这是COMSOL用户的常见问题，因此在COMSOL知识库中有专门的词条与之对应。
解决方法1. 积分值计算a） 空间积分 当模型计算完毕，计算积分值最方便的方法是在Result > Derived Values上右击并选择Integration，并根据几何维度选择是对体（Volume），面（Surface）还是线（Line）进行积分。
在设定（Settings）窗口中选中积分区域，表达式（Expression）中输入或选择待积分变量，并点击运算（Evaluate）按钮。
结果将显示在结果（Result）窗口中。
流体阀入口及出口流量随时间的变化b） 时间积分 算子timeint和timeavg只能作用于后处理结果运算，如果需要在模型里定义一个时变的积分，比如说需要引入一个新的相关变量I，它是变量u的时间积分： 而I对时间的微分由如下常微分公式定义： 根据具体需要，可以建立针对某个点或是全局标量的积分（Global ODE/Point ODE），或是场变量在体/面/边上的分布积分（Domain, Boundary, Edge ODE）。
外部I与U
外部I与U（）功能连接任意电压测量（例如，电路端子或电路端口边界或来自另一物理接口的线圈域）作为电路中两个节点之间的电压源。在电压测量的背景下，从第一节点到第二节点的所得电路电流通常被耦合回作为规定的电流源。
设备名称
输入外部I与U节点的设备名称。
节点连接
为电压源指定连接节点的两个节点名称。第一个节点代表正参考终端。
外部设备
输入电压源。如果在边界或域上定义了电路或电流激励端子或电路端口，或者在其他物理接口中定义了多圈线圈域，则这些在电压列表中显示为选项。同时选择用户定义选项并输入您自己的电压变量，例如，使用合适的耦合运算符。对于感应或电磁波传播模型，电压测量必须作为电场的积分来执行，因为电势仅不捕获感应的EMF。此外，必须在与本地波长相比较短的距离上执行积分。
除了耦合到电路端子，电路端口或线圈时，电流变量必须在电路中手动耦合回电压测量的环境。这在耦合到电流激励端子时也适用。此当前变量的名称遵循惯例cirn.IvsUm_i，其中cirn是电路接口节点的标记，IvsUm是外部I与U节点的标记。标签通常显示在模型构建器中的大括号{}内。
COMSOL Multiphysics参考手册中的组件耦合和耦合运算符
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外部对阵我
外部U与I（）功能将任意电流测量（例如，来自另一物理接口的线圈域）连接为电路中两个节点之间的电流源。在电流测量的上下文中，第一节点和第二节点之间的所得电路电压通常被耦合回作为规定的电压源。
设备名称
输入外部U与I节点的设备名称。
节点连接
为当前源指定连接节点的两个节点名称。电流从第一节点流向第二节点。
外部设备
输入Current的来源。在其他物理接口的边界上定义的电压激励端子或集总端口是自然候选，但在电压列表中不作为选项出现，因为它们没有准确的内置电流测量变量。必须选择用户定义的选项并输入当前变量，例如，使用合适的耦合运算符。
电压变量必须在电路中手动耦合回电流测量的环境。这在耦合到电压激励端子或集总端口时也适用。该电压变量的名称遵循惯例cirn.UvsIm_v，其中cirn是电路接口节点的标记，UvsIm是外部U对I节点的标记。标签通常显示在模型构建器中的大括号{}内。
COMSOL Multiphysics参考手册中的组件耦合和耦合运算符
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外部I-Terminal
外部I-Terminal（）功能将任意电压对地测量（例如，来自另一物理接口的电路端子）连接为电路中节点的电压对地分配。在电压测量的背景下，来自节点的所得电路电流通常被耦合回作为规定的电流源。当耦合到感应或电磁波传播模型时，该节点不适用，因为那时电压必须定义为两点之间的线积分，而不是单点电位测量。对于此类耦合，请改用External I与U节点。
设备名称
输入外部I终端的设备名称。
节点连接
为电压分配设置连接节点的节点名称。
外部终端
输入电压源。如果电路或电流激励端子在其他物理接口的边界上定义，则这些端子在电压列表中显示为选项。同时选择用户定义选项并输入电压变量，例如，使用合适的耦合运算符。
除了耦合到电路端子之外，电流变量必须在电路中手动耦合回电压测量的环境。这在耦合到电流激励端子时也适用。此当前变量的名称遵循约定cirn.termIm_i，其中cirn是电路接口节点的标记，termIm是外部I-Terminal节点的标记。标签通常显示在模型构建器中的大括号{}内。
COMSOL Multiphysics参考手册中的组件耦合和耦合运算符。
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External I vs. U
The External I vs. U () feature connects an arbitrary voltage measurement (for example, a circuit terminal or circuit port boundary or a coil domain from another physics interface) as a voltage source between two nodes in the electrical circuit. The resulting circuit current from the first node to the second node is typically coupled back as a prescribed current source in the context of the voltage measurement.
DEVICE NAME
Enter a Device name for the External I vs. U node.
Node Connections
Specify the two Node names for the connecting nodes for the voltage source. The first node represents the positive reference terminal.
External Device
Enter the source of the Voltage. If circuit or current excited terminals or circuit ports are defined on boundaries or domains or a multiturn coil domains is defined in other physics interfaces, these display as options in the Voltage list. Also select the User defined option and enter your own voltage variable, for example, using a suitable coupling operator. For inductive or electromagnetic wave propagation models, the voltage measurement must be performed as an integral of the electric field because the electric potential only does not capture induced EMF. Also the integration must be performed over a distance that is short compared to the local wavelength.
Except when coupling to a circuit terminal, circuit port, or coil, the current flow variable must be manually coupled back in the electrical circuit to the context of the voltage measurement. This applies also when coupling to a current excited terminal. The name of this current variable follows the convention cirn.IvsUm_i, where cirn is the tag of the Electrical Circuit interface node and IvsUm is the tag of the External I vs. U node. The tags are typically displayed within curly brackets {} in the Model Builder.
Component Couplings and Coupling Operators in the COMSOL Multiphysics Reference Manual
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External U vs. I
The External U vs. I () feature connects an arbitrary current measurement (for example, a coil domain from another physics interface) as a current source between two nodes in the electrical circuit. The resulting circuit voltage between the first node and the second node is typically coupled back as a prescribed voltage source in the context of the current measurement.
DEVICE NAME
Enter a Device name for the External U vs. I node.
Node Connections
Specify the two Node names for the connecting nodes for the current source. The current flows from the first node to the second node.
External Device
Enter the source of the Current. Voltage excited terminals or lumped ports defined on boundaries in other physics interfaces are natural candidates but do not appear as options in the Voltage list because those do not have an accurate built-in current measurement variable. A User defined option must be selected and a current variable entered, for example, using a suitable coupling operator.
The voltage variable must be manually coupled back in the electrical circuit to the context of the current measurement. This applies also when coupling to a voltage excited terminal or lumped port. The name of this voltage variable follows the convention cirn.UvsIm_v, where cirn is the tag of the Electrical Circuit interface node and UvsIm is the tag of the External U vs. I node. The tags are typically displayed within curly brackets {} in the Model Builder.
Component Couplings and Coupling Operators in the COMSOL Multiphysics Reference Manual
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External I-Terminal
The External I-Terminal () feature connects an arbitrary voltage-to-ground measurement (for example, a circuit terminal from another physics interface) as a voltage-to-ground assignment to a node in the electrical circuit. The resulting circuit current from the node is typically coupled back as a prescribed current source in the context of the voltage measurement. This node does not apply when coupling to inductive or electromagnetic wave propagation models because then voltage must be defined as a line integral between two points rather than a single point measurement of electric potential. For such couplings, use the External I vs. U node instead.
DEVICE NAME
Enter a Device name for the External I-terminal.
Node Connections
Set the Node name for the connecting node for the voltage assignment.
External Terminal
Enter the source of the Voltage. If circuit- or current-excited terminals are defined on boundaries in other physics interfaces, these display as options in the Voltage list. Also select the User defined option and enter a voltage variable, for example, using a suitable coupling operator.
Except when coupling to a circuit terminal, the current flow variable must be manually coupled back in the electrical circuit to the context of the voltage measurement. This applies also when coupling to a current excited terminal. The name of this current variable follows the convention cirn.termIm_i, where cirn is the tag of the Electrical Circuit interface node and termIm is the tag of the External I-Terminal node. The tags are typically displayed within curly brackets {} in the Model Builder.
Component Couplings and Coupling Operators in the COMSOL Multiphysics Reference Manual.
U vs I通常测量PDE模型中的电流，并在其中指定指定指定电压的源。
I vs U通常测量PDE模型中的电压，并在其中指定指定指定电流的源。
例如，磁场接口中的集总端口只能用电流激励，因为
电压不是模型中求解或包含的变量。因此，您需要定义I vs U，因为您需要分配一个电流。在许多其他接口中，例如电流，你可以在“正常边界条件”上分配驱动电压或电流，你可以使用U对I或I对U。
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