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1
Wu, Qiong, Lei Li, and Yi-Du Zhang. "Simulations and Experiments on Vibration Control of Aerospace Thin-Walled Parts via Preload." Shock and Vibration 2017 (2017): 1–7. http://dx.doi.org/10.1155/2017/8135120.
Повний текст джерелаАнотація:
Thin-walled parts primarily comprise the entire piece of rough machining, and the material removal rate can surpass 95%. Numerous components with thin-walled structures are preferred in the aerospace industry for their light weight, high strength, and other advantages. In aerospace thin-walled workpiece machining processes and practical applications, they are excited by the vibration. The preload changing the modal stiffness of the part is found and this change causes continuous changes in the natural frequency. Researching on the influence of pretightening force on dynamic characteristics of thin-walled components is highly significant for controlling vibration. In this study, the typical aviation thin-walled part is the research object. Finite element numerical simulation and experimental verification are employed to analyze the dynamic characteristics of 7075 aluminum alloy thin-walled plates under different preloads for exploring the relationship between natural frequency and preload. The relationship is validated by comparative results. Both the simulation and experimental results show that the natural frequencies of plates increase following the augmentation of the preload. Thus, this research introduces the method where vibration of aerospace thin-walled parts is reduced by preload. For practical engineering application, a program showing the relationship between natural frequency and preload is written using Visual Basic language.
2
Xia, Zhongxian, Yuhou Wu, Hua Wei, Kexuan Ren, Longfei Gao, Jian Sun, and Songhua Li. "Experimental Research on the Influence of Working Conditions on Vibration and Temperature Rise of Si3N4 Full-Ceramic Bearing Motors." Shock and Vibration 2021 (November 8, 2021): 1–16. http://dx.doi.org/10.1155/2021/1176566.
Повний текст джерелаАнотація:
Working conditions such as lubrication, preload, and rotational speed have important influence on vibration and temperature rise of the spindle motor. In this study, controlled variable experiments are carried out on the silicon nitride (Si3N4) full-ceramic ball bearing and steel bearing of the same type, and the vibration signal characteristics and temperature rise of the spindle motor are tested and analysed, by changing the lubrication conditions, preloads, and rotational speeds of the spindle motor. Through the research, it is found that as the rotational speed increases, the vibration velocity of the Si3N4 full-ceramic bearing spindle motor under different preloads and lubrication conditions shows an overall increasing trend; kurtosis generally presents a downward trend and gradually flattens, indicating that although the vibration velocity increases at high speeds, the vibration signal shows a relatively stable state. As the rotational speed increases, the difference of vibration velocity under the condition of applying preload and no preload decreases, indicating that the influence of preload on the vibration of full-ceramic bearing spindle motor decreases with the increase in rotational speeds. At the same time, it is found that fr and 5fr have greater impact on the vibration of full-ceramic bearing spindle motor, where fr is the frequency of the bearing in normal operation, and 5fr is 5 times of the normal operating frequency. Lubrication conditions have little effect on the temperature rise of full-ceramic bearing spindle motor, and the temperature rise under nonlubricated conditions is even slightly lower than that under grease lubrication conditions. The research results show that the vibration velocity and temperature rise of Si3N4 full-ceramic bearing spindle motor are less than those of steel bearing with the same type, indicating that full-ceramic bearing has better performance than steel bearing under the same working conditions.
3
Li, Xiao-hu, Yan-fei Zhang, Jun Hong, Hong Zhao, and Huan-feng Li. "Experiment analysis of spindle performance with rolling bearing under non-uniform preload." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 230, no. 17 (August 8, 2016): 3135–46. http://dx.doi.org/10.1177/0954406215605867.
Повний текст джерелаАнотація:
As a result of the manufacturing errors in the main parts of spindle, and the errors in assembly process of spindle, as well as the non-uniform heat distribution during spindle operation, the non-uniformly distributed preload in rolling bearing is inevitable. The non-uniform preload has not only axial force on the rolling bearing, but also the bending moment around the rolling bearing center. The effect of preload in bearing being non-uniform on the spindle performance is still unclear. In order to analyze the spindle performance with rolling bearing under non-uniform preload, a spindle test system with adjustable non-uniform distribution preload is built. By changing the magnitude of preload force on each action point, it can make the preload force distribute non-uniformly. In the static state of spindle, upon the change of non-uniformly distributed preload, the radial displacement of spindle shaft end is also changed, while in the dynamic state of spindle, it will lead to the change of the rotation center of spindle as a result of bending moment accompanying the non-uniform preload. Furthermore, the dynamic and static results show that when the preload is under non-uniform distribution, the spindle performance is significantly different from that under uniform preload. So this study would have certain reference value to check the spindle performance and explore novel preload method for rolling bearing.
4
Chen, Kai, Li Zu, and Li Wang. "Prediction of preload attenuation of ball screw based on support vector machine." Advances in Mechanical Engineering 10, no. 9 (September 2018): 168781401879916. http://dx.doi.org/10.1177/1687814018799161.
Повний текст джерелаАнотація:
Ball screw is a mechanical device widely used in mechanical field. The reverse clearance of ball screw will reduce its precision. In order to eliminate the reverse clearance, it is necessary to apply preload to the ball screw. It is very difficult to measure the preload in real time, and the data are large and time-consuming. By using machine learning method to predict and supervise preload, the changing trend of working condition of ball screw can be evaluated in advance, and the working precision of screw is controlled, which has important engineering significance. In this article, the relationship between the preload and the friction torque is obtained through theoretical derivation and experimental verification. Then, the support vector machine is used as a tool to model the friction torque of ball screw with the parameters of material, lubrication, and revolution, and predict the value and trend of preload to complete the supervision and prediction of the preload of the ball screw. By comparing the experimental results, it is proved that the support vector machine is feasible in predicting and supervising the attenuation of the preload of ball screw.
5
Scallan, Joshua P., John H. Wolpers, Mariappan Muthuchamy, David C. Zawieja, Anatoliy A. Gashev, and Michael J. Davis. "Independent and interactive effects of preload and afterload on the pump function of the isolated lymphangion." American Journal of Physiology-Heart and Circulatory Physiology 303, no. 7 (October 1, 2012): H809—H824. http://dx.doi.org/10.1152/ajpheart.01098.2011.
Повний текст джерелаАнотація:
We tested the responses of single, isolated lymphangions to selective changes in preload and the effects of changing preload on the response to an imposed afterload. The methods used were similar to those described in our companion paper. Step-wise increases in input pressure (Pin; preload) over a pressure range between 0.5 and 3 cmH2O, at constant output pressure (Pout), led to increases in end-diastolic diameter, decreases in end-systolic diameter, and increases in stroke volume. From a baseline of 1 cmH2O, Pin elevation by 2–7 cmH2O consistently produced an immediate fall in stroke volume that subsequently recovered over a time course of 2–3 min. Surprisingly, this adaptation was associated with an increase in the slope of the end-systolic pressure-volume relationship, indicative of an increase in contractility. Lymphangions subjected to Pout levels exceeding their initial ejection limit would often accommodate by increasing diastolic filling to strengthen contraction sufficiently to match Pout. The lymphangion adaptation to various pressure combinations (Pin ramps with low or high levels of Pout, Pout ramps at low or intermediate levels of Pin, and combined Pin + Pout ramps) were analyzed using pressure-volume data to calculate stroke work. Under relatively low imposed loads, stroke work was maximal at low preloads (Pin ∼2 cmH2O), whereas at more elevated afterloads, the optimal preload for maximal work displayed a broad plateau over a Pin range of 5–11 cmH2O. These results provide new insights into the normal operation of the lymphatic pump, its comparison with the cardiac pump, and its potential capacity to adapt to increased loads during edemagenic and/or gravitational stress.
6
ZANNOLI, ROMANO, IVAN CORAZZA, PAOLA CACCIAFESTA, and ANGELO BRANZI. "EVALUATING THE MECHANICAL BEHAVIOR OF A VENTRICULAR SIMULATOR." Journal of Mechanics in Medicine and Biology 05, no. 02 (June 2005): 369–73. http://dx.doi.org/10.1142/s0219519405001503.
Повний текст джерелаАнотація:
The mechanical performance of a ventricular simulator was characterized by recording Pressure-Volume loops for different preload and afterload conditions. The End Systolic Pressure-Volume Relationship was drawn to demonstrate a "physiological" behaviour. The external work of the artificial ventricle was calculated by the P-V loop area and the presence of the Frank–Starling mechanism was demonstrated. The P-V loop was obtained by recording the internal pressure and by integrating the flow signal recorded at the orifice of the artificial ventricular chamber. The preload was modified by increasing the level of the filling reservoir and the afterload was modified by shortening the thin tube that represents the hydraulic resistance. The measurements were repeated at two different volumes of the ventricular external chamber. The ventricular external work was calculated by measuring the P-V loop area in the different loading conditions. The sequence of the loops obtained by changing the preload and afterload show a well defined End Systolic Pressure-Volume Relationship that changes its slope by changing the volume of the ventricular external chamber. The ventricular mechanical simulator shows a "physiological" behaviour.
7
Alfares, Mohammed, Omar Saleem, and Majed Majeed. "Analytical study of thermal variation impact on dynamics of a spindle bearing system." Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 233, no. 4 (May 2019): 871–98. http://dx.doi.org/10.1177/1464419319841687.
Повний текст джерелаАнотація:
Changes in the thermal status of machine tools spindle-bearing system can have a noticeable effect on the performance of the machine itself, and therefore studying the thermal effect on the performance ball bearing during service is important. For this purpose, a study was carried out where a simple rotating shaft system supported by two angular contact ball bearings was taken into consideration. Heat was generated due to the contact between the balls and rings of the bearing. This thermal effect on the dynamics of the system was studied using a transient thermal model. The system was divided into nodes; each was assumed to be a uniform temperature. Thermal energy balance was used on each node to obtain a set of differential equations. ODE solver in MATLAB was used to solve the resulting system of differential equations. The thermal model considered an initial preload as well as the thermal preload that is caused by the uneven expansion of bearing components. In this research, a 5 DOF nonlinear dynamical system model is integrated with a spindle-bearing thermal model and then utilized to study the impact of preload variations on the spindle-bearing system of a grinding machine. The effect of different system parameters such as speed of rotation, type of bearing, ambient temperature, type of oil, initial preload on temperature output and thermal growth within the system was studied. The study shows that the heat generation rate is directly proportional to the rotational speed of the shaft and higher thermally induced preload is reached at higher speeds. It is also noticed that initial preload has a small effect on the heat generation, thermally induced preload, and temperature of the bearing. Also, the dominant frequency values of the spindle system generally increase with changing thermally induced preload values. This study is useful in predicting the thermal profile as well as preload value resulting in the bearing assembly, which in turn will be used to predict variation in the dynamics of the system.
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Yang, Xue, Chang Geng Shuai, and Shen Lin Yang. "Magnetorheological Effect of NDI Polyurethane-Based MR Elastomers." Advanced Materials Research 750-752 (August 2013): 832–35. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.832.
Повний текст джерелаАнотація:
The dynamic magnetorheological (MR) effects of 1,5-Naphthalene diisocyanate (NDI) polyurethane-based MR elastomers were tested by changing excitation frequency, excitation amplitude, magnetic strength, or preload. NDI polyurethane-based elastomers show high dynamic mechanical property, and were used as base material to prepare MR elastomers, whose mechanical performance and dynamic MR effect were tested. The results show that: (1) the prepared NDI polyurethane-based MR elastomers have high mechanical performance and MR effect; (2) their MR effect was reduced with the increase in excitation amplitude or preload, but did not change obviously with the increase in excitation frequency. Therefore, MR elastomer devices should be reasonably designed to maximize MR effect.
9
Turek, Paweł, Wacław Skoczyński, and Marek Stembalski. "Controlling the preload adjustment system of bearings in the machine spindle model using the LabVIEW environment." Mechanik 92, no. 11 (November 12, 2019): 698–700. http://dx.doi.org/10.17814/mechanik.2019.11.92.
Повний текст джерелаАнотація:
A test stand with a high speed spindle equipped with an active support, which provides the possibility of changing the preload of the bearings, was presented. The LabVIEW software environment was used for control. The benefits resulting from the use of the active system to reduce the amplitude of the vibration displacement of the spindle tip are presented.
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Long, Lian Chun, Zhong Ying Chen, and Zhi Guang Yang. "Research on Pre-Loaded Composite Irradiated by Laser Beam." Key Engineering Materials 462-463 (January 2011): 872–77. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.872.
Повний текст джерелаАнотація:
This paper investigates failure behavior tests of T300/AG80 composite laminated specimens under tensile and compressive preload using a load holding device and laser irradiation from an Nd: YAG laser. By changing the magnitudes of the preload and the power densities of the laser, the effects of preload and laser power density on the time-to-failure of the specimens were observed. The response process of specimens was synchronized taken in using high-speed camera in experiment. The experimental results showed that tensile mechanical properties of T300/AG80 composite laminated specimens were obviously superior to ones in compression test. The relational expressions between the time-to-failure of specimens and pre-loads as well as with laser power densities were acquired through fitting experiment data. The time-to-failure reduced with the pre-load increasing, the relationship is approximating linear when the laser power density kept invariable. When the pre-load kept unchanged, the time-to-failure reduced as the laser power density increased. The relationship is approximating exponential. A basis for life prediction of structure mechanically loaded in either tension or compression during the irradiation by laser is provided by fitting expression.
11
Brimioulle, Serge, Pierre Wauthy, Patricia Ewalenko, Benoı̂t Rondelet, Françoise Vermeulen, François Kerbaul, and Robert Naeije. "Single-beat estimation of right ventricular end-systolic pressure-volume relationship." American Journal of Physiology-Heart and Circulatory Physiology 284, no. 5 (May 1, 2003): H1625—H1630. http://dx.doi.org/10.1152/ajpheart.01023.2002.
Повний текст джерелаАнотація:
Assessement of right ventricular (RV) contractility from end-systolic pressure-volume relationships (ESPVR) is difficult due to problems in measuring RV instantaneous volume and to effects of changes in RV preload or afterload. We therefore investigated in anesthetized dogs whether RV ESPVR and contractility can be determined without measuring RV volume and without changing RV preload or afterload. The maximal RV pressure of isovolumic beats (Pmax) was predicted from isovolumic portions of RV pressure during ejecting beats and compared with Pmaxmeasured during the first beat after pulmonary artery clamping. In RV pressure-volume loops obtained from RV pressure and integrated pulmonary arterial flow, end-systolic elastance ( E es) was assessed as the slope of Pmax-derived ESPVR, pulmonary artery effective elastance ( E a) as the slope of end-diastolic to end-systolic relation, and coupling efficiency as the E es-to- E a ratio ( E es/ E a). Predicted Pmax correlated with observed Pmax( r = 0.98 ± 0.02). Dobutamine increased E es from 1.07 to 2.00 mmHg/ml and E es/ E a from 1.64 to 2.49, and propranolol decreased E es/ E a from 1.64 to 0.91 (all P < 0.05). After adrenergic blockade, preload reduction did not affect E es, whereas hypoxia and arterial constriction markedly increased E aand somewhat increased E es due to the Anrep effect. Low preload did not affect E es/ E a and high afterload decreased E es/ E a. In conclusion, in the right ventricle 1) Pmax can be calculated from normal beats, 2) Pmax can be used to determine ESPVR without change in load, and 3) Pmax-derived ESPVR can be used to assess ventricular contractility and ventricular-arterial coupling efficiency.
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CRON, THOMAS A., PATRICK HILTI, HARTMUT SCHACHINGER, CHRISTOS D. POUSKOULAS, DAGMAR I. KELLER, CHRISTIAN E. ZAUGG, PETER T. BUSER, MATTHIAS E. PFISTERER, and STEFAN OSSWALD. "Rate Response of a Closed-Loop Stimulation Pacing System to Changing Preload and Afterload Conditions." Pacing and Clinical Electrophysiology 26, no. 7p1 (July 2003): 1504–10. http://dx.doi.org/10.1046/j.1460-9592.2003.t01-1-00218.x.
Повний текст джерела
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Zhu, Bin Rong, Hai Jun Xing, and Jing Bo Yang. "Experimental and Finite Element Study on Mechanical Behavior of Bolted Joint with Bolt Clearance in Transmission Tower." Advanced Materials Research 625 (December 2012): 25–29. http://dx.doi.org/10.4028/www.scientific.net/amr.625.25.
Повний текст джерелаАнотація:
To accurately analyze the force and deformation of the transmission tower, it is necessary to study performance of bolted joint in the tower. In the paper single shear and double shear bolted joint with number of bolts changed is tested. Based on the actual data in test, nonlinear finite element model of bolted joint is established with ABAQUS, considering the bolt clearance and preload, and shows good agreement with test results, which is proved correct and applicable. Eventually, through a comparison of FEM and test results, the factors that affect bolt slip and the changing relationship of axial force of bolt and friction force is described.
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BAKOURI, MOHSEN, and MOHAMED YACIN SIKKANDAR. "NUMERICAL INVESTIGATION ON PRELOAD AND AFTERLOAD SENSITIVITY FOR USING VENTRICULAR ASSIST DEVICE ON HEART FAILURE PATIENTS." Journal of Mechanics in Medicine and Biology 20, no. 07 (September 2020): 2050042. http://dx.doi.org/10.1142/s0219519420500426.
Повний текст джерелаАнотація:
A left ventricular assist device (LVAD) is a surgically implanted mechanical pump being used for patients with end-stage heart failure (HF). One of the significant clinical challenges in using LVADs is its remarkable changes in hemodynamic parameters during a change in body position from supine to standing. In standing position, vasodilatation of veins occurs in the legs, which decreases left ventricular end-diastolic pressure, and, in turn, the preload to the LVAD. In this research, a numerical investigation is carried out to evaluate the effect of LVAD in cardiac hemodynamic parameters such as cardiac output (CO) and stroke work (SW) under preload, normal, and afterload conditions. A Proportional–integral–derivative (PID) controller associated with an LVAD pump model and cardiovascular system (CVS) model is developed to study the cardiac hemodynamic and its performance during HF condition by changing system parameters in one cardiac cycle. The performance of the proposed model is then evaluated using a pump cannulae model, real-time status detection of the aortic valve (av), and left ventricular stroke volume. The model parameters associated with HF, including contractility of the left and right ventricle ([Formula: see text] & [Formula: see text]), systemic peripheral resistance ([Formula: see text]) and total blood volume ([Formula: see text]) were set 0.71[Formula: see text]mmHg.s.mL[Formula: see text], 0.53[Formula: see text]mmHg.s.mL[Formula: see text], 1.11[Formula: see text]mmHg.s.mL[Formula: see text] and 5800[Formula: see text]mL, respectively, to allow simulation of HF conditions. The findings of this study show that the CO is increasing linearly with end-diastolic left ventricular volume (LVEDV) and end-diastolic right ventricular volume (RVEDV). However, other vital parameters behavior has a nonlinear relation to CO. Results of this study prove that the LVAD model is more sensitive to preload than afterload condition under different hemodynamical conditions.
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Chagué, F., A. Gudjoncik, C. Richard, F. Compagnon, O. Ganansia, V. Pasquereau, and Y. Cottin. "Effect of changing the preload on speckle-tracking-derived left ventricular contractility indexes in middle-aged ultra-trailers." Archives of Cardiovascular Diseases Supplements 9, no. 1 (January 2017): 57–58. http://dx.doi.org/10.1016/s1878-6480(17)30188-x.
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Osakue, Edward E., and Lucky Anetor. "Design of Elastic Screw Fasteners under Tensile Load." Mechanical Engineering Research 7, no. 1 (May 31, 2017): 13. http://dx.doi.org/10.5539/mer.v7n1p13.
Повний текст джерелаАнотація:
This paper presents an equivalent stress approach in the design of screw fasteners under tensile load. Design equations are formulated for sizing and verifying screw fastener selection. It considers axial tensile, direct shear, bending, and torsional stresses and combines them as appropriate into equivalent or effective stresses. The equivalent or effective stresses are compared with screw fastener material strength capabilities such as proof, yield, fatigue, and tensile strengths for failure assessment. Design factors are derived for assessing design adequacy the screw fastener. For elastic screw fasteners, these stresses must each be in the elastic range for the screw material. When the load is removed, elastic screw fasteners regain their original size and shape, behaving like springs. Two illustrative design examples are used to demonstrate both design verification and sizing tasks. Design verification was performed in the first example and the static yield design factors are found to be 0.77 and 0.68 for the preload and service load, respectively. These values are less than unity, representing a case of under-design in static yield failure modes. Without changing the specification of the screw fastener, the preload tension was reduced by 62.76%, and the static yield design factors changed to 1.42 and 1.12 for the preload and service load, respectively. This shows that the under-design condition resulted from high preload tension. When the screw pitch is changed from coarse to fine series, the design factors are worse off in fatigue stress resistance but indicated some improvement in static stress resistance. This suggests that fine pitch threads is not better than coarse pitch threads in fatigue stress capacity when direct shear and bending stresses are considered in Example 1. Both design sizing and verification are performed in Example 2. Design sizing suggests a screw fastener ( ) of slightly larger size than the previous solution ( ). Design verification indicates the previous solution and new solution has a minimum static yield design factor of 0.93 and 1.09, respectively for the service load. This suggests that the screw fastener of the previous solution may yield in service, if implemented. The new solution has a higher design factor in this failure mode and presents less risk of failure. From the illustrative examples presented, it seems that ignoring direct and bending stresses in screw fastener design can lead to under-design in some failure modes.
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Wright, G., and E. Hurn. "Cytochalasin inhibition of slow tension increase in rat aortic rings." American Journal of Physiology-Heart and Circulatory Physiology 267, no. 4 (October 1, 1994): H1437—H1446. http://dx.doi.org/10.1152/ajpheart.1994.267.4.h1437.
Повний текст джерелаАнотація:
We separated the K(+)-induced contraction of rat aortic rings into its initial (fast) and secondary (slow) components. It was found that temperature sensitivity, K+ depolarization, and Ca2+ dependency could each be utilized to differentiate between these two components of the contractile response. Increasing the passive tension preload of the tissue increased the fast response but had no significant effect on the secondary slow rise in tension. Cytochalasins, which inhibit actin polymerization, reversibly inhibited tension development by rat aortic rings with the effect selectively confined to the slow component of the K(+)-induced contraction. In a similar fashion, cytochalasin was shown to attenuate the slow tension increase caused by phorbol 12,13-dibutyrate. Finally, it was found that low concentrations of the protein kinase C (PKC) inhibitor staurosporine (8 x 10(-9) M) selectively attenuated the slow component of the K(+)-induced contraction. The results suggest that distinctly different mechanisms regulate the initial fast and secondary slow contractile responses induced by elevation of extracellular K+. Both mechanisms are voltage sensitive and use extracellular Ca2+. The fast but not the slow component was altered by changing the passive tension preload in a fashion consistent with a sliding filament mechanism of force development. The specific nature of the slow component is not certain but may involve low-level PKC activity and require the integrity and capability for remodeling of a specific portion of the actin-containing cytoskeleton.
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Pinsky, M. R., G. M. Matuschak, L. Bernardi, and M. Klain. "Hemodynamic effects of cardiac cycle-specific increases in intrathoracic pressure." Journal of Applied Physiology 60, no. 2 (February 1, 1986): 604–12. http://dx.doi.org/10.1152/jappl.1986.60.2.604.
Повний текст джерелаАнотація:
Changes in intrathoracic pressure (ITP) can influence cardiac performance by affecting ventricular loading conditions. Because both systemic venous return and factors determining left ventricular (LV) ejection may vary over the cardiac cycle, phasic increases in ITP may differentially affect preload or afterload if delivered at specific points within the cardiac cycle. We studied the hemodynamic effects of cardiac cycle-specific increases in ITP (pulses) delivered by a high-frequency jet ventilator in an acute closed-chested canine model (n = 11), using electromagnetic flow probes to measure biventricular stroke volume. Measurements were taken during a control condition after the induction of acute ventricular failure (AVF) by propranolol hydrochloride and volume infusion. ITP was independently varied without changing lung volume by the inflation of thoracoabdominal binders. Although synchronous pulses had minimal hemodynamic effects in unbound controls, binding pulses timed to occur in early diastole resulted in decreases in LV filling pressure and left ventricular stroke volume (SVlv) (P less than 0.05). In the AVF condition, pulses increased LV performance, evidenced by increases in SVlv (P less than 0.01), despite decreases in LV filling pressure (P less than 0.05). This effect is maximized by binding and by timing the pulses to occur in systole. We conclude that cardiac cycle-specific increases in ITP can significantly affect cardiac performance. These effects appear to be related to the ability of such timed pulses to selectively affect LV preload and afterload.
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McDonough, K. H., R. W. Barbee, C. Dobrescu, C. H. Lang, and J. J. Spitzer. "Enhanced myocardial depression in diabetic rats during E. coli sepsis." American Journal of Physiology-Heart and Circulatory Physiology 253, no. 2 (August 1, 1987): H276—H282. http://dx.doi.org/10.1152/ajpheart.1987.253.2.h276.
Повний текст джерелаАнотація:
The aim of this study was to determine whether diabetes enhanced the sensitivity of the myocardium to the deleterious effects of in vivo-administered Escherichia coli. Diabetes was induced in two groups of animals. One group received 70 mg/kg streptozotocin (iv) and exhibited a severe diabetes with elevated fasting and fed blood glucose concentrations and a markedly abnormal response to an oral glucose load. The second group received 45 mg/kg streptozotocin, was mildly diabetic (termed “latent” diabetes), and was characterized by normal fasting blood glucose but slightly elevated fed blood glucose and an abnormal response to a glucose load. A third group of rats received vehicle and served as time-matched control animals. Four weeks after induction of diabetes, all animals were catheterized under ether anesthesia and some received intraperitoneal injections of live E. coli. In vitro myocardial performance was assessed using the isolated, perfused working heart preparation. Ventricular function curves were generated by changing left atrial filling pressure and measuring changes in heart rate, cardiac output, and aortic peak systolic pressure. Cardiac performance in the severe diabetic group was depressed at the highest preload but was unchanged at lower preloads. Function in the latent diabetic group was not different from control. Sepsis induced a slight decrease in cardiac performance in the control group and resulted in larger reductions in the latent and severe diabetic groups. A depression in aortic flow was the major consequence of sepsis in the latent diabetic group, whereas decreased coronary flow was the primary change in the severe diabetic group.(ABSTRACT TRUNCATED AT 250 WORDS)
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Xu, Zhi Qian, Xiang Zhen Yan, and Xiu Juan Yang. "Sealing Structure Design and Analysis of Non-API Pipe Connection." Applied Mechanics and Materials 34-35 (October 2010): 811–14. http://dx.doi.org/10.4028/www.scientific.net/amm.34-35.811.
Повний текст джерелаАнотація:
In this paper, the main design parameters of seal structure for non-API pipe connection are studied. First, as the total contact pressure consists of the radial preload generated by interference fit and the radial pressure caused by gas pressure in pipe, the variation laws of their values changing with the sealing diameter are analyzed. The sealing diameter value which maximizes the total contact pressure can be obtained from the derivation formula for calculating the total contact pressure. Second, considering the yield condition of pipe connection under the internal and the external pressures, the minimum wall thickness of the seal structure is derived. Then the cone angle is calculated by the sealing length and the minimum wall thickness known. Finally, take the 7in casing connection for example, the main design parameters are calculated by the above analysis.
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Arpesella, G., E. Mikus, M. Arabia, A. Loforte, and P. M. Mikus. "Circulatory Assist with Centrifugal Pump as a Bridge to Recovery: Mathematical Analysis." International Journal of Artificial Organs 30, no. 7 (July 2007): 604–10. http://dx.doi.org/10.1177/039139880703000708.
Повний текст джерелаАнотація:
Mechanical circulatory support is an essential issue in the management of patients with end-stage cardiac failure. The aim of this study is to evaluate the efficacy of temporary support with a centrifugal blood pump as bridge to heart function recovery or bridge to transplantation. Heart recovery is achieved by improving ventricular mechanical working conditions with proper modifications of preload and afterload. This article assesses the advantages of a novel “cardiac chambers” cannulation setting versus the traditional one, in the case of biventricular or isolated right ventricular failure. The study was conducted using a numerical computer model based on the work by Guyton, Sagawa, Westerhof, and Noordergraaf. Simulation of the planned trials was achieved by changing the model parameters, the pump angular velocity, and the inflow and outflow settings. (Int J Artif Organs 2007; 30: 604–10)
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Matsumoto, T., Y. Mitamura, T. Shimooka, and T. Mikami. "The Effect of Left Ventricular Assist Device (Lvad) on Cardiac Reserve in Dogs." International Journal of Artificial Organs 12, no. 8 (August 1989): 533–38. http://dx.doi.org/10.1177/039139888901200809.
Повний текст джерелаАнотація:
The effect of LVAD on the preservation of cardiac reserve against ischemic damage was studied using Sarnoff's ventricular function curve. An LVAD was implanted between the canine left atrium and the aorta. Left ventricular function was measured by changing the height of the reservoir connected to the left atrium. The left ventricular function curve (LVFC) was drawn by plotting left ventricular stroke work (LVSW) against left atrial pressure (LAP). The coronary artery was occluded under a pump-on (ON group) or pump-off (OFF group). After reperfusion, measurements were repeated and changes in the LVFC caused by ischemia were compared in both groups. The gradient of the LVFC was significantly reduced by ischemia (107± 15ml/beat 80± 14, n= 13) but not in the ON group. LVSW under normal preload did not significantly change in either group. This suggests that the LVAD preserved cardiac reserve against ischemic damage.
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McDonough, K. H., V. Chen, and J. J. Spitzer. "Effect of altered thyroid status on in vitro cardiac performance in rats." American Journal of Physiology-Heart and Circulatory Physiology 252, no. 4 (April 1, 1987): H788—H795. http://dx.doi.org/10.1152/ajpheart.1987.252.4.h788.
Повний текст джерелаАнотація:
Effect of a chronic excess or deficit of thyroid hormone on intrinsic myocardial performance in rats was assessed. Animals were thyroidectomized or treated with thyroid hormone or vehicle 6-7 wk before the study. Body weight and heart weight were decreased in the hypothyroid group, and heart weight was elevated in the hyperthyroid group. Hearts were removed from thyroidectomized, euthyroid or thyroid-treated animals and studied as isolated, perfused working heart preparations. Ventricular function curves were generated by increasing left atrial filling pressure, whereas outflow resistance was not varied. Coronary flow, aortic outflow (and thus cardiac output), heart rate, and peak aortic systolic pressure were measured as a function of preload. These studies showed that performance of hearts from hyperthyroid animals was similar to that of euthyroid controls. Hearts from hypothyroid rats had decreased rate, pressure, and cardiac output but normal stroke volume. Since heart weight was 55% lower than control, normalization of volume work to dry heart weight reversed the difference in cardiac output. Comparison of hearts from hypothyroid animals to control rats of similar weight showed minimal differences in pump function. Thus hyperthyroidism did not result in altered in vitro cardiac output or peak systolic pressure as a function of changing preload when compared with age-matched euthyroid controls, hypothyroidism resulted in a decreased in vitro heart rate but greater cardiac output normalized to heart weight when compared with age-matched controls and hyperthyroid animals; external pacing of hypothyroid hearts yielded myocardial work parameters that were comparable to euthyroid control rats of similar body weight; and cardiac efficiency was significantly greater in hypothyroid hearts than in hyperthyroid hearts.(ABSTRACT TRUNCATED AT 250 WORDS)
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Hu, Sheng-Yen, Yuan Kang, Hsin-Ming Fu, and Chao-Ping Huang. "Identification of design parameters for spool-type restrictors." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, no. 1 (June 4, 2019): 63–72. http://dx.doi.org/10.1177/1350650119854248.
Повний текст джерелаАнотація:
This study presents the identification method of design parameters for single-action cylindrical spool-type restrictors of hydrostatic bearing. These parameters include restriction parameter, spool displacement parameter, and spring preload. The flow rates, inlet pressures, and outlet pressures are measured to be utilized for parameter identification of single-action cylindrical spool-type restrictors by using experimental equipment. This equipment-like an open-type planar hydrostatic bearing supports a worktable for changing recess pressure by changing apply load. Then, design parameters can be identified from the measurements of the inlet pressure, the recess pressure, average temperature, and the flow rate for each restrictor by using minimizing total error square between measured and identified quantities of flow rates. An identification method with experiments for single-action cylindrical spool-type restrictors of hydrostatic bearing is presented and designed. Also, the influences of design parameters on flow rate of single-action cylindrical spool-type restrictors are studied by experiments. The experimental equipment used in this study is our design, which can be used for all types of restrictors and hydrostatic bearings. This identification method for design parameters of the single-action cylindrical spool-type restrictors is reliable, valid, and accurate. The identification of design parameters is necessary for design change and calibration of single-action cylindrical spool-type.
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Li, Pu, and Qi Yuan. "Stress variation of a gas turbine tie-bolt rotor with Hirth serrations considering assembling and thermal effects." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 234, no. 24 (June 15, 2020): 4932–44. http://dx.doi.org/10.1177/0954406220932602.
Повний текст джерелаАнотація:
Tie-bolt rotors are commonly applied in heavy-duty gas turbines due to a better stiffness-mass ratio behavior compared to traditional integral rotors. In order to achieve a steady transformation from mechanical energy to electricity, the clamping force of the bolt is critical to keep multiple disks as a whole unit. However, the tensile stress of the bolt is changing during rotor assembly as well as operational conditions that should be considered carefully for the rotor safety. Moreover, subjected to mechanical as well as thermal loads, the stress of the rotor disks is a complicated mixture by different applied forces. In this manuscript, the preload variation during the process of rotor assembling is studied analytically with the help of the stiffness analysis. Then, a steady thermal analysis is performed with appropriate boundary conditions. Making use of the thermal-mechanical approach, a steady-stress distribution under different load combinations is achieved. Furthermore, a thorough insight into the stress level as well as the contact pressure of Hirth serrations is presented.
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Houlihan, D. F., C. Agnisola, A. R. Lyndon, C. Gray, and N. M. Hamilton. "Protein synthesis in a fish heart: responses to increased power output." Journal of Experimental Biology 137, no. 1 (July 1, 1988): 565–87. http://dx.doi.org/10.1242/jeb.137.1.565.
Повний текст джерелаАнотація:
The effects of exercise on the rates of protein synthesis in the chambers of the trout heart were investigated in vitro and in vivo. An in vitro rainbow trout heart preparation was developed which permitted perfusion of the coronary supply to the compact region of the ventricular muscle. This preparation was used to examine the mechanical responses to preload pressures, the oxygen consumption at different power outputs and the rates of protein synthesis in the various heart components. By increasing preload pressure it was possible to double cardiac output, oxygen consumption and power output without changing heart rate. Mechanical efficiency of the hearts was approximately 20%. Perfusion of the coronary vessels improved cardiac output. Protein synthesis was measured in isolated hearts by the incorporation of [3H]phenylalanine added at high concentration (1.35 mmol l-1) to the perfusion medium. The various chambers of the heart showed marked differences in their rates of protein synthesis. Increasing cardiac output and power output in vitro by twofold over 20 min increased the fractional rate of protein synthesis by approximately 2.5-fold in the atrium and ventricle but did not affect the rates in the bulbus arteriosus. Perfusion of the coronary vessels significantly increased the rates of protein synthesis of the compact layer of the ventricle. In vivo there were no significant differences in the fractional protein synthesis rates between the atrium and ventricle; slow-speed continuous swimming over 40 min (1.5 body lengths s-1) caused an increase in the rates of protein synthesis in all the chambers except the bulbus arteriosus. The stimulation in the fractional rates of protein synthesis by approximately 32% was not as great as in vitro. Both in vivo and in vitro the increased rates of protein synthesis occurred without any change in RNA to protein ratios, indicating an improved activity of protein synthesis per unit of RNA. It is concluded that short-term increases in cardiac contractility, possibly acting through the mechanical stretch on the cardiac muscle, stimulated protein synthesis, particularly in the ventricle, through increased ribosomal activity.
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Konecny, Filip. "The Left Ventricular End-Systolic Pressure Correlation with Aortic Valve Timing; a Novel Inotropic Index Description Using a Dual Pressure Catheter." Journal of Cardiology and Clinical Management 1, no. 1 (March 5, 2022): 1–16. http://dx.doi.org/10.56391/jccm.2022.1012.
Повний текст джерелаАнотація:
Myocardial contraction is generated by ventricular pressure in early systole by the isometric force against closed valves, as ventricle is contracting without changing volume. This initial contractile phase of cardiac cycle (early systole) is followed by rapid shortening, isotonic contraction, allowing ejection of the blood against changing LV afterload. LV is coupled to the systemic arterial pressure; hence LV ejection is closely linked to the properties of the aortic valve, aorta, and its distributing arteries. Isometric relationship in the LV was characterized using the load-dependent example (naïve vs. post-dobutamine), observed mostly in case of rate of rise of LVP, LV ESP and decrease of pulse wave velocity, characteristics of LV baroinometry. Furthermore, by performing load-independent maneuver, afterload (LV ESP) was adjusting at every cardiac cycle, while an assessment of LV ESP and aortic valve timing was able to be established. By plotting decaying LV ESP against aortic valve timing, highly linear correlation of load-independent isotonic, but also an isometric contractility was captured. Steeper linear slope and time-axis intercept (IC) were identified in case of post-inotropic challenge, recapitulating changes otherwise measured during pressure-volume exam. This relationship, measured by dual-pressure catheter, could serve as novel inotropic index of functional cardiac contractility. Keywords: Left Ventricle (LV); Contractility; Inotropy; Load-Dependent and Independent; Stressed Volume; Dual Pressure Catheter. 1. Assessment of cardiac contractility using dual pressure catheter. 2. IVCO inferior vena cava occlusion, ECC excitation-contraction coupling, EF ejection fraction, TTE transthoracic echocardiography, Ea end arterial elastance, PRSW preload recruitable stroke work, IC intercept, PWV pulse wave velocity.
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Bonello, Philip, Michael J. Brennan, Stephen J. Elliott, Julian F. V. Vincent, and George Jeronimidis. "Designs for an adaptive tuned vibration absorber with variable shape stiffness element." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 461, no. 2064 (October 4, 2005): 3955–76. http://dx.doi.org/10.1098/rspa.2005.1547.
Повний текст джерелаАнотація:
An adaptive tuned vibration absorber (ATVA) with a smart variable stiffness element is capable of retuning itself in response to a time-varying excitation frequency, enabling effective vibration control over a range of frequencies. This paper discusses novel methods of achieving variable stiffness in an ATVA by changing shape, as inspired by biological paradigms. It is shown that considerable variation in the tuned frequency can be achieved by actuating a shape change, provided that this is within the limits of the actuator. A feasible design for such an ATVA is one in which the device offers low resistance to the required shape change actuation while not being restricted to low values of the effective stiffness of the vibration absorber. Three such original designs are identified: (i) A pinned–pinned arch beam with fixed profile of slight curvature and variable preload through an adjustable natural curvature; (ii) a vibration absorber with a stiffness element formed from parallel curved beams of adjustable curvature vibrating longitudinally; (iii) a vibration absorber with a variable geometry linkage as stiffness element. The experimental results from demonstrators based on two of these designs show good correlation with the theory.
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Slinker, B. K., and S. A. Glantz. "Beat-to-beat regulation of left ventricular function in the intact cardiovascular system." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 256, no. 4 (April 1, 1989): R962—R975. http://dx.doi.org/10.1152/ajpregu.1989.256.4.r962.
Повний текст джерелаАнотація:
A variety of regulatory mechanisms have evolved to control the heart's pump function because the cardiovascular system must continually adapt to the changing demands that body functions place on it. This regulation takes place through many physiological systems; however, fine adjustments in cardiac pumping probably require adaptations more quickly than external control mechanisms (such as the autonomic nervous system) can compensate. Thus cardiac pumping is also regulated by mechanisms intrinsic to the heart. To better understand these intrinsic control mechanisms, we studied the beat-to-beat response of left ventricular function to continually varying changes in loading conditions produced by transiently occluding the pulmonary artery, venae cavae, and aorta. We used multiple linear regression to identify and quantify the important beat-to-beat determinants of left ventricular systolic function, quantified as stroke work. We could not adequately explain or predict beat-to-beat changes in stroke work with traditional determinants of ventricular function, preload, afterload, and heart rate, because a large systematic error remains after taking these traditional determinants of function into account. To eliminate this systematic error, we had to include some function of previous beat stroke volume and end-systolic size and pressure. This additional information significantly improved both our ability to model the observed transient changes in left ventricular stroke work and to predict additional observations that were not used to develop our model. We conclude that previous beat contraction history is an important determinant of left ventricular function and implies an important regulatory mechanism whereby the left ventricle can fine tune its function from beat to beat in response to continually changing loading conditions.
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Wang, Yingying, Cong Wang, Guoheng Liu, Chong Zhang, and Jianchang Li. "An Assessment Method of Sealing Performance and Stress Intensity Factors at Crack Tip of Subsea Connector Metal Sealing Rings." Energies 15, no. 13 (June 26, 2022): 4680. http://dx.doi.org/10.3390/en15134680.
Повний текст джерелаАнотація:
Subsea connectors are of a critical part for the sealing of subsea production systems. The working environment makes cracks initiate easily on subsea connector sealing rings. In order to ensure the safety and reliability of the sealing rings, it is necessary to study the crack’s influence on them. In this study, the main parameters that may influence stress intensity factors at crack tip are discussed. The sealing requirements of the subsea connector metal sealing rings were conducted. A finite element model was established to obtain the maximum equivalent stress and maximum equivalent plastic strain of crack-free sealing ring. Meanwhile, the influence of crack depths, crack positions, and crack angles on the sealing performance in preload and operating states was simulated through changing XFEM crack’s parameters in ABAQUS software, as well as their influence on stress intensity factors at the crack tip. The research shows that although the cracks have little effect on the sealing performance of sealing rings in the early stage, the stress intensity factors increase with the crack depths. Long-term use leads to crack propagation, structure breakage, and sealing failure. The research results are of some reference value for improving the safety and reliability of subsea connectors in practical engineering applications.
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Mou, Shann-Chyi. "Structure Design and Stepping Characteristics Analysis of the Biaxial Piezoelectric Actuated Stage Using a Thin-Disc Piezoelectric Actuator." Advances in Mechanical Engineering 6 (January 1, 2014): 121497. http://dx.doi.org/10.1155/2014/121497.
Повний текст джерелаАнотація:
In this paper, a novel thin-disc piezoelectric actuator, 4-9-9-14 piezoelectric actuator, is used to construct and drive the micro/nanometer level biaxial piezoelectric actuated stage. The 4-9-9-14 piezoelectric actuator offers a better balanced capability of forward rotation and reverse rotation than the conventional edge-driving piezoelectric actuator. The biaxial piezoelectric actuated stage structure comprises a base, a V-shaped guide rail, an optical scale measurement system, a preload adjusting structure, and a load-carrying stage. The movement signals of the piezoelectric actuated stage are read and analyzed by means of NI PCI-6115 data acquisition card and LabVIEW software operating in conjunction with a linear optical scale. The new consideration of tuning Ton time is used in place of the traditional method of changing the magnitude of driving voltage to control the stepping distance of the stage. A combined driving signal is based on the sum of a continuous driving signal for Ton time and a DC signal for Ton time; the combined driving signal is continuously output in this manner to form a continuous driving pulse chain. Under a constant driving voltage, the displacement of the stage increases with Ton time and the displacement of the stage decreases with Ton time.
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Wi, Jun-Hee, Kwang-Hee Lee, and Chul-Hee Lee. "Self-loosening of 3D printed bolted joints for engineering applications." MATEC Web of Conferences 185 (2018): 00029. http://dx.doi.org/10.1051/matecconf/201818500029.
Повний текст джерелаАнотація:
A bolt joint is a simple element that joins mechanical components. Self-loosening of bolted joints occurs due to the vibrations caused by motors and engines, resulting in the breakage of machines, and potentially serious safety problems. Recently, developments in 3D printing technologies have enabled the fabrication of detailed components. These technologies can be used for producing fasteners using 3D printed bolts. Many researchers have proposed a theoretical model for self-loosening of the bolt, and experimental studies on the self-loosening phenomenon have been advanced. However, studies on the self-loosening of 3D printed bolts have not been conducted. Therefore, it aims to confirm the self-loosening phenomenon and the safety of 3D printed bolts through experiments and finite element simulation. A lateral vibration test system is constructed and self-loosening of the bolt is evaluated by observing the axial force according to the vibration cycle by using a strain gauge. This study compared the self-loosening of 3D printed bolts and steel bolts by changing the preload and amplitude. In addition, the experimental results are verified through finite element simulation. Through this study, it is expected that 3D printed bolts will be used more frequently in situations where specially shaped bolts are needed.
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Nour, Sayed, Guifu Wu, Zheng Zhensheng, Juan C. Chachques, Alain Carpentier, and Didier Payen. "The Forgotten Driving Forces in Right Heart Failure: New Concept and Device." Asian Cardiovascular and Thoracic Annals 17, no. 5 (October 2009): 525–30. http://dx.doi.org/10.1177/0218492309348638.
Повний текст джерелаАнотація:
Background: Right heart failure is a frequent hemodynamic disturbance in pediatric cardiac patients. Besides inotropic and chronotropic drugs, fluid administration and inhaled nitric oxide, right ventricular mechanical assistance remains difficult to perform. A circulatory assist device adapted for the right heart biophysics and physiology might be more efficient. Materials and Methods: We are developing a prototype of a non-invasive cardiac assist device (CAD) for neonates and pediatrics. It is based on a pulsatile suit device covering and affecting all territories of the right heart circuit. It will be tested in a neonatal animal model of right ventricular (RV) failure. Experimental models will be matched and compared with control and sham groups. Expected results would be immediate hemodynamic improvement due to synchronized diastolic reduction of stagnant venous capacitance, increasing preload and contractility. On long term, increased shear stress with changing intrathoracic pressure in a phasic way would improve and remodel the pulmonary circulation. Future studies will be focused on: hemodynamic, biochemistry, endothelium function test, and angiogenesis. Comments: A non-invasive CAD guarantees better hemodynamics and endothelial function preservation with low morbidity and mortality. This is a physiological approach, cost-effective method, and particularly interesting in neonates and pediatrics with RV failure.
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Ghafoor, Abdul, Jian S. Dai, and Joseph Duffy. "Stiffness Modeling of the Soft-Finger Contact in Robotic Grasping." Journal of Mechanical Design 126, no. 4 (July 1, 2004): 646–56. http://dx.doi.org/10.1115/1.1758255.
Повний текст джерелаАнотація:
This paper investigates the soft-finger contact by presenting the contact with a set of line springs based on screw theory, reveals the rotational effects, and identifies the stiffness properties of the contact. An elastic model of a soft-finger contact is proposed and a generalized contact stiffness matrix is developed by applying the congruence transformation and by introducing stiffness mapping of the line springs in translational directions and rotational axes. The effective stiffnesses along these directions and axes are hence obtained and the rotational stiffnesses are revealed. This helps create a screw representation of a six-dimensional soft-finger contact and produce an approach of analyzing and synthesizing a robotic grasp without resorting to the point contact representation. The correlation between the rotational stiffness, the number of equivalent point contacts and the number of equivalent contours is given and the stiffness synthesis is presented with both modular and direct approaches. The grasp thus achieved from the stiffness analysis contributes to both translational and rotational restraint and the stiffness matrix so developed is proven to be symmetric and positive definite. Case studies are presented with a two-soft-finger grasp and a three-soft-finger grasp. The grasps are analyzed with a general stiffness matrix which is used to control the fine displacements of a grasped object by changing the preload on the contact.
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Sun, Y., M. Beshara, R. J. Lucariello, and S. A. Chiaramida. "A comprehensive model for right-left heart interaction under the influence of pericardium and baroreflex." American Journal of Physiology-Heart and Circulatory Physiology 272, no. 3 (March 1, 1997): H1499—H1515. http://dx.doi.org/10.1152/ajpheart.1997.272.3.h1499.
Повний текст джерелаАнотація:
A phenomenological model of the cardiopulmonary circulation is developed with a focus on the interaction between the right heart and the left heart. The model predicts the hemodynamic consequences of changing circulatory parameters in terms of a broad spectrum of pressure and flow waveforms. Hemodynamics are characterized by use of an electrical analog incorporating mechanisms for transseptal pressure coupling, pericardial volume coupling, intrathoracic pressure, and baroreflex control of heart rate. Computer simulations are accomplished by numerically integrating 28 differential equations that contain nonlinear and time-varying coefficients. Validity of the model is supported by its accurate fit to clinical pressure and Doppler echocardiographic recordings. The model characterizes the hemodynamic waveforms for mitral stenosis, mitral regurgitation, left heart failure, right heart failure, cardiac tamponade, pulsus paradoxus, and the Valsalva maneuver. The wave shapes of pulmonary capillary wedge pressure under the above conditions are also accurately represented. Sensitivity analysis reveals that simulated hemodynamics are insensitive to most individual model parameters with the exception of afterload resistance, preload capacitances, intrathoracic pressure, contractility, and pericardial fluid volume. Baseline hemodynamics are minimally affected by transseptal coupling (up to 2%) and significantly affected by pericardial coupling (up to 20%). The model should be useful for quantitative studies of cardiopulmonary dynamics related to the right-left heart interaction under normal and disease conditions.
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Zhong, Lingwei, Haijun Wang, Xuhua Ren, and Lei Tang. "Influence of the Cyclic Loading Path on Rock Deformation Memory Effect." Geofluids 2020 (November 23, 2020): 1–14. http://dx.doi.org/10.1155/2020/8896344.
Повний текст джерелаАнотація:
Deformation rate analysis utilizes deformation memory effect (DME) that is one of the fundamental properties of rock, to estimate in situ stress underground. It could be influenced by the stress history which has been subjected to in the past. To understand the influence under the cyclic loading path, in the experimental study, different stress levels were applied on sandstone samples and two types of granite samples. In the theoretical investigation, the sliding friction model consisting of multiple microstructure surfaces is considered in this paper. Both experiments and the theoretical model show that when the number of cyclic loading times keeps increasing, (1) the stress read at the DRA inflection is getting closer to the previously cyclic stress; (2) the angle at the DRA inflection becomes sharper, which gives clearer inflection point; and (3) the strain differential amplitude in the DRA curve gradually decreases and then toward a stable value. An upper limit exists for influence, indicating that the best cyclic loading times occur when the pulse amplitude of the strain differential stops changing. It is confirmed that the multiple cyclic loading method provides a better outcome for experiment using artificial preload when DME is utilized for stress reconstruction. Without other factors disturbing, the memory information of the in situ stress would hardly lose under the history of cyclic loading.
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Piene, H., and E. S. Myhre. "Position of interventricular septum during heart cycle in anesthetized dogs." American Journal of Physiology-Heart and Circulatory Physiology 260, no. 1 (January 1, 1991): H158—H164. http://dx.doi.org/10.1152/ajpheart.1991.260.1.h158.
Повний текст джерелаАнотація:
The impact of the transseptal pressure gradient (TSP) during the entire heart cycle has not been assessed. This study explores in anesthetized open-chest dogs the interventricular septum's relative position to the anteroposterior transverse diameter (Dap) of the left ventricle (LV). By varying preload and afterload for both LV and right ventricle (RV) and inotropy in LV, a wide range of TSP was generated. By ultrasonomicrometry the distance between the Dap and the midpoint of septum was recorded. 1) Loops of the septal-LV free-wall diameter vs. Dap showed that the LV transverse cross section independent of loading conditions tended to reach a circular form during systole. 2) Paradoxical movement of the intraventricular septum occurred when TSP was less than zero but was not dependent on an increase of TSP. 3) TSP's influence on septum's position was reduced to one-tenth when changing from end diastole to end systole. 4) During systole independent of level of LV performance, LV pressure had approximately 50% less influence on septal position than RV pressure. 5) During depressed LV performance a similar pattern was evident during diastole. 6) The pericardium had no influence on septum's position. This study demonstrates that the position of the intraventricular septum is significantly influenced by the time-varying elastance of LV and the septum itself, and that RV pressure changes have a greater impact on septal position than LV pressure changes.
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Prabhu, S. D., M. M. Rozek, D. R. Murray, and G. L. Freeman. "Ryanodine and left ventricular function in intact dogs: dissociation of force-based and velocity-based indexes." American Journal of Physiology-Heart and Circulatory Physiology 273, no. 3 (September 1, 1997): H1561—H1568. http://dx.doi.org/10.1152/ajpheart.1997.273.3.h1561.
Повний текст джерелаАнотація:
After anesthesia and autonomic blockade, nine dogs chronically instrumented with left ventricular (LV) micromanometers and piezoelectric dimension crystals were studied before and after the intravenous administration of 4 micrograms/kg ryanodine, a specific inhibitor of the sarcoplasmic reticulum Ca2+ release channel. Ryanodine prolonged LV contraction and relaxation (P < 0.001) without changing heart rate, end-diastolic volume (EDV), or end-systolic pressure. Velocity-dependent mechanical parameters were significantly depressed, including the maximal rate of LV pressure rise (dP/dtmax; P < 0.002), the mean velocity of circumferential fiber shortening (P < 0.002), the slope of the dP/dtmax-EDV relation (P < 0.05), and the time constant of LV relaxation (P < 0.01). In contrast, the slopes of the end-systolic pressure-volume (PES-VES) and stroke work (SW)-EDV relations, both force-based parameters, were increased (P < 0.05) or maintained, respectively. Ryanodine reduced overall LV contractile performance, evidenced by significant rightward shifts of the PES-VES, dP/dtmax-EDV, and SW-EDV relations and reduced SW at constant preload (P < 0.02). Thus, in the closed-chest dog, low-dose ryanodine resulted in 1) generalized slowing of LV mechanical events without changes in heart rate or load, 2) dissociation of velocity-based and force-based measures of LV function, with depression of the former but enhancement or maintenance of the latter, and 3) reduced overall LV inotropic performance. These effects are consistent with ryanodine-induced alterations of the Ca2+ transient and altered sarcoplasmic reticulum Ca2+ availability.
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Calbet, José A. L., and Robert Boushel. "Assessment of cardiac output with transpulmonary thermodilution during exercise in humans." Journal of Applied Physiology 118, no. 1 (January 1, 2015): 1–10. http://dx.doi.org/10.1152/japplphysiol.00686.2014.
Повний текст джерелаАнотація:
The accuracy and reproducibility of transpulmonary thermodilution (TPTd) to assess cardiac output (Q̇) in exercising men was determined using indocyanine green (ICG) dilution as a reference method. TPTd has been utilized for the assessment of Q̇ and preload indexes of global end-diastolic volume and intrathoracic blood volume, as well as extravascular lung water (EVLW) in resting humans. It remains unknown if this technique is also accurate and reproducible during exercise. Sixteen healthy men underwent catheterization of the right femoral vein (for iced saline injection), an antecubital vein (ICG injection), and femoral artery (thermistor) to determine their Q̇ by TPTd and ICG concentration during incremental one- and two-legged pedaling on a cycle ergometer and combined arm cranking with leg pedaling to exhaustion. There was a close relationship between TPTd-Q̇ and ICG-Q̇ ( r = 0.95, n = 151, standard error of the estimate: 1.452 l/min, P < 0.001; mean difference of 0.06 l/min; limits of agreement −2.98 to 2.86 l/min), and TPTd-Q̇ and ICG-Q̇ increased linearly with oxygen uptake with similar intercepts and slopes. Both methods had mean coefficients of variation close to 5% for Q̇, global end-diastolic volume, and intrathoracic blood volume. The mean coefficient of variation of EVLW, assessed with both indicators (ICG and thermal) was 17% and was sensitive enough to detect a reduction in EVLW of 107 ml when changing from resting supine to upright exercise. In summary, TPTd with bolus injection into the femoral vein is an accurate and reproducible method to assess Q̇ during exercise in humans.
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Weber, Howard S. "Serial echocardiographic Doppler evaluation of diastolic function in the normal human fetus." Cardiology in the Young 6, no. 1 (January 1996): 32–36. http://dx.doi.org/10.1017/s1047951100003218.
Повний текст джерелаАнотація:
AbstractThe assessment of diastolic function in the developing fetus is difficult because of constantly changing conditions of loading. Previous reports suggesting improved ventricular compliance with fetal development are limited by the Doppler indices utilized. Using load-dependent and independent variables, we examined and compared serially right and left ventricular diastolic function in 11 normal fetuses (44 echocardiographic studies) at 22±1.0 weeks; 30±1.0 weeks; 36±1.0 weeks of gestation and 64±25 hours postnatally. Load-dependent indices included early to late time velocity integral ratios and percentage of early filling to total diastolic filling. The load-independent index was the peak filling rate normalized to the total time velocity integral. Both right and left ventricular time velocity integral ratios were similar initially, and shifted from late to early diastole with increasing gestational age (greater ratios). The shift in left ventricular ratios was greater, and increased earlier in fetal development. The right ventricular normalized peak filling rate decreased with increasing gestational age, while the left ventricular normalized peak filling rate remained constant, but was greater than the right ventricular rate postnatally. Both right and left ventricular filling shifts from late “active” to early “passive” diastole during fetal development. Left ventricular ratios are greater and increase earlier in fetal development, likely influenced by changes in preload. The right and left ventricular normalized peak filling rates were similar prenatally, indicating similar diastolic filling properties, but disparate postnatally, consistent with improved left ventricular relaxation immediately preceding or at the time of onset of transitional circulation.
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Yang, Kun, Lei Zhou, Gang Wang, Tao Nie, and Xin Wu. "Experimental study on the performance of ultra high pressure common rail system." Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University 39, no. 4 (August 2021): 883–90. http://dx.doi.org/10.1051/jnwpu/20213940883.
Повний текст джерелаАнотація:
In order to overcome the difficulties of high pressure source design and parts integration in the injector, realizing the ultra high pressure injection and controllable fuel injection rate, an ultra high pressure common rail system based on domestic basic materials and manufacturing technology level was proposed and designed. The working principle of this system was first introduced; the performance test bench of ultra high pressure common rail system was built. Then, the influence of pressure-amplifier device structure parameters on the pressurization pressure peak was analyzed quantitatively, and on the basis of selecting the most appropriate combination of parameters, the pressure and fuel injection rate control characteristics were conducted. The results show that ultra high pressure common rail system can magnify fuel pressure to ultra high pressure state (more than 200 MPa) and by changing the control signal timing of pressure-amplifier device and injector solenoid valve, the flexible and controllable fuel injection rate can be achieved. Under the condition of the same pressurization ratio, the peak value of pressurization pressure increases gradually, and with the increase of pressurization ratio, the increasing trend of the pressurization pressure peak value is nonlinear. At the same time, under the same condition of spring preload, the greater of the spring stiffness, the higher of the rail base pressure can bear, that means the pressure-amplifier device can achieve pressurization at a higher base pressure. But if the spring stiffness is too large, the solenoid valve of pressure-amplifier device will not be opened due to insufficient electromagnetic force, so the specific selection should be considered in a compromise.
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How, Ole-Jakob, Ellen Aasum, Stanley Kunnathu, David L. Severson, Eivind S. P. Myhre, and Terje S. Larsen. "Influence of substrate supply on cardiac efficiency, as measured by pressure-volume analysis in ex vivo mouse hearts." American Journal of Physiology-Heart and Circulatory Physiology 288, no. 6 (June 2005): H2979—H2985. http://dx.doi.org/10.1152/ajpheart.00084.2005.
Повний текст джерелаАнотація:
In the present study, we tested the reliability of measurements of pressure-volume area (PVA) and oxygen consumption (MV̇o2) in ex vivo mouse hearts, combining the use of a miniaturized conductance catheter and a fiber-optic oxygen sensor. Second, we tested whether we could reproduce the influence of increased myocardial fatty acid (FA) metabolism on cardiac efficiency in the isolated working mouse heart model, which has already been documented in large animal models. The hearts were perfused with crystalloid buffer containing 11 mM glucose and two different concentrations of FA bound to 3% BSA. The initial concentration was 0.3 ± 0.1 mM, which was subsequently raised to 0.9 ± 0.1 mM. End-systolic and end-diastolic pressure-volume relationships were assessed by temporarily occluding the preload line. Different steady-state PVA-MV̇o2 relationships were obtained by changing the loading conditions (pre- and afterload) of the heart. There were no apparent changes in baseline cardiac performance or contractile efficiency (slope of the PVA-MV̇o2 regression line) in response to the elevation of the perfusate FA concentration. However, all hearts ( n = 8) showed an increase in the y-intercept of the PVA-MV̇o2 regression line after elevation of the palmitate concentration, indicating an FA-induced increase in the unloaded MV̇o2. Therefore, in the present model, unloaded MV̇o2 is not independent of metabolic substrate. This is, to our knowledge, the first report of a PVA-MV̇o2 relationship in ex vivo perfused murine hearts, using a pressure-volume catheter. The methodology can be an important tool for phenotypic assessment of the relationship among metabolism, contractile performance, and cardiac efficiency in various mouse models.
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Knight, Jason, Simon Fels, Benjamin Beazley, George Haritos, and Andrew Lewis. "Fluid–Structure Interaction of Symmetrical and Cambered Spring-Mounted Wings Using Various Spring Preloads and Pivot Point Locations." Applied Mechanics 2, no. 3 (August 27, 2021): 591–612. http://dx.doi.org/10.3390/applmech2030034.
Повний текст джерелаАнотація:
The fluid–structure interaction of a pivoting rigid wing connected to a spring and subjected to freestream airflow in a wind tunnel is presented. Fluid–structure interactions can, on the one hand, lead to undesirable aerodynamic behaviour or, in extreme cases, to structural failure. On the other hand, improved aerodynamic performance can be achieved if a controlled application within certain limitations is provided. One application is the reduction of drag of road vehicles at higher speeds on a straight, while maintaining downforce at lower speeds during cornering. Conversely, another application concerns increased downforce at higher windspeeds, enhancing vehicle stability. In our wind tunnel experiments, the angle of incidence of the spring-mounted wing is either increased or decreased depending on the pivot point location and spring torque. Starting from a specified initial angle, the aerodynamic forces overcome a pre-set spring preload at incrementally increased freestream velocity. Reynolds numbers at a range of Re = 3 × 104 up to Re = 1.37 × 105 are considered. The application of a symmetrical NACA 0012 and a cambered NACA 6412 airfoil are tested in the wind tunnel and compared. For both airfoils mounted ahead of the aerodynamic centre, stable results were achieved for angles above 15 and below 12 degrees for the symmetrical airfoil, and above 25 and between 10 and −2 degrees for the cambered airfoil. Unsteady motions were observed around the stall region for both airfoils with all spring torque settings and also below −2 degrees for the cambered airfoil. Stable results were also found outside of the stall region when both airfoils were mounted behind the aerodynamic centre, although the velocity ranges were much smaller and highly dependent on the pivot point location. An analysis is reported concerning how changing the spring torque settings at each pivot point location effects performance. The differences in performance between the symmetrical and cambered profiles are then presented. Finally, an evaluation of the systems’ effects was conducted with conclusions, future improvements, and potential applications.
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Tamatam, Lakshminarayana Reddy, Daniele Botto, and Stefano Zucca. "A novel test rig to study the effect of fretting wear on the forced response dynamics with a friction contact." Nonlinear Dynamics 105, no. 2 (July 2021): 1405–26. http://dx.doi.org/10.1007/s11071-021-06658-y.
Повний текст джерелаАнотація:
AbstractThis paper presents a novel test rig to study the effect of fretting wear and of the contact surface evolution on the forced response of systems with dry friction contact. This rig allows simulating contacts similar to the type of contacts present between the shrouds at the blade tip. Several research groups have been studying how fretting wear affects the dynamic response of mechanical systems, developing numerical prediction tools that consider dry friction contact and nonlinearity. The aim of this work is to experimentally study the evolution of contact interfaces and how this evolution affects the system dynamics. Experimental results will aid to validate the numerical predictions. The test rig developed for this activity is made of a cantilever beam fixed at one end and with a friction contact at the free end. The contact couple is made of two replaceable specimens. The contact is loaded via a lifting mechanism through a screw with fine thread. Fretting wear test was performed at a constant frequency and force amplitude, exciting the beam with an electromagnetic shaker. To emphasize the change of the dynamic response, frequency sweeps were performed at various intervals during the wear test. The full range test with ‘changing preload’ due to progressing wear was performed until a full loss of contact. This paper describes the test rig design, intent, set-up, instrumentation, test plan and results. Results include the frequency response curves for unworn contact, wear profiles at multiple intervals and the effect of wear on the frequency response. Though energy dissipation per cycle is quite small, wear leads to material loss at the contact with a sufficiently large number of cumulative cycles and substantially affects the dynamic response. Results collected in this research activity are of particular importance to validate numerical tool that aim to simulate the dynamic behaviour of systems with dry friction contacts that undergo material loss caused by wear.
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Poberezhny, L., S. Tregubenko, L. Poberezhna, A. Hrytsanchuk, and A. Stanetsky. "Influence of loads in the process of laying on the resource of sea pipelines." Archives of Materials Science and Engineering 2, no. 96 (April 1, 2019): 63–72. http://dx.doi.org/10.5604/01.3001.0013.2385.
Повний текст джерелаАнотація:
Purpose: In the process of laying on the bottom of the sea material of the pipeline undergoes single-cycle alternating load. The purpose of the work is to determine the effect of pre-operational loads on the resource of marine pipelines. Design/methodology/approach: The influence of the method of construction of pipelines on their stress-strain state is analysed. According to the real modes of packing of sea pipelines, the loading regime is programmed and the laboratory modelling of the pipe- laying process by the S-method has been programmed. Findings: According to the results of one-cycle shift load were obtained characteristics of the hysteresis loop. It is proposed to simplify the mathematical description of the hysteresis loop of the pipeline laying cycle in the given form. It was shown that the preload during the construction process negatively affects the durability of the pipeline material due to the exhaustion of its plasticity resource, reducing it to 70%. Research limitations/implications: In the future, investigations into the effect of overloading and overloading during the repair of pipeline sections on their durability and on the safe exploitation of resources should be continued. Practical implications: The developed method of estimation of influence of pre- operational loads in the process of pipeline laying on its safe exploitation resource is used in gas-extraction enterprises. Originality/value: To forecast the deformation behaviour of the pipeline material in the laying cycle, it is efficient to use diagrams of a sign-changing single-cycle bend, which were built considering the creep. The fatigue life capability of a steel pipeline depends on the history of the pipeline load in the laying cycle. Ratio σ*0.2c / σ*0.2t and ε yc / ε yt can use as power and deformation criteria for evaluating Bauschinger effect. It is suggested that fatigue damage is determined by the width of the hysteresis loop.
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Коновалов, Vladimir Konovalov, Симанин, Nikolay Simanin, Петрова, and Svetlana Petrova. "IMPROVEMENT OF DETAILS CONNECTION ASSEMBLY TECHNOLOGY WITH INTERFERENCE." Bulletin Samara State Agricultural Academy 1, no. 2 (May 5, 2016): 30–34. http://dx.doi.org/10.12737/18678.
Повний текст джерелаАнотація:
The purpose of the study is to increase the strength of the collected compounds and to expand the technological accuracy of the method of Assembly with an interference fit. Fixed press-fit connection with interference are widely used in machine building, when the transfer of substantial axial forces are required, torques or combined loads from their joint action. Resistance to mutual misalignment of the parts in these compounds is created and supported by the forces of elastic deformation on the mating surface of the covered part (shaft) and stretching on the mating surfaces of the covering parts (holes) is proportional to the magnitude of the preload in the connection. In such compounds, the diameter of the shaft before Assembly is always larger than the diameter of the hole. In the article the analysis of the known different ways of joining parts with interference fit, including hydraulic presses. The second problem is solved due to the fact that the connection details with tightness is carried out by pressing the press stroke from one detail to another, and the breakdown of the compounds obtained by the relative longitudinal movement of parts, in which the breakdown is carried out periodically in the process of pushing through the transfer of force from the press stroke to pressed items to the elastic connection. The force on the press stroke is created by a hydraulic cylinder with large displacement, a resilient connection between the slider and pressed item performs in the cylinder, the fluid pressure and volume which can be adjusted by changing the stiffness and capacity of the drive RAM, as well as the magnitude of its longitudinal movement during the disruption. The scheme of Assembly of the connection de-hoist with tension. Original technical solution for press fit connection parts extends the technological possibilities of the equipment, increases the strength of the collected compounds and can be used in machine building, particularly in mechanical Assembly processes and, in particular, in the repair and production of agricultural machinery.
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Suh, Junho, and Cheolho Hwang. "Thermal Deformation Induced Preload Changein the Tilting Pad Journal Bearing." Journal of the Korean Society of Tribologists and Lubrication Engineers 32, no. 1 (February 29, 2016): 1–8. http://dx.doi.org/10.9725/kstle.2016.32.1.1.
Повний текст джерела
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Wu, S.-J., C.-J. Yang, Y.-Q. Xie, L. Yang, and Y. Chen. "Development of a single-shot linear actuator for a deep-sea sampling valve." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 223, no. 10 (June 25, 2009): 2399–404. http://dx.doi.org/10.1243/09544062jmes1414.
Повний текст джерелаАнотація:
In this article, a new kind of linear actuator for the deep-sea sampling valve has been described. Based on the working principle of the triggering ring, the actuator employs a preloaded spring to generate an output force and linear movement. The actuator is designed to be used 4000 m underwater and can produce a force of 510 N at the maximal output displacement of 3.5 mm, which can be easily modified by changing the preloaded spring and spring seats. The actuator has been successfully tested to actuate the sampling valve at an ambient pressure of 40 MPa.
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Mínguez, José María, and Jeffrey Vogwell. "Theoretical Analysis of Preloaded Bolted Joints Subjected to Cyclic Loading." International Journal of Mechanical Engineering Education 33, no. 4 (October 2005): 349–57. http://dx.doi.org/10.7227/ijmee.33.4.5.
Повний текст джерелаАнотація:
In this paper the performance of preloaded bolted joints is analysed. The prior torque tightening creates compression in the clamped members and tension in the bolt. So, when an external tensile load is applied to the joint a large amount of it is taken up by the members, thereby relaxing their compression, at the expense of only a slight increase in bolt tension. In this way preloading the joint has the effect of changing the bolt fatigue regime from a low mean load with high alternating load to a high mean load with a low alternating load. This is beneficial for its fatigue life.
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Salman, Hamza Mahdi, and Mohannad Husain Al-Sherrawi. "Finite Element Modeling of a Reinforced Concrete Column Strengthened with Steel Jacket." Civil Engineering Journal 4, no. 5 (June 3, 2018): 916. http://dx.doi.org/10.28991/cej-0309144.
Повний текст джерелаАнотація:
The reinforced concrete column is designed to have a nominal axial resistance. Under different conditions like errors in design, and changing the use of the building from residential to public or storage (extra live loads), the reinforced concrete column will not be able to sustain the desired applied load, and the strengthening is required. This paper presents a finite element model to simulate and investigate the behavior of adding steel jacket to a preloaded and non-damaged reinforced concrete column. Depending on the loading state of the non-strengthened reinforced concrete column and the purpose of adding the steel jacket, two possible cases have been studied. In the first case, which is suitable to investigate the reinforced concrete column with design errors, the steel jacket has been added to the unloaded reinforced concrete column; while the second case is suitable for adding steel jacket to the pre-loaded non-damaged reinforced concrete column. The finite element model was carried out using the ABAQUS/standard v. 6.13 software. The results obtained by the proposed finite element model showed fairly good agreement with the existing experimental and analytical results.