Dynamic Finite Element Model Research Articles

Assessment of submarine pipeline damages subjected to falling object impact considering the effect of seabed

Untrenched submarine pipelines lying on the seabed are vulnerable and can be damaged by the impact of falling objects. This may cause significant economic costs for repair and even environmental contamination in case of rupture and oil leakage. This paper presents assessment of submarine pipeline damage subjected to falling object impact considering the effect of seabed through nonlinear explicit dynamic finite element modelling. The numerical model was first verified against existing experimental results and established studies. A total of 209 cases of parametric study was then conducted to assess pipeline damage by accounting for various factors, including object mass, velocity and seabed conditions. The results show that the pipeline damage can be directly related to the impact kinetic energy of the falling object for pipelines sitting on rigid bed. In other words, falling objects with the same impact energy (while mass and velocity may vary) cause the same damage to a pipeline. For a pipeline on a soil seabed, however, this study shows that pipeline damage is no longer simplistically determined by the impact kinetic energy of the falling objects. Falling objects with different mass and velocity may cause different pipeline damages, even though the impact energy is the same. It is interesting to find out that objects with a smaller mass (i.e. higher velocity) tend to cause greater damage than objects with a greater mass (i.e. lower velocity), when the total impact kinetic energy of the falling objects is the same. These observations are explored in this paper, which is explained with the variation of the energy absorption due to the existence of soil seabed.

Computational simulation of pacifier deformation and interaction with the palate.

ObjectivesThe objective of this study is to demonstrate that computational finite element models can be used to reliably simulate dynamic interaction between a pacifier, the palate, and the tongue during nonnutritive sucking (NNS). The interactions can be quantified by the results of finite element analyses which include deformation, strain, stress, contact force, and contact area.Materials and MethodsA finite element model was created based upon CAD solid models of an infant pacifier and palate. The silicone pacifier bulb is represented by a hyperelastic constitutive law. Contact surfaces are defined between the pacifier and palate. A time and spatially varying pressure load is applied to the bulb representing peristaltic interaction with the tongue. A second time‐varying, periodic pressure representing NNS is applied to the model simultaneously. A large displacement, nonlinear transient dynamic analysis is run over two NNS cycles.ResultsResults from the finite element analysis show the deformed shape of the bulb with maximum principal elastic strain of 0.23 and a range of maximum principal stress on the palate from 0.60 MPa (tensile) to −0.27 MPa (compressive) over the NNS cycles. The areas of contact between the pacifier and the palate are shown in surface contour plots.ConclusionsA nonlinear transient dynamic finite element model can simulate the mechanical behavior of a pacifier and its interaction with the tongue and contact with the palate subject to NNS. Quantitative results predicting deformation, strain, stress, contact force, and contact area can be used in comparative studies to provide insight on how pacifiers cause changes in dental, orthognathic, and facial development.

On the Dynamic Tensile Behaviour of Thermoplastic Composite Carbon/Polyamide 6.6 Using Split Hopkinson Pressure Bar.

A dynamic tensile experiment was performed on a rectangular specimen of a non-crimp fabric (NCF) thermoplastic composite T700 carbon/polyamide 6.6 specimens using a split Hopkinson pressure (Kolsky) bar (SHPB). The experiment successfully provided useful information on the strain-rate sensitivity of the NCF carbon/thermoplastic material system. The average tensile strength at three varying strain rates: 700, 1400, and 2100/s was calculated and compared to the tensile strength measured from a standardized (quasi-static) procedure. The increase in tensile strength was found to be 3.5, 24.2, and 45.1% at 700, 1400, and 2100/s strain rate, respectively. The experimental findings were used as input parameters for the numerical model developed using a commercial finite element (FE) explicit solver LS-DYNA®. The dynamic FE model was validated against experimental gathering and used to predict the composite system’s behavior in various engineering applications under high strain-rate loading conditions. The SHPB tension test detailed in this study provided the enhanced understanding of the T700/polyamide 6.6 composite material’s behavior under different strain rates and allowed for the prediction of the material’s behavior under real-world, dynamic loading conditions, such as low-velocity and high-velocity impact.

Investigation on impact pressure and residual stress of water jet peening on AL6061-T6 with an inclined surface

Water jet peening (WJP) is a surface enhancement technique that can use the impact pressure to induce compressive residual stress in the narrow concave area of metal components. For WJP on the inclined surface, this research reveals the impact pressure evolution and the forming mechanism of compressive residual stress field (CRSF). Mathematical models of predicting the critical inclined angle θc and the maximum water hammer pressure Pm are developed. Besides, a 3D dynamic finite element model of WJP is developed. Then, the simulation model is verified by the experimental results of the inclined surface. Moreover, the influence of parameters such as inclined angle θ, jet velocity v, and jet diameter d on θc, Pm, and CRSF is investigated by simulation. The results indicate that Pm essentially determines the CRSF, and WJP parameters indirectly affect the CRSF by changing Pm. v determines θc, and θc increases with increasing v. θ and v determine Pm, and Pm decreases with increasing θ while increases with increasing v. The magnitude and depth of CRSF decrease with increasing θ while increases with increasing v. But d only affects the depth of CRSF, which increases with increasing d.

Research on Feature Extraction Method of Engine Misfire Fault Based on Signal Sparse Decomposition

Engine vibration signals are easy to be interfered by other noise, causing feature signals that represent its operating status get submerged and further leading to difficulty in engine fault diagnosis. In addition, most of the signals utilized to verify the extraction method are derived from numerical simulation, which are far away from the real engine signals. To address these problems, this paper combines the priority of signal sparse decomposition and engine finite element model to research a novel feature extraction method for engine misfire diagnosis. Firstly, in order to highlight resonance regions related with impact features, the vibration signal is performed with a high-pass filter process. Secondly, the dictionary with clear physical meaning is constructed by the unit impulse function, whose parameters are associated with engine system modal characteristics. Afterwards, the signals that indicate the engine operating status are accurately reconstructed by segmental matching pursuit. Finally, a series of precise simulation signals originated from the engine dynamic finite element model, and experimental signals on the automotive engine are used to verify the proposed method’s effectiveness and antinoise performance. Additionally, comparisons with wavelet decomposition further show the proposed method to be more reliable in engine misfire diagnosis.

The performance optimization of the stripper rubber for the rotating blowout preventer based on experiments and simulation

The rotating blowout preventer (RBOP) is an essential safety-ensuring equipment in underbalanced drilling. RBOP is vulnerable to fatigue failure resulted from being subject to a cyclic alternating load during pressure drilling. To enhance the lifespan of RBOP, this paper used a finite element simulation combined with experiments to realize a structural optimization of RBOP. The results showed that the optimal thickness of the iron frame for the stripper rubber is 34 mm, the optimal radius of the fillet is 12 mm, and the optimal inner diameters for the stripper rubber that seals 2–3/8″, 2–7/8″, 3–1/2″, 4″, 4–1/2″, and 5″ drill pipes are respectively 48 mm, 58 mm, 75 mm, 87 mm, 95 mm, and 100 mm. The optimized RBOP was examined in a test center and demonstrated a lifespan that was 2.18 times the national standard. When it was deployed in the drilling site, its lifespan was 2.8 times that before optimization. The improvement in the performance and lifespan of RBOP is very meaningful for ensuring security in the drilling site and lowering drilling cost for oil production. • Constitutive model of the rubber matrix is described. • A dynamic finite element model for stripper rubber is established. • The dynamic sealing process of stripper rubber is simulated. • The structure of the stripper rubber for failed parts was optimized. • The optimized stripper rubber was verified in the indoor and oilfield test.

Dynamics of perforated nanobeams subject to moving mass using the nonlocal strain gradient theory

In the present manuscript, based on the nonlocal strain gradient theory, a nonclassical dynamic finite element model is developed to study and analyze the dynamic behavior of perforated nanobeam structures under moving mass/load. In the context of nonclassical continuum mechanics and Timoshenko beam theory, dynamic equations of motion of perforated nanobeams are derived including both size scale (nonlocal) and microstructure (strain gradient) effects. The modification of the geometrical parameters due to the perforation process is included in the equations of motion for squared holes arranged in the arrayed form. The effect of the moving mass (the inertia, Coriolis and centripetal forces, and the gravity force) or moving load are included in the proposed model. To remove shear locking problem in slender nanobeams, finite element model on nonclassical shape function basis is developed. Elements stiffness and mass matrices and force vector including the nonlocal and strain gradient effects are derived. The proposed model is verified and checked with previous works. Impacts of perforation, mass/load velocities, inertia of mass, microstructure parameter and nonlocal size scale effects on the dynamic and vibration responses of perforated nanobeam structures have been investigated in a wide context. The following model is beneficial for the design of MEMS/NEMS structures such as frequency filters, resonators, relay switches, accelerometers, and mass flow sensors, with perforation.

Effect of the inlet oil temperature on vibration characteristics of the high-speed turbocharger rotor system

The inlet oil temperature of the rotor system with high-speed and light-load turbocharger will change during operation, which will change the vibration characteristics of the rotor system and even cause vibration accidents. Taking a certain type of high-speed and light-load turbocharger rotor system as the research object, the changes in oil film viscosity, friction power consumption, oil film temperature rise, and ring speed ratio with the inlet oil temperature of floating ring bearings are analyzed. A dynamic finite-element model of the turbocharger rotor–floating-ring-bearing system is constructed, and the finite-element model is verified through the critical speed and colormap spectrogram. The Newmark integral method is used to analyze the nonlinear transient response of the rotor system, and the influence of the inlet oil temperature on the vibration response characteristics of the rotor system is studied. The results show that an increase in the inlet oil temperature leads to a decrease in the internal and external oil film viscosities, frictional power consumption, temperature rise, and an increase in the ring speed ratio. When the inlet oil temperature increases from 50 °C to 130 °C, the amplitude of the inner oil film oscillation will gradually decrease, but the amplitude of the outer oil film vortex will gradually increase, and the journal speed point where the inner oil film oscillation and the outer oil film vortex will appear about 30% in advance. In summary, the rotor vibration is better when the inlet oil temperature is about 90 °C. The conclusion of this paper can provide a theoretical reference for selecting the operating parameters of the rotor system with the least vibration for high-speed light-load turbochargers.

Contact characteristic and vibration mechanism of rolling element bearing in the process of fault evolution

The vibration response of rolling element bearing has a close relation with its fault. An accurate evaluation of the bearing vibration response is essential to the bearing fault diagnosis. At present, most bearing dynamics models are built based on rigid assumptions, which may not faithfully reveal the dynamic characteristics of bearing in the presence of fault. Moreover, previous similar works mainly focus on the fault with a specified size without considering the varying contact characteristics as the fault evolves. This paper developed an explicit dynamics finite element model for the bearing with three types of raceway faults considering the flexibility of each bearing component in order to accurately study the contact characteristic and vibration mechanism of defective bearings in the process of fault evolution. The developed model is validated by comparing its simulation results with both analytical and experimental results. The dynamic contact patterns between the rolling elements and the fault, the additional displacement due to the fault and the faulty characteristics within the bearing vibration signal during the fault evolution process are investigated. The analysis results from this work can provide practitioners an in-depth understanding towards the internal contact characteristics with the existence of raceway fault and theoretical basis for rolling bearing fault diagnosis.

Comparative study on tunnel blast-induced vibration for the underground cavern group

Seismic wave induced by blasting excavation of tunnel may exert adverse effects to the surrounding rock. To study the different characteristics and attenuation of blast-induced vibration in the blasting tunnel and adjacent tunnel, field blasting tests are carried out to record velocity–time histories during blasting in Wanhua Underground Gas Storage. The characteristics and attenuation of vibration velocity and energy are presented based on the field data. And the dynamic finite-element model is established to further study the vibration attenuation law. Results demonstrate that PPV and vibration energy of the adjacent tunnel is greater than that in the blasting tunnel and attenuates more readily when monitoring points are near the blasting area. The dominant frequencies of the adjacent tunnel are higher than that in the blasting tunnel at three orthogonal directions. Adopting vibration energy as the evaluation index of seismic intensity, the fitting formula has favorable prediction accuracy, which will provide more accurate guidance for controlling the adverse effects of tunnel blasting.

Numerical analysis for estimating ballistic performance of armour material

Ballistic performance of naval ship structured material is analysed by formulating numerical simulation technique using 3-D explicit dynamic nonlinear finite element model in ANSYS®19. The methodology includes the effects of plastic deformation and facture of material describing flow stress, strain and strain rate hardening parameter under terminal high velocity ballistic impact. Initially, numerical simulation was carried on Weldox700E armour plate using Johnson-Cook strength and failure criteria with NATO ball bullet as impacting projectile for validation purpose. Further, the validated model is used to simulate the impact behaviour of Al5083 structural material subjected to high velocity impact of 7.62 × 39 mm mild steel core bullet having different thickness. The former simulation result was compared with available literature while the latter is evaluated using the experimental test findings. Residual velocity of projectile, failure mode and deformation pattern of target plate, projectile displacement and energy summary were used to determine characteristics of ballistic event. The methodology used in this paper demonstrates significant efficiency and adequacy of the implemented Johnson Cook model to determine a non-linear physical penetration mechanism and its experimental measurable parameters.

A Bioinspired Soft Robot Combining the Growth Adaptability of Vine Plants with a Coordinated Control System.

Tip-extending soft robots, taking flexible film or rubber as body material and fluid pressure as input power, exhibit excellent advantages in constrained and cluttered environments for detection and manipulation. However, existing soft continuum robots are of great challenges in achieving multiple, mutually independent, and on-demand active steering over a long distance without precise steering control. In this paper, we introduce a vine-like soft robot made up of a pressurized thin-walled vessel integrated with the high controllability of a control system with multiple degrees of freedom in three dimensions. Moreover, steering and kinematic models to relate the steering angle and robot length to the location of the robot tip are provided, and a dynamic finite element model for analyzing the motion of the spatial consecutive steering is established. We demonstrate the abilities of disinfection of the robot moving in a long and tortuous pipeline and detection in a multi-obstacle constrained environment. It is established that the robot exhibits great advantages in active consecutive steering over a long distance, high controllability in completing more complex path planning, and significant ability of carrying operational tools for ventilation pipeline disinfection and multi-obstacle detection. The bionic soft robot shows great promise for use in environment sensing, target detecting, and equipment servicing.

Settlement simulation of soft clay in the subway under dynamic load based on Midas GTS NX

The subway has become the main way for people to travel nowadays. The saturated soft clay area has a large population and subway construction is the most extensively distributed. The saturated soft clay foundation will settle under the dynamic load of the subway train, which will affect the service life and structural safety. To study the settlement characteristics of soft clay under the dynamic load of the subway, a three-dimensional dynamic finite element model was established based on the finite element software Midas GTS NX, and the soft clay under the normal design speed (80 km/h) and the high-speed (120 km/h) were compared and analyzed. The research results show that the higher the train speed, the larger the lateral influence range of the surface settlement trough, but the settlement decreases with the increase of the subway running speed. The settlement of the subway line after one year of operation is about 45mm, and the settlement after 20 years is about 58mm. The growth rate of the settlement prediction curve decreases gradually, and the settlement increment is very small for a long time in the later period of operation.

Application of Improved Dynamic Substructure Finite Element Model-Based State-Space Techniques in Mistuned Blisks

Aeroengine is a complex mechanical equipment, and it works at high temperature, pressure, rotational-speed, and severe loads. One of the core problems is that the vibration and mistuning of bladed disk lead to failure and affect the safety and reliability of aeroengine. Previously, one sector taken as the research object is not suitable; the integrally mistuned bladed disk (blisk) is taken as the research object is very necessary; however, the computational efficiency of mistuned blisk is very low. Therefore, a reduced-order model approach, i.e., an improved dynamic substructure finite element model-based state-space technique (IDSFEM-SST), is proposed to investigate the mistuned blisk. Firstly, the reduced-order substructure finite element model is established by this method, and then, the modal frequencies and modal strain energy amplitudes are investigated. Secondly, the maximum displacement responses are analyzed. Finally, the computational efficiency and accuracy of mistuned blisk via IDSFEM-SST is compared with that of the classical dynamic substructure finite element model and the high-fidelity finite element model to verify the effectiveness of this approach. This study has significance to the dynamic research and engineering practices for complex mechanical structures.

Organization of autonomous truck platoon considering energy saving and pavement fatigue

Autonomous truck platoons are currently proposed to drive in an aligned form for saving fuel, which will cause repeated wheel loads and shorten pavements’ service life. Therefore, platoon’s form needs to be reconsidered. Several forms were proposed from the aspects of vehicle number, longitudinal interval and lateral offset. Their influence was evaluated based on the computational fluid dynamics simulations and finite element model. Parameters in the simulations were collected from laboratory tests. The average fuel-saving rate for a two-truck platoon is 3.8–8.9% when the longitudinal interval varies from 5L to 0.5L. The fuel-saving rate, however, grows at a decreasing rate with the increase in truck number. Besides, the lateral offset is found to be effective when organizing the two-truck platoon, and above 30% decrease in pavement fatigue damage and 8% fuel savings will be obtained concurrently. The findings help the policy makers to reconsider the management of platoons.

Multi-Modal Natural Frequency Response of Utility Transmission Tapered Wood Poles Under Various Soil Foundation Conditions

Studied herein is the multi-modal natural frequency response of utility transmission tapered wood poles under various soil foundation conditions. Strong winds and hurricanes in various parts of the world have resulted in collapse of such utility poles and have resulted in the disruption of electrical distribution systems in addition to creating hazardous conditions for the public. To avoid the development of resonance under such dynamic loading, the multi-modal natural vibration of the utility poles first needs to be understood in the presence of practical soil foundation conditions. To capture the soil-structure interaction effects on the multi-modal frequencies, a SAP2000 dynamic finite element model is created in which the foundation soil stiffness is characterized by means of a series of ‘soil springs’ below the ground level. The properties of the soil springs vary with types of foundation soils and depths. Three types of foundation soils are considered, namely sandy, clayey soils and Granite (Rock). The results are compared to a standard fixed base model. It is found that the fundamental natural frequencies decreased by 52%, 37%, and 3% for sandy, clayey soils and granite, respectively, when compared to fixed base model. It was observed that there was an increase in the frequencies of the embedded utility poles in clay and granite, when compared to those with the fixed based after the 1st mode whereas, poles embedded in sandy soils showed increase in modal frequencies after the 3rd mode. The 10th mode appears to be a starting point of modal frequency convergence, while an apparent convergence occurs after the 20th mode. The convergent modal frequency was about 740 Hz for the Class H1 utility pole. However, there was a significant increase in the higher modal frequencies such as nearly 55% at the 20th mode, in all soil types when compared to the fixed base model.

Multi-Modal Natural Frequency Response of Utility Transmission Tapered Wood Poles Under Various Soil Foundation Conditions

Studied herein is the multi-modal natural frequency response of utility transmission tapered wood poles under various soil foundation conditions. Strong winds and hurricanes in various parts of the world have resulted in collapse of such utility poles and have resulted in the disruption of electrical distribution systems in addition to creating hazardous conditions for the public. To avoid the development of resonance under such dynamic loading, the multi-modal natural vibration of the utility poles first needs to be understood in the presence of practical soil foundation conditions. To capture the soil-structure interaction effects on the multi-modal frequencies, a SAP2000 dynamic finite element model is created in which the foundation soil stiffness is characterized by means of a series of ‘soil springs’ below the ground level. The properties of the soil springs vary with types of foundation soils and depths. Three types of foundation soils are considered, namely sandy, clayey soils and Granite (Rock). The results are compared to a standard fixed base model. It is found that the fundamental natural frequencies decreased by 52%, 37%, and 3% for sandy, clayey soils and granite, respectively, when compared to fixed base model. It was observed that there was an increase in the frequencies of the embedded utility poles in clay and granite, when compared to those with the fixed based after the 1st mode whereas, poles embedded in sandy soils showed increase in modal frequencies after the 3rd mode. The 10th mode appears to be a starting point of modal frequency convergence, while an apparent convergence occurs after the 20th mode. The convergent modal frequency was about 740 Hz for the Class H1 utility pole. However, there was a significant increase in the higher modal frequencies such as nearly 55% at the 20th mode, in all soil types when compared to the fixed base model.

Representative Environmental Condition for Fatigue Analysis of Offshore Jacket Substructure

The 20-year cumulative fatigue damage of an offshore jacket substructure was estimated under the long-term local environmental conditions in the Taiwan Strait. Because of the nonlinearity of wave load for slender members of the structure, time-domain simulations of the dynamic finite element model were conducted for each sea state. By utilizing the Dirlik method to process the stress signals, the fatigue damages of joints were computed. Concerning the computational time, we propose a probability-based method of using a representative combination of environmental conditions in this study, which can considerably reduce the required number of evaluations prior to determining fatigue damage, thereby improving the process of preliminary design. The results show that only three sea states among 120 can represent 28% of the average damage ratio, and up to 17 sea states fully resolved the fatigue life.

Evaluation of variable permeability model in simulation of seismic behavior of uniform level and gently sloping sand layers

In this study, a fully coupled dynamic finite element model was employed for numerical simulation of the response of level to gently sloping saturated sand layers subjected to cyclic loading. This model utilized a critical state two-surface-plasticity constitutive model to simulate the cyclic behavior of sandy soil. Moreover, a recently proposed variable permeability function was implemented in the numerical model to reflect the effects of soil permeability variations during the liquefaction phenomenon. The numerical model was validated by simulating a number of well-documented geotechnical centrifuge tests with different relative density of sand, base acceleration time history, and surface slope of the sand layer. The obtained results confirmed that the developed model was capable of simulating the behavior of saturated sand under cyclic loading for both level and gently sloping conditions.

Crush and crash analysis of an automotive battery-pack enclosure for lightweight design

The undesirable stresses and deformations during a high-speed crash can cause a short circuit or sudden fire in the battery packs, which represents a significant safety concern for vehicles. In this paper, computer-aided simulations are conducted to provide a supplemental and economic approach to evaluate the crashworthiness of a battery-pack enclosure. First, a nonlinear dynamic finite element model of a battery-pack enclosure is established and validated using the modal test. The crush and crash simulations, based on the governing equations and explicit FE code, LS-DYNA, are performed according to the test standard. Second, three high-strength steel materials are used in the validated finite-element model to perform a crashworthiness simulation with respect to robustness and lightweight design. The results show how both materials and thickness affect the crashworthiness of an automotive battery-pack enclosure. Finally, the weight of the battery-pack enclosure is reduced, while the crashworthiness is improved as well.