The force transmissibility of MDOF structures with a non-linear viscous damping device

In the present study, the concept of the Output Frequency Response Function (OFRF), recently proposed by the authors, is applied to theoretically investigate the force transmissibility of MDOF structures with a cubic non-linear viscous damping device. The results analytically show that the introduction of cubic non-linear damping can significantly reduce the transmissibility over all resonance regions for a Multiple Degree of Freedom (MDOF) structure and at the same time leave the transmissibility over the isolation region virtually unaffected. The analysis also indicates that a strong linear damping may shift the system resonances and compromise the beneficial effects of cubic non-linear viscous damping on the force transmissibility of MDOF structures. This suggests that a less significant linear damping together with a strong cubic non-linear damping can be used in MDOF structures to achieve a desired vibration isolation performance. This research work has a significant implication for the design of viscously damped MDOF structures for a wide range of practical applications.     

Effect of gravity on the mechanical properties of lunar regolith tested using a low gravity simulation device

Simulations of the bearing capacity and shear strength of regolith under Earth’s gravity produce different results from those under low gravity. A low-gravity simulation device was developed in this study, and an internal stress model of regolith simulant was established to correct the errors. The model revealed additional force on both shear plane in the shear test and the press plate area in the pressure–sinkage test. The sinkage and shear test results showed that low gravity decreased the deformable index n, frictional modulus k_φ and cohesion c, whereas there were no obvious changes to the cohesive modulus k_c and internal friction angle φ. The sinkage generally increased as the gravity decreased under a consistent normal load larger than 50 N, but when the wheel load was lower than 50 N, the sinkage of the TYII-1 simulant was larger under 1 G than 1/6 G. Gravity had little effect on the shear strength of the regolith. However, the tractive thrust of the TYII-1 simulant was lower under 1/6 G than 1 G. The smaller difference was due to differences in the way the soils responded to changes in the gravity level for the TYII-2 simulant.     

Measurement of the aerodynamic forces on a small particle attached to a wall

Using operating principles similar to that applied in atomic force microscopes, we have developed a novel measuring method to study the aerodynamic forces, in particular the lift and drag force, acting on a small particle attached to a wall and immersed in a linear shear flow. Results thus far have shown that the system is capable of measuring both the minute aerodynamic lift and drag forces that a particle experiences as a result of the flow.C. Muthanna has also published under the name C. M. Kolera

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Measurement of rheological properties of soft biological tissue with a novel torsional resonator device

A new device for measuring the rheological properties of soft biological tissues is presented. The mechanical response is characterized for harmonic shear deformations at high frequencies (up to 10 kHz) and small strains (up to 0.2%). Experiments are performed using a cylindrical rod excited to torsional resonance. One extremity of the rod is in contact with the soft tissue and adherence is ensured by vacuum clamping. The damping characteristics and the resonance frequency of the vibrating system are inferred from the control variables of a phase stabilization loop. Due to the contact with the soft tissue, and depending on the rheological properties of the tissue, changes occur in the Q-factor and in the resonance frequency of the system. The shear modulus of the soft tissue is determined from the experimental results with an analytical model. The reliability of the proposed technique is evaluated through repeatability tests and comparative measurements with synthetic materials. The results of measurements on bovine organs demonstrate the suitability of the experimental procedure for the characterization of biological tissues and provide some insight in their rheological properties at frequencies in the range 1–10 kHz.     

Measurement of very small liquid flows

A measuring principle for the flow rate of liquid follows consists in the determination of the volume change of a liquid in a tank in relation to unit of time. The development and the realization of three measurement systems based on this principle are presented in this paper. The devices can measure liquid flows below 0.2 L/h. One flow meter uses an air bubble in the form of a stopper as tracer. A special design keeps the bubble in the measuring tube; it does not have to be replaced. Another flow meter measures the volume changes by determining the pressure at the bottom of a vertical tube. To achieve a continuous operation, a differential design with two corresponding tubes was realized. The third flow meter measures the mass of a drop at the end of a horizontal silicone tube working as a bending beam. The liquid flows through the tube and is forced to form drops at its end. Owing to their design, each of the three devices has distinctive characteristics. A theory of measurement systems that facilitates synthesis and analysis of measuring devices serves as the basis for the development of the flow meters.     

Design of a 6-DOF force device for virtual assembly (FDVA-6) of mechanical parts

Among different interaction modalities, force feedback is one of the key technologies to increase the interactivity and immersion of a virtual assembly process. This paper presents a 6-DOF force device with its forward kinematic analysis, workspace simulation, and gravity compensation. To evaluate the device, a prototype system is developed and a case study is conducted to assemble a mechanical product. The users have given positive feedback on the gravity compensation implemented and the general performance of the device.     

Stability of viscoelastic rectangular plate with a piezoelectric layer subjected to follower force

The effects of a piezoelectric layer on the stability of viscoelastic plates subjected to the follower forces are evaluated. The differential equation of motion of the viscoelastic plate with the piezoelectric layer is formulated using the two-dimensional viscoelastic differential constitutive relation and the thin plate theory. The weak integral form of the differential equations and the force boundary conditions are obtained. Using the element-free Galerkin method, the governing equation of the viscoelastic rectangular plate with elastic dilatation and Kelvin–Voigt distortion is derived, subjected to the follower forces coupled with the piezoelectric effect. A generalized complex eigenvalue problem is solved, and the force excited by the piezoelectric layer due to external voltage is modeled as the follower tensile force; this force is used to improve the stability of the non-conservative viscoelastic plate. For the viscoelastic plate with various boundary conditions, the results for the instability type and the critical loads are presented to show the variations in these factors with respect to the location of the piezoelectric layers and the applied voltages. The stability of the viscoelastic plates can be effectively improved by the determination of the optimal location for the piezoelectric layers and the most favorable voltage assignment.     

Limit cycles of a double pendulum subject to a follower force

It is shown that there is a magnitude of the follower force at which two limit cycles, stable and unstable, are born in the phase space of a double simple pendulum     

Active feedback control of a beam subjected to a nonconservative force

This study examines the possibility of controlling through feedback a thin cantilevered beam subjected to a nonconservative follower force. A converging frequency flutter instability which occurs in this model is similar to classical bending-torsion flutter of an aircraft wing. Because of the similar nature of the instabilities, the beam under the follower force can be a useful vehicle for investigating the fundamental aspects of stabilization of wing flutter by feedback control. A modal approach is used for obtaining the mathematical model and control laws. A standard root locus technique for simple analytical models is also used to understand and explain the control of the beam. Experiments are carried out to verify the validity of this theoretical model. Good correlation is shown between theoretically and experimentally determined stability boundaries as well as for modal frequency and damping variation with follower force.     

Velocity in a liquid subjected to a shear force at the liquid surface with a receding velocity

The development of the Stokes layer in a liquid subjected to a constant shear force at the liquid surface with mass erosion is studied in this paper. It is shown that the velocity in the Stokes layer is weakened by surface receding and the relative decrease of the maximal liquid velocity due to surface recession is a unique function of the time normalized by the recession/diffusion balance time scale, defined as the ratio between the kinematic viscosity and the square of the receding velocity. At a time much larger than the diffusion/recession balance time scale, the role of the surface receding is rather important: instead of being pushed into the liquid at the receding velocity, the development of the Stokes layer is effectively prohibited by surface receding. The project supported by the National Natural Science Foundation of China (10025210) and the China NKBRSF project (2001CB409600)     

A device to regulate rotational speed using a rotating regulator with electrorheological fluid

The authors propose a device consisting of a rotating regulator within an electrorheological fluid (ERF), in which the rotational speed of the rotating body can be regulated by supplying an electric field. This new type of device with ERF is relevant to engineering applications and can play a role in braking as well as in rotation regulation. The ERF used here consists of a colloidal suspension of smectite particles in a solvent. The experimental conditions are fixed in a range of comparatively small rotational speed. The authors clarified the hydrodynamic and electrical effects of the shape of the rotating disk, the kind of solvent contained in the ERF, the temperature, the electrode gap and the electric field strength on the steady characteristics of the torque, the electric current density and the electric power to a rotational speed. From the torque and rotational speed data, empirical equations were derived using nondimensional parameters for the purpose of convenient engineering design. The authors also clarified the correlation between the hydrodynamic and steady electric characteristics of the device and the transient characteristics of torque, the electric current and the rotational speed.     

Elastic stability of a uniform cantilevered beam on elastic foundation with a shear layer subjected to a follower force

Summary The problem of the elastic stability of a uniform contilevered beam on an elastic elements connected by shear layers and subjected to a follower force, is there reopened.The critical loads for several values of the tangency coefficient and modulus of the foundation are shown.

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Sommario Viene riproposto il problema della stabilità elastica di una trave uniforme a sbalzo su una fondazione generalizzata, sottoposta ad una forza di tipo follower.Si indicano i valori dei carichi critici per differenti valori del coefficiente di tangenza e delle costanti della fondazione.

     

Application of the finite segment method to stabilisation of the force in a riser connection with a wellhead

This paper presents a spatial model of riser dynamics formulated using the segment method and its applications. The model has been validated by comparison of the authors’ own results with those obtained from experimental measurements and Abaqus on the basis of forced vibration with large amplitude for the riser submerged in water. The influence of the sea environment is considered. Correctness and numerical effectiveness of the model enable us to formulate and solve the force stabilisation problem. A dynamic optimisation problem is formulated and solved. As a result vertical courses of movement of the upper end of the riser are obtained which compensate the horizontal movement of the base and stabilise the force in the connection of the riser with a wellhead.     

小型高压引爆装置冲击电流简易测量方法

依据脉冲放电电路的等效电路及其微分方程,采用Levenberg-Marquarat算法对主电容放电电压测试波形数据进行衰减系数识别,从而获得模拟电流波形。该方法克服了分流器法和Rogowski线圈法等直接测量小型高压引爆装置冲击电流时,因附加电路引起的电流波形失真。MATLAB模拟结果表明,该方法得到的电流模拟波形与真实电流波形拟合精度高,可用于直列式引信电子安全与解除保险装置和低能冲击片雷管的优化匹配设计。