Pulsating Force Research Articles

Efficiency improvement and evaluation of a centrifugal pump with vaned diffuser

In order to enhance the efficiency of centrifugal pump, the structure of a centrifugal pump with vaned diffuser, whose specific speed is 190, was numerically improved by trimming back-blades of impeller and smoothing sharp corner in annular chamber. The energy performance, the internal flow field, the axial force, the radial force, and the pressure pulsation of the pump were analyzed. Results show that efficiency of the improving scheme 1 under the design flow rate is 77.47%, which can balance 69.82% of the axial force, while efficiency of the improving scheme 2 under the design flow rate is the maximum, which could still balance 62.74% of the axial force. The pressure pulsations of the improving scheme 2 at the typical monitoring points are less than that of the improving scheme 1 and the original scheme. The difference of the radial force peak between the improving scheme 1 and the improving scheme 2 is very small. The vector distributions of the radial force of the improving scheme 1 and the improving scheme 2 are more uniform than that of the original scheme. Considering the efficiency, pressure pulsation, and axial force, experiment measurements on the improving scheme 2 were carried out to verify the effectiveness of the improvement result. Results of energy performance experiment show that efficiency of the improving scheme 2 under the design flow rate is 76.48%, which is 5.26 percentage points higher than that of the original scheme.

Orbital atherectomy for calcified femoropopliteal lesions: a current review.

The orbital atherectomy system is a novel form of atherectomy that uses orbital sanding and pulsatile forces, an effective method of treatment for peripheral atherosclerotic lesions with varying levels of occlusion. Although the devices only has a general indication from the FDA to treat atherosclerotic lesions, they are effective in treating all kinds of lesions, and can therefore mitigate effects of all severities of peripheral artery disease. This approach to endovascular therapy involves the use of differential sanding to preferentially ablate fibrous, fibrofatty and calcified lesions, while deflecting healthy intima away from the crown. The eccentrically mounted crown design allows the device to employ rhythmic pulsating forces that penetrate the medial layer, and cause cracking in the lesions in order to facilitate easier balloon inflation and intravascular drug elution. The combination of vessel modification and lumen enlargement through sanding can effectively restore blood flow to the extremities, and can eliminate risk of critical limb ischemia, as well as subsequent amputation. Extensive lab testing and clinical trials have confirmed the high success rates and low major adverse events associated with this form of treatment. The device is economically viable as well, since its cost is offset by the lower frequency of adjunctive therapy sessions when compared to other devices. Considering the results outlined in this manuscript, the Diamondback 360° is an effective form of atherectomy therapy for peripheral artery disease. In-depth understanding of the operation preparation, procedure, and best imaging techniques can help to optimize outcomes.

Experimental Investigation of Unsteady Characteristics in a Single-Channel Pump

Abstract Single-channel pumps are a specific type of centrifugal pump that is widely used in the sewage treatment of raw wastewater and effluent pumping applications. In single-channel pumps, the rotor–stator interactions may generate unbalanced pressures that change during one impeller revolution. A specific experiment rig was constructed to investigate the unsteady characteristics synchronously, including energy performance, head pulsation, pressure pulsation, and radial force. It was found that the difference between the maximum and minimum head was greater than 5 m under all flow rates during a rotation period. With the increase of the flow rate, the head reached its minimum value slowly and achieved its maximum value more quickly. The static pressure distribution at the impeller outlet was the most uniform at 1.0Qd. The high-pressure region located initially downstream of the tongue gradually moved toward the upstream end of the tongue with an increase in the flow rate. When the blade outlet goes through the tongue, the pressure pulsation appears at its peak at the eighth cross section of the volute. The peak position moves toward the upstream with the rotation of the impeller. In the single-channel pumps, the absolute pressure pulsation achieved its peak at the blade passing frequency, and the pressure pulsation amplitude for fBPF varied gradually with an increase in the flow rate. The radial force reached a minimum value near the optimal efficiency point and its direction was mostly downstream of the tongue. To meet the hydraulic balance of the impeller, it was suggested that a balance piece be adapted to counteract the radial force.

Numerical Investigation on Pressure Pulsation Characteristics and Radial Force of a Deep‐Sea Electric Lifting Pump at Off‐Design Conditions

To predict the vibrational conditions, the generation mechanism, and action law of pressure pulsation and radial force, a computational fluid dynamics (CFD) study of a deep‐sea electric lifting pump operating under different off‐design conditions was performed. The time‐domain and frequency‐domain response of the pressure pulsation at different monitoring points and the radial force of impeller distribution were obtained. Differences in pressure pulsation characteristics between the first stage and second stage were observed. The variation law and influential factors of the radial force under different flow rates were discussed. The present investigation shows that the flow field caused by rotor‐stator interaction is not uniform, resulting in uneven pressure distribution and pressure pulsation, the combined effects of which produce fluctuating radial forces. Parameters obtained via simulations including head, efficiency, and power, which can reflect the hydraulic performance of the pump, agree well with experimental results; thus, the accuracy of the simulation model and the calculation method was verified. This study provides a basis for improving the structure and reliability of an electric lifting pump.

Design of a high-specific speed turbine with non-uniform blade cascade

This paper presents the hydraulic design of Kaplan type turbine in fully axial configuration. The turbine model consists of a straight pipe intake, a rib which covers the shaft, five axial guide vanes, a six blade runner and a 10,6°-full angle draft tube. Due to the presence of non-uniform velocity field behind the rib and interaction between stator and rotor, the pressure pulsations occur and cause some excitation forces acting on the runner. To reduce these negative phenomena the six non-uniform blade runner has been designed using computational fluid dynamics modelling (CFD). The runner blades are placed in various axial distances from the guide vanes. This new design should reduce the pressure pulsations caused by interaction between the rib and the runner, which is the main negative effect by the current design. The forces and torque which are acting on the runner blades as well as the pressure inside the turbine are observed in time domain. The amplitudes and frequencies are analysed using Fast Fourier Transform (FFT). The frequencies are compared to the modal analysis results of the runner submerged in water. This hydraulic design is based on previous axial turbine, which was designed for small hydro power plant located at Lužnice River. The design point is defined by head H = 1,5 m, volumetric flow rate Q = 2,1 m3/s and RPM n = 260 min-1. This turbine was designed using six runner blades to reduce the pressure, force and torque pulsations caused mainly by wakes, which were observed behind the rib.

Resistance force pulsations of annular flow in the Couette-Taylor system with counter-rotating cylinders

The paper presents the results of an experimental study of the Couette-Taylor flow fluctuations in a ring channel with oppositely rotating multicylinder rotors. Experiments were carried out using water-glycerine solutions as a working fluid. The rotation resistance moment and its pulsations were investigated, using the system for measuring the torque resistance of rotation of rotors, made in the form of a digital dynamometer based on a tension sensor. The investigations made it possible to establish that the classic dependence of the appearance of Taylor vortices is observed in the slit flow of a multicylinder system rotating oppositely. It was shown that in the range of Reynolds numbers Re = (100 – 500), pulsations of dissipative processes with variable frequency and amplitude up to 10% of the mean value of rotation resistance are observed.

Analysis of dynamic characteristics of two-component granular mixture segregation in thin shear cell

Particle separation is important in industrial production. The granular powder exhibits the property that is like both fluid property and solid property, which makes it difficult to establish a mathematical model to reveal the particle motion mechanism. The fluid property of the granular powder can be partly explained by the classical fluid theory, but the solid property cannot be covered. Theories combining the fluid and solid properties are also used to explain the particle separation phenomenon. However, they are not in consensus about the granular theory to explain the particle separation mechanism. Friction dissipation, which represents the particle pairwise damp interactions, greatly influences the particle separation process. In order to understand the particle separation mechanism and the effect of friction coefficient on the particle motion, a three-dimensional discrete element model is used to simulate the separation of three-dimensional spherical binary particles in a cylindrical groove （shear cell）in this paper. Initially, the large particle is placed at the bottom and the other small particles pile into the groove. The shear flow of the particles is established by rotating the bottom plate of the groove. The large particles gradually jump to the top of the groove under the shearing action. The effect of particle friction coefficient on the separation is studied. Focusing on the characteristics of kinematics and dynamics in the jumping process of large particle, the influence of the friction coefficient on the trajectory, velocity and acceleration of particle are quantitatively analyzed. The conclusions are obtained as follows. 1) The process of large particle jumping can be divided into three stages: relaxation stage (the large particle stays at the bottom of the groove), the take-off stage (the large particle rises up), and the equilibrium stage(the large particle moves to the top and stays there). 2) The relaxation time decreases with friction coefficient increasing. 3) The equilibrium height of particles increases with friction coefficient increasing. 4) The amplitude of the force pulsation of the large particle increases with friction coefficient increasing. For the behavior analysis of the ascending motion of the large particle, we propose a neighborhood analysis method and define a floating factor. The ratio of the number of small particles arranged in the upper to that in the lower adjacent space of the large particle is defined as the buoyancy factor. It is found that the buoyancy factor drops sharply at the jumping point of the large particle, forming the opportunity for the large particle jumping. It is revealed that the take-off of the large particle is the result of both the high-frequency characteristics of force fluctuation and the steep drop of buoyancy factor. The rising motion of the big particle is determined by the force and the surrounding space.

RELATION BETWEEN STATIONARY AND MOVING PEDESTRIAN LOAD MODELS

The dynamic analysis of footbridges became common in recent years, but the approach to modelling pedestrian induced load is still inconsistent. This paper compares two different ways of modelling single pedestrian load. The response of the structure to stationary pulsating force is compared to the results given by the same force moving along simply supported beam. 300 randomly generated beams were used in this parametric study to describe the relation among these two approaches and parameters of the structure. The proposed formula was successfully applied to get more realistic estimation of response of the structure to a single walking pedestrian using stationary pulsating force.

A time domain three-dimensional sono-elastic method for ships’ vibration and acoustic radiation analysis in water

The classical three-dimensional hydroelasticity of ships is extend to include the effect of fluid compressibility, which yields the three-dimensional sono-elasticity of ships. To enable the predictions of coupled transient or nonlinear vibrations and acoustic radiations of ship structures, a time domain three-dimensional sono-elastic analysis method of acoustic responses of a floating structure is presented. The frequency domain added mass and radiation damping coefficients of the ship are first calculated by a three-dimensional frequency domain analysis method, from which a retardation function is derived and converted into the generalized time domain radiation force through a convolution integral. On this basis the generalized time domain sono-elastic equations of motion of the ship hull in water are established for calculation of the steady-state or transient-state excitation induced coupled vibrations and acoustic radiations of the ship. The generalized hydrodynamic coefficients, structural vibrations and underwater acoustic radiations of an elastic spherical shell excited by a concentrated pulsating force are illustrated and compared with analytical solutions with good agreement. The numerical results of a rectangular floating body are also presented to discuss the numerical error resultant from truncation of the upper integration limit in the Fourier integral of the frequency domain added mass coefficients for the retardation function.

The effects of the rotor-stator interaction on unsteady pressure pulsation and radial force in a centrifugal pump

An unsteady numerical analysis has been conducted to study the strong interaction between impeller blade and volute tongue of a centrifugal pump. The 3-D-URANS equations were solved with the shear stress transport turbulence model for a wide range of flow rates. These unsteady interactions are mostly related to the unsteady radial force due to an imbalance in the pressure field at the impeller periphery. This force represents dynamic load that are one of the most important sources of vibration and hydraulic noise. Based on this phenomenon, this work analyzes and gives a more realistic prediction of the pressure fluctuation and the radial force during steady and unsteady calculation by considering the effect of the change in the pump operating point. Actually, the pressure fluctuations in the impeller and the volute were recorded by mounting nine monitoring points on the impeller and volute casing. The results of the existing analysis has proven that the pressure fluctuation is periodic due to the relative position of impeller blade to volute tongue. The characteristics of the time domain and frequency domain of the pressure pulsation were analyzed under different coupling conditions. Fast Fourier transform was performed to obtain the spectra of pressure pulsation. Besides, the steady and unsteady forces were calculated around the impeller periphery to fully characterize the pump behavior. The obtained pump performance curves were numerically compared with the experimental ones, and the outcome have shown an acceptable agreement between both curves.

Bending-torsional instability of a viscoelastic cantilevered pipe conveying pulsating fluid with an inclined terminal nozzle

In the present study, dynamic stability of a viscoelastic cantilevered pipe conveying fluid which fluctuates harmonically about a mean flow velocity is considered; while the fluid flow is exhausted through an inclined end nozzle. The Euler-Bernoulli beam theory is used to model the pipe and fluid flow effects are modelled as a distributed load along the pipe which contains the inertia, Coriolis, centrifugal and induced pulsating fluid flow forces. Moreover, the end nozzle is modelled as a follower force which couples bending vibrations with torsional ones. The extended Hamilton's principle and the Galerkin method are used to derive the bending-torsional equations of motion. The coupled equations of motion are solved using Runge-Kutta algorithm with adaptive time step and the instability boundary is determined using the Floquet theory. Numerical results present effects of some parameters such as fluid flow fluctuation, bending-to-torsional rigidity ratio, nozzle inclination angle, nozzle mass and viscoelastic material on the stability margin of the system and some conclusions are drawn.

SPECIFIC ASSESSMENT METHOD OF RAILWAY BALLAST PARTICLE DEGRADATION BASED ON UNIQUE LABORATORY TEST

Purpose. There are specific, standardized laboratory test methods to assess railway ballast particle degradation; they are the Los Angeles (EN 1097-2) and the Micro-Deval abrasion (EN 1097-1) tests. These testing methods can’t take into consideration the real railway stress-strain circumstances of ballast materials, and they particles. In this paper the authors represent a specific laboratory fatigue breakage test of railway ballast materials. With this kind of testing method, the deterioration process of railway ballast particles can be assessed more realistic and precisely. Methodology. A special layer structure is built-up with elastic sublayer system and 30 cm thick ballast samples (from two different type andesite base rocks) that is loaded by dynamic, pulsating forces. Particle size distribution functions have to be recorded before and after a more million cycle fatigue test, but intermediate measurements are also executed. The measured data should be processed, and different parameters have to be calculated that are offered by international literature and researches. The test doesn’t consider the particle breakage due to hand-made and machine-made tamping, but it can simulate particle degradation due to more years’ railway traffic in laboratory circumstances. Findings. There is a development after the R&D work made and published in 2014: in 2017 and 2018 years the ballast particle deterioration process is given according to more intermediate fatigue cycles with individual measurements, that show more precise «picture» about the full particle degradation, i.e. breakage process. The authors give more precise correlation functions between the calculated parameters and load cycles during fatigue. Originality. The paper summed up the results of a specific developed laboratory test method for assessment of the breakage process of railway ballast particles according to two different railway ballast materials from andesite base rocks. Practical value. The results help with the calculation of approximate time interval of required ballast screening (cleaning) work in the future. This research is supported by the UNKP-17-4 New National Excellence Program of Ministry of Human Capacities.

Rubber friction: The contribution from the area of real contact.

There are two contributions to the friction force when a rubber block is sliding on a hard and rough substrate surface, namely, a contribution Fad = τf A from the area of real contact A and a viscoelastic contribution Fvisc from the pulsating forces exerted by the substrate asperities on the rubber block. Here we present experimental results obtained at different sliding speeds and temperatures, and we show that the temperature dependency of the shear stress τf, for temperatures above the rubber glass transition temperature Tg, is weaker than that of the bulk viscoelastic modulus. The physical origin of τf for T > Tg is discussed, and we propose that its temperature dependency is determined by the rubber molecule segment mobility at the sliding interface, which is higher than in the bulk because of increased free-volume effect due to the short-wavelength surface roughness. This is consistent with the often observed reduction in the glass transition temperature in nanometer-thick surface layers of glassy polymers. For temperatures T < Tg, the shear stress τf is nearly velocity independent and of similar magnitude as observed for glassy polymers such as PMMA or polyethylene. In this case, the rubber undergoes plastic deformations in the asperity contact regions and the contact area is determined by the rubber penetration hardness. For this case, we propose that the frictional shear stress is due to slip at the interface between the rubber and a transfer film adsorbed on the concrete surface.

Ships Bottom Cavities as Shock Absorbers in Waves

Bottom ventilated cavitation is the successfully proven ship drag reduction technology, but the impact of sea waves on ships with bottom cavities is the substantial concern for a broad technology implementation. The influence of waves on vertical force experienced by such ships is analyzed in this paper using a perturbation technique. The unperturbed cavity shape at given Froude number and cavity length was found from a nonlinear steady ideal fluid problem. The ship response to an impact of a wave of the given length and amplitude is considered as the one-frequency perturbation. This perturbation was found by combined consideration of compressible flow in the cavity and incompressible flow in the surrounding water. Computational examples relate to an earlier tested model with the bottom cavity restricted by skegs. The vertical forces on the model with bottom cavities and in cavitation-free conditions were compared in head and following seas. It was found that within the major part of the consider range of wavelengths the cavity acts as a shock absorber significantly reducing the vertical force pulsation and ship acceleration in waves.

Effect of Blade Wrap Angle on Performance of a Single-Channel Pump

To study the effect of blade wrap angle on energy performance and unsteady characteristics of the single-channel pump, a single-channel pump with specific speed of 140 was selected as experimental test model and three impeller models with blade wrap angle of 290°, 340° and 390° were respectively designed. The performance of different single-channel pumps with blade wrap angle of 290°, 340° and 390° respectively were tested. Based on the experimental study, the effect of blade wrap angle on the energy characteristics, head pulsation, pressure fluctuation and radial force of the single-channel pump was obtained and analyzed. The results show that with blade wrap angle increases from 290° to 390°, the maximum pump head and efficiency gradually increases and the maximum increase amplitude is 7.3% and 7.79% respectively. The minimum static pressure at impeller outlet under three schemes all occurs at 1.0Qd and bigger blade wrap angle can reduce the mixing loss at impeller outlet. With the increase of blade wrap angle, the head pulsation and pressure fluctuation all decrease gradually. The maximum eighth section under the small flow rate and under the big flow rate occurs at the volute second the section. A higher pressure fluctuation exists around volute tongue. The time-averaged radial force decreases as the blade wrap angle increases and its increase amplitude decreases as the flow rate increases. The research fruits can provide some reference and theoretical basis for the optimization of single-channel pumps.

Effect of the blade loading distribution on hydrodynamic performance of a centrifugal pump with cylindrical blades

The effect of the blade loading distribution on head, radial force and pressure pulsation of a low specific-speed centrifugal pump with cylindrical impeller blades were investigated in the present study. Blade shapes were obtained by adopting the 1D inverse design method, impellers with different blade loading curves were obtained while the distribution of the blade loading was carefully tailored. Threedimensional URANS simulation method based on the Shear stress transport (SST) k-ω turbulence model was employed for the analyzation of flow patterns. Numerical results including the pressure distribution and velocity profile were validated by comparing with the available experimental data, and an acceptable agreement was obtained. Three typical parameters of the blade loading curve, including the location of the fore-loading point (mpre), location of the aft-loading point (mpost) and slope of the rectilinear segment (K), were analyzed. Results showed that the well-designed blade loading curve, such as the fore-loading impeller, can effectively reduce the pressure pulsation amplitude and the radial force. The significant effect of the variation of the aft-loading point on pump hydrodynamic performance was also investigated. Meanwhile, pressure and velocity distributions at different slopes of the blade loading curves show that the fore-loading impeller produces more uniform flow issuing from the impeller than that of the pump with aft-loading impeller, thus reduces the radial force and pressure pulsation of the pump.

Mitigation of radial exciting force of rotary lobe pump by gradually varied gap

ABSTRACTThis paper presents a new structure of a rotary lobe pump cavity with gradually varied gap to mitigate the magnitude and fluctuation of the radial exciting force on the rotor. The geometry of the rotary lobe pump cavity is specially designed, so that the gap between the rotor and cavity is gradually changed during the rotors’ engaging. The flow in this geometry is numerically studied, and its effect on the pressure pulsation and radial exciting force is analysed, based on the dynamic mesh and local mesh reconstruction. Also, the mechanism of the mitigation of radial exciting force is briefly discussed. The value of the gap is an addition of gradually varied gap r (0∼rmax) and the base gap (original constant gap: 0.2 mm). As for the results, it is found that as the varied gap rmax value increases, the intensity of the reverse rotating vortex at the outlet decreases, and the secondary flow pulsation of the outlet section is effectively weakened. When rmax =0.1 mm, the radial exciting force in the y-direction on the rotor is reduced by 12% comparing with the equal gap, and the radial exciting force pulsation coefficient is 0.31. Meanwhile, the radial exciting force in the x-direction is reduced by 19% accordingly. The gradually varied gap cavity can effectively reduce the peak value of the pressure pulsation at outlet, weakening the influence of the rapid change of the outlet pressure on the radial exciting force. It is found that an optimal rmax of 0.1∼0.15 mm has a remarkable effect on the mitigation of pressure pulsation and radial exciting force.

The Response and Instability of Cross-Rope Suspension Towers Under Harmonic Excitation

The galloping or vortex-induced vibration of transmission lines will lead to a periodic excitations to the masts of the cross-rope suspension tower (CRST). The mast of the CRST is modeled as a straight beam with an elastic support subjected to a pulsating axial force on the top, which will change the stiffness of the mast, thereby resulting in produce harmonic excitation and instability. The dynamic characteristics of the system are investigated, which show that the bending frequency of the CRST decreases linearly with increase in axial static load, while it increases nonlinearly with the increase in boundary stiffness. Then, the method of multiple scales is adopted to analyze the vibration. It is found that the wind load on the mast brings primary resonance, but has no effects on instability. In addition, the steady state solution of the primary resonance is obtained by the polar form of the reduced amplitude modulation equations (RAMEs), with the effects of the following parameters on the vibration amplitude of the mast studied: the prestressing load in the guy, magnitude of the dynamic force, detuning parameter and wind load. Finally, the instability regions of two cases ([Formula: see text] near [Formula: see text] and [Formula: see text] near [Formula: see text]) are studied by the Cartesian form of the RAMEs, with focus on the influence of the axial harmonic load produced by the galloping of the transmission lines on the instability area. It is observed that the magnitude of excitation frequency of the dynamic force in the range of instability region becomes larger until the spring stiffness is increased up to a certain value.

The effects of blade stacking lean angle to 1400 MW canned nuclear coolant pump hydraulic performance

Canned nuclear coolant pump is used in the advanced third generation pressurized water reactor and is key equipment and unique rotating equipment in the first loop of a nuclear power plant. High efficiency, low power consumption, low axial force and low pressure pulsation are the significant hydraulic performance demanding to hydraulic components. Impeller is a key component of canned nuclear coolant pump. The blade stacking lean angle is one of the main geometric parameters in impeller design. Therefore, an investigation into the stacking lean angle to the canned nuclear coolant pump can be useful. In order to understand effects of stacking lean angle to canned nuclear coolant pump, this paper numerically investigated three different stacking lean angles. The validity of numerical simulation was confirmed through a comparison between numerical and experimental results. The performance change of canned nuclear coolant pump with the stacking lean angle was acquired. Hydraulic performance curve, axial force curve, static pressure distribution at impeller outlet and static pressure pulsation were performed to investigate the performance changes caused by the stacking lean angle. The results show that the stacking lean angle has important influence on the performance of canned nuclear coolant pump and should be paid attention to in the impeller design. Positive stacking lean angle is good for efficiency and reducing pressure pulsation in impeller. Negative stacking lean angle is good for increasing the head and reducing the axial force, while reducing pressure pulsation in static components.

In vitro validation of a novel mechanical model for testing the anchorage capacity of pedicle screws using physiological load application.

Biomechanical in vitro tests analysing screw loosening often include high standard deviations caused by high variabilities in bone mineral density and pedicle geometry, whereas standardized mechanical models made of PU foam often do not integrate anatomical or physiological boundary conditions. The purpose of this study was to develop a most realistic mechanical model for the standardized and reproducible testing of pedicle screws regarding the resistance against screw loosening and the holding force as well as to validate this model by in vitro experiments. The novel mechanical testing model represents all anatomical structures of a human vertebra and is consisting of PU foam to simulate cancellous bone, as well as a novel pedicle model made of short carbon fibre filled epoxy. Six monoaxial cannulated pedicle screws (Ø6.5 × 45mm) were tested using the mechanical testing model as well as human vertebra specimens by applying complex physiological cyclic loading (shear, tension, and bending; 5Hz testing frequency; sinusoidal pulsating forces) in a dynamic materials testing machine with stepwise increasing load after each 50.000 cycles (100.0N shear force + 20.0N per step, 51.0N tension force + 10.2N per step, 4.2Nm bending moment + 0.8Nm per step) until screw loosening was detected. The pedicle screw head was fixed on a firmly clamped rod while the load was applied in the vertebral body. For the in vitro experiments, six human lumbar vertebrae (L1-3, BMD 75.4 ± 4.0mg/cc HA, pedicle width 9.8 ± 0.6mm) were tested after implanting pedicle screws under X-ray control. Relative motions of pedicle screw, specimen fixture, and rod fixture were detected using an optical motion tracking system. Translational motions of the mechanical testing model experiments in the point of load introduction (0.9-2.2mm at 240N shear force) were reproducible within the variation range of the in vitro experiments (0.6-3.5mm at 240N shear force). Screw loosening occurred continuously in each case between 140N and 280N, while abrupt failures of the specimen were observed only in vitro. In the mechanical testing model, no translational motion was detected in the screw entry point, while in vitro, translational motions of up to 2.5mm in inferior direction were found, leading to a slight shift of the centre of rotation towards the screw tip. Translational motions of the screw tip of about 5mm in superior direction were observed both in vitro and in the mechanical testing model, while they were continuous in the mechanical testing model and rapidly increasing after screw loosening initiation in vitro. The overall pedicle screw loosening characteristics were qualitatively and quantitatively similar between the mechanical testing model and the human vertebral specimens as long as there was no translation of the screw at the screw entrance point. Therefore, the novel mechanical testing model represents a promising method for the standardized testing of pedicle screws regarding screw loosening for cases where the screw rotates around a point close to the screw entry point.