Backward Force Research Articles

An innovative joint-space dynamic theory for mobile multi-axis system with unilateral constraint

The wheel-ground unilateral constraint is essential in establishing the complete mobile multi-axis system dynamics. To reduce the calculation complexity and improve the dynamic performance, an innovative joint-space dynamic theory for mobile multi-axis systems with unilateral constraints is proposed. This present study builds on our existing explicit dynamics studies of tree-chain rigid multi-axis systems. By analyzing the formulation of the unilateral constraints, the complexity of establishing the constraint equations is reduced while the physical implications are clear. The constraint equations are derived and established based on the explicit partial derivative equations, where the expression of the constraint equations is greatly simplified. Then, based on the process of backward force iteration and in combination with the derived dynamic and unilateral constraint equations, the solution and analytical procedure for unilateral constraints are presented. The accuracy of the proposed method is proved by the three-wheeled multi-axis system and Mars rover examples. The proposed method is explicit, canonical, and symbolic and has the advantages of simple modeling and low computational complexity, which is analyzed by comparing it with the Open Dynamic Engine's approach.

Dynamics of centipede locomotion revealed by large-scale traction force microscopy.

We present a novel approach to traction force microscopy (TFM) for studying the locomotion of 10 cm long walking centipedes on soft substrates. Leveraging the remarkable elasticity and ductility of kudzu starch gels, we use them as a deformable gel substrate, providing resilience against the centipedes' sharp leg tips. By optimizing fiducial marker size and density and fine-tuning imaging conditions, we enhance measurement accuracy. Our TFM investigation reveals traction forces along the centipede's longitudinal axis that effectively counterbalance inertial forces within the 0-10 mN range, providing the first report of non-vanishing inertia forces in TFM studies. Interestingly, we observe waves of forces propagating from the head to the tail of the centipede, corresponding to its locomotion speed. Furthermore, we discover a characteristic cycle of leg clusters engaging with the substrate: forward force (friction) upon leg tip contact, backward force (traction) as the leg pulls the substrate while stationary, and subsequent forward force as the leg tip detaches to reposition itself in the anterior direction. This work opens perspectives for TFM applications in ethology, tribology and robotics.

Multi-objective optimization of a bistable curved shell with controllable thickness based on machine learning

Bistable curved shells have become a promising low-cost application in energy absorption fields owing to recent advances in material and technology. Significant research has been conducted to improve their energy absorption effect through forward prediction and single-objective optimization. However, these approaches may not fully explore their functional potential. In this study, we propose a multi-objective optimization framework based on the principle of main objective optimization that combines neural networks and genetic algorithms. The energy absorption effect and backward snapping force of the bistable curved shell are improved synchronously. Meanwhile, a reverse design algorithm is developed to generate the preset load-displacement curve, which further expands the application of machine learning methods in the field of multi-objective optimization. The combination of machine learning and multi-objective optimization is highly effective for building meta-structures with specific performance requirements and has potential applications in solving complex optimization tasks in various fields.

Heat transfer performance of copper foam/paraffin composite phase change material under different centrifugal forces-A visual experimental study

Copper foam is used to enhance the heat transfer of phase change material (PCM) due to its high thermal conductivity. However, its porous structure can restrict the convection of PCM. The natural convection of PCM embedded in copper foam under external force remains unclear. A visual experimental system was established to investigate the effect of copper foam on the heat transfer process of PCM under external force. The phase interface, temperature distribution, and heat storage rate of composite PCM (CPCM) were conducted under centrifugal forces from -5 g to 5 g. Results indicate that there is a significant difference in the melting rate and temperature distribution of PCM under different forces. Under forward force, the convection of PCM is inhibited, and the isotherm is parallel to the end-state isobars line, increasing the total melting time of CPCM and creating a large temperature gradient near the heat source. Conversely, under the backward force, the melting rate of CPCM is increased due to the enhanced natural convection of liquid PCM. The development of isotherms is influenced by buoyancy, which results in a more uniform temperature distribution of CPCM. However, the enhancement effect of the backward force is limited when it exceeds -3 g. In general, CPCM exhibits more apparent improvement in heat transfer performance under the backward force. This article provides references for the optimization design of thermal management systems.

Discussion on internal fixation of Hoffa fractures

Hoffa fracture is an unstable intra-articular fracture with significant redisplacement tendency. It is easy to be missed diagnosis when accompanied by distal intercondylar or supracondylar fracture of femur. CT scan is the gold standard for the diagnosis of Hoffa fracture. The treatment principles are anatomic reduction of the articular surface, reliable internal fixation, and early functional activity. At present, the main treatment is arthroscopic screw fixation. During screw fixation, the tail cap of screw should be buried, resulting in non-healing iatrogenic injury of articular cartilage. In the early postoperative functional activity of knee joint, fracture block was repeatedly subjected to backward and upward shear force under the action of the tibial plateau, which is the main reason for the failure of internal fixation. Plate assisted screw fixation could increase local mechanical stability, but it still cannot avoid the defects of iatrogenic cartilage injury. At the same time, plate molding is required during the operation due to the absence of special anatomical plates, resulting in increased surgical trauma and time-consuming surgery. The ideal fixation method for Hoffa fracture should include:(1) Avoid iatrogenic injury of articular surface cartilage. (2) With the rear anti-shear barrier plate function.(3) The internal fixator is closer to the load interface, so as to obtain greater load and better fixed strength.

Clinical significance of dynamical network indices of surface electromyography for reticular neuromuscular control assessment

BackgroundThere is currently no objective and accurate clinical assessment of reticular neuromuscular control in healthy subjects or patients with upper motor neuron injury. As a result, clinical dysfunctions of neuromuscular control could just be semi-quantified, efficacies and mechanisms of various therapies for neuromuscular control improving are difficult to verify.MethodsFourteen healthy participants were required to maintain standing balance in the kinetostatics model of Gusu Constraint Standing Training (GCST). A backward and upward constraint force was applied to their trunk at 0°, 20° and 25°, respectively. The multiplex recurrence network (MRN) was applied to analyze the surface electromyography signals of 16 muscles of bilateral lower limbs during the tests. Different levels of MRN network indices were utilized to assess reticular neuromuscular control.ResultsCompared with the 0° test, the MRN indices related to muscle coordination of bilateral lower limbs, of unilateral lower limb and of inter limbs showed significant increase when participants stood in 20° and 25° tests (P < 0.05). The indices related to muscle contribution of gluteal, anterior thigh and calf muscles significantly increased when participants stood in 20° and 25° tests (P < 0.05).ConclusionsThis study applied the dynamical network indices of MRN to analyze the changes of neuromuscular control of lower limbs of healthy participants in the kinetostatics model of GCST. Results showed that the overall coordination of lower limb muscles would be significantly enhanced during performing GCST, partly by the enhancement of neuromuscular control of single lower limb, and partly by the enhancement of joint control across lower limbs. In particular, the muscles in buttocks, anterior thighs and calves played a more important role in the overall coordination, and their involvement was significantly increased. The MRN could provide details of control at the bilateral lower limbs, unilateral lower limb, inter limbs, and single muscle levels, and has the potential to be a new tool for assessing the reticular neuromuscular control.Trial registration ChiCTR2100055090

Machine learning-based design and optimization of double curved beams for multi-stable honeycomb structures

Curved beams with bistable and negative stiffness properties can be used to design multi-stable metamaterials or honeycomb structures. Consequently, the deformation patterns and mechanical properties of curved beams under load have attracted many attentions. However, due to the nonlinear characteristics of variable thickness double curved beams, it is impossible to exhaust all possible structural forms through experimental and theoretical approaches. This paper presents a machine learning (ML) method for designing and optimizing double curved beam structures. The ML model is used to establish the underlying mapping relationship between thickness parameters and mechanical properties. After optimizing the double curved beam in different directions, the optimal thickness distributions of the backward snapping force and energy absorption are obtained. Double curved beams with optimal thickness distributions are used to construct multi-stable honeycomb structures, demonstrating the optimization process from single cell structure to periodic structure. Under the same mass, compared to the constant thickness honeycomb structure, the optimized variable thickness honeycomb structures exhibit a 140% increase in backward snapping force and a 57% increase in energy absorption. The objective of this study is to utilize machine learning technique to obtain a general approach for optimizing model of ‘multi-parameter input’ to ‘single-parameter output’, which is valuable for guiding the optimization and design of metamaterial structures in the future. This paper is a good case study of the mechanical structure performance optimization, whose implementation path is given detailly in appendix. Other disciplines with similar optimization goals can also use this method to carry out researches.

Generative optimization of bistable plates with deep learning

Bistate plates have found extensive applications in the domains of smart structures and energy harvesting devices. Most bistable curved plates are characterized by a constant thickness profile. Regrettably, due to the inherent complexity of this problem, relatively little attention has been devoted to this area. In this study, we demonstrate how deep learning can facilitate the discovery of novel plate profiles that cater to multiple objectives, including maximizing stiffness, forward snapping force, and backward snapping force. Our proposed approach is distinguished by its efficiency in terms of low computational energy consumption and high effectiveness. It holds promise for future applications in the design and optimization of multistable structures with diverse objectives, addressing the requirements of various fields.

Aerodynamic Analysis of Conventional and Boundary Layer Ingesting Propellers

Abstract The boundary layer ingestion (BLI) concept has emerged as a novel technology for reducing aircraft fuel consumption. Several studies designed BLI-fans for aircraft. BLI-propellers, although, have still received little attention, and the choice of open-rotors or ducted propellers is still an open question regarding the best performance. The blade design is also challenging because the BLI-propulsors ingest a nonuniform flow. These aspects emphasize further investigation of unducted and ducted BLI-propulsors and the use of optimization frameworks, coupled with computational fluid dynamics simulations, to design the propeller to adapt to the incoming flow. This paper uses a multi-objective NSGA-II optimization framework, coupled with three-dimensional RANS simulations and radial basis function (RBF) metamodeling, used for the design and optimization of three propeller configurations at cruise conditions: (a) conventional propeller operating in the freestream, (b) unducted BLI-propeller, and (c) ducted BLI-propeller, both ingesting the airframe boundary layer. The optimization results showed a significant increase in chord and a decrease in the blade angles in the BLI configurations, emphasizing that these geometric parameters optimization highly affects the BLI-blade design. The unducted BLI-propeller needs approximately 40% less shaft power than the conventional propeller to generate the same amount of propeller force. The ducted BLI-propeller needs even less power, 47%. The duct contributes to the tip vortex weakening, recovering the swirl, and turning into propeller force, as noticed from 80% of the blade span to the tip. However, the unducted and ducted BLI-configurations presented a higher backward force, 26% and 46%, respectively, compared to the conventional propeller, which can be detrimental and narrow the use of these configurations.

Study of clinicoradiological and functional outcomes of intramedullary nailing in diaphyseal radius ulna fractures in adults

Introduction: One of the most common fractures is a forearm fracture. The most common causes of these fractures include high-energy incidents, direct trauma, and falls from great heights. It's not unusual to have open wounds with a neurovascular impairment. Supination of the forearm with a backward and upward loading force with a forward angulation while falling on an outstretched hand is comparatively a less severe mechanism than pronation and upward force. Direct impact which is referred to as ‘Nightstick injury’ also lead to shaft of ulna fracture. The goal of this study was to assess the results of closed fixation in radius ulna fractures with intramedullary nailing for a minimum of 6 months. Nailing with square nails, titanium elastic nails (TENS nails), or long Kirschner wire has proven to be extremely effective. Method: Over the course of one year, this is a retrospective case series investigation of forearm bone fractures and the treatment options available. We chose patients where intramedullary nailing was used as a therapy option and were followed for at least 6 months. Galeazzi variety, monteggia variety, pathological fracture, and non-union following previous surgery were all ruled out. Disabilities of the arm, shoulder, and hand (DASH) score and Grace and Eversmann functional outcome score were used to assess the results. Results: Of the 25 patients, 14 patients had excellent functional outcome according to Grace and Eversmann score, 8 patients had good outcome, 4 patients had acceptable while 1 was unacceptable. The mean DASH score was 16.32. Conclusion: This study shows that closed method for fixation by intramedullary nailing of both bone forearm fractures leads to excellent to good functional outcomes (according to DASH score and Grace and Eversmann score) with less complications. In 6 months follow up x ray there is radiological union in all cases with no angulation, malunion or non-union.

Neglected physical human-robot interaction may explain variable outcomes in gait neurorehabilitation research.

During gait neurorehabilitation, many factors influence the quality of gait patterns, particularly the chosen body-weight support (BWS) device. Consequently, robotic BWS devices play a key role in gait rehabilitation of people with neurological disorders. The device transparency, support force vector direction, and attachment to the harness vary widely across existing robotic BWS devices, but the influence of these factors on the production of gait remains unknown. Because this information is key to designing an optimal BWS, we systematically studied these determinants in this work. We report that with a highly transparent device and a conventional harness, healthy participants select a small backward force when asked for optimal BWS conditions. This unexpected finding challenges the view that during human-robot interactions, humans predominantly optimize energy efficiency. Instead, they might seek to increase their feeling of stability and safety. We also demonstrate that the location of the attachment points on the harness strongly affects gait patterns, yet harness attachment is hardly reported in literature. Our results establish principles for the design of BWS devices and personalization of BWS settings for gait neurorehabilitation.

Left paratracheal pressure versus cricoid pressure for successful laryngeal mask airway insertion in adult patients: a randomized, non-inferiority trial.

Cricoid pressure (CP) is used to prevent pulmonary aspiration of regurgitated gastric contents and gastric insufflation during positive-pressure ventilation. However, CP impedes the successful insertion of laryngeal mask airway (LMA). Left paratracheal pressure (LPP), a maneuver of applying backward digital force at the lower left paratracheal level, was recently introduced as an alternative to CP. We assessed whether LPP is non-inferior to CP in successful LMA insertion on the first attempt in adult patients undergoing general anesthesia. In this non-inferiority randomized controlled trial, 108 patients undergoing general anesthesia were randomly allocated to receive either LPP or CP during LMA insertion. The primary outcome was the success rate of LMA insertion on the first attempt. The margin of non-inferiority was defined as 15%. The success rate of LMA insertion on the first attempt was 68.5% (37/54) in the LPP group and 51.9% (28/54) in the CP group (P=0.077) with between-group difference of 16.7% (two-sided 95% CI, -1.9% to 35.2%). Time for successful device insertion was comparable in the two groups (P=0.355), whereas LMA insertion was easier in the LPP group than in the CP group (P=0.001). There was no significant difference between the two groups for change in antral cross-sectional area measured before and after mask ventilation (P=0.081). No serious complication was evident in any group. This randomized clinical trial demonstrated the non-inferiority of LPP over CP in the success rate of LMA insertion on the first attempt in adult patients undergoing general anesthesia.

Interaction of the wakes of two flapping wings on control forces and moment

Control forces and moments of a flapping-wing system are highly affected by wakes and their interaction, but most studies have relied on estimations with an aerodynamic model, which cannot cover the effects of the wakes and the interaction. In this study, the effect of the wakes on the longitudinal control force and moment was investigated. A mean sweeping angle in various sets of wingbeat motion profiles was considered as a control input, and the forces and moments obtained from a rigid wing with an aspect ratio of four, which were controlled by a scaled-up robotic model, were converted to that on a virtual body. The results showed that adjusting a mean sweeping angle, which is originally expected to produce a nose-down moment and a consequent thrust to move forward by tilting a lift force, rather produced a considerable backward force due to the interaction of the wakes. This backward force was larger than the estimations, and the difference gradually increased with an increase in the mean sweeping angle in most of the motion profiles. The force was equivalent to 12.7% of the lift force at maximum, sufficient to resist an initial transition of a flapping-wing system during rapid maneuvers, which needs a strong control force. This suggests that at least for a mean sweeping angle, the effect of wakes must be taken into account.

KONTRIBUSI KEKUATAN OTOT LENGAN OTOT PERUT FLEKSIBILITAS TOGOK SERTA DAYA LEDAK OTOT TUNGKAI

Reject bullets are influenced by physical and engineering factors. Physical condition factors involve components of the body muscles, namely arm muscles, abdominal muscles, flexibility of the togok, as well as explosiveness in the limb muscles, and posture. While the technical factors involve stages such as the way or style used by the bullet repellent, one of which is the backward force (O'Brien style). This study aims to find out how much strength contributes to the arm muscles, to the abdominal muscles, the flexibility of the togok, as well as the explosiveness of the limb muscles, and contributes together strength to the arm muscles, strength in the abdominal muscles, flexibility of the togok, as well as explosiveness in the limb muscles to the results of repulsion pretence in the number of reject bullets using the O'Brien style. This type of research is descriptive research analysis with correlational method approach using coefficient of determination analysis. The population used in this study amounts to 58 students. Sampling techniques using total sampling. Based on the results of the analysis of research data can be found that the contribution of strength in the arm muscles to the results of repulsion achievement in the number of reject bullets using O'Brien style by 21.53%. The contribution of strength in the abdominal muscles to the results of repulsion in bullet reject numbers using O'Brien's style was 20.16%. The contribution of togok flexibility to the results of repulsion performance in the O'Brien-style reject number was 19.27%. The contribution of explosiveness in the limb muscles to the results of repulsion performance in the number of reject bullets using the O'Brien force was 17.14%. And from the double correlation analysis that has been done obtained a double coefficient of determination between the strength of the arm muscles, strength in the abdominal muscles, flexibility of the togok, as well as explosiveness in the limb muscles simultaneously contributed to the results of repulsion achievement in the number of reject bullets using O'Brien style of 45.10%.

Making Ecology Developmental: China’s Environmental Sciences and Green Modernization in Global Context

Although the science of ecology is often understood in antimodernizing terms, this article shows how ecology in China has become a means to articulate green modernization and sustainable development. As scholars predominantly focus on the policy rhetoric surrounding China’s national modernization and sustainable development program called “ecological civilization building,” the origins of how ecology came to take on developmental meanings remain obscure. This article highlights moments of global exchange and knowledge production by Chinese Marxists, earth systems scientists, and economists that produced eco-developmental logics. These logics define an interventionist role for the state, frame urbanization as moral progress, and refashion the role of the peasantry from the revolutionary vanguard to a backward social force impeding modernization. Ecological sciences in China, therefore, lay an epistemological foundation for legitimizing state-led technocratic practices of socioenvironmental engineering and naturalizing social inequalities between “urban” and “rural” people. In highlighting Chinese scientists’ agency in producing knowledge, this article counters diffusionist accounts of science as singular systematically organized branches of knowledge that emanate from the West. Instead, I demonstrate how ecology is contingent on the historical and political conditions through which it takes on meaning. In the context of China, ecology has become integral to environmental governance, state formation, and uneven relations of power.

From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats

We present a theory for the self-propulsion of symmetric, half-spherical Marangoni boats (soap or camphor boats) at low Reynolds numbers. Propulsion is generated by release (diffusive emission or dissolution) of water-soluble surfactant molecules, which modulate the air–water interfacial tension. Propulsion either requires asymmetric release or spontaneous symmetry breaking by coupling to advection for a perfectly symmetrical swimmer. We study the diffusion–advection problem for a sphere in Stokes flow analytically and numerically both for constant concentration and constant flux boundary conditions. We derive novel results for concentration profiles under constant flux boundary conditions and for the Nusselt number (the dimensionless ratio of total emitted flux and diffusive flux). Based on these results, we analyze the Marangoni boat for small Marangoni propulsion (low Peclet number) and show that two swimming regimes exist, a diffusive regime at low velocities and an advection-dominated regime at high swimmer velocities. We describe both the limit of large Marangoni propulsion (high Peclet number) and the effects from evaporation by approximative analytical theories. The swimming velocity is determined by force balance, and we obtain a general expression for the Marangoni forces, which comprises both direct Marangoni forces from the surface tension gradient along the air–water–swimmer contact line and Marangoni flow forces. We unravel whether the Marangoni flow contribution is exerting a forward or backward force during propulsion. Our main result is the relation between Peclet number and swimming velocity. Spontaneous symmetry breaking and, thus, swimming occur for a perfectly symmetrical swimmer above a critical Peclet number, which becomes small for large system sizes. We find a supercritical swimming bifurcation for a symmetric swimmer and an avoided bifurcation in the presence of an asymmetry.Graphic abstract

Improving reliability in electric drive systems during IGBT short‐circuit fault

To improve the reliability of electric drive systems during the insulated-gate bipolar transistor short-circuit fault, a control method is proposed for Y-connected 3-phase induction motors. This method allows the operation of 3-phase induction motor drives under the insulated-gate bipolar transistor short-circuit fault without the requirement of a specific inverter topology and control strategy. At first, a modified inverter topology that can rectify the problem produced by an insulated-gate bipolar transistor short-circuit fault is presented. Then, based on the introduced inverter topology, a developed model for Y-connected 3-phase induction motors is presented. According to this model, an indirect vector control system for the faulted drive system based on the calculation of forward and backward magneto-motive force of the motor is proposed. The performance of the control system is validated using experimental tests for a 1HP Y-connected 3-phase induction motor drive system. This research also compares the performance of the proposed indirect vector control technique with conventional indirect vector control techniques during the insulated-gate bipolar transistor short-circuit fault.

Energy-Saving Electrospinning with a Concentric Teflon-Core Rod Spinneret to Create Medicated Nanofibers.

Although electrospun nanofibers are expanding their potential commercial applications in various fields, the issue of energy savings, which are important for cost reduction and technological feasibility, has received little attention to date. In this study, a concentric spinneret with a solid Teflon-core rod was developed to implement an energy-saving electrospinning process. Ketoprofen and polyvinylpyrrolidone (PVP) were used as a model of a poorly water-soluble drug and a filament-forming matrix, respectively, to obtain nanofibrous films via traditional tube-based electrospinning and the proposed solid rod-based electrospinning method. The functional performances of the films were compared through in vitro drug dissolution experiments and ex vivo sublingual drug permeation tests. Results demonstrated that both types of nanofibrous films do not significantly differ in terms of medical applications. However, the new process required only 53.9% of the energy consumed by the traditional method. This achievement was realized by the introduction of several engineering improvements based on applied surface modifications, such as a less energy dispersive air-epoxy resin surface of the spinneret, a free liquid guiding without backward capillary force of the Teflon-core rod, and a smaller fluid–Teflon adhesive force. Other non-conductive materials could be explored to develop new spinnerets offering good engineering control and energy savings to obtain low-cost electrospun polymeric nanofibers.

Optimized Tension for AZ31B Thin Sheets Rolled with On-Line Heating Rolling

On-line heating rolling mill which could efficiently preheat sheet and apply tensile force on both ends of the sheet along rolling direction (RD) was used to investigate the effect of tension on mechanical behavior and shape quality of magnesium sheets. For revealing the influence mechanism, many analysis techniques including optical microscope, electron backscattered diffraction, macrotexture and transmission electron microscope were performed. The shape defect, edge wave, could be eliminated under higher tension along RD, which was attributed to more uniform distribution of microstructure and microstrain. Nevertheless, it is undesirable that the forward tensile force exceeds 3 kN in present work because the strength decreased for high recrystallization level when the tensile force is beyond this value. Furthermore, the main deformation mode was still slip during rolling process despite of accompanying twining, e.g., double twins, but more prismatic slip activated when tensile force exceeds 3 kN. The distribution of shear bands was affected by the applied tensile force that they appear as “V” shape along RD at a low forward or backward tensile force, while they appear as reticulate shape under applied tensile force of 5 kN.

Machine learning-based design and optimization of curved beams for multistable structures and metamaterials

Curved beams have been wildly used in MEMS (Micro-electromechanical systems) devices and energy absorption materials owing to its bistability. Almost all curved beams in previous studies have a constant thickness. Although better performance can be achieved by changing the thickness distribution, such as beams of uniform strength, lack of design and optimization tool limits the development and application of curved beams with varying thickness. In this paper, we demonstrate a new approach to design and optimize curved beams based on machine learning, which has been successful in many fields owing to its ability to process big data that can also be used in structural design and optimization. This machine learning-based model is able to achieve accurate predictions of nonlinear structure–property relationships. The optimized designs with different optimization objectives, such as stiffness, forward snapping force, and backward snapping force, are obtained efficiently and precisely. Experimental testing is conducted on specimens with optimized profiles, which are fabricated using a high-resolution multi-material 3D printer. The computational results are validated by the experimental results. The machine learning-based optimization approach developed here can provide a promising tool for the design and optimization of beam-based structures and mechanical metamaterials.