. A new computational model is established to obtain a wave equation that can describe the dynamic response of a large-diameter thin-walled pipe pile to a transient point load during a low strain integrity test. An analytical solution in the time domain is deduced using the separation of variables and variation of constant methods. The validity of this new solution is verifi ed by an existing analytical solution under free boundary conditions. The results of this time domain solution are also compared with the results of a frequency domain solution and fi eld test data. The comparisons indicate that the new solution agrees well with the results of previous solutions. Parametric studies using the new solution with reference to a case study are also carried out. The results show that the mode number affects the accuracy of the dynamic response. A mode number greater than 10 is required to enable the calculated dynamic responses to be independent of the mode number. The dynamic response is also greatly affected by soil properties. The larger the side resistance, the smaller the displacement response and the smaller the refl ected velocity wave crest. The displacement increases as the stress waves propagate along the pile when the pile shaft is free. The incident waves of displacement and velocity responses of the pile are not the same among different points in the circumferential direction on the pile top. However, the arrival time and peak value of the pile tip refl ected waves are almost the same among different points on the pile top.

Stability of columns with original defects under periodic transient loadings

To study the influence of original defects on the dynamic stability of the columns under periodic transient loadings,the approximate solution method and the Fourier method of the stable periodic solution are adopted while considering the influence of original defects on columns.The dynamic stability of the columns under periodic transient loadings is analyzed theoretically.Through the study of different deflections,the dynamic instability of the columns is obtained by Maple software.The results of theoretical analysis show that the larger the original defects,the greater the unstable area,the stable solution amplitude of columns and the risk of instability caused by parametric resonance will be.The damping of columns is a vital factor in reducing dynamic instability at the same original defects.On the basis of the Mathieu-Hill equation,the relationship between the original defects and deflection is deduced,and the dynamic instability region of the columns under different original defects is obtained.Therefore,reducing the original defects of columns can further enhance the dynamic stability of the compressed columns in practical engineering.

Transient Simulation on Dynamic Response of Liquid Annular Seals

Transient change of the operating parameters has a serious influence on the stability of liquid annular seals.Take the liquid annular seals as a research object,a numerical method based on six-degree-of-freedom(6DOF)to analyze the dynamic response of liquid annular seals under gravity impact load.The variations of the force of liquid seal and pressure as well as the axis trajectory in time history are investigated.The influence of different sealing clearance,different liquid viscosity and different rotor speed is also studied.The results show that the maximum sealing pressure and sealing force of gravity direction will increase greatly in a very short time and then reduce rapidly.When sealing clearance increases,the displacement response amplitudes of axis trajectory,the maximum sealing force of gravity direction and maximum sealing pressure also increase.When liquid viscosity increases,the displacement response amplitudes of axis trajectory,the maximum sealing force of gravity direction and maximum sealing pressure decrease.We also found that different rotor speed has almost no influence on the maximum sealing force of gravity direction and maximum sealing pressure.

Characteristics of the transient thermal load and deformation of the evacuated receiver in solar parabolic trough collector

As a core element in solar parabolic trough collector, the evaluated receiver often runs under severe thermal conditions. Worse still, the transient thermal load is more likely to cause structural deformation and damage. This work develops an efficient transient multi-level multi-dimensional(M2) analysis method to address photo-thermal-elastic problems, thereby estimating transient thermal load and deformation for the receiver:(i) one-dimensional(1-D) thermo-hydraulic model is adopted to determine the transient thermo-hydraulic state,(ii) 3-D finite volume method(FVM) model for the receiver tube is established to obtain the real-time temperature distribution,(iii) 3-D finite element method(FEM) model is employed to make thermoelastic analysis. Based on this M2 method, the typical transient cases are conducted in cold-start, disturbed-operation and regulatedprocess. Three indicators(average temperature of the wall(ATW), radial temperature difference(RTD), circumferential temperature difference(CTD)) are defined for overall analysis of the receiver thermal load. It is found that in the transient process,receivers face response delay and endure significant thermal load fluctuation. The response time for a single HCE(heat collecting element) under lower mass flow rate(1.5 kg s-1) could sustain 280 s. During the cold-start stage(DNI=200 W m-2 to 800 W m-2), the maximum value of CTD in receiver is as high as 11.67℃, corresponding to a maximum deflection of 1.05 cm.When the mass flow rate decreases sharply by 80%, the CTD reaches 33.04℃, causing a 2.06-cm deflection. It should be pointed out that in the cold-start stage and the lower mass flow rate operation for solar parabolic trough collector, alleviating the transient thermal load and deformation is of importance for safely and efficiently running evaluated receiver.

Analytical solution to the transient beam loading effects of a superconducting cavity

Transient beam loading is one of the key issues in any high beam current intensity superconducting accelerators, and needs to be carefully investigated. The core problem in the analysis is to obtain the time evolution of effective cavity voltage under transient beam loading. To simplify the problem, the second order ordinary differential equation describing the behavior of the effective cavity voltage is intuitively simplified to a first order one, with the aid of two critical approximations which lack proof of their validity. In this paper, the validity is examined mathematically in some specific cases, resulting in a criterion for the simplification. It is popular to solve the approximate equation for the effective cavity voltage numerically, while this paper shows that it can also be solved analytically under the step function approximation for the driven term. With the analytical solution to the effective cavity voltage, the transient reflected power from the cavity and the energy gain of the central particle in the bunch can also be calculated analytically. The validity of the step function approximation for the driven term is examined by direct evaluations.After that, the analytical results are compared with the numerical ones.

Experimental investigation into transient pressure pulses during pneumatic conveying of fine powders using Shannon entropy

This paper presents the results of an ongoing investigation into transient pressure pulses using Shan- non entropy. Pressure fluctuations （produced by gas-solid two-phase flow during fluidized dense-phase conveying） are recorded by pressure transducers installed at strategic locations along a pipeline. This work validates previous work on identifying the flow mode from pressure signals （Mittal, Mallick, ＆ Wypych, 2014）. Two different powders, namely fly ash （median particle diameter 45 μm, particle den- sity 1950 kg/m3. loosely poured bulk density 950 kg/m3） and cement （median particle diameter 15 p,m, particle density 3060 kg/m3, loosely poured bulk density 1070 kg/m3）, are conveyed through different pipelines （51 mm I.D. × 70 m length and 63 mm I.D. × 24 m length）. The transient nature of pressure fluc- tuations （instead of steady-state behavior） is considered in investigating flow characteristics. Shannon entropy is found to increase along straight pipe sections for both solids and both pipelines. However, Shannon entropy decreases after a bend. A comparison of Shannon entropy among different ranges of superficial air velocity reveals that high Shannon entropy corresponds to very low velocities （i.e. 3-5 m/s） and very high velocities （i.e. 11-14 m/s） while low Shannon entropy corresponds to mid-range velocities （i.e. 6-8 m/s）.

A 3 A sink/source current fast transient response low-dropout Gm driven linear regulator

A 3 A sink/source G_m-driven CMOS low-dropout regulator（LDO）,specially designed for low input voltage and low cost,is presented by utilizing the structure of a current mirror G_m（transconductance）driving technique,which provides high stability as well as a fast load transient response.The proposed LDO was fabricated by a 0.5μm standard CMOS process,and the die size is as small as 1.0 mm^2.The proposed LDO dissipates 220μA of quiescent current in no-load conditions and is able to deliver up to 3 A of load current.The measured results show that the output voltage can be resumed within 2μs with a less than 1mV overshoot and undershoot in the output current step from-1.8 to 1.8 A with a 0.1μs rising and falling time at three 10μF ceramic capacitors.

Optimization of the co-closing law of guide vanes and blades for bulb turbines based on CFD

The load rejection transient process of bulb turbine units is critical to safety of hydropower stations,and determining appropriate closing laws of guide vanes(GVs)and runner blades(RBs)for this process is of significance.In this study,we proposed a procedure to optimize the co-closing law of GVs and RBs by using computational fluid dynamics(CFD),combined with the design of experiment(DOE)method,approximation model,and genetic optimization algorithm.The sensitivity of closing law parameters on the histories of head,speed,and thrust was analyzed,and a two-stage GVs’closing law associating with a linear RBs’closing law was proposed.The results show that GVs dominate the transient characteristics by controlling the change of discharge.Speeding GVs’first-stage closing speed while shortening first-stage closing time can not only significantly reduce the maximum rotational speed but also suppress the water hammer pressure;slowing GVs’second-stage closing speed is conducive to controlling the maximum reverse axial force.RBs directly affect the runner force.Slowing RBs’closing speed can further reduce the rotational speed and the maximum reverse axial force.The safety margin of each control parameter,flow patterns,and pressure pulsations of a practical hydropower station were all improved after optimization,demonstrating the effectiveness of this method.

A 200 mA CMOS low-dropout regulator with double frequency compensation techniques for SoC applications

This paper presents a 200 mA low-dropout （LDO） linear regulator using two modified techniques for frequency compensation. One technique is that the error amplifier uses a common source stage with variable load, which is controlled by the output current, is served as the second stage for a stable frequency response. The other technique is that the LDO uses a pole-zero tracking compensation technique at the error amplifier to achieve a good frequency response. The proposed circuit was fabricated and tested in HJTC 0.18 μm CMOS technology. The designed LDO linear regulator works under the input voltage of 2.8-5 V and provides up to 200 mA load current for an output voltage of 1.8 V. The total error of the output voltage due to line and load variation is less than 0.015%. The LDO die area is 630 x 550 μm^2 and the quiescent current is 130 μA.

Tracking code simulation for passive harmonic cavity in the SSRF storage ring

Background A passive third harmonic cavity is planned to install in the Shanghai Synchrotron Radiation Facility(SSRF)storage ring to increase the beam lifetime.Transient beam loading effect generated by the gap between the bunch trains can suppress the bunch lengthening effect of the third harmonic cavity.Besides,the field excited in the passive operation of the harmonic cavity depends on the bunch distribution.Purpose To estimate the effect of transient beam loading,the tracking codes have been developed.Methods The tracking simulation has been performed for three uniform filling cases and a nonuniform filling case.The lengthened bunch distribution has also been included into tracking code simulation.The effect of the lengthened bunch has also been investigated.Results The uniform filling pattern with shorter bunch trains shows lower transient beam loading effect and can give much higher bunch lengthening factors compared to those of non-uniform filling case.The effect caused by the reduction of the harmonic voltage generated by lengthened bunch distribution causes a great reduction on bunch lengthening effect in uniform filling case,while the lengthening factor of non-uniform filling case does not affect much in this issue.Conclusion The tracking codes have been developed to estimate the effect of transient beam loading for three uniform filling cases and a non-uniform filling case.The larger gap in the filling pattern can cause the higher transient beam loading effect and lower bunch lengthening effect.The lengthened bunch distribution has also been included into tracking code simulation.The effect of the lengthened bunch has also been investigated.The more the bunch is lengthened,the greater reduction on bunch lengthening effect.