Transfer Path Analysis Method Research Articles

A modified dynamic stiffness calculation method of rubber isolator considering frequency, amplitude and preload dependency and its application in transfer path analysis of vehicle bodies

An accurate prediction of the dynamic stiffness of the rubber isolator is critical to vehicle noise, vibration, and harshness performance. However, it is rather difficult due to the fact that it is simultaneously influenced by their application environment factors such as frequency, amplitude, and preload, etc. So far, related studies are still few. In the present study, taking the typically used chassis rubber bushing as the research object, a series of dynamic stiffness tests for rubber bushings was conducted under different frequencies, amplitudes, and preloads conditions. The Zener model was adopted to consider the frequency dependence, and an operation coefficient was introduced to quantify the amplitude and preload dependence. In order to obtain the actual dynamic stiffness of such rubber isolator, a modified calculation method considering the frequency, amplitude, and preloads dependence was proposed. The effectiveness of the proposed method was validated through comparing the accelerations synthesized by the transfer path analysis method with experimentally measured values. Compared to the traditional approach, the response can be more accurately calculated by the proposed method. It was further applied in solving the abnormal door vibration problem in a typical SUV. The vibration contribution analysis shows that the reasons for the door vibration problem caused by excessive transmitted forces at the rear stabilizer bar bushing in the x-direction and z-direction. A solution based on the analysis of the influence of corresponding bushing dynamic stiffness on target acceleration was therefore adopted to solve the abnormal door vibration problem effectively.

Research on Transfer Characteristics of Engine Vibration Load to Cabin Seat

Aeroengine is one of the main vibration sources that affect the passenger comfort. The contribution of engine vibration to the vibration response of seat will provide basic data for the design of airliner vibration comfort and engine vibration isolation installation. Firstly, the dynamical model of middle fuselage compartment with double-beam wing was established. Then, based on the typical vibration load spectrum of the engine, the acceleration responses of the key nodes of the wing beam and the seat connection points were analyzed, and the main path of engine vibration transmission to seats was identified. Finally, using operational transfer path analysis (OTPA) method, the contribution of engine front and rear mount point vibration to the vertical acceleration response of the seats was compared, and the three-dimensional information of wing structure vibration transmission was explored. The results show that the fundamental frequency component of low-pressure rotor of engine vibration has the greatest impact on the seat vertical response under takeoff and cruise conditions, the contribution rate of the front mount point vibration is about 71% and 67% respectively. However, the fundamental and its 3/2 times frequency components of high-pressure rotor have relatively large impact on the seats vertical response under flight idle state, and the contribution rate of engine front mount point vibration is about 45% and 60% respectively. In addition, the engine vibration is mainly transmitted from the wing front beam to the seat vertical response. The vertical direction of the wing beam and the rotation direction around the fuselage are also the main direction of vibration transmission.

Operational Transfer Path Analysis Based on Signal Decoupling

Abstract This study proposes an input decoupling analysis method based on the pulse test and the traditional operational transfer path analysis (OTPA) method for the OTPA transmission path analysis when the input is strongly coupled, and the algorithm is verified for analysis optimization of results. An experimental model of the dual excitation source is established in the laboratory. Experimental comparison studies show that the OTPA method, which is based on signal decoupling, inhibits the influence of cross-coupling among the source signals during OTPA analysis and effectively improves the accuracy of the transmission path test and analysis. The OTPA method is applied to analyze the transfer path of the vibration and noise of the carriages of the electric multiple unit (EMU) train (a high-speed train in China). The false peak frequency in the traditional OTPA method is eliminated, and the accuracy of the analysis is improved.

A Consideration of the Transfer Path Analysis Method Based on GTDT

A Consideration of the Transfer Path Analysis Method Based on GTDT

Transfer Path Analysis and Contribution Evaluation Using SVD- and PCA-Based Operational Transfer Path Analysis

To quantitatively identify the transfer paths and evaluate path contributions of shell structures, an singular value decomposition- (SVD-) and principal component analysis- (PCA-) based operational transfer path analysis method is constructed and studied in this paper. Firstly, SVD is used to determine the contribution of each path and reduce crosstalk. Secondly, PCA is applied to reduce the influence of unwanted frequency components and thus reduce noises. This allows the presented OTPA to be more accurate than its traditional counterpart. Once the transmissibility function is obtained, the response synthesis is determined, and the transfer path analysis and path contribution evaluation can be effectively carried out. Numerical and experimental case studies are carried out to validate and test the performance of the presented method. Furthermore, a comprehensive observing the influences of correlation between sources and distance of sources and receiver is also provided. Generally, this paper provides accurate transfer path analysis and path contributions for mechanical systems, which can benefit vibration and noise monitoring and reduction through vibration reduction structure design for new equipment or vibration damping on the major vibration transfer paths for current equipment.

Simulated Operational Path Analysis Method for the Separation of Intake and Exhaust Noises

The classical transfer path analysis (TPA) method has become a standard measurement method. It has high accuracy but remains a time-consuming and complex measurement, which limits its application in industry. The operational transfer path analysis (OTPA) method is known for its high efficiency; however, the accuracy of this method for industrial application is controversial. To separate the intake and exhaust noises in the vehicle, this study presents a novel TPA method called simulated operational path analysis (SOPA). The transmissibility from the reference point to the target response point is estimated by using an external noise source to simulate the intake and exhaust noises under operating condition. In addition, the improved dual-microphone noise reduction technology is used to eliminate the background noise in the reference response. The method is validated by an experimental bench. The result shows that its high accuracy can be compared with the classical TPA method. Because there is no need to use a special miniature volume source to estimate the passive subsystem frequency response functions and identify the operational source loads, the efficiency of the SOPA method is higher than the classic TPA method and is close to the OTPA method.

Combining classical and component-based TPA for equivalent load identification

The transfer path analysis (TPA) has become a rather standard tool for solving noise and vibration problems, as it helps understanding the mechanisms responsible for the generation and transmission of those quantities. By better understanding the intricate role of multiple sources and propagation paths, it is possible to diagnose and propose effective modifications that would addresses such issues at specific target locations. Although originally an experimental approach, hybrid methods that include modeled sub-systems have been proposed, which allow the assessment of key system features even at stages prior to the construction of full physical prototypes. However, in classical TPA, the operational forces are characteristics of the complete system, which implies that, with each modification in one subsystem, it is necessary to redo all the tests for the correct determination of target functions. For this reason, in recent years, interest has been renewed in the development of faster and simpler techniques for analyzing energy transfer paths, which offer a compromise between workload and accuracy. More specifically, a set of methods called component-based TPA is highlighted, which consists of characterizing the excitation of a source through a set of equivalent forces (or even interface velocities) inherent only to the active subsystem. In this way, the responses at target locations on the passive subsystem could be calculated using these equivalent loads and the dynamics of the complete system, obtained numerically, experimentally or under a hybrid framework. This work presents a critical analysis of the component-based TPA methods and proposes the combined use of these methods with a classical TPA approach in the process of determining equivalent forces of the active subsystem. This set of equivalent forces, combined with the passive subsystem dynamics, allows the prediction of the vibrational behavior of the full assembly at targeted locations, without the need for a full experimental analysis of the assembled system. As the case study presented here consists of a modular academic setup, it allows the qualitative assessment of the method in distinct assembly boundary conditions, in which the subsystems are connected via rigid or flexible joints.

Transfer Path Analysis for Semisubmersible Platforms Based on Noisy Measured Data

A new energy transfer path analysis (TPA) method that aims to analyze the transfer path of components with characteristic frequencies in semisubmersible platform structures is proposed in this paper. Due to the complexity of semisubmersible platforms, traditional TPA methods based on measurements are no longer applicable. In the proposed method, the structure is considered to be a “source-path-receiver” system and the vibration signals from the source-points are analyzed first to determine the characteristic components. Then, the signals from the source-points and the receiver-points are decomposed by introducing a state–space model. Through correlation functions, the characteristic components can be extracted, and the transfer path can be obtained by calculating the transmissibility functions. By using transmissibility functions, the proposed method only relies on the output responses and avoids the measurement of force and transfer functions. Three examples, one numerical example containing a two-degree-of-freedom (2-DOF) model and a 5-DOF model, one experiment implemented on a barge, and the data from a dynamic positioning (DP) cabin of a semisubmersible platform were used to investigate the performance of the proposed method. The results show that the proposed method can be used to assess the transfer path quantitatively and has potential value of application in engineering.

On the vibration transfer path analysis of aero-engines using bond graph theory

Due to increases in fossil fuel prices worldwide, aero-engine manufacturers in the aerospace industry are introducing innovative designs that emphasize mass reduction, improving efficiency and lowering operating costs. However, this phenomenon has increased the exposure of aero-engines to vibration transfer, due to internal excitation loadings produced by issues such as rotor system unbalance. Due to these circumstances and the general advancement of aero-engine design technology, the demand for reductions in interior fuselage noise and vibration has increased. In this research, bond graph transfer path analysis (TPA) is extended to apply to aero-engines, with the goal of analyzing vibration propagation through the aero-engine's structural pathways. Bond graph TPA is a reliable and valuable method that can be utilized to efficiently diagnose and minimize noise and vibration problems during the design phase, prior to prototyping. One of the main advantages of bond graph TPA is its analytical algorithm, which attempts to circumvent the empirical limitations imposed by previously available TPA models such as operational path analysis and operational path analysis with exogenous inputs. The result is superior time efficiency when analyzing vibration propagation in structures such as aero-engines, especially as compared to earlier TPA methods which demand vast and extensive amount of experimental measurements which could be an inefficient approach at times In this study, the bond graph transfer path analysis methodology is explored and implemented on a reduced lumped model of an aero-engine in order to demonstrate this novel transmissibility analysis approach. Using this unique process, the concepts of global and direct transmissibility and path contribution in aero-engines were investigated based on the TPA methodology, and vibration reduction strategies proposed that will help to minimize vibration transfer to aircraft fuselages that originates from rotor's unbalanced forces.

An experimental investigation of resonance sources and vibration transmission for a pure electric bus

Electric vehicles generally have a better noise, vibration, and harshness quality than traditional vehicles due to the relatively quiet electric motors. By contrast, the noise, vibration, and harshness issues of the driveline system become more outstanding and significant in the absence of the “masking effect” by the engine. The electrification of the powertrain has also brought many changes in the sources or transmission of vibration, which has led to some new noise, vibration, and harshness issues. Specifically, the intense vibration of the prototype bus appears when driving in third gear, which makes the passengers uncomfortable. This paper presents an efficient analytical strategy for identifying the resonance sources and vibration transmission for a pure electric bus. The strategy incorporates order analysis, operating deflection shape, and transfer path analysis. Order analysis shows that the resonance is primarily caused by the second-order excitation associated with the driveline, and the vibration sources are further identified using operating deflection shape analysis. Moreover, the vibration transfer paths from the driveline to the bus floor are quantitatively determined by the transfer path analysis method. The results show that the coupling vibration of the powertrain and the rear drive axle, which amplifies the resonance of the whole driveline, is transmitted to the bus floor primarily through powertrain mounts and V rods. Based on the results, the design and structure modifications of the driveline and transfer paths are recommended to handle this issue. The proposed identification strategy would be beneficial for accurate and efficient engineering troubleshooting on the vibration issues.

Unbalanced pump detection using modified transfer path analysis

Unbalance is the term in a rotating machine that used for a mass distribution which is not rotationally symmetric. Vibration from unbalancing pump affects to other pumps located on the same single base frame due to transmissibility. However, the unbalanced vibration can disturb and give a negative impact to other pumps on the same base frame. Therefore it is important to detect unbalance pump early which transmitted through the base frame because it can save large amounts of money. The aim of this research is evaluating the modification of transfer path analysis method that applied as a detecting pump damage method compare to International Standard. In this research, Modified Transfer Path Analysis (MTPA) is equal to the operational force that found by convolution of the natural frequencies with operational acceleration. The value of natural frequencies are determined using experimental modal analysis and the value of operational acceleration is determined by measuring the acceleration when the vibration source (pump machine) is running on steady condition. ISO 13373-1 was used as the reference for damage detection on the pump system. The results show that MTPA has the same characteristics and in agreement with ISO 13373-1 in detecting unbalance pump condition for machinery condition monitoring. Unbalance is the term in a rotating machine that used for a mass distribution which is not rotationally symmetric. Vibration from unbalancing pump affects to other pumps located on the same single base frame due to transmissibility. However, the unbalanced vibration can disturb and give a negative impact to other pumps on the same base frame. Therefore it is important to detect unbalance pump early which transmitted through the base frame because it can save large amounts of money. The aim of this research is evaluating the modification of transfer path analysis method that applied as a detecting pump damage method compare to International Standard. In this research, Modified Transfer Path Analysis (MTPA) is equal to the operational force that found by convolution of the natural frequencies with operational acceleration. The value of natural frequencies are determined using experimental modal analysis and the value of operational acceleration is determined by measuring the acceleration when the vibratio...

Vibration source identification of a heavy commercial vehicle cab based on operational transfer path analysis

Operational transfer path analysis is applied in this study to identify the vibration source and its critical transfer path. A simple analytical five-degrees-of-freedom mechanical isolation system is first taken as an example to illustrate the analysis flow and to validate the accuracy of operational transfer path analysis. The acceleration amplitude spectrum of the receiver is used to prove the accuracy, and the path contribution of each path is used to identify the critical path. Operational transfer path analysis is then applied to the cab mount system of a heavy commercial vehicle to identify the vibration source and its critical transfer path. The vibration energy propagation capabilities from the four cab mounts to the driver’s seat are analyzed by operational transfer path analysis with the path contribution analysis, and the maximum vibration source is identified by the path operation contribution analysis. The analysis and evaluation method of the operational transfer path analysis introduced in this study can provide a research foundation and reference for vibration or noise source identification in mechanical systems.

A Comparison of Two Source Characterisation Techniques Proposed for Standardisation

<div class="section abstract"><div class="htmlview paragraph">Automotive industry shows an increased tendency towards characterisation of vibration sources by independent quantities such as blocked forces and free velocities. Currently two independent ISO working groups propose standards for this source characterisation process. Both standards are still under development.</div><div class="htmlview paragraph">In this paper it is shown how the different approaches can be derived and compared using the general framework for Transfer Path Analysis (TPA). It is shown how one standard clearly relates to classical TPA methods (using interface forces), while the other standard adheres the component-based TPA principles (using blocked forces). Practical guidelines found in the standard proposals are reviewed, allowing for a qualitative comparison of the proposed procedures. To address typical problems regarding completeness of the interface, an addition is proposed that incorporates the use of 6-DoF Virtual Point forces and moments. It is shown how this approach can be applied to any force characterisation, improving the general usefulness of the found forces. A simulated numerical test case shows the procedure of both standards and discusses the added value of including rotational moments in the source-describing force vectors. An industrial application case demonstrates the application of the second standard with the addition of virtual point forces and moments, leading to perfect agreement with the on-board validation sensor.</div></div>

Sound quality evaluation of automobile interior noise under transient and steady-state running conditions

Sound quality can reflect people's subjective auditory feelings; thus, it plays an important role in automobile interior noise evaluation in recent years. Most research focuses on steady-state running conditions. In this paper, automobile vibration and noise transfer paths were measured with the binaural transfer path analysis (BTPA) method under both transient and steady-state running conditions. Then, loudness, sharpness, roughness, and A-weighted sound pressure level were used for studying properties and differences of automobile interior noise among different running conditions. Moreover, an experiment was carried out for the subjects to mark the annoyance of all noise samples. After that, the artificial neural network was applied to create the sound quality model to assess automobile interior noise without subjective experiments. According to the scores and binaural transfer path synthesis(BTPS) results, structural improvement methods were proposed for better sound quality of the automobile.

An improved OPAX method based on moving multi-band model

Abstract In this paper, a transfer path analysis (TPA) method – OPAX is further improved. The new method uses multiple estimates of the dynamic mount stiffness in the multi-band OPAX method to increase the estimation accuracy. A moving multi-band model is used to establish the parametric load model. Two statistical metrics are introduced to evaluate the estimation uncertainty, and a strategy for iteratively calculating operational forces whilst quantitatively assessing estimation accuracy is proposed by combining the two metrics. A numerical case is used to illustrate the proposed method. The results show that this method not only produces better estimation than the multi-band model method, but also evaluates estimation accuracy quantitatively by itself. Then the proposed method is investigated and demonstrated by a vehicle example and a rule of thumb is formulated. Lastly, a test campaign is carried out on a full vehicle to validate the proposed method.

The transfer path analysis method on the use of artificial excitation: Numerical and experimental studies

Transfer path analysis (TPA) method is a powerful tool used to study the noise, vibration and harshness (NVH) behavior of mechanical systems. With the development of detecting and testing technology, more powerful and accurate tools for vibration and noise troubleshooting are required. The classical TPA works as the system is disassembled, and thus it is very time-consuming and the boundary conditions are not correct anymore. These topics makes classical TPA still an active research area.In this paper, a TPA method on the use of artificial excitation is presented. In the method artificial excitation is applied on the active part for providing sufficient incoherent forces to improve the estimation. The known force is applied on the passive part for establishing a relationship between the responses and loads. The advantages of this method are that it estimates the uncoupled transfer function of the passive part on the basis of in-situ measurements, without disassembling the system. The proposed method is validated by numerical and experimental case studies. Some remarks and practical aspects are discussed.

Investigation and refinement of gearbox whine noise

Structure borne noises can be transmitted to interior cabin via physical connections by gearbox as well as other active components. Experimental Transfer Path Analysis (TPA) methods are utilized to investigate main paths of vibrations which are eventually perceived as noise components inside the cabin. In this study, contribution ranking of transmission paths from active system components through the physical connections into the interior cabin are investigated by Operational Path Analysis with Exogenous Inputs (OPAX) method. In addition, the sensitivity and rigidity characterization of the body through dominant paths according to OPAX were measured to reveal the reason for the whine noise to the inner cabin because of the operational forces generated in the dominant structure-borne paths. And also, operational modal analysis was carried out to examine the modes of the dominant path components. The modifications are applied on dominant transfer paths according to dominant paths characterization by operational deflection shape analyses. Thus, the root causes are investigated on vehicle level NVH tests while observing the variations in the interior cabin noise level.

Improved vehicle interior structure-borne noise induced by the powertrain using parallel dry friction damper

Because of the higher requirements for vehicle comfort and people’s increasing ecological consciousness, research on the interior noise in a vehicle has received wide attention, among which structure-borne noise is hard to diagnose. To solve the problem, the transfer path analysis method of powertrain structure-borne noise has been systematically analyzed. By introduction of the powertrain source-path-receiver model, this method enables the researchers to estimate and study the noise, vibration, and harshness transfer functions and their operational forces. The aim is to further improve noise, vibration, and harshness with minimal negative impact on other vehicle attributes, such as ride comfort, handling, drivability, durability, etc. In this article, a parallel dry friction damper was added to the vehicle nearside powertrain mount, which is the most significant one to the receiver of passenger vehicle for improving its interior structure-borne noise induced by the engine. The test vehicle was a midsize executive vehicle. Since the structure-borne noise is composed of multiple paths, then the transfer path analysis test of the vehicle was carried out, and the transfer function and operational data at speed range started from 20 to 100 km/h were obtained. On the basis of the transfer path analysis results and the above principle, the friction damper on the body side of the nearside mount is improved by combination of the experimental transfer path analysis and the final measurements. The results indicate that a significant reduction for the A-weighted sound pressure level of the interior noise has been gained when the frictional damper was added to conventional mount.

Virtual decoupling method: a novel method to obtain the FRFs of subsystems

An important procedure in transfer path analysis (TPA) is to measure the frequency response functions (FRFs) of the decoupled passive subsystem. The classical TPA method obtains the passive subsystem’s FRFs by direct measuring when the system is disassembled. The main shortcoming of the classical method to measure the FRFs is that it is time-consuming due to the necessity to dismount the active part. In this paper, a novel method is proposed to estimate the passive subsystem’ FRF matrix without disassembling the coupled mechanical structure. The key idea of this method is that the effect of a coupled subsystem will be canceled out if the links which connect this subsystem with the other one have no deformation, since the coupled systems influence each other only through the links which can be regarded as combinations of connecting springs and dampers. Following this idea, the expression of the passive subsystem’s FRF matrix can be deduced from the entire system’s FRF matrix directly. The proposed method in this paper is called the virtual decoupling method, since the decoupling is not ‘real’ but ‘virtual’. Obviously, the actual decoupling procedure is avoided so that the shortcoming mentioned above is overcome. The method is validated by a numerical model and a finite element model.

Blocked pressure based Transfer Path Analysis (TPA) method to diagnose airborne sound transfer through building partitions

Airborne sound transmission through building elements or the sound insulation of the building element is usually rated by its Sound Reduction Index (SRI) or the Sound Transmission Class (STC). SRI/STC quantifies the overall sound transfer but gives no information about how the transfer takes place and what are the contributions of different sound transfer paths involved. Such problems are fairly common to the vehicle acoustics industry and are generally tackled by TPA techniques. The paper formulates an in-situ Airborne TPA technique to quantify the contributions of different sound transfer paths to the transmitted pressure. The airborne source is characterized by its blocked pressure and its direct measurement is discussed. Results are presented for dual leaf partitions excited by an airborne source. The method has shown to be significantly faster than the Blocked force based TPA method which relies on inverse measurement methods. The accuracy of the method is closely related to the wavelength of incident airborne waves.