CN104483085B - Design method of special test base for force transmissibility of vibration equipment - Google Patents

Abstract

The invention relates to a method for designing a special test base for the force transmission rate of vibration equipment, which takes base structure parameters as design variables, takes the impedance of the base equal to the mechanical impedance of the vibration equipment as an optimization target, performs optimal analysis on the base, selects a genetic algorithm as an optimization method, and finds the optimal base structure parameters to minimize the difference between the vibration level drop and the force transmission rate; establishing an actual base model according to the optimized base structure parameters; and performing vibration test to verify and test the vibration isolation effect of the base. The method is a simple, efficient and reliable base design method. By the method, the corresponding special test base is designed and obtained and is used for accurately evaluating the vibration isolation effect of the equipment and the system.

Description

Design method of special test base for force transmission rate of vibration equipment

technical field

The invention relates to the field of test equipment design, in particular to a design method for a special test base for the force transmission rate of vibration equipment.

Background technique

The parameters for evaluating the vibration isolation effect of mechanical equipment vibration isolation devices are force transfer rate and vibration level drop. The force transmission rate is defined as the ratio between the vibration force (the output force of the mechanical equipment vibration isolation system) and the exciting force on the foundation after the mechanical equipment is elastically installed. For this vibration isolation system, since the excitation force generated by the equipment during operation cannot be obtained directly, the vibration force at the foot of the equipment is taken as the input force of this vibration isolation system. The input force of the vibration isolation system is obtained through the force sensor at the measuring point of each machine foot ; At the same time, the output force of the vibration isolation system is obtained through the force sensors at the measuring points of the base . The experiment is a multi-point measurement, and the force transmission rate can be expressed by the average value of each measurement point,

;

The vibration level drop is defined as the ratio of the vibration response on the foundation to the vibration response at the foot of the equipment after the mechanical equipment is elastically installed. The vibration level drop is expressed by the acceleration vibration level drop. The experiment is a multi-point measurement, and the vibration level drop can be expressed by the average value of each measuring point.

In the formula, is the logarithmic average value of the acceleration total vibration level of each measuring point of the equipment machine foot, is the logarithmic mean value of the acceleration total vibration level of each measuring point on the base panel, and its expression is shown in the following formula.

In the formula, is the acceleration vibration level at the i -th measuring point of the machine foot, is the acceleration vibration level at the i -th measuring point on the base panel, is the total number of measuring points.

In engineering, the vibration level difference between the upper and lower ends of the shock absorber (acceleration level) is often used to represent the vibration isolation effect of the vibration isolation system. However, there are certain defects in this index, that is, when the characteristics of the vibration isolator are determined, the impedance characteristics of the foundation have a great impact on the vibration level drop, and in some cases, misjudgment may occur, and it cannot objectively reflect the vibration level difference. vibration effect. Therefore, it is more reasonable to characterize the vibration isolation effect by the force transmission rate. However, compared with the vibration level drop, testing the force transmission rate of the vibration isolation system requires connecting the force sensor in series in the vibration isolation system, which is difficult to achieve in field measurement. On the other hand, the insertion of the force sensor will also affect the characteristics of the vibration isolation system. Therefore, if the force transmission rate can be equivalently obtained by using the vibration level difference, the vibration isolation effect of the vibration isolation system will be better characterized. But in fact, these two evaluation indicators are not equivalent, and they are very different under normal circumstances. Only when the base meets certain conditions and has a specific impedance, the difference between the two evaluation indicators of vibration level drop and force transmission rate There is an equivalence relationship. Aiming at this problem, the present invention provides a base design method.

Contents of the invention

The invention aims at the problem that the impedance characteristics of the base have a great influence on the vibration level drop and the force transfer rate of the vibration isolation device, and proposes a special test base design method for the force transfer rate of vibration equipment to ensure that the impedance of the foundation has a great influence on the isolation of the elastic system. The vibration effect and the influence of equipment vibration are reduced to the minimum, so as to realize the accurate evaluation of equipment vibration and system vibration isolation effect.

The technical solution of the present invention is: a method for designing a special test base for the force transmission rate of vibration equipment, which specifically includes the following steps:

1) Select the vibration isolator according to the weight of the vibration equipment and the number of installation points of the machine feet, analyze the dynamic characteristics of the vibration equipment and the vibration isolator through test or simulation, and obtain the distance between the connection points of each machine foot of the vibration equipment. And the acceleration admittance matrix between the upper and lower installation points of the vibration isolator;

2) According to the geometric structure and dynamic characteristics of the vibration equipment, establish the initial model of the base, select the structural parameters of the base, use the analytical method or the finite element method to establish a parametric model of the base, and obtain the connection points of each vibration isolator of the base The acceleration admittance matrix between;

3) Obtain the impedance matrix through the admittance data of the vibration equipment, vibration isolator and base, and use , with Represent the mechanical impedance of the vibrating device, the isolator, and the base, and solve for the isolator:

The difference between the vibration level drop and the transmissibility is:

,

Since the impedance Z _I of the vibration isolator is much smaller than the impedance Z _M and Z _F of the equipment and the base, the above formula can be further simplified as:

with The smaller the difference, the better the vibration isolation effect;

4) Taking the structural parameters of the base in step 2) as the design variables, and taking the impedance of the base equal to the mechanical impedance of the vibration equipment as the optimization goal, conduct an optimization analysis on the base, and select the genetic algorithm as the optimization method to find the optimal base Structural parameters, so that the difference between the vibration level drop and the force transmission rate is the smallest;

5) Establish the actual foundation model according to the optimized foundation structure parameters;

6) Conduct vibration test to verify the vibration isolation effect of the test base.

In the above step 1), the vibration equipment test can be placed in an elastic suspension state through the suspension cable, and the input admittance and transfer admittance between the measuring points of each machine foot of the vibration equipment can be tested through the hammer test, so as to form the acceleration of the vibration equipment Admittance matrix; the dynamic characteristics of the isolator can be measured by impedance bench test.

The beneficial effect of the present invention is that: the special test base design method for the force transmission rate of the vibration equipment of the present invention is a simple, efficient and reliable base design method. Through this method, the corresponding special test base is designed and used for accurate evaluation of equipment vibration and system vibration isolation effect.

Description of drawings

Fig. 1 is the model diagram of the low-noise water pump of the embodiment of the present invention;

Fig. 2 is the acceleration admittance curve diagram between the connection points of the machine foot vibration isolator of the embodiment of the present invention;

Fig. 3 is a schematic diagram of a special test base model of an embodiment of the present invention;

Fig. 4 is a schematic diagram of the vibration level drop and force transmission rate of the system after the base of the embodiment of the present invention is optimized.

detailed description

The present invention carries out base design according to the dynamic admittance characteristics of the equipment, and finds the most ideal base structure parameters through an optimization method, so that the influence of the foundation impedance on the vibration isolation effect of the elastic system and the vibration of the equipment is minimized. The specific method As follows:

(1) Select a suitable vibration isolator according to the weight of the vibrating equipment and the number of machine foot installation points. Analyze the dynamic characteristics of equipment and vibration isolators through experimental testing or simulation. The acceleration admittance matrices between the connection points of each machine foot of the equipment and between the upper and lower installation points of the vibration isolator are respectively obtained.

(2) According to the geometric structure and dynamic characteristics of the vibration equipment, establish the initial model of the foundation. Select the appropriate structural parameters of the base, use the analytical method or the finite element method to establish a parametric model of the base, and obtain the acceleration admittance matrix between the connection points of each vibration isolator of the base. The dynamic characteristics of the base can be tuned by changing the design parameters.

(3) Through the admittance data of vibration equipment, vibration isolator and base, their impedance matrix can be obtained, respectively using , with Represent the mechanical impedance of the unit, vibration isolator and base, so as to solve the whole vibration isolation system.

At this time, the force transmission rate of the vibration isolation system is:

The vibration level drop is:

Considering that the impedance Z _I of the vibration isolator is much smaller than the impedance Z _M and Z _F of the equipment and the base, the difference between the vibration level drop and the transmissibility can be simplified as:

It can be seen from the above formula that the difference between the vibration level drop and the force transmission rate can be expressed by the impedance of the equipment and the base. When the two are equal, the vibration level drop can be used instead of the force transmission rate to represent the isolation system. vibration effect.

(4) Based on the above content, in order to meet the design requirements, the base needs to have the same dynamic characteristics as the test equipment. Taking the structural parameters selected in (2) as design variables, and taking the impedance characteristics of the foundation as the optimization target, under certain constraint conditions, the optimization analysis of the foundation is carried out. Because there are many design variables in the optimization model, and the objective function and design variables are not in a gradient relationship, genetic algorithm is chosen as the optimization method. Find the optimal base structure parameters to minimize the difference between vibration level drop and force transmission rate.

(5) Establish the actual foundation model according to the optimized foundation structure parameters.

(6) Vibration test is carried out to verify that the test base designed by this method can accurately evaluate the vibration and vibration isolation effect of the equipment.

According to the design method of the special test base for vibration equipment mentioned above, a special test base for the low-noise water pump is designed, and its effect is verified by experiments.

The schematic diagram of the model of the low-noise water pump is shown in Figure 1, and the points 1 to 4 in the figure are the connection points of the vibration isolator of the machine foot. The water pump is in an elastic suspension state through the suspension cable, and the free-free boundary condition is simulated. Through the hammer test, the input admittance and transfer admittance between the measuring points of each machine foot of the water pump are tested, so as to form the acceleration admittance matrix of the water pump (see Figure 2 for the equipment admittance curve). The dynamic characteristics of the vibration isolator can be measured by impedance bench test.

The impedance matrix is obtained according to the dynamic admittance characteristics of the equipment, and the corresponding initial base model is designed according to its geometric structure (see Figure 3). Base model is made up of support frame 31 and base plate 32 two parts (in sequence number Fig. 3 has added). The bottom plate is a rectangular plate of variable thickness to produce different mass distributions. The support frame is located at the center of the base, and its structure refers to the machine foot connecting plate (10 in FIG. 1 ) of the equipment, and reinforcing ribs are respectively arranged around the support frame 31 . The thickness of the support frame 31 and the plate thickness of different regions of the bottom plate 32 are respectively selected as parameters, and the dynamic model of the foundation is established by using the finite element method, and the acceleration impedance matrix between the connection points of the vibration isolator is calculated.

According to the optimization model in method (4), the base is optimally designed. Using the optimized base, establish a vibration isolation system model and solve it to obtain the vibration level drop and force transfer rate (see Figure 4), thus proving the effectiveness and practicability of the design method.

Claims (2)

1. A special test base design method for vibration equipment force transmission rate, is characterized in that, specifically comprises the following steps: 1) Select the vibration isolator according to the weight of the vibration equipment and the number of installation points of the machine feet, analyze the dynamic characteristics of the vibration equipment and the vibration isolator through test or simulation, and obtain the distance between the connection points of each machine foot of the vibration equipment. And the acceleration admittance matrix between the upper and lower installation points of the vibration isolator; 2) According to the geometric structure and dynamic characteristics of the vibration equipment, establish the initial model of the base, select the structural parameters of the base, use the analytical method or the finite element method to establish a parametric model of the base, and obtain the connection points of each vibration isolator of the base The acceleration admittance matrix between; 3) Obtain the impedance matrix through the admittance data of the vibration equipment, vibration isolator and base, use Z _M , Z _I and Z _F to represent the mechanical impedance of the vibration equipment, vibration isolator and base respectively, and carry out the Solve: The difference between the vibration level drop and the force transmission rate is: ${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; g</span>}\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; ,</span>$ Since the mechanical impedance Z _I of the vibration isolator is much smaller than the mechanical impedance Z _M and Z _F of the vibrating equipment and the base, the above formula is further simplified to: ${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; \&ap;</span>\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; g</span>}\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; g</span>}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\frac{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}}$ The smaller the difference between Z _M and Z _F , the better the vibration isolation effect; 4) Taking the structural parameters of the base in step 2) as the design variables, and taking the mechanical impedance of the base equal to the mechanical impedance of the vibrating equipment as the optimization target, carry out optimization analysis on the base, select the genetic algorithm as the optimization method, and find the optimal The structural parameters of the base make the difference between the vibration level drop and the force transmission rate the smallest; 5) Establish the actual foundation model according to the optimized foundation structure parameters; 6) Conduct vibration test to verify the vibration isolation effect of the test base. 2. according to claim 1, the special test base design method for the force transmission rate of the vibration equipment is characterized in that, in the step 1), the vibration equipment test is made to be in an elastic suspension state by a suspension cable, and the vibration is tested by a hammer test The input admittance and transfer admittance between the measuring points of each machine foot of the equipment form the acceleration admittance matrix of the vibrating equipment; the dynamic characteristics of the vibration isolator are measured by the impedance table test.